Evaluating deficit irrigation management strategies for grain sorghum using AquaCrop

Many wells in the US Central Plains can no longer meet full crop water requirements due to declines in Ogallala aquifer water levels. A study was conducted in Southwest Kansas to determine optimum limited irrigation strategies for grain sorghum. Objectives were to (1) calibrate and validate the AquaCrop model, (2) apply AquaCrop to assess the effect of varying climate, planting dates, and soil types on yield, and (3) evaluate water productivities and optimal irrigation needs. Experimental data of grain sorghum were used to calibrate and validate AquaCrop. Planting date was found to substantially affect biomass and grain yield, and hence, considerably affect water productivities. The highest grain water productivities were obtained with late planting in a wet season. Late planting was associated with lower irrigation requirements. Depending on local conditions, we recommend planting to occur between June 1st and June 10th. Grain sorghum yield was optimized on sandy soils of southwestern Kansas with irrigation of 100–275 mm for early, 150–275 mm for normal and 100–275 mm for late planting. The optimal irrigation on silt loam soils for the corresponding planting dates were 175–350, 175–250 and 125–250 mm, respectively, with the lowest and highest in the range being for the wet and dry climate season conditions. Fluctuations in grain sorghum prices had a substantial impact on economic water productivity. Overall planting grain sorghum under optimum conditions combined with deficit irrigation improved water productivity.     

Responses of grain sorghum to variable water supply under two irrigation frequencies

Summary Two experiments were conducted with Sorghum bicolor (L.) Moench Cv. Pioneer 846 in a deep loam soil in the 1977 season. Experiment I consisted of two line-source sprinkler plots, one irrigated at two-day intervals (HF) and the other every 10 to 14 days (NF). In comparable treatments of both regimes, the seasonal amount of water applied was the same. Since the subsoil was very dry at planting, the different amounts of water applied led to the development of a range of water stresses from none to severe. Experiment II was conducted in an adjacent area with a fully wetted soil profile. The treatments were irrigated every week (I) and nonirrigated (NI). Applied water was measured after each irrigation. Soil water content, leaf water potential, leaf-area index, ground cover and dry-matter accumulation were measured at frequent intervals, and yields were taken at the end of the growing season. Linear relations were found between both total dry-matter production and grain yield and seasonal evapotranspiration (ET) in both HF and NF regimes. With seasonal values of ET near the potential, grain yield and dry-matter production did not differ between irrigation frequencies. At low seasonal ET values, however, the NF regime gave greater yields of dry-matter and grain than did the HF regime.     

Replanting strategies for grain sorghum under risk

Risk analysis of replanting strategies for grain sorghum at three Kansas locations was conducted using stochastic dominance techniques. Yield data were simulated for seven planting dates, six seeding rates or target plant populations, and three maturity classes over a 33-year period using weather data for each year at each location. The results showed that optimal planting dates, seeding rates, and maturity classes vary by location and risk preference. In northeast and southcentral Kansas, planting at later rather than earlier dates was preferred as risk aversion increased. In southwest Kansas, generally no change occurred in the preferred strategy as the level of risk aversion increased. Early- and medium-maturing hybrids and low-to-moderate seeding rates often were selected. Late-maturing hybrids never were selected by risk-averse managers. The degree of risk aversion did not significantly affect the selection of a replanting strategy for southcentral and southwest Kansas, but did for northeast Kansas. However, whether managers replanted immediately or delayed, replanting varied with the replanting decision date and degree of risk aversion. Replanting on the first replanting decision date in southwest Kansas rather than delaying 2 weeks or more was preferred by all risk-averse managers. More strongly risk-averse managers in the northeast and all risk-averse producers in southcentral Kansas preferred to delay replanting of damaged stands, in some cases by 2–4 weeks after the decision date. Results also showed that when a stand was damaged late in the season, the expected yield from the damaged stand had to be lower than that from a stand damaged early in the season in order for replanting to occur. Price changes had only minor impacts on the preferred replanting strategies. A higher crop price caused replanting to occur more often, because the yield reduction of a damaged stand required for replanting to be economically feasible grew smaller as the price increased.     

