Evaluating irrigation strategies for lettuce by simulation: 2. Nitrogen budget

A mechanistic water-flow, solute transport and crop growth model was used to compare three irrigation strategies for lettuce in French Mediterranean conditions: (1) the current strategy based on the occurrence of rainfall, (2) a strategy based on a simplified modelling of the soil water balance and (3) a strategy based on tensiometer readings. Water and solute instantaneous fluxes versus time were simulated for two growing periods (summer and autumn) over 100 years. The climatic data were provided by a weather generator. Leenhardt et al. (1998) compared the three strategies with regard to their effects on water flows in the soil. The present paper deals with their effects on the nitrogen balance and particularly nitrate leaching.

The three strategies rank similarly for all processes of the N cycle. Strategy 1 generates soil water content conditions favourable to denitrification and nitrate leaching and less favourable to mineralisation and nitrification, leading to a low NO⁻₃ availability for the crop, and thus a low nitrate uptake. Strategy 1 minimizes the water stress but induces the maximum nitrogen stress. At the other extreme is strategy 3, whereas strategy 2 has an intermediate position, but closer, however, to strategy 3 than 1. A direct conclusion would suggest avoiding strategy 1 and choosing strategy 3.     

Analysis of maize growth for different irrigation strategies in northeastern Spain

Water availability is the key factor determining maize yields in NE Spain. Irrigation is needed to obtain economic yields but it is costly and water supply is sometimes insufficient. The aim of this research was to test a simple simulation model for evaluating different irrigation strategies, especially under water-limited conditions. The LINTUL model was adapted and parameterized using experimental data from the 1995 season. Most parameters were obtained from experiments, although some were taken from the literature. This model is based on the concept of light use efficiency, incorporates a soil water balance and simulates phenology, crop leaf area, biomass accumulation and yield. It was tested on independent data from the 1995 and 1996 seasons under different irrigation treatments. The model predicted the flowering date within ±5 days of the observed values. Leaf area index was predicted satisfactorily, except under extreme water-stress conditions, where it was overestimated. In general, soil moisture content and yield were accurately predicted. In the 1996 experiment measured yields ranged from 6.4 to 13.6 t ha⁻¹ and simulated yields from 6.5 to 12.2 t ha⁻¹. These results show that the LINTUL model can be used as a tool for exploring the consequences on maize yields of different irrigation strategies in NE Spain. Analysis of the model identified a process that strongly affects yield loss due to drought, but for which present understanding is still insufficient: the effects of drought on leaf senescence and canopy architecture.     

Effect of Irrigation and N-Fertilization (Fertigation) Scheduling on Tomato in the Jordan Valley

Tomato ( Lycopersicon esculentum mill. cv. Petopride ) is the most important vegetable crop in Jordan; its production is characterized by inadequate irrigation and fertilization practices, especially under open field conditions. A field study was carried out to determine the effect of different irrigation intervals and different N-fertilizer doses on water use, tomato yields and residual soil nitrogen.
Results indicated significant differences in water use and tomato yields between irrigation treatments. Highest yield (51.4 ton ha⁻¹) was obtained under three irrigations per week with 504 mm total water supply, whereas under irrigation once a week 35.3 ton ha⁻¹were produced with 353 mm total water supply. There were no significant differences in yield between fertigation with ten equal time intervals and fertigations with intervals as per crop requirements, the yields were 47.1 ton ha⁻¹ and 44.5 ton ha⁻¹, respectively. However, yield was significantly lower with three fertigations at equal intervals and equal doses (35.8 ton ha⁻¹) throughout the season. There were no significant differences between mineral nitrogen forms in terms of yield effects. Significant irrigation effects were observed on total soil nitrogen. Residual soil N was 0.052% in the surface layer (0–30 cm), and 0.030% in the subsurface layer (30–60 cm).     

