Levels Of Supplemental Irrigation Research Articles

Exogenously applied 5-aminolevulinic acid modulates growth, yield, and physiological parameters in lentil (Lens culinaris Medik.) under rain-fed and supplemental irrigation conditions

Lentils are a significant source of plant protein and are cultivated across Asia, Europe, and North Africa. Plants are subjected to various environmental stresses, which can hinder growth, yield, and productivity. 5-aminolevulinic acid (ALA) is a compound that acts as a precursor in the biosynthesis of tetrapyrroles and can increase plant tolerance to different abiotic stressors. However, the effects of exogenously applied ALA on lentil growth, yield, and physiological parameters under rain-fed and supplemental irrigation conditions are not well-known. In this study, a split plot experiment was conducted to investigate the impact of ALA foliar application and supplemental irrigation on lentil (Lens culinaris Medik.). The experiment was designed based on a randomized complete block with three replications. The main plot included four levels of supplemental irrigation [(supplementary irrigation in the flowering and early seed-filling stages, supplementary irrigation in the flowering stage, supplementary irrigation in the early seed-filling along with rain-fed conditions (no irrigation)]. The subplot considered foliar application of ALA at varying levels [(0 (control), 50 and 100 ppm)]. The results showed that water regimes and foliar spray with ALA significantly (P ˂ 0.01) affected plant height, number of pods per plant, pod weight, number of seeds per pod and weight of 1000 seeds, biological yield, seed yield, and harvest index. The highest total chlorophyll content was observed in plants that were subjected to supplementary irrigation in flowering and early seed filling stages and foliar sprayed with 100 ppm ALA. The study also found that exogenous ALA improved drought tolerance in lentil plants under rain-fed conditions mainly by regulating antioxidant enzymes, which ultimately protected the cellular membranes against overproduction of H2O2. Furthermore, ALA application increased total carbohydrate contents at all supplemental irrigation levels, but the rate was higher in complementary irrigation conditions during flowering and early seed-filling stages. Malondialdehyde (MDA), H2O2, and proline contents were increased in field-grown plants under rain-fed conditions without exogenous ALA application. In conclusion, this study sheds light on the effects of ALA foliar spray and supplemental irrigation on lentil growth, yield, and physiological parameters. The findings suggest that exogenous ALA can improve plant tolerance to various abiotic stressors and enhance plant growth, yield, and physiological parameters.

Nitrogen management and supplemental irrigation affected greenhouse gas emissions, yield and nutritional quality of fodder maize in an arid region

Deficit and erratic precipitation in arid regions and imbalance nitrogen (N) fertilization can result in lower yield and nutritional quality of fodder maize. The objectives of the experiment were to investigate the effect of N (urea 46% N) rates i.e., 225 (N1), 300 (N2) and 375 kg N ha–1 (N3) under 600 (W1) and 900 mm ha–1 (W2) supplemental irrigation levels on the greenhouse gas (GHG) emissions, yield and nutritional quality of fodder maize. The treatments combination comprised of N1W1, N2W1, N3W1, N1W2, N2W2 and N3W2. N fertilization and supplemental irrigation levels significantly affected soil moisture content (SMC) and soil temperature (ST), whereas maximum SMC and minimum ST were recorded in N3W2. Increasing N rate decreased soil ammonium nitrogen content (NH4+-N) and increased nitrate nitrogen content (NO3–-N) and maximum NH4+-N was recorded in N1W1 and maximum NO3–-N in N3W1. Methane (CH4) uptake was higher in W1 compared with the W2, and maximum CH4 uptake was recorded in N3W1 followed by N3W2. Nitrous oxide (N2O) and carbon dioxide (CO2) emissions were higher in W1 compared with the W2, and maximum N2O and CO2 emissions were recorded in N3W1. Cumulative emission of N2O and CO2, CH4 uptake, global warming potential (GWP), and greenhouse gas intensity (GHGI) were higher in W1 compared with W2 and their maximum values were recorded in N3W1. Treatment N3W2 significantly improved the forage yield and nutritional quality of fodder maize by improving the crude protein content and ether extract content, while reducing neutral detergent and acid detergent fibers contents. In conclusion, treatment N3W2 improved SMC, forage yield, grain yield, and nutritional quality of fodder maize as well as reduced GHG emissions, GWP and GHGI in an arid region.