Response of corn, grain sorghum, and sunflower to irrigation in the High Plains of Kansas

Groundwater is being mined in much of the irrigated area of the central and southern High Plains of the USA. Profits and risks inherent in irrigation management depend on the association between crop yield and level of water application. Research was conducted over a 14 year period (1974–1987) to establish the yield vs. water application relationships of corn, grain sorghum, and sunflower. The research was located near Tribune, Kansas, USA on a Ulysses silt loam soil. Plots were level-basins to which water was added individually through gated pipe. Irrigation studies of the three crops were located adjacent to each other. Irrigation treatments were arranged in completely randomized blocks with three replications. As total irrigation amount increased from 100 to 200, 200 to 300, and 300 to 400 mm, sunflower yield increased by 0.53 Mg ha⁻¹, 0.43 Mg ha⁻¹, and 0.37 Mg ha⁻¹, respectively. Corn outyielded grain sorghum at total irrigation amounts of 345 mm and above. Yield increase over continuous dryland was greater in corn than in grain sorghum at total irrigation amounts above 206 mm. Therefore, if grain mass is the consideration, grain sorghum is a better choice than corn at less than 206 mm of irrigation, whereas corn is a better choice than grain sorghum at more than 206 mm of irrigation.     

Design of a farm layout for irrigation with limited discharges

In order to improve the irrigation efficiencies of small farms employing cavity wells for their water supply, an experimental study was conducted at the Central Soil Salinity Research Institute, Karnal. The cavity wells of the Karnal region do not have any discharge regulating devices for improving the irrigation efficiencies. The only way of improving these efficiencies is by designing an efficient irrigation layout, so that uniform water application is accomplished. The present study involves field determination of the opportunity time at each point along the border from advance and recession curves and computing the depth of cumulative infiltration from the infiltration rate curve. The irrigation efficiencies are also calculated from soil moisture measurements made before and after each irrigation.The results of this study show that a realistic field assessment of the irrigated border efficiencies is obtained through a soil moisture measurement procedure. The procedure, based on opportunity time and infiltration, overestimates the irrigation efficiencies due to the empirical nature of the infiltration equation. For small farms, with a limited discharge of 10 l/s, an irrigation layout of borders of 50–70 m in length and 6–8 m in width is recommended.     

Modelling seasonal grain sorghum yields in subtropical Australia

The seasonal variability of irrigated grain sorghum yields has been examined in terms of the quantitative effects of environmental variables on the yield components of the average genotype using stepwise regression techniques. Flow models have been formulated of yield development indicating the likely pattern of interaction between plant and environmental factors.Growth before anthesis affected both leaf area development (amount and display) and the number of sites (flowers) where grain could be produced. The most important yield component was grain number per unit ground area and this, more than grain size, affected the amount of photosynthate which could be stored. An equation was developed in which the assimilate produced before anthesis could be partitioned between vegetative dry matter production and number of flowers, according to accumulated temperature and radiation.Anthesis assimilate supply played a rôle in determining actual grain number set and influenced initial grain growth rates—and hence potential grain size.Post-anthesis assimilate surplus determined actual grain development and was related to temperature and radiation terms. It has been postulated that the balance between assimilate supply and respiratory loads during grainfilling dictates not only the magnitude of the optimum temperature response surface but also the tuning of the optimal temperature. Under reduced assimilate surplus, grain sorghum showed temperate, rather than tropical, growth behaviour, posing potential limits for tropical production zones.     

