Impact of fertilisation practices on nitrogen leaching under irrigation

Field experiments were carried out over a 2-year period on a loamy soil plot under corn in Montpellier (south-east France). The effectiveness of improved irrigation practices in reducing the adverse impact of irrigation on the environment was assessed. Different irrigation and fertiliser treatments were applied to identify the best irrigation and fertilisation strategy for each technique (furrow and sprinkler) to ensure both good yields and lower NO₃^- leaching. No significant differences in corn yield and NO₃^- leaching were found for the climatic scenario of 1999 between sprinkler and furrow irrigation during the irrigation season. Following the rainy events occurring after plant maturity (and the irrigation season), differences in N leaching were observed between the treatments. The study shows that both the fertiliser method, consisting of applying a fertiliser just before ridging the furrows, and the two-dimensional (2D) infiltration process, greatly influence the N distribution in the soil. N distribution seems to have a beneficial impact on both yield and N leaching under heavy irrigation rates during the cropping season. But, under rainy events (particularly those occurring after harvesting), the N, stored in the upper part of the ridge and not previously taken up by plants, can be released into the deeper soil layers in a furrow-irrigated plot. In contrast, the 1D infiltration process occurring during sprinkler irrigation events affects the entire soil surface in the same way. As a result the same irrigation rate would probably increase N leaching under sprinkler irrigation to a greater extent than under furrow-irrigation during an irrigation period. In order to assess the robustness of these interpretations derived from soil N-profile analysis, a modelling approach was used to test the irrigation and fertilisation strategies under heavy irrigation rates such as those occurring at the downstream part of closed-end furrows. The RAIEOPT and STICS models were used to simulate water application depths, crop yield and NO₃^- leaching on three measurement sites located along the central furrow of each treatment. The use of a 2D water- and solute-transport model such as HYDRUS-2D enabled us to strengthen the conclusions derived from the observations made on the N distribution under a cross-section of furrow. This model helped to illustrate the risk of over-estimation of N leaching when using a simplified 1D solute-transport model such as STICS.     

Water requirements of subsurface drip-irrigated faba bean in California

A 3-year study was done in central California to determine the water requirements for growing faba bean (Vicia faba L.) as a winter cover crop using subsurface drip irrigation (SDI). Water was applied at 0, 50, and 100% of the estimated crop evapotranspiration (ET_c) the first 2 years and 50, 100, and 150% ET_c the third year, with drip laterals installed 0.30, 0.45, or 0.60 m deep. Rainfall was above normal the first year (>330 mm) and irrigation had no effect on crop production. Irrigation improved production and water-use efficiency the following years, however. Production was higher when drip laterals were located at 0.30 or 0.45 m than at 0.60 m depth, even though roots tended to be concentrated near the laterals (later in the season) regardless of depth. Overall, well-irrigated faba bean required 231-297 mm of water to produce 3.0-4.4 t ha^у of dry vegetative biomass.     

Agronomic and economic response to furrow diking tillage in irrigated and non-irrigated cotton (Gossypium hirsutum L.)

The Southeast U.S. receives an average of 1300 mm annual rainfall, however poor seasonal distribution of rainfall often limits production. Irrigation is used during the growing season to supplement rainfall to sustain profitable crop production. Increased water capture would improve water use efficiency and reduce irrigation requirements. Furrow diking has been proposed as a cost effective management practice that is designed to create a series of storage basins in the furrow between crop rows to catch and retain rainfall and irrigation water. Furrow diking has received much attention in arid and semi-arid regions with mixed results, yet has not been adapted for cotton production in the Southeast U.S. Our objectives were to evaluate the agronomic response and economic feasibility of producing cotton with and without furrow diking in conventional tillage over a range of irrigation rates including no irrigation. Studies were conducted at two research sites each year from 2005 to 2007. Irrigation scheduling was based on Irrigator Pro for Cotton software. The use of furrow diking in these studies periodically reduced water consumption and improved yield and net returns. In 2006 and 2007, when irrigation scheduling was based on soil water status, an average of 76 mm ha⁻¹ of irrigation water was saved by furrow diking, producing similar cotton yield and net returns. Furrow diking improved cotton yield an average of 171 kg ha⁻¹ and net return by $245 ha⁻¹ over multiple irrigation rates, in 1 of 3 years. We conclude that furrow diking has the capability to reduce irrigation requirements and the costs associated with irrigation when rainfall is periodic and drought is not severe.     

