Soil Water Distribution Research Articles

Modeling soil water dynamics in a drip-irrigated intercropping field under plastic mulch

Intercropping, drip irrigation, and the use of plastic mulch are important management practices, which can, when utilized simultaneously, increase crop production and save irrigation water. Investigating soil water dynamics in the root zone of the intercropping field under such conditions is essential in order to understand the combined effects of these practices and to promote their wider use. However, not much work has been done to investigate soil water dynamics in the root zone of drip-irrigated, strip intercropping fields under plastic mulch. Three field experiments with different irrigation treatments (high T1, moderate T2, and low T3) were conducted to evaluate soil water contents (SWC) at different locations, for different irrigation treatments, and with respect to dripper lines and plants (corn and tomatoes). Experimental data were then used to calibrate the HYDRUS (2D/3D) model. Comparison between experimental data and model simulations showed that HYDRUS (2D/3D) described different irrigation events and SWC in the root zone well, with average relative errors of 10.8, 9.5, and 11.6 % for irrigation treatments T1, T2, and T3, respectively, and with corresponding root mean square errors of 0.043, 0.035, and 0.040 cm3 cm−3, respectively. The results showed that the SWC in the shallow root zone (0–40 cm) was lower under non-mulched locations than under mulched locations, irrespective of the irrigation treatment, while no significant differences in the SWC were observed in the deeper root zone (40–100 cm). The SWC in the shallow root zone was significantly higher for the high irrigation treatment (T1) than for the low irrigation treatment, while, again, no differences were observed in the deeper root zone. Simulations of two-dimensional SWC distributions revealed that the low irrigation treatment (T3) produced serious severe water stress (with SWCs near the wilting point) in the 30–40 cm part of the root zone, and that using separate drip emitter lines for each crop is well suited for producing the optimal soil water distribution pattern in the root zone of the intercropping field. The results of this study can be very useful in designing an optimal irrigation plan for intercropped fields.

Compensatory uptake functions in empirical macroscopic root water uptake models – Experimental and numerical analysis

Macroscopic empirical root water uptake (RWU) models are often used in hydrological studies to predict water dynamics through the soil–plant–atmosphere continuum. RWU in macroscopic models is highly dependent on root density distribution (RDD). Therefore, compensatory uptake mechanisms are being increasingly considered to remedy this weakness. A common formulation of compensatory functions is to relate compensatory uptake rate to the plant water-stress status. This paper examines the efficiency of such compensatory functions to reduce the sensitivity of simulated actual transpiration (Ta), drainage (Draina) and RWU patterns to RDD. The possibility to replace the compensatory RWU functions by an adequate description of RDD is also discussed. The study was based on experimental and numerical analysis of two-dimensional soil-water dynamics of 11 maize plots, irrigated using sprinkler (Asp), subsurface drip (SDI) systems, or rainfed (RF). Soil-water dynamics were simulated using a physically-based soil-water flow model coupled to a macroscopic empirical compensatory RWU model. For each plot, simulation scenarios involved crossing 6 RDD profiles with 6 compensatory levels. RDD was found to be the main factor in the determination of RWU patterns, Ta and Draina rates, with and without the compensatory mechanism. The use of a water-tracking RDD, i.e., higher uptake intensity in expected wetter soil regions, was found a surrogate for compensatory RWU functions in surface-watering simulations (Asp and RF). However, in SDI simulations, a water-tracking RDD should be combined to a high level of compensatory uptake to satisfactorily reproduce real RWU patterns. Our results further suggest that the compensatory RWU process is independent of the plant stress status and should be seen as a response to heterogeneous soil-water distribution. Our results contribute to the identification of optimum parameterization of empirical RWU models as a function of watering methods.