Comparative effect of seed treatment with thyme essential oil and Paraburkholderia phytofirmans on growth, photosynthetic capacity, grain yield, δ15N and δ13C of durum wheat under drought and heat stress

AbstractAbiotic stresses such as drought and heat constitute one of the major constraints to global crop production, and climate change will worsen the scenario. There is growing interest in investigating the application of biostimulants to palliate yield losses due to the impact of drought and heat stress. This study focuses on assessing the impact of coating seeds with either thyme essential oil or Paraburkholderia phytofirmans PsJN strain on agronomic performance of durum wheat subjected to contrasting levels of irrigation. For this aim, the Tunisian durum wheat genotype Karim was cultivated in a field experiment in a semi‐arid climate, with two supplemental irrigation levels (SI): moderate drought stress (100% SI) and severe drought stress (50% SI). The impact of the seed coating technique was assessed on grain yield (GY) and its agronomic components (spikes/m2, straw yield [SY], 1,000 kernel weight [TKW] and the harvest index [HI]) across two consecutive crop seasons; 2015–16 and 2016–17. In addition, the effect on leaf nitrogen and carbon isotope composition (δ15N, δ13C) and nitrogen and carbon contents of leaves at grain filling was also assessed in the 2016–17 season. The two seed coating treatments (SCTs) enhanced GY, SY, spikes/m2, TKW and HI under both moderate stress (100% SI) and severe stress (50% SI). The positive effect of the SCTs on GY and agronomic yield components was more marked under the combined heat–water stress conditions of the first season (2015–16). In general, thyme oil enhanced vegetative growth, tillering and tiller fertility, while, PsJN had a positive effect, more centred on the grain filling stage. Under moderate stress, both SCTs decreased δ15N and δ13C at grain filling and straw N content at harvest, illustrating a better carbon and nitrogen uptake and mobilisation. Under severe water stress, both SCTs induced higher leaf total N, and lower δ13C, and leaf total C at grain filling. The effect on physiological traits and carbon and nitrogen metabolism is discussed. The findings emphasise a practical implication of these biostimulants.

Interactive effects of plastic film mulching with supplemental irrigation on winter wheat photosynthesis, chlorophyll fluorescence and yield under simulated precipitation conditions

Water shortages continuously threaten agricultural productivity in semi-arid regions. Efficient water-saving management practices urgently need to be developed. In the present study, a mobile rain shelter was used with two cultivation modes: (1) the ridge furrow (R) rainfall harvesting system; and (2) traditional flat planting (F). In addition, two supplemental irrigation levels (150, 75 mm) and three precipitation levels (1: 275, 2: 200, 3: 125 mm) were included in this study. We demonstrated that the R system with 150 mm supplemental irrigation and 200 mm simulated rainfall can significantly improve winter wheat net photosynthesis rate (Pn), electron transport rate (ETR), effective quantum yield of PS II (ΦpsII), maximum quantum efficiency of PSII (Fv/Fm), variable fluorescence (Fv), energy transformation potential of PSII (Fv/Fo), and leaf photosynthetic performance index of PSⅡ (Fv/Fmʹ), at the jointing, flowering, and later stage of grain filling. These improvements were due to significantly increased soil moisture content, total chlorophyll ab contents (13.1%), and chlorophyll stability index (88.3%) of flag leaves, and decreased (32.7%) evapotranspiration (ET) at field scales and soil temperature, all of which increased the grain yield (18.9%) and water use efficiency (WUE, 75.8%) compared with traditional flat planting. The chlorophyll fluorescence parameters of winter wheat were significantly positively correlated with the Pn, total Chl, WUE, and grain yield (except ET). These results suggest that the R system with 150 mm supplemental irrigation and 200 mm simulated rainfall was the best cultivation practice for improving photosynthesis, chlorophyll fluorescence, WUE, and yield of winter wheat in semi-arid regions.

Cultivar by environment effects of perennial ryegrass cultivars selected for high water soluble carbohydrates managed under differing precipitation levels