Yield and quality of two tomato (Solanum lycopersicum L.) cultivars as influenced by drip and furrow irrigation using waters having high residual sodium carbonate

Performance of tomato when irrigated with sodic waters particularly under drip irrigation is not well known. A field experiment was conducted for 3 years to study the response of tomato crop to sodic water irrigation on a sandy loam soil. Irrigation waters having 0, 5 and 10 mmol_c L⁻¹ residual sodium carbonate (RSC) were applied through drip and furrow irrigation to two tomato cultivars, Edkawi (a salt tolerant cultivar) and Punjab Chhuhara (PC). High RSC of irrigation water significantly increased soil pH, ECe and exchangeable sodium percentage progressively; the increases were higher in furrow compared to drip irrigation. Effect of high RSC on increasing bulk density and decreasing infiltration rate of soil was also pronounced in furrow-irrigated plots. Higher soil moisture and lower salinity near the plant was maintained under drip irrigation than under furrow irrigation. Performance of the two cultivars was significantly different; pooled over 2002–03 and 2003–04 seasons, PC yielded 38.8 and 30.0 Mg ha⁻¹ and Edkawi yielded 31.8 and 22.9 Mg ha⁻¹ under drip and furrow irrigation, respectively. At RSC10, cultivar PC produced 38 and 46% higher fruit yield than cultivar Edkawi under drip and furrow irrigation, respectively. Reduction in fruit yield at higher RSC was due to lower fruit weight under drip irrigation and due to reduced fruit number as well as fruit weight under furrow irrigation. Decrease in fruit weight was more pronounced in cultivar Edkawi than in cultivar PC. Increase in RSC lowered quality of the fruits except the ascorbic acid content. High RSC under drip irrigation, in general, had lesser deteriorating effect on the fruit quality particularly for cultivar PC than under furrow irrigation. For obtaining high tomato yield and better-quality fruits using high RSC sodic waters, drip irrigation should be preferred over furrow irrigation. Better performance of local cultivar PC compared to Edkawi at medium and high RSC suggests that cultivars categorized as tolerant to salinity should be evaluated in the sodic environment particularly when irrigated with high RSC sodic waters.     

Comparison of sprinkler,trickle and furrow irrigation efficiencies for onion production

In the Mesilla Valley of southern New Mexico, furrow irrigation is the primary source of water for growing onions. As the demand for water increases, there will be increasing competition for this limited resource. Water management will become an essential practice used by farmers. Irrigation efficiency (IE) is an important factor into improving water management but so is economic return. Therefore, our objectives were to determine the irrigation efficiency, irrigation water use efficiency (IWUE) and water use efficiency (WUE), under sprinkler, furrow, and drip irrigated onions for different yield potential levels and to determine the IE associated with the amount of water application for a sprinkler and drip irrigation systems that had the highest economic return.Maximum IE (100%) and economic return were obtained with a sprinkler system at New Mexico State University’s Agriculture Science Center at Farmington, NM. This IE compared with the 54–80% obtained with the sprinkler irrigation used by the farmers. The IEs obtained for onion fields irrigated with subsurface drip irrigation methods ranged from 45 to 77%. The 45% represents the nonstressed treatments, in which an extra amount of irrigation above the evapotranspiration (Et) requirement was applied to keep the base of the onion plates wet. The irrigation water that was not used for Et went to deep drainage water. The return on the investment cost to install a drip system operated at a IE of 45 was 29%. Operating the drip system at a IE of 79% resulted in a yield similar to surface irrigated onions and consequently, it was not economical to install a drip system. The IEs at the furrow-irrigated onion fields ranged from 79 to 82%. However, the IEs at the furrow-irrigated onion fields were high because farmers have limited water resources. Consequently, they used the concept of deficit irrigation to irrigate their onion crops, resulting in lower yields. The maximum IWUE (0.084 t ha⁻¹ mm⁻¹ of water applied) was obtained using the sprinkler system, in which water applied to the field was limited to the amount needed to replace the onions’ Et requirements. The maximum IWUE values for onions using the subsurface drip was 0.059 and 0.046 t ha⁻¹ mm⁻¹ of water applied for furrow-irrigated onions. The lower IWUE values obtained under subsurface drip and furrow irrigation systems compared with sprinkler irrigation was due to excessive irrigation under subsurface drip and higher evaporation rates from fields using furrow irrigation. The maximum WUE for onions was 0.009 t ha⁻¹ mm⁻¹ of Et. In addition, WUE values are reduced by allowing the onions to suffer from water stress.     