Recuperação da estrutura de um Latossolo vermelho degradado utilizando lodo de esgoto

The aim of this study was to investigate the influence of sewage in the recovery of the structure of a degraded Red Latosol (Oxisol) being cultivated for 4 years with eucalyptus (Eucalyptus citriodora) and (Brachiaria decumbens) in Selvíria, MS, Brazil. We used a randomized block design with 6 treatments and 4 replications. The treatments were: control (without the use of sewage sludge and mineral fertilizers); mineral fertilizer, 30 t ha-1 of sewage sludge; 60 t ha-1 of sewage sludge, todos with soil cultivated with eucalyptus and pasture, and two witnesses: savannah vegetation and exposed soil. In 2007, we evaluated physical soil properties: the distribution of pore size, soil bulk density, distribution of soil aggregate stability and water; and chemical soil properties: phosphorus, potassium, calcium, magnesium, organic matter; potential acidity( pH), sum of bases, cation exchange capacity and base saturation, in depths: 0.00 to 0.05, 0.05-0.10, 0.10 -0.20 and 0.20-0.40 m; resistance to moisture penetration and gravity, in depths: 0.00 to 0.15, 0.15 to 0.30 and from 0.30 to 0.45 m. It is concluded that the sewage sludge yielded positive changes in soil structure and recovery of soil chemical properties.

Assessing the influence of the rhizosphere on soil hydraulic properties using X-ray computed tomography and numerical modelling.

Understanding the dynamics of water distribution in soil is crucial for enhancing our knowledge of managing soil and water resources. The application of X-ray computed tomography (CT) to the plant and soil sciences is now well established. However, few studies have utilized the technique for visualizing water in soil pore spaces. Here this method is utilized to visualize the water in soil in situ and in three-dimensions at successive reductive matric potentials in bulk and rhizosphere soil. The measurements are combined with numerical modelling to determine the unsaturated hydraulic conductivity, providing a complete picture of the hydraulic properties of the soil. The technique was performed on soil cores that were sampled adjacent to established roots (rhizosphere soil) and from soil that had not been influenced by roots (bulk soil). A water release curve was obtained for the different soil types using measurements of their pore geometries derived from CT imaging and verified using conventional methods, such as pressure plates. The water, soil, and air phases from the images were segmented and quantified using image analysis. The water release characteristics obtained for the contrasting soils showed clear differences in hydraulic properties between rhizosphere and bulk soil, especially in clay soil. The data suggest that soils influenced by roots (rhizosphere soil) are less porous due to increased aggregation when compared with bulk soil. The information and insights obtained on the hydraulic properties of rhizosphere and bulk soil will enhance our understanding of rhizosphere biophysics and improve current water uptake models.

Effect of Soil Water Content on the Removal of Volatile Chlorinated Hydrocarbons from Soil by Mechanical Soil Aeration

Mechanical soil aeration is an easy, effective, and low-cost soil remediation technology; in particular, it is suitable for large sites contaminated by volatile chlorinated hydrocarbons (VCHs). Mechanical soil aeration encourages the volatilization of soil contaminants, but soil moisture, which reduces the amount of open pores, may hinder this process. The present study examined the remediation of silty soil containing 1,2-dichloroethane (1,2-DCA), chloroform (TCM), trichloroethylene (TCE), and tetrachloroethylene (PCE) using mechanical soil aeration and evaluated the influence of soil water content on the efficiency of the process. For artificially contaminated soil, the following conclusions were reached: (i) moisture undermines the volatilization of contaminants. When the soil water content increased from 5% to 20%, the residual concentrations of 1,2-DCA, TCM, TCE, and PCE in the soil increased from 0.08, 0.10, 0.09, and 0.48 mg/kg to 1.43, 0.81, 1.16, and 1.43 mg/kg, respectively. The effective diffusion coefficients also decreased from 1.88×10-2, 1.43×10-2, 1.88×10-2, and 1.30×10-2 cm2/s to 1.71×10-6, 1.30×10-6, 1.71×10-6, and 1.18×10-6 cm2/s, respectively. (ii) Residual contaminants are related to the octanol-water partition coefficient. The soil-water distribution coefficient of PCE was highest among the hydrocarbons (3.72), and the residual contaminants were mainly adsorbed on soil particles. The soil-water distribution coefficient of DCA was lowest (0.42), and the residual contaminants were mainly dissolved in the soil water.

