Root growth, water potential and yield of irrigated wheat

Root length density (LV), mid-day leaf water potential (Ψ _leaf) and yield of wheat were studied in 1983 – 1984 and 1984 – 1985 on a Phoolbagh clay loam (Typic Haplaquoll) and on a Beni silty clay loam (Aquic Hapludoll) in the Tarai region of Uttar Pradesh under naturally fluctuating shallow (0.4 – 0.9 m, SWT) and medium-depth (0.8 – 1.3 m, MWT) water table conditions with six water regimes: rainfed (I₀); irrigation at cown root initiation (I₁); at crown root initiation and milk (I₂); at crown root initiation, maximum tillering and milk (I₃); at crown root initiation, maximum tillering, flowering and milk (I₄); and at crown root initiation, maximum tillering, flowering, milk and dough (I₅). Maximum rooting depth (0.8 m under SWT and 1.05 m under MWT conditions) was attained at the dough stage (115 days after sowing, DAS) and was more strongly influenced by fluctuations in water table depth than by the water regime. For wet regimes (I₂– I₅), roots were concentrated at and above the water table interface and had greater horizontal development, whereas in dry regimens (I₀ and I₁), due to deficient moisture conditions in the upper soil layer (0.45 m) they invaded lower horizons and had a greater vertical distribution Ψ _leaf was not significantly affected by water regime (I₁– I₅) up to 94 DAS during a wet year (1983 – 1984) and up to 74 DAS during a dry year (1984 – 1985), but was significantly affected thereafter. Grain yields with water regimens I₁– I₅ during a wet year and for the I₂– I₅ treatments during a dry year at either water table depth were not significantly different, but there was a (non-significant) trend to lower yield with increasing soil water deficit. Under SWT in I₂, the average grain yield wsa 5130 kg ha^–1 and under the I₃ regime, 5200 kg ha^–1. Likewise, under MWT in I₃, it was 5188 kg ha^–1 and under the I₄ regime, 5218 kg ha^–1. The results indicate that application of irrigation of more than 120 and 180 mm under SWT and MWT conditions, respectively, did not raise yield. Irrigation given as per schedule I₂ under SWT and I₃ under MWT conditions in the Tarai situation, appears to be more effective than a very wet regime (I₅). Received: 9 December 1997     

Irrigation and tillage effects on root development,water use and yield of wheat on coarse textured soils

Summary Rapid drying of surface layers of coarse-textured soils early in the growth season increases soil strength and restricts root growth. This constraint on root growth may be countered by deep tillage and/or early irrigation. We investigated tillage and irrigation effects on root growth, water use, dry matter and grain yield of wheat on loamy sand and sandy loam soils for three years. Treatments included all combinations of two tillage systems i) conventional tillage (CT) — stirring the soil to 10 cm depth, ii) deep tillage (DT) — subsoiling with a single-tine chisel down to 35–40 cm, 40 cm apart followed by CT; and four irrigation regimes, i) I₀ — no post-seeding irrigation, ii) I₁ — 50 mm irrigation 30 days after seeding (DAS), iii) I₂ — 50 mm irrigation 30 DAS and subsequent irrigations of 75 mm each when net evaporation from USWB class A open pan (PAN-E) since previous irrigation accumulated to 82 mm, and iv) I₃ — same as in I² but irrigation applied when PAN-E accumulated to 62 mm. The crop of wheat (Triticum aestivum L. HD 2329) was fertilized with 20kg P, 10kg K and 5kg Zn ha^–1 at seeding. The rate of nitrogen fertilization was 60 kg ha^–1 in the unirrigated and 120 kg ha^–1 in the irrigated treatments. Tillage decreased soil strength and so did the early post-seeding irrigation. Both deep tillage and early irrigation shortened the time needed for the root system to reach a specified depth. Subsequent wetting through rain/irrigation reduced the rate of root penetration down the profile and also negated deep tillage effects on rooting depth. However, tillage/irrigation increased root length density in the rooted profile even in a wet year. Better rooting resulted in greater profile water depletion, more favourable plant water status and higher dry matter and grain yields. In a dry year, the wheat in the DT plots used 46 mm more water, remained 3.3 °C cooler at grain-fill and yielded 68% more grain than in CT when unirrigated and grown in the loamy sand. Early irrigation also increased profile water depletion, more so in CT than DT. Averaged over three years, grain yield in DT was 12 and 9% higher than in CT on loamy sand and sandy loam, respectively. Benefits of DT decreased with increase in rainfall and irrigation. Irrigation significantly increased grain yield on both soils, but the response was greatly influenced by soil type, tillage system and year. The study shows that soil related constraints on root growth may be alleviated through deep tillage and/or early irrigation.     

