Quantifying rainfall-runoff relationships on the Dera Calcic Fluvic Regosol ecotope in Ethiopia

Droughts, resulting in low crop yields, are common in the semi-arid areas of Ethiopia and adversely influence the well-being of many people. The objective of this study was to assess the benefit that in-field rainwater harvesting (IRWH) would have, compared to conventional tillage, on maize yields on a semi-arid ecotope at Dera situated on the eastern part of the Rift Valley. Rainfall-runoff measurements were made during 2003 and 2004 on 2 m × 2 m plots provided with a runoff measuring system and replicated three times for each treatment. There were two treatments: conventional tillage (CT) and no-till (NT), the latter with a flat surface that promotes runoff and therefore IRWH. Rainfall intensity was measured at 1 min intervals with an automatic tipping bucket instrument, and runoff was measured after each rain event. Measured runoff as a function of rainfall intensity and duration from half the rainfall-runoff events was used to determine the critical parameters of a appropriate runoff model. The calibrated model was found to be capable of predicting runoff in a satisfactory way.Rainfall-runoff measurements were made during the rain seasons in 2003 and 2004 during which there were 25 rain events with >9 mm of rain. There was no statistical difference between the runoff on the two treatments. The measured runoff (R) for the two rain seasons, expressed as a fraction of the rainfall during the measuring period (P), i.e. R/P, gave values of 0.46 and 0.39 for the NT and CT treatments, respectively.Results from 7 years of field experiments with IRWH at Glen in South Africa were used to estimate the yield benefit of NT for Dera compared to CT. The results were 696 and 494 kg ha⁻¹ for 2003 and 2004, respectively. Based on the estimated average long-term maize yield of 2000 kg ha⁻¹ at Dera, this was an estimated yield increase ranging from 25% to 35%.     

Water use and distribution profile under pulse and oilseed crops in semiarid northern high latitude areas

Oilseed and pulse crops have been increasingly used to replace conventional summer fallow and diversify cropping systems in northern high latitude areas. The knowledge of water use (WU) and its distribution profile in the soil is essential for optimizing cropping systems aimed at improving water use efficiency (WUE). This study characterized water use and distribution profile for pulse and oilseed crops compared to spring wheat (Triticum aestivum L.) in a semiarid environment. Three oilseeds [canola (Brassica napus L.), mustard (Brassica juncea L.) and flax (Linum usitatissimum L.)], three pulses [chickpea (Cicer arietinum L.), dry pea (Pisum sativum L.) and lentil (Lens culinaris Medik.)], and spring wheat were seeded in removable 100 cm deep × 15 cm diameter lysimeters placed in an Aridic Haploboroll soil, in southwest Saskatchewan in 2006 and 2007. Crops were studied under rainfed and irrigated conditions where lysimeters were removed and sampled for plant biomass and WU at various soil depths. Wheat yields were greater than pulse crop yields which were greater than oilseed yields, and WUE averaged 4.08 kg ha⁻¹ mm⁻¹ for pulse crops, 3.64 kg ha⁻¹ mm⁻¹ for oilseeds, and ranged between 5.5 and 7.0 kg ha⁻¹ mm⁻¹ for wheat. Wheat used water faster than pulse and oilseed crops with crop growth. Pulse crops extracted water mostly from the upper 60 cm soil depths, and left more water unused in the profile at maturity compared to oilseeds or wheat. Among the three pulses, lentil used the least amount of water and appeared to have a shallower rooting depth than chickpea and dry pea. Soil WU and distribution profile under canola and mustard were generally similar; both using more water than flax. Differences in WU and distribution profile were similar for crops grown under rainfall and irrigation conditions. A deep rooting crop grown after pulses may receive more benefits from water conservation in the soil profile than when grown after oilseed or wheat. Alternating pulse crops with oilseeds or wheat in a well-planned crop sequence may improve WUE for the entire cropping systems in semiarid environments.     

