European Journal of Agronomy

Published by Elsevier
Online ISSN: 1161-0301
Publications
Article
The introduction of perennials in the Mediterranean crop rotations can have a positive effect on soil organic matter (SOM) concentration, thus improving the long-term sustainability of cropping systems, affected by the progressive degradation in soil fertility. Ramie [Boehmeria nivea (L.) Gaud.], a perennial herbaceous species used for its high quality bast fibre, has recently received renewed attention for production in Europe due to the increasing natural fibre demand globally. Little attention has been focused on the ramie cultivation management and on its effect on soil chemical characteristics. A long-term field experiment was carried out in Pisa (Central Italy, 43°40′ N; 10°19′ E) since 1996, with the aim to assess the long-term environmental sustainability of ramie in terms of productivity, nutrient balance, soil fertility and SOM pool. The fertiliser management of ramie consisted of 150–100–100 kg N–P–K ha−1 in the establishment year and 150–65–165 kg N–P–K ha−1 year−1 from the second year onwards. Plant nutrient uptake was analysed to optimise the crop mineral nutrition and to evaluate the nutrient balance and the efficiency of fertiliser management. The SOM dynamic was evaluated using the actual investigated data and Hénin–Dupuis's equation in order to estimate the organic requirements for SOM equilibrium. Over the 13-year cultivation period, a mean value of 14 Mg ha−1 year−1 of total above-ground dry biomass was obtained. In the 0–30 cm soil depth, SOM, total nitrogen (N), available phosphorus (P), exchangeable potassium (K) and pH varied significantly throughout the cultivation period. SOM increased significantly, from 13.4 g kg−1 to 25.3 g kg−1. A significant correlation between the measured SOM and the cumulative organic matter (OM) inputs (r2 = 0.908; P = 0.012) was found. The average annual N and P balances were positive (equal to 14 kg ha−1 and 38 kg ha−1, respectively), while the K balance was negative (−57 kg ha−1). The results show that ramie crop has a positive effect on SOM pool, thus representing an interesting sustainable fibre crop for the Mediterranean area.Graphical abstractHighlights► The effects of ramie, a new interesting fibre crop, on soil fertility are assessed. ► Stocks of SOM, N and P significantly increase after 13 years of cultivation. ► Measured SOM is positively related to the above and below-ground crop residues. ► Hénin–Depuis's equation accurately predicts SOM pool. ► Ramie can represent an alternative crop in rainfed Mediterranean cropping systems.
 
Article
Silage maize has replaced fodder beet as energy-rich winter forage for housed cattle. In Denmark silage maize now occupies more than 4% of the arable land, but little is known on the effect of continuous silage maize on soil carbon dynamics under NW European cropping conditions. Soil total-C and natural abundance were determined every 2–3 years in four Danish arable soils (0–20 cm) continuously cropped to maize for 14 years under identical climatic conditions. A set of soils was sampled after 11 years with maize and analysed for total-C and maize-derived C in >2 mm plant residues, in <2 mm soil, and in 250–2000 μm particulate organic matter (POM). Inputs of C in maize roots and stubbles induced an average annual increase in soil total-C of 90–470 kg C ha−1. When soils were amended with an additional annual input of 8 t DM ha−1 in chopped above-ground maize biomass, soil C storage increased 110–940 kg C ha−1 per year. No changes in soil C/N ratio were observed. Carbon from maize roots and stubbles accumulated in the soil at an annual rate of 250–490 kg C ha−1; with an additional annual input of 8 t DM ha−1, the accumulation rate was 710–980 kg maize-C ha−1. After 14 years with continuous silage maize, maize-derived C accounted for 7–18% of the total soil C; with additional maize biomass inputs, maize-C made up 18–31%. The retention in soil of the C added in above-ground maize biomass averaged 11–15%. The >2 mm maize residues accounted for 7–21% of all the maize-C retained in soil after 11 years of maize cropping. Between 17 and 41% of the maize-C found in <2 mm soil was associated with POM. The amount and composition of the POM reflected the intensity of maize residue inputs but POM did also include biologically recalcitrant organic matter derived from pre-maize vegetations. In Danish light-textured soils with moderate C concentrations and with a history of cereal dominated cropping, continuous silage maize was able to increase soil C storage. Changes in natural abundance showed that the accumulation of maize-C was substantial even in soil showing moderate changes in soil total-C.
 
Article
Shoots of white clover plants were pulse-labelled with in order to establish the partitioning of recently assimilated carbon among the different parts of the plant–soil system with special interest in below-ground compartments. The did not change significantly after 24 h chase period. Leaves and stolons contained more than half of the total radioactivity recovered (%TRR). Soil residues (microbial biomass and non-metabolised rhizodeposits) accounted for 7%TRR and rhizosphere CO2 was 25%TRR. In order to investigate seasonal effects on assimilate partitioning below ground, we compared low photoperiod and day/night temperature conditions (10 h—20°C/18°C, PTL treatment) with high photoperiod and day/night temperature conditions (16 h—25°C/20°C, PTH treatment). Plants of PTH conditions favoured partitioning to leaves at the expense of storage organs such as stolons and roots. This was supported by distribution of the relative specific activity (RSA) which indicated a significant higher activity of leaves compared to roots. The reduction of allocated to roots (from 11%TRR in PTL treatment to 7%TRR in PTH conditions) was accompanied by a reduction of found in rhizosphere CO2 (from 25%TRR to 12%TRR) and in soil residues (from 7%TRR to 3%TRR). This indicated that rhizodeposition of recently fixed carbon is correlated to C allocation to roots. A moderate defoliation (27% of leaf biomass removed) did not modify within the plant–soil system. A severe defoliation (51% of leaf biomass removed) increased allocated to remaining leaves from 28%TRR to 37%TRR at the expense of stolons. Partitioning of labelled assimilates to below ground remained unchanged. It is suggested that the age of a plant strongly influences its response to leaf removal.
 
Comparison of mean values for subclover and grass characteristics obtained in both years and each cut
Comparison of N 2 fixation (mean %Ndfa and total N 2 fixed) by subterranean clover in each year determined by ID, NA and ND techniques, using the t-test
Comparison of some crop characteristics in each year, by t-test
Article
Pasture legumes are used as a source of biologically fixed N2. Several methods have been used to evaluate the amount of N2 fixed in mixed pastures, but none is considered clearly superior. In a Eutric Leptosol of southern Portugal, N2 fixation by subterranean clover mixed with grasses was evaluated over 2 years and subjected to several cuts by dilution (ID), natural abundance (NA) and N difference (ND) techniques. The amount of fixed N2 in subterranean clover determined by natural abundance with correction for isotopic fractionation ranged from 32 kg N ha−1 in 1992/1993 to 37 kg N ha−1 in 1993/1994. Assuming that no isotopic fractionation occurred during fixation (B=0‰), fixation capacities at around 80% of nitrogen derived from the atmosphere (Ndfa) were found by the natural abundance technique. However, with correction for isotopic fractionation during N2 fixation (B=−1.13‰), fixation capacities closer to 50% Ndfa were obtained, similar to the value obtained in the second-year experiment with the isotopic dilution method. In year 1, the fixation capacity, as estimated by the isotopic dilution method, was about 37% Ndfa. The nitrogen difference (clover N−grass N) calculations underestimated the amount of N2 fixed in 1992/1993. This method assumes that both legumes and non-legumes absorb the same amount of N from the soil, which may not be true. Also, only the above-ground legume herbage was analyzed in this experiment. From the results, either ID or NA methods, particularly with a correction for the B-value, can be used to estimate N2 fixation in mixed pastures, rather than the ND method. The natural abundance (NA) technique can be more versatile than the ID technique, allowing frequent sampling in undisturbed grassland ecosystems with reduced costs. Nitrogen fixation decreased in June, in both years, probably due to a lower soil water content and higher soil temperature.
 
Article
In southern Europe, information on the biological nitrogen (N2) fixation capacity of grain legumes in the field is scarce. At two locations in Portugal on Haplic Luvisols, N2 fixation by fababean, pea and chickpea was evaluated over two consecutive years by the isotope dilution technique, using barley as the control crop. Crop growth and N2 fixation varied between sites and years. The legumes derived more than 60% of their N from the atmosphere under favourable soil conditions, but the proportion was reduced when the availability of soil moisture and molybdenum (Mo) were constrained. Annual rates of N2 fixation by uninoculated fababean varied from 76 to 125 kg N ha−1, with a regular rainfall distribution during the growth cycle (the first year experiment), and from 55 to 72 kg N ha−1 under drought stress (the second year experiment). Annual rates of N2 fixation by uninoculated peas varied from 31 to 107 kg N ha−1 with regular precipitation, and from 4 to 37 kg N ha−1 under drought stress. Chickpea was tested only in a drought year, when it fixed from 19 to 24 kg N ha−1. Mean values for N derived from the atmosphere by chickpea varied from more than 70% at one location to less than 45% at another, where Mo was later found to be deficient. Inoculation with Rhizobium leguminosarum did not significantly affect the N2 fixed by fababean in the drought year, whereas peas fixed 50% or more N after inoculation. Inoculation with Bradyrhyzobium cicer did not improve fixation by chickpea. Based on the N economy of the shoots, it appeared that any N addition to the soil in harvest residues varied with crop and location.
 