Effects of sand column, furrow and supplemental irrigation on agricultural production in an arid environment

The effects of supplemental irrigation, sand columns and blocked furrows on soil water distribution and barley yield were studied on arid soils affected by surface crusts. The sand columns were 50 mm diameter, 600 mm deep, and filled with sand of 0.375 mm mean diameter. The blocked furrows were trenches about 250 mm deep, 300 mm wide, and 6 m long established perpendicular to the slope direction. Sand column and furrow treatments significantly increased soil water storage compared with natural or control treatments. Soil water storage significantly increased by about 210% and 230% near the center of the sand column and the furrow treatments, respectively, relative to the control treatment. For sand column treatments, soil water storage decreased linearly with distance from the center of the sand column to about 2.5 m, while for the furrow treatment soil water storage decreased logarithmically to a distance of about 1.0 m, beyond which the soil water storage was not significantly different from the natural or control treatments. The furrow and sand column treatments significantly increased the water application efficiency, seasonal consumptive use and barley grain and straw yields compared with natural and control treatments. Increasing furrow spacing increased the catchment area and consequently crop production per furrow, but decreased crop production per unit total (cultivated and catchment) area. Decreasing sand column spacing reduced surface runoff and increased soil water storage and consequently barley grain and straw yields. Supplemental irrigation is essential for grain production in limited rainfall areas. Soil management is also required to overcome the problems of the soil surface crusting and the low permeability of subsurface soil layers for maximum rainwater efficiency, and for optimal crop production with minimum supplemental irrigation water. Where agricultural land is not limited, furrowed soil surfaces appear to be the most suitable technique for barley grain production. Sand columns with sprinkler irrigation might be more suitable for growing barley as forage crop where agricultural land is limited. Received: 19 October 1998     

Yield and water use efficiency of wheat and cotton under alternate furrow and check-basin irrigation with canal and tube well water in Punjab, India

A 4-year field experiment was conducted in a semi-arid area to evaluate the response of each furrow and alternate furrow irrigation in wheat-cotton system using irrigation waters of different qualities in a calcareous soil. Irrigation was applied to each and alternate furrow of bed-planted wheat followed by ridge-planted cotton for comparison with standard check-basin method of irrigation to both the crops. These methods of irrigation were evaluated under three water qualities namely good quality canal water (CW), poor quality tube well water (TW) and pre-sowing irrigation to each crop with CW and all subsequent irrigations with TW (CWpsi + TW). The pooled results over 4 years revealed that wheat grain yield was not affected significantly with quality of irrigation water, but significant yield reduction was observed in alternate bed irrigation under canal water and tube well water irrigations. In cotton, poor quality tube well water significantly reduced the seed cotton yield in all the three methods of planting. The pre-sowing irrigation with canal water and all subsequent irrigations with tube well water improved the seed cotton yield when compared with tube well water alone. However, this yield increase was significant only in alternate furrow irrigation, and the yield obtained was on a par with yield under alternate furrow in CW. When compared to check-basin irrigation, each furrow and alternate furrow irrigation resulted in a saving of 30 and 49% of irrigation water in bed-planted wheat, whereas the corresponding savings in ridge-planted cotton were 20 and 42%, respectively. Reduced use of irrigation water under alternate furrow, without any significant reduction in yield, resulted in 28.1, 23.9 and 43.2% higher water use efficiency in wheat under CW, TW and CWpsi + TW, respectively. The corresponding increase under cotton was 8.2, 2.1 and 19.5%. The implementation of alternate furrow irrigation improved the water use efficiency without any loss in yield, thus reduced use of irrigation water especially under poor quality irrigation water with pre-sowing irrigation with canal water reduced the deteriorating effects on yield and soil under these calcareous soils.     

