Water use efficiency of irrigated wheat in the Tarai region of India

Experiments were conducted during the winter seasons of 1983–1984 and 1984–1985 to identify suitable irrigation regimes s for wheat grown after rice in soils with naturally fluctuating shallow water table (SWT) at a depth of 0.4 to 0.9 m and medium water table (MWT) at a depth of 0.8 to 1.3 m. Based on physiological stages, the crop was subjected to six irrigation regimes viz., rainfed (I₀); irrigation only at crown root initiation (I₁); at only 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). Tube-well water with an EC <0.4 dsm^–1 was used for irrigation. Based on 166 mm effective precipitation during the cropping season, 1983–1984 was designated as a wet year and 1984–1985 with 51 mm as a dry year. The change in profile soil water content W (depletion) in the wet year was less (23%) under SWT and 10% under MWT as compared to the dry year. The ground water contribution (GWC) to evapotranspiration (ET) was 58% under SWT and 42% under MWT conditions in both the years. The GWC in the wet year was 20% under SWT and 23% under MWT. Of the total net water use (NWU), about 85% was ET and 15% drainage losses. The NWU was highest (641 and 586 mm) in I₅ under SWT and MWT conditions, respectively, but not the yield (5069 kg ha^–1). Compared to I₅, NWU in I₂ treatment decreased by 10% in the wet and 25% in the dry year. A similar trend was observed in the I₃ treatment under MWT condition. However, there was no statistically significant difference between yields of the I₁ to I₅ treatments of either water table depth during the wet year. This was also true during the dry year for the I₂ to I₅ treatments. Under SWT, in I₂, the grain yield was 5130 kg ha^–1 and under I₃ regime, 5200 kg ha^–1. Under MWT in I₃, the yield was 5188 kg ha^–1 and under I₄ regime, 5218 kg ha^–1. Thus it appears that in the Tarai region where the water table remains shallow (<0.9 m) and medium (<1.3 m) for most of the wheat growing season applications of more than 120 and 180 mm irrigation under SWT and MWT conditions, respectively were not necessary. Irrigation given only at crown root initiation and milk stages under shallow water table conditions, and at crown root initiation, maximum tillering and milk stages under medium water table conditions, appears to be as effective as frequent irrigations.     

Root growth, water potential, and yield of irrigated rice

Root length density (Lv), leaf water potential (Ψ leaf) and yield of rice were studied in 1983 and 1984 on a Phool bagh clay loam (Typic Haplaquoll) and on a Beni silty clay loam (Aquic Hapludoll) in the Tarai region of Uttar Pradesh under naturally fluctuating shallow (0.07–0.92 m) and medium-depth (0.13–1.26 m) water table conditions with six water regimes ranging from continuous submergence under 0.05 m ± 0.02 m (Ic) to completely rainfed (Io). In irrigation treatments, Ic1, Ic3, Ic5, and Ic7, 0.07 m irrigation was applied on days 1, 3, 5, and 7 respectively, after the disappearance of ponded water. Maximum rooting depth (0.55 m in the shallow and 0.65 m in the medium-depth water table) was attained at the dough stage (125 days after transplanting) and was more strongly influenced by fluctuations in water table depth than by the water regime. For wet regimes (Ic1–Ic5), roots were concentrated at and above the water table interface and had greater horizontal development, whereas in dry regimes, (Ic7 and Io) they were concentrated in lower horizons and had a more vertical distribution. Like Lv, Ψ leaf was not significantly affected by water regime up to 90–95 days after rice transplanting but was significantly affected thereafter, except for Lv beneath 0.2 m–0.25 m. Grain yields with irrigation treatments Ic1 and Ic3 under shallow and Ic1 under medium-depth water table conditions were not significantly different from those under continuous submergence, but there was a (nonsignificant) trend to lower yield with less water. However, differences among the wet regimes (Ic, Ic1, and Ic3) were small (141–490 kg ha^–1) under shallow and 413–727 kg ha^–1 under medium-depth water table conditions. The results demonstrate that optimum yield (5500–6000 kg ha^–1) could be obtained under Tarai conditions by adopting an intermittent irrigation schedule of 3–5 days after the disappearance of ponded water under shallow, and of 1–3 days under medium-depth water table conditions, in place of continuous submergence. Received: 26 February 1996     

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.     