Effects of tillage pan on soil water distribution in alfalfa-corn crop rotation systems using a dye tracer and geostatistical methods

The present study was designed to assess the potential effects of tillage pan on the distribution and the movement of soil water. Two different tillage regimes of an alfalfa-corn crop rotation system were carefully selected. Plot 1 contained alfalfa without tillage for the past 10 years. Plot 2 contained alfalfa with no tillage for the first 5 years and corn with conventional tillage for the succeeding 5 years. A dye tracer was introduced to these plots and the different types of water flow were visualized using classified dye-stained patterns. In addition, the kriging maps of gravimetric soil water content were used to indicate potential distribution characteristics. Semivariance analysis was performed to determine spatial variability on a centimeter scale. The role of macropore flow was weaker in the alfalfa plot than in the corn plot because of the difference in flow path and distribution. A belt of high soil moisture content appeared in the vertical soil profile of the alfalfa plot, indicating that the macropore flow showed a deeper stained depth. Several scattered locations in the corn plot contained high amounts of water, suggesting that macropore flow also occurred. The soil water content in the corn plot demonstrated infiltration patterns with higher degrees of fragmentation than that in the alfalfa plot. Moreover, a lateral flow with a wider stained width was triggered by the compacted tillage pan in the corn plot. Thus, the role of lateral flow was more dominant in the corn plot than in the alfalfa plot. The spatial correlation distance of the soil water content of infiltration patterns was 23.08cm in the alfalfa plot compared with 10.52cm in the corn plot. This trend indicated a high spatial variation of moisture in water infiltration patterns of the alfalfa field. In addition, strong spatial autocorrelation was observed in soil water infiltration patterns in both plots (nugget percentages of <25%). Our results highlighted a significant change of soil water behaviors in crop rotation from alfalfa to corn. In particular, downward water flow was restricted by a compacted tillage pan; thus, water was stored in the loose soil structure of the corn plot.

Soil water and root distribution under jujube plantations in the semiarid Loess Plateau region, China

This study aimed to analyze the spatial correlation between soil water and root distribution in dense-dwarf jujube plantations in the Hilly Loess Region (HLR) of China. The soil coring method was used to sample roots at different depths within the 0–1,000 cm soil profile. The results showed that increase in average annual root depth decreased with increasing jujube stand age. The maximum root depth of the 12-year-old jujube was 520 cm. The difference between the maximum and minimum root depths in the 12-year-old jujube trees was 180 cm. Lateral roots started developing intersection networks 3 years after planting. Soil water fluctuation was not induced by vertical root systems of dense-dwarf jujube plants. With increasing jujube stand age, root depth, dry soil layer depth (below 240 cm) and annual soil water variance within the top 0–200 cm soil layer increased. However, root-zone soil water content decreased with increasing stand age while dry soil layer depth was slightly larger than root depth. The results of this study have important significance to provide vital technical support for jujube cultivation especially under semiarid conditions and were expected to find application in water management for plantations in the HLR.

Three‐dimensional quantification of soil hydraulic properties using X‐ray Computed Tomography and image‐based modeling

AbstractWe demonstrate the application of a high‐resolution X‐ray Computed Tomography (CT) method to quantify water distribution in soil pores under successive reductive drying. We focus on the wet end of the water release characteristic (WRC) (0 to −75 kPa) to investigate changes in soil water distribution in contrasting soil textures (sand and clay) and structures (sieved and field structured) and to determine the impact of soil structure on hydraulic behavior. The 3‐D structure of each soil was obtained from the CT images (at a 10 μm resolution). Stokes equations for flow were solved computationally for each measured structure to estimate hydraulic conductivity. The simulated values obtained compared extremely well with the measured saturated hydraulic conductivity values. By considering different sample sizes we were able to identify the smallest possible representative sample size which is required to determine a globally valid hydraulic conductivity.