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.     

Integrated management of irrigation water and fertilizers for wheat crop using field experiments and simulation modeling

The reported study aimed at developing an integrated management strategy for irrigation water and fertilizers in case of wheat crop in a sub-tropical sub-humid region. Field experiments were conducted on wheat crop (cultivar Sonalika) during the years 2002–2003, 2003–2004 and 2004–2005. Each experiment included four fertilizer treatments and three irrigation treatments during the wheat growth period. During the experiment, the irrigation treatments considered were I₁ = 10% maximum allowable depletion (MAD) of available soil water (ASW); I₂ = 40% MAD of ASW; I₃ = 60% MAD of ASW. The fertilizer treatments considered in the experiments were F₁ = control treatment with N:P₂O₅:K₂O as 0:0:0 kg ha⁻¹, F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha⁻¹; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha⁻¹ and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha⁻¹. In this study CERES-wheat crop growth model of the DSSAT v4.0 was used to simulate the growth, development and yield of wheat crop using soil, daily weather and management inputs, to aid farmers and decision makers in developing strategies for effective management of inputs. The results of the investigation revealed that magnitudes of grain yield, straw yield and maximum LAI of wheat crop were higher in low volume high frequency irrigation (I₁) than the high volume low frequency irrigation (I₃). The grain yield, straw yield and maximum LAI increased with increase in fertilization rate for the wheat crop. The results also revealed that increase in level of fertilization increased water use efficiency (WUE) considerably. However, WUE of the I₂ irrigation schedule was comparatively higher than the I₁ and I₃ irrigation schedules due to higher grain yield per unit use of water. Therefore, irrigation schedule with 40% maximum allowable depletion of available soil water (I₂) could safely be maintained during the non-critical stages to save water without sacrificing the crop yield. Increase in level of fertilization increases the WUE but it will cause environmental problem beyond certain limit. The calibrated CERES-wheat model could predict the grain yield, straw yield and maximum LAI of wheat crop with considerable accuracy and therefore can be recommended for decision-making in similar regions.     

Influence of irrigation frequencies and phosphate fertilization on actual evapotranspiration rate, yield and water use pattern of rajmash (Phaseolus vulgaris L.)

The hypothesis was tested, whether soil wetness and phosphorus status could regulate the evapotranspiration rate (ET_R), which is of special interest in the lower Gangetic Plain. Rajmash was grown during November-February of 2003-2004 and 2004-2005 on a sandy loam soil, and was irrigated when cumulative pan evaporation (CPE) attained the value of 33 mm (CPE₃₃); 44 mm (CPE₄₄) and 66 mm (CPE₆₆). Four levels of phosphate application were 0 kg P₂O₅ ha⁻¹ (P₀); 30 kg P₂O₅ ha⁻¹ (P₃₀); 60 kg P₂O₅ ha⁻¹ (P₆₀) and 90 kg P₂O₅ ha⁻¹ (P₉₀). Seed yield under CPE₃₃ was 1.37 Mg ha⁻¹ and reduced by 18% and 35%, respectively under CPE₄₄ and CPE₆₆. Continuous increasing trend in yield was recorded with an increase in phosphate level (PL). Irrespective of growth stages, similar trends were recorded for leaf area index (LAI). Maximum variation in LAI among the treatments was recorded at 60 days after sowing. On average, actual ET_R was 1.37 mm day⁻¹ under CPE₃₃ and declined by 13% and 16% under CPE₄₄ and CPE₆₆, respectively. Variation in ET_R under different PL was highest under CPE₃₃ and lowest under CPE₄₄. Except P₉₀, irrespective of PL, highest value of water use efficiency (WUE) was obtained under CPE₄₄. However, magnitude of net evapotranspiration efficiency (WUE_ET) and irrigation efficiency (WUE_I) attained the highest level under CPE₃₃ regime. All water use indices showed an increasing trend with the increase in phosphate level from 0 to 90 kg ha⁻¹. Impact of phosphorus on various parameters was pronounced under CPE₃₃.     

