Soil Water Content Profiles Research Articles

Approximate analytical solutions for one-dimensional soil water movement equation with arbitrary initial conditions

Simple analytical solutions of one-dimensional horizontal and vertical soil water movement are of great importance for the soil hydraulic parameters estimation and precision irrigation. We present the approximate analytical solutions for the problem of horizontal absorption and vertical infiltration in soil under arbitrary initial conditions and constant boundary conditions based on the principle of least action and the variational principle. The algebraic functions of soil water content (SWC) profile, cumulative infiltration, infiltration rate and infiltration time about the wetting front distance/depth (WFD) and the parameters of Brooks-Corey model are obtained. Compared with the numerical results simulated by HYDRUS-1D, the algebraic results calculated by approximate analytical solutions have high precision to predict the horizontal and vertical soil water infiltration based on the known WFD. Contrary to the linear relationship in horizontal absorption with uniform initial conditions, the relationships between cumulative infiltration and WFD, infiltration rate and reciprocal of WFD, square of WFD and infiltration time are nonlinear for the arbitrary heterogeneous initial conditions. However, the initial conditions have little effect on the relationship between infiltration rate and WFD when the initial SWCs are lower than 0.6 θs. Based on the nonlinear relationships of infiltration rate and WFD in vertical infiltration, the WFD and time of the stable infiltration are obtained.

Redesign of dryland apple orchards by intercropping the bioenergy crop canola (Brassica napus L.): Achieving sustainable intensification

AbstractChina's Loess Plateau (LOP) contains around 22% of all the world's apple trees, mainly on smallholdings run by farmers. However, business‐as‐usual (BAU) intensification has reduced the ecological resilience of orchards. Agroforestry is considered to be an important method of realizing sustainable intensification of agroecosystems. However, the design of practical agroforestry systems in drylands remains poorly researched. We hypothesized that crop density is a key factor in designing dryland apple tree‐based agroforestry systems. We carried out an experiment in apple orchards in the semiarid LOP, where the bioenergy crop canola (Brassica napus L.) was intercropped at low, medium, and high densities with row spacings of 25, 50, and 100 cm, respectively, to study its effects on water, carbon, and production. We found that intercropping of canola at different densities clearly decreased soil water content (SWC) in the top 60 cm soil layer at all sampling locations, reduced midday leaf water potential (Ψm) and leaf water content (LWC), and caused apple trees to produce more fine roots at greater depths. However, intercropping did not affect SWC in soil layers below 60 cm. The SWC profiles, Ψm and LWC, progressively recovered over the mulching period. Introduction of canola also significantly (p < 0.05) increased SOC content in the surface layer, an effect less visible in deeper layers, and increased the quality of apple fruit to varying degrees while not affecting apple yield measurably. Overall, higher intercropping density does not lead to severer water deficit but have better carbon sequestration benefit than lower density, and therefore seems more appropriate in our study site. Our findings provide solid evidence that agroforestry helps achieve sustainable intensification of dryland orchards.

Influence of cover crop on water and nitrogen balances and cash crop yield in a temperate climate: A modelling approach using the STICS soil-crop model

Cover crops are crucial to diversify cropping systems into more agroecological systems by providing ecosystem services, such as reduction of nitrate leaching, provision of a green manure effect, and soil carbon storage. However, they can influence water drainage and nitrogen (N) or water availability for the succeeding crop, depending on their management and the climate. In this simulation study, we used the STICS model to predict the influence of cover crop species, date of sowing and termination, and cover crop residue management on N and water balances, and the yield and stress of the succeeding cash crop. We performed 25-year simulations for five contrasting sites in south-western France, which is a temperate region of Europe with dry summers. As expected, cover crops decreased nitrate leaching effectively but also decreased drainage by a mean of 5–40 mm. This decrease depended mainly on the sowing and termination dates, while the decrease in nitrate leaching varied greatly among sites and depended most on sowing date, followed by cover crop species and then termination date. Cover crops had little influence on soil water content in the upper 0.1 m of soil at sowing of the succeeding cash crop, but decreased soil water content of the total soil profile by 0–30 mm. Soil water content depended most on termination date, followed by species and then site. Total soil mineral N content (SNC) also decreased, by 5–40 kg N.ha−1, at the three driest sites and up to 10 kg N.ha−1 at the rainiest site. Termination date, the second-most influential factor on SNC, indicated that later termination resulted in lower SNC than that after bare soil. N uptake by the succeeding cash crop depended on species and termination date, and a legume cover crop and earlier termination date resulted in higher N uptake. The decrease in maize and sunflower yield was due mainly to changes in the N stress index during the vegetative phase for maize, and both vegetative and reproductive phases for sunflower. No water stress or increase in irrigation volumes was predicted or was correlated with yield changes, except at dry sites for the few years that experienced a severe drought in spring. While cover crops decreased nitrate leaching effectively, they decreased drainage and could induce N stress for the succeeding crop, particularly in dry regions. Including legumes in mixtures and adapting the termination date to local climate conditions could decrease or avoid these negative effects.