Nutrient management adaptation for dryland maize yields and water use efficiency to long-term rainfall variability in China

Rainfed crop production in northern China is constrained by low and variable rainfall, and by improper management practices. This study explored both the impact of long-term rainfall variability and the long-term effects of various combinations of maize stover, cattle manure and mineral fertiliser (NP) applications on maize (Zea mays L.) yields and water use efficiency (WUE) under reduced tillage practices, at Shouyang Dryland Farming Experimental Station in northern China from 1993 onwards. The experiment was set up according to an incomplete, optimal design, with 3 factors at five levels and 12 treatments including a control with two replications. Grain yields were greatly influenced by the amount of rain during the growing season, and by soil water at sowing. Annual mean grain yields ranged from 3 to 10 t ha⁻¹ and treatment mean yields from 4.2 to 7.2 t ha⁻¹. The WUE ranged from 40 in treatments with balanced nutrient inputs in dry (weather/or soil) years to 6.5 kg ha⁻¹ mm⁻¹ for the control treatments in wet years. The WUE averaged over the 15-year period ranged from 11 to 19 kg ha⁻¹ mm⁻¹. Balanced combination of stover (3000-6000 kg), manure (1500-6000 kg) and N fertiliser (105 kg) gave the highest yield and hence WUE. It is suggested that 100 kg N per ha should be a best choice, to be adapted according to availability of stover and manure. Possible management options under variable rainfall conditions to alleviate occurring moisture stress for crops must be tailored to the rainfall pattern. The potentials of split applications, targeted to the need of the growing crop (response nutrient management), should be explored to further improve grain yield and WUE.     

Effects of conservation tillage practices on winter wheat water-use efficiency and crop yield on the Loess Plateau,China

In the semi-humid to arid loess plateau areas of North China, water is the limiting factor for rain-fed crop yields. Conservation tillage has been proposed to improve soil and water conservation in these areas. From 1999 to 2005, we conducted a field experiment on winter wheat (Triticum aestivum L.) to investigate the effects of conservation tillage on soil water conservation, crop yield, and water-use efficiency. The field experiment was conducted using reduced tillage (RT), no tillage with mulching (NT), subsoil tillage with mulching (ST), and conventional tillage (CT). NT and ST improved water conversation, with the average soil water storage in 0–200 cm soil depth over the six years increased 25.24 mm at the end of summer fallow periods, whereas RT soil water storage decreased 12 mm, compared to CT. At wheat planting times, the available soil water on NT and ST plots was significantly higher than those using CT and RT. The winter wheat yields were also significantly affected by the tillage methods. The average winter wheat yields over 6 years on NT or ST plots were significantly higher than that in CT or RT plots. CT and RT yields did not vary significantly between them. In each study year, NT and ST water-use efficiency (WUE) was higher than that of CT and RT. In the dry growing seasons of 1999–2000, 2004–2005 and the low-rainfall fallow season of 2002, the WUE of NT and ST was significantly higher than that of CT and RT, but did not vary significantly in the other years. For all years, CT and RT showed no WUE advantage. In relation to CT, the economic benefit of RT, NT, and ST increased 62, 1754, and 1467 yuan ha⁻¹, respectively, and the output/input ratio of conservation tillage was higher than that of CT. The overall results showed that NT and ST are the optimum tillage systems for increasing water storage and wheat yields, enhancing WUE and saving energy on the Loess Plateau.     

Effects of rainfall harvesting and mulching technologies on water use efficiency and crop yield in the semi-arid Loess Plateau, China

In semi-arid areas, crop growth is greatly limited by water. Amount of available water in soil can be increased by surface mulching and other soil management practices. Field experiments were conducted in 2005 and 2006 at Gaolan, Gansu, China, to determine the influence of ridge and furrow rainfall harvesting system (RFRHS), surface mulching and supplementary irrigation (SI) in various combinations on rainwater harvesting, amount of moisture in soil, water use efficiency (WUE), biomass yield of sweet sorghum (Sorghum bicolour L.) and seed yield of maize (Zea mays L.). In conventional fields without RFRHS, gravel-sand mulching produced higher biomass yield than plastic-mulching or straw-mulching. In plastic-mulched fields, an increasing amount of supplemental irrigation was needed to improve crop yield. There was no effect of RFRHS without plastic-covered ridge on rainwater harvesting when natural precipitation was less than 5 mm per event. This was due to little runoff of rainwater from frequent low precipitation showers, and most of the harvested rainwater gathered at the soil surface is lost to evaporation. In the RFRHS, crop yield and WUE were higher with plastic-covered ridges than bare ridges, and also higher with gravel-sand-mulched furrows than bare furrows in most cases, or straw-mulched furrows in some cases. This was most likely due to decreased evaporation with plastic or gravel-sand mulch. In the RFRHS with plastic-covered ridges and gravel-sand-mulched furrows, application of 30 mm supplemental irrigation produced the highest yield and WUE for sweet sorghum and maize in most cases. In conclusion, the findings suggested the integrated use of RFRHS, mulching and supplementary irrigation to improve rainwater availability for high sustainable crop yield. However, the high additional costs of supplemental irrigation and construction of RFRHS for rainwater harvesting need to be considered before using these practices on a commercial scale.     

