Soil Surface Evaporation Research Articles

Water evaporation reduction by the agrivoltaic systems development

The triple benefits of the AgriVoltaic Systems Development (AVSD) have been well demonstrated, not only for the PV electricity generation but also for reduced water evaporation, enhancing further the benefits of simultaneously crop growth on the same land area. However, the reduction rate of the water evaporation of AVSD has not been investigated in a quantitative way. Therefore, this study conducted experiments to measure water evaporation reduction under the Concentrated-lighting Agrivoltaic System (CAS) and the Even-lighting Agrivoltaic System (EAS). Evaporation containers and pans were placed in the bare soil (CK) under the CAS and the EAS. Our results showed a significant reduction in water evaporation under CAS and EAS. Cumulative soil surface evaporation of CK, CAS, and EAS for 45 days was 80.53 mm, 63.38 mm, and 54.14 mm. The cumulative water evaporation from soil and pan surfaces decreased by 21 % and 14 % (under CAS), 33 %, and 19 % (under EAS), respectively. The slope β1 ≠ 0 of simple linear regression showed a significant positive relationship between evaporation time and cumulative water evaporation. The correlation coefficient in all treatments was more than 0.91, suggesting a robust linear relationship. The feasibility of AVSD could significantly reduce irrigation water, enhance crop growth, and generate electricity simultaneously on the same agricultural land.

Effects of water allocation process on greenhouse gas emissions in drip-irrigated apple orchards on the Loess Plateau, China

Apple tree (Malus pumila Mill.) is a perennial and deciduous tree with large water demand in the growth period. Drip irrigation, as a mature and high-efficiency water-saving irrigation technology, has been widely used in apples, grapes and other economic crops around the world, achieving huge economic benefits. However, studies addressing the effects of drip irrigation on soil greenhouse gas emissions from apple orchards on the Loess Plateau in China are limited, and little is known about the potential drivers of the global warming potential based on the water allocation processes in apple orchards under drip irrigation technology. Hence, the goal of this study was to evaluate the impact of water allocation processes on soil greenhouse gas emissions and potential drivers of the global warming potential in apple orchards based on different irrigation water treatments under drip irrigation technology for a two-year consecutive field experiment in 2019 and 2020. The results showed that soil water-filled pore space, daily mean soil surface evaporation and plant transpiration were all significantly increased by drip irrigation. The peaks of carbon dioxide and nitrous oxide fluxes showed a lagged effect, with fluxes proportional to irrigation amount (with emissions occurring throughout the growth period) while methane fluxes were consumptive. Overall, using higher drip irrigation water in apple orchards increased the growth-period mean emissions of carbon dioxide and nitrous oxide and decreased the growth-period mean uptake of methane. Therefore, optimization of drip irrigation water is needed in practice to mitigate greenhouse gas emissions from apple orchard production. Furthermore, the global warming potential was directly driven by soil water-filled pore space, soil surface evaporation, plant transpiration and indirectly driven by rainfall and drip irrigation. The different water allocation processes were closely linked and interacted with each other, thereby affecting the global warming potential directly or indirectly.

Water Evaporation Reduction Using Sunlight Splitting Technology

The imbalance between precipitation and water evaporation has caused crop yield reduction, drought, and desertification. Furthermore, most parts of the world are short of water, including China. We proposed a low-cost polymer multilayer film to reduce water evaporation by only passing through several sunlight wavelengths necessary for photosynthesis. A series of experiments were conducted to characterize the influence of partial sunlight on the reduction of water evaporation. Evaporation containers and evaporation pans were placed in open-air (CK), under a glass shed (GS), and under a glass-shed covered with multilayer films (GMF). Our results showed a significant reduction in water evaporation under GMF. Cumulative soil surface evaporation of CK, GS and GMF over 45 days was 80.53 mm, 68.12 mm, and 56.79 mm, respectively. Under GMF, cumulative water evaporation from soil and pan surfaces decreased by 29% and 26%. The slope (β1≠0) of simple linear regression showed a significant relationship between evaporation time and cumulative water evaporation (p = 0.000 < α = 0.05 shown in the ANOVA table). The correlation coefficient was more than 0.91 in all treatments, suggesting a strong positive linear relationship. This study may contribute to future drought resistance and agrivoltaic sustainability development.

