The dependence of irrigation requirements on water-table depth in drained lands

The amount of irrigation water required to maintain an optimal average water content in the root zone for maximum crop yield is dependent on the water-table depth as well as on evapotranspiration. An approximate expression is derived in terms of soil constants for the vertical soil water flux, which may be directed upwards or downwards, above the water table. This has been used in a water-balance equation in order to estimate the irrigation requirement. Satisfactory agreement is found between results calculated using this theoretical relationship and published experimental work.     

基于遥感的农业用水效率评价方法研究进展

遥感技术的发展为区域尺度蒸散发计算、作物分布识别及估产提供了一条有效途径,为基于遥感信息的灌区灌溉水利用效率及作物水分利用效率定量评价奠定了基础。回顾总结了遥感蒸散发模型、瞬时蒸散发升尺度方法、日蒸散发插值方法、作物分布识别方法及作物估产模型的研究进展,评述了遥感蒸散发及作物估产结果在灌区灌溉水利用效率及作物水分利用效率评价中的应用情况。提出了相关领域需要进一步研究的问题,包括适合非均匀下垫面特点且具有较强物理基础的灌区遥感蒸散发模型、日蒸散发插值中灌溉或降雨引起土壤含水量突变情况的处理、农田蒸散发中灌溉水有效消耗量的准确估算、能适应复杂种植结构并且适用于多年的作物分布遥感识别模型以及精度较高且可操作性强的遥感估产模型等。     

Application of a simulation based optimization model for winter wheat irrigation scheduling in North China

Irrigation needs to be scheduled properly for winter wheat, the main food crop in North China where the water resources are limited. We optimized the irrigation timing of crops under limited water supply by integrating a soil water balance model, dated water production function with cumulative function of water sensitivity index, and a nonlinear search method. The optimization produced the optimal irrigation date series with the predetermined irrigation quota for each application, which aims to obtain higher crop yield with limited irrigation water and be convenient for irrigation management. This simulation–optimization model was used to investigate the irrigation scheduling of winter wheat in Xiaohe irrigation Area in North China. Results show that optimal irrigation date series, corresponding relative yield and relative evapotranspiration are all closely related to the irrigation quota and initial soil water conditions. For rich and medium initial soil water conditions in medium precipitation year, it takes four times of irrigation (60 mm each time) after greening in order to obtain higher crop yield. But it increases to five times for poor initial condition. With limited irrigation water, irrigation should generally be applied in the preferential sequence of early May or late April (in the jointing stage), then mid and late May (in the heading stage), and finally March (in the greening stage). Irrigation should be applied earlier with lower initial soil water storage. Higher irrigation quota increases the crop yield but tends to decrease the marginal value, especially when irrigation quota exceeds 180 mm. The study also indicates that the optimized relative yield is generally higher than that obtained in field experiment. Based on the optimization, we proposed to use the quadratic polynomial function to describe the frontier water production function, which shows the mathematical relationship between optimized relative yield and relative evapotranspiration.     

Irrigation planning in cotton through simulation modeling

Experiments were undertaken at CCS Haryana Agricultural University Farm, Sirsa (India) to estimate the optimum irrigation schedule for cotton resulting in minimum percolation losses. The sprinkler line source technique was adopted for creating various irrigation regimes at different crop growth stages. The SWASALT (Simulation of Water And SALT) model after calibration and validation provided water balance components. The wa-ter management response indicators (WMRI's) such as transpiration efficiency E_t/(Irr + P), relative transpiration E_t/E_tp, evapotranspiration efficiency ET/(Irr + P), soil moisture storage change ΔW/W_int (deficit/excess) and percolation loss Perc/(Irr. + P) were evaluated using water balance components as estimated by the simulation study. Under limited water supply conditions, the optimum irrigation depth was found to be 57 mm at crop growth stages with pre-sowing and 1^st irrigation of 120 mm and 80 mm respectively for sandy clay loam underlain by sandy loam soil (Type I). The corresponding values of relative transpiration, transpiration efficiency and evapotranspiration efficiency were 0.65, 0.65 and 0.89 respectively. The crop yield varied linearly with increasing irrigation depth which was evident from increase in relative transpiration with increasing depth of water application. However, increased depth of irrigation resulted in less moisture utilisation from soil storage (20% depletion at 40 mm depth and 4.4% moisture built up at 100 mm depth). The extended simulation study for sandy soil underlain by loamy sand (Type II) indicated that two pre-sowing irrigations each 40 mm and subsequent irrigations of 40 mm at an interval of 20 days depending upon rainfall were optimum. This irrigation scenario resulted in zero percolation loss accompanied by 74% relative transpiration and 14 per cent soil moisture depletion. Received: 20 November 1995     