Water use and water use efficiency of sweet corn under different weather conditions and soil moisture regimes

Plant growth and development are influenced by weather conditions that also affect water use (WU) and water use efficiency (WUE) and ultimately, yield. The overall goal of this study was to determine the impact of weather and soil moisture conditions on WU and WUE of sweet corn (Zea mays L. var rugosa). An experiment consisting on three planting dates was conducted in 2006 at The University of Georgia, USA. A sweet corn genotype sh2 was planted on March 27 under irrigated and rainfed conditions and on April 10 and 25 under irrigated conditions only. Soil moisture was monitored using PR2 probes. Rainfall and irrigation were recorded with rain gauges installed in the experimental area while other weather variables were recorded with an automatic weather station located nearby. A water balance was used to obtain the crop's daily evapotranspiration (ETc). WUE was calculated as the ratio of fresh and dry matter ear yield and cumulative ETc. The potential soil moisture deficit (Dp) approach was used to determine the crop's moisture stress. Results were analyzed using a single degree freedom contrast, linear regression, and the least significant difference. WU and WUE of sweet corn were both markedly affected by the intra-seasonal weather variability and Dp. For both variables, significant (p < 0.05) differences were found between planting dates under irrigated conditions and between the irrigated and rainfed treatments. WU was as high as 268 mm for the April 10 planting date under irrigated conditions and as low as 122 mm for the March 27 planting date under rainfed conditions. The maximum soil moisture deficit was reached at the milky kernel stage and was as high as 343 mm for the March 27 planting date under rainfed conditions and as low as 260 mm for the April 10 planting date under irrigated conditions. Further work should focus on the impact of the intra-seasonal weather variability and soil moisture conditions during different crop stages to determine critical periods that affect yield.     

Irrigation strategies to improve the water use efficiency of wheat-maize double cropping systems in North China Plain

Water is the most important limiting factor of wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping systems in the North China Plain (NCP). A two-year experiment with four irrigation levels based on crop growth stages was used to calibrate and validate RZWQM2, a hybrid model that combines the Root Zone Water Quality Model (RZWQM) and DSSAT4.0. The calibrated model was then used to investigate various irrigation strategies for high yield and water use efficiency (WUE) using weather data from 1961 to 1999. The model simulated soil moisture, crop yield, above-ground biomass and WUE in responses to irrigation schedules well, with root mean square errors (RMSEs) of 0.029 cm³ cm⁻³, 0.59 Mg ha⁻¹, 2.05 Mg ha⁻¹, and 0.19 kg m⁻³, respectively, for wheat; and 0.027 cm³ cm⁻³, 0.71 Mg ha⁻¹, 1.51 Mg ha⁻¹ and 0.35 kg m⁻³, respectively, for maize. WUE increased with the amount of irrigation applied during the dry growing season of 2001-2002, but was less sensitive to irrigation during the wet season of 2002-2003. Long-term simulation using weather data from 1961 to 1999 showed that initial soil water at planting was adequate (at 82% of crop available water) for wheat establishment due to the high rainfall during the previous maize season. Preseason irrigation for wheat commonly practiced by local farmers should be postponed to the most sensitive growth stage (stem extension) for higher yield and WUE in the area. Preseason irrigation for maize is needed in 40% of the years. With limited irrigation available (100, 150, 200, or 250 mm per year), 80% of the water allocated to the critical wheat growth stages and 20% applied at maize planting achieved the highest WUE and the least water drainage overall for the two crops.     