Modeling the water transport and nitrogen dynamics in irrigated salad crops

The use of N fertilizers in agriculture is crucial, and agricultural techniques need to be implemented that improve significantly N fertilizer management by reducing downward movements of solutes through the soil. To achieve this, it is essential to develop and test models against experimental conditions in order to improve them and to make sure that they can be applied to a broad range of soil and climatic conditions. A field experiment was carried out in the French department of Gard. The soil was a clay loam (26.7% clay, 44.7% fine and coarse silt, and 28.6% fine and coarse sand). Salad vegetables (Cichorium endivia, Lactuca sativa) were cultivated during two consecutive periods (spring and summer crops). The crops were planted on punched and permeable plastic mulching bands. The field was irrigated with a sprinkler watering system. Local measurements were made combining a neutron probe, tensiometers, and ceramic porous cups to estimate NO₃-N concentrations. The model is one-dimensional and is based on Richards' equation for describing saturated-unsaturated water flow in soil. At the soil surface, the model is designed to handle flux-type or imposed-pressure boundary conditions. In addition, provision is made in the model, for example, to account for a mulch plastic sheet that limits evaporation. The model accounts for heat transport by diffusion and by convection, while the modeling of the displacement of nitrate and ammonium in the soil is based on the convection-dispersion equation. Nitrate uptake by the crop is modeled assuming Michaelis-Menten kinetics. Nitrogen cycle modeling accounts for the following major transformations: mineralization of organic matter, nitrification of ammonium, and denitrification. The results showed that the overall trend of the water potential in the soil profile was correctly described during the crop seasons. Mineralization was high for the spring crop (4.7 kg NO₃-N day^–1 ha^–1), whereas the other sink components, such as root uptake, drainage, and denitrification, were smaller (1.9, 1.4, and 0.2 kg NO₃-N day^–1 ha^–1, respectively). For the summer crop, intensive denitrification was found in the soil layer at 0.15–0.90 m (5.7 kg NO₃-N day^–1 ha^–1), while the mineralization was always an important component (9.2 kg NO₃-N day^–1 ha^–1) and the sink terms were 1.7 and 1.7 kg NO₃-N day^–1 ha^–1 for root uptake and drainage, respectively. Similar high denitrification rates were found in the literature under intensive irrigated field conditions. Received: 25 October 1995     

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.     

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.     

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.     

Root biomass, crop response and water-yield relationship of mustard (Brassica juncea L.) grown under combinations of irrigation and nutrient application