Historic results of perennial ryegrass (Lolium perenne L.) breeding include improved disease resistance, biomass, and nutritional quality. Yet, lack of tolerance to water stress limits its wide use. Recent efforts to increase water soluble carbohydrate (WSC) content in perennial ryegrass may increase drought tolerance. Herein, we report results of a multi-year and location evaluation of differing precipitation/irrigations levels on genetic and genotype × environment interaction effects of various agronomic traits in perennial ryegrass. The study included two UK environments (Aberystwyth, Wales and Edinburgh, Scotland) and four USA environments located in Logan, UT and consisting in four supplemental irrigation levels in a line-source irrigation design. Data included herbage dry matter, dry matter digestibility, crude protein, and WSC, collected from 2011 to 2013. There were differences (P < 0.05) among the included cultivars for each phenotype when evaluated across environments. There was observed cultivar × environment interaction for each phenotype, which precluded the identification of the best cultivar over all environments. Additive main effect and multiplicative interaction modeling allowed for grouping of the individual environments to mega-environments. The analysis identified three mega-environments for each phenotype: (1) the UK environments, (2) the two highest Logan irrigation levels, and (3) the two lowest Logan irrigation levels. Mega-environments designations corresponded to water stress, temperature, and inherent geographic/climate differences between the environments. The evidence for the potential of increased WSC to improve drought tolerance under water stress was inconclusive, but high WSC cultivars also exhibited high herbage production under the imposed water stress.

English

This study aims to evaluate the effect of supplemental irrigation levels on vegetative parameters of bell pepper grown in open field and under shade mesh. The experimental design was a randomized complete block with four replications and ten treatments in factorial scheme (four irrigation levels combined with shade). Irrigation treatments consisted in 0.25, 0.50, 0.75 and 1.0 rate of crop evapotranspiration and the control (no-irrigation).Shading treatment was of 50% reduction of the photosynthetically active radiation compared to open field conditions. Vegetative parameters were influenced by irrigation. The growth rate of plants present no significant difference. The growth rate of stem diameter present difference, being treatments 0.50 and 0.75 the highest.Significant interaction was present in the rate of chlorophyll, dry matter, leaf area index and number of leaves per plant. Plots under shade mesh showed the highest growth rate in plant height and stem diameter and leaf area index, number of leaves per plant, dry matter and lower chlorophyll index. As irrigation strategy, considering the water use efficient and vegetative characteristics of bell pepper, the most favorable irrigation levels were 0.5 and 0.75 of ETc, under shade and in open field, respectively, without affecting the vegetative parameters and yield. &nbsp; Key words: Capsicum annuum, water stress, water use efficiency, drip irrigation.

Supplemental Irrigation Requirements of Zoysiagrass and Bermudagrass Cultivars

ABSTRACTMunicipal water restrictions have become commonplace throughout much of the southern United States. The objectives of this 2‐yr study were to (i) determine supplemental irrigation requirements necessary for achieving acceptable quality in 15 zoysiagrass (Zoysia japonica and Zoysia matrella) and bermudagrass (Cynodon ssp.) cultivars when managed under a 2 d/wk irrigation frequency, (ii) determine the effects of mowing height on irrigation requirements, and (iii) evaluate root development differences between the species and cultivars at the completion of the study. A linear gradient irrigation system (LGIS) was used to provide an irrigation gradient across field plots. Plots were evaluated along the gradient six times over two summers to determine the level of supplemental irrigation, relative to reference evapotranspiration (ETo), necessary for maintaining acceptable visual quality. The fine‐textured, sports‐type bermudagrass cultivars required the least supplemental irrigation (∼10 to 15% × ETo) to maintain acceptable quality in the study. The medium‐textured amenity bermudagrasses and Japanese lawngrass (Zoysia japonica Steud.) cultivars required similar but somewhat greater irrigation requirements (∼15 to 20% × ETo) than the fine‐textured bermudagrasses. Manilagrass cultivars (Z. matrella) required the highest supplemental irrigation requirements (∼25 to 33% × ETo) for maintaining acceptable appearance within 2 d/wk irrigation regime. Mowing height did not consistently affect irrigation requirements for either group of bermudagrass but affected the Zoysia species differently. Tall mowing heights generally reduced irrigation requirements in Z. japonica but increased irrigation requirements for Z. matrella cultivars. While few intraspecific root development differences occurred within the 0 to 25 cm soil depth, Z. matrella root development was limited relative to bermudagrass and Z. japonica cultivars within deeper (25–50 cm) soil, which may have contributed to the higher irrigation requirements for the species. The results emphasize differences in supplemental irrigation levels needed for maintaining acceptable appearance among warm‐season turfgrass species and cultivars during 2 d/wk irrigation.