基于作物耗水特性的夹砂地膜下滴灌模式优选

在2个灌水水平下（I1：高水,I2：低水）以不同滴灌带间距（A1：1m,A2：0.5m）与覆膜方式（M1：全膜覆盖,M2：半膜覆盖）进行2a田间试验,结合作物产量、作物水分利用效率（WUE）以及产投比筛选适宜的膜下滴灌模式,并利用产量水分敏感系数（ky）确定最优的膜下滴灌模式。结果表明：在低频灌溉模式下,部分覆膜处理的蒸腾（ET）高于全覆膜处理,而产量和WUE低于全覆膜处理。尽管滴灌带间距对ET的影响不明显,然而在高水处理下,“一管单行”作物的产量与WUE高于“一管双行”。高频灌溉模式下,作物产量及WUE对灌溉量、覆膜方式、滴灌带间距的响应呈现耦合性。低频灌溉条件下,ky对灌溉量及滴灌带间距的响应均不显著,而部分覆盖处理WUE低,ky高,对水分胁迫的响应敏感。高频灌溉条件下,覆膜方式、灌溉量以及滴灌带间距均对ky 产生影响。高频灌溉条件下,ky能对经WUE筛选出的膜下滴灌处理进行进一步的优选。基于ky的结果,结合产量、水分利用效率与产投比,建议在高频灌溉条件下采取“全膜低水+一管双行”模式或“半膜高水+一管单行”模式,在低频灌溉条件下采取全膜高水模式。     

Assessment of alternative water management options for irrigated agriculture

A simulation study on alternative water management strategies was carried out for Sirsa Irrigation Circle in Haryana, covering an area of about 4800 km². Results showed that crop evapotranspiration and soil salinity development under reduction in canal water supply and increase in groundwater use, are largely influenced by the amount and distribution of rainfall. Reduction in canal water supply by 25% during the rainy season is unlikely to have any adverse effect on the salinity development in the study area. Reduction in crop evapotranspiration due to decreased canal water supply can partly be compensated by the increase in groundwater use. Leaching of salts due to monsoon rains in the study area shows that groundwater of even relatively poor quality can be used for irrigation without excessive long-term build up of soil salinity under deep groundwater depth conditions. However, increased groundwater extraction without associated actions will not be very effective to solve the problem of rising groundwater levels.     

Modeling crop yield as affected by uniformity of sprinkler irrigation system

The effect of sprinkler irrigation uniformity on crop yield is an important consideration for the design of sprinkler irrigation system. A model that relates yield response to evapotranspiration deficits at special growth stages to evaluate the impacts of uniformity on crop yield was developed from a crop water production function. The simulation results of the model showed that crop yield increased with increasing uniformity. Optimum irrigation amount and uniformity for the maximum net return were determined with the model. The optimum irrigation amount depends on irrigation uniformity and on economic factors, decreasing with the uniformity but increasing with the ratio of product price to water cost. The optimum uniformity increased with an increase of irrigation amount expressed by a ratio between gross and required irrigation amount, but approximated 90% when the ratio exceeded 0.85. Field experiments conducted to study the relationship between spatial distribution of soil moisture and sprinkler application uniformity demonstrated that the water in the soil was more uniformly distributed than that measured for the application at the soil surface.     