Evaluation of options for increasing yield and water productivity of wheat in Punjab, India using the DSSAT-CSM-CERES-Wheat model

The DSSAT-CSM-CERES-Wheat V4.0 model was calibrated for yield and irrigation scheduling of wheat with 2004–2005 data and validated with 13 independent data sets from experiments conducted during 2002–2006 at the Punjab Agricultural University (PAU) farm, Ludhiana, and in a farmer's field near PAU at Phillaur, Punjab, India. Subsequently, the validated model was used to estimate long-term mean and variability of potential yield (Y_p), drainage, runoff, evapo-transpiration (ET), crop water productivity (CWP), and irrigation water productivity (IWP) of wheat cv. PBW343 using 36 years (1970–1971 to 2005–2006) of historical weather data from Ludhiana. Seven sowing dates in fortnightly intervals, ranging from early October to early January, and three irrigation scheduling methods [soil water deficit (SWD)-based, growth stage-based, and ET-based] were evaluated. For the SWD-based scheduling, irrigation management depth was set to 75 cm with irrigation scheduled when SWD reached 50% to replace 100% of the deficit. For growth stage-based scheduling, irrigation was applied either only once at one of the key growth stages [crown root initiation (CRI), booting, flowering, and grain filling], twice (two stages in various combinations), thrice (three stages in various combinations), or four times (all four stages). For ET-driven irrigation, irrigations were scheduled based on cumulative net ETo (ETo-rain) since the previous irrigation, for a range of net ETo (25, 75, 125, 150, and 175 mm). Five main irrigation schedules (SWD-based, ET-driven with irrigation applied after accumulation of either 75 or 125 mm of ETo, i.e., ET75 or ET125, and growth stage-based with irrigation applied at CRI plus booting, or at CRI plus booting plus flowering stage) were chosen for detailed analysis of yield, water balance, and CWP and IWP. Nitrogen was non-limiting in all the simulations.Mean Y_p across 36 years ranged from 5.2 t ha⁻¹ (10 October sowing) to 6.4 t ha⁻¹ (10 November sowing), with yield variations due to seasonal weather greater than variations across sowing dates. Yields under different irrigation scheduling, CWP and IWP were highest for 10 November sowing. Yields and CWP were higher for SWD and ET75-based irrigations on both soils, but IWP was higher for ET75-based irrigation on sandy loam and for ET150-based irrigation on loam. Simulation results suggest that yields, CWP, and IWP of PBW343 would be highest for sowing between late October and mid-November in the Indian Punjab. It is recommended that sowing be done within this planting period and that irrigation be applied based on the atmospheric demand and soil water status and not on the growth stage. Despite the potential limitations recognised with simulation results, we can conclude that DSSAT-CSM-CERES-Wheat V4.0 is a useful decision support system to help farmers to optimally schedule and manage irrigation in wheat grown in coarse-textured soils under declining groundwater table situations of the Indian Punjab. Further, the validated model and the simulation results can also be extrapolated to other areas with similar climatic and soil environments in Asia where crop, soil, weather, and management data are available.     

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.     

Barley yield response to irrigation and potential profits in the Texas High Plains

Summary Irrigated winter barley (Hordeum vulgare L.) can be a profitable alternative to some low profit major crops in the Texas High Plains. A six-year evaluation of yield response related to total spring irrigation water, applied by surface methods (furrow), and seasonal precipitation resulted in a multivariate function explaining 74% of the yield variation. Predicted yields varied from a low of 3.69 Mg ha^–1 to a maximum 6.18 Mg ha^–1 with 0 and 389 mm, respectively, based on average monthly precipitation quantities. Precipitation is skewed to less than average in th semi-arid Texas High Plains. Using modal precipitation amounts of 40% of average precipitation, yield estimates were reduced to 2.29 Mg ha^–1 with zero spring irrigation and to 5.63 Mg ha^–1 at the peak with 450 mm. A second multivariate yield response function related to alternative timings of single and multiple spring irrigations explained 76% of the variation in yields. Among all combinations of 1, 2, 3, and 4 spring irrigations, irrigation water-use efficiency was estimated to be highest with one application at the boot stage of development. All other single and combinations of multiple irrigations resulted in lower water-use efficiencies. A comparison of enterprise budgets of four irrigation timing alternatives and levels of application indicated highest profit over variable costs, $ 287 ha^–1, was attained by applying a total of 307 mm in three spring applications at the boot, head, and milk stages. A lower level of 217 mm applied at boot and milk stages was $ 12 ha^–1 less profitable and a higher level of 425 mm was $ 24 ha^–1 less profitable. When fixed costs of irrigation facilities, land, and machinery were considered, returns to management and risk were highest, $ 101 ha^–1, with 217 mm. Using 40% of average precipitation, profits were reduced $ 65 ha^–1 with 217 mm and $ 69 ha^–1 with 307 mm spring irrigation levels.Respectively, agricultural economist, research scientist, and research associate, Texas Agr. Exp. Station, Amarillo, Texas; Emeritus Extension agronomist, Texas Agr. Ext. Service, Amarillo, Texas; agricultural engineer, Texas Agr. Exp. Station, Amarillo, Texas     