沙漠绿洲隔沟交替灌溉辣椒的耗水特征及作物系数研究

为研究交替灌溉条件下辣椒的作物系数及土壤水分变化,用水量平衡法测定辣椒各生育期耗水量及土壤水分动态,实测得到辣椒各生育期的作物系数,并将作物系数与辣椒叶面积指数回归分析,研究隔沟交替灌溉辣椒各生育期的耗水特征及作物系数。结果表明,辣椒结果盛期是耗水量最大的时期,在辣椒定植—坐果期和结果末期交替灌溉处理作物的总耗水量与对照无显著差异,但结果盛期交替灌溉的总耗水量显著减少。辣椒交替灌溉下0~60 cm土层是土壤含水量变化活跃层。交替灌溉对辣椒的作物系数有显著影响,且随亏水程度的增大作物系数减小,‘美国红’的作物系数小于‘陇椒2号’。辣椒叶面积指数与作物系数呈显著的线性正相关。     

Combining the simulation crop model AquaCrop with an economic model for the optimization of irrigation management at farm level

Water resources used in irrigated agriculture are increasingly scarce, particularly in many countries where irrigation has undergone recent expansion. To optimize the limited resources available, optimization models provide useful tools for technical and economic analyses. One of the key inputs of these models is the yield response to water which is often simulated with empirical water production functions. At present, dynamic crop simulation models, such as AquaCrop (Steduto et al., 2009) offer alternative predictions of crop responses to different irrigation strategies as inputs to economic optimization. A model at farm scale was developed and applied to an area in South-western Spain to assist farmers in pre-season decision making on cropping patterns and on irrigation strategies. Yield predictions were obtained from the AquaCrop model which was validated for four different crops. The model simulated the impact on farm income of: (a) irrigation water constraints; (b) variations in agricultural policies; (c) changes in product and water prices; and, (d) variations in the communication to farmers of the specific level of irrigation water allocation. The applications of the models to the study area showed that currently, the changes in cropping patterns induced by the agricultural policy will encourage water savings more than an increase in water prices. Under water restrictions, the best strategy combines planting of low water use crops in part of the area to release water to grow more profitable crops with greater water needs. The model predicted a strong negative impact on farm income of delaying a decision on the level of seasonal water allocation by the water authority, reaching up to 300 € ha⁻¹ in the case of the study area.     

Productivity and water use efficiency of sweet sorghum as affected by soil water deficit occurring at different vegetative growth stages

The growth and production of sweet sorghum [Sorghum bicolor (L.) Moench] crops under semi-arid conditions in the Mediterranean environment of southern Italy are constrained by water stress. The effects of temporary water stress on growth and productivity of sweet sorghum were studied during three seasons at Rutigliano (Bari, Italy). The aim of this research was to evaluate the sensitivity of phenological stages subjected to the same water deficit. In a preliminary study it was observed that stomata closed when pre-dawn leaf water potential (Ψ_b) became lower than −0.4 MPa. This criterion was used in monitoring plant water status in three different plots: one never stressed and two stressed at different phenological stages (‘leaf’ and ‘stem’) when mainly leaves or stems were growing, respectively. An evaluation of the sensitivity of phenological stages subjected to identical water stress was obtained by comparing the above-ground biomass and WUE of drought crops with those of the well-irrigated crop (up to 32.5 t ha⁻¹ of dry matter and 5.7 g kg⁻¹). The sensitivity was greatest at the early stage (‘leaf’), when a temporary soil water stress reduced the biomass production by up to 30% with respect to the control and WUE was 4.8 g kg⁻¹ (average of three seasons). These results help quantify the effects of water constraints on sweet sorghum productivity. An irrigation strategy based on phenological stage sensitivity is suggested.     

利用农田水量平衡模型评价棉田不同的灌溉制度

本文以田间试验为基础，应用农田水量平衡理论和棉花对不同水分亏缺的反应，建立了一个棉花不同灌溉制度的评价模型，文中用ＦＡＯ－４６提供的Ｐｅｎｍａｎ－Ｍｏｎｔｅｉｔｈ方法计算了棉花生育期间逐日参考作物蒸散量，利用Ｉｓａｒｅｇ模型［５］计算了棉田逐日实际蒸散量。研究结果表明，利用农田水量平衡模型可对棉花灌溉进行有效管理。通过对几种灌溉方案的评价，定量化地分析了不同灌溉制度对棉花产量的影响程度和水分胁迫出现的时间；明确了在黄淮海平原棉田灌溉重点在棉花生育前期，即苗期，盛蕾－初花期；给出了该地区棉花各生育时期的需水量和每日的平均耗水强度     