Corn yield responses under crop evapotranspiration-based irrigation management

Improving irrigation water management is becoming important to produce a profitable crop in South Texas as the water supplies shrink. This study was conducted to investigate grain yield responses of corn (Zea mays) under irrigation management based on crop evapotranspiration (ET_C) as well as a possibility to monitor plant water deficiencies using some of physiological and environmental factors. Three commercial corn cultivars were grown in a center-pivot-irrigated field with low energy precision application (LEPA) at Texas AgriLife Research Center in Uvalde, TX from 2002 to 2004. The field was treated with conventional and reduced tillage practices and irrigation regimes of 100%, 75%, and 50% ET_C. Grain yield was increased as irrigation increased. There were significant differences between 100% and 50% ET_C in volumetric water content (θ), leaf relative water content (RWC), and canopy temperature (T_C). It is considered that irrigation management of corn at 75% ET_C is feasible with 10% reduction of grain yield and with increased water use efficiency (WUE). The greatest WUE (1.6 g m⁻² mm⁻¹) achieved at 456 mm of water input while grain yield plateaued at less than 600 mm. The result demonstrates that ET_C-based irrigation can be one of the efficient water delivery schemes. The results also demonstrate that grain yield reduction of corn is qualitatively describable using the variables of RWC and T_C. Therefore, it appears that water status can be monitored with measurement of the variables, promising future development of real-time irrigation scheduling.     

Soil water dynamics and water use efficiency in spring maize (Zea mays L.) fields subjected to different water management practices on the Loess Plateau, China

Soil water supply is the main limiting factor to crop production across the Loess Plateau, China. A 2-year field experiment was conducted at the Changwu agro-ecosystem research station to evaluate various water management practices for achieving favorable grain yield (GY) with high water use efficiency (WUE) of spring maize (Zea mays L.). Four practices were examined: a rain-fed (RF) system as the control; supplementary irrigation (SI); film mulching (FM); and straw mulching (SM) (in 2008 only). The soil profile water storage (W) and the crop evapotranspiration (ET) levels were studied during the maize growing season, and the GY as well as the WUE were also compared. The results showed that mean soil water storage in the top 200 cm of the profile was significantly (P < 0.05) increased in the SI (380 mm in 2007, 411 mm in 2008) and SM (414 mm in 2008) compared to the FM (361 mm in 2007, 381 mm in 2008) and RF (360 mm in 2007, 384 mm in 2008) treatments. The soil water content was lower at the end of growing season than before planting in the 60-140 cm part of the profile in both the RF and FM treatments. Cumulative ET and average crop coefficiency (K_c) throughout the whole maize growing season were significantly (P < 0.05) higher in the SI (ET, 501 mm in 2007, 431 mm in 2008; K_c, 1.0 in 2007, 0.9 in 2008) treatment than in the other treatments. Both FM and SI significantly improved the GY. The WUE were increased significantly (23-25%; P < 0.05) under the FM treatment. It was concluded that both SI and FM are beneficial for improving the yield of spring maize on the Loess Plateau. However, FM is preferable because of the shortage of available water in the area.     

Water use efficiency and associated traits in winter wheat cultivars in the North China Plain

Selecting more water efficient cultivars is an important way to reduce water use in a water-scarce region. The objectives of this study were to measure the grain yield and water use efficiency (WUE) of winter wheat (Triticum aestivum L.) cultivars to understand the genetic gains in yield and WUE and their associated physiological and agronomic traits in Hebei province, North China Plain (NCP). Two groups of winter wheat cultivars were tested. Group 1 included 16 winter wheat cultivars that were released between 1998 and 2002 and were tested during the 2002/2003 and 2003/2004 seasons under two water regimes. Group 2 included 10 cultivars released between 1970 and 2000, and were tested during the 2005/2006 and 2006/2007 seasons under three water regimes. Results showed that WUE increased substantially from 1.0-1.2 kg m⁻³ for cultivars from the early 1970s to 1.4-1.5 kg m⁻³ for recently released cultivars. There was also a variation in yield and WUE of about 20% among Group 1 cultivars. Most of the cultivars in both groups had similar responses to water supply. WUE was greater for less irrigated treatments and maximum grain production was achieved with moderate water deficit. The genetic gains in grain yield were associated with increasing in biomass, harvest index and kernel numbers per spike for cultivars released in different years. Among the Group 1 cultivars, the ones with higher yield generally had higher WUE. No significant correlations were found between WUE and physiological traits such as ash content, chlorophyll content, or relative water content among the cultivars released recently. However, a significant relationship was found between stomatal conductance or ash contents and WUE or grain yield among the Group 2 cultivars. Relationships were apparent between WUE and date of anthesis and harvest index (P < 0.05) in Group 1. Earlier flowering cultivars tended to have higher grain yield. In Group 2, flowering date was advancing by about 4 days over the 30 years of crop breeding. The positive relationship between grain yield and WUE for all the cultivars indicated that using a higher yielding cultivar has the potential to improve WUE and thereby to save water.     