Article
The influence of fertiliser incorporation and band injection on immobilisation and nitrification of ammonium-nitrogen (N) was investigated in a bare soil field experiment. Total and inorganic forms of in the 0–20 cm soil layer were measured on days 0, 7 and 16 after application in framed micro-plots. Injection of the nitrogen fertiliser in a concentrated band reduced immobilisation, leaving more of the applied fertiliser-N available to plants. Band injection also reduced the nitrification rate from 2.7 to 1.8 kg N ha−1 per day and thus reduced the risk of N leaching losses until depletion of the soil inorganic N pool by crop uptake.In a parallel field experiment, crop recovery of inorganic N forms was studied in framed micro-plots. Bands of , or solutions were injected parallel to a single row of spring wheat at early tillering. The injection depth as well as the band distance from the crop row was 5 cm. Root damage by injector tine was simulated using a knife. In addition, a treatment without root cut-off was included for the application to study effects of injector-tine-caused root damage on uptake. The crop recovery was calculated on eight sampling dates during the elongation phase; a sigmoid growth function was fitted for each of the four treatments and uptake parameters were estimated.The crop uptake of banded nitrogen occurred within 4 weeks after application and the average maximum crop recovery of 65% was not significantly affected by the treatments. Maximum uptake rate varied within 5.6–8.2 kg N ha−1 per day. Simulation of an injector tine by root cut-off delayed the start of uptake by 2–3 days, and reduced the maximum uptake rate by 2.6 kg N ha−1 per day. Differences between the ammonium- and nitrate-derived uptake courses were not significant. In contrast to findings for broadspread N-fertilisers, the crop uptake of ammonium-N and nitrate-N may be considered as similar after band injection of the fertiliser.
 
Article
The residual effect of 2-year-old swards of clover-ryegrass mixture and ryegrass in monoculture on yield and N uptake in a subsequent winter wheat crop was investigated by use of the 15N dilution method and by mathematical modelling. The amount of N in the wheat crop, derived from clover-ryegrass residues was 25–43% greater than that derived from residues of ryegrass which had been growing in monoculture. Expressed in absolute values, the N uptake in the subsequent winter wheat crop was 23–28 kg N ha −1 greater after clover-ryegrass mixture than after ryegrass in monoculture. Up to about 54 kg N ha−1 of the N mineralised from the clover-ryegrass crop was calculated to be leached, whereas only 11 kg N ha−1 was leached following ryegrass in monoculture.
 
Article
In order to avoid nitrogen overfertilization, fertilizer rates must be adjusted to meet crop requirements. Two field experiments with sunflower (Helianthus annuus L.) were performed in the western part of the Pampas, Argentina, to: (i) assess nitrogen fertilization effects on seed yield, grain oil content, and plant lodging, (ii) determine N requirement per unit of yield, crop recovery of fertilizer N, and whether these two parameters were affected by N and other nutrient additions. Nitrogen fertilization increased the seed yield only by 17% at one site. Crop nitrogen requirement per unit yield (b-value) increased from 37 to 42 kg Mg−1 due to nitrogen fertilization only at the site where there was not a yield response. Therefore, if a yield response is expected, it is not necessary to use different b-values for non fertilized or fertilized crop. Reduction of seed oil content due to N addition was relatively small (2–5%), and was overcompensated by the seed yield increase at the responsive site. Recovery of fertilizer 15N was of 51%. This efficiency of absorption should be considered for making fertilizer recommendations. Application of further nutrients including P and K had no influence on seed yield.
 
Article
The fate of 15NH4-N labelled cattle slurry applied before sowing in September of a winter wheat crop was studied on a loamy sand soil. The aim was to quantify immobilization of slurry NH4-N into microbial biomass, the speed at which nitrate derived from the slurry NH4-N was transported down the soil profile, and the utilization of slurry NH4-N by the winter wheat crop. Cattle slurry was applied at a rate corresponding to 75 kg NH4-N ha−1 , with very little loss by volatilization (<4%) due to rapid incorporation by ploughing. The slurry amendment resulted in a doubling of soil surface CO2 flux, an index of microbial activity, over non-amended soil within the first c. 2 weeks, but ceased again after c. 4 weeks, due to depletion of the easily degradable substances, e.g. volatile fatty acids, in the slurry. Nitrification of the applied NH4-N was fast and complete by 3 weeks from application, and at this time, the maximum immobilization of slurry NH4-N into the microbial biomass (23% of applied 15NH4-N) was also observed, although no significant increase in total microbial biomass was observed. Rapid turnover of the microbial biomass quickly diluted the assimilated 15N, with only 6% of applied 15NH4-N remaining in the microbial biomass by next spring. Downwards transport of nitrate was rapid in spite of lower than normal precipitation, and slurry-derived 15NO3-N appeared in ceramic suction cups installed at 60 cm depth already 2 months after slurry application. Due to the unusually low winter precipitation in the experimental year, wheat yields were high, and the recovery of N in above-ground plant biomass derived from slurry NH4-N at harvest reached 32%. An additional 45% of the applied slurry NH4-N could be found in the soil to a depth of 100 cm (mostly in organic form in the plough layer), indicating that 23% had been lost by leaching or in gaseous form. It was concluded that although significant immobilization of slurry NH4-N did occur, this was not sufficient to prevent leaching of slurry-derived N over the winter and that the relatively high recovery of slurry-derived N in the wheat crop was due partly to lower than normal winter percolation and partly to a relatively high rooting depth on this particular site.
 
Some characteristics of the Haplic Luvisol at Elvasa
Residual N in the Haplic Luvisol, as affected by year, treatment, and depth, and results of ANOVA to evaluate the effects of year, depth, and treatment on residual soil Na
Article
We studied the fate of 15N-labelled fertilizers applied to winter wheat (Triticum aestivum L., cv. Tejo) grown for 3 years on a Haplic Luvisol in southern Portugal. The nitrogen rate used was 60 kg ha−1 using ammonium nitrate as basal dressing, and two top-dressings of 60 kg ha−1 of N each, either as urea or calcium nitrate. Microplots (PVC cylinders with 30 cm diameter) with ceramic cups placed at the bottom were used, so that leachates could be collected by hand pumping. A greater percentage of plant N was derived from the fertilizer in the driest year (year 1) than in the other two years. However, biomass accumulation was smaller in that year and, therefore, plants took up less N. As a result, the recovery of 15N-labelled fertilizer in the crop was in the range of 22–40%, with no significant differences between years or treatments. Considerable amounts of N derived from fertilizer remained in the soil after harvest (15 to 66% of total fertilizer N). In years 1 and 2, the 15N in the soil derived from fertilizer was similar, and not significantly affected by N form. In year 3, top-dressing with urea led to more of the 15N from fertilizer remaining in the soil, compared with applying nitrate, and to greater values of total soil N, nitrate and extractable ammonium. There was evidence of nitrate leaching in years 2 and 3, particularly after the first two N applications, during the autumn–winter period, but not significantly affected by treatment. A significant amount of 15N remaining in the soil was in fixed in the clay fraction, especially in the surface layers and with urea application, suggesting that ammonium fixation in montmorillonite was an important process for removing NH+4 from solution and protection from nitrification. N losses were similar (35 to 55%) in years 1 and 2 with both treatments, and in year 3 with ammonium nitrate+calcium nitrate application. In year 3 the ammonium nitrate+urea treatment resulted in a complete recovery of 15N applied.
 
Article
Changes in yield potential brought about by durum wheat breeding in Italy can be used to define future breeding objectives for durum improvement in Mediterranean environments. The grain yield of 20 durum wheat cultivars, grouped according to their period of release, into ‘old’ (up to 1950), ‘intermediate’ (1950–1973) and ‘modern’ (1974–2000), was compared in an irrigated 2-year field trial, in which two sowing dates and two nitrogen fertilisation rates were imposed. The grain yield of the intermediate cultivars was 39% higher than that of those in the old group, but 18% less than that of the modern material. This increase was associated with earliness, kernel number, harvest index and total nitrogen uptake. Total above-ground biomass and individual kernel weight, on the other hand, were largely unaffected by breeding. Sowing date did not affect the ranking of cultivars, although the more modern cultivars benefited most from the availability of more soil nitrogen. By accessing syriacum germplasm, Italian breeders achieved a substantial improvement in the earliness and productivity of durum wheat well before the introduction of Rht genes. The introduction of dwarfing genes reduced lodging susceptibility, increased harvest index, and marginally delayed flowering time. Modern cultivars also out-performed their predecessors both when sown later and when provided with suboptimal levels of N fertiliser.
 
Article
Mineral balances, especially nitrogen balances, are analysed for 138 dairy farms over 3 consecutive years, 1997, 1998 and 1999, together with analyses of annual changes in strategy concerning the use of mineral fertiliser at the farm scale. Information was obtained from mineral balance sheets of dairy farmers who shipped milk to the dairy plant Dairy Skåne. The mineral balance sheets for N, P and K were constructed using the farm gate model and a balance was calculated for the whole farm. Arable land was approximately 65 hectares and the annual milk delivery per hectare was around 6800 kg. Nitrogen surplus per hectare among dairy farms in the south of Sweden is lower than that found in the intensive milk production regions in Western Europe. Dairy farms that had an output of both crop and animal products had a lower N surplus and a higher N efficiency. The N surplus among the investigated dairy farms decreased between 1997 and 1999. Input of N from purchased mineral fertiliser decreased significantly from the first year.
 
Article
SOILPAR 2 is a program for estimating soil parameters. It allows: (1) storing soil data in a georeferenced database, (2) computing estimates of soil hydrological parameters using 15 procedures, (3) comparing the estimates against measured data using both statistical indices and graphics, and (4) creating maps using the ESRI format. An interface to/from Excel and CropSyst is provided. Eleven methods estimate one or more of the following characteristics: soil water content at predefined soil matrix tension, saturated hydraulic conductivity, and bulk density. Three methods estimate the parameters of well-known soil water retention functions (Brooks-Corey, Hutson-Cass, van Genuchten), and one estimates both saturated soil hydraulic conductivity and the soil water retention curve parameters (Campbell). The software runs under Windows 98/NT/2000/XP and is freely downloadable via internet.
 