Frequency and depth of irrigation for groundnut

Studies on frequency and depth of irrigation for groundnut (Arachis hypogaea) for two summer seasons at Tirupati campus of Andhra Pradesh Agricultural University, India showed that, keeping the total quantity of applied irrigation water almost the same, high frequency irrigation gave the highest yield. For each irrigation frequency, highest yields were obtained when the depth of water applied was equal to that lost in evapotranspiration. Low irrigation frequency and low depth of irrigation resulted in lower yields. Increase in yield with increase in frequency and depth of water was due to optimum available moisture and nutrients in the root zone throughout the crop period. The results from the trial indicated that on sandy loam soils of poor water retentive capacity, high yields can be obtained with frequent irrigations with the depth of water applied equal to that lost in evapotranspiration.     

Assessing the response of chickpea (Cicer aeritinum L.) yield to irrigation water on two soils in Punjab (India): A simulation analysis using the CROPMAN model

Shrinking water resources in northwest India calls for diversification from a rice–wheat cropping system to low-water-requiring crops and development of water-efficient technologies in Punjab state. Chickpea, because of its lower water demand (evapotranspiration) and irrigation requirement has been identified as a suitable alternate crop to wheat. Simulations, averaged over 18 years, using the CROPMAN model indicated that the yield of chickpea on coarse- to medium-textured soils was higher in a rice–chickpea cropping system compared with maize–chickpea and mung–chickpea systems because of increased availability of water. Yield response of chickpea to irrigation depended upon soil texture, the timings and number of irrigations. The optimum yield (2 t ha⁻¹) on coarse- to medium-textured soils after rice can be obtained with one heavy pre-plant and two post-plant irrigations, i.e., one in mid-February and one in mid-March synchronizing irrigations with flowering and grain development stages. Grain yield with irrigation water followed a quadratic function and linear with evapotranspiration. Water use efficiency and evapotranspiration was curvilinear. Grain yield was significantly sensitive to water stress during the pod setting to grain development period irrespective of soil texture.     

DRAINMOD-S: Water management model for irrigated arid lands,crop yield and applications

The primary objective of an agriculture water management system is to provide crop needs to sustain high yields. Another objective of equal or greater importance in some regions is to reduce agriculture impacts on surface and groundwater quality. Kandil et al. (1992) modified the water management model DRAINMOD to predict soil salinity as affected by irrigation water quality and drainage system design. The objectives of this study are to incorporate an algorithm to quantify the effects of stresses due to soil salinity on crop yields and to demonstrate the applications of the model. DRAINMOD-S, is capable of predicting the long-term effects of different irrigation and drainage practices on crop yields. The overall crop function in the model includes the effects of stresses caused by excessive soil water conditions (waterlogging), soil water-deficits, salinity, and planting delays. Three irrigation strategies and six drain spacings were considered for all crops. In the first irrigation strategy, the irrigation amounts were equal to evapotranspiration requirements by the crops, with the addition of a 10 cm depth of water for leaching applied during each growing season. In the second strategy, the leaching depth (10 cm) was applied before the growing season. In the third strategy, a leaching depth of 15 cm was applied before the growing season for each crop. Another strategy (4th) with more leaching was considered for bean which is the crop most sensitive to salinity. In the fourth strategy, 14 days intervals were used instead of 7 and leaching irrigations were applied: 15 cm before the growing season and 10 cm at the middle of the growing season for bean. The objective function for these simulations was crop yield. Soil water conditions and soil salinity were continuously simulated for a crop rotation of bean, cotton, maize, soybean, and wheat over a 19 years period. Yields of individual crops were predicted for each growing season. Results showed that the third irrigation strategy resulted in the highest yields for cotton, maize, soybean and wheat. Highest yields for bean were obtained by the fourth irrigation strategy. Results are also presented on the effects of drain depth and spacing on yields. DRAINMOD-S is written in Fortran and requires a PC with math-coprocessor. It was concluded that DRAINMOD-S is a useful tool for design and evaluation of irrigation and drainage systems in irrigated arid lands.     

