[show abstract][hide abstract] ABSTRACT: a b s t r a c t Soil texture greatly influences soil water movement, thus may affect the water balance and vegetation growth in the deserteLoess Plateau transition zone. This study is to determine if the water balance differs in homogeneous and layered soils with Caragana korshinkii stands in semiarid region. Soil water measure-ments up to 500-cm depth were taken in 2006 and 2007 on homogeneous sandy soil, homogeneous silt loam soil, and layered soil with sand overlying silt loam. HYDRUS-1D was used to simulate the soil water balance. The results indicated the annual water balance components were greatly affected by soil layering. The ratio of average actual evapotranspiration (ET a) to precipitation (P) during the two years in the layered soil was slightly lower than that in homogeneous soils. The ratios of annual actual transpiration (T r) to evapotranspiration were 50.9%, 41.2% and 30.6% in layered soil, homogeneous sandy soil, and homogeneous silt loam soil, respectively. C. korshinkii grown in layered soil had deeper soil water recharge and higher T r / ET a ratio, thus had more available water for transpiration than that in homogeneous soils. This study suggested the layered soil with sand overlying silt loam is more favorable to C. korshinkii growth in terms of water use than homogeneous soils in the deserteLoess Plateau transition zone.
[show abstract][hide abstract] ABSTRACT: Soil texture and evaporative demand have been reported to be the main factors which influence the transpirational response to soil water deficits. However, experimental evidences are not enough. The objective of this study was to investigate the transpirational response to soil water availability in soils of different textures under different evaporative demand levels. The three main soils of the Loess Plateau of China (loamy clay, clay loam and sandy loam) were selected and six constant soil water treatments were applied for winter wheat (Triticum aestivum L.) grown in pots. In order to reduce the influence of environmental conditions and plant factors, a normalized daily transpiration rate was used to develop the relationships with volumetric soil water content and soil water suction. Results showed that, under various levels of evaporative demand, a linear-plateau function with a critical value could be used to describe the dynamic change of the normalized transpiration rate with soil drying. Soil texture significantly influenced both the critical and the slope values of the linear-plateau equations, however, evaporative demand significantly affected the critical values of volumetric soil water content and soil suction for the loamy clay and clay loam only. Therefore, for saving water, different strategies are needed for these three soils.
Agricultural Water Management 01/2011; 98(4):569-576. · 2.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: Pots used for experiments conducted on plants grown in them create rooting environments that are affected by limited soil volume, which can affect various physiological processes, including transpiration, and plant growth. However, the applicability of results from pot experiments to the field has received limited attention. The objective of this study was to compare the growth and transpiration of maize (Zea mays L.) and winter wheat (Triticum aestivum L.) when grown in pots and field plots under various constant water deficits. The experiments were conducted under similar environmental conditions for both pots and plots. Transpirational responses at both transient (RTTr) and daily (RDTr) time scales to a decreasing fraction of available soil water (FASW) were analyzed. For a comparable FASW, there was a significant reduction in shoot dry weight and total transpiration for plants in pots compared to those in plots. A parabolic relationship between shoot dry weight and total transpiration existed and was not influenced by soil volume or crop type. The plot experiment data for both crops was consistent with pot data for the response of RDTr and RTTr to changes in FASW, which was represented by a linear-plateau function. However, the threshold values were significantly different for the two time scales. The threshold values and slopes of the linear-plateau function for maize and wheat were not significantly different in the response of RTTr to FASW, but were significantly different in the response of RDTr to FASW. Therefore, the transpirational responses of the selected maize and winter wheat hybrids to soil drought were different at the daily and transient time scales.
Environmental and Experimental Botany - ENVIRON EXP BOT. 01/2011; 71(1):65-71.
[show abstract][hide abstract] ABSTRACT: Although plant density should affect soil carbon dioxide (CO 2) efflux and carbon cycling in semi-arid regions, the effects of plant density on soil CO 2 efflux are not well known. This study was performed to investigate the responses of soil CO 2 efflux of two dominant shrubs (Caragana korshinkii and Salix psammophila) to plant density in the northern Loess Plateau of China. Two plant density treatments, low and high, were included for C. korshinkii (average 20,000 plants ha -1 and average 66,667 plants ha -1) and S. psammophila (average 9,583 plants ha -1 and average 31,250 plants ha -1). Soil CO 2 efflux was measured every other day with an Ultra-light portable photosynthesis system (CI-340, CID Inc., USA) from July to October 2009. Soil CO 2 efflux with high plant density was significantly larger than that with low plant density for both shrub species. Plant density did not change the temporal pattern of CO 2 efflux during the study period. Our results indicated that root biomass and aboveground biomass were the significant biotic factors mediating the response of soil CO 2 efflux to plant density for the two shrubs. Moreover, both soil water contents in the 0 -6 cm soil layer and in deeper soil layer partly regulated the responses of soil CO 2 efflux to the shrub density treatments in the semi-arid region.