Implications of Hysteresis on the Horizontal Soil Water Redistribution after Infiltration

Although soil water redistribution is critical for a number of problems, a rather limited study of this process has been reported up to now and especially as regards the implications of hysteresis on horizontal soil water redistribution after infiltration. To this end, a thorough theoretical and numerical investigation of the redistributed soil water content profiles formed after the cessation of a horizontal infiltration is presented. A number of different initial soil water contents before the initiation of the horizontal infiltration and different infiltration depths were analyzed using the HYDRUS-1D software package considering the appropriate hysteretic wetting and drying curves. The effect of neglecting hysteresis was also investigated for the same conditions. The main wetting and drying boundary curves of the studied porous medium and the hydraulic conductivity at saturation were experimentally determined. The theoretical and numerical analysis indicated that the form of the redistributed soil water content profiles in the presence of hysteresis was similar to the original infiltration profile independently of whether the initial soil water content was taken on the boundary wetting or drying curve and independently of the porous medium type. Specifically, in a relatively short time after the initiation of the redistribution process, the magnitude of the soil matrix head gradient tended to zero due to hysteresis, and this resulted in an insignificant soil water movement, although the soil water content and the hydraulic conductivity values were still high. In addition, the redistribution proceeded at a faster rate than the smallest depth of infiltration water prior to the redistribution, and it was faster during the early stages of the redistribution. Accordingly, hysteresis is important for the simulation of horizontal soil water redistribution as it is, for example, in the case of localized irrigation systems’ design and management.

Detecting crop water requirement indicators in irrigated agroecosystems from soil water content profiles: An application for a citrus orchard

Most perennial crops sensitive to water scarcity, such as citrus, can benefit from efficient water management, which allows for reduced water consumption while increasing crop production on a long-term basis. However, when implementing water-saving strategies, it is necessary to monitor soil and/or plant water status in order to determine crop water demand. A plethora of devices providing indirect measurements of volumetric soil water content, such as the “drill and drop” multi-sensors probes (Sentek, Inc., Stepney, Australia), have been developed over the last decade.The objective of the paper was to analyse time-series of soil water content profiles and meteorological data collected in an adult citrus orchard over three years of field observations (2017–2020) in order to estimate actual crop evapotranspiration and derive crop coefficients. Simultaneous measurements of sap fluxes also allowed for the estimation of the basal crop coefficient, Kcb, used as a control variable.The temporal dynamics of soil water content profiles following rainfall or irrigation events provided information on soil evaporation, root water uptake, and actual crop transpiration. After soil wetting events, in particular, it was possible to recognize patterns of actual crop evapotranspiration similar to those detected with sap flow sensors. The knowledge of actual crop evapotranspiration at the daily time-step, in conjunction with the corresponding reference crop evapotranspiration, allowed for appropriate estimations of the crop coefficient associated with the various development stages. The proposed method provided interesting insights into the dynamics of root water uptake and crop evapotranspiration of the studied citrus orchard, and it represents a promising tool for precise irrigation scheduling in other agroecosystems.

