Soil Water Evaporation Research Articles

Suppressive effects of geotextiles on soil water evaporation

Geotextiles find wide applications in the field for filtration and drainage. When applied on the soil surface they influence soil evaporation. The objective of this work is twofold: (a) to assess the effectiveness of four different geotextiles as cover materials on soil evaporation, (b) to study the combined effect of geotextile and perforated mechanical barriers on soil evaporation. The first set of experimental programs consisted of three soil samples i.e. kaolin, dredged mud from the port of Brisbane and a locally obtained red mud sample from Queensland, Australia tested with four types of non-woven geotextiles under four controlled climatic conditions. All the 4 geotextiles had suppression effects on soil evaporation to degrees that varied with the type of soil, ratio of pore size to thickness of geotextiles (M*), product of pore size to thickness of the geotextiles (N*) and climatic conditions. Geotextiles with a higher pore size (O95) and M* allowed water vapor to move through relatively easily leading to higher evaporation rates. Geotextile with a higher thickness and N* value provided a higher suppression effect on soil evaporation. In a recently introduced dewatering method involving perforated ventilated well method, evaporation from soil take place through geotextiles and the perforated well. Mimicking this, impacts on soil evaporation with geotextiles sandwiched between soil sample and perforated sections were also studied. Maintaining similar number and arrangement of the perforations, soil evaporation was noted to be higher with rectangular shaped perforation compared to circular shaped perforations.

Impact of clod (aggregate) size on evaporation rate and soil moisture profile during the drying process

AbstractLarge clods (centimetres in size) can be formed by tillage in clayey paddy fields where upland crops are planted. These clods cause early water depletion near the soil surface, which decreases crop germination and emergence rates. Because of the difficulty in reducing clod size, desiccation damage to seeds can be avoided by adjusting the seeding depth based on the clod size‐dependent soil moisture profile. This study aimed to clarify the effect of clod size on (1) the evaporation rate (E) and soil moisture profile and (2) the mobility of soil water during the drying process. Evaporation experiments were conducted in an air‐conditioned greenhouse with natural light using cylindrical columns filled with artificially made clods 3 (L columns) and 1 cm (S columns) in diameter. We measured E, potential evaporation rate (PE), and total soil moisture content (wtot) throughout the experiment and the soil moisture profiles at the end of the experiment. The water diffusivity (Dw) and apparent vapour diffusion coefficient (dvap) were calculated as the mobility of soil water and water vapour, respectively. We found that wtot was lower in the L column than in the S column, although not at the onset of the experiment. At the end of the experiment, the soil moisture content was lower in the L column than in the S column throughout the soil layer. In contrast, E/PE was higher in the L column than in the S column throughout the experiment and even at the same wtot. Regarding mobility, Dw was slightly greater in the L column than in the S column in the soil moisture content range, where vapour movement could be greater than liquid water movement. In addition, the ratio of dvap to the diffusion coefficient of water vapour in soil was higher than unity in both columns and was 2.4–3.2 times higher in the L column than in the S column. In summary, larger clods caused a higher evaporation rate and lower soil moisture content, owing to the increased enhancement of water vapour movement probably induced by wind.

Seasonal variations and sources of the dew from stable isotopes in alpine meadows

AbstractThe dew is closely related to the micro‐use water of plants and the large‐scale hydrological processes, its formation on grassland plays a vital role especially in maintaining the eco‐hydrological cycle. We used structural equation modelling to investigate how environmental factors would affect dew formation on alpine graminoid‐Kobresia meadow in northern Qinghai‐Tibet Plateau. The stable isotope information of dew, ambient vapour, soil water, plant water, creek water and precipitation were tracked to explore the source of dew, the dew transport route of the six dominant species by Mix SIAR model. Our results showed that the frequency of dew on the graminoid‐Kobresia meadow in 2020 and 2021 was 42.86% and 45.83%, respectively. Both atmospheric pressure (r = 0.4) and temperature (r = 0.382) showed significant positive effects dew formation while wind speed (r = −0.309) had a negative effect. The contribution rates of soil water, plant water and ambient water vapour to dew were 48.20 ± 5.46%, 38.30 ± 5.07%, and 13.50 ± 1.82%, respectively. The proportion of dew utilization in the dominant species had no significant species differences. Our results provided an improved understanding of dew formation based on isotope technology on alpine meadow in northern Qinghai‐Tibet Plateau.