Article
Root chicory is a potential alternative sugar crop which accumulates a high amount of linear fructose polymers (fructan) in its roots. Lengthening the growing season by early sowing may increase root chicory yield potential, and thus increase its competitiveness with traditional sugar crops. A field experiment was conducted in 1998 and 1999 on a sandy loam soil (Haplic Luvisol) at Braunschweig, Germany, to study the consequences of early sowing on emergence, bolting, yield, and quality of root chicory. In each year, the cultivars Tilda, Wixor, Hicor, Cassel, Bergues, Fredonia Nova, and Regalo were sown at three dates ranging from mid March to early May. The mean emergence rates for the early sowings in March were insufficient in 1998 (45%) but adequate in 1999 (82%). Averaged across years and cultivars, emergence took 25, 21, and 13 days at early, medium, and late sowing. While bolters were almost absent at medium and late sowing, average bolting percentage at early sowing amounted to 18.3% in 1998 and 22.7% in 1999. Each percent of bolters reduced fructose yield by 1.1% in 1998, and 1.2% in 1999. In 1998, the fructose yield of the most productive cultivars at early sowing (Bergues) and at medium sowing (Fredonia Nova) were not significantly different. In 1999, early sown Bergues produced a significantly higher fructose yield than any other cultivar and sowing date combination. It is concluded that increasing root chicory yield potential by early sowing is not limited by a lack of bolting-resistant cultivars, but by the risk of poor crop establishment due to unfavourable weather conditions.
 
Article
Fourteen durum wheat (Triticum durum Desf.) cultivars introduced in Italy between 1900 and 1990 were grown for 2 years (2001 and 2002) at Foggia (Italy) in field trials with three agronomic treatments in order to assess the genetic improvement in agronomic and qualitative parameters. The traits were measured in the field to describe the biomass production and its partitioning to the grain, the phenological behaviours and the photosynthetic properties. Grain protein content, alveograph's W-index, carotenoid pigments content, ash content and the glutenin and gliadin subunit compositions were then measured to assess grain quality. The results showed that differences in agronomic traits among durum wheat cultivars released in Italy in the last century are generally similar to differences observed in hexaploid wheat, with an annual genetic yield gain of 19.9 kg ha−1 year−1. The genetic gain was most clearly associated with a higher kernels number m−2 indicating a larger grain-sink size and a higher number of spikes m−2. The gradual reduction in plant height associated with an increased harvest index has represented the main breeding goal with an effect on the sink capacity and on the biomass partitioning. The progressive incorporation into recent cultivars, of favourable alleles (7 + 8 glutenin subunit composition) coding for superior quality subunits reflects the improvement in pasta making quality of the recent genotypes.
 
Simulated vs. observed values (validation set) of flowering date (ADAT), maturity date (MDAT), crop weight at harvest (CWAH) and final leaf number (L#AM). The thin line represents 1:1 relationship between simulated and observed values. The bold lines above and below the 1:1 line represent +10 and −10% of the observed values. Also represented is the root mean square error of the agreement between simulated and observed (dap = days after planting).  
Combinations of planting dates and cultivars tested in the field experiment for each year
Estimated genetic coefficients (average of the number of estimates/treatments) for six cultivars based on a 3-year field experiment with combinations of cultivars and planting dates
Article
Maize (Zea mays L.) silage is of major importance for milk production in the Northwest of Portugal. Farmers typically have a variety of maize hybrids to choose from according to cycle length and sowing date. The general recommendation regarding cultivar selection is to use long cycle cultivars for early sowing dates and vice versa. Cycle length, sowing date and temperature regime will determine the harvest date. Because weather regime is unknown at sowing date, there is a need to develop decision support based on historical weather series to help farmers optimize silage production. Production optimization occurs through a better matching of cycle length to sowing date to produce more and better silage at optimal harvest dates. The CERES-Maize crop model was used to establish decision support to help farmers identify the best cultivar and sowing date combinations. Cultivar parameters were estimated from 3-year field experiments involving five planting dates and six cycle lengths (FAO 200 to 700). The model was run with 39 years of historical weather data, simulating 18 sowing dates and 6 cycle lengths. Decision support was developed based on the analysis of simulation outputs and three integrated risk management strategies. Tactical use of guidelines is illustrated with examples. Current limitations of the model for maize silage simulation are also discussed.
 
Article
During 31 years (1969–1999), we measured the yields of permanent grassland and of 3-year temporary leys alternating with 3-year periods of arable forage crops. The average feed energy yields of both types of grasslands, respectively 75.1 and 73.3 GJ Net Energy for Lactation ha−1, were not significantly different. Possible preconditions for the lasting high production level of the 31-year old, never reseeded permanent pasture were the high fertilization level (200–350 kgN ha−1 year−1) and the preservation of a fairly good botanical composition. The temporary grasslands produced as much as the permanent grassland without the necessity to apply higher amounts of fertilizer N during their 3-year lifetime.
 
Article
Information on the amount and spatial distribution of plant roots is increasingly needed for understanding and managing crop behaviour. Soil electrical resistivity (ρ) tomography has been proposed as a non-destructive method for root biomass quantification and mapping in trees but evidence is needed on the applicability of the technique at low root density and in herbaceous plants.We produced high-resolution 3D DC soil resistivity tomograms in containers with bare soil (B), and alfalfa (Medicago sativa L.) (A1) on a silt loam soil, and alfalfa on a loam (A2). Root biomass (RMD), root length density (RLD), soil electrical conductivity (EC) and water content (θ) were measured destructively.The pattern of soil resistivity matched the spatial distribution of θ in bare soil and of RMD in rooted soil. Univariate linear relations were found between ρ and θ in bare soil and between ρ, RLD and RMD in rooted soil. Across all data RMD and soil texture (P < 0.01) explained a high proportion of variability in soil resistivity.This allows to conclude that soil resistivity is quantitatively related to root biomass in herbaceous plants even at low root density (biomass < 0.001 Mg m−3), providing a basis for the development of resistivity-founded methods for the non-destructive spatial detection of root mass in situ, but the response in ρ is of the same order of magnitude as the effects of grain size and water content. Therefore in field studies reciprocal masking of low-density roots and other soil features is possible, and the effect of variation in other soil properties should be explicitly addressed.
 
Article
Improving current cultural practices often involves more precise timing of the management activity based on crop development. Using crop simulation models to predict crop development and phenology has several problems. First, most existing models do not simulate sufficient developmental and phenological detail required to optimize selected management practices. Second, crop models normally emphasize the cultivars and conditions for the region in which they were developed, and may not generate satisfactory results when applied in new regions. Lastly, when users apply these models to new regions they often lack the specific data and knowledge of the model to adequately determine the crop parameters. Our objective was to assess whether the simulation model SHOOTGRO 4.0, which had the necessary level of developmental and phenological detail required for use as a management decision aid, could be easily and adequately parameterized to simulate winter wheat phenology and grain yield in the Czech Republic. We found that only a few parameters from the generic winter wheat cultivar used for the Central Great Plains in the USA needed to be changed, and the information needed to determine these few parameters were readily obtainable. The result was that the dates of anthesis and physiological maturity and final grain yield were predicted well at sites within the three major crop production regions of the Czech Republic. Sensitivity analysis also showed that the most sensitive management practices and initial conditions in SHOOTGRO are relatively easy to determine (e.g. sowing date, N fertilizer rate and timing, daily temperature), while it is not overly sensitive to those variables more difficult to determine (e.g. initial soil water in the profile). Based on this study, farmers and scientists needing wheat development information to increase the efficacy of their management practices can use SHOOTGRO 4.0 as a tool.
 
Article
Maize (Zea mays L.) growth in non-typical maize growing regions has several limitations with respect to agronomic characteristics of cultivars, and their reactions on changes of production system in specific climate. Two long term field experiments were carried out to investigate the effect of plant populations (PP) on the leaf area index (LAI), grain yield and cob characteristics of maize cultivars in Maribor, Slovenia. In the first experiment, an increase of PP from 4.5 to 13.5 plants per m2 did not affect the LAI of four older maize cultivars at the 7–9-leaf stage, but significant differences between cultivars, years and PP appeared at brooming (from 1.58 to 7.07). In this stage, a strong correlation existed between LAI and grain yield (r=0.87**). Reduction of LAI from brooming to waxy maturity averaged 9.7%. PP explained 93–99% of the variation in grain yield depending on cultivars. Some cultivars lodged at the highest PP in some years. Increased PP significantly changed the following cob characteristics, weight of 1000 kernels, cob length, number of kernel rows, and number of kernels per row. In the second experiment, 11 recent cultivars expressed a relatively small trend of grain yield increases when PP was increased from 7 to 13 plants per m2. At high PP, the percent of plants decaying after emergence increased up to 27% during the vegetation period. Therefore, we conclude that the information on suitable PP for each maize cultivar is one of the key factors for planning maize production.
 