AFRICAN JOURNAL OF BIOTECHNOLOGY 11/2010; 9:6916-6926. · 0.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: Evapotranspiration (ET) is deemed critical for water resources management. Even in the same climatic and meteorological conditions, actual ET (ETa) may exhibit remarkable spatial variability across different vegetation covers, agricultural land use practices, and differing types of urban land development. The main objectives of this study are (1) to evaluate the possible closure of the heat balance equation using Oklahoma's unique environmental monitoring network; and (2) to estimate ETa and determine the variation with regards to varying types of land use and land cover in urban settings. In this study, a Surface-Energy-Balance ET algorithm was implemented to estimate ETa at a higher spatial resolution using Landsat 5 satellite images while the Oklahoma Mesonet observations can be used as our ground truth data. Accuracy of the estimated ETa was assessed using latent heat flux measurements provided by AmeriFlux towers. The associated bias ratios of daily mean ETa with respect to both burn and control sites are -0.92%, and -8.86% with a correlation of 0.83 and 0.81, respectively. Additionally, estimated ETa from a water balance budget analysis and the remotely sensed ETa are cross-validated with a low bias ratio of 5.2%, and a correlation coefficient of 0.7 at the catchment scale. The lowest ETa was observed for developed urban areas and highest for open water bodies. The ETa difference is also demonstrated from two contrasting counties. The results show Garfield County (agricultural) has higher ETa values than Oklahoma County (urban) for all land cover types except open water bodies.
[show abstract][hide abstract] ABSTRACT: Reforestation is a primary end use for reconstructed soils following oil sands mining in northern Alberta, Canada. Limited soil water conditions strongly restrict plant growth. Previous research has shown that layering of sandy soils can produce enhanced water availability for plant growth; however, the effect of gradation on these enhancements is not well defined. The objective of this study was to evaluate the effect of soil texture (gradation and layering) on plant available water and consequently on forest productivity for reclaimed coarse textured soils. A previously validated system dynamics (SD) model of soil moisture dynamics was coupled with ecophysiological and biogeochemical processes model, Biome-BGC-SD, to simulate forest dynamics for different soil profiles. These profiles included contrasting 50 cm textural layers of finer sand overlying coarser sand in which the sand layers had either a well graded or uniform soil texture. These profiles were compared to uniform profiles of the same sands. Three tree species of jack pine (Pinus banksiana Lamb.), white spruce (Picea glauce Voss.), and trembling aspen (Populus tremuloides Michx.) were simulated using a 50 year climatic data base from northern Alberta. Available water holding capacity (AWHC) was used to identify soil moisture regime, and leaf area index (LAI) and net primary production (NPP) were used as indices of forest productivity. Published physiological parameters were used in the Biome-BGC-SD model. Relative productivity was assessed by comparing model predictions to the measured above-ground biomass dynamics for the three tree species, and was then used to study the responses of forest leaf area index and potential productivity to AWHC on different soil profiles. Simulated results indicated soil layering could significantly increase AWHC in the 1-m profile for coarse textured soils. This enhanced AWHC could result in an increase in forest LAI and NPP. The increased extent varied with soil textures and vegetative types. The simulated results showed that the presence of 50 cm of coarser graded sand overlying 50 cm of finer graded sand is the most effective reclaimed prescription to increase AWHC and forest productivity among the studied soil profiles.
[show abstract][hide abstract] ABSTRACT: The objective of this study was to examine the trends of changes in streamflow in a watershed of the Loess Plateau, where
a series of soil conservation measures were implemented since the late 1950s. Both parametric and non-parametric Mann–Kendall
test were used to identify the trends in hydrologic variables over the last 50years, and it showed significant downward trends
in annual runoff, surface runoff and baseflow. The Pettitt’s test was used to detect the change points of runoff, which occurred
in 1973, and the whole 50-year records could be divided into contrast (from 1957 to 1973) and treated (from 1974 to 2006)
periods. It was observed that the average annual runoff during treated period reduced by 60%, surface runoff and baseflow
reduced by 65% and 55%, respectively in comparing with the contrast period. But the proportion of baseflow to total runoff
showed a significant increasing from 0.57 to 0.63. Seasonal runoff also showed decreased trend with the highest reduction
occurring in summer and lowest in winter. Annual precipitation in whole period showed no significant trend, so the changes
in hydrologic variables were induced by conservation measures. Comparison of the flow duration curves for the two periods
showed that reductions in high and low flows varied greatly. Results showed that conservation measures have resulted obvious
changes in the hydrologic variables in a watershed of Loess Plateau.