Hydraulic redistribution by deeply rooted grasses and its ecohydrologic implications in the southern Great Plains of North America

AbstractPerennial bioenergy crops with deep (>1 m) rooting systems, such as switchgrass (Panicum virgatum L.), are hypothesized to increase carbon storage in deep soil. Deeply rooted plants may also affect soil hydrology by accessing deep soil water for transpiration, which can affect soil water content and infiltration in deep soil layers, thereby affecting groundwater recharge. Using stable H and O isotope (δ2H and δ18O) and 3H values, we studied the soil water conditions at 20–30 cm intervals to depths of 2.4–3.6 m in paired fields of switchgrass and shallow rooted crops at three sites in the southern Great Plains of North America. We found that soil under switchgrass had consistently higher soil water content than nearby soil under shallow‐rooted annual crops by a margin of 15%–100%. Soil water content and isotopic depth profiles indicated that hydraulic redistribution of deep soil water by switchgrass roots explained these observed soil water differences. To our knowledge, these are the first observations of hydraulic redistribution in deeply rooted grasses, and complement earlier observations of dynamic soil water fluxes under shallow‐rooted grasses. Hydraulic redistribution by switchgrass may be a strategy for drought avoidance, wherein the plant may actively prevent water limitation. This raises the possibility that deeply rooted grasses may be used to passively subsidize soil water to more shallow‐rooted species in inter‐cropping arrangements.

Water budgeting in conservation agriculture-based sub-surface drip irrigation in tropical maize using HYDRUS-2D in South Asia

In water scarce regions of South Asia, diversification of rice with maize is being advocated towards sustainability of cereal-based cropping systems. Adoption of innovative agronomic management practices, i.e., conservation agriculture (CA) and sub-surface drip irrigation (SSDI) are considered as key strategies for much needed interventions to address the challenges of water scarcity under projected climate change. Benefits from CA and SSDI concerning water economy are well-established, however, information about their complementarity and water budgeting in cereal-based systems are lacking. A field study was conducted with process-based model (HYDRUS-2D) to understand water transport, root water uptake and components of soil water balance in maize grown in rotation with wheat after five years of continuous adoption of conservation agriculture. In this study, altogether eight treatments comprising of 6 CA+ treatments (CA coupled with SSDI); permanent beds using sub-surface drip (PB-SSD) with (WR) and without (WOR) crop residue at different N rates, 0, 120 and 150 kg N ha−1 were compared with CA (PB using furrow irrigation-FI with crop residue-120 kg N ha−1) and conventional tillage practices (CT) (CT using FI without crop residue-120 kg N ha−1). Results showed that the model could simulate the daily changes in profile soil water content with reasonable accuracy in all the treatments. Simulated soil water balance indicated higher cumulative root water uptake (CRWU), lower cumulative evaporation (CE) and higher soil water retention in CA+ (PB-SSD+ crop residue at 150 and 120 kg N ha−1) than CA and CT plots. Hydrus-2D model efficiency > 0, RMSE between 0.009–0.026 and R2 value between 0.80–0.92 at P < 0.01 indicates that the model is performing efficiently. The mean evaporation from CA+ treatments was 10 and 36% less than CA and CT treatments, respectively. On average, CRWU under CA+ treatments were 14–48% higher than FI treatments. The mean cumulative deep drainage in CA+ plots was 80–100 mm less than CA and CT plots. In CA+ based plots significantly higher biomass production and radiation use efficiency were observed with reduced water use than CA and CT. Therefore, the study justifies the water-saving nature of CA+, while maintaining higher productivity and meeting the transpiration demand of crops and halting unnecessary evaporation and deep drainage losses.

Multi-Step Calibration Approach for SWAT Model Using Soil Moisture and Crop Yields in a Small Agricultural Catchment

The quantitative prediction of hydrological components through hydrological models could serve as a basis for developing better land and water management policies. This study provides a comprehensive step by step modelling approach for a small agricultural watershed using the SWAT model. The watershed is situated in Petzenkirchen in the western part of Lower Austria and has total area of 66 hectares. At present, 87% of the catchment area is arable land, 5% is used as pasture, 6% is forested and 2% is paved. The calibration approach involves a sequential calibration of the model starting from surface runoff, and groundwater flow, followed by crop yields and then soil moisture, and finally total streamflow and sediment yields. Calibration and validation are carried out using the r-package SWATplusR. The impact of each calibration step on sediment yields and total streamflow is evaluated. The results of this approach are compared with those of the conventional model calibration approach, where all the parameters governing various hydrological processes are calibrated simultaneously. Results showed that the model was capable of successfully predicting surface runoff, groundwater flow, soil profile water content, total streamflow and sediment yields with Nash-Sutcliffe efficiency (NSE) of greater than 0.75. Crop yields were also well simulated with a percent bias (PBIAS) ranging from −17% to 14%. Surface runoff calibration had the highest impact on streamflow output, improving NSE from 0.39 to 0.77. The step-wise calibration approach performed better for streamflow prediction than the simultaneous calibration approach. The results of this study show that the step-wise calibration approach is more accurate, and provides a better representation of different hydrological components and processes than the simultaneous calibration approach.