Performance of temperate aerobic rice under different water regimes in North China

Since the late 1990s, aerobic rice varieties have been released to farmers in the North China Plain to grow rice as a supplementary-irrigated upland crop to cope with water scarcity. Little is known about their yield potential, water use, water productivity (WP), and flood tolerance. In 2001–2002, experiments with aerobic rice varieties HD502 and HD297 and lowland rice variety JD305 were conducted under aerobic and flooded conditions. Under aerobic conditions, five irrigation treatments were implemented. Under flooded conditions, JD305 yielded up to 8.8 t ha⁻¹, HD502 up to 6.8 t ha⁻¹, and HD297 up to 5.4 t ha⁻¹. Under aerobic conditions, the aerobic varieties yielded higher than the lowland variety. HD502 produced 3–3.5 t ha⁻¹ with 450–500 mm total water input and 5.3–5.7 t ha⁻¹ with 650 mm water input and more. HD297 produced 3–3.5 t ha⁻¹ with 450–500 mm total water input and 4.7–5.3 t ha⁻¹ with 650 mm water input and more. The water productivity of aerobic rice under aerobic conditions was higher or on a par with that of the lowland variety under flooded conditions, reaching values of 0.6–0.8 g grain kg⁻¹ water. The relatively high yields of the aerobic varieties under aerobic soil conditions were obtained under “harsh” conditions for growing rice. The soil contained more than 80% sand, was permeable, and held water above field capacity for a few hours after irrigation only. The groundwater table was deeper than 20 m, the soil moisture content in the rootzone was mostly between 50 and 80% of saturation, and soil moisture tension went up to 90 kPa. We conclude that the aerobic rice varieties HD502 and HD297 are suitable for water-scarce environments, and can stand being periodically flooded.     

Water-use efficiency of irrigated winter maize under cool weather conditions of India

Field experiments were conducted during 1993/94 and 1994/95 in the sub-humid tropic environment of northern India to identify suitable irrigation schedule(s) for winter maize (December to May). Based on plant growth stages, viz. knee-high, tasselling, flowering, silking, grain-filling and dough, which occurred, respectively, at 55, 75, 95, 105, 125 and 145 days after planting, the crop was subjected to six irrigation treatments, which were: no irrigation (I₀); irrigation given at all the growth stages (I₁); irrigation missed at knee-high (I₂); at knee-high and dough (I₃); at knee-high, flowering and grain-filling (I₄); and at knee-high, flowering, silking and dough stages (I₅). The change in profile soil water content, (W (depletion) of the entire crop-growing season was found to be in the order I₀ >I₅ >I₄ >I₃ >I₂ >I₁. Of the total net water use (NWU), about 87% was evapotranspiration and 13% deep percolation losses. The NWU was highest (472 and 431 mm) under I₁ and lowest (223 and 240 mm) under the I₀ treatment during the two cropping seasons. Compared to I₁, NWU in I₃ decreased by 23% and 12.3% and in I₄ by 33.8% and 24.2% in the two cropping seasons. However, there was no statistically significant difference (at LSD, P=0.05) between yields of the I₁ to I₄ treatments during either year. The NWU was found to be in the order I₁ >I₂ >I₃ >I₄ >I₅ >I₀, whereas the water-use efficiency (WUE) based on NWU was found to be in the reverse order: I₅ >I₄ >I₃ >I₀ >I₂ >I₁. Maximum yield (5.14 t ha^-1) with WUE of 1.39 kg m^-3 was obtained under the I₃ treatment. However, optimum yield (4.91 t ha^-1) with high WUE of 1.54 kg m^-3 was under I₄. Accordingly, irrigation applications greater than 240 mm did not provide additional yield of winter maize. Frequent irrigations (I₁) proved detrimental to grain yield of winter maize in the northern Indian plains, especially under cool weather conditions, where minimum temperature (6°C) can be accompanied by occasional frost.     

