Effect of salinity on water stress, growth, and yield of maize and sunflower

Maize and sunflower were grown in tanks filled with loam and clay, and were irrigated with water of three different levels of salinity. Predawn leaf-water potential and stomatal conductance were used as parameters for water stress. The predawn leaf-water potential of maize was higher than that of sunflower, but the effect of salinity and soil texture on the predawn leaf-water potential was the same for both crops. The stomatal conductance of sunflower was much higher and more severely affected by salinity and soil texture than the stomatal conductance of maize.

Although salinity had a more serious effect on the development of leaf area and canopy dry matter of sunflower, its effect on evapotranspiration and grain yield was the same for both crops. Soil texture had a stronger effect on the development of leaf area and canopy dry matter of sunflower, which also appeared in the evapotranspiration and grain yield, indicating that sunflower is more sensitive to drought than maize.     

Model for assessing impact of salinity on soil water availability and crop yield

The salinity condition in the root zone hinders moisture extraction from soil by plants, because of osmotic potential development in soil water due to presence of salts, which ultimately, decreases transpiration of plants and thereby affects crop yield. Therefore, an effort was made in this study to quantify the impact of salinity on soil water availability to plants. The movement of salts under irrigation and evapotranspiration regimes in root zone of soil profile was studied throughout the growing season of wheat crop with adopting exponential pattern of root water uptake. A model was developed to analyze soil water balance to find out moisture deficit because of salinity. A non-linear relationship was formulated between moisture content and salt concentration for simultaneous prediction. The Crank–Nicolson method of Finite Differencing was used to solve the differential equations of soil water and solute transport. The effect of various salt concentrations on transpiration was analyzed to develop a relationship between relative evapotranspiration and relative yield. Relationships among salt concentration, matric potential, moisture deficit and actual transpiration were also established to provide better understanding about impact of salinization and to provide guidelines for obtaining better crop yields in saline soils.     

On quantifying soil water deficit of a partially wetted root zone by the response of canopy or leaf conductance

Quantifying the soil water deficit (SWD) and its relation to canopy or leaf conductance is essential for application of the Penman–Monteith equation to water-stressed plants. As the water uptake of a single root depends on the water content of the soil in its immediate vicinity, the non-uniform distribution of water and roots in the soil profile does not allow simple quantification of SWD from soil-based measurements. Using measurements of stem sap flux (with a heat pulse technique), soil evaporation (with micro-lysimeters) and meteorological parameters the canopy conductance was obtained through inversion of the Penman–Monteith equation. SWD was evaluated by averaging the soil water content profile of the root zone (monitored by layers with the TDR sensors) weighted by root distribution of the layers. The average canopy conductance at midday (11:00–15:00, Israel Summer Time), denoted as G_noon, was computed for each day of the experimental period. Stable summer weather, typical of the Mediterranean region, and the fully developed crop canopy, made water stress the only plausible cause of a G_noon decline. However, the daily decline of G_noon did not occur at the same weighted average soil water content during the successive drying cycles. For the cycle with less irrigation, the decline in G_noon occurred at higher soil moisture levels. Alternatively, when SWD was determined from the water balance, i.e., by defining water deficit as irrigation minus accumulated evapotranspiration, the G_noon decline occurred at the same value of water deficit for all irrigation cycles. We conclude that a climate-based soil water balance model is a better means of quantifying SWD than a solely soil-based measurement.     

A mathematical model for simulating water balances in cropped sandy soil with conventional flood irrigation applied

In this paper, a model that integrates various complex model components for the purposes of water balance modeling throughout crop development in arid inland region under the conventional flood irrigation practiced is presented. These components are modules for calculating dynamic soil water content based Richard's equation, potential and actual evapotranspiration, and crop root water uptake. Soil water content in the active root zone and soil evaporation simulation obtained from the model were test using field data in 2003. The low values of MARE and high values of R² and PE in the active root zone of soil profile as well as daily soil evaporation indicated that the soil water balance simulation model presented in the paper can be used with reliable accuracy to simulate the components of water balance in cropped sandy soil under the conventional flood irrigation condition in arid inland regions. The model simulation on components of water balance using observed field data in 2004 indicated that large quantities – about 43% of irrigation water (amounting to 840 mm) – were consumed by deep percolation, only small (less than 41%) proportions of irrigation water used by the plants for transpiration. The current irrigation scheme is characterized by the unreasonable agricultural water management with the waste of water in the irrigational system in this region. The impact of irrigation scheduling on water balance presented in this paper showed that the reasonable irrigation scheme with more frequent irrigation and less amounts is more suitable for the irrigation of spring wheat in Heihe River basin, northwest China. Therefore, to establish a decision-making system for agricultural irrigation scheme and to utilize the limited water resources in this region have become an urgent problem that needs to be solved.     