Effects of salinity on TSS, TA and TSS:TA ratio of lemon fruits of Fino 49 grafted on Citrus Macrophylla in year 2000. Trees were grown under three irrigation water salinity treatments: S0 (1 dS/m), S1 (2.5 dS/m) and S2 (4.0 dS/m) and two amounts of applied water: 100ETc and 125ETc. Each values is the mean of five samples of fifteen fruits (9/S.E.).  
Effects of salinity on leaf area of Fino 49 lemon grafted on Citrus Macrophylla in year 1999. Trees were grown under three irrigation water salinity treatments: S0 (1 dS/m), S1 (2.5 dS/m) and S2 (4.0 dS/m). Each value is the mean of twenty leaves (9/S.E.).  
Effects of salinity on leaf chloride and sodium concentrations of Fino 49 lemon grafted on Citrus Macrophylla in year 1999. Trees were grown under three irrigation water salinity treatments: S0 (1 dS/m), S1 (2.5 dS/m) and S2 (4.0 dS/m). Each value is the mean of four samples (9/S.E.).  
Effects of salinity on potassium, magnesium, calcium and phosphorus concentrations in leaves of Fino 49 grafted on Citrus Macrophylla in year 1999. Trees were grown under three irrigation water salinity treatments: S0 (1 dS/m), S1 (2.5 dS/m) and S2 (4.0 dS/ m). Each value is the mean of four samples (9/S.E.).
Effects of salinity on total-N and nitrate-N concentrations in leaves for Fino 49 grafted on Citrus Macrophylla in year 1999. Trees were grown under three irrigation water salinity treatments: S0 (1 dS/m), S1 (2.5 dS/m) and S2 (4.0 dS/m). Each value is the mean of four samples (9/S.E.).  
Article
Potential problems associated with saline irrigation waters can be compounded by irrigation practices. Methods for water application become of prime importance under saline conditions. The effect of irrigation water quantity and salinity on fruit yield, fruit quality and leaf mineral composition were studied in a field experiment with 6-year-old lemon trees, cv. Fino 49, on the Macrophylla (Citrus Macrophylla Wester) rootstock during 1998–2000. Trees were irrigated with three different qualities of water, having an electrical conductivity 1, 2.5 and 4 dS/m, respectively. For each salinity treatment, trees were irrigated with two different quantities of water, 100 and 125% crop evapotranspiration. Lemon fruit yield significantly decreased with increasing salinity, due to a decrease in the number of fruits per tree. This reduction was caused by an increase in fruitlet drop off induced by salinity. A significant increase of lemon fruit yield was observed in the last year by increasing the quantity of water. Salinity and amount of water applied affected fruit quality. The percentage of fruit juice, with respect to the total fruit weight, was greater in fruits from the control than for those in the salinity treatments. The opposite effect was observed for peel and pulp contents. Titratable acidity (TA) and total soluble solids (TSS) decreased with salinity, although the ratio TSS:TA was similar in all treatments. Chloride and sodium concentrations in leaves were raised by salinity and amounts of water applied. Data on accumulation of other nutrients in relation to salinity, water application and season are also presented.
 
Simulated water contents of a soil layer (depth: 0.55 Á/ 0.70 m, Mezö tú r, Hungary, 1987) characterised by bimodal porosity.
Simulated water contents of a soil layer of a profile (depth: 0.50 Á/0.70 m, Nyirö lapos, Hungary, 1999) with shrinking Á/swelling characteristics.
Article
4M is an easy-to-handle software that has been designed for both educational and scientific purposes. Our main goal in developing 4M was to preserve the features of CERES in a user-friendly software that can be easily extended with additional modules. The package has several characteristics that make it more than a simple crop model. 4M offers optional routines for several processes of the described soil-plant-atmosphere system. The users can build different system models, according to specific purposes. 4M includes input data generators for estimating soil and weather input data that are difficult to measure. 4M is able to simulate crop rotations by using the final conditions of the system after crop harvest as initial conditions for the following crop.
 
Article
Grasslands species, like others crops, no longer benefit from high atmospheric sulphur deposition. This may cause sulphur limitation and in turn may induce a shift in plant communities by altering species performance and competitive abilities. To test this hypothesis, a greenhouse pot experiment was designed to investigate the interacting effects of sulphur (S) and nitrogen (N) availability on production, morphology and competitive abilities of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). Plants were grown in monocultures and mixtures during 4 months. They were supplied with combinations of three levels of S and three levels of N and subjected to three defoliation events. Both S and N gradients altered plants performance and modulated competitive interactions. In L. perenne, above- and below-ground dry matter production, leaf and tiller number and contribution to mixture DM production were little affected by S, but highly by N. For T. repens, these traits were significantly increased by S, but only slightly by N. At establishment, T. repens was subjected to a significant interspecific competition at low N–low S and high N–high S. But at regrowth (cuts 2 and 3), T. repens was much more affected by intra- than interspecific competition. L. perenne was only sensitive to competition (intraspecific) when N supply was combined with no or moderate S supply. We conclude that N:S ratio of soil appears to drive species production, morphology and competitive abilities, which in turn affect leguminous–gramineous species ratio and grassland plant community structure. Since the growth of T. repens was significantly reduced in low S treatments, our results suggest that the drastic fall in atmospheric sulphur deposition could restrict leguminous species in high N soil conditions.
 
Article
Evening primrose (Oenothera spp.) is a high-value oilseed crop for temperate areas which may be either overwintered or spring–sown. Light absorption, light use efficiency, water loss and biomass water ratio were compared between overwintered and spring–sown crops of cv. Merlin in two years of field trials. An overwintered crop of cv. Peter was also studied in year two. The energy content of evening primrose plant material was shown to be similar to other crops. Both overwintered and spring–sown crops can achieve full canopy closure and maintain high fractional photosynthetically active radiation (PAR) interception for long periods but canopy closure occurred much later than in other temperate seed crops. In spring–sown evening primrose, maximum PAR interception did not occur until August, by which time incident light levels were declining and consequently the proportion of incident light energy captured during the main growing season was low. Most light was intercepted by green leaves and very little shading by senescent tissue and flowers occurred. Light conversion efficiencies for the main growing period were comparable with other temperate C3 crops, but in year two a steep decline in light conversion efficiency was observed as the crops matured and the soil water deficit exceeded 60 mm. In year one, water loss from both the overwintered and spring–sown crops were low and the soil water deficit increased relatively slowly. By contrast, in the year two crop water loss was high and the soil water deficit built up very rapidly between the end of June and crop maturity. No significant differences in biomass water ratio (water use efficiency) were recorded between overwintered and spring–sown crops but ratios were 50% higher in year one than in year two. Although no relationship was detected between biomass water ratio corrected for vapour pressure deficit (“normalised”) and soil water deficit, after canopy closure normalised daily water loss declined with increasing soil water deficit. Earlier canopy closure, particularly in the spring crop, and the avoidance of soil water deficits through irrigation, would lead to substantial improvements in the size and consistency of seed yields of evening primrose crops.
 
Article
Like most plants, pea (Pisum sativum L.) becomes tolerant to frost if it is first exposed to low non-freezing temperatures, a process known as cold acclimation. Cold acclimation is a complex process involving many physiological and metabolic changes. Two spring dry peas, two winter dry peas and one winter forage line were exposed to cold temperature in a controlled environment in two experiments, one using low light intensity and the other regular light intensity. Plants were harvested throughout the experiment and dry matter accumulation, water content, soluble and insoluble sugar concentrations were determined from shoot and root samples. Cold acclimation did not occur when temperatures were low if light intensity was low, even in winter peas. In contrast, with regular light intensity, the winter peas acquired more freezing tolerance than spring peas and a close relationship was found between the soluble sugar concentration of leaves just before the frost and the degree of freezing tolerance obtained by the different genotypes. Relationships between freezing tolerance and carbon partitioning between shoot and roots are discussed.
 
Article
Nitrogen balance sheets are in widespread use in the Netherlands. First introduced in the 1980s as a voluntary management instrument for dairy farmers, the method has since been developed and formalised in the MINerals Accounting System (MINAS) policy instrument. This is designed to reduce nitrogen (N) and phosphorus (P) losses. As from 2003, MINAS allows a maximum N surplus on grassland of 180 kg N ha−1 on clay/peat soils and 140 kg N ha−1 on dry sandy soils. In 1997, the mean N surplus on dairy farms in the Netherlands was 324 kg N ha−1. Meeting the MINAS loss standards for 2003 was the objective for the farmers participating in the Cows&Opportunities project. Each farm received a tailor-made fertilisation scheme to reduce N losses and optimise N use. Most farms succeeded in realising a lower N loss than planned in their fertilisation schemes. On the experimental dairy farm De Marke the aim is to get the nitrate content in the shallow groundwater below the EU standard of 50 mg l−1 (=11, 3 mg N l−1). Since 1993 the farm has succeeded in realising low N surpluses (1997: 76 kg N ha−1) and low nitrate concentrations (1993–1999 mean: 55 mg l−1). A clear relation was found between N management, as expressed by the N surplus, and nitrate concentration in the groundwater. However, in some years this relation was disturbed. The results show the value of N balance sheets for reducing N losses. From an agricultural point of view, a major advantage of a system such as MINAS is the autonomy it gives farmers to determine how and where they will reduce the N surplus. Using MINAS, however, is no guarantee that a nitrate concentration of 50 mg l−1 will always be achieved.
 
Article
Field experiments conducted in 2007/08 and 2008/09 at the Changwu Agricultural Research Station on the Loess Plateau of China comprised three seeding rates (SR1: 225 seeds m−2, SR2: 280 seeds m−2, and SR3: 340 seeds m−2) and two root pruning treatments (W: root pruning in the over-wintering period and S: root pruning at the spring-growth stage), with the un-pruned wheat plants as controls. In the severe drought toward the end of the growing season of 2008, grain yield decreased as the seeding rate increased, but under the more favorable conditions in 2009 the reverse was true. Averaged over the seeding rates, grain yield was significantly increased in both W and S in both years; grain yield and yield components were higher in W; and S recorded the highest water use efficiency. The interaction between seeding rate and root pruning was not statistically significant. Leaf area index (LAI) and tiller density were higher as seeding rates increased whereas in W and S, increased LAI and decreased tillers significantly, but had no effect on fertile tillers. The rate of leaf photosynthesis was lower and root respiration was significantly higher at higher seeding rates, whereas in root pruning treatments, significantly higher leaf photosynthetic rate and lower root respiration were observed. Soil water contents were lower as seeding rate increased. A significant decrease in water use before stem elongation was observed in W, while S consumed less soil water than W and the control over the whole growing season. Post-heading accumulation of dry matter and its remobilization from vegetative parts to the grain was significantly greater at higher seeding rates. Post-heading accumulations of dry matter and grain yield were also significantly greater in W and S than the un-pruned plants, although pruning reduced both dry matter remobilization and its contribution to grain yield. The possibility of reducing the proliferation of roots to increase yields at higher seeding rates and conserving the soil water at different growing stages in water-limited environments is discussed.
 