Forage sorghum yield and water use efficiency under variable irrigation

The response of forage sorghum [Sorghum bicolor (L.) Moench] to three irrigation treatments in a semiarid environment was studied in the field for two seasons. Treatments were light frequent, moderate less frequent, and heavy infrequent irrigation, where irriga-tion water at 8 mm day^–1 was delivered every 7, 10, and 13 days, respectively. These irrigation regimes meant heavier water inputs with increasing irrigation frequency. Plant heights and leaf area indices of forage sorghum were higher in the frequently watered plots than in plots where irrigation water was delivered less frequently. Averaged over the two seasons, maximum dry matter (DM) yields were 16.3, 11.8, and 10.5 tonnes ha^–1 for frequent, intermediate, and infrequent irrigation regimes, respectively. Light, frequent irrigation resulted in a significantly higher water use efficiency (WUE) compared to the other two regimes, thus increasing the return from irrigation. These results suggest that in such semiarid environments, DM yields and WUE of forage sorghum could be increased by combining light irrigation with a short interval. Received: 6 February 1997     

Corn and alfalfa production as influenced by limited irrigation

Summary Several corn and alfalfa varieties were subjected to varying levels of water deficits under field conditions over a two-year period at the Utah State University Evans farm at Logan, Utah. Dry matter yields of corn and alfalfa varieties showed a linear relationship to evapotranspiration (E _t . In most cases grain yields also showed a linear response to E _t . When relative yields of dry matter and grain of corn varieties were related to relative E _t it was found that the slopes of the linear regression lines changed more between the two years than between the varieties within a given year. It was found that yields predicted by Hanks' (1974) model were highly correlated with measured yields for both corn and alfalfa.in coperation with Agric. Exp. StnGraduate student and professor, respectively     

Effects of limited irrigation on lettuce and chinese cabbage yields

Summary Yield response of lettuce (Lactuca sativa L.) and Chinese cabbage (Brassica campestris L. Group pekinensis) to eight different drip irrigation rates was determined in 1980–1984 at Lalamilo, Hawaii. Treatments were arranged in a gradient irrigation design replicated three times and were irrigated daily with amounts ranging from 0.76 mm to 6.09 mm. Yield response from a 0 treatment, equal to rainfall, was also measured. Marketable yield increased linearly with increased water application up to 49.7 Mg/ha for lettuce and 73.1 Mg/ha for Chinese cabbage with an associated seasonal evapotranspiration of 205 mm and 209 mm for lettuce and Chinese cabbage, respectively. The relationship between deficit relative yield (yield divided by maximum yield) and deficit relative evapotranspiration (evapotranspiration divided by maximum evapotranspiration) was linear with a deficit response coefficient of 1.07 for lettuce and 1.35 for Chinese cabbage. Marketable percentage of total potential biomass production decreased linearly with a decrease in marketable yield. Lettuce head size also decreased linearly with a decrease in marketable yield. Water use efficiency (yield divided by water applied) was 24 and 36 kg/m3 of water for lettuce and Chinese cabbage, respectively.     

Sugar beet production as influenced by limited irrigation

Summary Sugar beets (Beta vulgaris L.) were grown on a Millville silt loam soil at Logan, Utah to study the relationships between yield (total dry matter, fresh root, and sucrose) and various levels of irrigation simulating different types of limited irrigation under drought conditions. There were four harvest dates. A model, PLANTGRO, was tested for yield prediction under the imposed conditions. A line source sprinkler irrigation system which applied irrigation water from an excess to a zero amount, was used to impose the various levels of irrigation. Irrigation was continued throughout the season on half of the area and terminated at mid-season on the other half. For both irrigation treatments, yield responses to irrigation levels were large. Unlike continuous irrigation throughout the season, when irrigation was terminated in mid-season, there was no increase in yield (total dry matter, fresh root, or sucrose) from harvest 1 to harvest 4. The relation of yield to termination of irrigation depended on the amount of stored soil water at the time of termination. Yield and relative yield exhibited a strong linear relationship with ET. Percent sucrose was not significantly affected by irrigation regimes or harvest date, but tended to increase as amount of applied irrigation water increased. The model PLANTGRO gave good predictions for relative yields of fresh roots, sucrose, and total dry matter under full-season irrigation. The relative yield relations of fresh roots, sucrose and total dry matter were similar. Where irrigation was terminated in mid-season the model slightly under-predicted yield at high irrigation levels.Contribution from Utah Agricultural Experiment Station, Utah State University, UT 84322, USA     