Water Resources Management 01/2009; 23(10):1935-1949. · 2.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: Water is a key limiting factor for vegetation restoration in the semi-arid areas of China. Caragana korshinkii Kom is a shrub that is widely planted in this region to control soil erosion and land desertification. The objective of this
study was to investigate the fine root distribution of mature C. korshinkii and its water consumption, when grown in either silt loam or sandy soils, in order to understand differences between the
water cycles of two such soils found in the transition zone between fertile loess hills and desert of the Northern Loess Plateau.
Fine root distributions were measured using the trench-profile method. Soil water dynamics were monitored with a neutron probe
during two growing seasons. The results showed that fine root area density (FRAD) declined with increasing soil depth in both
soils, with 70.7% and 96.6% of the total fine roots being concentrated in the upper 1-m layer of the silt loam and sandy soils,
respectively. Water consumption by C. korshinkii in the silt loam was close to that in the sandy soil. Most water consumption in both soil types was from the upper 1-m layer.
Little variation in plant available water (PAW) occurred in the 3–6m soil layer during the whole study period. However, in
this layer, the PAW was significantly lower in the silt loam soil than in the sandy soil. Total actual evapotranspiration
(ETa) was slightly higher from the sandy soil plots than from those of the silt loam soil during both growing seasons. Our study
indicated that mature C. korshinkii effectively uses about the same amount of water from either the silt loam or sandy soils, but that more soil water at depth
was extracted from silt loam soil than from sandy soil.
Plant and Soil 01/2009; 315(1):149-161. · 2.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: For improving soil and water conservation and developing livestock production, an alfalfa (Medicago sativa L.) and crop rotation practice has been widely employed in the dryland region of the Loess Plateau in China. This system typically involves establishing alfalfa for 2–10 years, and then removing it by cutting and returning to a cropping rotation for 2–7 years. The length of alfalfa phase is essential for attaining high pasture yield and remaining enough soil water for subsequent crops. To determine the optimal length of alfalfa phase, one continuous growing alfalfa treatment and nine other treatments, including eight alfalfa/crop rotations and a crop/crop rotation, were studied at the Changwu Agri-ecological Station of the Loess Plateau in China from 1985 to 2001. Results showed that alfalfa yield decreased with time at a rate of 0.629 t ha−1 year−1 and soil water storage in the 0–500 cm profile by 33.5 mm year−1. After alfalfa grew for >8 years, its yield responded very vigorously to seasonal precipitation variations, and the yield age coefficient (YAC), which reflects the effects of alfalfa growing age and soil water deficit on pasture yield, was less than 1.0. Our analysis also showed that the average soil water content within the profile from 300 to 1000 cm was less than 0.18 cm3 cm−3, this was determined to be a threshold value for creating a strong water stress to alfalfa growth. Considering all the factors, this study recommends that the optimal length of alfalfa phase in the alfalfa/crop rotation system should not more than 8 years.
[show abstract][hide abstract] ABSTRACT: Soil erosion is the most significant threat to land productivity and environmental quality on the Loess Plateau of China. The annual total sediment load of the Yellow River is 1.6 billion tons, with about 90 percent coming from soil erosion from the Loess Plateau. To reduce soil erosion from the Loess Plateau, conservation practices, including tree planting, ridge construction between fields and around gullies, terrace and ditch construction perpendicular to the main slope, and dam construction are being implemented. An evaluation of these conservation practices is required before they are implemented at the large scale. The objective of this study is to evaluate the effectiveness of conservation practices to control runoff and sediment yield from paired watersheds in the hilly gully region of the Loess Plateau. The advantage of the paired watershed approach is its sensibility in detecting differences in runoff and sediment transport by monitoring both watersheds during two periods, an initial period with no conservation practices and a treatment period with only one watershed subjected to conservation practices. Implementation of the conservation practices resulted in (1) cumulative runoff and sediment yield that were, respectively, 25 and 38 percent less from the treatment watershed than from the control, (2) a decrease in the number of rainfall events producing runoff and sediment transport (94 in the control versus 63 in treatment), and (3) a reduction in the maximum discharge and maximum suspended sediment concentration.