Mulch Application and Plant Spacing Influence on Growth Traits, Pests, Insects and Weeds in Cotton (Gossypium hirsutum L.) Varieties

Mulch Application and Plant Spacing Influence on Growth Traits, Pests, Insects and Weeds in Cotton (Gossypium hirsutum L.) Varieties

Agro-physiological responses of Tepary bean to planting patterns and plant densities

Planting pattern and plant density are efficient management tools for maximizing crop yield by reducing soil surface evaporation and optimizing resource utilization such as light, nutrients, and water. A two-year (2017-18) field trial was conducted to determine the effects of plant density and planting pattern on some agro-physiological and biochemical traits of Tepary bean (Phaseolus acutifolius L.) at the Research Station of Islamic Azad University, Arak Branch, Iran. The experiment was performed as a split-plot arranged in a randomized complete block design with three replications. The treatments were two planting patterns (one-row and two-row plantations) and three plant densities (30, 40, and 50 plants per m2). The results showed that that one-row planting pattern and 40 plants per m2 improved seed yield by 75% and 65% compared to 30 and 50 plants per m2 in one-row planting pattern in the second year, respectively. The plant chlorophyll content increased by 20% with two-row plantation and medium plant density compared to high and low plant density in the first year. The highest accumulation of seed carbohydrates (38.26 mg. g-1 FW) was obtained with two-row cultivation and medium plant density in the second year. The relative seed water content significantly decreased with one-row plantation and low plant density compared to a two-row plantation and medium plant density. The least malondialdehyde and proline aggregation (3.2 and 225 µ mol. g-1 FW, respectively) was achieved with two-row plantation and medium plant density. Finally, a two-row planting pattern with medium-density cultivation is recommended to obtain optimal Tepary bean seed yield in the region.

Soil Surface Evaporation Control by Plant-based Mulching during the Energy Limiting and Falling Rate Evaporation Stages

Huge quantities of plant by-products and plant wastes generated are stressing to assess their re-usability, probably as mulching, in conserving soil moisture. Magnitude and timing of evaporation reduction by mulching is vital in scheduling irrigation, particularly in dry areas. This study experimentally investigated the effects of six different plant based mulch treatments [coconut coir dust, coconut husk chips, Gliricidia leaves (Gliricidia Sepium), paddy straw, rice husk and saw dust] on controlling soil surface evaporation in sandy loam soil during the two stages of evaporation (energy limiting and falling rate) and degree of dependence of the soil surface evaporation on weather parameters. During the energy limiting evaporation stage, in comparison to the bare soil, all the mulch treatments exhibited the greatest differences in the soil surface evaporation rates (ANOVA, p 0.05) during the falling rate evaporation stage, proved as the least effective mulch in providing prolonged evaporation restriction. Evaporation in saw dust mulched soil was highly dependent on temperature (p<0.01) and relative humidity (p<0.01) during the energy limiting stage.

ESTIMATION OF WATER BALANCE UNDER THE CONDITIONS OF CROPS GROWING ON DRY PEAT SOILS OF POLISSІA ZONE

The paper presents the data concerning the researches which point out to the fact that the soil water flow plays an important role in the natural conditions biological complex as well as in the amelioration practice. The intensity of the soil water-intake process has been characterized by its variability and depends on the porousness, mechanical, mineral, chemical composition as well as on itscultivation, soil spaces, cracks, moles, roots and other openings. The water balance of meliorated soils includes some components such as the precipitation, surface and subsurface waters, which comes from he nearest headers, infiltrated rivers and storages lakes waters as well as from condensed waters, transpiration, soil and water surface evaporation in particular. The research of the matter needs the detail scientific substantiation under the conditions of different crops growing on dry soils of Polissya zone. The water balance of cropsgrowing on dry peat soils during the vegetation period for the layer of 0-50 cm has been investigated. The calculations showed that the process of water supply optimization on dry peat soils had an essential effect on its yielding level, herewith the crops efficiency under the regulated and controlled soils water levels increased greatly. Natural LSW comprise to special years as well as to theperiods of plant vegetation. In this case, the methods of moisture intensive management and modelling usage, can supply plant biological necessity under the efficient and qualitative yielding formation. The optimal moisture under the layer of 0-50 cm on dry peat soils during the period of yield forming for the perennial grasses and vetch-oat mixtures made up 77-89%. It has become possible to achieve the highest efficiency of crops green mass due to a givenmoisture parameters.