Response of wheat to irrigation with small amounts of water applied in various ways

In dry land agriculture, crop failure is often due to dry seed beds which hamper crop stand establishment and root growth. Irrigation with small amounts of water may make the difference between success and failure of the crop. A 2-year field study on a sandy loam soil evaluated the response of wheat to irrigation with 4—60 mm water applied in various ways. An amount of 4 or 6 mm water applied in the furrow enhanced above-ground plant growth, root growth, grain yield and water use considerably compared to the same amount of water surface applied to seeded rows. With surface irrigation of 40 or 60 mm water, crop growth and grain yield increased further; however, a significantly higher grain yield was obtained with post-seeding rather than pre-seeding irrigation.     

Response of cotton to different soil water deficits on clay soils

Summary Cotton was grown under sprinkler irrigation on a silty clay soil at Keiser, Arkansas, for the 1987, 1988 and 1989 growing seasons. Irrigation treatments consisted of maximum soil water deficits (SWD) of 25, 50 and 75 mm and a nonirrigated control. While the irrigated treatments were significantly different from the control for plant height and total seedcotton yield, significant differences among the three irrigated treatments were only observed for plant height. Yields were significantly lower in 1989 than in the other two years of the study, due in part to later planting. The 3-year averages for total seedcotton yield were 3280 and 2870 kg ha^–1 for irrigated and nonirrigated, respectively, for an average increase corresponding to irrigation of 416 kg ha^–1 or 14.5% of the nonirrigated yield. The maximum increase was observed in 1988 as 602 kg ha^–1 or 20.6% of the nonirrigated yield for that year. The 75 mm allowable SWD was the most efficient treatment and resulted in a 3-year average of 3.85 kg ha^–1 additional seedcotton (above the nonirrigated) harvested for each 1 mm of irrigation applied. Maintaining the SWD below a 75 mm maximum required an average of four irrigations and 110 mm of irrigation water per year.     

Cotton yields under different furrow irrigation management techniques in the Southeastern Anatolia Project (GAP) area,Turkey

The continuous flow furrow irrigation (COFFI), surge flow furrow irrigation (SUFFI), cutback flow furrow irrigation (CUFFI), variable alternate flow furrow irrigation (VAFFI), and tail water reuse system furrow (TWRSF) techniques with the same inflow rate of 0.072 m³ min⁻¹ were compared in relation to the cotton yield and water use efficiency at a 3-year field study conducted on cotton (Gossypium spp.) in the Southeastern Anatolia Project (GAP) area of Turkey. Yields revealed significant statistical differences between the furrow management techniques (P < 0.05). The maximum yield was obtained from the COFFI treatment (2,630 and 2,920 kg ha⁻¹) in the first 2 years, and from SUFFI and CUFFI treatments (3,690 and 3,780 kg ha⁻¹, respectively) in the last year. There were significant yield reductions, which varied from 10 to 35% in TWRSF and from 11 to 19% in VAFFI treatments although 43 and 28% more water was applied to the TWRSF than to CUFFI and SUFFI treatments, respectively. The average total water use efficiencies (WUE_ET) varied from 4.14 (VAFFI) to 2.59 (COFFI). The corresponding values were 0.37 and 0.36 kg ha⁻¹ m⁻³ for CUFFI and SUFFI, respectively. The average irrigation water use efficiency (WUE_IR) for CUFFI and SUFFI treatments were 0.30 and 0.23 kg ha⁻¹ m⁻³, respectively.     