Water-use efficiency of wheat-based rotation systems in a Mediterranean environment

Crop production in Mediterranean-type environments is invariably limited by low and erratic rainfall (200-600 mm year⁻¹), and thus soil moisture, and by high evapotranspiration resulting from high temperature. Consequently, a major research challenge is to devise cropping systems that maximize water-use efficiency (WUE). In a long-term trial in northern Syria (1986-1998) we compared the effects of seven wheat-based rotations on soil water dynamics and WUE in both the wheat and non-wheat phase. The cropping systems were durum wheat (Triticum turgidum L.) in rotation with fallow, watermelon (Citrullus vulgaris), lentil (Lens culinaris), chickpea (Cicer arietinum), vetch (Vicia sativa), medic pasture (Medicago spp.), and wheat. Seasonal recharge/discharge were identified using the neutron probe. Depth of wetting varied with seasonal rainfall (233-503 mm). Based on crop yields, WUE was calculated for each cropping option in relation to the durum wheat crop.The greatest limitation to growth was the supply of water and not the soil moisture storage potential. Wheat grain yield was dictated by the extent to which the alternative crops in the rotation dried out the soil profile, in addition to seasonal rainfall and its distribution. Chickpea and medic extracted as much water as continuous wheat. Wheat after these crops was solely dependent on current seasonal rainfall, but fallow, lentil, watermelon, and vetch did not deplete soil moisture to the same extent, leaving some residual soil moisture for the succeeding wheat crop. This difference in soil water resulted in a significant difference in wheat yield and hence WUE, which decreased in the following crop rotation sequence: fallow, medic, lentil, chickpea, and continuous wheat. However, on the system basis, the wheat/lentil or wheat/vetch systems were most efficient at using rainfall, producing 27% more grain than the wheat/fallow, while the wheat/chickpea system was as efficient as wheat/fallow system, with continuous wheat being least efficient. With N added to the cereal phase, system WUE of the system increased, being least for continuous wheat and greatest for wheat/lentil. Wheat-legume rotation systems with additional N input in the wheat phase not only can maintain sustainable production system, but also are more efficient in utilizing limited rainfall.     

灌水模式对油葵耗水量产量及经济效益的影响

通过5种灌水处理模式和对照旱地油葵田间试验,探讨了灌水模式对油葵耗水量、产量、水分利用效率以及经济收入的影响。结果表明,油葵出盘前和灌浆后耗水量比其他时段多50％以上。在油葵不同生育阶段耗水量随着灌水量增加而增加;灌水定额120mm,灌两次水的灌水模式的产量最高,为2268kg／hm^2,而水分利用效率最大值出现在灌水定额66mm的灌水模式,灌水量增加反而使水分利用效率下降。经济分析结果表明,纯收入最高值出现在灌水模式93mm灌二水的处理,为2871元／hm^2,灌水定额增加或减少均导致经济收入下降。统计分析结果表明,干旱年份（全生育期有效降水量123mm）灌二水时,为了兼顾产量、水分利用效率以及经济收入,油葵最佳总灌水量以208-218mm为宜。全生育期有效降水量超过350mm的丰水年份不应该再灌水。     

Effects of winter crop and supplemental irrigation on crop yield,water use efficiency and profitability in rainfed rice based cropping system of eastern India

Soil moisture availability is the main limiting factor for growing second crops in rainfed rice fallows of eastern India. Only rainfed rice is grown with traditional practices during the rainy season (June–October) with large areas (13 m ha⁻¹) remaining fallow during the subsequent dry season (November–March) inspite of annual rainfall of the order 1000–2000 mm. In this study an attempt was made to improve productivity of rainfed rice during rainy season and to grow second crops in rice fallow during dry (winter) season with supplemental irrigation from harvested rainwater. Rice was grown as first crop with improved as well as traditional farmers’ management practices to compare the productivity between these two treatments. Study revealed that 87.1–95.6% higher yield of rice was obtained with improved management over farmers’ practices. Five crops viz., maize, groundnut, sunflower, wheat and potato were grown in rice fallow during dry (winter) season with two, three and four supplemental irrigations and improved management. Sufficient amount of excess rainwater (runoff) was available (381 mm at 75% probability level) to store and recycle for supplementary irrigation to second crops grown after rice. Study revealed that supplemental irrigation had significant effect (P < 0.001) on grain yield of dry season crops and with two irrigation mean yields of 1845, 785, 905, 1420, 8050 kg ha⁻¹ were obtained with maize (grain), groundnut, sunflower, wheat and potato (tuber), respectively. With four irrigations 214, 89, 78, 81, 54% yield was enhanced over two irrigations in respective five crops. Water use efficiency (WUE) of 13.8, 3.35, 3.39, 5.85 and 28.7 kg ha⁻¹ was obtained in maize, groundnut, sunflower, wheat, potato (tuber), respectively with four irrigations. The different plant growth parameters like maximum above ground biomass, leaf area index and root length were also recorded with different levels of supplemental irrigation. The study amply revealed that there was scope to improve productivity of rainfed rice during rainy season and to grow another profitable crops during winter/dry season in rice fallow with supplemental irrigation from harvested rainwater of rainy season.     