Water use, crop coefficients, and irrigation management criteria for camelina production in arid regions

Camelina sativa (L.) Crantz is an oilseed crop touted as being suitable for production in the arid southwestern USA. However, because any significant development of the crop has been limited to cooler, rain-fed climate-areas, information and guidance for managing irrigated-camelina are lacking. This study measured the crop water use of a November-through-April camelina crop in Arizona using frequent measurements of soil water contents. The crop was grown under surface irrigation using five treatment levels of soil water depletion. The seed yields of treatments averaged 1,142 kg ha⁻¹ (8.0% seed moisture) and were generally comparable with camelina yields reported in other parts of the USA. Varying total irrigation water amounts to treatments (295–330 mm) did not significantly affect yield, whereas total crop evapotranspiration (ET_c) was increased for the most frequently irrigated treatment. However, total ET_c for the camelina treatments (332–371 mm) was markedly less than that typically needed by grain and vegetable crops (600–655 mm), which are commonly grown during the same timeframe in Arizona. The camelina water-use data were used to develop crop coefficients based on days past planting, growing degree days, and canopy spectral reflectance. The crop coefficient curves, along with information presented on camelina soil water depletion and root zone water extraction characteristics will provide camelina growers in arid regions with practical tools for managing irrigations.     

微喷补灌对夏玉米产量和水分利用效率的影响

[目的]提高夏玉米用水效率.[方法]2018—2019年设置4个微喷补灌处理,分别以0～10(W10)、0～20(W20)、0～30(W30)和0～40(W40)cm为目标湿润土层,补灌的目标土壤含水率为相应土层的田间持水率,补灌时期均为夏玉米播种时、拔节期开始时和抽雄期开始时;以传统畦灌模式(CK)为对照,研究了不同...     

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.     

Compaction of sandy soils for irrigation management

Summary Several irrigation management experiments were conducted at different locations on sandy soils in Haryana State to overcome excessive permeability, poor soil moisture retention and storage in the root zone. Subsurface compaction to 30–40 cm depth created by 6 passes of a 1,500 kg tractor-driven iron roller, 24 to 48 h after irrigation, was found to be beneficial in reducing irrigation requirement. In general, yield of different crops was not affected significantly by surface rolling, except that of mustard which increased significantly. Slight increase in subsurface compaction, about 0.1 g cm^–3, increased the soil moisture retention and reduced the infiltration rate and saturated hydraulic conductivity. Hydraulic conductivity was a better parameter than bulk density for evaluating the effect of rolling. The depth of irrigation water applied in rolling treatment was about 58–74% that of the no-rolling control. Compaction thus reduced water input to these sandy soils without adversely affecting the crop yield.     

Managing irrigation and drainage systems in arid areas in the presence of shallow groundwater: case studies

Two field studies were conducted on the west side of the San Joaquin Valley of California to demonstrate the potential for integrated management of irrigation and drainage systems. The first study used a modified cotton crop coefficient to calculate the irrigation schedule controlling the operation of a subsurface drip system irrigating cotton in an area with saline groundwater at a depth of 1.5 m. Use of the coefficient resulted in 40% of the crop water requirement coming from the groundwater without a loss in lint yield. The second study evaluated the impact of the installation of controls on a subsurface drainage system installed on a 65 hectare field. As a result of the drainage controls, 140 mm less water was applied to the tomato crop without a yield loss. A smaller relative weight of tomatoes classified as limited use, was found in the areas with the water table closest to the soil surface.     