Evaluation of CERES-Wheat and CropSyst models for water–nitrogen interactions in wheat crop

Crop simulation models can provide an alternative, less time-consuming and inexpensive means of determining the optimum crop N and irrigation requirements under varied soil and climatic conditions. In this context, two dynamic mechanistic models (CERES (Crop Environment REsource Synthesis)-Wheat and CropSyst (Cropping Systems Simulation Model)) were validated for predicting growth and yield of wheat (Triticum aestivum L) under different nitrogen and water management conditions. Their potential as N and water management tool was evaluated for New Delhi representing semi-arid irrigated ecosystems in the Indo-Gangetic Plains. The field experiment was carried out on a silty clay loam soil at the Research Farm of the Indian Agricultural Research Institute, New Delhi, India during 2000–2001 to collect the input data for the calibration and validation of both the models on wheat crop (variety HD 2687). The models were evaluated for three water regimes [I4 (4 irrigations within the growing season), I3 (3 irrigations within the growing season) and I2 (2 irrigations within the growing season)] and five N treatments (N₀, N₆₀, N₉₀, N₁₂₀ and N₁₅₀). Both the models were calibrated using data obtained from the treatments receiving maximum nitrogen and irrigations, i.e., N₁₅₀ and I4 treatments. The models were then validated against other water and nitrogen treatments. For performance evaluation, in addition to coefficient of determination (R²), root mean square error (RMSE), mean absolute error (MAE) and Wilmot's index of agreement (IoA) were estimated. Both CERES-Wheat and CropSyst provided very satisfactory estimates for the emergence, flowering and physiological maturity dates. For CERES-Wheat overall prediction (pooled result of the three water regimes) of grain yield was satisfactory with significant R² values (0.88). The model, however, under estimated the biomass under all water regimes and N levels except for N₀ level, under which biomass was overpredicted. CropSyst predicted yield and biomass of wheat more closely than CERES-Wheat. The combined RMSE for the three water regimes between predicted and observed grain yield was 0.36 Mg ha⁻¹ for CropSyst as compared to 0.63 Mg ha⁻¹ for CERES-Wheat. Similarly, RMSE between observed and predicted biomass by CropSyst was 1.27 Mg ha⁻¹ as compared to 1.94 Mg ha⁻¹ between observed and predicted biomass by CERES-Wheat. Wilmot's index of agreement (IoA) also indicated that CropSyst model is more appropriate than CERES-Wheat in predicting growth and yield of wheat under different N and irrigation application situations in this study.     

Irrigation for crops in a sub-humid environment VII. Evaluation of irrigation strategies for cotton

Summary Empirical functions to predict the nitrogen uptake, increase in LAI and minimum leaf water potential (LWP) of cotton were incorporated into a water balance model for the Namoi Valley, N.S.W. A function was then developed to describe the lint yield of irrigated cotton as a function of water stress days at 4 stages of development, total nitrogen uptake and days of waterlogging. A water stress day was defined as predicted minimum leaf water potential less than -1.8 MPa up to 90 days after sowing and -2.4 MPa there-after; stress reduced yield by up to 40 kg lint ha^–1 d^–1 with greatest sensitivity at 81–140 days after sowing and when N uptake was highest. Nitrogen uptake was reduced by 0.98 kg per ha and yield reduced by 33.2 kg lint ha^–1 for each day of waterlogging. The model was used to evaluate various irrigation strategies by simulating production of cotton from historical rainfall data. With a water supply from off farm storage, net returns ($ M1^–1) were maximized by allocating 7 Ml ha^–1 of crop. The optimum practice was not to irrigate until 60 days from sowing and until the deficit in the root zone reached 50%. When the supply of water was less than 7 Ml ha^–1 there was no advantage in either delaying the start of irrigation or irrigating at a greater deficit; it was economically more rational to reduce the area shown or, if already sown, to irrigate part with 6 Ml ha^–1 and leave the rest as a raingrown crop. Irrigation decisions are compromises between reducing the risk of water stress and increasing the risk of waterlogging. The simulation showed that there is no single set of practices that is always best in every season; in a number of seasons practices other than those which on average are best, give better results.     