Relations between relative evapotranspiration and predawn leaf water potential in soybean grown in several locations

Summary The measurement of water consumption in the field is normally restricted to research purposes, although the development of practical field criteria for timing water application is required to improve crop productivity. To develop such criteria irrigation experiments on Soybean were conducted from flowering to grain filling at four locations which differed in their soil properties and the convective contribution of their climates to potential evapotranspiration. The energy balance, predawn leaf water potential (PLWP), soil moisture depletion, and a crop water stress index (CWSI) based on foliage temperature were measured. The range of soil, atmospheric, phenological and irrigation conditions, produced a common, linear relation between relative evapotranspiration (rET) and the logarithm of -PLWP. Correlation with the temperature based CWSI was weak. A similar relation with PLWP for other C₃ plants was also derived from data in the literature. This relation could be helpful for irrigation scheduling once the critical values of rET for crop productivity are known.     

河西绿洲灌区主要作物需水量及作物系数试验研究

利用Penman-Monteith公式计算了甘肃张掖绿洲主要作物各生育期参考作物蒸散量,利用农田水量平衡方程及土壤水分胁迫系数计算了作物实际蒸发蒸腾量,并计算比较了充分灌溉和非充分灌溉条件下不同生育期作物需水特征,确定了非充分灌溉条件下主要作物的作物系数。结果表明,非充分灌溉条件下,主要作物各生育期需水规律和充分灌溉具有一致变化趋势。非充分灌溉条件下,小麦、玉米、马铃薯全生育期作物系数平均值分别为0.81、0.7和0.73。在全生育期当中,随生育期的延续,主要作物叶面蒸腾比例逐渐增大,棵间蒸发逐渐减少。     

Seasonal water production functions and yield response factors for maize and onion in Perkerra,Kenya

Water production functions (wpf) giving the relation between crop yield and water application under furrow irrigation on a clay loam soil in the semi-arid region in Kenya (Perkerra) were derived for maize and onion. Due to deep percolation the functions were found to be curvilinear. The seasonal yield response factors K_y, giving the relationship between evapotranspiration deficit and yield depression for maize and onion for the area was computed as 1.21 and 1.28, respectively. Analytical analysis using the derived wpf for maize and existing conditions in an irrigation system located in the area confirmed that if rainfall is significant, deficit irrigation will be more attractive, and at a certain point, it is profitable to cultivate all available area.     