Effect of soil organic matter on sorption of water vapor and associated hysteresis

AbstractIn‐depth knowledge about the impact of organic matter (OM) on soil water vapor sorption (SWVS) and associated hysteresis related to various water activity (aw) levels is limited. The objective of this study was to elucidate the effect of OM on SWVS and sorption hysteresis for different aw levels. We measured water sorption isotherms and physicochemical properties of eight soils with varying clay (6%–47%) and OM (2.0%–7.8%) contents before and after OM removal. In general, OM increased SWVS, but the effect of OM on SWVS varied for different aw ranges. The presence of OM generally increased water vapor sorption during the adsorption process. For soils with OM content above 4.6%, the presence of OM decreased water vapor sorption during the condensation process. The local hysteresis (Hw) of soils with OM was higher than that of soils without OM for soils with OM contents above 3.4%. For aw < ∼0.75, the water vapor sorption hysteresis of soils with and without OM showed a significant correlation with cation exchange capacity (CEC), and the Hw values of soils with OM were lower than that of soils without OM for the same CEC. The OM can affect water vapor sorption and the associated hysteresis at low aw levels through adsorbed cations and organic functional groups, and at high aw levels through the structures of pores and OM.

Technical note: Lessons from and best practices for the deployment of the Soil Water Isotope Storage System

Abstract. Soil water isotope datasets are useful for understanding connections between the hydrosphere, atmosphere, biosphere, and geosphere. However, they have been underproduced because of the technical challenges associated with collecting those datasets. Here, we present the results of testing and automation of the Soil Water Isotope Storage System (SWISS). The unique innovation of the SWISS is that we are able to automatically collect water vapor from the critical zone at a regular time interval and then store that water vapor until it can be measured back in a laboratory setting. Through a series of quality assurance and quality control tests, we tested whether the SWISS is resistant to both atmospheric intrusion and leaking in both laboratory and field settings. We assessed the accuracy and precision of the SWISS through a series of experiments in which water vapor of known composition was introduced into the flasks, stored for 14 d, and then measured. From these experiments, after applying an offset correction to report our values relative to Vienna Standard Mean Ocean Water (VSMOW), we assess the precision of the SWISS to be ±0.9 ‰ and ±3.7 ‰ for δ18O and δ2H, respectively. We deployed three SWISS units at three different field sites to demonstrate that the SWISS stores water vapor reliably enough that we are able to differentiate dynamics both between the sites as well within a single soil column. Overall, we demonstrate that the SWISS retains the stable isotope composition of soil water vapor for long enough to allow researchers to address a wide range of ecohydrologic questions.

Effects of Bio-Organic Fertilizer on Soil Infiltration, Water Distribution, and Leaching Loss under Muddy Water Irrigation Conditions

This study analyzes the soil water infiltration characteristics under muddy water irrigation and bio-organic fertilizer conditions in the current context of muddy water irrigation rarely being used in agricultural production and in combination with the problems of water resource shortages and low soil fertility in arid and semi-arid regions. An indoor one-dimensional soil column infiltration device was used for studying the effects of four muddy water sediment concentration levels (ρ0: 0; ρ1: 4%; ρ2: 8%; ρ3: 12%) and four bio-organic fertilizer levels (FO0: 0; FO1: 2250 kg·hm−2; FO2: 4500 kg·hm−2; sFO3: 6750 kg·hm−2) on soil water infiltration, evaporation characteristics, and leaching loss. The results demonstrated that a higher muddy water sediment concentration and fertilization level resulted in a smaller wetting front distance and cumulative infiltration amount within the same time, but the infiltration reduction rate (η) gradually increased. The three infiltration models (Kostiakov, Philip, and Horton) were fitted, and it was discovered that all three had good fitting results (R2 > 0.8), with the Kostiakov model displaying the best fit and the Horton model exhibiting the worst fit. The cumulative evaporation amount and evaporation time in muddy water irrigation and fertilization conditions was consistent with the Black and Rose evaporation models (R2 > 0.9), the Black model was proved to be higher than the Rose model. In comparison to ρ0, muddy water irrigation increased conductivity and total dissolved solids (TDS) in the leaching solution, but it reduced cumulative evaporation, soil moisture content, the uniformity coefficient of soil water distribution, and leaching solution volume. Compared with FO0, the application of bio-organic fertilizer increased soil water content and reduced soil water evaporation while also reducing the leaching solution volume, conductivity, and TDS in the leaching solution. The results of this research can provide scientific reference for the efficient utilization of muddy water irrigation and the rational application of bio-organic fertilizer.