Water savings in irrigated potato production by varying hill-furrow or bed-furrow configuration

Current agronomic practices for potato production in the irrigated areas of southern Alberta involve a hill/furrow configuration that was adopted from elsewhere, and designed to shed rainfall away from the hill and into the furrow. However, the principal intent of supplemental irrigation is to capture as much of the applied water into the hill, where the potato tubers and roots are located, and minimize water accumulating in the furrow. A three-year project began in 2006 to quantify the potential irrigation water savings of altered hill shapes for potato production. The three treatments (standard hill, flat-topped hill, and double-planted wide-bed) were arranged in a randomized strip plot design replicated four times. Soil water in each treatment was generally kept between 60 and 90% of available. A fourth treatment, triple-planted wide bed, was added to the project in 2008. The irrigation requirements to maintain the treatments were 487, 442, and 449 mm for the standard hill, flat-topped hill, and double-planted bed, respectively, in 2006 and 442, 408 and 411 mm for the same treatments in 2007. This translates into approximately 10% less irrigation water required for the flat-topped hill shape compared to the standard hill shape. The flat-topped hill shape required 5.0% more irrigation than the standard hill in 2008, but the double and triple-planted wide beds required 8.0 and 9.9%, respectively, less irrigation water than the standard. Although not always statistically significant, water use efficiency was greater in all years for the altered bed shapes compared to the standard hill geometry. Greater water use efficiency can be interpreted as more of the applied water infiltrated into the hill, where the potato plant could use it for transpiration and tuber development. Total yield was greater in 2006 for both the flat-topped hill (72.3 Mg ha⁻¹) and wide-bed hill (69.2 Mg ha⁻¹) compared to the standard hill (61.4 Mg ha⁻¹); however, the treatments were not significantly different. Significantly greater marketable yield was realized from the flat-topped hill treatment in 2006. This treatment also had a significantly greater number of marketable size tubers. In 2007, there were no significant differences in total yield; however, the standard and flat-topped treatments had a significantly greater number and yield of tubers in the 113-170 g size category. Significant differences in total yield were found in 2008. The triple-planted wide bed had significantly greater yield in the smaller size categories compared to the standard treatment and significantly greater total tuber numbers than the other treatments, but the increase was in the smaller size categories, less than 170 g. There were no significant differences among the treatments in yield or total number of tubers in the size categories greater than 171 g in 2008.     

Wheat yield response to line source sprinkler irrigation and soil management practices on medium-textured shallow soils of arid environment

A field experiment was conducted for 3 years to evaluate the effect of deficit irrigation under different soil management practices on biomass production, grain yield, yield components and water productivity of spring wheat (Triticum estivum L.). Soil management practices consisted of tillage (conventional and deep tillage) and Farmyard manure (0 and 10 t ha^?1 FYM). Line source sprinkler laterals were used to generate one full- (ETm) and four deficit irrigation treatments that were 88, 75, 62 and 46 % of ETm, and designated as ETd₁, ETd₂, ETd₃, and ETd₄. Deep tillage significantly enhanced grain yield (14–18 %) and water productivity (1.27–1.34 kg m^?3) over conventional tillage. Similarly, application of FYM at 10 t ha^?1 significantly improved grain yield (10–13 %) and water productivity (1.25–1.31 kg m^?3) in comparison with no FYM. Grain yield response to irrigation varied significantly (5,281–2,704 kg ha^?1) due to differences in soil water contents. Water productivity varied from 1.05 to 1.34 kg m^?3, among the treatments in 3 years. The interactive effect of irrigation × tillage practices and irrigation × FYM on grain yield was significant. Yield performance proved that deficit irrigation (ETd₂) subjected to 75 % soil water deficit had the smallest yield decline with significant water saving would be the most appropriate irrigation level for wheat production in arid regions.     