A 3-year study was carried out to assess the root biomass production, crop growth rate, yield attributes, canopy temperature and water-yield relationships in Indian mustard grown under combinations of irrigation and nutrient application for revealing the dynamic relationship of crop yield (Y) and seasonal evapotranspiration (ET). Three post-sowing irrigation treatments viz. no irrigation (I ₁), one irrigation at flowering (I ₂) and two irrigations one each at rosette and flowering stage (I ₃), three nutrient treatments viz. no fertilizer or manure (F ₁), 100% recommended NPK i.e., 60 kg N, 13.1 kg P and 16.6 kg K ha⁻¹ (F ₂) and 100% recommended NPK plus farmyard manure @ 10 Mg ha⁻¹ (F ₃) were tested in a split-plot design. Root biomass was significantly greater in I ₃ than I ₂ and I ₁, and in F ₃ than F ₂ and F ₁. The I ₃ × F ₃, I ₂ × F ₃ and I ₃ × F ₂ combinations maintained significantly greater crop growth rate, plant height, yield components, ET and crop yield and better plant water status in terms of canopy temperature, canopy-air temperature difference (CATD) and relative leaf water content (RLWC). Number of siliqua plant⁻¹ and seeds siliqua⁻¹ were the major contributors to the seed yield. Marginal analysis of water production function was used to establish Y–ET relationship. The elasticity of water production (E _wp) provides a means to assess relative changes in Y and ET, and gives an indication of improvement of Y due to nutrient application. The ET–Y relationships were linear with marginal water use efficiency (WUE_m) of 3.09, 4.23 and 3.95 kg ha⁻¹ mm⁻¹ in F ₁, F ₂ and F ₃, respectively, and the corresponding E _wp were 0.63, 0.71 and 0.61. This implies that the scope for improving yield and WUE with 100% NPK was little compared with 100% NPK + farmyard manure. The crop yield was highest in I ₃ × F ₃ combination, and the similar yield was obtained in I ₂ × F ₃ and I ₃ × F ₂ combinations. Application of organic manure along with 100% NPK fertilizers maintained greater crop growth rate, better water relation in plants, yield attributes and saved one post-sowing irrigation.     

Characterisation of water use by Sultana grapevines (Vitis vinifera L.) on their own roots or on Ramsey rootstock drip-irrigated with water of different salinities

Seasonal evapotranspiration (ET) was determined for Sultana grapevines grown on their own roots (Own-rooted) or grafted onto Ramsey rootstock (Grafted), and irrigated with water of three salinity levels – low (0.4 dS m^–1), medium (1.8 dS m^–1) and high (3.6 dS m^–1) – during the 1994/1995 growing season in south-eastern Australia. Transpiration (T) was determined from sap flux, soil evaporation (E _s) with a model, and soil water (S) with a neutron probe. Total ET for the season was similar for both Own-rooted and Grafted, averaging 382 mm. However, Grafted partitioned a mean of 193.5 mm (50.8%) of the ET through T compared to 146.7 mm (38.4%) by Own-rooted. Daily rates of T were generally low and attained peaks of 1.2 mm (9.9 l per vine) for Grafted and 0.9 mm (7.5 l) for Own-rooted in late November, and changed very little until after harvest in February. In contrast to T, the E _s rate was consistently higher for Own-rooted than for Grafted from November onwards, and at the end of the season totalled 237 mm for Own-rooted compared to 187 mm for Grafted. Differences between Own-rooted and Grafted in their partitioning of ET into T and E _s were associated with their canopy development. Grafted had a higher rate of canopy development than Own-rooted, and in mid-season, the former intercepted about 50% more incident radiation than Own-rooted. The crop factors, i. e. ratio of water use to evaporative demand, based on ET were similar for both vine types with an average seasonal value of 0.25, but when based on T were 0.12 for Grafted and 0.10 for Own-rooted. The ratio of fresh fruit weight to total water used at harvest, i. e. crop water use efficiency (CWUE), based on ET, had a mean of 86 kg mm^–1 ha^–1 for Grafted and 43 kg mm^–1 ha^–1 for Own-rooted, and when based on T, was 165 and 115 kg mm^–1 ha^–1, respectively; however, supplementary data obtained during the 1993/1994 season, indicated a CWUE based on T of 294 and 266 kg mm^–1 ha^–1 for Grafted and Own-rooted, respectively. Salinity did not have significant effects on canopy development and water use for most of the 1994/1995 growing season. The study shows ET and crop factors for the drip-irrigated grapevines to be much lower than previously reported for this district. Received: 6 May 1996     

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.     