Real-time adaptive irrigation scheduling under a limited water supply

The problem of real-time irrigation scheduling under limited water supply is considered. The goal is to develop an irrigation operation policy which maximizes crop yields and is responsive to current season changes in weather and other variables. Because irrigation decisions are sequential and dependent on crop and soil water status, and also because crop yields can only be known at the end of the season, the decisions are arrived at by a two-stage process. In the first or the design stage, irrigations are planned for the entire season at weekly intervals using historical data and an optimal irrigation scheduling model. In the second stage, the decisions for the subsequent weeks are revised each week after updating the status of the system with real time data up to that week and solving the irrigation optimization model once again for the new conditions. Thus, each week an irrigation decision is made, the entire planning horizon is kept in view. The procedure is illustrated by application to a case study.     

两茬收割饲用甜高粱灌溉定额试验研究

为探索饲用甜高粱最佳灌溉定额和节水效果,设置了不同灌溉定额(2 400, 3 000, 3 600, 4 200, 4 800 m³/hm²)对两茬收割饲用甜高粱生长和生物产量的影响的田间试验.结果表明,甜高粱茎粗和株高的峰值分别出现在播后62 d和158 d.随灌溉定额增加甜高粱在形态上表现为株高增加、茎粗减小的趋势.在头茬收割(播后76 d)时,株高日增长率最大,为4.00~4.89 cm/d.两茬收割甜高粱鲜生物学产量为63.9~115.5 t/hm²,干生物学产量为12.7~21.4 t/hm²,全生育期耗水量为326.95~504.24 mm,鲜生物学产量WUE为15.53~24.63 kg/m³,干生物学产量WUE为3.89~4.51 kg/m³.灌溉定额为4 200 m³/hm²时,甜高粱总鲜、干生物量最大,灌溉定额为4 800 m³/hm²时,甜高粱总鲜、干生物量增幅不大.从节水和增加生物量角度而言,畦灌方式下的两茬收割饲用甜高粱全生育期灌水4次,灌水定额为1 050 m³/hm²,灌溉定额为4 200 m³/hm²的灌溉效果最佳.     

A rule-based method for the development of crop management systems applied to grain sorghum in south-western France

A generic approach is proposed for the development and testing of crop management systems in contrasting situations of water availability. Ecophysiological knowledge, expertise, regional references and simulation models are combined to devise management strategies adapted to production targets and constraints. The next stage consists of converting these crop management strategies into logical and consistent sets of decision rules. Each rule describes the reasoning which is used to apply a technical decision by taking account of observed or simulated environmental conditions or predicted agronomic risks.

This approach was applied to design crop management systems for grain sorghum (Sorghum bicolor L. Moench.) in south-western France. For spring-sown crops, management (sowing date, plant density, varietal choice, N fertilizer rate and timing) was based on water availability, both for economic and environmental reasons. Specific sets of decision rules were written for irrigated and rainfed conditions. The establishment of rules was based on agronomic principles (e.g. for plant density) or on the application of a simulation model (e.g. for sowing date, variety). N fertilization and irrigation were applied using combined N and water dynamic models.

A novel methodology combining crop diagnosis, analytical trials and crop simulation was developed to evaluate the management systems. An irrigated and a rainfed rule-based management system were compared near Toulouse (S.W. France) from 1995 to 2002. The profitability of rainfed low-input management was confirmed for sorghum in spite of high yields under irrigation (up to 10 t ha⁻¹). The adaptation of sorghum management in rainfed conditions was mainly achieved through early maturing cultivars and by reducing N applications by 65%.     