Effect and Application of Different Amendments on Salinized Soil Remediation

At present, China's saline-alkali soil area is very large. In the saline-alkali soil, the salinity will affect the growth of plants in the severe areas, so the plants cannot survive. How to maintain soil quality and prevent soil salt from being high has become an important research goal of soil improvement. Soil amendments can combine many small soil particles together to form large water stable aggregates. And it is widely used to prevent soil erosion, reduce soil water evaporation or excessive evaporation, save the amount of irrigation and promote the healthy growth of plants. This study through the use of homemade iron han ecological amendments, phosphogypsum, garden waste decay secondary materials, five materials mixed polyacrylamide and microbial amendments, combined with the water salt engineering comparison experiment, the whole experiment for three, respectively is composite amendments and water salt engineering comprehensive improvement measures (TG1, TG2), the traditional composite amendments (G 1, G 2) and tai tian shallow water conservancy salt project (T) single measures. In the above experiments, the best effects are TG 1 (comprehensive improvement measures of Tiehan ecological amendments) and TG 2 (comprehensive improvement measures of Heka amendments). Although the amount of reagent applied is different, the treatment effect is very good. The results show that different improvement measures significantly reduced the salt content and reduced the PH value of soil, and improved the soil nutrients. This measurement data provides a certain theoretical basis for the repair and study of salinized soil. It also shows that soil amendments have obvious guidance for the application of salinized soil.

Assessment of agricultural adaptations to climate change from a water-energy-food nexus perspective

Adapting agriculture to climate change without deteriorating natural resources (e.g., water and energy) is critical to sustainable development. In this paper, we first comprehensively evaluate six agricultural adaptations in response to climate change (2021–2050) through the lens of the water-energy-food (WEF) nexus in Saskatchewan, Canada, using a previously developed nexus model—WEF-Sask. The adaptations involve agronomic measures (early planting date, reducing soil evaporation, irrigation expansion), genetic improvement (cultivars with larger growing degree days (GDD) requirement), and combinations of individual adaptations. The results show that the selected adaptations compensate for crop yield losses (wheat, canola, pea), caused by climate change, to various extents. However, from a nexus perspective, there are mixed effects on water productivity (WP), total agricultural water (green and blue) use, energy consumption for irrigation, and hydropower generation. Individual adaptations such as early planting date and increased GDD requirement compensate for yield losses in both rainfed (0–60 %) and irrigated (18–100 %) conditions with extra use of green water (5–7 %), blue water (2–14 %), and energy for irrigation (2–14 %). Reducing soil water evaporation benefits the overall WEF nexus by compensating for rainfed yield losses (25–82 %) with less use of blue water and energy consumption for irrigation. The combination of the above three adaptations has the potential to sustain agricultural production in water-scarce regions. If irrigation expansion is also included, the combined adaptation almost fully offsets agricultural production losses from climate change but significantly increases blue water use (143–174 %) and energy consumption for irrigation while reducing hydropower production (3 %). This study provides an approach to comprehensively evaluating agricultural adaptation strategies, in response to climate change, and insights to inform decision-makers.