Effects of Deficit Drip Irrigation Ratios on Cotton (Gossypium hirsutum L.) Yield and Fibre Quality

Increasing irrigation costs and declining water availability compel producers to adapt irrigation strategies for maximum crop yield and water use efficiency. A field trial was conducted to observe the effects of various drip irrigation ratios (IR-0, IR-25, IR-50, IR-75 and IR-100) on water use efficiency (WUE), the irrigation water use efficiency (IWUE), lint yield, yield components and fibre quality at two upland cotton varieties during 2004 and 2005. WUE was found to increase from 0.62 to 0.71 kg m⁻³ as the irrigation water applied was reduced from 100 % to 75 % of soil water depletion. Deficit irrigation of cotton with drip irrigation at 75 % treatment level (IR-75) did not decrease seed cotton yield and yield components during 2 years, with the exception of the number of bolls in 2005. Among fibre quality parameters, no significant differences in fibre length, fineness, uniformity index and elongation were detected between the 100 % and 75 % irrigation levels in 2005. The results revealed that irrigation of cotton with a drip irrigation method at 75 % level had significant benefits in terms of saved irrigation water without reducing yield, and high WUE indicated a definitive advantage of employing deficit irrigation under limited water supply conditions.     

Influence of Variable Amounts of Irrigation Water and Nitrogen Fertilizer on Growth, Yield and Water Use of Grain Sorghum

Sorghum hybrid CSH-6 was grown in fields in Delhi, India between July–November 1986 in order to study the effect of nitrogen nutrition and irrigation on dry matter accumulation, grain yield and water use. The treatments included 40 Kg Nha⁻¹ combined with two irrigations (30 DAS, 60 DAS), one irrigation (60 DAS) and no irrigation respectively. Rainfall during the crop season was only 17 cm. The unirrigated plants were considerably water stressed and exhibited very low leaf water potential, less leaf area, delayed anthesis, longer crop duration but shorter grain filling duration. The ears showed sterility and yield was only 0.41 t ha⁻¹ without nitrogen fertilization. Addition of nitrogen fertilizer had no significant effect on yield in unirrigated plants. A single irrigation 60 DAS increased yield due to increase in both grain number and grain weight per ear in fertilized and unfertilized crop respectively. Two irrigations in the unfertilized crop increased the yield to 2.2 t ha⁻¹ while similar treatment in the fertilized crop did not increase the yield significantly. Irrigation increased the WUE for grain yield. The results indicate that nitrogen stress and water stress reduced grain yield primarily through grain number rather than grain weight. Irrigation relieved both water stress and nutrient stress. Nitrogen nutrition was not beneficial under severe water stress conditions but was considerably helpful under mild stress. Biomass, grain yield and harvest index show significant correlation with preanthesis water use.     

Irrigation Scheduling and Watermelon Yield Model for the Jordan Valley

A crop yield and soil water management simulation model (CRPSM) developed at Utah State University was modified, calibrated and tested using local weather data and field results from a trickle irrigation experiment with different mulching on watermelon ( Citrullus lanatus ), carried out at the University of Jordan Research Station, in the Jordan Valley.
Simulated irrigation schedules were then applied with some of the four options provided by the model. The water yield index, WYI, introduced by B attikhi and H ill (1985) to select the most efficient schedule as based on yield and water use efficiency, was then determined. WYI ranged from 27 to 87. The field schedule, WM₂, had a WYI of 62. Whereas, the model provided a much better schedule, WM₇ (WYI = 86). WM₇ requires 17 irrigations of 2.0 cm per irrigation totaling a water supply of 44.1 cm with an irrigation season starting on April 7 to give a yield equivalent to the potential yield, 80.0 MT/ha. On the other hand, the best field schedule, WM₂ under transparent mulch, required 14 irrigations to provide 45.9 cm (including rainfall and soil moisture change), with a season starting on April 28 resulted in a yield of 68.8 MT/ha. So we can see that by using the same amounts of total water supply but with different schedule we can get the potential yield. The model has, therefore, provided few better schedules that can be tested in the field at lower costs before final recommendations are made.     