Measurement of soil profile water content with the Profile Probe

Measurement of soil profile water content with the Profile Probe

Efficient prediction of profile mean soil water content for hillslope-scale Caragana korshinskii plantation using temporal stability analysis

Spatio-temporal variability in soil water content (SWC) increases the difficulty in soil water resource management and vegetation construction in arid and semi-arid regions. Our objectives were to investigate the spatial variability and temporal stability of SWC and identify representative locations for reliably predicting the profile mean SWC (MSWC) of a 33-year-old Caragana korshinskii plantation on typical sunny and shady hillslopes on the Loess Plateau, China. The profile SWC (0–180 cm) in three sampling belts and five hillslope positions (upper position, UP; upper-middle position, UMP; middle position, MP; lower-middle position, LMP; lower position, LP) were measured 27 times for both the hillslopes in 2018 and 2019. The mean relative difference (MRD), the standard deviation of the MRD (SDRD), and an index of temporal stability (ITS) were used to identify representative locations of the MSWC. The results indicated that the SWC presented different horizontal but similar vertical change trends in the five hillslope positions. The profile MSWC on the sunny hillslope (8.89%) was lower than that on the shady hillslope (9.44%). The mean Spearman correlation coefficients of the temporal patterns ranged from 0.6 to 0.8 for the five soil layers on both hillslopes. The characteristics of temporal stability differed in both temporal persistence and the representative locations for the five soil layers on the sunny and shady hillslopes. The mean ITS values generally decreased with increasing soil depth. Ultimately, the representative locations for estimating the profile MSWC were determined to be the MP-2 location on the sunny hillslope and the MP-3 location on the shady hillslope based on the MRD, SDRD, and ITS values. The representative locations have the lowest ITS values and represent the MSWC accurately, with root mean square error (RMSE) and mean error (ME) values of less than 1%. In addition, the soil organic carbon, clay, silt, and sand contents greatly affect the spatial and temporal distributions of the soil water at the hillslope scale. Our study provides a rapid and accurate method for determining profile MSWC in C. korshinskii plantations on typical sunny and shady hillslopes and could also support valuable guidance for the rational management of hillslope-scale SWC resources for similar dry regions.

Corn residue baling and grazing impacts on corn yield under irrigated conservation tillage systems

AbstractCrop residue grazing or baling is common in the western Corn Belt. However, its impacts on subsequent crop yields under different irrigation levels and tillage systems are unclear. We investigated the impacts of corn (Zea mays L.) residue baling and cattle grazing on soil compaction, water content, and corn yield under full and limited irrigated no‐till in Nebraska during three years. In Years 2 and 3, an additional tillage treatment (strip till) was implemented to evaluate its effects on grain yield under the above treatments. Residue removal effects on compaction and water content did not vary with irrigation level. Grazing (3.68 animal units ha−1) minimally impacted compaction and soil profile water content compared to no removal. Baling increased cone index by 34–53% in the 0‐to‐12.5‐cm depth and decreased water content by 6 cm compared to no removal. Residue removal effects on yield did not depend on irrigation. Residue removal impacts depended on tillage in Year 3 only. Full irrigation increased corn yields up to 11% compared to limited irrigation. Strip till increased yield by 11% compared to no‐till in Year 2 only. Baling and grazing had no effect on corn yield in Year 1, but baling and grazing increased yield by 9% compared to no removal in Year 2, likely due to lower water content. In Year 3, grazing and baling increased yield by 9% under no‐till but not strip till. Overall, grazing had minimal impacts while baling increased yield and compaction and decreased water content with few variations due to irrigation or tillage.