Long-term manure and cropping systems effect on soil water vapour sorption characteristics is controlled by soil texture

Increasing studies indicate that long-term experiments (LTEs) involving manure application and optimal cropping systems can significantly improve soil physicochemical properties, which may also affect the soil water retention curve (WRC) in the wet region (pF < 4.2). However, few studies have explored the effect of long-term manure application and cropping systems on soil WRC in the dry region (water vapour sorption isotherms, WSIs) (pF > 4.2) as well as the associated soil physicochemical properties. To overcome this knowledge gap, we investigated the effect of long-term manure application (24 to 177 years) and different cropping systems (71 to 82 years) on soil organic carbon (SOC) content, WSIs, hysteresis, and specific surface area (SSA). Soil samples were collected from five long-term manure experiments in Sweden, the United Kingdom, Spain, Germany, and Denmark, and two long-term cropping systems experiments in the United Kingdom. The five manure LTEs comprised three soil textures (silty clay, silt loam, and sandy loam) with one to four crops grown in the fields, including wheat, barley, maize, and grass/clover. The cropping system LTEs comprised silt loam and sandy loam including bare fallow (BF), arable rotation, ley–arable rotation, and permanent grass. Results showed that long-term manure application increased SOC content in each site, but it had little effect on the soil WSIs, hysteresis, and SSA in silty clay soils. The changes of soil WSIs, hysteresis, and SSA in silt loam and sandy loam arising from manure application largely depend on the crops grown in the field. For the long-term cropping systems experiments, permanent grass had the most significant effect in increasing SOC content, soil WSIs in silt loam and sandy loam, and hysteresis and SSA in silt loam compared to other treatments. Compared to BF, arable rotation and ley-arable rotation had no effect on SOC and soil WSIs in silt loam, and on hysteresis and SSA in silt loam and sandy loam. Multiple linear regression models including SOC, clay, and silt contents sufficiently explained the variabilities observed in the soil WSIs, hysteresis, and SSA for both manure and cropping systems LTEs.

Using hydrogen and oxygen stable isotopes to estimate soil water evaporation loss under continuous evaporation conditions

AbstractThe use of hydrogen and oxygen stable isotopes in estimating soil water evaporation loss under continuous evaporation conditions is crucial for gaining insight into soil water movement processes under different conditions. In this study, via high‐frequency meteorological monitoring and continuous soil water measurements, we investigated the variation of hydrogen and oxygen stable isotopes and soil water fluxes with soil depth and time for soil water at different depths under continuous evaporation conditions. The precipitation isotope δrain and soil water flux changes were determined using the Craig‐Gordon model. It was shown that the isotopic fractionation of soil water in the surface layer 0–30 cm was dominated by a gaseous‐dominated transport process, and that both the δ18O and δD values and evaporative intensity decreased with increasing soil depth. In terms of time dynamics, the evaporation loss of soil water varies continuously with seasons and is the highest during summer. The use of δ18O to quantify the soil water evaporation loss provides greater accuracy than that provided by δD. The relative errors in the evaporation loss calculated based on δ18O and δD were 13% and 34%, respectively. A sensitivity analysis of each parameter indicated that the relative error calculated by the model is primarily determined by temperature and relative humidity uncertainty. The sensitivity analysis reveals the critical evaporation intensity of soil water at various depths from unsteady to steady state evaporation. When the relative humidity changes by 1%, the evaporation loss fraction changes from 0.001 to 0.034. The results of this study are important for quantifying the soil water resources in arid and semi‐arid areas without precipitation using stable isotopes of hydrogen and oxygen.