Evapotranspiration Characteristics Distinct to Mangrove Ecosystems Are Revealed by Multiple‐Site Observations and a Modified Two‐Source Model

AbstractA quantitative accounting of how mangrove ecosystems respond to tidal perturbations is needed to anticipate changes in these ecosystems when sea level rises. Here we use long‐term field observations and a two‐source ecohydrological model to reveal specialized characteristics of evapotranspiration (ET), soil surface evaporation (E), and canopy transpiration (T) in three subtropical mangrove ecosystems in southeastern China. Average wintertime ET observed in these three mangrove forests (2.6 mm day–1) was consistent with values for semiarid ecosystems, while average summertime ET (6.2 mm day–1) approached that observed in rainforests. By contrast, T fluxes were small year‐round, averaging 1.3 mm day–1 in winter and 2.5 mm day–1 in summer. Combining our results with measurements from three Florida mangroves, observed values of T ranged from 350 to 870 mm year−1, varying primarily with salinity, while T/ET increased exponentially from 30% to 70% with rising leaf area index. Simulations of half‐hourly ET and T using a modified two‐source model were highly correlated with eddy covariance observations of ET (I, index of agreement &gt;0.93 at all three sites) and sap flow gauge‐based estimates of T (I = 0.93 at the Yunxiao site). Variations of T in mangrove ecosystems are distinguished from those in terrestrial forests mainly by the sensitivity of stomatal conductance to leaf temperature, with tidal and salinity effects superimposed. Our modified model accounts for these effects and therefore holds promise for improving our understanding of how mangrove ecosystems may respond to changing stress conditions under global warming and sea level rise.

Fixed and variable components of evapotranspiration in a Mediterranean wild-olive - grass landscape mosaic

Dry regions are typically characterized by heterogeneous ecosystems where trees are competing with the surrounding grasses for limited amount of water. In these regions, evapotranspiration (ET) is the leading loss term in the soil water budget, and its estimate, and the dynamic contribution of each ET component (i.e. tree and grass transpiration, and dry bare soil and wet surface evaporation), are still poorly quantified. In a typical heterogeneous Mediterranean ecosystem in Sardinia, we combined eddy-covariance estimates of ET with sap flux and energy balance estimates of wild-olive tree transpiration, a common tree species of the region, and with modeled evapotranspiration from the seasonal grass. Trees located in the southern edge of clumps, thus receiving more radiation, transpired more and showed a greater sensitivity to increasing vapor pressure deficit and soil moisture than trees located in clump centers or northern edges. Transpiration of the tree clumps in the footprint (Et), summed up with the modeled evapotranspiration components of the surrounding grass (mostly transpiration during the wet season and evaporation during the dry season), matched latent heat flux measurements, lending confidence in the estimates. Proper accounting for heterogeneity of sources within the eddy covariance footprint seems to have overcome potential errors from not preserving an important assumption of the method, the land-surface homogeneity, highlighting the methods reliability in such inhomogeneous ecosystem. Compared to ET, Et of wild olives was nearly constant over the hydrologic year, insensitive to variation in soil moisture and atmospheric conditions. In contrast, under favorable spring environmental conditions (radiation, vapor pressure deficit, and soil moisture), the pasture leaf area transpires at high rates, contributing to, and dominating the high ET during that season. Conversely, in dry periods, when evapotranspiration from the grass cover is dominated by low evaporation from the, principally, bare soil, Et dominants ecosystem ET.