JAWRA Journal of the American Water Resources Association 06/2007; 39(5):1197 - 1207. · 1.96 Impact Factor
[show abstract][hide abstract] ABSTRACT: Because of the high income resulting from apple production, apple orchards have widely spread since the 1980's in the gully region of Loess Plateau of China. Compared to winter wheat, a major crop in this region, apple trees deplete most of the available water in the 0–10 m soil profile after 30 years, resulting in a decline of apple yield and profitability. Apple trees older than 30 years are often cut, and orchards reconverted to winter wheat, but wheat planted after apple trees suffers from low yield, and groundwater from low recharge rate due to reduced soil water content. The objective of this study was to determine, with the one-dimensional simulation model Simultaneous Heat and Water Transfer (SHAW), the time required for soil water to recover after apple tree cutting. Recovery time is defined as the amount of time required for a field just cut of its apple trees to recover to the same soil water content of a field that has always been cropped to wheat. SHAW soil and crop parameters were calibrated (1984–1989) and validated (1989–1994) using measured soil water contents in bare soil and winter wheat plots. Using calibrated soil and crop parameters, soil water content variations in the 0–10 m soil profile was simulated under winter wheat conditions for forty randomly generated climatic sequences based on observed 48-year historical data (1957–2004). Results show that the recovery time varies from 6.5 to 19.5 years, with an average of 13.7 years, for the 0–10 m soil profile, and from 4.4 to 8.4 years, with an average of 7.3 years, for upper 0–3 m soil profile. Due to lower soil water content, the mean groundwater recharge rate would be 9.3 mm year−1 in orchard cut plots during the recovery period, compared to 18.3 mm year−1 for land that had always been in winter wheat. Considering the long-term effects of apple orchards on land productivity and groundwater recharge, areas in apple orchards should be restricted to maintain sustainable agriculture in this region.
[show abstract][hide abstract] ABSTRACT: High evaporative demand and limited precipitation restrict the yield of winter wheat (Triticum aestivum L.) grown in the Loess Plateau of China under semiarid climatic conditions. Grain yield can be improved by effective water management practices. A 13-year field experiment was conducted at the CERN Changwu Agro-ecological Experimental Station of the Loess Plateau to determine optimal irrigation strategies under limited water supply and to develop relationships among grain yield (Y), seasonal evapotranspiration (SET) and water-use efficiency (WUE). The experiment consisted of five irrigation treatments and three blocks. Measurements included grain yield, soil water content at various depth intervals in the 0–3,000mm layer, irrigation amount, and precipitation. Results showed that winter wheat grown in this area experienced serious water stress during critical growth stages for the no-irrigation treatment. The amount and timing of irrigation had an important effect on grain yield, but significant differences in yield were not observed between the three-irrigation and the four-irrigation treatments. Grain yield was linearly related (R2=0.66) to SET, but differences in WUE were not significant for any of the treatments. The relationship between WUE and Y was best represented by a second order polynomial (R2=0.65) consisting of a nearly linear portion between 1.5 and 5.0Mg ha–1. Optimum water management of winter wheat in the Loess Plateau should consist of three 87.5mm irrigations applied at stem elongation, booting, and anthesis.
[show abstract][hide abstract] ABSTRACT: Winter wheat monoculture occupies a large area of the Loess Plateau dryland region of China. Its yield is mainly limited by available water and fertilization. From the mid-1980s, yield of winter wheat increased with fertilizer application, and this increased productivity may increase soil-water depletion and reduce available soil-water at planting. Besides rainfall during the growing season, an important source of water for the crops is stored soil-water at planting. In the long run, increasing fertilization may not be sufficient to maintain higher yield. To develop better dryland crop and water management practices, a 15-year experiment of winter wheat monoculture was conducted at the Changwu Agri-ecological Station of the Loess Plateau from 1984 to 1999. Different levels of productivity were implemented by the application of chemical fertilizers and manure. The experimental design consisted of a control treatment (CTL) and three fertilizer treatments: nitrogen, phosphorus and manure (NPM), nitrogen and phosphorus (NP), and manure (M). Compared to CTL, on average, treatments NPM, NP and M increased yield by 148, 110 and 59%, and decreased soil-water at planting by 102.6, 59.1 and 31.6 mm within the 300 cm profile, and soil-water at harvest by 142.3, 102.5 and 70.2 mm, respectively. There was a decrease of soil-water with time for fertilizer treatments. Crop yield with high fertilization treatments responded more to rainfall variations. Considering the importance of soil-water at planting for crop yield in dryland farming, winter wheat monoculture with high fertilization does not appear to be a sustainable management practice in the Loess Plateau dryland region of China.