Technical feasibility of using a geotextile waste material as an alternative to agrofilm for mulching in lettuce

ABSTRACT In semiarid regions, water deficit can be a problem affecting agricultural production. Agrofilm mulches can be used to reduce soil water evaporation as well as to control weeds. The SoilTain DW® geotextile blanket, which is a solid waste material generated in water treatment plants, has the potential to be used for mulching in agriculture. The aim of this study was to evaluate the technical feasibility of using this geotextile waste material as an alternative to different agrofilms for mulching in lettuce under the semiarid conditions of the state of Alagoas, Brazil. Four experiments were carried out in 2020–2021, each with four mulching treatments (white and black polyethylene, geotextile blanket, uncovered soil). Soil surface temperature, plant density, weeds and biometric parameters of the lettuce were assessed and evaluated by univariate and multivariate statistical analyses. Significant treatments × experimental period interactions for all lettuce parameters were observed, except for root biomass. Experiment 2 (winter) presented the most favourable environmental conditions for plant development (mild temperatures) and resulted in an average yield of 25.0 Mg ha−1. In Experiment 1 (autumn/winter), high temperatures (47.9°C) under the black polyethylene reduced plant density (96,800 plants ha−1), though leaf length (16.2 cm) and yield (13.1 Mg ha−1) were not significantly affected. The two canonical variables explained 97.7% of the total variation, forming three similarity groups by Tocher method. All mulches effectively controlled the weeds. Application of the geotextile blanket was concluded to be technically feasible, but it was not recommended for use in the summer when temperatures are high.

Determination of dry soil layer and its soil heat flux distribution using actively heated distributed temperature sensing

A dry soil layer (DSL) of certain thickness is usually formed on the sandy soil surface during the soil water evaporation process, with the bottom boundary of DSL corresponding to the evaporating surface. As the water transfer mechanism in the DSL is different from that beneath the DSL, in the numerical analysis, it is essential to know such DSL in particular in terms of initial conditions. Moreover, the change in water transfer mechanism further leads to the change in energy transfer mechanism in the DSL, rendering the whole soil drying process more complex. To master the DSL distribution and its accompanying energy changes, a new method for determining the DSL and its soil heat flux (G) distribution based on the actively heated distributed temperature sensing (AH-DTS) technology is proposed. Through in-situ tests on the Loess Plateau in Yan'an, China, the DSL thickness and the G profiles in sandy soil are determined successfully. The results show that there is a DSL with a thickness of 0.25 m in the test site. The G in the DSL fluctuates with depth, and its value is significantly higher than that of the soil below the DSL, indicating that the G in the DSL provides energy for water evaporation at the evaporating surface. Note that the AH-DTS technology can realize multi-parameter measurement at the same time with high-resolution, which is effective and reliable for determining the DSL thickness and the G distribution. In practical applications, it is recommended that the DSL thickness be determined according to both soil temperature (T0) profile and volumetric water content (θ) profile. Moreover, it is suggested that a reasonable heating time-interval of at least two hours and the close contact between the AH-DTS sensor and the surrounding soil be guaranteed to ensure the accuracy of G profile determination.

Parameterization of soil evaporation and coupled transport of moisture and heat for arid and semiarid regions

Soil moisture is an important parameter in numerical weather forecasting and climate projection studies, and it is extremely important for arid and semiarid areas. Different from those in relatively wet areas, for arid and semiarid areas, mechanisms associated with the transportation, condensation, and evaporation of water vapor in soil interior cannot be neglected. In this paper, schemes associated with soil evaporation and coupled transport of soil moisture and heat were developed for the integrated urban land model (IUM) to improve the simulation of soil moisture in arid and semiarid areas. The whole layer soil evaporation (WSE) scheme was developed to improve the simulation of soil evaporation. The soil’s inner layer water vapor transport is considered a part of WSE. The transport of water and heat in the inner soil was linked to the phase change of water. The NASA Soil Moisture Active Passive (SMAP) mission Level-4 Soil Moisture product and 10-cm volumetric soil moisture observations in 358 autonomic soil moisture observation sites were used for validating the simulation results. The results indicate that after using the WSE scheme and considering the coupled transport of moisture and heat in the soil interior, the simulation of soil moisture was improved definitely. For June, July, and August, the biases of soil moisture simulation decreased by approximately 22.5, 34.4, and 27.5%, respectively, while the RMSEs decrease by approximately 7.0, 8.7, and 9.6%, respectively. The improvement of soil moisture simulation indicates that in arid and semiarid areas soil water vapor transport is important and cannot be neglected.