FAO56 crop and water stress coefficients for cotton using subsurface drip irrigation in an arid US climate

Water shortages are a continuing reality for today’s irrigated agriculture especially in the arid US southwest where cotton (Gossypium hirsutum L.) is an important crop. Decreasing water availability in the region coupled with high cotton water requirements are inducing water conservation practices, including adoption of subsurface drip irrigation (SDI) and deficit irrigation management. A 3-year cotton study (2016, 2017, and 2018) was conducted on a sandy loam soil using SDI at Maricopa, Arizona, USA. The objectives were to determine the actual single (Kc act) and basal (Kcb act) crop coefficients, corresponding growth stage lengths, and water stress adjustment criterion for estimating crop evapotranspiration (ETc) by the widely used FAO56 crop coefficient procedures. Treatments evaluated were full irrigation (100%) and deficit irrigation (70%), both replicated three times and managed at an optimum N rate. Irrigation scheduling was based on a FAO56 Kcb curve locally developed in earlier studies at the Maricopa location using furrow irrigation. Actual ETc (ETc act) was determined by a soil water balance using 0–1.9-m soil profile water content measurements made every 6–14-days. The study also quantified the effects on ETc act and yield due to the deficit irrigation treatment. ETc act rates were high for the 100% treatment, often exceeding 12.0 mm d−1 during the mid-season stage in all years. Cumulative ETc act for the 100% treatment was 961, 1039, and 1008 mm; and lint yield was 1470, 1780, and 2200 kg ha−1 in 2016, 2017, and 2018, respectively. Treatment effects on both ETc act and cotton yield were significant in all years. Cumulative ETc act for the 70% treatment was 21–23% less than that for the 100% in each year. Lint yields for the 70% treatments were reduced 15–16% in two of the years, and by 36% in 2017 when soil water stress occurred earlier in the growing season. The 3-year average values of Kc act and Kcb act at mid-season were 1.31 and 1.26, respectively. Though higher than those previously reported for cotton at this location, these mid-season values are considered appropriate in this arid climate when using SDI and were consistent with the FAO56 mid-season standard cotton values after local climate adjustment. The observed average Kc act and Kcb act during the initial stage were ≈ 0.21 and they were 0.37 at the end of season, closely agreeing with the FAO56 tabulated cotton values for those stages. The average growth stage lengths determined for the SDI cotton are 33, 42, 51, and 28 for the initial, development, mid-season, and late season stages, respectively. The FAO56 water stress coefficient (Ks) was modeled for the 70% treatment using five different baseline values of depletion fraction for no stress (p) that varied from 0.60 to 0.70 in 0.025 increments. Best correlation coefficients (r) between the ETc act ratio of the 70% and 100% treatments with the modeled Ks of the 70% treatment were obtained with baseline p values of 0.60, 0.675, and 0.675 in 2016, 2017, and 2018, respectively. The three 3-year average baseline p value of 0.65, which is the same baseline p value for cotton in FAO56, is recommended for estimating ETc reduction due to water stress.

Soil Water Deficit and Fertilizer Placement Effects on Root Biomass Distribution, Soil Water Extraction, Water Use, Yield, and Yield Components of Soybean [Glycine max (L.) Merr.] Grown in 1-m Rooting Columns.

Typical small-pot culture systems are not ideal for controlled environment phenotyping for drought tolerance, especially for root-related traits. We grew soybean plants in a greenhouse in 1-m rooting columns filled with amended field soil to test the effects of drought stress on water use, root growth, shoot growth, and yield components. There were three watering treatments, beginning at first flower: watered daily to 100% of the maximum soil water holding capacity (control), 75% (mild drought stress), or 50% (drought stress). We also tested whether applying fertilizer throughout the 1-m soil depth instead of only in the top 30 cm would modify root distribution by depth in the soil profile and thereby affect responses to drought stress. Distributing the fertilizer over the entire 1-m soil depth altered the root biomass distribution and volumetric soil water content profile at first flower, but these effects did not persist to maturity and thus did not enhance drought tolerance. Compared to the control (100%) watering treatment, the 50% watering treatment significantly reduced seed yield by 40%, pod number by 42%, seeds per pod by 3%, shoot dry matter by 48%, root dry matter by 53%, and water use by 52%. Effects of the 75% watering treatment were intermittent between the 50 and 100%. The 50% treatment significantly increased root-to-shoot dry matter ratio by 23%, harvest index by 17%, and water-use efficiency by 7%. Seed size was not affected by either fertilizer or watering treatments. More than 65% of the total root dry matter was distributed in the upper 20 cm of the profile in all watering treatments. However, the two drought stress treatments, especially the mild drought stress, had a greater proportion of root dry matter located in the deeper soil layers. The overall coefficient of variation for seed yield was low at 5.3%, suggesting good repeatability of the treatments. Drought stress imposed in this culture system affected yield components similarly to what is observed in the field, with pod number being the component most strongly affected. This system should be useful for identifying variation among soybean lines for a wide variety of traits related to drought tolerance.