Evaporation and Soil Surface Resistance of the Water Storage Pit Irrigation Trees in the Loess Plateau

As an important step for formulating a water-saving agricultural strategy, it is essential to make quantitative calculations for orchard soil evaporation and confirm its inner mechanism, so as to reduce ineffective water consumption and improve the utilization efficiency of water resources. To reveal the effect of water storage pits under water storage pit irrigation conditions in orchard soil evaporation, micro-lysimeters were used to measure the soil evaporation in two different forms (soil surface evaporation and pit wall evaporation) under diverse irrigation systems using water storage pit irrigation in the apple growth period of 2018. To calculate the orchard soil evaporation of water storage pit irrigation, the pit irrigation coefficient was introduced and a model was constructed. To illustrate the inner mechanism of orchard soil evaporation, the soil surface resistance under water storage pit irrigation conditions was analyzed and calculated quantitatively. The results show that: (1) introducing the pit irrigation coefficient can boost the calculation precision of the orchard soil evaporation under water storage pit irrigation conditions; (2) when applying the soil evaporation of the water storage pit irrigation model for calculation of the orchard soil evaporation, R 2 can reach 0.92; and (3) the mechanisms of the two orchard soil evaporation forms under water storage pit irrigation are very different. When soil surface evaporation and pit wall evaporation were calculated by the soil surface resistance of water storage pit irrigation model, R 2 values were 0.95 and 0.96, respectively.

Spectral Mixture Analysis as a Unified Framework for the Remote Sensing of Evapotranspiration

This study illustrates a unified, physically-based framework for mapping landscape parameters of evapotranspiration (ET) using spectral mixture analysis (SMA). The framework integrates two widely used approaches by relating radiometric surface temperature to subpixel fractions of substrate (S), vegetation (V), and dark (D) spectral endmembers (EMs). Spatial and temporal variations in these spectral endmember fractions reflect process-driven variations in soil moisture, vegetation phenology, and illumination. Using all available Landsat 8 scenes from the peak growing season in the agriculturally diverse Sacramento Valley of northern California, we characterize the spatiotemporal relationships between each of the S, V, D land cover fractions and apparent brightness temperature (T) using bivariate distributions in the ET parameter spaces. The dark fraction scales inversely with shortwave broadband albedo (ρ &lt; −0.98), and show a multilinear relationship to T. Substrate fraction estimates show a consistent (ρ ≈ 0.7 to 0.9) linear relationship to T. The vegetation fraction showed the expected triangular relationship to T. However, the bivariate distribution of V and T shows more distinct clustering than the distributions of Normalized Difference Vegetation Index (NDVI)-based proxies and T. Following the Triangle Method, the V fraction is used with T to compute the spatial maps of the ET fraction (EF; the ratio of the actual total ET to the net radiation) and moisture availability (Mo; the ratio of the actual soil surface evaporation to potential ET at the soil surface). EF and Mo estimates derived from the V fraction distinguish among rice growth stages, and between rice and non-rice agriculture, more clearly than those derived from transformed NDVI proxies. Met station-based reference ET &amp; soil temperatures also track vegetation fraction-based estimates of EF &amp; Mo more closely than do NDVI-based estimates of EF &amp; Mo. The proposed approach using S, V, D land cover fractions in conjunction with T (SVD+T) provides a physically-based conceptual framework that unifies two widely-used approaches by simultaneously mapping the effects of albedo and vegetation abundance on the surface temperature field. The additional information provided by the third (Substrate) fraction suggests a potential avenue for ET model improvement by providing an explicit observational constraint on the exposed soil fraction and its moisture-modulated brightness. The structures of the T, EF &amp; Mo vs SVD feature spaces are complementary and that can be interpreted in the context of physical variables that scale linearly and that can be represented directly in process models. Using the structure of the feature spaces to represent the spatiotemporal trajectory of crop phenology is possible in agricultural settings, because variations in the timing of planting and irrigation result in continuous trajectories in the physical parameter spaces that are represented by the feature spaces. The linear scaling properties of the SMA fraction estimates from meter to kilometer scales also facilitate the vicarious validation of ET estimates using multiple resolutions of imagery.