The Presence of the Biochar Interlayer Effectively Inhibits Soil Water Evaporation and Salt Migration to the Soil Surface

To reveal the mechanisms of water conservation and soil salinity control in the biochar interlayer, the effects of biochar addition as an interlayer on soil water infiltration, evaporation, and salt transport were studied. Through the indoor soil-column simulation test, soil columns were set up by packing homogeneous soil (CK) and biochar spacers into columns at different burial depths of 10, 20, and 30 cm. The biochar interlayer decreased the infiltration capacity of the soil, with the average infiltration rate decreasing from 0.72 cm·h−1 to the ranges of 0.39–0.48 cm·h−1 in the CK soil column, and salt leaching efficiency was improved. The salt content in the bottom layer of soil in the CK column was reduced to within the range of 19.96–47.46% compared with that in the barrier soil column. The presence of the biochar interlayer improved the distribution of soil water and salt. The soil water content in the upper layer above the interlayer was around 7.79–13.68% higher than that in CK, whereas the average salt content was 6.44–60.40% lower than that in CK. The biochar interlayer inhibited soil water evaporation, and cumulative evaporation in this layer decreased by 32.34–42.10% compared with that in CK. The salt accumulation in the interlayer in the soil column decreased within the range of 16.36–51.36% compared with that in the CK soil column. The biochar interlayer could not only retain water for a long time, but also adsorb the salt leached from the upper layer, and thus, inhibit the reverse salt flux from the lower layer. The creation of the biochar interlayer of 30 cm could play a role in soil salinity control and water conservation, and can also provide a basis and reference for the improvement of saline-alkali farmland in arid and semi-arid areas.

Use of microlysimeters to determine soil water evaporation as a function of drainage

The aim of this study was to test two models and two sizes of microlysimeters to determine soil water evaporation as a function of the removal of water by drainage at the bottom of the units. The experiment was conducted at the experimental field of the State University of Mato Grosso (UNEMAT) in Tangará da Serra, Mato Grosso, Brazil. Soil water evaporation was determined using microlysimeters constructed from rigid PVC tubes, of which two models and two sizes were tested. The four microlysimeter treatments were: 100 mm diameter without drainage (ML100WD), 100 mm diameter with drainage (ML100D), 150 mm diameter without drainage (ML150WD), and 150 mm diameter with drainage (ML150D). The microlysimeters were fitted to an irrigation blade of 60 mm and compared to applications with four irrigation blade sizes (15, 30, 45, and 60 mm). Water evaporation from the soil was obtained from the mass variation of the microlysimeters, and was then compared to the soil water evaporation determined using weighing lysimeters. The obtained data were analyzed using descriptive statistical techniques, tests of means, and regression analysis. The soil water evaporation values present significant differences between the two microlysimeter sizes (100 and 150 mm diameter) and the two models (with and without water drainage). Soil water evaporation is affected by the water drainage that occurs at the bottom of the microlysimeters. There was no difference in soil water evaporation between irrigation rates within the same microlysimeter size and model. The two models and the two microlysimeter sizes tested can be used for the quantification of soil water evaporation, due to the high determination coefficients observed when compared to the evaporation observed with the weighing lysimeters.

ET Partitioning Assessment Using the TSEB Model and sUAS Information across California Central Valley Vineyards