宁夏引黄灌区滴灌条件下春小麦干物质转移与灌浆特征

为优化春小麦滴灌灌溉制度,提高水分利用效率,对宁夏引黄灌区滴灌条件下灌水对春小麦千粒质量、干物质转移和灌浆特征的影响展开研究。在总灌水量一致的条件下,分别设置增大三叶期、分蘖期和拔节期灌水量(W1)、增大分蘖期、拔节期和抽穗期灌水量(W2)、增大拔节期、抽穗期和灌浆期灌水量(W3)、各生育期灌水量平均分配(W4)和对照(CK)5个水量分配处理,研究春小麦千粒质量、各营养器官干物质转移量及籽粒灌浆特性。W3籽粒千粒质量最大,花后37 d其千粒质量为53.96 g,较CK大2.64%。W2的干物质转移总量、同化物转移总量和干物质转移对籽粒的贡献率均为最大,分别为0.67 g/株、2.992 g/株和22.165%。不同水量分配下小麦籽粒灌浆速率满足Logistic模型,经过水量优化分配,W2最大灌浆速率出现时间提前0.366 d,虽然最大灌浆速率有所降低,但是通过增加快增期时间(增加0.15 d)和活跃灌浆期时间(增加2.35 d),可以显著提高籽粒干物质积累量,收获时穗粒质量较CK提高32.1%,该处理籽粒产量也达到最大,较CK提高6.88%。因此可以通过优化灌水量分配,增加小麦千粒质量,提高各器官对籽粒的干物质转移量及灌浆速率,进而达到高产高效的目的。     

灌水控制下限对冬小麦产量和品质的影响

为制定冬小麦的优质高效灌溉指标,通过3个生长季（2005－2008年）的人工控水试验,研究了不同灌水控制下限对冬小麦生长、产量和品质的影响。结果表明,与对照相比,播种—拔节前期水分胁迫对冬小麦生长、产量及品质的负面影响不明显,且可节水11.68%～18.18%,水分利用效率提高8.33%～12.5%;拔节—抽穗前期水分胁迫对冬小麦生长的抑制作用最明显,使籽粒出粉率、蛋白质质量分数显著降低,面团形成时间和稳定时间显著缩短,产量降低6.56%～9.08%,但可节水24.29%～31.95%,水分利用效率提高6.19%～10.63%;抽穗扬花期水分胁迫对冬小麦生长没有明显影响,虽显著提高了籽粒蛋白质、湿面筋、氨基酸质量分数和出粉率,但减产9.96%～11.35%,水分利用效率仅提高了4.12%～5.62%;灌浆成熟期水分胁迫对冬小麦生长影响最小,籽粒蛋白质、湿面筋、氨基酸质量分数和出粉率均显著提高,但大幅度降低了产量,水分利用效率只提高了1.03%～5.95%。华北地区冬小麦优质高效节水灌溉指标是：播种—拔节前期、拔节—抽穗前期、抽穗扬花期和灌浆成熟期的灌水控制下限分别为50%、65%、70%和65%田间持水率。     

Water-use efficiency of sorghum and groundnut under traditional and current irrigation in the Gezira scheme, Sudan

In the Gezira irrigation scheme in central Sudan, serious symptoms of water waste have been identified in the last two decades, especially in sorghum and groundnut fields. To quantify losses, water-use efficiencies and related parameters were obtained for these two food crops under the traditional attended daytime water application and the newly evolved unattended continuous watering method. In this on-farm research, the neutron scattering method was used to determine the actual soil water deficits of the two crops. A simple Penman equation was used for approximating reference crop evapotranspiration and evaporation losses from standing water and wet soil surface. An updated approach using the Penman-Monteith equation was additionally applied. The study revealed wastage of irrigation water in both irrigation methods but at different rates and also differently for each crop. In the attended field, the average seasonal over-irrigation, which is the difference between average application depth Q and average soil moisture deficit SWD, was observed to range between 0.4 and 1.5 of SWD (0.3 and 0.6 of Q) and the corresponding values in the unattended field were 0.6 and 3.2 of SWD (0.4 and 0.8 of Q). Higher values are shown by the groundnut subplots, which crop also suffers from excess water, and by the drier year as well as in the unattended fields. A first approximation is given, still including readily available water at harvest, of minimum water requirements in attended watering for maximum yields. In the drier year, when more irrigation water was applied, an amount equal to 30-50% of these minimum water requirements was lost in evaporation from standing water/wet surface, which is the main unproductive water. More frequent land levelling aiming at minimum standing water in better attended irrigation and farm management (e.g. weeding) are priority measures proposed. The quantitative on-farm water waste determinations represent the innovative content of this paper. Knowing precisely how large the problem is and being able to quantify its components will contribute much to the arguments of those who wish to take the proposed measures.     