Effects of microtopography on spatial point pattern of forest stands on the semi-arid Loess Plateau, China

Microtopography may affect the distribution of forests through its effect on rain redistribution and soil water distribution on the semi-arid Loess Plateau, China. In this study, we investigated the characteristics of microtopography on two shady slopes (slope A, 5 hm2, uniform slope; slope B, 5 hm2, microtopography slope) and surveyed the height, the diameter at breast height and the location (x, y coordinates) of all selected individual trees (Robinia pseudoacacia Linn., Pyrus betulifolia Bunge, Populus hopeiensis Hu & Chow, Armeniaca sibirica Lam., Populus simonii Carr. and Ulmus pumila Linn.) on slope A and slope B in the watersheds of Wuqi county, Shaanxi province. Subsequently, the effects of microtopography on the spatial pattern of forest stands were analyzed using Ripley’s K(r) function. The results showed that: (1) The maximal aggregation radiuses of the tree species on the uniform slope (slope A) were larger than 40 m, whereas those of the tree species on the microtopography slope (slope B) were smaller than 30 m. (2) On slope B, the spatial association of R. pseudoacacia with P. betulifolia, A. sibirica, P. simonii and U. pumila varied from being strongly negative to positive at microtopography scales. The spatial association of Populus hopeiensis Hu & Chow with U. pumila also varied from being strongly negative to positive at microtopography scales. However, there was no spatial association between P. betulifolia and P. hopeiensis, P. betulifolia and A. sibirica, P. betulifolia and P. simonii, P. betulifolia and U. pumila, P. hopeiensis and A. sibirica, P. hopeiensis and P. simonii, A. sibirica and P. simonii, A. sibirica and U. pumila, and P. simonii and U. pumila. On slope A, the spatial association between tree species were strongly negative. The results suggest that microtopography may shape tree distribution patterns on the semi-arid Loess Plateau.

Quantifying and predicting soil water evaporation as influenced by runoff strip lengths and mulch cover

Soil water evaporation from the cropping surface is a wasteful loss of potentially productive rainwater, thus efficient use of rainwater can help to sustain dryland production. The purpose of this study was to quantify the effect of canopy shading (CS) and mulch levels (ML) on soil water evaporation (Es) from each 1m section of in-field rainwater harvesting (IRWH) and to evaluate the Ritchie (α′) and Stroosnijder (β′) soil evaporation models on the effect of surface treatments. A microlysimetric method was used to measure Es from beneath maize (Zea mays L.) canopy for three consecutive drying cycles across the basin and runoff sections of IRWH on fine sandy loam soil of Bainsvlei Kenilworth ecotope. First, main effects of four runoff strip lengths (RSL) and three ML treatments were statistically analysed on the weighted Es values. Second, the ML treatments were allocated to the main plots and four levels of CS allocated according to lengths of the runoff sections. Third, cumulative Es (∑Es) measurements were used to evaluate empirical equations related to time (α′) and potential evaporation (β′). The two models for Es were compared by considering the effects of surface treatments. A significantly higher Es was observed from a bare (ML0%) treatment compared with either of two mulched treatments viz. mulch level 39% and 96% cover (ML39% and ML96%); no significant differences were found between the mulched treatments. The insignificant effect of RSL treatments on Es implied the dynamics of spatial distribution of soil water and energy that influenced evaporation were as a result of green mulch or shading cover (CS) on Es beneath the canopy. Less suppressive Es properties were developed from bare surface and efficient Es restriction was found under high mulch and shading cover treatments. The α′ and β′ values ranged from 2.34 to 4.26mmd−0.5 and from 1.38 to 2.06mmd−0.5, respectively. In all the treatments the simulated ∑Es was underestimated by the Ritchie model and overestimated by the Stroosnijder model. The main effect of shading was due to the dominant effect of energy limited evaporation (stage-1), while the mulched treatments were mainly driven by soil limited stage (stage-2) of evaporation. The Ritchie model performed well to estimate ∑Es from the basin area and the potential Stroosnijder model from the unshaded runoff strips. The microclimate of the cropping system changed according to surface treatments that highly influenced the Es losses in IRWH of dryland production.