Spatiotemporal Variability in Soil Water Content Profiles under Young and Mature Oil Palm Plantations in North Bengkulu Regency

Soil water content (SWC) profile refers to the vertical distribution of volumetric SWC at a certain depth of soil concerning the plant water availability. The current study aimed to evaluate the vertically spatial distributions and temporal variations in SWC profiles under young and mature oil palm trees during the end period of the rainy season. Twenty couples of sensors were inserted into 5 cm soil depth intervals up to 100 cm. Each sensor pair was connected to the dielectric instrument to measure the electrical impedance (Z, in kΩ) at each soil layer. The measured Z was then converted to the gravimetric SWC (θg, in g.g-1) using an equation of θg = 0.62.Z-0.2 found in our previous study. The gravimetric SWC data were then multiplied by soil bulk density for corresponding layers to get volumetric SWC (θv, in cm3.cm-3). Results showed that soil water profiles' depths were 40 to 70 mm higher under mature than under young oil palm plantations during six weeks of measurements. The vertical distribution of soil bulk density could be why the spatiotemporal variability in water content profile. Looser layers throughout the young oil palm soil profile might cause a higher proportion of drainage pores and result in less water content compared to the denser layers under the mature oil palm.

Analytical Solution for Field Soil Water Content Profiles

AbstractQuantifying the spatial and temporal dynamics of soil moisture is an important subject in vadose zone hydrology. Although progress has been made to measure soil water content, soil water flow needs to be simulated for many applications. An analytical solution for soil water content, resulting from vertical flow and simplified mathematical conditions and hydraulic properties, was derived with the Cole‐Hopf transformation. The solution serves as a transfer function with the calibrated boundary condition and water content as respective input and output. This transfer function was applied to time series of soil water content, obtained from weekly observations with a neutron probe over a 1282‐day period at five depths and 16 locations. Water retention and saturated hydraulic conductivity were measured on soil samples in the laboratory. The transfer function was calibrated to observed time series of soil water content θ(t) with a median coefficient of determination R2 = 0.980. It was then used to predict θ(t) using constants from the calibration location and hydraulic parameters from the prediction location. There was a fairly good correspondence between predicted and observed θ(t) using calibrations elsewhere (R2 = 0.783). As an alternative, an observed time series θ(t) was scaled by multiplying it by the ratio of experimental saturated water contents for prediction and observation location. This scaling approach led to poorer predictions (R2 = 0.651). The analytical solution provides a flexible approach to quantify soil moisture for a variety of scenarios regarding available data on topography, climate, soil properties, and soil hydraulic parameters.

No-tillage with mulching improves maize yield in dryland farming through regulating soil temperature, water and nitrate-N