Yield and water relations of wheat as influenced by irrigation and depth of tillage

Summary Development of a ploughpan has been reported in Bangladesh for almost all ploughed soils which are puddled for transplanted rice cultivation. Field information on the water requirement of dryland crops such as wheat and the effects of loosening the dense layer on crop yield and water use efficiency are very limited. Field experiments were, therefore, conducted in the grey floodplain soil of Sonatala series (Aeric Haplaquept) to study the irrigation and tillage effects on the yield and water relations of wheat (Triticum aestivum L. cv. Sonalika). The split plot design experiment comprised four irrigation treatments in the mainplots viz. W₀ = no irrigation, W₁ = irrigation of 5 cm at 4 weeks after planting, W₂-W₁ + irrigation(s) of 5 cm each at irrigation water to cummulative pan evaporation (IW/CPE) ratio of 0.75 and W₃- W₁ + irrigation(s) of 5 cm eacht at IW/CPE ratio of 0.50. The sub-plot tillage depth treatments were: A-7.5 cm (traditional), B-15 cm, C-22.5 cm, D-22.5 cm practised in alternate wheat seasons. Measurements were made of grain and straw yield, soil water depletion and water expense efficiency.Irrigation had no effect on grain or straw yield. Tillage to 15 cm increased wheat yield by about 15% over traditional depth to ploughing. In general, deep tillage coupled with one irrigation at four weeks after planting produced the largest wheat yield.Soil water depletion (SWD) in the 0–90 cm profile was greatest in the treatment receiving two irrigations, one at 4 weeks and again at IW/CPE ratio of 0.50. The average SWD in this treatment was 113 in 1982–83 and 82 mm in 1983–84. Plots receiving traditional tillage (7.5 cm) had the greatest SWD. Total water expense were the greatest in treatments receiving three irrigations. The maximum water expense efficiency (WEE) of wheat was observed in the non-irrigated plots in 1982–83 and 1983–84, respectively. Deep tillage treatments, in general, had significantly greater WEE than those under traditional ploughing. Intensive irrigation and efficient soil and water management are important factors in enhancing crop productivity. The former not only permits judicious water use but also better utilization of other production factors thereby leading to increased crop yield which, in turn, helps stabilize the farming economy. The best way to meet increasing demand for water is to adopt efficient water management practices to increase water use efficiency.Irrigation should aim at restoring the soil water in the root zone to a level at which the crop can fully meet its evapo-transpiration (ET) requirement. The amount of water to be applied at each irrigation and how often a soil should be irrigated depend, however, on several factors such as the degree of soil water deficit before irrigation, soil types, crops, and climatic conditions (Chaudhury and Gupta 1980).Knowledge of movement of water through the soil is imperative to efficient water management and utilization. The presence of a dense pan impedes water movement into the sub-soil. As a result, the top soil becomes saturated by irrigation and sensitive dryland crops can fail as this plough layer impedes the penetration of roots into deeper soil layers and decreases water extraction. Crops growing in these soils often undergo severe water stress within 5–8 days after rainfall or irrigation (Lowry et al. 1970). Due to decrease rates of water flow, the lower soil layer may remain unsaturated and as a result, the recharge and soil water storage in the profile are considerably decreased (Sur et al. 1981).In Bangladesh, ploughpans develop to varying degree in almost all ploughed soils (Brammer 1980). They are particularly marked in soils which are puddled for transplanted rice cultivation where the pan is usually only 8–10 cm below the soil surface and 3–5 cm thick. Its presence is generally regarded as advantageous for cultivation of transplanted rice in that it prevents excessive deep percolation losses of water. But in the same soil this cultivation for a subsequent dryland crop would adversely affect yield. A slight modification of the plough layer could enable good yields of both rice and a dryland crop to be obtained in the same soil in different seasons (Brammer 1980). The sub soils have a good bearing capacity, both when wet and dry and the pan can easily be reformed, if desired, for cultivating transplanted rice after a dryland crop like wheat.Professor of Soil Science, Dhaka University, Dhaka, Bangladesh     