Monitoring Electrical Conductivity and Nitrate Concentrations in an Andisol Field Using Time Domain Reflectometry

To establish sustainable agricultural practices, monitoring soil water and solute distributions in actual field conditions is important. Because the estimation of electrical conductivity (EC) using time domain reflectometry (TDR) is considered to be affected by Andisols because of their unique dielectric properties, in this study, we investigate the potential for the continuous monitoring of EC and nitrate concentrations using TDR in an Andisol field. The study was performed from December 2007 to August 2008. To estimate soil solution EC (ECw), the relationship among ECw, apparent EC (ECa) and volumetric water content (θ) for an Andisol was investigated, and three models (Rhoades model, Extended Rhoades model and Hilhorst model) were applied to describe this relationship. The Rhoades model was found to be reasonably accurate in describing the ECw-ECa-θ relationship, while the Hilhorst model showed reasonable agreement with the experimental data. In the field experiment, ECw values estimated using TDR with the Rhoades model correlated with those obtained from solution samples and a linear regression between ECw and soil nitrate concentrations was obtained from the field experimental data. The use of this regression with ECw estimated from TDR measurements, together with the Rhoades model, is considered a useful tool for the continuous monitoring of soil nitrate concentrations in Andisol fields under transient conditions.

Plant species diversity affects infiltration capacity in an experimental grassland through changes in soil properties

Soil hydraulic properties drive water distribution and availability in soil. There exists limited knowledge of how plant species diversity might influence soil hydraulic properties. We quantified the change in infiltration capacity affected by soil structural variables (soil bulk density, porosity and organic carbon content) along a gradient of soil texture, plant species richness (1, 2, 4, 8, 16 and 60) and functional group composition (grasses, legumes, small herbs, tall herbs). We conducted two infiltration measurement campaigns (May and October 2012) using a hood infiltrometer. Plant species richness significantly increased infiltration capacity in the studied grasslands. Both soil porosity (or inversely bulk density) and organic carbon played an important role in mediating the plant species richness effect. Soil texture did not correlate with infiltration capacity. In spring 2012, earthworm biomass increased infiltration capacity, but this effect could not be attributed to changes in soil structural variables. We experimentally identified important ecological drivers of infiltration capacity, suggesting complex interactions between plant species richness, earthworms, and soil structural variables, while showing little impact of soil texture. Changes in plant species richness may thus have significant effects on soil hydraulic properties with potential consequences for surface run-off and soil erosion.

Distribution of water in sandy soil applied by drip

The search for the use of water with high levels of efficiency has motivated the use of drip irrigation in several agricultural systems. However, for the efficiency be ensured, it is necessary that the water distribution in the soil profile must to be known in more details. As it is a highly variable process, function of the local characteristics, is essential the study of each case. The objective of this research was evaluating the water distribution in the soil profile, from drippers installed in surface and 0.15 m below the soil surface. The experiment was realized in the Technical Center of Irrigation (TCI) of the State University of Maringá - PR. The water monitoring in the soil profile was done with TDR probes installed in a box containing sandy soil, at the depths from 0.05 to 0.80 m; and 0.05 to 0.35 m of lateral spacing, at intervals of 0.05 m, totalizing 30 probes. The treatments were differentiated in relation of the installation depth of the emitters (0.0 and 0.15 m) and flow (1, 2, 4, 6, and 8 L h-1). The irrigation time was 8 hours continuous with reading of the TDR probes each 30 minutes. The results allowed concluding that the wet area with the emitter positioned on the soil surface was directly proportional to the flow increase. For the underground dripper, this area was substantially smaller and the water losses by percolation were higher, mainly to the flows higher than 4 L h-1, which provided to unacceptable water losses that should be avoided.