Yield and water-production functions of two durum wheat cultivars grown under different irrigation and nitrogen regimes

Wheat (Triticum durum L.) yields in the semi-arid regions are limited by inadequate water supply late in the cropping season. Planning suitable irrigation strategy and nitrogen fertilization with the appropriate crop phenology will produce optimum grain yields. A 3-year experiment was conducted on deep, fairly drained clay soil, at Tal Amara Research Station in the central Bekaa Valley of Lebanon to investigate the response of durum wheat to supplemental irrigation (IRR) and nitrogen rate (NR). Three water supply levels (rainfed and two treatments irrigated at half and full soil water deficit) were coupled with three N fertilization rates (100, 150 and 200 kg N ha⁻¹) and two cultivars (Waha and Haurani) under the same cropping practices (sowing date, seeding rate, row space and seeding depth). Averaged across N treatments and years, rainfed treatment yielded 3.49 Mg ha⁻¹ and it was 25% and 28% less than half and full irrigation treatments, respectively, for Waha, while for Haurani the rainfed treatment yielded 3.21 Mg ha⁻¹, and it was 18% and 22% less than half and full irrigation, respectively. On the other hand, N fertilization of 150 and 200 kg N ha⁻¹ increased grain yield in Waha by 12% and 16%, respectively, in comparison with N fertilization of 100 kg N ha⁻¹, while for cultivar Haurani the increases were 24% and 38%, respectively. Regardless of cultivar, results showed that supplemental irrigation significantly increased grain number per square meter and grain weight with respect to the rainfed treatment, while nitrogen fertilization was observed to have significant effects only on grain number per square meter. Moreover, results showed that grain yield for cultivar Haurani was less affected by supplemental irrigation and more affected by nitrogen fertilization than cultivar Waha in all years. However, cultivar effects were of lower magnitude compared with those of irrigation and nitrogen. We conclude that optimum yield was produced for both cultivars at 50% of soil water deficit as supplemental irrigation and N rate of 150 kg N ha⁻¹. However, Harvest index (HI) and water use efficiency (WUE) in both cultivars were not significantly affected neither by supplemental irrigation nor by nitrogen rate. Evapotranspiration (ET) of rainfed wheat ranged from 300 to 400 mm, while irrigated wheat had seasonal ET ranging from 450 to 650 mm. On the other hand, irrigation treatments significantly affected ET after normalizing for vapor pressure deficit (ET/VPD) during the growing season. Supplemental irrigation at 50% and 100% of soil water deficit had approximately 26 and 52 mm mbar⁻¹ more ET/VPD, respectively, than those grown under rainfed conditions.     

Effect of timing of a deficit-irrigation allocation on corn evapotranspiration, yield, water use efficiency and dry mass