Spatial and temporal variability of nitrate in irrigated salad crops

The objective of this study was to analyze the spatial and seasonal variations in NO₃ ^–-N concentration in soil samples and solution samplers and the N leaching of an irrigated crop cultivated intensively in the Mediterranean zone. Although much information is available from controlled field experiments concerning N concentration and its spatial variability, quantitative estimates of nitrate fluxes under normal farming conditions and when the field is directly managed by farmers are rare. This is particularly true for gardening crops in the Mediterranean zone, where high evapotranspiration rates lead to intensive irrigation and may be responsible for N leaching. A field experiment was conducted in the Departement du Gard under agricultural conditions. Salads (Cichorium endivia, Lactuca sativa) were planted in three consecutive periods. The field was irrigated with sprinklers. Local measurements with a neutron probe were made at two sites (row, interrow), and an experimental plot (95 m×25 m) was surveyed at 36 points located on a 10 m×10 m equilateral grid to analyze the spatial variability of water and NO₃ ^–-N balances. To analyze the basic statistical properties of our sampling scheme, random fields of soil concentration were simulated with the turning-bands method. Sampling strategy simulations indicated that when a spatial structure exists, sampling according to a regular grid was more efficient than a purely random sampling strategy. Global trends indicated high spatial variability for nitrate leaching with differences between periods of different irrigation intensity (97 kg ha^–1 NO₃ ^–-N leaching during the spring and summer, and 199 kg ha^–1 NO₃ ^–-N leaching during autumn and winter). Leaching caused temporal variations in the spatial distributions of NO₃ ^–-N. The origin of the spatial variability of N leaching was explained by first, the variability in NO₃ ^–-N concentration in the soil profile, and second, by spatial variability in irrigation. Furthermore, the spatial distribution of the NO₃ ^–-N concentration was time dependent, and NO₃ ^–-N spatial distributions became independent after approximately 2 or 3 months under our conditions. Our results show that better management of irrigation and fertilizer in spring and summer may reduce N leaching and, thus, improve ground water quality. Received: 15 March 1996     

In-season wheat root growth and soil water extraction in the Mediterranean environment of northern Syria

Wheat is the most important cereal crop in the semi-arid eastern Mediterranean region that includes northern Syria. Knowledge of wheat root depth and the vertical distribution during the winter growing season is needed for sound scheduling of irrigation and efficient use of water. This article reports evaluation of root development for three winter-grown bread (Triticum aestivum L.) and durum (Triticum turgidum L.) wheat under four soil water regimes (rainfed and full irrigation with two intermediate levels of 33 and 66% of full irrigation). Roots were sampled by soil coring to a depth of 0.75 m at four occasions during 2005-2006 growing season. Two distinct phases of root development were identified, a rapid downward penetration from emergence to end tillering phase, followed by a substantial root mass growth along the profile from tillering to mid-stem-elongation phase. Roots were detected as deep as 0.75 m during the initial rapid penetration, yet only 29% of the total seasonal root mass was developed. This downward penetration rate averaged 7 mm d⁻¹ and produced 10.8 kg ha⁻¹ d⁻¹ of root dry-biomass. The bulging of root mass from tillering to mid-stem-elongation coincided with vigorous shoot growth, doubling root dry-biomass at a rate of 52 kg ha⁻¹ d⁻¹, compared to the seasonal root growth rate of 18.3 kg ha⁻¹ d⁻¹. A second-degree equation described the total root dry-biomass as a function of days after emergence (r² = 0.85), whereas a simpler equation predicted it as a function of cumulative growing degree days (r² = 0.85). The final grain yield was a strong function of irrigation regimes, varying from 3.0 to 6.5 t ha⁻¹, but showed no correlation with root biomass which remained similar as soil water regimes changed. This observation must be viewed with care as it lacks statistical evidence. Results showed 90% of root mass at first irrigation (15 April) confined in the top 0.60-0.75 m soil in bread wheat. Presence of shallow restricting soil layers limited root depth of durum wheat to 0.45 m, yet total seasonal root mass and grain yield were comparable with non-restricted bread wheat. Most root growth occurred during the cool rainy season and prior to the late irrigation season. The root sampling is short of rigorous, but results complement the limited field data in literature collectively suggesting that irrigation following the rainy season may best be scheduled assuming a well developed root zone as deep as the effective soil depth within the top meter of soil.     