Forage quality, water use and nitrogen utilization efficiencies of pearl millet (Pennisetum americanum L.) grown under different soil moisture and nitrogen levels

The increasing scarcity of water for irrigation is becoming the most important problem for producing forage in all arid and semi-arid regions. Pearl millet is a key crop in these regions which needs relatively less water than other crops. In this research, a field study was conducted to identify the best combination of irrigation and nitrogen (N) management to achieve acceptable pearl millet forage both in quantity and quality aspects. Pearl millet was subjected to four irrigation treatments with interaction of N fertilizer (0, 75, 150 and 225 kg ha⁻¹). The irrigation treatments were 40%, 60%, 80% and 100% of total available soil water (I₄₀, I₆₀, I₈₀ and I₁₀₀, respectively). The results showed that increasing moisture stress (from I₄₀ to I₁₀₀) resulted in progressively less total dry matter (TDM), leaf area index (LAI), and nitrogen utilization efficiency (NUzE), while water use efficiency (WUE) and the percentage of crude protein (CP%) increased. The highest TDM and LAI were found to be 21.45 t ha⁻¹ and 8.65, in I₄₀ treatment, respectively. TDM, WUE, CP% and profit responses to N rates were positive. The maximum WUE of 4.19 kg DM/m³ was achieved at I₁₀₀ with 150 kg N ha⁻¹. The results of this research indicate that the maximum profit of forage production was obtained in plots which were fully irrigated (I₄₀) and received 225 kg N ha⁻¹. However, in the situation which water is often limited and not available, application of 150 kg N ha⁻¹ can produce high forage quality and guaranty acceptable benefits for farmers.     

A comparison between the gross energy requirements of different irrigation systems in Israel

Summary The energy requirements for manufacturing irrigation equipment were evaluated from a survey of a number of factories and workshops in Israel.Based on the results obtained and the life span of the components, the annual amortization of energy by high-pressure (overhead sprinklers), medium-pressure (undertree sprinklers and sprayers) and low-pressure (drip lines) irrigation systems was calculated for citrus orchards and cotton crops as irrigated in Israel. For citrus orchards a low-pressure sprayer system amortized 1.5 GJ ha^–1 y^–1 more energy than a medium-pressure undertree sprinkler system, and 2.7 GJ ha^–1 y^–1 more than a high-pressure, overhead sprinkler system. For irrigating a cotton crop, the low-pressure drip system used 6.8 GJ ha^–1 y^–1 more embodied energy than the movable, high-pressure overhead sprinkler system.The annual energy invested in irrigation water conveyance through the National Water Carrier, at the current hydraulic pressure of 500 kPa at the farm gate, varies for a cotton crop from 20 to 45 GJ ha^–1 y^–1 in the northern region and from 70 to 215 GJ ha^–1 y^–1 in the southern region of Israel, when irrigated with 4,050 m³ ha^–1. For a citrus orchard this energy input varies from 60 to 75 GJ ha^–1 y^–1 in the central region and from 120 to 375 GJ ha^–1 y^–1 in the southern regions, when irrigated with 7,200 m³ ha^–1. For obtaining the same yield in the south as in the north, the energy input for water conveyance has to be increased by 12% in the case of a cotton crop and by 7% in the case of a citrus orchard. Thus, in the north the annual energy amortization of a dripline irrigation system amounts to one third of that expended on water conveyance but in the south amounts to one-eighteenth or less, indicating the large regional dependency of energy inputs for irrigation.Calculations show that the reduction in energy requirement for water conveyance needed by irrigation systems operating at lower pressures compensates for their higher energy losses in system amortization. For example, in citrus irrigation the substitution of medium-pressure undertree sprinkler systems for high-pressure overhead sprinkler systems was calculated to save 8% of the total energy expenditure for water conveyance to the farm gate. This would amount to a saving of 7 GJ ha^–1 y^–1 for citrus in the central region and of 8 GJ ha^–1 y^–1 in the south. For cotton the substitution of low pressure dripline systems for high-pressure overhead sprinkler systems could save 16% of the total energy expenditure for pressurized water conveyance. This would amount to a saving of 8 GJ ha^–1 y^–1 in the northern region increasing to 10 GJ ha^–1 y^–1 in the south, taking into account a higher irrigation water requirement.Contribution from the Agricultural Research Organization, Bet Dagan, Israel. No. 1589-E, 1985 series     