Article
Durum wheat (Triticum turgidum subsp. durum L.) is being increasingly grown in many areas of the world, but there is a lack of information about the physiological processes limiting grain yield. In this study, different rates of N and P fertilization were applied and the source:sink ratio was manipulated to examine the factor(s) limiting grain filling under rainfed conditions. Plants exposed to four fertilization treatments (control, 80 kg N ha−1 (N), 50 kg P ha−1 (P) and 80 kg N ha−1 and 50 kg P ha−1 (N–P)) and were artificially modified to obtain a range of different source:sink ratios. The treatments were (I) control; (II) half of the spike was removed; (III) all the spike was removed. The cultivar Cosmodur was used, which is widely grown in Greece and other Mediterranean countries and is quite productive especially under rainfed conditions. The distribution of dry matter, N and P among grains, stems and leaves was analyzed at anthesis and harvesting. Dry matter accumulation and partitioning into different plant parts was different between the fertilization treatments and the control. At anthesis, leaf + culm dry matter was higher than the chaff dry matter. Total aboveground biomass increased after anthesis in both years and at all fertilization treatments. N fertilization affected N concentration at the whole plant level at anthesis and at maturity. There was an average increase of 20% in N concentration with N application at anthesis in both years relative to the control. N content was affected by the fertilization treatments and it was increased by 33% over the 2 years of the study compared with the control. In addition, P fertilization affected P concentration both at anthesis and maturity in every plant organ, and there was also a significant effect of the change of P concentration at the two different growth stages. P accumulation was also affected by the fertilization regime and by the spike halving treatment. Dry matter translocation was an average of 22% higher at the fertilized treatments compared with the control, which indicates that fertilization led plants to translocate higher amount of dry matter. N and P translocation were affected by the fertilization treatment and in some treatments by the sink reduction. The spike reduction treatment increased the pre-anthesis contribution to seed indicating that the N and P remobilization from vegetative tissues were very important for grain development. The present study indicates that N and P fertilization and sink size can affect dry matter, N, and P accumulation, partitioning, and retranslocation of durum wheat which can affect seed yield.
 
Article
Effects of mineral nutrition and temperature on accumulation and composition of protein in wheat grains and on baking quality were studied under controlled environments. Under a moderate temperature regimen of 24 °C days and 17 °C nights (24/17 °C), post-anthesis N:P:K 20:20:20 (NPK) supplied by continuous drip irrigation increased the rate of protein accumulation, doubled flour protein percentage and slightly increased final single kernel weight. In contrast, post-anthesis NPK had almost no effect on rate or duration of protein accumulation or flour protein percentage under a high temperature regimen of 37 °C days and 28 °C nights (37/28 °C). The 37/28 °C regimen shortened and compressed the stages of grain fill, reduced the duration of dry matter accumulation, and reduced single kernel weight by 50%. Rate and duration of protein accumulation in thermal time and total protein per grain at 37/28 °C with or without NPK were similar to that at 24/17 °C in the absence of post-anthesis NPK. Protein percentage was higher for flour from grain produced at 37/28 °C with or without NPK than at 24/17 °C in the presence of post-anthesis NPK. Transcript and protein profiling studies confirmed that the 37/28 °C regimen compressed development without disrupting coordinate synthesis of gliadins and glutenin subunits, although some specific effects of NPK and temperature on relative amounts of individual gliadins and glutenins were observed. Transcript levels for ω-gliadins, α-gliadins and high molecular weight glutenin subunits (HMW-GS) declined at 24/17 °C in the absence of post-anthesis NPK, whereas transcript levels for low molecular weight glutenin subunits (LMW-GS) and γ-gliadins showed little change. Two-dimensional gel electrophoresis (2DE) demonstrated that relative spot volumes for several ω-gliadins, α-gliadins and HMW-GS were lower at 24/17 °C in the absence than in the presence of post-anthesis NPK, whereas the relative spot volume for a major LMW-GS was lower in the presence of NPK. Effects of temperature on relative spot volume were generally smaller than effects of NPK. Compared to the 24/17 °C regimen in the absence of post-anthesis NPK, relative spot volume for some α-gliadins and HMW-GS were higher at 37/28 °C, with or without NPK, and relative spot volume for a major LMW-GS decreased at 37/28 °C. Loaf volume was correlated with flour protein percentage regardless of temperature regimen but mixing tolerance was highest for flour from grain produced under the 24/17 °C regimens with NPK.
 
Article
The use of winter cover crops in conjunction with minimum tillage may eliminate or at least mitigate the environmental problems associated with traditional maize tillage. The main goal of the present research was to study the accumulation of nitrogen and dry matter in the tops of silage maize under three cropping systems: (1) PLOUGH (=maize sown into an autumn-ploughed soil), (2) NW/MT (maize sown into frost-killed residues of the non-winterhardy phacelia and white mustard cover crops, and (3) RYE/MT (=maize sown into a stubble of forage rye whose above-ground phytomass was removed from the field shortly before maize planting). The experiments were conducted in the Swiss midlands and in the Jura range. Averaged across the five environments (=site × year combinations) tested, dry matter and nitrogen yields of maize were highest under PLOUGH and lowest under RYE/MT. These differences occurred as early as the 3rd leaf stage and remained until the end of the growing season of maize, but there were significant (P <0.05) interactions between environment and cropping system. Total yields of dry matter and nitrogen (maize plus rye) of the RYE/MT system tended to be higher than the dry matter and nitrogen yields of maize in the other systems. The effect of method of seedbed preparation (rototilling vs. band rotary hoeing) on the yields of dry matter and nitrogen was not significant; there were no interactions between maize cropping system and manner of seedbed preparation. Under RYE/MT, both the mineral nitrogen content of the soil (0–90 cm depth) prior to maize sowing and the nitrogen concentration in the maize tops throughout the growing season of maize were relatively low, indicating that the rye cover crop reduced the nitrogen supply to the succeeding maize crop through pre-emptive competition.
 
Article
Annual clovers are very popular forage crops in the Mediterranean areas. However, their herbage and seed yields are often reduced by high temperatures and water stress occurring during spring and summer. Field experiments using the four most widely grown forage legumes, berseem (Trifolium alexandrinum L.), crimson clover (T. incarnatum L.), Persian clover (T. resupinatum L.) and squarrosum clover (T. squarrosum L.), were conducted in 1992 and 1993 at Foggia (Italy) to evaluate the osmotic adjustment capability and the relevant contribution of inorganic and organic solutes in response to water deficits. Soil water depletion reduced leaf water potential (Ψw) and leaf osmotic potential at full turgor (Ψπ100) in both years. In particular, berseem and squarrosum clovers showed lower values (−1.46 and −1.51 MPa on average, for Ψw and Ψπ100, respectively). Furthermore, water-stressed plants showed an increase in potassium, reducing sugars and proline concentrations and a decrease in non-reducing sugar contents. Generally, about 80% of the measured cellular osmotic potential was attributable to assayed osmotically active solutes; the inorganic ions represented the major contributors (about 59%). However, only proline levels appeared to change clearly in terms of relative contribution to Ψπ100, showing an increase of about 2.2%, under water-stressed conditions. Statistically significant differences (P≤0.05) in the osmotic adjustment trait were not found for either species or year. Because clover species showed the same value for solute accumulation capability (0.34 MPa), degree of tolerance to dehydration and turgor maintenance but differed in leaf water parameters, other physiological and/or morphological traits will have to be investigated to better explain the performance of each species under water-stress conditions. However, the tendency of crimson and Persian clovers to maintain high leaf water potentials could be an example of a stress-avoidance mechanism.
 
Article
Weed suppression and green manure effects are two potential benefits of including a legume cover crop in vegetable cropping systems. A requirement for using autumn established cover crops, however, is to find species and cultivars adapted to the local climate and latitude. Knowledge about optimal sowing time is also needed. The objective of this study was to monitor the crop behavior, with special emphasis on winter survival and biomass production, of winter annual and biennial legumes sown at various times of year before the establishment of vegetables in the subsequent year. Low growing species/cultivars, including annual medics (Medicago spp.) and subterranean clover (T. subterraneum L. cv. Denmark), which may be suitable when vegetables transplanted directly into a senesced living mulch, showed poor winter survival and are thus not recommended for our climate. Taller species, including hairy vetch (Vicia villosa Roth.), crimson clover (T. incarnatum L.) and yellow sweetclover [Melilotus officinalis (L.)], which require mowing before the establishing of vegetables, showed much better winter survival and biomass production the subsequent year. The study showed however, that the suitability of these cover crops depends on cultivar, sowing time and climate region. The mineralization study showed that hairy vetch and white clover were rich in N and showed a high N mineralization rate. Mineralization of N from crimson clover and yellow sweetclover was lower. We conclude that hairy vetch, crimson clover and yellow sweetclover, used in the proper way, have potential as cover crops under northern conditions.
 