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。     

Response of wheat to saline irrigation and drainage

The response of wheat (Triticum aestiuum L.) to varying depths of irrigation, quantity of water applied and to the drainage conditions was studied in 2 m × 2 m × 2 m size lysimeters filled in with a sandy loam soil. Saline water with an electrical conductivity of 8.6 dS m⁻¹ was used for irrigation. The treatments included four irrigations of 5 cm depth, four irrigations of 7 cm, and three irrigations of 9 cm, scheduled on the basis of cumulative pan evaporation, while the drainage conditions were represented by the drained and undrained lysimeters. Another treatment, using good quality water for irrigation, represented the potential yield of the crop. The growth parameters, as well as the yield, showed an improvement with larger irrigation depth increments in the drained lysimeters. But, in contrast, in the undrained lysimeters, the yield was reduced with larger irrigation depth increments, mainly due to a sharp rise in water table depth during the irrigation cycles. The rise and fall in water table showed a high sensitivity and were also highly disproportionate to the irrigation and evapotranspiration events. The yield tended to be higher with a smaller depth of water applied more frequently in the undrained lysimeters. But, in view of the limitations of conventional surface irrigation to apply water in smaller depth increments, an improved drainage is imperative for cropping in shallow saline water table conditions.     

Effect of subsurface drip irrigation on onion yield

Subsurface drip system is the latest method of irrigation. The design of subsurface drip system involves consideration of structure and texture of soil, and crop’s root development pattern. A 3-year experiment was conducted on onion (Allium Cepa L., cv. Creole Red) in a sandy loam soil from October to May in 2002–2003, 2003–2004 and 2004–2005 to study the effect of depth of placement of drip lateral and different levels of irrigation on yield. Tests for uniformity of water application through the system were carried out in December of each year. Three different irrigation levels of 60, 80 and 100% of the crop evapotranspiration and six placement depths of the drip laterals (surface (0), 5, 10, 15, 20 and 30 cm) were maintained in the study. Onion yield was significantly affected by the placement depth of the drip lateral. Maximum yield (25.7 t ha⁻¹) was obtained by applying the 60.7 cm of irrigation water and by placing the drip lateral at 10 cm soil depth. Maximum irrigation water use efficiency (IWUE) (0.55 t ha⁻¹ cm⁻¹) was obtained by placing the drip lateral at 10 cm depth. The greater vertical movement of water in the sandy-loam soil took place because of the predominant role of gravity rather than that of the capillary forces. Therefore, placement of drip lateral at shallow depths is recommended in onion crop to get higher yield.     

Effect of seasonal water stress imposed on drip irrigated second crop watermelon grown in semi-arid climatic conditions

A study was conducted to determine the water stress effect on yield and some physiological parameters including crop water stress index for drip irrigated second crop watermelon. Irrigations were scheduled based on replenishment of 100, 75, 50, 25, and 0% soil water depletion from 90 cm soil depth with 3-day irrigation interval. Seasonal crop evapotranspiration (ET) for I₁₀₀, I₇₅, I₅₀, I₂₅, and I₀ were 660, 525, 396, 210, and 70 mm in 2003 and 677, 529, 405, 221, and 75 mm in 2004. Fruit yield was significantly lowered by irrigation water stress. Average water-yield response factor for both of the years was 1.14. The highest yield was obtained from full irrigated treatment as 34.5 and 38.2 t ha⁻¹ in 2003 and 2004, respectively. Lower ET rates and irrigation amounts in water stress treatments resulted in reductions in all measured parameters, except water-soluble dry matter concentrations (SDM). Canopy dry weights, leaf relative water content, and total leaf chlorophyll content were significantly lowered by water stress. Yield and seasonal ET were linearly correlated with mean CWSI values. An average threshold CWSI value of 0.17 before irrigation produced the maximum yield and it could be used to initiate the irrigation for watermelon.