Genotypic differences of maize in grain yield response to deficit irrigation

This study was undertaken to investigate genotypic differences of five maize cultivars in grain yield response to two different modes of deficit irrigation, conventional deficit irrigation and partial root zone irrigation. Three irrigation treatments were implemented: (1) FULL irrigation, the control treatment where plant water requirement, 100% Class-A pan evaporation, was fully met and the furrows on both sides of the plant rows were irrigated; (2) partial root zone irrigation (PRI), 35% deficit irrigation, compared to FULL treatment, was applied in every other furrow thus irrigating only one side of the plant rows. The furrows irrigated were alternated every irrigation; (3) conventional deficit irrigation (CDI), the same amount of water as PRI was applied in furrows on both sides of the plant rows, similar to FULL irrigation treatment. Five maize cultivars (P.31.G.98, P.3394, Rx:9292, Tector and Tietar) showing extreme growth response to water stress were selected out of ten cultivars tested with earlier completed greenhouse-pot experiment. A split-plot experimental design, comprising three irrigation treatments and five maize cultivars with four replicates, was used during two years of work, in 2005 and 2006. Total of nine irrigations, with one-week irrigation interval, were annually applied using a drip-irrigation system. Soil water status was monitored using a neutron moisture gauge, in addition to measuring leaf water potential and above-ground biomass production throughout the growing season. Grain yield and other yield attributes were measured at harvest as well as assessing differences in plant root distributions. Decrease in grain yield and harvest index of the tested cultivars, compared to FULL treatment, was proportionally less under PRI than CDI. Whether or not a significant yield advantage can be obtained under PRI compared to CDI showed significant (P < 0.05) genotypic variability. Tector and Tietar among the tested cultivars of maize showed significantly higher grain yield (P < 0.05) under PRI than CDI. The yield advantage of the genotypes (P.3394 and Tector) under PRI compared to CDI seems related to their enhanced root biomass developed under PRI.     

The effect of an intelligent surface drip irrigation method on sorghum biomass, energy and water savings

Over the last few decades, precipitation has decreased as a result of climate change. This change increases crop water requirements, while irrigation water is wasted because of improper irrigation scheduling. Soil moisture sensors could be used to improve irrigation scheduling and save both water and energy. The objective was to study the energy and water savings, and the gross margin achieved, when using an intelligent surface drip irrigation method on sorghum bicolor (L.) Moench. In the years 2008 and 2009, a study was conducted at the farm of the University of Thessaly, Central Greece. A Class A evaporation pan and an automated frequency domain reflectometry soil moisture sensor were used for irrigation scheduling. Two treatments in four replications were organized in a randomized complete block design: (1) pan surface drip irrigation (PSDI100) and amount of water equal to 100 % of the daily evapotranspiration (ETd), as determined by a Class A evaporation pan, and (2) automated surface drip irrigation (ASDI100) and amount of water equal to 100 % of the ETd, as determined by an automated soil moisture sensor. The mean dry biomass production and the gross margin were greater in the PSDI100 treatment. The fully automated treatment remained profitable despite the high first costs. The mean water saving was 12.5 %, while the mean energy saving was 12.4 %, and the irrigation water-use efficiency was higher in the ASDI100 treatment.     

Response of sorghum to moisture stress using line source sprinkler irrigation I. Plant-water relations

The response of sorghum (Sorghum bicolor L.) to moisture stress during the post-rainy season was studied at ICRISAT research center on a medium deep Alfisol using a line source sprinkler irrigation system. Changes in soil moisture content, stomatal conductance, leaf-water potential and leaf temperature of sorghum as a function of distance away from the line source sprinkler system were monitored throughout the season. Use of the line source technique facilitated the imposition of a range of moisture stress levels as indicated by increased water use by sorghum closer to the line source compared with the crop farther away from the line source. Canopy response measured in terms of stomatal conductance, leaf-water potential, and leaf temperature clearly reflected the gradient in moisture stress perpendicular to the line source.