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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.