The Relationship between Soil Moisture and Root Density under Different Types &lt;i&gt;Phyllostachys edulis&lt;/i&gt; Forests in Northern Fujian

The soil moisture of three typical P. edulis forests (P. edulis and Cunninghamia lanceolata mixed forest, P. edulis pure forest , P. edulis and broad-leaved tree mixed forest ) in the North of Fujian province were studied in comparison with C. lanceolata pure forest and evergreen broad-leaved forest. Based on the routine observation, characteristics of spatial and temporal change of soil water content were studied. According to the roots distribution which were analyzed on different forest stand, the Linear and relationship model were established about the soil water and roots distribution. Results showed that the forest stand roots density decreasing with increasing soil depth, roots density and spatial distribution of soil moisture are related closely.

Choosing an optimal land-use pattern for restoring eco-environments in a semiarid region of the Chinese Loess Plateau

The natural environments in the semiarid regions of the Chinese Loess Plateau (CLP) are fragile due to the serious soil erosion and the weak ecological services of the plants. To ascertain and then evaluate a sustainable land-use pattern in these regions, we selected six typical land-use patterns (i.e., a farmland, a natural grassland, a homogeneous shrubland (S), a mix of shrubland and cultivated grassland (S–Alf), a mix of shrubland and orchard (S–O) and a mix of shrubland and grassland (S–G)) on the plateau and then measured the soil water, related soil properties and plant root indices to a depth of 1800cm. We also measured the aboveground net primary productivities (ANPPs). The mean soil water content (SWC) within the 0–1800cm profile was significantly highest (15.2%) in farmland, followed by grassland (11.4%) and S–Alf (8.0%). The available water (AW), the ratio between AW and AW capacity, and the thickness of the dried soil layers also demonstrated that farmland had the best conditions of soil water, followed by grassland and shrubland. The aboveground biomasses of grassland in both non-growing (140gm−2) and growing (370gm−2) seasons were significantly higher than those of shrublands. The ANPPs of the grassland (2.0gm−2d−1) demonstrated a similar trend. The patterns of land use (including the mixtures of different plant species) greatly affected the patterns of vertical distribution and quantities of soil water within the 1800-cm profile. The data for the soil–water regime and the ANPP further indicated that grassland would be an optimal use of the land for these semiarid regions. This information should be useful to the ecological scientists and policy makers for developing strategies for the sustainable management of vegetation on the CLP and possibly other water-limited regions around the world.

Stable oxygen isotope and flux partitioning demonstrates understory of an oak savanna contributes up to half of ecosystem carbon and water exchange.

Semi-arid ecosystems contribute about 40% to global net primary production (GPP) even though water is a major factor limiting carbon uptake. Evapotranspiration (ET) accounts for up to 95% of the water loss and in addition, vegetation can also mitigate drought effects by altering soil water distribution. Hence, partitioning of carbon and water fluxes between the soil and vegetation components is crucial to gain mechanistic understanding of vegetation effects on carbon and water cycling. However, the possible impact of herbaceous vegetation in savanna type ecosystems is often overlooked. Therefore, we aimed at quantifying understory vegetation effects on the water balance and productivity of a Mediterranean oak savanna. ET and net ecosystem CO2 exchange (NEE) were partitioned based on flux and stable oxygen isotope measurements and also rain infiltration was estimated. The understory vegetation contributed importantly to total ecosystem ET and GPP with a maximum of 43 and 51%, respectively. It reached water-use efficiencies (WUE; ratio of carbon gain by water loss) similar to cork-oak trees. The understory vegetation inhibited soil evaporation (E) and, although E was large during wet periods, it did not diminish WUE during water-limited times. The understory strongly increased soil water infiltration, specifically following major rain events. At the same time, the understory itself was vulnerable to drought, which led to an earlier senescence of the understory growing under trees as compared to open areas, due to competition for water. Thus, beneficial understory effects are dominant and contribute to the resilience of this ecosystem. At the same time the vulnerability of the understory to drought suggests that future climate change scenarios for the Mediterranean basin threaten understory development. This in turn will very likely diminish beneficial understory effects like infiltration and ground water recharge and therefore ecosystem resilience to drought.