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.     

Water use, crop coefficients, and irrigation management criteria for camelina production in arid regions

Camelina sativa (L.) Crantz is an oilseed crop touted as being suitable for production in the arid southwestern USA. However, because any significant development of the crop has been limited to cooler, rain-fed climate-areas, information and guidance for managing irrigated-camelina are lacking. This study measured the crop water use of a November-through-April camelina crop in Arizona using frequent measurements of soil water contents. The crop was grown under surface irrigation using five treatment levels of soil water depletion. The seed yields of treatments averaged 1,142 kg ha⁻¹ (8.0% seed moisture) and were generally comparable with camelina yields reported in other parts of the USA. Varying total irrigation water amounts to treatments (295–330 mm) did not significantly affect yield, whereas total crop evapotranspiration (ET_c) was increased for the most frequently irrigated treatment. However, total ET_c for the camelina treatments (332–371 mm) was markedly less than that typically needed by grain and vegetable crops (600–655 mm), which are commonly grown during the same timeframe in Arizona. The camelina water-use data were used to develop crop coefficients based on days past planting, growing degree days, and canopy spectral reflectance. The crop coefficient curves, along with information presented on camelina soil water depletion and root zone water extraction characteristics will provide camelina growers in arid regions with practical tools for managing irrigations.     

Irrigation, tillage and mulching effects on soybean yield and water productivity in relation to soil texture

Depleting groundwater resources in Indian Punjab call for diversifying from rice to crops with low evapo-transpiration needs and adopting water-saving technologies. Soybean offers a diversification option in coarse- to medium-textured soils. However, its productivity in these soils is constrained by high soil mechanical resistance and high soil temperature during early part of the growing season. These constraints can be alleviated through irrigation, deep tillage and straw mulching. This 3-years field study examines the individual and combined effects of irrigation, deep tillage, and straw mulching regimes on soybean yield and water productivity (WP) in relation to soil texture. Combinations of two irrigation regimes viz., full irrigation (I_f), and partial irrigation (I_p) in the main plot; two tillage regimes viz., conventional-till (CT)-soil stirring to 0.10 m depth, and deep tillage (DT)-chiseling down to 0.35 m depth followed by CT in the subplot; and two mulch rates viz., 0 (M₀) and 6 t ha⁻¹ (M) in the sub-subplot on two soils differing in available water capacity were evaluated.Seed yield was greater in the sandy loam than in the loamy sand reflecting the effects of available water capacity. Irrigation effects were greater on loamy sand (40%) than on sandy loam (5%) soil. Deep tillage benefits were also more on loamy sand (14%) compared to sandy loam (5%) soil. Yield gains with mulching were comparable on the two soils (19%). An evaluation of interaction effects showed that mulching response was slightly more in I_p (20%) than in I_f regimes (17%) in the sandy loam; while in the loamy sand, mulching gains were comparable (18-19%) in both irrigation regimes. Benefits of deep tillage in the loamy sand soil were more in I_p (20%) than in I_f regimes (17%). Deep tillage and straw mulching enhanced WP (ratio of seed yield/water use) from 1.39 to 1.97 kg ha⁻¹ mm⁻¹ in I_p regime, and from 1.87 to 2.33 kg ha⁻¹ mm⁻¹ in I_f regime in the loamy sand soil. These effects on WP were less in the sandy loam soil with greater available water capacity. Yield and WP gains are ascribed to deeper and denser rooting due to moderation of soil temperature and water conservation with straw mulching and tillage-induced reduction in soil mechanical resistance. Root mass in CTM₀, CTM, DTM₀ and DTM was 2.79, 5.88, 5.34 and 5.58 mg cm⁻² at pod-filling in the loamy sand soil. Comparable yield responses to deep tillage or mulching in the loamy sand soil suggest that either of the options, depending on their cost and availability considerations, can be employed for improving soybean yield and water productivity.     