Effects of Organic Mulch Materials on Soil Surface Evaporation

The effects of organic mulching material on soil surface evaporation were studied in Abia State. The objective of the study was to compare impact of mulch materials on saturated hydraulic conductivity and surface evaporation. The organic mulch materials were composted and non-composted Calapogonuim, Chromolena and Panicum spp. The design was randomized complete block design (RCBD). Data generated were statistically analysed. Analysis of variance was used to compare the influence of mulch materials on the measured soil properties and significant means were separated using least significant differences at 5% level of probability. Line graph was used to represent the impact of mulch materials on the surface evaporation. Results showed that saturated hydraulic conductivity of the soils increased significantly (P ≤ 0.05) with the application of the mulch materials. Soil applied with non-composted Chromolena spp. mulch material had the highest saturated hydraulic conductivity (73.00 cm hr-1). Soil surface evaporation varied with both composted and non-composted mulch materials at 3rd and 9th day. The volume of soil moisture lost to the atmosphere was lower in non-composted Calapogonuim mulch material compared with the other mulch materials under study (3rd to 9th day, 3.9 to 11.0 cm3 respectively). Composted and non-composted Panicum mulch was observed to be a more efficient physical barrier to prevent the loss of moisture to the atmosphere as compared to other mulch materials studied. From the present study, it was evident that application of mulch reduced the actual evaporation rates in the initial days after irrigation (coinciding with early periods of plant growth). The water was thus conserved and could be used by the crop subsequently during the later period of its growth.

Shallow groundwater effects on evaporation and soil temperature in two windblown sands (Eutric Cambisol and Chromic Luvisol) in South Africa

The aim of this study was to investigate the effect of shallow groundwater tables on soil surface evaporation and its effect on temperature distribution on two aeolian soils in South Africa, Clovelly (Eutric Cambisol) and Hutton (Chromic Luvisol) soil forms. The study was conducted at a lysimeter under semi-arid climatic conditions. A constant groundwater tables were created at different depths (0 mm, 500 mm, 1000 mm, 1500 mm and a No WT (no water table treatment as a control) and each of the lysimeters were equipped with a 1200 mm long DFM soil moisture probe to measure the profile water content and soil temperature at 6 depths along the profile (every 200 mm depth). The research site was also equipped with a movable shelter to prevent rain water dilution during rainfall events. Finally, evaporation is calculated by the water balance approach. The ANOVA showed that there was a highly significant difference (P < .01) in rate of evaporation from the water table depths and soil types. The minimum and maximum evaporation were recorded in the deepest and shallowest water table depths. The diurnal soil water content shows that the maximum water content in the two soil profiles was recorded in the early morning times (6:00) and the minimum was in the late afternoon times (between 16:00–17:00). The diurnal variation of soil water content also increased with decreasing water table depth. Regarding the soil temperature, the ANOVA showed that the soil temperature was influenced by the interaction between water table and measurement depths. Hence, the top five minimum soil temperatures were recorded in the shallower (≤500 mm) water tables and the top 5 maximums were recorded in the deeper water table depths (1000, 1500 and No WT). Generally, as the groundwater table depth increased from the surface down the profile, the rate of evaporation decreased resulting an increase in the variation of temperature with in the diurnal cycle.

Estimation of bare soil evaporation for different depths of water table in the wind-blown sand area of the Ordos Basin, China

Soil surface evaporation is a significant component of the hydrological cycle, occurring at the interface between the atmosphere and vadose zone, but it is affected by factors such as groundwater level, soil properties, solar radiation and others. In order to understand the soil evaporation characteristics in arid regions, a field experiment was conducted in the Ordos Basin, central China, and high accuracy sensors of soil moisture, moisture potential and temperature were installed in three field soil profiles with water-table depths (WTDs) of about 0.4, 1.4 and 2.2 m. Soil-surface-evaporation values were estimated by observed data combined with Darcy’s law. Results showed that: (1) soil-surface-evaporation rate is linked to moisture content and it is also affected by air temperature. When there is sufficient moisture in the soil profile, soil evaporation increases with rising air temperature. For a WTD larger than the height of capillary rise, the soil evaporation is related to soil moisture content, and when air temperature is above 25 °C, the soil moisture content reduces quickly and the evaporation rate lowers; (2) phreatic water contributes to soil surface evaporation under conditions in which the WTD is within the capillary fringe. This indicates that phreatic water would not participate in soil evaporation for a WTD larger than the height of capillary rise. This finding developed further the understanding of phreatic evaporation, and this study provides valuable information on recognized soil evaporation processes in the arid environment.