Water Use and Yield of Wheat under Unmulched and Mulched Conditions in Laterite Soil of the Indian Sub-continent

A held experiment was conducted during three winter seasons on West Bengal laterite soil to study the effect of irrigation and paddy straw mulch on water consumption. Water use efficiency and yield of wheat are reported. Both irrigation and mulch increased wheat yield significantly; there was also significant interaction between irrigation and straw mulch application: three irrigations combined with mulch resulted in 21.6 q ha^-1 wheat grain yield compared with 17.5 q ha^-1 for three irrigations without mulch. Mulch consistently increased irrigation response. Both irrigation and mulch increased water consumption and water use efficiency of the wheat crop. To compare the two irrigation treatments, irrigation at crown root initiation followed up by at flowering stage gave higher values of water use efficiency as well as higher grain yield than that of irrigation applied at panicle stage followed by at crown root initiation.     

Assessment of irrigation scenarios to improve performances of Lingot bean (Phaseolus vulgaris) in southwest France

In the context of climate change, producing the same amount of food with less water has become a challenge all over the world. This is also true for the Lingot bean production in the area of Castelnaudary of southwest France where market competition with imported bean has made it crucial to achieve high yields to maintain production in the area. The use of an appropriate and robust crop model can help to identify crop management solutions to face such issues. We used SSM-legumes, a crop model generic to legume species, as well as field observations recorded over five years on eight farms of the Castelnaudary area to assess the effect of different irrigation scenarios on bean yield and water consumption. First, it was demonstrated that the SSM-legumes model is robust in simulating the development and growth of Lingot bean in non-stressed or moderately stressed conditions of this region regarding water and nutrient availability. Then, the use of the model to compare irrigation scenarios provided guidance on how to improve irrigation management for Lingot bean production. These results showed that farmers could achieve slightly higher yields with less water by basing irrigation decisions on the water content of the soil.     

Performance of Rapeseed-mustard Cultivars under Various Moisture Regimes on the Gangetic Alluvial Plain of West Bengal

A Field trial was conducted during 1988–89 and 1989–90 at Water Management Research Station, Memari. Bidhan Chandra Krishi Viswavidyalaya, Burdwan, to study the effect of three different irrigation regimes, namely rainfed (I₁) (No irrigation), one irrigation (I₂) at flowering and two irrigations (I₃ at flowering and at sihqua formation stages) on the grain yield and water expenses on four different rapeseed-mustard cultivars, namely Pusa Bold, Pusa Baroni, Varuna and DIR 247. The variety DIR 247 recorded maximum grain yield (12.1 qha') followed by Pusa Baroni (11.8 q ha⁻¹). The variety Varuna showed the lowest water use efficiency (48.1 kg ha⁻¹ cm⁻¹) while DIR 247 showed the maximum value of 57.0 kg ha⁻¹ cm⁻¹. The number of irrigations significantly increased the grain yield. Two irrigations, one at flowering and at siliqua formation stage increased grain yield by 28 % over the rainfed plots. During the crop growth period the actual water expenses among the cultivars in any moisture regime were more or less similar. The interaction between varieties and irrigation levels were, however, not significant.     

冬小麦优化灌溉模型研究及其应用

在土壤－植物－大气系统中，土壤有效水分贮存量、作物耗水量和有效降水量是农田水分平衡的主要组成因子。土壤水分预报模型综合分析了它们的动态变化，给出了未来农田实际蒸散量和土壤有效水分含量；决策模型则根据不同生育阶段的作物水分批、产量反庆系数、和以取得最大目的的目标函数，优化函数决策－灌或不灌、灌溉期和灌溉量。     

Adaptation of crop management to water-limited environments

Farmers must combine various crop management strategies to cope with water deficit resulting from soil, weather or limited irrigation: drought escape, avoidance or tolerance, crop rationing, irrigation (supplemental, deficit). These strategies can be translated into six objectives: (i) increasing soil stored water at plant sowing, (ii) increasing soil water extraction, (iii) reducing the contribution of soil evaporation to total water-use, (iv) optimizing the seasonal water use pattern between pre- and post-anthesis, (v) tolerate water stress and recover after stress alleviation, and (vi) irrigate at the most-sensitive growth phases. To reach these objectives, tactical decisions concern soil tillage, type of crop and cultivar, sowing date and density, N fertilization, irrigation timing, amount and frequency. Flexible crop management systems based on decision rules should be preferred to the recommendation of fixed packages of techniques. Timing, intensity, and predictability of drought (intermittent, terminal) are important features for choosing the cropping alternatives. Simulation models may help the farmer to select best-bet management options on the basis of historical long-term weather records. Simple soil and plant indicators associated with real-time decision support systems should be developed to revise the initial management plan by integrating in-season weather information.     