Water–yield relationships and optimal water management for winter wheat in the Loess Plateau of China

High evaporative demand and limited precipitation restrict the yield of winter wheat (Triticum aestivum L.) grown in the Loess Plateau of China under semiarid climatic conditions. Grain yield can be improved by effective water management practices. A 13-year field experiment was conducted at the CERN Changwu Agro-ecological Experimental Station of the Loess Plateau to determine optimal irrigation strategies under limited water supply and to develop relationships among grain yield (Y), seasonal evapotranspiration (SET) and water-use efficiency (WUE). The experiment consisted of five irrigation treatments and three blocks. Measurements included grain yield, soil water content at various depth intervals in the 0–3,000 mm layer, irrigation amount, and precipitation. Results showed that winter wheat grown in this area experienced serious water stress during critical growth stages for the no-irrigation treatment. The amount and timing of irrigation had an important effect on grain yield, but significant differences in yield were not observed between the three-irrigation and the four-irrigation treatments. Grain yield was linearly related (R²=0.66) to SET, but differences in WUE were not significant for any of the treatments. The relationship between WUE and Y was best represented by a second order polynomial (R²=0.65) consisting of a nearly linear portion between 1.5 and 5.0 Mg ha^–1. Optimum water management of winter wheat in the Loess Plateau should consist of three 87.5 mm irrigations applied at stem elongation, booting, and anthesis.Communicated by J.E. Ayars     

Proceedings of the Sixth International Conference on Precision Agriculture and Other Precision Resources Managemen on CD-ROM | Robert,P.C. et al., (Ed.), American Society of Agronomy/Crop Science Society of America/Soil Science Society of America,Madison, WI, 2003, USA, 2095 pp. Price: US$14.00.CD-ROM

The objective of this paper is to examine the impacts of terminating rice [Oryza sativa] irrigation earlier than usual. One straightforward result of this would be the associated cost savings (≈$10 ha⁻¹ per irrigation or more with deep wells) without placing a value on the water itself. However, another option exists for some farms. An assumption is that the typical farm will be constrained from irrigating all of the soybean [Glycine max (L.) Merr] crop due to constraints in any or all of water supply, pumping capacity, and labor availability. In these cases, a portion of the land in soybean production would be non-irrigated for the first part of the growing season. This study explores the possibility of transferring irrigation water to the soybean crop after the needs of the rice crop are met. If rice and soybean planting dates are planned optimally, this partial irrigation can lead to substantial soybean yield improvements and therefore a more profitable rice/soybean production system. On average, across a 41 year period, net revenue gains from partially irrigating the soybean crop were consistently positive, ranging from $41 to $458 ha⁻¹. While these numbers are interesting, the reader is cautioned that the results are based on simulation models and therefore the marginal analysis results are more realistic. On clayey and silt loam soils at Keiser and Stuttgart, respectively, the change in returns for moving from the least to the most water saving rice irrigation strategy was $190 and $99 ha⁻¹, respectively. In addition, for any given year, financial losses are typically restricted to the irrigation setup costs of $17 ha⁻¹. The irrigation termination strategies therefore show high economic potential with little risk of loss.     

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 small irrigation amounts on the yield of wheat

Yields of dryland crops are governed by the moisture in the soil profile at seeding and by rainfall during the growing season. Occasionally limited amounts of water may also be available for irrigation. Field experiments were conducted over a period of 4 years on loamy sand and 3 years on sandy loam to study the effects of pre-seeding, post-seeding and split application of limited amounts of water on root growth, water use, dry matter accumulation and grain yield of wheat. This article reports the treatment effects on dry matter accumulation and grain yield.Early season water stress decreased the rate of dry matter accumulation. Grain yield responded significantly to irrigation 30 days after seeding irrespective of the amount of water, year and soil type. Yield with post-seeding irrigation averaged 3518 kg ha^?1 against 2317 kg ha^?1 for unirrigated control in loamy sand and 4440 kg ha^?1 against 3391 kg ha^?1 in sandy loam. The increase in yield was manifested by a significant increase in the number of effective tillers per m row length, number of grains per ear and thousand grain weight.     