Water use efficiency of narrow row cotton

Summary A field experiment was conducted on the west side of the San Joaquin Valley in California to determine water use, crop growth, yield and water use efficiency of Acala (SJ-2) cotton (Gossypium hirsutum L.) grown in 0.5 m spaced rows on a Panoche clay loam soil (Typic Torriorthents). Evapotranspiration was determined by water balance techniques utilizing neutron soil moisture measurements. All neutron measurements were made within a 3 m soil profile in 0.20 m increments. The measured evapotranspiration was compared to climatic estimates of potential evapotranspiration, and to calculations using a one-dimensional soil water balance model that separately computed soil water evaporation and plant transpiration. Crop growth was determined by weekly destructive plant sampling. Leaf area was determined along with dry matter components of leaves, stems, fruiting parts (flowers and squares) and bolls. Final yield was determined by machine harvesting (brush stripper) 720 m² from each plot. Lint yields and fiber quality were determined by sample ginning and fiber analysis at the U.S. Cotton Research Station at Shafter, California. Three irrigation regimes were established that resulted in an evapotranspiration range from a high deficit condition to full irrigation at the calculated atmospheric demand.The measured evapotranspiration of narrow row cotton under a full irrigation regime was 778 mm, 594 mm under a limited irrigation regime and 441 mm under a regime with no post-plant irrigation. The evapotranspiration from these irrigation treatments was accurately simulated by a water balance model. that used inputs of potential evapotranspiration, leaf area index, soil water holding capacity and root development.The average lint yield from narrow row cotton with a full irrigation regime was 1583 kg/ha, the average lint yield from a limited irrigation regime was 1423 kg/ha and the average lint yield from a treatment with no postplant irrigation (fully recharged soil profile at planting) was 601 kg/ha. The full irrigation regime resulted in a dry matter production of approximately 16 t/ha while the limited irrigated regime produce 11 t/ha and the no-postplant irrigation regime produced 7 t/ha of dry matter. The fiber quality results indicated significant (0.05 level) differences only in 50% span length and micronaire, with the 2.5% span length, uniformity index, elongation and strength indicating no difference.Cotton lint yield was found to be directly related to total evapotranspiration although the relationship was slightly non-linear while dry matter yield was found to be linearly related to evapotranspiration. Both lint and dry matter yield were found to have a linear relationship to estimated transpiration from the water balance model calculations.Contribution from the Unived States Department of Agriculture, Agricultural Research Service, Western Region and the University of California     

Numerical assessment of effective evapotranspiration from maize plots to estimate groundwater recharge in lowlands

To maximize the irrigation efficiency and to protect groundwater from agrochemical pollution, two variables must be known with good accuracy: effective evapotranspiration and infiltration, especially in lowland areas were the run-off is minimal. Three different experimental plots cultivated with maize were equipped with tensiometers and soil moisture probes to monitor every day the water movement in the unsaturated zone. Other relevant parameters of the various soil layers, as hydraulic conductivity and water retention curve, were obtained in laboratory experiments, while boundary conditions, as precipitations, temperature and root growth, were obtained on site. Inverse modeling was performed using HYDRUS-1D to assess the degree of uncertainty on model parameters. Results showed a good model fit of water content and head pressure at various depths, in each site, using Penman-Monteith formula for daily potential evapotranspiration calculation, but poor fit applying the Hargreves and Turk formulas. Best performance of model fit was observed for S-shaped equation employed to simulate the root water-uptake reduction with respect to Feddes equation. The soil parameters uncertainty was limited and remained within analytical errors, thus a robust estimation of cumulative infiltration and evapotranspiration has been derived. This study points out that evapotranspiration is the most important variable in defining groundwater recharge for maize crops in lowlands.     

Water balance and nitrate leaching in an irrigated maize crop in SW Spain

During 3 consecutive years (1991–1993) a field experiment was conducted in an intensively irrigated agricultural soil in SW Spain. The main objective of this study was to determine the water flow and nitrate (N0₃) leaching, below the root zone, under an irrigated maize crop and after the growing season (bare soil and rainy period). The experiment was carried out on a furrow-irrigated maize crop at two different nitrogen (N)-fertilization rates, one the highest traditionally used by farmers in the region (about 500 kg N ha⁻¹ per year) and the other one-third of the former (170 kg N ha⁻¹ per year). The aim was to obtain data that could be used to propose modifications in N-fertilization to maintain crop yield and to prevent the degradation of the environment. The terms for water balance (crop evapotranspiration, drainage and soil water storage) and nitrate leaching were determined by intensive field monitoring of the soil water content, soil water potential and extraction of the soil solution by a combination of neutron probe, tensiometers and ceramic suction cups. Nitrogen uptake by the plant and N0₃-N produced by mineralization were also determined.The results showed that, in terms of water balance, crop evapotranspiration was similar at both N-fertilization rates used. During the irrigation period, drainage below the root zone was limited. Only in 1992 did the occurrence of rainfall during the early growing period, when the soil was wet from previous irrigation, cause considerable drainage. Nitrate leaching during the whole experimental period amounted to 150 and 43 kg ha⁻¹ in the treatments with high and low N-fertilization, respectively. This occurred mainly during the bare soil and rainy periods, except in 1992 when considerable nitrate leaching was observed during the crop season due to the high drainage. Nitrate leaching was not so high during the bare soil period as might have been expected because of the brought during the experimental period. A reduction of N-fertilization thus strongly decreased nitrate leaching without decreasing yield.     