Time and amount of supplemental irrigation at different distances from tree trunks influence on soil water distribution, evaporation and evapotranspiration in rainfed fig orchards

This study was carried out in Estahban, Iran, during 2013 and 2014 to identify the optimal time and amount of supplemental irrigation at different distances from tree trunks on a rainfed fig orchard. This region is distinguished as the largest producer of dried figs in Iran and the world and its production is highly dependent on precipitation. A split–split plot statistical design with four replicates was used to conduct the experiment. Irrigation treatments based on the position of application around trees were: in a micro-catchment close to tree trunks; in three holes inside of tree canopies with a mean canopy of 3.2 m diameter (placed 1–1.1 m from tree trunks); and in four holes outside of tree canopies placed 2.1–2.2 m from tree trunks were used in this experiment. Irrigation time treatments consisted of: (a) in early spring; (b) in mid-summer and the three different volumes of irrigation water were used: no supplemental irrigation (control), and either 1000 or 2000 l of irrigation water per tree. Results showed a high evaporation rate in the area which used nearly half of the rainfall during autumn and winter. There was a significant positive correlation between soil water content (SWC) and temporal rainfall distribution as r** = 0.63 (p < 0.001) over two years. Under drought conditions, irrigated trees showed higher ETa that was close to the ETa in years with normal rainfall. Compared to irrigation in summer, irrigation in early spring kept higher SWC for a longer time period in the soil profile and irrigation far from trees increased soil surface evaporation especially in summer. This study suggests that using supplemental irrigation with 2000 l per tree of water in early spring near tree trunk could provide higher SWC and lower surface evaporation for rainfed fig orchards during drought conditions.

Evaluation of different mulch materials for reducing soil surface evaporation in semi‐arid region

AbstractIn recent years, the use of new mulches for soil water conservation in arid regions has been introduced as an alternative to conventional (plastic) mulches. However, systematic studies concerning the effects of different organic [pistachio shell mulch (PSM), wheat straw mulch, de‐oiled olive pomace mulch (DOM) or wood chips mulch], chemical [superabsorbent polymer (HM) or organic‐based emulsion polymer (PEM)] and mineral [gravel mulch (GM)] covers on soil and water conservation are scarce. Therefore, two experiments were carried out. Experiment 1 was aimed at evaluating the effects of mulches of different composition on soil surface evaporation, whereas in experiment 2 we investigated the effects of this decrease in soil evaporation due to different mulch materials on some olive tree physiological responses to soil drying. We analysed stem water potential, transpiration rate, stomatal conductance, leaf density and maximum efficiency of photosystem II photochemistry (Fv/Fm) of 2‐yr‐old plants of ‘Konservalia’ olive, grown in pots in open field. The results showed that different mulch materials had different efficiency on soil water conservation and DOM and pistachio shell mulch PSM – as new mulch materials – seems more favourable for conserving soil water. Water stress caused reductions in all parameters measured and increment in leaf density compared with unstressed treatment. Olive plants grown using different soil mulch presented higher values of stem water potential, transpiration rate, stomatal conductance and Fv/Fm ratio compared to control plants. Although all the mulch treatments improved the water content of soil, DOM and PSM were found to be superior in maintaining optimum soil water content for olive use.

Safflower model for simulation of growth and yield under various irrigation strategies, planting methods and nitrogen fertilization

Development and use of crop growth models is an effective tool for agricultural planningand decision making in agricultural industry. Besides, the drought and limited supplies of waterin many areas of the world has increased attention to favourable strategies in farm managementsuch as efficient irrigation and planting methods. The objective of this study was to develop acrop model for safflower known as a multi-purpose crop under various irrigation regimes,planting methods and nitrogen fertilization. The experiment was designed as split-split plot thatarranged in randomized complete blocks with irrigation strategy as the main plot, plantingmethod as the subplot and nitrogen levels as the sub-subplot in three replications. The irrigationstrategies consisted of ordinary furrow irrigation (OFI) and variable alternate furrow irrigation(VAFI) as a partial root drying (PRD) technique. The planting methods were on-ridge planting(P1) and in-furrow planting (P2) methods. The fertilizer levels were 0 (N0), 100 (N1) and200 (N2) kg ha-1 of urea as 0, 46 and 92 kg N ha-1. Two years of the experiment carried out in asemi-arid area from 2012 to 2014. The field data of the second year of experiment were used todevelop the model and it was validated by the data of first year. The results indicated that theproposed safflower model is able to estimate evapotranspiration, soil water content, leaf areaindex, soil surface evaporation, crop transpiration, biomass, straw and seed yield of safflower inan appropriate manner. The safflower model is useful for having better field management andreducing administrative costs with respect to the model simplicity and its briefness in data input.