Yield, water and nitrogen-use response of rice to zeolite and nitrogen fertilization in a semi-arid environment

Water scarcity and soil nitrogen (N) loss are important limitations for agricultural production in semi-arid region especially for rice production. Zeolite (Z) as a soil conditioner can be used to retrain water and nitrogen in near-surface soil layer in lowland rice production system. The objectives of this study were to investigate the effects of different application rates of natural zeolite (clinoptilolite) and nitrogen on rice yield, yield components, soil nitrogen, water use, water productivity in a silty clay soil in 2004 and 2005. Zeolite was only applied in the first year. In order to study the long-term and continuous effect of zeolite on the objectives of the study, no zeolite was applied in the second year and the study was conducted on the same land as the first year. Zeolite and N were applied at rates of 0, 2, 4, and 8 t ha⁻¹ and 0, 20, 40, and 80 kg ha⁻¹, respectively in 2004. In 2005, each plot received the same amount of N as received in 2004. It is concluded that by decreasing N application rates, higher Z application rate is needed to improve grain yield. Highest grain yield was obtained at N application rate of 80 kg ha⁻¹ and Z application rate of 4 t ha⁻¹. Higher grain yield was mostly attributed to lower unfilled grain percentage and higher 1000-grain weight that were a result of higher N application rate and N retention in soil due to Z application. Nitrogen and Z applications resulted in higher grain protein contents and nitrogen recovery efficiency (NRE). Based on these results and due to higher N retention in soil under Z application, improved grain yield quality, nitrogen-use efficiency (NUE), and nitrogen recovery efficiency (NRE) could be obtained at Z application rate of 8 t ha⁻¹ and N application rate of 80 kg ha⁻¹ or more. However, this was not satisfied for NUE. Moreover, it is found that at higher N application rates lower Z application rates are needed to effectively retain soil residual mineral nitrogen. Furthermore, at N application rates of 80 kg ha⁻¹ or more, Z application increased soil water retention and resulted in lower seasonal water use and higher water productivity. In general, it was concluded that the effect of Z application in retaining soil N was also effective in the second year.     

Rice growth, yield and water productivity responses to irrigation scheduling prior to the delayed application of continuous flooding in south-east Australia

The majority of rice grown in south-east Australia is continuously flooded for much of its growing season, but reduced irrigation water availability brought about by a combination of drought and environmental flow legislation has presented a need to maintain (or even increase) rice production with less irrigation water. Delaying the application of continuous flooding until prior to panicle initiation can increase input water productivity by reducing non-beneficial evaporation losses from free water and the soil. A field experiment was conducted over two growing seasons, 2008/9 and 2009/10, comparing a conventional dry seeded treatment (the control - continuous flooding from the 3 leaf stage) with delayed continuous flooding (10-20 days prior to panicle initiation) with several irrigation scheduling treatments prior to flooding commencement. In the first year, the delayed water treatments were irrigated at intervals of 40, 80 and 160 mm of cumulative reference evapotranspiration (ETo) prior to delayed continuous flooding, thereby imposing differing degrees of crop water stress. In year 2, the 80 and 160 mm treatments were modified by use of a crop factor (Kc) when the plants were small and the 40 mm treatment was replaced with a continuously flooded treatment throughout the crop duration.Decreases in net water input (irrigation + rain − surface drainage) and increases in input water productivity were achieved by reducing the flush irrigation frequency during the pre-flood period. Savings of 150 and 230 mm (10 and 15%) were achieved in Year 1 from the 80 and 160 mm cumulative ETo irrigation frequency treatments, respectively, in comparison to the control. In the second year, net water input savings of 230 and 330 mm (15 and 22%) were achieved with the 80/Kc and 160/Kc mm treatments, respectively. Input water productivity of the 160 mm treatment was 0.06 kg/m³ (8%) higher than the control in Year 1, while in Year 2 a 0.15 kg/m³ (17%) increase in input water productivity above the control was achieved by the 160/Kc mm treatment. Delaying the application of continuous flooding in the second year greatly extended the period of crop growth suggesting the need for earlier sowing (by 7-10 days) to ensure pollen microspore still occurs at the best time to minimise yield loss due to cold damage. Nitrogen fertiliser management is an important issue when delaying continuous flooding, and nitrogen losses appeared to increase with the frequency of irrigation prior to continuous flooding. This was likely due to increased denitrification from alternate wetting and drying of the soil. Further research is required to determine the most appropriate nitrogen management strategies, and to also better define the optimal pre-flood irrigation frequency.