Photosynthesis,plant growth and dry matter distribution in kiwifruit as influenced by water deficits

The effects of water deficits on photosynthesis, plant growth and dry matter accumulation and distribution in the kiwifruit, cv Hayward, grown under controlled conditions in the glasshouse were studied. Water stress was imposed by irrigating the plants with 100%, 85%, 65% and 40% of water needed to reach pot capacity in the soil. Water deficits reduced the rate of photosynthesis by up to 53–64% in relation to the control. This decline was attributed to stomatal closure, since stomatal conductance was reduced significantly, or/and to inhibition of photosynthesis at chloroplast level. Severe water stress reduced plant height by 78–84%, total dry weight by 58–66% and total leaf area by 72–77%. The root to shoot ratio was 3.5 times higher in water-stressed plants, showing that water stress in kiwifruit alters the pattern of dry matter distribution favouring the roots. The decrease in growth induced by water deficits was a consequence of a reduction in both photosynthesis and photosynthates partitioning, which adversely affects leaf area development.     

河西地区滴灌春玉米对不同灌溉决策方法的响应

基于3种灌溉决策方法(土壤水分、蒸散量、土水势),设置10个灌溉处理(CK,W₁,W₂,E_P100,E_P80,E_F100,E_F80,P₂₅,P₄₅,P₆₅),研究不同灌溉决策方法对河西地区春玉米生长、产量及水分利用效率WUE的影响.结果表明:基于土壤水分、蒸散量、土水势调控灌溉下产量最高的处理分别为CK,E_P100和P₂₅;处理CK的产量比E_P100和P₂₅分别增大6.90%和8.28%.CK的春玉米生长和干物质积累最优,但是耗水量最大,为718.54 mm,比E_P100增大26.13%和11.57%.处理E_P100的产量显著低于CK,但WUE显著高于CK.处理P₂₅较CK和E _P100灌水次数多,产量和水分利用效率表现均不突出.处理E_P80和E_P100的产量和WUE差异不具有统计学意义.综合考虑产量、水分利用效率和灌溉决策方法的适用性,基于过去蒸散量调控灌溉,每周灌水定额为80%ET₀(E_P80)是最适合河西地区春玉米高效稳产的灌溉决策方法.     

Water use efficiency of controlled alternate irrigation on root-divided maize plants

A new method of irrigation was designed and tested for its water use efficiency (WUE). Maize plants were grown in pots with their roots divided and established into two or three separated containers of which irrigation and soil drying were controlled alternately. Results showed that when the two halves of the root system were alternatively exposed to a drying soil and a soil with its water content maintained above 55% or 65% of its field capacity, water consumption was reduced by 34.4–36.8% and the total biomass production was reduced by only 6–11%, when compared to the well-irrigated plants. Significant increase in WUE, root to shoot ratio and stomatal resistance for water diffusion were observed as a result of such treatment. Leaf transpiration was reduced substantially while the rate of photosynthesis and leaf water content were not significantly altered. The results were also compared to root-divided plants of which irrigation was fixed to one container only and showed that a better WUE, root development and distribution, shoot biomass production were achieved by the alternate drying and rewetting. We conclude that the controlled alternate irrigation (CAI) is an effective and water-saving irrigation method and may have the potential to be used in the field.     

Irrigation scheduling for traditional,low-density olive orchards: Water relations and influence on oil characteristics