Evapotranspiration (ET) is a crucial part of commercial grapevine production in California, and the partitioning of this quantity allows the separate assessment of soil and vine water and energy fluxes. This partitioning has an important role in agriculture since it is related to grapevine stress, yield quality, irrigation efficiency, and growth. Satellite remote sensing-based methods provide an opportunity for ET partitioning at a subfield scale. However, medium-resolution satellite imagery from platforms such as Landsat is often insufficient for precision agricultural management at the plant scale. Small, unmanned aerial systems (sUAS) such as the AggieAir platform from Utah State University enable ET estimation and its partitioning over vineyards via the two-source energy balance (TSEB) model. This study explores the assessment of ET and ET partitioning (i.e., soil water evaporation and plant transpiration), considering three different resistance models using ground-based information and aerial high-resolution imagery from the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX). We developed a new method for temperature partitioning that incorporated a quantile technique separation (QTS) and high-resolution sUAS information. This new method, coupled with the TSEB model (called TSEB-2TQ), improved sensible heat flux (H) estimation, regarding the bias, with around 61% and 35% compared with the H from the TSEB-PT and TSEB-2T, respectively. Comparisons among ET partitioning estimates from three different methods (Modified Relaxed Eddy Accumulation—MREA; Flux Variance Similarity—FVS; and Conditional Eddy Covariance—CEC) based on EC flux tower data show that the transpiration estimates obtained from the FVS method are statistically different from the estimates from the MREA and the CEC methods, but the transpiration from the MREA and CEC methods are statistically the same. By using the transpiration from the CEC method to compare with the transpiration modeled by different TSEB models, the TSEB-2TQ shows better agreement with the transpiration obtained via the CEC method. Additionally, the transpiration estimation from TSEB-2TQ coupled with different resistance models resulted in insignificant differences. This comparison is one of the first for evaluating ET partitioning estimation from sUAS imagery based on eddy covariance-based partitioning methods.

Variations in water sources used by winter wheat across distinct rainfall years in the North China Plain

Quantifying water availability in different soil layers to crop root water uptake (RWU) in different rainfall years helps deliver strategies to combat water scarcity and improve water productivity. To investigate the responses of RWU to soil water availability across distinct rainfall years, a field experiment of winter wheat was conducted in 2017–2018 (wet year), 2018–2019 (dry year), and 2019–2020 (ordinary year) in the North China Plain. Stable isotopes (δ18O and δD) in precipitation, irrigation water, xylem water, and soil water, as well as soil water content (SWC), were investigated during the three wheat growth seasons and were used to determine the soil water evaporation line (SWEL: the linear relationship between δD and δ18O in soil water), the line-conditioned excess (lc-excess: the deviation between δD and the local meteoric water line in the dual-isotope space) and the proportion of RWU from different soil layers with the MixSIAR model. The results indicated that there were significant differences in δ18O and δD in soil water and xylem water across different rainfall years. The slopes of SWEL and lc-excess of the 0–100 cm soil layer in the dry year were significantly smaller than those in the ordinary and wet years, which suggests that more substantial soil evaporation occurred in the dry year. The MixSIAR results revealed that the three-year wheat RWU exhibited different patterns, which were related to soil water availability. Wheat mainly utilized soil water from the 0–20 cm and 20–60 cm layers during the greening to filling stage under the dry year, while it mainly utilized the 0–20 cm soil layer under the wet and ordinary years. However, at the harvest stage, wheat under all precipitation years could transfer its main RWU zone to the 20–60 cm soil layer. There were significantly different proportions of RWU from 0 to 60 cm under different rainfall years, shown as 75.3 %, 67.5 %, and 69.5 % in the wet year, dry year, and ordinary year, respectively. These findings indicated that the appropriate irrigation wetting depth should be set as<60 cm for all kinds of rainfall years.

Considering spatio-temporal dynamics of soil water with evapotranspiration partitioning helps to clarify water utilization characteristics of summer maize under deficit irrigation