Article
The influence of crop density on the remobilization of dry matter and nitrogen from vegetative plant parts to the developing grain, was investigated in the durum wheat (Triticum durum Desf.) varieties Creso, Simeto and Svevo cultivated in the field at three seeding rates, 200, 250 and 400 seeds m−2. Variety × seeding rate interaction was unsignificant for all recorded characters. Grain yield declined in the order Svevo > Simeto > Creso. Yield differences mainly depended on the different number of kernels per unit land and, secondly, on mean kernel weight. Spike components differed among varieties: Svevo and Simeto showed more kernels per spikelet and Creso more spikelets per spike. Grain yield was highest with 400 seeds m−2 primarily due to the higher number of spikes per unit area, and secondly, to the higher mean kernel weight. Post-heading dry matter accumulation was highest in Svevo and lowest in Creso, but varieties showed a reverse order for dry matter remobilization and contribution of dry matter remobilization to grain yield. The increase of seeding rate increased both the post-heading dry matter accumulation and the dry matter remobilization from vegetative plant parts to grain. Nitrogen uptake of the whole crop and N content of grain was higher in Simeto and Svevo than in Creso. The N concentration of grain did not vary among varieties, but Svevo showed a markedly lower N concentration and N content of culms at maturity, which may be consequence of the high N remobilization efficiency performed by this variety. The N uptake by the crop was highest with 400 seeds m−2, but the N concentration of culms, leaves and even grain was slightly lower than with the lower seed rates. The post-heading N accumulation was by far higher in Simeto and Svevo than in Creso, whereas remobilization was highest in Svevo and lowest in Simeto. The percentage contribution of N remobilization to grain N was by far higher in Creso than in the other two varieties. Post-heading N accumulation and N remobilization were highest with the highest plant density, but the contribution of N remobilization to N grain content did not differ between seeding rates.
 
Article
The objective of the research was to quantify the changes in the accumulation of dry matter and N and P content of four durum wheat (Triticum durum Desf.) varieties grown on two soil types (sandy-loam and clay-loam), differing for texture, nitrogen content and water holding capacity. Plants were grown in containers and were rainfed until anthesis; irrigation was performed during grain filling to avoid water stress. The difference in total vegetative weight and nitrogen and phosphorus content of plants between anthesis and maturity was used to indirectly estimate the relative contribution of pre-anthesis assimilation and remobilization to grain yield. The behaviour of the four varieties was similar as they ranked in the same order for pre-anthesis and post-anthesis dry matter accumulation and grain yield and differences in soil characteristics induced similar changes in dry matter, N and P accumulation and remobilization. Soil type greatly affected the patterns of dry matter, N and P accumulation and remobilization. Plants grown on clay-loam soil had higher dry weight and N and P content both at anthesis and at maturity and higher grain yield at maturity, compared to plants grown on sandy-loam soil and the remobilization of dry matter, N and P were 75, 140 and 55% higher. Most of the grain carbohydrates originated from photosynthates produced during grain fill, as the contribution of remobilization of dry matter to grain yield did not reach 30%, while most of the grain N and P originated from the remobilization of N and P accumulated prior to anthesis as remobilization of N accounted for 73–82% of grain N content and remobilization of P accounted for 56–63% of grain P content.
 
Article
The understanding of growth and yield determining processes and of a wheat crop by optimizing controllable production inputs in a Sahelian environment can lead to improved crop productivity. In a 2 year study, wheat response to incremental irrigation and nitrogen (N) supply on crop growth and its association with biomass yield was examined. Increasing irrigation resulted in progressively higher leaf area index, increased crop growth rate, and increased above-ground biomass. Increasing N supply up to 120 kg N ha−1 resulted in more leaf area, chlorophyll, crop growth rate and above-ground biomass. Interaction between irrigation and N was significant for biomass yield. The highest response of crop growth parameters to N application was seen in the fully irrigated regime, the degree of response declined with the magnitude of deficit irrigation. Full benefit of water was observed in maximizing biomass yield when N was supplied at the rate of 120 kg N ha−1 in both years, harvest index was maximized when both inputs were optimal. There was a strong association between productive tillers, crop growth rate during the reproductive phase, leaf area and chlorophyll production with above ground biomass. Rooting depth as estimated by water extraction patterns differed in three irrigation regimes and were modified by N supply. The evapotranspiration (ET) biomass yield relationship was linear with a regression slope of 20.6 kg biomass per mm of ET over both years. This study showed that reduction in biomass yield in wheat limits the feasibility of reducing irrigation in the Sahel if the goal is to maximize above ground biomass and harvest index per unit area. Optimization of water and N inputs during the cropping season is critical for wheat to enhance crop growth processes and subsequent biomass yield and harvest index. With a limited water supply, water managers can either provide water to a few growers to meet full crop demand or adopt deficit irrigation to supply water to a larger number of farmers, providing more equitable distribution of scarce resources.
 
Article
A 4-year field study was carried out to determine dry matter and nitrogen accumulation until anthesis and at grain filling period and dry matter translocation and utilization in grain filling of barley. Twenty two-rowed spring barley (Hordeum vulgare ssp. distichum L.) cultivars originated from different countries (Yugoslavia, Germany, Australia, the Czeck Republic, Netherlands, France and USA) were grown during 1995–1998 on a non-calcareous chernozem soil near Novi Sad (45° 20′N, 15° 51′E, 86 m asl). Dry matter and nitrogen accumulation depended on the cultivar and year. In a year with favorable weather conditions, 58% of dry matter was accumulated during pre-anthesis, while in a year with less favorable weather the amount was 48%. In the favorable year 91% and in unfavorable year 65% of nitrogen was accumulated until anthesis. The results indicated that the greater amount of dry matter and nitrogen accumulated before anthesis. Dry matter translocation efficiency depended on the cultivar and ranged from 3 to 16.4%, while the contribution of pre-anthesis assimilates to kernel varied from 4 to 24.2%. Cultivars that have been developed for the growing conditions of the area where the experimental site was located, i.e. adapted ones, did not use pre-anthesis dry matter for grain filling. High positive correlations (P<0.01) were found between biomass at anthesis and biological yield, dry matter translocation efficiency, contribution of translocated dry matter to grain yield, and total plant nitrogen at maturity. Accumulated nitrogen at anthesis was positively correlated (P<0.01) with growing degree–days until anthesis, dry matter at anthesis and dry matter translocation parameters. Heritability for the investigated characters was rather high, over 0.60.
 
Article
Mineral accumulation in vegetative plant parts and in mature kernels has been proposed as an indirect selection criterion, either in addition to, or in substitution of, carbon isotope discrimination (Δ), to assess grain yield of temperate cereals in Mediterranean areas. However, the association between mineral concentration, in different plant parts, and grain yield is not yet fully understood. In order to study these relationships, four rain-fed trials were established in northeastern Spain involving 10 two-rowed barley (Hordeum vulgare L.) cultivars. Carbon isotope discrimination and total ash concentration were measured at maturity in kernels and straw. As expected, the Δ values of kernels (Δ-K) and straw (Δ-S) were positively correlated within environments. By contrast, Δ-K and ash concentration in kernels were often negatively related within environments, which suggests that mineral accumulation in kernels is not associated with the transpiration efficiency of the plants during grain filling. The lack of a positive relationship between ash concentration in the straw and either Δ-K or Δ-S indicates that ash concentration in vegetative tissues sampled at maturity may be of limited value as a surrogate of Δ. Grain yield correlated positively with either Δ-K or Δ-S, and negatively with ash concentration in kernels, especially in the poorest rain-fed environments. However, the ash concentration in the straw was not consistently associated with grain yield. While our results confirm that Δ traits are valid indicators of grain yield under Mediterranean conditions, the use of ash concentration in kernels for screening purposes is not warranted at this time due to the lack of a more accurate understanding of the physiological mechanisms underlying mineral accumulation in kernels. Prediction of grain yield through multiple linear regression has shown, however, that ash concentration in kernels could be used as a complementary criterion to Δ in poor rain-fed environments.
 
Article
Weather plays a critical role in eco-environmental and agricultural systems. Limited availability of meteorological records often constrains the applications of simulation models and related decision support tools. The Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) provides daily weather variables on a 0.5 latitude–longitude grid across the conterminous USA. Daily weather data from the VEMAP (1961–1990) for the state of Georgia were compared with data from 52 individual ground stations of the National Weather Service Cooperative Observer Program (COOP). Additionally, simulated crop grain yields of soybean (Glycine max) were compared using the two data sources. Averaged daily maximum and minimum temperatures (Tmax and Tmin, respectively), solar radiation (SRAD), and precipitation (PPT) differed by 0.2 °C, −0.2 °C, 1.7 MJ m−2 d−1, and 0 mm, respectively. Mean absolute errors (MAEs) for Tmax, Tmin, SRAD, and PPT were 4.2 °C, 4.4 °C, 4.4 MJ m−2 d−1, and 6.1 mm, respectively, and root mean squared errors (RMSEs) for Tmax, Tmin, SRAD, and PPT were 5.5 °C, 5.9 °C, 5.8 MJ m−2 d−1, and 13.6 mm, respectively. Temperature differences were lowest during summer months. Simulations of grain yield using the two data sources were strongly correlated (r = 0.68, p < 0.01). The MAE of grain yield was 552 kg ha−1. The RMSE of grain yield was 714 kg ha−1. Hybrid analyses indicated that the variation of simulated yield was mainly associated with the differences in rainfall. The results showed that the VEMAP daily weather data were able to be adequately applied to crop growth simulation at spatial and temporal scales, especially for long-term climate change research. Overall, the VEMAP weather data appears to be a promising source for crop growth modeling concerned with scale to 0.5° coordinate grid.
 