Water regulations have decreased irrigation water supplies in Nebraska and some other areas of the USA Great Plains. When available water is not enough to meet crop water requirements during the entire growing cycle, it becomes critical to know the proper irrigation timing that would maximize yields and profits. This study evaluated the effect of timing of a deficit-irrigation allocation (150 mm) on crop evapotranspiration (ETc), yield, water use efficiency (WUE = yield/ETc), irrigation water use efficiency (IWUE = yield/irrigation), and dry mass (DM) of corn (Zea mays L.) irrigated with subsurface drip irrigation in the semiarid climate of North Platte, NE. During 2005 and 2006, a total of sixteen irrigation treatments (eight each year) were evaluated, which received different percentages of the water allocation during July, August, and September. During both years, all treatments resulted in no crop stress during the vegetative period and stress during the reproductive stages, which affected ETc, DM, yield, WUE and IWUE. Among treatments, ETc varied by 7.2 and 18.8%; yield by 17 and 33%; WUE by 12 and 22%, and IWUE by 18 and 33% in 2005 and 2006, respectively. Yield and WUE both increased linearly with ETc and with ETc/ETp (ETp = seasonal ETc with no water stress), and WUE increased linearly with yield. The yield response factor (ky) averaged 1.50 over the two seasons. Irrigation timing affected the DM of the plant, grain, and cob, but not that of the stover. It also affected the percent of DM partitioned to the grain (harvest index), which increased linearly with ETc and averaged 56.2% over the two seasons, but did not affect the percent allocated to the cob or stover. Irrigation applied in July had the highest positive coefficient of determination (R²) with yield. This high positive correlation decreased considerably for irrigation applied in August, and became negative for irrigation applied in September. The best positive correlation between the soil water deficit factor (Ks) and yield occurred during weeks 12-14 from crop emergence, during the “milk” and “dough” growth stages. Yield was poorly correlated to stress during weeks 15 and 16, and the correlation became negative after week 17. Dividing the 150 mm allocation about evenly among July, August and September was a good strategy resulting in the highest yields in 2005, but not in 2006. Applying a larger proportion of the allocation in July was a good strategy during both years, and the opposite resulted when applying a large proportion of the allocation in September. The different results obtained between years indicate that flexible irrigation scheduling techniques should be adopted, rather than relying on fixed timing strategies.     

三种豆科作物与玉米间作对水分利用的影响

在甘肃河西灌区,对蚕豆、豌豆、大豆3种豆科作物与玉米间作下水分利用情况进行了研究,结果表明:在不同时间和氮水平下,3种豆科作物土壤水分含量变化不同。3种豆科作物与玉米间作相对于单作,不施氮条件下,蚕豆/玉米间作水分用量(WU)减少5.05%,水分利用效率(WUE)增加26.23%;大豆/玉米间作WU和WUE分别减少0.97%、23.12%;豌豆/玉米间作WU增加13.05%、WUE减少17.08%。在225 kg/hm2氮水平下,3种豆科作物与玉米间作相对于单作WU减少3.69%~7.26%,蚕豆/玉米和豌豆/玉米间作相对于单作WUE增加33.33%和23.45%,而大豆/玉米间作WUE减少12.92%。     

Water use efficiency and crop coefficients of dry season oilseed crops

Eastern India receives higher average annual rainfall (1000–2000 mm) but 80% of it occurs within the June–September (rainy season), whereas the winter season (November–March) is dry. Due to a shortage of soil moisture, most rainfed areas of the region remain fallow during the winter season and cultivation (mainly rice) is confined to the rainy season only (June–September). To explore the possibility of double cropping in the rainfed rice areas, three oilseed crops, viz., linseed (Linum usitatissimum L.), safflower (Carthamous tinctorious L.), mustard (Brassica juncea L.), were grown in a representative rainfed area of eastern India, i.e. Dhenkanal, Orissa, during the dry/winter season by applying irrigation water at phonological stages. Study revealed that with three supplemental irrigations, the highest WUE was achieved by safflower followed by linseed with the mean values being 3.04 and 2.59 kg ha⁻¹ mm⁻¹, respectively. Whereas, with one irrigation, the highest water use efficiency (WUE) was achieved for safflower (1.23 kg ha⁻¹ mm⁻¹) followed by linseed (0.93 kg ha⁻¹ mm⁻¹). Of the three crops studied, safflower withdrew maximum water followed by mustard and crops were shown to use 90–105 mm more water than linseed. With three irrigations, average maximum rooting depths were 1.66, 1.17 and 0.67 m for safflower, mustard and linseed, respectively, which were 13.5, 10.6 and 11.4% higher than for single irrigated crops because of more wet sub soils and decrease of soil strength. The crop growth parameters like leaf area, dry biomass were also recorded with different levels of irrigation. The research work amply revealed the potential of growing these low water requiring oilseed crops in rice fallow during dry/winter season utilizing limited irrigation from harvested rainwater of rainy season. Crop coefficients (K_c) of three winter season oilseed crops were derived using field water balance approach. Study showed that LAI was significantly correlated with K_c values with the R² values of 0.91, 0.89 and 0.94 in linseed, safflower and mustard, respectively. When LAI exceeded 3.0, the K_c value was 1 in safflower and mustard whereas in linseed corresponding LAI was 2.5. Study revealed that the K_c values for the development and mid season stage were slightly higher to that obtained by the procedure proposed by FAO, which might be due to local advection.     