Winter wheat with subsurface drip irrigation (SDI): Crop coefficients, water-use estimates, and effects of SDI on grain yield and water use efficiency

Winter wheat (Triticum aestivum L.) production in the North China Plain (NCP) is threatened by insufficient water supply. Interest in microirrigation is increasing in the NCP, while data and guidance for microirrigation scheduling are lacking. An accurate estimation of actual crop evapotranspiration (ETa) is critical for appropriate water management. In this study, therefore, the SIMDualKc model was calibrated with the data from a three-season experiment, and ETa of winter wheat with subsurface drip irrigation (SDI) was estimated with the dual crop coefficient approach and stress adjustments described in the FAO-56 using the data of the other two treatments. The mean value of basal crop coefficient (Kcb) for the winter wheat at the initial-, mid-, and late-season growth stages over the three seasons was 0.25, 1.06, and 0.34, respectively. Over the three growing seasons, the ETa for subsurface drip-irrigated wheat with three irrigation treatments ranged from 393 to 449mm. The Kc-local (ETa/ETo) values for the winter wheat with SDI were 0.34–0.80, 0.91–1.11, and 0.41–0.98, respectively, at the initial-, mid-, and late-season growth stages. Results indicated that the procedure of the dual Kc approach and stress adjustments simulated ETa of the winter wheat reasonably well, with the average absolute error (AAE) of 0.36mmd−1, the root mean square error (RMSE) of 0.43mmd−1,the index of agreement (d) of 0.98, the Nash–Sutcliffe efficiency (NSE) of 0.91, and the RMSE-observations standard deviation ratio (RSR) of 0.31. Discrepancy between the simulated and measured data was mainly attributed to the assumption of a uniform distribution of soil water around an emitter. Irrigation rates have significant effects on ETa, grain yield and WUE. Based on effects of irrigation rates on grain yield and WUE, irrigation schedule for optimum yield and WUE was developed for winter wheat. It was estimated that grain yield and WUE of winter wheat with the optimum irrigation schedule was 7780kgha−1 and 1.83kgm−3, respectively. The simulated results can be used as a reference for irrigation schedule and water management for winter wheat in the NCP.

Distribution of Water and Nitrogen in Soil under Drip and Microsprinkler Irrigation Fertigation of Garlic (Allium sativum L.) Crop

Distribution of Water and Nitrogen in Soil under Drip and Microsprinkler Irrigation Fertigation of Garlic (Allium sativum L.) Crop

Factors controlling soil organic carbon persistence along an eroding hillslope on the loess belt

The integration of hydrologic, geomorphic and biogeochemical approaches is required to determine organic carbon (OC) persistence and dynamics within landscapes. Here, we studied the persistence of OC along an eroding hillslope using soil in situ surface heterotrophic respiration measurement as an indicator. Along this topographical gradient, we quantified the space-time distribution of soil water and temperature as well as the amount of labile OC (i.e. NaOCl-non-resistant) in relation to CO2 fluxes. We used a Generalized Least Square (GLS) regression model (i) to identify the role of each abiotic factor as well as their interactions, and (ii) to quantify spatial differences in CO2 fluxes along the hillslope.We observed significant differences in respiration along the topographical gradient, i.e. 30% more at the downslope and 50% more at the backslope, relative to the uneroded summit position. Soil OC persistence along the hillslope was mainly controlled by the labile OC stock and moisture content. Our in-situ measurements also indicated that the temperature sensitivity of soil OC (as expressed by Q10 values) was strongly related to soil water content. The large stock of OC stored in colluvial soils has a higher temperature sensitivity (Q10 = 3.72 ± 0.17) than in non-depositional slope positions (Q10 = 1.77 ± 0.18 to 2.59 ± 0.13). Given the large stock of labile OC, its high temperature sensitivity and the high water contents that are needed to stabilize OC, we conclude that the OC stored in colluvial soils is particularly vulnerable to OC mineralization under drier/warmer conditions. When considering the large amount of OC that has been buried globally as a result of agricultural erosion during the last decades, the long-term stability of this pool under future land use and/or climate disturbance is an area of concern.