Nitrogen uptake and N-use efficiency of Mediterranean cotton under varied deficit irrigation and N fertilization

Efficient N management is essential to optimize yields and reduce degradation of the environment, but requires knowledge of deficit irrigation effects on crop yields and crop N outputs. This study assessed the N content and N-use efficiency of cotton over the 2008 and 2009 growing seasons in a single field site of the Thessaly Plain (central Greece). The experiment consisted of nine treatments with three fertilizer rates (60, 110 and 160 kg N ha⁻¹) split into three irrigation levels (approx. 1.0, 0.7 and 0.4 of the amount applied by the producer). Reduced water supply induced a shift in the distribution of N within the plant with seeds becoming an N sink under conditions of water stress. Total crop N increased linearly with irrigation level and reached a maximum average of 261 and 192 kg N ha⁻¹ in 2008 and 2009, respectively. Fertilizer application did not trigger a crop N or yield response and indicated that N inputs were in excess of crop needs. Variation in weather patterns appeared to explain annual differences of nitrate-N in the top soil and N uptake by the crop.The index of lint production efficiency (iNUE) detected crop responses caused by irrigation and annual effects, but failed to account for excessive N inputs due to mineral fertilizer applications. A maximum average iNUE of 9.6 was obtained under deficit irrigation, whereas an iNUE of 8.1 was obtained under 40 cm irrigation when crop N uptake was not excessive (192 kg ha⁻¹ in 2009). In contrast, NUE, as an estimator of N recovery efficiency, identified excessive fertilizer inputs as N losses to the environment and indicated that 60 kg N ha⁻¹ was a rate of high N removal efficiency and long-term N balance. However, NUE failed to account for crop N responses to irrigation and weather/management patterns. In this case study, neither index was able to detect all the factors influencing the N mass balance and both were required in order to provide a comprehensive evaluation of the environmental performance of our cropping system.     

水氮耦合对地膜玉米免耕轮作小麦干物质积累及产量的影响

前茬地膜玉米免耕种植后茬小麦水氮高效利用生产技术是绿洲灌区作物高效生产的新型农田管理技术。为构建该区地膜减量和水氮高效生产技术, 2015—2017年通过3年田间试验, 研究两种耕作方式、2种灌水水平和3个施氮量组合对小麦干物质积累和产量及产量构成的协同效应, 其中耕作方式为覆膜玉米茬免耕直播(NT)和玉米茬传统耕作(CT), 灌水量为传统灌水(I2)和传统灌水减量20% (I1), 施氮量为纯N 225 kg hm ^-2 (N3)、180 kg hm ^-2 (N2)和135 kg hm ^-2 (N1)。结果表明, 耕作方式、灌水水平、施氮量对小麦群体生长速率、干物质积累量均有显著影响。与CT相比, NT显著增大全生育期生长速率, 提高22.0%~28.0%, NT促进小麦地上干物质积累, 提高6.4%~7.4%, 收获期生物产量提高5.4%~15.1%。免耕低灌(NTI1)较传统耕作高灌(CTI2)的生长速率增大7.7%~13.4%, 干物质积累量提高3.1%~5.9%, 收获期生物产量提高8.7%~10.5%。免耕低灌中施氮(NTI1N2)较传统耕作高灌中、高施氮(CTI2N2、CTI2N3) 生长速率分别增大6.9%~20.5%与4.1%~14.0%, 收获期生物产量分别提高7.8%~9.7%与4.8%~10.2%。NT比CT增产10.1%~10.4%, NTI1较CTI2、CTI1分别增产13.0%~14.8%与9.4%~10.1%, NTI1N2比CTI2N2、CTI2N3分别增产3.7%~9.8%与15.2%~22.0%。从产量构成因素分析, NTI1N2提高了单位面积成穗数、穗粒数和千粒重, NTI1N2处理组合更有利于穗数、千粒重的增加。通径分析进一步证明, NTI1N2增产的主要原因是增加了单位面积穗数和千粒重。因此, 在施氮量为180 kg hm ^-2的基础上, 玉米茬地膜再利用免耕技术组装减少20%灌溉量(1920 m ³ hm ^-2)轮作小麦模式是河西灌区小麦高效生产的可行措施。     