Increasing crop yield in water scarce environments using locally available materials: An experience from semi-arid areas in Mpwapwa District, central Tanzania

This paper presents experience on working with farmers in water scarce environments in improving crop yield through the application of locally available materials in semi-arid areas of Mpwapwa District, central Tanzania. Findings are presented from the interdisciplinary study that involved documenting farmers perceptions and on-farm field experimentation. In the farmers’ perceptions study, three different traditional tillage practices applied by smallholder farmers in the area were identified. These are traditional no-till (TNT), shallow tillage (ST) and ridging tillage (RT). The impacts of various tillage practices on soil fertility improvement, reduced weed infestation, soil moisture retention and crop yield were the main factors considered by farmers when selecting a particular tillage practice to apply. In two cropping seasons (i.e. 2006/7 and 2007/8) on-farm field experimentations were carried to test the effects of the three traditional tillage practices, manure and mulching practices on soil moisture retention and crop yield. Results from this experiment showed traditional no-till fields to have the lowest soil moisture retention capacity and the lowest infiltration flow rate as well as lowest crop yield compared to other studied practices. It was observed that improving the current tillage practices by the application of manure to both ST and RT, and mulching to ST at rates affordable to smallholder farmers as identified during perception study (i.e. 5 tons/ha for manure and 3 tons/ha for mulching materials) results in increased crop yield. When the grain yield is compared between traditional no-till and shallow tillage with manure and mulching practices, the yield increase is between 50 and 100%. It was concluded that crop yield in water scarce environments such as the semi-arid areas of Mpwapwa District can be increased by applying locally available materials such as cow manure and mulching at rates affordable to smallholder farmers.     

Validation and testing of the AquaCrop model under full and deficit irrigated wheat production in Iran

Accurate crop development models are important tools in evaluating the effects of water deficits on crop yield or productivity and predicting yields to optimize irrigation under limited available water for enhanced sustainability and profitable production. Food and Agricultural Organization (FAO) of United Nations addresses this need by providing a yield response to water simulation model (AquaCrop) with limited sophistication. The objectives of this study were to evaluate the AquaCrop model for its ability to simulate wheat (Triticum aestivum L.) performance under full and deficit water conditions in a hot dry environment in south of Iran, to study the effect of different scenarios of irrigation (crop growth stages and depth of water applied) on wheat yield. The AquaCrop model was evaluated with experimental data collected during the three field experiments conducted in Ahvaz. The AquaCrop model was able to accurately simulate soil water content of root zone, crop biomass and grain yield, with normalized root mean square error (RMSE) less than 10%. The analysis of irrigation scenarios showed that the highest grain yield could be obtained by applying four irrigations (200 mm) at sowing, tillering, stem elongation and flowering or grain filing stages for wet years, four irrigations (200 mm) at sowing, stem elongation and flowering stages for normal years and six irrigations (300 mm) at sowing, emergence, tillering, stem elongation, flowering and grain filing stages for dry years. The least amount of irrigation water to provide enough water to response to evaporative demand of environment and to obtain high WUE for wet, normal and dry years were 100, 200 and 250 mm, respectively.     

Root growth, available soil water, and water-use efficiency of winter wheat under different irrigation regimes applied at different growth stages in North China

Field experiments were conducted at the Luancheng Agro-Ecosystem Experimental Station of the Chinese Academy of Sciences during the winter wheat growing seasons in 2006-2007 and 2007-2008. Experiments involving winter wheat with 1, 2, and 3 irrigation applications at jointing, heading, or milking were conducted, and the total irrigation water supplied was maintained at 120 mm. The results indicated that irrigation during the later part of the winter wheat growing season and increase in irrigation frequency decreased the available soil water; this result was mainly due to the changes in the vertical distribution of root length density. In ≤30-cm-deep soil profiles, 3 times irrigation at jointing, heading, and milking increased the root length density, while in >30-cm-deep soil profiles, 1 time irrigation at jointing resulted in the highest root length density. With regard to evapotranspiration (ET), there was no significant (LSD, P < 0.05) difference between the regimes wherein irrigation was applied only once at jointing; 2 times at jointing and heading; and 3 times at jointing, heading, and milking. Compared with 1 and 3 times irrigation during the winter wheat growing season, 2 times irrigation increased grain yield and 2 times irrigation at jointing and heading produced the highest water-use efficiency (WUE). Combining the results obtained regarding grain yield and WUE, it can be concluded that irrigation at the jointing and heading stages results in high grain yield and WUE, which will offer a sound measurement for developing deficit irrigation regimes in North China.