Nitrogen (N) losses from cropland soils contribute to a series of ecological problems. No-tillage and mulching are widely regarded as practices that can minimize the disturbance of the agro-ecosystem and regulate the water cycle in dryland farming. However, detailed understanding of water and nitrate-N transport in soil and their effects on the soil ecosystem under no-tillage with mulching is lacking. To improve our understanding, a long-term continuous maize field experiment was conducted in the southern Loess Plateau, China. This article reports experimental data form a complete growth year for spring-sowing maize, including the fallow period (from October 2017 to April 2018) and the growth period (from May 2018 to September 2018) after 15 years maize planting. Treatments included conventional tillage (CT), no-tillage (NT), no-tillage with biochar (NB), no-tillage with straw mulching (NS), no-tillage with plastic film mulching (NP), and no-tillage with straw-plastic film mulching (NSP). Overall, the results revealed that the effect of different treatments on soil temperature gradually weakened with increased maize growth and increased soil depth. The NP had the highest average temperature during the whole growth period, and NS had the lowest. Average soil profile water content (SWC) and the soil water storage (SWS) of the mulching treatments (NSP, NP, NS) were higher than the non-mulching (CT, NT, NB) at each stage. The SWS of NSP in the maturity period was significantly greater by 7.1 % compared with CT. Our results indicated that there was no nitrate-N leaching in NSP and NP below 40 cm, and the nitrate-N accumulation followed the order of CT > NT > NS > NB > NP > NSP. Conventional tillage exhibited a nitrate-N accumulation peak in deep soil layers (140−180 cm), while nitrate-N peaks of the NT, NS, and NB treatments in the shallow soil layers (40−90 cm) decreased with seasonal variation. However, the NSP and NP increased yields by 36.5 % and 34.1 %, NT decreased yields by 14.8 %, respectively, compared to CT. These suggest that no-tillage alone (NT) does not effectively improve soil water use efficiency and may even reduce yields, but reduce nitrate leaching. No-tillage with straw-plastic film mulching (NSP) was the most effective measure to facilitate the sustainable development of agriculture in dryland farming.

Precipitation dominates the transpiration of both the economic forest (Malus pumila) and ecological forest (Robinia pseudoacacia) on the Loess Plateau after about 15 years of water depletion in deep soil

Understanding how different tree species consume soil water is critical for land management, especially in areas with limited water resources. This study examined the soil water consumption characteristics of two exotic tree species—economic forest apple tree (Malus pumila) and ecological forest black locust (Robinia pseudoacacia)—and the effect of soil desiccation on plant transpiration in the 2018 growing season in a semi-arid region of the Loess Plateau. We investigated root distribution and deep soil water content in the vertical soil profile and used hydrogen and oxygen stable isotopes to identify the contribution of water to transpiration in shallow (0–2 m) and deep (>2 m) soil. We also measured sap flow changes using thermal dissipation probes during the growing season. The apple orchard had a maximum rooting depth of about 16 m, with a deep soil water deficit of about 771 mm. The corresponding figures for the black locust forest were about 25 m and 1926 mm. In previous years, the apple trees consumed 51.4 mm yr–1 of deep soil water and black locust consumed 120.4 mm yr–1. In the 2018 growing season, soil water content varied from 0–200 cm depth, with no significant changes beyond 200 cm in either species. Shallow soil water contributed, on average, 68.1% and 80.9% to transpiration in the apple orchard and black locust forest, respectively, and both they had a similar amount of transpiration during the growing season. These results indicate that rapid deep soil desiccation leads to a lack of sustainable root water uptake in deep soil, and the dominance of transpiration by precipitation in this region. This study increased our understanding on how intensive water extraction from deep soil affects tree transpiration, which is significant for sustainable afforestation in the Loess Plateau and other regions with similar hydrogeology.

A long-term (2005–2016) dataset of hourly integrated land–atmosphere interaction observations on the Tibetan Plateau

Abstract. The Tibetan Plateau (TP) plays a critical role in influencing regional and global climate, via both thermal and dynamical mechanisms. Meanwhile, as the largest high-elevation part of the cryosphere outside the polar regions, with vast areas of mountain glaciers, permafrost and seasonally frozen ground, the TP is characterized as an area sensitive to global climate change. However, meteorological stations are biased and sparsely distributed over the TP, owing to the harsh environmental conditions, high elevations, complex topography and heterogeneous surfaces. Moreover, due to the weak representation of the stations, atmospheric conditions and the local land–atmosphere coupled system over the TP as well as its effects on surrounding regions are poorly quantified. This paper presents a long-term (2005–2016) in situ observational dataset of hourly land–atmosphere interaction observations from an integrated high-elevation and cold-region observation network, composed of six field stations on the TP. These in situ observations contain both meteorological and micrometeorological measurements including gradient meteorology, surface radiation, eddy covariance (EC), soil temperature and soil water content profiles. Meteorological data were monitored by automatic weather stations (AWSs) or planetary boundary layer (PBL) observation systems. Multilayer soil temperature and moisture were recorded to capture vertical hydrothermal variations and the soil freeze–thaw process. In addition, an EC system consisting of an ultrasonic anemometer and an infrared gas analyzer was installed at each station to capture the high-frequency vertical exchanges of energy, momentum, water vapor and carbon dioxide within the atmospheric boundary layer. The release of these continuous and long-term datasets with hourly resolution represents a leap forward in scientific data sharing across the TP, and it has been partially used in the past to assist in understanding key land surface processes. This dataset is described here comprehensively for facilitating a broader multidisciplinary community by enabling the evaluation and development of existing or new remote sensing algorithms as well as geophysical models for climate research and forecasting. The whole datasets are freely available at the Science Data Bank (https://doi.org/10.11922/sciencedb.00103; Ma et al., 2020) and additionally at the National Tibetan Plateau Data Center (https://doi.org/10.11888/Meteoro.tpdc.270910, Ma 2020).