Article
The post-anthesis dynamics of the water content of whole sunflower achene and its major parts (pericarp, embryo) were examined for seven genotypes that spanned a broad range of final achene size (30–100 mg achene−1). Objectives were: (i) to establish the relative contributions of pericarp and embryo to whole-achene water content dynamics, (ii) to determine the relationship between maximum water content of the pericarp and final achene size, and (iii) to examine the effect of final achene size (as affected by genotype and environment) on achene dry-down dynamics after physiological maturity (=maximum achene weight). Four experiments were conducted over 2 years under field and glasshouse conditions. Across genotypes and growth conditions, whole-achene and pericarp water contents peaked earlier and more sharply during grain filling (ca. 35% of grain filling duration, or 30% of final achene weight), maximum embryo water content was achieved somewhat later and declined less sharply. Although the pericarp was a minor (17–35%) component of final achene dry weight, it contained 65–70% of achene maximum water content. Absolute pericarp water content did not fall to values close to those of the embryo until after physiological maturity. Final achene and embryo dry weights were closely (r2 0.90 and 0.85, respectively) associated with maximum pericarp water content. After maximum achene water content, rates of whole-achene dry-down were linear (ca. 1.35% d−1), and absolute rates of water loss per achene (range = 1.1–3.7 mg H2O achene−1 d−1) were strongly associated with achene maximum water content and final achene dry weight (r2 0.86 and 0.75, respectively). Excluding the inbred line HA89, the remaining genotypes achieved harvest (17%) and storage (11%) achene water concentrations at about 15 and 20 d, respectively, after physiological maturity, largely because absolute rates of achene water loss increased with achene size. We conclude that the pericarp is the dominant component of whole-achene water content dynamics, and that pericarp and achene maximum water contents are good indicators of potential final achene and embryo sizes and achene dry-down rates. Present results also provide a first approximation to the quantification of post-physiological maturity dry-down in this crop.
 
Article
Livestock slurry in animal houses, in manure stores and applied on fields is in Denmark the most important source of ammonia (NH3) in the atmosphere. The emitted NH3 is a source of NH3 and ammonium (NH4+) deposition, which causes eutrophication of N-deficient ecosystems and may form NH4+-based particles in the air, which are a risk to health. This study examines the reductions in NH3 emissions from pig houses, manure stores and manure applied in the field achieved by acidifying the slurry in-house. Sulphuric acid was used to acidify pig slurry to pH < 6 and the system was constructed is such a way as to prevent foaming in the animal house as well as during storage. Acidification of the pig slurry reduced the NH3 emission from pig houses by 70% compared with standard techniques. Acidification reduced NH3 emission from stored slurry to less than 10% of the emission from untreated slurry, and the NH3 emission from applied slurry was reduced by 67%. The mineral fertilizer equivalent (MFE) of acidified slurry was 43% higher compared with the MFE of untreated slurry when applied to the soil. The odour emission from the slurry was not affected significantly by the treatment. The slurry acidification system is approved Best Available Technology (BAT) in Denmark.
 
Article
No-till management has rapidly increased the cultivated area in Brazil. To control soil acidity in no-till systems, lime is broadcast on the surface without incorporation. The effectiveness of surface application of lime to soils under a no-till system, particularly with regard to subsoil acidity, is uncertain. Crop root growth and grain yield can be affected by chemical modifications in the soil profile due to surface lime application. A 3-year field trial examined the effect of newly and previously surface-applied lime in a long-term no-till system on the root growth and crop yield of corn (Zea mays L.), soybean (Glycine max L. Merrill), and wheat (Triticum aestivum L.) on a loamy, kaolinitic, thermic Typic Hapludox in Paraná State, Brazil. The experiment consisted of four lime treatments: (i) no lime (control); (ii) liming at 3 t ha⁻¹ in 2000; (iii) liming at 6 t ha⁻¹ in 1993; (iv) liming in 1993 and re-liming in 2000. Corn was grown in 2000–2001 and soybeans were grown in 2001–2002 and 2002–2003 without rainfall limitation. Wheat was grown in 2003 with a water deficit during the vegetative stage and soon after flowering.
 
Article
A major portion of phosphorus (P) applied as fertilizers is bound in soils as P compounds of variable adsorption strength, reducing the effectiveness of P fertilization. Plant genotypes equipped with mechanisms for utilizing the adsorbed P more efficiently can, therefore, enhance the effectiveness of P fertilization. Such genotypes will also enrich plant gene pools for further analysis and upgrading of P efficiency by selection and breeding. We studied the variation and the mechanisms of P uptake of two winter barley (Hordeum vulgare L.) cultivars Marinka and Sonate (parents of existing 200 haploid progeny lines), by laboratory and field experiments. After cultivation in nutrient solution for 21 days, Marinka produced more roots than Sonate, but similar amounts of dry shoots of lower P content (Marinka 3.4±0.4 mg g−1, Sonate 4.9±0.6 mg g−1). The total P uptake per plant did not differ between the cultivars. Marinka retained more P in roots as indicated by the higher concentration of P in the roots (Marinka 3.9±0.3 mg g−1 and Sonate 3.0±0.4 mg g−1). In sterile nutrient solution culture, the cultivars differed mainly in release of organic acids from the roots, with Marinka releasing three times more citric acid and nearly two times more acetic acid than Sonate. The cultivars had similar root hair lengths and they did not differ (P>0.05) in depletion of available soil P fraction (extracted with 0.5 M NaHCO3) in the rhizosphere. Marinka absorbed nearly twice as much P from the strongly adsorbed soil P fraction (extracted with 0.1M NaOH). Also under field conditions, Marinka absorbed more P and produced more shoot dry matter. The higher P uptake by Marinka than Sonate can be attributed to its ability to acquire P from strongly adsorbed soil P by releasing more organic acids, especially citric acid, from its roots.
 
Article
The fate of metobromuron and aclonifen, two sunflower herbicides, in soil was studied in laboratory and in field lysimeters under different water regimes. Laboratory degradation followed first-order kinetics, with half-lives ranging from 19 to 44 days for metobromuron and from 40 to 49 days for aclonifen under different incubation conditions. The influence of temperature on degradation was evident for metobromuron and negligible for aclonifen, while the influence of soil moisture was negligible for both herbicides. Adsorption was well described by an S-type isotherm with a 1/n value near unity and koc values, ranking metobromuron as a ‘transition’ pesticide and aclonifen as a ‘non-leacher’, according to the classification proposed by Gustafson (Environ. Toxicol. Chem. 8 (1989) 339). The movement in lysimeters depended on the water regimes adopted. In lysimeters that received water by the drip irrigation system (6 mm h−1) to counter evapotranspiration, metobromuron reached 60 cm depth at days 17 and 31 from treatment, while aclonifen remained in the top 20 cm layer. In lysimeters with a groundwater table at 60 cm constant depth, metobromuron reached a maximum depth of 30 cm, while aclonifen did not exceed 10 cm depth. In lysimeters that underwent three leaching events, metobromuron reached 120 cm depth at day 17 from treatment, while aclonifen remained within 30 cm depth. After three leaching events (for a total of 80 mm percolation), a total of 0.48% metobromuron (540 μg) was found in the water samples, while aclonifen was never detected. It can be concluded that, under the experimental condition tested, the two sunflower herbicides do not represent a real hazard for groundwater pollution.
 
Article
Phenological development, leaf emergence, tillering and leaf area index (LAI), and duration (LAD) of spring wheat cv. Minaret, grown in open-top chambers at different sites throughout Europe for up to 3 years at each site, were investigated in response to elevated CO2 (ambient CO2×2) and ozone (ambient ozone ×1.5) concentrations.Phenological development varied among experiments and was partly explained by differences in temperature among sites and years. There was a weak positive relationship between the thermal rate of development and the mean daylength for the period from emergence to anthesis. Main stems produced on average 7.7 leaves with little variation among experiments. Variation was higher for the thermal rate of leaf emergence, which was partly explained by differences in the rate of change of daylength at plant emergence among seasons. Phenological development, rate of leaf emergence and final leaf number were not affected by CO2 and ozone exposure. Responses of tillering and LAI to CO2 and ozone exposure were significant only in some experiments. However, the direction of responses was consistent for most experiments. The number of tillers and ears per plant, respectively, was increased as a result of CO2 enrichment by about 13% at the beginning of stem elongation (DC31), at anthesis and at maturity. Exposure to ozone had no effect on tillering. LAI was increased as a result of CO2 elevation by about 11% at DC31 and by about 14% at anthesis. Ozone exposure reduced LAI at anthesis by about 9%. No such effect was observed at DC31. There were very few interactive effects of CO2 and ozone on tillering and LAI. Variations in tillering and LAI, and their responses to CO2 and ozone exposure, were partly explained by single linear relationships considering differences in plant density, tiller density and the duration of developmental phases among experiments. Consideration of temperature and incident photosynthetically active radiation in this analysis did not reduce the unexplained variation. There was a negative effect of ozone exposure on leaf area duration at most sites. Direct effects of elevated CO2 concentration on leaf senescence, both positive and negative, were observed in some experiments. There was evidence in several experiments that elevated CO2 concentration ameliorated the negative effect of ozone on leaf area duration. It was concluded from these results that an analysis of the interactive effects of climate, CO2 and ozone on canopy development requires reference to the physiological processes involved.
 