Monitoring the pollution risk and water use in orchard terraces with mango and cherimoya trees by drainage lysimeters

Agricultural nonpoint-source pollution is the leading cause of water-quality degeneration of rivers and groundwater. In this context, the coast of Granada province (SE Spain) is economically an important area for the subtropical fruit cultivation. This intensively irrigated agriculture often uses excessive fertilizers, resulting to water pollution. Therefore, a 2-year experiment was conducted using drainage lysimeters to determine the potential risk of nutrient pollution in mango (Mangifera indica L. cv. Osteen) and cherimoya (Annona cherimola Mill. cv. Fino de Jete) orchards. These lysimeters were used to estimate the nutrient budgeting for each crop. NO₃-N, NH₄-N, PO₄-P and K losses according to lysimeters were, respectively, 55.1, 12.4, 3.7, and 0.6 for mango and 61.8, 17.8, 4.9, and 0.5 kg ha⁻¹ yr⁻¹, for cherimoya. NO₃, concentrations in the leachates ranged from 1.8 to 44.3 mg L⁻¹, and from 23.0 to 51.0 mg L⁻¹, for mango and cherimoya, respectively, in some cases exceeding the limits for safe drinking water. PO₄ also exceeded the permitted concentrations related to eutrophication of water, ranging from 0.07 to 0.5 mg L⁻¹ and from 0.12 to 0.68 mg L⁻¹ from mango and cherimoya lysimeters, respectively. With respect to the nutrient balance, N, P, and K removed by cherimoya fruits was 76.4, 5.5, and 22.6 kg ha⁻¹ yr⁻¹, and for mango fruits 30.2, 3.3 and 27.8 kg ha⁻¹ yr⁻¹, respectively. Nutrient losses in the leachates were surprisingly low, considering total N, P, and K applied during the year, in mango lysimeters 3.8, 0.11, and 12.6%, and in cherimoya lysimeters 7.7, 0.23 and 16.0%, respectively, indicating a potential soil accumulation and eventual loss risk, especially during torrential rains. Crop coefficient (Kc) values of mango trees varied within ranges of 0.35–0.67, 0.55–0.89, and 0.39–0.80 at flowering, fruit set, and fruit growth, respectively. Kc values for cherimoya trees had ranges of 0.58–0.67, 0.61–0.68, and 0.43–0.62 at flowering, fruit set and fruit growth, respectively. In this study, the Kc values of mango and cherimoya were significantly correlated to julian days. Therefore, the estimated WUE in the mango and cherimoya orchards reached 21.2 and 14.0 kg ha⁻¹ mm⁻¹, respectively. Thus, this study highlights the urgency to establish the optimal use of fertilizers and irrigation water with respect to crop requirements, to preserve surface-water and groundwater quality, thereby achieving more sustainable agriculture in orchard terraces.     

Partitioning of seasonal evapotranspiration from a commercial furrow-irrigated Sultana vineyard