Seasonal simulation of water, salinity and nitrate dynamics under drip irrigated mandarin (Citrus reticulata) and assessing management options for drainage and nitrate leaching

• The seasonal water, salinity and nitrate distribution in soil was simulated by HYDRUS-2D. • Deep drainage accounts for 33.5% and water uptake 49% of applied water by mandarin crop. • Model simulation predicted 15% leaching of applied nitrate as fertilizer . • Higher N uptake recorded for fertigation during one hour before the last hour in an irrigation event. • Irrigation cut by 30% during 2nd half of the crop season reduced drainage and N leaching significantly. Estimation of all water fluxes temporally and spatially within and out of the crop root zone, and evaluation of issues like salinity and nutrient leaching, are necessary to fully appraise the efficiency of irrigation systems. Simulation models can be used to investigate these issues over several seasons when the cost of long term monitoring is prohibitive. Model results can be used to advise growers if improvements are required to various aspects of irrigation system operations. In this study, HYDRUS-2D was used to evaluate data measured during one season in a young mandarin ( Citrus reticulata ) orchard, irrigated with an intensive surface drip fertigation system. Water contents, salinities, and nitrate concentrations measured weekly in the field were compared with model predictions. The temporal mean absolute error ( MAE ) values between weekly measured and simulated water contents ranged from 0.01 to 0.04 cm 3 cm −3 . However, modelling error ( MAE ) was slightly larger at 10 cm depth (0.04 cm 3 cm −3 ), as compared to greater depths (0.02–0.03 cm 3 cm −3 ). Similarly, the errors were larger in the surface soil layer (25 cm depth) for nitrate–nitrogen, NO 3 − –N (1.52 mmol (c) L −1 ), as compared to greater depths. The spatial and temporal soil solution salinity ( EC sw ) and NO 3 − –N data showed accumulation of salts and nitrate within the soil up until day 150 of the simulation (December, 2006), followed by leaching due to high precipitation and over irrigation at later times. Only 49% of applied water was used by the mandarin trees, while 33.5% was leached. On the other hand, the simulation revealed that a significant amount of applied nitrogen (85%) was taken up by the mandarin trees, and the remaining 15% was leached. The results indicate that the irrigation and fertigation schedule needs modifying as there was overwatering from December onwards. Different permutations and combinations of irrigation and fertigation scheduling were evaluated to optimise the water and nitrogen uptake and to reduce their leaching out of the crop root zone. Slightly higher nitrogen uptake (1.73 kg ha −1 ) was recorded when fertigation was applied second to last hour in an irrigation event, as compared to applying it earlier during an irrigation event. Similarly, a 20% reduction in irrigation and N application produced a pronounced reduction in drainage (28%) and N leaching (46.4%), but it also decreased plant N uptake by 15.8% and water uptake by 4.8%, and increased salinity by 25.8%, as compared to the normal practice. This management would adversely impact the sustainability of this expensive irrigation system. However, reducing only irrigation by 30% during the 2nd half of the crop season (January to August) reduced drainage and N leaching by 37.2% and 50.5%, respectively, and increased N uptake by 6.9%. Such management of irrigation would be quite promising for the sustainability of the entire system. It is concluded that judicious manipulations of irrigation and fertilizer applications can be helpful in designing drip irrigation schedules for perennial horticultural crops to achieve improved efficiency of irrigation and fertigation applications and reduced contamination of receiving water bodies.