Article
Research about spatio-temporal variation of crop yield does not abound. From a precision agriculture (PA) perspective and particularly considering site-specific crop management (SSCM), this is an aberration. There is a serious need to further question how temporal variation of crop yield impacts ones ability to manage spatial variation. The aim of this study is to consider and develop new and existing approaches to this question. Spatio-temporal analysis was undertaken for two wheat fields in South Australia with 3 and 4 years of wheat yield data. Temporal analysis included the calculation of semi-variance across each field between pairs of years for the creation of maps and the calculation of rank correlations between pairs of years. These analyses supported previous notions that the magnitude of temporal variation is large compared with spatial variation. However, some consistence of spatial patterns between years was also observed for each of the fields indicating that considering magnitudes of variation alone is not an exhaustive analysis. A long-term (100 years) temporal analysis using variograms was undertaken for a single point simulated using the Agricultural Production Simulator Model (APSIM). The long-term analysis overcame the fact that 3 or 4 years of yield data are an extremely small sample size for the time dimension. This analysis provided some useful insight into temporal variation such as a large nugget variance accounting for 75% of the temporal variation and the cyclical nature of temporal yield variation. A novel use of pseudo cross semi-variograms was applied to a spatio-temporal analysis of yield variation for the two fields. This analysis provides a preliminary insight into identifying space–time variance equivalents. With greater depth of temporal crop yield data this is a promising perspective from which to identify optimal spatial management strategies.
 
Article
This paper describes the effects of elevated CO2 (550 and 680 μl l−1) and O3 (60 nl l−1 O3 as an 8 h mean), alone or in combination, on canopy development and senescence in potato (Solanum tuberosum L. cv Bintje) across a range of European agro-climatic conditions. The assessments were made within the European CHIP project (CHanging climate and potential Impacts on Potato yield and quality) that was conducted for two growing seasons (1998 and 1999) in free air CO2 enrichment systems (FACE) and open-top chamber facilities (OTCs) at seven European sites. A comparison of chambered and unchambered experimental plots was included to examine the effects of chamber enclosure. Phenological growth stages, plant height, leaf area index (LAI) and the number of green and yellow leaves were recorded non-destructively throughout the growing season and by a destructive intermediate harvest at maximum leaf area (MLA). In the dynamic growth analysis CO2 and O3 effects were studied over three developmental stages: canopy expansion, full canopy and canopy senescence. Chamber enclosures promoted potato crop development (taller plants, more leaves) during the initial growth stages and led to a faster decline of LAI and a higher number of yellow leaves. The growth in ambient plots varied between sites and seasons, as did the scale of the treatment responses. Despite the large background variation, some overall treatment effects could be detected across all sites. Both levels of increased CO2 reduced final plant height in comparison to ambient concentrations, which indicates a premature ending of the active plant growth. At the stage of full canopy and crop senescence the average number of green leaves was significantly (P<0.05) decreased by 680 μl l−1 CO2 (OTC experiments) and LAI showed the same tendency (P=0.07). As there was however no indication of a decreased leaf formation during initial growth and at full canopy, this must have been due to an earlier leaf fall. In the FACE experiments LAI had already began to decline at the stage of full canopy at 550 μl l−1 CO2 but not in ambient CO2 (DAE×CO2, P<0.05). These observations strongly indicated that elevated CO2 induced a premature senescence during full canopy. O3 did not have an overall detrimental effect on crop development during initial growth nor at full canopy, but did induce a faster reduction of LAI during crop senescence (DAE×O3, P<0.05). Final plant height was not affected by O3. There were few CO2×O3 interactions detected. There was a suggestion (P=0.06) that O3 counteracted the CO2-induced decrease of green leaves at full canopy, but on the other hand during crop senescence the decline of LAI due to elevated O3 was faster at ambient compared to elevated CO2 (P<0.05). These responses of canopy development to elevated CO2 and O3 help to explain the treatment responses of potato yield within the CHIP project at sites across Europe.
 
Article
The EC Nitrate Directive (91/676), agreed by the EC Environment Council in 1991, is an environmental measure designed to protect water against pollution caused by nitrate from agriculture. In 2000, the River Ythan catchment, a 68 000 ha area of predominantly agricultural land in NE Scotland, was designated a nitrate vulnerable zone (NVZ) by the Scottish Executive. A combination of reasons for designation was suggested, including evidence of elevated nitrate concentrations in the surface waters of the catchment together with the criteria set out at Annex IA(3) of the EC Nitrates Directive, i.e. that the estuary is eutrophic or in the near future may become eutrophic. Evidence from the Scottish Environment Protection Agency surface water monitoring sites has revealed several tributaries of the Ythan with nitrate concentrations exceeding the maximum permitted level of 50 mg l−1 (11.3 mg l−1 NO3–N) and a rising trend in the main river channel. There has been an approximate threefold increase in surface water nitrate concentrations since the early 1960s to a current value of ∼35 mg l−1 (8 mg l−1 NO3–N). There is separate evidence of elevated nitrate concentrations in groundwater. The amounts of fertiliser N applied annually has also increased substantially and in 1994 these were estimated to be ∼60% of the total N (equivalent to 194 kg ha−1) added to the catchment. Various stages have been involved in the decision to designate including documents for public consultation and a proposed Action Programme. However, several issues remain to be resolved, especially the extent to which a causal relationship actually exists between the increased loss of nitrate to the estuary and algal growth. Being able to accurately apportion sources of N ‘supply’ with periods of ‘uptake’ within the aquatic system is complicated. Here we suggest that an estimated 70% of the terrestrially derived nitrate input to the estuarine system actually occur out with the main period of algal growth. This emphasises the need for a greater understanding of the spatial and temporal linkages that exist between N cycling in terrestrial and aquatic ecosystems particularly as this will directly influence the likely success and cost effectiveness of remedial measures taken to relieve the symptoms of eutrophication.
 
Article
Since 1994 Lithuania is engaged in BEAROP—the international study of agriculturally derived runoff of nutrients from the countries round the Baltic Sea, proposed by Swedish scientists. One of the demonstration watersheds chosen for this project, river Graisupis watershed, is located in the agricultural plains region of Middle Lithuania. Crop yield and nutrient balance data obtained for V. Liutkevičius Demonstration farm at the scale of farm and field are discussed. It was evident after calculations of the flow and balance of N, P and K to observe a discrepancy between actual and estimated values of crop yield. This is a common problem in Lithuania where an unbalanced fertilisation system still exists on many farms, when farmers choose the fertiliser rates, too little attention is paid to the soil analysis and soil nutrient balance. In order to make the fertilisation system more rational, a balanced fertilisation computer model was created at Lithuanian Institute of Agriculture (LIA) and used for that purpose at the Demonstration farm. A drained system of 7.4 ha divided into separate fields, growing a mixture of ley at the Demonstration farm was chosen for the nutrient balance calculation in 1997 and 1998. Calculations of major nutrient flows at the field level have shown that the N balance in this field was positive and P almost in balance, however, the potassium balance was negative. It may be rational to utilise such a local organic fertiliser as urine in this field. The regression equation was developed that relates N surplus with nitrate loss and could be used more widely provided data were available on drainage discharge, total N content in soil, humus content, fertilisation rate. Soil testing at the Demonstration farm should be extended to the areas examined more than 10 years ago. More attention has to be given to the integrated plant protection and soil cultivation measures in order to obtain the planned yields.
 
Article
In intensive integrated crop-livestock farming systems, the surplus of N at the farm scale may be large and reflects on the N balance at the field scale. A study was conducted to assess the N fertilizer efficiency in four private farms in intensively cropped areas of NW Italy, and to monitor the effects of agricultural practices on the mineral N concentration of the soil solution, sampled every 2 weeks for 2 years and considered as an indicator of potential leaching. Two cultivation systems were compared in each farm, one involving continuous maize rotation, the other assuring a continuous soil cover (permanent meadow or winter cereal-maize double cropping system). The fertilization level in the arable crops was high (369–509 kg N ha−1 year−1) compared to the crop removals, and resulted in a low efficiency, as indicated by the four examined efficiency indexes (calculated N surplus, N removal-fertilizer ratio, N apparent recovery, N use efficiency). The soil-water-nitrate concentration showed large temporal variations in the range of 1–150 mg l−1 for five out of the eight cropping situations, while concentrations smaller than 10 mg l−1 were always recorded in the meadows and in one of the four soils (Aeric epiaquept). The fertilizer management that characterized each cropping system affected the soil-mineral-nitrate content in shallow arable soils. The longer soil cover duration in double-cropping systems did not result in a reduction of soil N compared to maize as a single crop, not even in winter (the bare-soil intercropping period in maize-based systems). However, the temporal oscillations of the concentration were buffered by the crop cover duration and by the presence of a shallow water table (1 m deep) in the soil profile. The average nitrate content of the soil could be predicted by the N uptake of the crop, the N removal–fertilizer ratio, the soil pH and sand content, however no simple explanatory relationship was found with the experimental factors. Hence, in farm conditions, in the absence of sufficient data for a deterministic model approach, the target of reducing the risk of leaching should be achieved by maximizing the fertilizer efficiency.
 
Article
The Mediterranean regions are submitted to a large variety of climates. In general, the environments are arid and semi-arid with summers characterised by high temperatures and small precipitation. Due to the scarcity of water resources, the correct evaluation of water losses by the crops as evapotranspiration (ET) is very important in these regions. In this paper, we initially present the most known ET measurement methods classified according to the used approach: hydrological, micrometeorological and plant physiological. In the following, we describe the methods to estimate ET, distinguishing the methods based on analytical approaches from the methods based on empirical approaches. Ten methods are reviewed: soil water balance, weighing lysimeter, energy balance/Bowen ratio, aerodynamic method, eddy covariance, sap flow method, chambers system, Penman–Monteith model, crop coefficient approach and soil water balance modelling approach. In the presentation of each method, we have recalled the basic principles, underlined the time and space scale of its application and analysed its accuracy and suitability for use in arid and semi-arid environments. A specific section is dedicated to advection. Finally, the specific problems of each method for correct use in the Mediterranean region are underlined. In conclusion, we focus attention on the most interesting new guidelines for research on the measurement and estimation of actual crop evapotranspiration.
 
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Jørgen Eivind Olesen
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James W Jones
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Joe Ritchie
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William Batchelor
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Cheryl H Porter
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