Seasonal partitioning of evapotranspiration (ET) between transpiration by grapevines (Vitis vinifera) (T _gp) and by cover crops of a ryegrass/clover mixture (T _cc), and soil evaporation (E _s) was performed for a furrow-irrigated vineyard during the 1994/1995 and 1995/1996 growing seasons in south-eastern Australia. ET, determined with a water balance approach, averaged 622 mm. The ET rate averaged over the two seasons increased from 2 mm day^–1 in spring (September to November), when it was dominated by T _cc, to peak rates of around 5 mm d^–1 in summer (December to February) when it was dominated by E _s. T _gp, determined with either heat-pulse sensors or the Penman-Monteith equation, attained peak rates of 0.75 and 0.98 mm d^–1, or 6.2 and 8.1 l vine^–1 day^–1 in the first and second seasons, respectively. Total seasonal T _gp of 109.1 mm (900 l vine^–1) in 1994/1995 and 118.8 mm (980 l vine^–1) in 1995/1996 constituted just 18 – 19% of total ET. T _cc totalled 214 mm (34% of ET) in the first season, when pasture cover was sparse and present for 5 months of the growing season (September to February), and 196 mm (30% of ET) in the second season when pasture cover was heavy but present for only 3 months (September to November). E _s averaged 49% of total ET over both seasons. At least 30% of water used for ET was contributed by antecedent soil water in both seasons. The crop factor (K _c) was largely constant throughout the season with an average value of 0.48. The depletion pattern of soil water indicated that the vine explored the soil profile well beyond 1.0 mm depth and almost evenly up to a distance of 1.5 m from the trunk. Water use efficiencies for fresh fruit yield (WUE), i. e., the ratio of fruit weight to total water use at harvest,were 13.3 and 40.5 kg ha^–1 mm^–1 when based on ET in 1994/1995 and 1995/1996, respectively, and 84.0 and 211.1 kg ha^–1 mm^–1, respectively, when based on T _gp. The T _gp data were used to verify three models of vine transpiration developed in an earlier study. Models based on the green area index or on fraction of incident radiation intercepted by the vine canopy produced good agreement with T _gp. The model based on canopy resistance performed poorly, indicating the difficulty of extrapolating the stomatal response to environmental variables from one set of experimental conditions to another. Received: 23 September 1996     

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.     

Differences in water-use efficiency among perennial forages used by the dairy industry under optimum and deficit irrigation

The cost and scarcity of water is placing increasing pressure on Australian dairy farmers to utilise water for forage production as efficiently as possible. This study aimed to identify perennial forage species with greater water-use efficiency (WUE) than the current dominant species, perennial ryegrass (Lolium perenne L.). Fifteen perennial forage species were investigated under optimum irrigation and two deficit irrigation treatments, over three years at Camden, NSW, on a brown Dermsol in a warm temperate climate. Under optimal irrigation, there was a nearly twofold difference in mean WUE_t (total yield/evapotranspiration) between forages, with kikuyu (Pennisetum clandestinum Hochst. ex. chiov.) having the highest (27.3 kg ha⁻¹ mm⁻¹) and birdsfoot trefoil (Lotus corniculatus L.) the lowest (14.8 kg ha⁻¹ mm⁻¹). Kikuyu was also the most water use efficient forage under the extreme deficit irrigation treatment, although its mean WUE_t declined by 15% to 23.2 kg ha⁻¹ mm⁻¹, while white clover (Trifolium repens L.) in the same treatment had the largest decline of 44% and the lowest WUE_t of only 8.8 kg ha⁻¹ mm⁻¹. In order to maximise WUE for any forage, it is necessary to maximise yield, as there is a strong positive relationship between yield and WUE_t.     

Irrigation effects on the growth, yield, and water use efficiency of alfalfa

A field study was conducted in the semiarid region of northern Sudan to investigate the effects of variable irrigation on the growth, yield, and water use efficiency (WUE) of alfalfa (Medicago sativa L.). Treatments were 65 mm of water applied every 7 days, 80 mm of water applied every 10 days, or 104 mm of water applied every 13 days. The heavy, infrequent irrigation reduced stem height, stem density, leaf area index (LAI), total biomass production, and the WUE of alfalfa plants. Maximum yields for six harvests were 15.3, 12.9, and 11.2 ton ha^–1 and the WUE values were 0.12, 0.10, and 0.08 ton ha^–1 cm^–1 for the frequent, less-frequent, and infrequent irrigation regimes, respectively. In all the treatments, alfalfa dry matter yield was positively correlated with stem height and LAI. The relationship between dry matter yield and total water use was a linear function (R ²=0.99), regardless of the irrigation treatment. Alfalfa growth, yield, and WUE remained high during the relatively cool months and declined during the hot period under the three water regimes. It was concluded that alfalfa grown under semiarid conditions should be watered lightly and frequently to attain high yields and high WUE. Received: 19 February 1996