An experiment was performed in a low-density olive orchard (69 trees ha⁻¹) to study the recovery from water stress of olive trees under different irrigation managements. The effect of water stress on oil quality was also examined. The trees were subjected to one of four irrigation treatments: rain-fed conditions, irrigation with either 100% or 125% of the crop evapotranspiration (ET_c) level, or a deficit treatment in which only 60 mm of water were provided (at different times depending on the weather and phenological stage of the crop). The irrigation water in the deficit treatment was some 43% of the water applied in the 125% treatment. Plant water relations were determined periodically by measuring the water potential of covered leaves and the stomatal conductance at midday. The trees in the water deficit and rain-fed treatments rapidly recovered from water stress after receiving irrigation water or autumn rainwater, respectively, reaching the condition of the fully irrigated trees. However, stomatal conductance took longer to recover. Recovery at mid-summer in the deficit treatment was related to the amount of water in the soil; in autumn, however, this relationship was not so clear in rain-fed trees. The effect on oil quality was recorded in terms of the total concentration of phenolic compounds (TP). This was strongly related to the water stress integral, suggesting that the effect of irrigation on this variable occurs year-round and not just during the oil accumulation phase. Thus, even with low doses of water it should be possible to significantly reduce the TP concentration. Since recovery from water stress is rapid when irrigation is concentrated in the second half of summer, such an irrigation regimen might allow efficient use of the limited amounts of water available in central Spain.     

Sap flow in the stem of water stressed soybean and maize plants

Summary Water stress was imposed upon soybean [Glyxine max (L.) Merr. cv. Williams] and maize [Zea mays (L.) cv. Pioneer 3377] plants grown under controlled-environment conditions during a growing period of several irrigation cycles. Transpiration rates of individual plants were measured with a calibrated heat-pulse method and correlated to the rate of water loss obtained from successive weighings of the pots containing irrigated or water-stressed plants. Transpiration rate was reduced in the stressed plants of both species, but the reduction was not linear with decreasing soil matric potential. Transpiration rates declined rapidly at high soil matric potential, and dropped more slowly as the soil dried. Although measured transpiration rate declined by nearly 30% following a reduction of soil matric potential to -0.1 MPa, differences in leaf water potential and CO₂ assimilation rate were small and less than the sensitivity of the measurement techniques used. Total system resistance to water flow increased as the soil dried.     

Comparison of drainage estimation methods in irrigated citrus orchards

Three different methods of measuring drainage were selected and applied to two irrigated citrus orchards for 3 years. The methods were: (1) a simple soil water capacity model, (2) a chloride balance, and (3) the LEACHM model. In the first method, the soil is assumed to have a given water holding capacity, plants cannot extract water from soil below a certain level, and evapotranspiration varies with soil water content in a well-defined pattern. In the second method, drainage in a given period of time is estimated from the chloride input to soil (mainly with the irrigation and rain water), the changes in soil chloride, and the average chloride concentration of soil solution at the depth where drainage is estimated. In the LEACHM model, water transport in soil is assumed to follow Richards equation, and evapotranspiration depends in soil water content, soil hydraulic properties, the evaporative conditions of the air, and root properties and distribution. Two citrus orchards planted with mature trees, under flood irrigation, were used for the comparison of methods. The three methods provided drainage estimates that differed in most cases by less than 13%, although in some particular season and plot, a given method deviated from the other two by up to 56%. The soil water capacity model is appealing because it only needs a few parameters for calibration, and can be easily programmed in a spreadsheet. The main advantage of the chloride balance approach is that it requires neither calibration nor an estimate of evapotranspiration; this latter fact converts the chloride balance into a good alternative method of measuring evapotranspiration. The precision of the drainage estimates by chloride balance is mainly determined by the spatial variability of soil chloride relative to the chloride input to the soil in the measurement period; in most cases, to obtain a reasonable precision, this period should be longer than 1 or 2 months. The LEACHM model requires more data for calibration, but it can provide additional information on water and solute distribution in the soil profile with time.     

Water balance estimates over Greece

Water balance for 31 locations in Greece is calculated on the basis of long-term average monthly precipitation, evapotranspiration and combined soil and vegetation characteristics, according to the method proposed by Thomthwaite and Mather. Monthly evapotranspiration estimates are calculated from 27 years (1960–1987) of routine meteorological data using the original Penman method. Soil and vegetation characteristics specific for the locations under study are combined in the water capacity of the root zone (WCRZ). similar water balance calculations were carried out using various fixed values of WCRZ for all stations, to evaluate the effects of soil and vegetation through the WCRZ in the final estimates of soil moisture deficits. Water balance calculations were also performed using average monthly evapotranspiration estimates calculated according to the empirical Tbomthwaite method. Results were compared in order to show possible differences that could be attributed to the method of estimating evapotranspiration. Finally, results obtained with a value of WCRZ fixed at 300 mm and potential evapotranspiration estimated by the Thomthwaite method for the period 1969–1987 were compared with existing similar results over a longer period in the past (1931–1968), in order to detect diachronic changes in the water balance components over the same regions in Greece.     