Continuously increasing the utilization efficiency of agricultural water resources is vital to ensuring future water and food security. Deficit irrigation (DI) could provide a solution to optimize crop water productivity. Research on the spatio-temporal dynamics of soil water coupled with evapotranspiration partitioning is important for clarifying summer maize (Zea mays L.) water utilization characteristics and crop water productivity under different DI strategies, especially in semi-arid regions. Consequently, a three-year field experiment with full irrigation (CK) and eight DI treatments (T1–T8, comprised of combinations of 100 %, 80 %, and 60 % of crop evapotranspiration) was conducted. Data from large-scale weighing lysimeters, micro-lysimeters, and TDR sensors were combined to assess daily root water absorption at different soil depths, actual evapotranspiration (ETa) partitioning into plant transpiration (T) and soil water evaporation (E), and water use efficiency (WUE). Results showed that soil water consumption mainly occurred in the 0–40 cm, 0–60 cm, and 0–80 cm soil layers during the maize growth stages of planting–V6, V6–V12, and V12–R6, respectively. Water absorption above the 60-cm soil depth accounted for more than 92 % of the total water consumption. The appropriate irrigation wetting depth for summer maize could be controlled in the top 80-cm layer to avoid deep percolation. DI affected soil water distribution and availability, and thus decreased soil water consumption rate (WCR) and root water absorption amount. Under moderate water deficit conditions, WCR was rapidly restored to the non-water-stressed irrigation treatment level, and even exceeded that level in the deeper layers after a subsequent irrigation was applied, especially in the early maize growth stages. E/ETa was 31.0–32.5 % under full irrigation. DI decreased total soil water evaporation amount, but increased the E/ETa ratio. The threshold soil water value for defining when maize was subjected to water stress was 22.0 % (72 % of FC) during V3–V12, and 18.0 % (60 % of FC) during V12–R1. Our results suggest that less water was used in T1 (moderate DI) than with the full irrigation treatment. WUE increased by 5.5 %–7.5 % as irrigation amount decreased by 12.3–14.5 % and yield decreased by 3.3 %–8.0 %. These results improve our understanding of maize water consumption characteristics with regard to soil water absorption in different soil layers and evapotranspiration partitioning, and provide implications for efficient water management in arid areas of northwest China.

Effect of Organic Mulch and Water Supply on Yield and Profitability in Black Nightshade (Solanum Scabrum Mill.) in West Cameroon

Water shortage and increased soil water evaporation are among challenges facing farmers in tropical regions subjected to prevailing climate change. Combinations of agricultural practices expected to improve yields of cultivated crops such as mulching has been described as a method to improve soil water storage and yields of cultivated crops including black nightshade. Unfortunately, up to date, few research works have addressed the yields and profitability of black nightshade. Combinations of rate of water, frequency of irrigation, mulch rate were tested during the 2021 and 2022 off-seasons for large-scale and cost-effective production of black nightshade, a staple food crop. A total of 18 triptych combinations of three irrigation volumes (Vn), three irrigation frequencies (Fn) and two mulch rates (Mn) were tested. Results showed that the best 5 yielding combinations (mean: 42.08 t/ha) represented 124% of the trial mean (33.80 t/ha) independently of the cropping year. However, combination V1F3M10 i.e. applying an average of 5.8 mm/day of water every 3 days on 10 t/ha-mulch plots led to the highest yield (47.16 t/ha) and profit (304.60%). Therefore, the combination V1F3M10 should be adopted for off-season production of black nightshade on Oxisol from West-Cameroon. Soil mulching at 10 t/ha promoted water saving by 402.3 mm and probably reduced soil water evaporation, weeds control, and improved water use efficiency.

Analytic model for calculation of soil temperature and heat balance of bare soil surface in solar greenhouse

This study establishes a soil temperature model of a solar greenhouse, which takes into account the soil water evaporation, solar radiation, thermal radiation and convective heat transfer on the soil surface. The model is utilized to obtain the mathematical function of soil temperature distribution according to solar radiation and air temperature in a solar greenhouse. The model is validated in two greenhouses with and without plants. Based on the model, the heat gain and loss of solar greenhouse soil are calculated. The results show that the heat accumulated by the greenhouse soil is mainly by absorbing solar radiation during the day and the heat lost by the greenhouse soil is mainly by water evaporation during the day and thermal radiation at night. Then, according to the small convective heat transfer between soil and air in the solar greenhouse, the solar-air temperature calculation equation is simplified, so that the simplified model can predict the soil temperature based on solar radiation and outdoor air temperature, which provides an important soil boundary condition for the solar greenhouse thermal model and CFD prediction. Finally, the evaporation coefficient is proposed to characterize the effect of water evaporation intensity on the soil temperature in a solar greenhouse. In this case, the average soil temperature increases by about 2℃ for every 0.1 decrease in evaporation coefficient.