Water stress imposed on muskmelon (Cucumis Melo L.) with subsurface and surface drip irrigation systems under semi-arid climatic conditions

In 2005 and 2006, a study was conducted to determine the effect of subsurface and surface drip irrigation systems and to determine optimum irrigation water using six different irrigation levels imposed on muskmelon (Cucumis Melo L. cv. Ananas F1) under semi-arid climatic conditions. Irrigation treatments received 0, 25, 50, 75, 100, and 125% of class A pan evaporation rates. In 2005, average yield from subsurface and surface drip irrigation systems ranged from 16.2 (I ₀) to 31.1 (I ₇₅) t ha⁻¹ and from 16.2 (I ₀) to 43.8 (I ₇₅) t ha⁻¹, respectively. While in 2006, fruit yields for the same systems ranged from 8.2 (I ₀) to 40.4 (I ₇₅) t ha⁻¹ and from 8.2 (I ₀) to 38.9 (I ₁₀₀) t ha⁻¹. Regression analysis of the yield data indicated no significant (P > 0.05) difference between years and irrigation systems. The highest muskmelon yields from subsurface and surface drip irrigation systems were obtained at 83 and 92% of class A pan. Bigger fruits were obtained with optimum irrigation amounts for both of the irrigation systems. However, there was no clear indication of irrigation water amounts on total soluble solid and flesh thickness of muskmelon fruits.     

Yield and quality of melon grown under different irrigation and nitrogen rates

During 2 years, a melon crop (Cucumis melo L. cv. Sancho) was grown under field conditions to investigate the effects of different nitrogen (N) and irrigation (I) levels on fruit yield, fruit quality, irrigation water use efficiency (IWUE) and nitrogen applied efficiency (NAE). The statistical design was a split-plot with four replications, where irrigation was the main factor of variation and N was the secondary factor. In 2005, irrigation treatments consisted of applying daily a moderate water stress equivalent to 75% of ETc (crop evapotranspiration), a 100% ETc control and an excess irrigation of 125% ETc (designated as I₇₅, I₁₀₀ and I₁₂₅), while the N treatments were 30, 85, 112 and 139 kg N ha⁻¹ (designated as N₃₀, N₈₅, N₁₁₂ and N₁₃₉). In 2006, both the irrigation and N treatments applied were: 60, 100 and 140% ETc (I₆₀, I₁₀₀ and I₁₄₀) and 93, 243 and 393 kg N ha⁻¹ (N₉₃, N₂₄₃ and N₃₉₃). Moderate water stress did not reduce melon yield and high IWUE was obtained. Under severe deficit irrigation, the yield was reduced by 22% mainly due to decrease fruit weight. The relative yield (yield/maximum yield) was higher than 95% when the irrigation depth applied was in the range of 87-136% ETc. In 2006, the interaction between irrigation and N was significant for yield, fruit weight and IWUE. The best yield, 41.3 Mg ha⁻¹, was obtained with 100% ETc at N₉₃. The flesh firmness and the placenta and seeds weight increased when the irrigation level was reduced by 60% ETc. The highest NAE was obtained with quantities of water close to 100% ETc and increased as the N level was reduced. The highest IWUE was obtained with applications close to 90 kg N ha⁻¹. The I₂₄₃ and I₃₉₃ treatments produced inferior fruits due to higher skin ratios and lower flesh ratios. These results suggest that it is possible to apply moderate deficit irrigation, around 90% ETc, and reduce nitrogen input to 90 kg ha⁻¹ without lessening quality and yields.     

The effect of irrigation and nitrogen fertilizer on rapeseed (Brassica napus) production in South-Eastern Australia

Summary A field trial was conducted to determine the response of rapeseed (Brassica napus cv. Marnoo) to two irrigation treatments and six nitrogen fertilizer treatments. Response to nitrogen was greater with than without irrigation. Oil content was increased with irrigation but decreased under increasing nitrogen application, and was inversely related to seed nitrogen concentration. Oil yields averaged 1,168 kg ha^–1 under irrigated treatments compared with 835 kg ha^–1 under rainfed treatments. Maximum oil yield (approx. 1,557 kg ha^–1) was obtained from the irrigated treatment fertilized with 100 kg N ha^–1 applied at sowing.     