Применение быстрого автоматического дифференцирования при нахождении испарения с поверхности почвы

Применение быстрого автоматического дифференцирования при нахождении испарения с поверхности почвы

An Inverse Method to Estimate the Root Water Uptake Source-Sink Term in Soil Water Transport Equation under the Effect of Superabsorbent Polymer.

The widespread use of superabsorbent polymers (SAPs) in arid regions improves the efficiency of local land and water use. However, SAPs’ repeated absorption and release of water has periodic and unstable effects on both soil’s physical and chemical properties and on the growth of plant roots, which complicates modeling of water movement in SAP-treated soils. In this paper, we proposea model of soil water movement for SAP-treated soils. The residence time of SAP in the soil and the duration of the experiment were considered as the same parameter t. This simplifies previously proposed models in which the residence time of SAP in the soil and the experiment’s duration were considered as two independent parameters. Numerical testing was carried out on the inverse method of estimating the source/sink term of root water uptake in the model of soil water movement under the effect of SAP. The test results show that time interval, hydraulic parameters, test error, and instrument precision had a significant influence on the stability of the inverse method, while time step, layering of soil, and boundary conditions had relatively smaller effects. A comprehensive analysis of the method’s stability, calculation, and accuracy suggests that the proposed inverse method applies if the following conditions are satisfied: the time interval is between 5 d and 17 d; the time step is between 1000 and 10000; the test error is ≥ 0.9; the instrument precision is ≤ 0.03; and the rate of soil surface evaporation is ≤ 0.6 mm/d.

Evaluation of evapotranspiration and deep percolation under mulched drip irrigation in an oasis of Tarim basin, China

Summary Mulched drip irrigation for cotton field is an effective measure for the utilization of saline water, and the regulation of soil water and salt. However, the reasonable methods for quantifying actual evapotranspiration (ET) and deep percolation of recharge to groundwater are still not very well understood, which restricts the accurate regulation of soil water and salt for cotton growth in oasis. In this paper, a set of experiments of mulched drip irrigation with brackish water were conducted in a typical arid region of Tarim basin in southern Xinjiang, China. The irrigation events were recorded, and ET and fluctuations of groundwater table were carefully measured for two consecutive irrigation periods of flowering and bolling stages. A group of upscaling conversion methods were used to quantify the ET, in which canopy structure was considered to estimate the transpiration from leaf scale to a unit of field scale. The groundwater table had a significant response to the irrigation events, thus the deep percolation was estimated using water-table fluctuation method (WTF). Results showed that during the two irrigation events of flowering and bolling stages, the total ET was 31.1 mm with the soil surface evaporation of only 0.4 mm. The total percolation of recharge to groundwater was 48.2 mm which contributed to the groundwater run-off of 22.1 mm. Transpiration of 30.7 mm accounted for 98.6% of the total ET of 31.1 mm and 34.3% of the irrigation water of 90.6 mm. Compared with transpiration, the deep percolation accounted for 53.2% of irrigation water, indicating a serious excessive irrigation that recharged to groundwater. Soil salt budget showed that the salt leached into groundwater was 1.56 times of the input from brackish irrigation water and fertilization during the two irrigation periods. Even for the irrigation practice with brackish water, the accumulated salt of soil profile could also be leached out under large amount of irrigation water (e.g. 90.6 mm for the two irrigation periods, 10 days). However, the waste of enormous water which for instance occupied 53.2% of the irrigation water in this study was not conducive to the sustainable utilization of water resources in the arid oasis. Furthermore, the methods introduced in this paper for ET and deep percolation calculation of cotton filed could be used to quantify the oasis hydrologic cycle of micro-irrigation, to gain a better understanding of the ecological process.