Isohydrodynamic behavior in deficit-irrigated Cabernet Sauvignon and Malbec and its relationship between yield and berry composition

Cabernet Sauvignon and Malbec grapevines were irrigated at 70 or 23 % of estimated crop evapotranspiration throughout berry development over four growing seasons. Stomatal behavior was characterized by relating predawn leaf water potential and mid-morning stomatal conductance to mid-morning leaf water potential. Seasonal average weekly midday leaf water potential was lower in Cabernet Sauvignon than Malbec despite similar irrigation amounts. Both cultivars exhibited anisohydric behavior with midday leaf water potential decreasing linearly with declining predawn leaf water potential (r ² = 0.51) and stomatal conductance (r ² = 0.42). However, both cultivars utilized hydrodynamic mechanisms to maintain a soil-to-leaf water potential gradient of ?0.62 (±0.03) MPa under standard irrigation and ?0.75 (±0.04) MPa under reduced irrigation. Berry fresh weight and titratable acidity decreased, and the concentration of total anthocyanins increased in both cultivars in response to decreases in midday leaf water potential. The slope of regression equations for seasonal mean midday leaf water potential was used to estimate cultivar-specific levels of water stress associated with changes in berry weight and berry composition at fruit maturity.     

基于概念模型的棉田土壤水分变化模拟研究

农田土壤水分模拟是农业用水管理的重要依据。以根系层土体水量平衡方程为依据,考虑根系层下界面水分通量,构建了农田土壤水分变化模拟模型,该模型由作物蒸发蒸腾量模型、根区下界面水分通量模型以及水量平衡方程等组成。依据山西水利职业技术学院试验基地2006-2008年3年棉花试验资料,确定了模型参数。结果表明,土壤储水量模拟计算值与实测值有较好的一致性,其相关系数达到0.928 7,F检验结果(F=96.44F0.001=3.27)达到高度显著水平,所建立的土壤水分变化模拟模型可用于棉花田间土壤水分的模拟计算,计算精度平均达到5.3%~15.8%;模型较好地反映了农田土壤水分转化过程以及降水、蒸发和深层土壤水分对作物蒸发蒸腾及产量的影响。     

基于地面观测和Sentinel-2数据的玉米实际蒸散发估算

基于遥感技术估算作物蒸散发(Evapotranspiration,ET)对农业用水效率评价和精量灌溉决策具有重要意义。结合Sentinel-2数据和农田连续地面观测资料,利用混合双源蒸散发模型(Hybrid dual-source scheme and trapezoid framework-based evapotranspiration model,HTEM)对宁夏回族自治区中卫市2019年两个试验田玉米主要生育期(5—8月)的蒸散发量进行估算,并用水量平衡法对遥感估算结果进行验证和评价。结果表明:Sentinel-2数据具有高时空分辨率,能够与研究区复杂的种植地块相匹配,减少了混合像元的数量;遥感反演参数与地面观测数据拟合度较高,研究区2019年遥感反演的玉米田净辐射量均方根误差为36.256 W/m²。利用HTEM模型估算可得,主要生育期内研究区两个玉米试验田的日均实际蒸散发量分别为4.269 mm/d和4.339 mm/d,实际蒸散发总量分别为525.114 mm和533.690 mm,其中植被蒸腾量分别为363.483 mm和358.196 mm,生育初期主要以土壤蒸发形式消耗水分,随着作物的生长,在生育中后期主要以植被蒸腾的形式消耗水分。ET遥感反演结果与水量平衡结果之间差别不显著,两个观测点绝对误差分别为13.533 mm和7.774 mm。因此,结合地面连续观测系统和Sentinel-2数据估算研究区玉米生育阶段蒸散发量具有较高的精度,可为作物耗水规律研究及区域农业水管理提供技术支撑。