Tillage and irrigation effects on crop yields and soil properties under the rice-wheat system in the Indian Himalayas

Conservation tillage systems generally improve soil organic C (SOC), plant available water capacity (PAWC), aggregation and soil water transmission. A field experiment was conducted for 4 years (2001-2002 to 2004-2005) to study tillage (conventional tillage (CT) and zero tillage (ZT)) systems. The selected irrigation treatments were at four levels (I₁: pre-sowing (PS), I₂: PS + active tillering (AT)/crown root initiation (CRI), I₃: PS + AT/CRI + panicle initiation (PI)/flowering (FL), and I₄: PS + AT/CRI + PI/FL + grain filling (GF)), applied at the critical growth stages on rice (Oryza sativa L.) and wheat (Triticum aestivum L.). Their effects on direct seeded rice productivity and soil properties (SOC and selected physical properties) after rice and wheat harvest were investigated. Soil organic C contents after rice and wheat harvest in the 0-15 cm soil depth were higher under ZT than under CT. Soil organic C increased significantly with I₂ over I₁ for both crops and with I₄ over I₂ for the wheat crop. The PAWC was significantly higher with ZT than CT. Zero tilled and frequently irrigated plots showed enhanced infiltration characteristics (infiltration rate, cumulative infiltration and sorptivity) and saturated hydraulic conductivity. Both direct seeded rice and wheat yields were not significantly different in the plots under ZT and CT. There was a significant increase in both rice and wheat yields in the plots under I₂ over I₁. However, water use efficiency between irrigation treatments was not significantly different. Hence, under direct seeded rice-wheat system in a sandy clay loam soil of the sub-temperate Indian Himalayas, farmers may adopt ZT with two irrigations in each crop for optimum resource conservation.     

Irrigation for crops in a sub-humid environment

Summary In this paper the soil water balance model developed and tested in Part III (Mason and Smith, 1980) for soybeans grown in the variable rainfall environment of the Namoi Valley of New South Wales was used to investigate the potential advantages of a computer-based system of irrigation scheduling. The advantages were evaluated using historical rainfall data for the 25 seasons from 1953/54 to 1977/78. The effects on irrigation efficiency of soil water holding capacity, the allowable soil water deficit prior to irrigation, and ordering irrigation water in advance were evaluated with the model. Reducing the allowed deficit prior to irrigation by 20% compared to the recommended level increased the number of irrigations by an average of 2.8 per year and irrigation requirements by 0.73 X 10³ m³ ha^–1. The need to order water 6 days in advance because of delays in delivery also increased requirements by 1.46 X 10³ m³ ha^–1 due to a reduced ability to utilize natural rainfall. Average farm irrigation efficiencies calculated from actual pumping records were found to be low by world standards for the 3-year period 1975/76 to 1977/78. It was concluded that if increased production per unit of water became a high priority in the Namoi Valley, then irrigation efficiency for the three year period discussed could have been increased from 35 to 47%, a saving of 1.3 X 10³ m³ ha^–1 year^–1.     

Varying irrigation rates effect on yield and yield components of chickpea

This study was conducted to determine the effect of different supplemental irrigation rates on chickpea grown under semiarid climatic conditions. Chickpea plots were irrigated with drip irrigation system and irrigation rates included the applications of 0 (I ₀) 25 (I ₂₅), 50 (I ₅₀), 75 (I ₇₅), 100 (I ₁₀₀), and 125 % (I ₁₂₅) of gravimetrically measured soil water deficit. Plant height, 1,000 seed weight, yield, biomass, and harvest index (HI) parameters were determined in addition to yield-water functions, evapotranspiration (ET), water use efficiency (WUE), and irrigation water use efficiency (IWUE). Significant differences were noted for plant height (ranging from 24.0 to 37.5 cm), 1,000 seed weight (ranging from 192.0 to 428.7 g), and aboveground biomass (ranging from 2,722 to 6,083 kg ha^?1) for water applications of I ₀ and I ₁₂₅. Statistical analysis indicated a strong relationship between the amount of irrigation and yield, which ranged from 256.5 to 1,957.3 kg ha^?1. Harvest index values ranged between 0.092 and 0.325, while WUE and IWUE values ranged between 1.15–4.55 and 1.34–8.36 (kg ha^?1 mm^?1), respectively.     