Measurements and modeling of hydrological responses to summer pruning in dryland apple orchards

Long-term imbalance of water demand over supply in drylands can result in serious ecological issues such as severe soil desiccation, posing a great challenge to sustainable development of dryland orchards. This study examined the effects of multi-intensity summer pruning on water balance, production and water use efficiency of apple orchards on China’s Loess Plateau using in situ measurements and the process-based MAESPA model. A field experiment with four intensities representing no (0% or control), light (10%), moderate (25%) and heavy (40%) pruning of branches was carried out in three replicates under each treatment. The pruning intensities dictated transpiration, soil moisture and drainage. Although light pruning had weak impacts on these factors, moderate and heavy pruning significantly reduced growing-season transpiration by an average 10.4% and 28.5%, respectively. However, the effects progressively faded away with time at both diurnal and seasonal scales. Moderate and heavy pruning also increased soil water content in the 20–180 cm by an average 18.3% and 20.8%, respectively, and thus enhanced drainage below 180 cm (>220 mm), relative to light pruning and control (<170 mm). Furthermore, light and moderate pruning clearly promoted apple yield and water use efficiency whereas heavy pruning significantly reduced (24.7%) apple yield. Thus, moderate pruning can be a good choice for apple orchards in normal precipitation years while heavy pruning may be an alternative in severe drought years. The MAESPA model reliably simulated seasonal variations of transpiration (R2: 0.799–0.910, root mean square error (RMSE): 0.111–0.207 mm), soil evaporation (R2: 0.368–0.628, RMSE: 0.468–1.076 mm), and profile soil water content (R2: 0.400–0.894, RMSE: 0.005–0.024 cm3 cm−3) for all treatments and can be used as a tool to quantify the effects of pruning on hydrological processes in dryland apple orchards. This study provides insights into the development of a sustainable management strategy in dryland orchards.

Simulation of Water and Salt Dynamics in the Soil Profile in the Semi-Arid Region of Tunisia—Evaluation of the Irrigation Method for a Tomato Crop

In Tunisia, water used for irrigation is often saline, increasing the risk of salinization for soils and crops. In this study, an experiment was conducted on a tomato crop cultivated on a silty-clay soil irrigated with three different water qualities: 0, 3.5, and 7 dS·m−1. Experimental data were then used to calibrate and validate the Hydrus-1D model, which simulates water flow and salt transfer in soils. The successfully-calibrated and validated model was then used to study the combined effects of the soil osmotic and soil matrix potentials on root water uptake. The values of the root mean square error (RMSE), the coefficient of determination (CD), the modeling efficiency (EF), and the coefficient of residual mass (CRM) were close to their optimal values for both soil water content and soil electrical conductivity profiles, indicating the reliability of the model to reproduce water and salt dynamics. Relative yields (Yr), indirectly estimated using actual and potential root water uptake (transpiration), indicated that the multiplicative stress response model (using the S-shape model) satisfactorily simulates measured yields and reproduces the effects of irrigation with saline waters on crop yields. An alternative scenario using a reduction of water requirements by 50% was investigated to assess an irrigation method with considerable water savings. As the results show that relative yields, Yr, were only slightly reduced, the crop water requirements estimated by CROPWAT 8.0 must have been overestimated. The variation of the soil salinity in the root zone highlighted a high salinization risk in the short-term when water of 7 dS·m−1 is used for irrigation.