Establishment of a crop evapotranspiration calculation model and its validation

In order to contribute knowledge on the method used to calculate the actual crop evapotranspiration, soil, crop, atmosphere, and water spatial structure were integrated into a complete system. Based on the energy balance equation and aerodynamic equation, the meteorological data was reduced and the crop physiological parameter was increased, then the crop evapotranspiration calculation model under natural conditions was derived. The crop evapotranspiration calculation model was verified by the water balance formula using data generated from corn, potato, and flue-cured tobacco grown under field conditions for three consecutive years from 2017 to 2019. The results showed that: from 2017 to 2019, the average root mean square error for measured and calculated evapotranspiration of corn, potato, and flue-cured tobacco at different growth times were 0.5948, 0.4753, and 0.3326, respectively, the mean deviation, mean absolute error, and mean relative error were small, and the coefficient of determination and consistency index were both greater than 0.9100. The measured and calculated crop evapotranspiration of the selected crops increased at first and then decreased gradually as the crops matured, and finally decreased to harvest evapotranspiration, showing a parabolic trend. The crop evapotranspiration calculation model not only reflects the actual evapotranspiration of crops at different growth time but also reflects the change law of actual crop evapotranspiration. The model does not need the correction of soil moisture content, irrigation method, and crop coefficient and can directly calculate the actual crop evapotranspiration. It has the characteristics of consistency between the calculated value and the measured value, strong applicability, simple calculation process, and high accuracy and has the best effect on monitoring soil moisture and crop water shortage sensitivity. The model is significance in that it guides for monitoring soil moisture, determining actual crop evapotranspiration, crop water shortage index, and high yield and efficiency under water-saving conditions.     

气候变化情景下阿拉善盟灌溉玉米对水资源的适应性研究

为了研究未来气候变化情景下,非充分灌溉对玉米产量的影响情况及玉米生产可采取的节水型灌溉方式,利用作物模型和PRECIS模拟输出的吉兰泰地区的未来时段的气候数据、历史观测数据,模拟设计了多个灌溉水平,分析当地玉米的水分生产力,并选取最优灌溉方案。结果表明：当前种植中存在灌溉用水偏多、无效灌溉现象明显;未来气候变化情景下,不同的灌溉水平对玉米生育期的影响较小,主要影响产量和生物量;A2、B2气候情景下,采用58%充分灌溉量的灌溉方式其水分生产力均达0.68、0.80 kg/m³的最大值,玉米单产可达充分灌溉条件下的77%~82%,并且比充分灌溉方式节约用水2700 m³/hm²。因此,当地应采取选择非充分灌溉方式,节约农用水,提高水分生产力。     

Saline Drainage Water, Irrigation Frequency and Crop Species Effects on Some Physical Properties of Soils

This field study evaluated the effects of water quality, irrigation frequency and crop species on some physical properties of soils. The experiment had a split-split-plot design, with three irrigation water qualities (normal water, drainage water and a 1 : 1 mixture of freshwater and drainage water) as the main treatments, two irrigation frequencies (at 7- and 14-day intervals) as the subtreatments and two crops (barley and alfalfa) as the subsubtreatments. The soil infiltration rate was highest in the barley plot receiving freshwater irrigation at weekly intervals. The lowest soil infiltration rate was found in alfalfa plots receiving saline irrigation water at 14-day intervals. Bulk density and proportions of micropores [pore radius (r) < 1.4 µm] were higher and the proportion of macropores (r > 14.4 µm) was lower in barley than in alfalfa. Saline irrigation caused the greatest decrease in total porosity. The soil infiltration rate was higher with more frequent irrigation, and was highest in alfalfa plots receiving freshwater irrigation. The decrease in soil bulk density and infiltration rate was greater with saline drainage water, irrespective of the crop grown and the irrigation frequency.