The fate of nitrogen applied to sugarcane by trickle irrigation

Fertigation can be a more efficient means of applying crop nutrients, particularly nitrogen (N), so that nutrient application rates can be reduced in fertigated crops. However, there is little information on the extent of the possible reduction in N application rate for fertigated sugarcane, one of the major row crops grown under trickle irrigation, nor the fate of N in fertigated sugarcane systems if N application rates are not reduced. An experiment was established to determine the response of cane and sugar production to different N rates (0–240 kg ha^–1 year^–1) spanning that recommended for conventional irrigation systems (160 kg ha^–1 year^–1). As well as yield, N removed in the crop and changes in soil mineral N were determined annually for four crops (a plant and three ratoon crops). ¹⁵N values were also measured in selected treatments at selected times to assess possible N inputs to the experiment via biological N fixation (BFN). Yields of cane and sugar responded to application of N fertiliser in the three ratoon crops, but they were not significantly increased by applying more than 80 kg ha^–1 of N. There were no N responses in the plant crop, as there was >200 kg ha^–1 of soil mineral N (SMN) to 2 m depth at the site prior to planting, and much of this SMN was depleted in the treatment receiving no N. There was no evidence of N input from BFN in the experiment. During the 4-year study period, net removal of N from the treatment with no applied N totalled 207 kg ha^–1. When 80 or 120 kg ha^–1 year^–1 of N was applied to ratoon crops, outputs of N from the harvested crop approximately balanced inputs from fertiliser and depletion of SMN during the experiment. Inputs clearly exceeded output at higher N application rates. Assuming that the net removal of N from the treatment with no applied N was the same as the net mineralisation of N from soil organic matter in all treatments in the experiment, 204–639 kg ha^–1 of N was unaccounted for in the treatments with applied N over the duration of the experiment. While some of this N (e.g. 45 kg ha^–1) may have resulted in small (and undetectable) increases in total soil N, much of it would have been lost to the environment. We suggest that the high soil water contents maintained with daily application of irrigation water through the trickle system promotes mineralisation of soil organic matter and hence losses of N to the environment. Thus, particular care is required to avoid over-application of N in fertigated sugarcane.Communicated by K. Bristow     

Effects of deficit irrigation on the yield and yield components of drip irrigated cotton in a mediterranean environment

A field study on cotton (Gossypium hirsutum L., cv.) was carried out from 2005 to 2008 in the Çukurova Region, Eastern Mediterranean, Turkey. Treatments were designated as I₁₀₀ full irrigation; DI₇₀, DI₅₀ and DI₀₀ which received 70, 50, and 0% of the irrigation water amount applied in the I₁₀₀ treatment. The irrigation water amount to be applied to the plots was calculated using cumulative pan evaporation that occurred during the irrigation intervals. The effect of water deficit or water stress on crop yield and some plant growth parameters such as yield response, water use efficiencies, dry matter yield (DM), leaf area index (LAI) as well as on lint quality components was evaluated. The average seasonal evapotranspiration ranged from 287 ± 15 (DI₀₀) to 584 ± 80 mm (I₁₀₀). Deficit irrigation significantly affected crop yield and all yield components considered in this study. The average seed cotton yield varied from 1369 ± 197 (DI₀₀) to 3397 ± 508 kg ha⁻¹ (I₁₀₀). The average water use efficiency (WUE_ET) ranged from 6.0 ± 1.6 (I₁₀₀) to 4.8 ± 0.9 kg ha⁻¹ mm⁻¹ (DI₀₀), while average irrigation water use efficiency (WUE_I) was between 9.4 ± 3.0 (I₁₀₀) and 14.4 ± 4.8 kg ha⁻¹ mm⁻¹ (DI₅₀). Deficit irrigation increased the harvest index (HI) values from 0.26 ± 0.054 (I₁₀₀) to 0.32 ± 0.052 kg kg⁻¹ (DI₅₀). Yield response factor (Ky) was determined to be 0.98 based on four-year average. Leaf area index (LAI) and dry matter yields (DM) increased with increasing water use. This study demonstrated that the full irrigated treatment (I₁₀₀) should be used for semiarid conditions with no water shortage. However, DI₇₀ treatment needs to be considered as a viable alternative for the development of reduced irrigation strategies in semiarid regions where irrigation water supplies are limited.