Effect of supplemental irrigation on yield and water productivity of dry season crops in Andaman and Nicobar Islands

Field experiments were conducted with different supplemental irrigation levels for growing maize, greengram, sesame, okra and chilies during the dry season of 2006–07 and 2007–08 in A &amp; N Islands. The results indicated that though the yields achieved with supplemental irrigation has not achieved at par with that of farmers, practice (I5) of irrigating the crop as and when required (4 160 and 10 398 kg/ha during 2006–07 and 2007–08 respectively), it has increased the yield significantly in both the years vis-à-vis I0 i e, no irrigation (1 355 and 5 640 kg/ha during 2006–07 and 2007–08 respectively). The percent yield increase over I0 when supplemental irrigation was provided one (I1), two (I2), three(I3) and four (I4) times due to supplemental irrigation was 48, 95, 133 and 178 in I1, I2, I3 and I4 during 2006–07 and 13, 27, 53, 62 in I1, I2, I3 and I4 during 2007–08 respectively. Thus by providing supplemental irrigation at different critical crop growth stages, higher yield and economic returns were achieved with lesser irrigation water usage, an important consideration for raising dry season crops in the rice fallows from the harvested rainwater of rainy season under Island conditions. However, the results also underlined the fact that cultivation of vegetables like okra and chillies on residual soil moisture alone without irrigation during dry season in the islands may be riskier and result in economic loss if the rainf all during the cropping period is very low.

Cotton-Grain Sorghum Rotation under Extreme Deficit Irrigation Conditions

There are over 1.0 million ha of cultivated land in the Southern High Plains of Texas, with about 40% in dryland production. Strategies that couple dryland production methods with very low levels of supplemental irrigation in contrast to current irrigated practices could stabilize crop output for an extended period at the expense of reduced agricultural productivity. An eight-year field experiment was conducted from 2001 to 2008 to develop cropping data for economic analysis. The principle goal was to compare a cotton (Gossypium hirsute L.) - sorghum [Sorghum bicolor (L.) Moench] (2:1) rotation system to a continuous cotton system, both efficiently irrigated at levels well below the evapotranspiration rate of these crops. Seasonal irrigation capacities were approximately 0%, 20%, and 40% of peak evapotranspiration rates. The rotation strategy from 2003 to 2005 allowed the movement of limited irrigation between crops based on relative water needs at critical growth periods, and from 2006 to 2008, based on water needs of the crop with the higher economic value. The results showed that in years of below average rain, cotton following sorghum resulted in 18% to 44% higher lint yields compared to continuous cotton. In years of average rain, cotton lint yields following grain sorghum were generally higher than those of continuous cotton, averaging 21%, with a portion of the increase due to higher irrigation. And, in years of above average rain, significant yield differences due to rotation were minimal, particularly at the highest irrigation capacity. Directing available irrigation to the crop of higher value (cotton) at the expense of the lower value crop (sorghum) appeared to be a major factor in elevating seasonal irrigation water use efficiency (0.448 to 0.513 kg lint m-3) compared to irrigating the most water stressed crop (0.200 to 0.35 kg lint m-3). Although cotton lint yield tended to be higher in the rotation than the continuous cotton treatments, the rotation resulted in significantly lower gross irrigation value than the continuous cotton cropping system in most years.

Optimizing supplemental irrigation: Tradeoffs between profitability and sustainability

Water production functions are used to model yield response to various levels of supplemental irrigation (SI), to assess water productivity coefficients, and to identify optimum irrigation under various input–output price scenarios. The SI production function is taken as the difference between the total water production function (irrigation + rain) and that of rainwater. Theoretical analysis of the unconstrained objective function shows that the seasonal depth of SI to maximize profit occurs when the marginal product of water equals the ratio of unit water cost to unit product sale price. Applying this analysis to wheat in northern Syria, the production functions of SI under different rainfall conditions are developed. Coupled with current and projected water costs and wheat sale prices, the functions are used to develop an easy-to-use chart for determining seasonal irrigation rates to maximize profit under a range of seasonal rainfall amounts. Results show that, for a given seasonal rainfall, there is a critical value for the ratio of irrigation cost to production price beyond which SI becomes less profitable than rainfed production. Higher product prices and lower irrigation costs encourage the use of more water. Policies supporting high wheat prices and low irrigation costs encourage maximizing yields but with low water productivity. The resulting farmer practice threatens the sustainability of water resources. Balancing profitability versus sustainability is a challenge for policy makers. Our analysis can help national and local water authorities and policy makers determine appropriate policies for water valuation and allocation; and assist extension services and farmers in planning irrigation infrastructure and farm water management.

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

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

Water use efficiency of winter-sown chickpea under supplemental irrigation in a mediterranean environment

Chickpea is one of the major legume crops grown in the West Asia and North Africa (WANA) region. It has considerable importance as a food, feed and fodder. Traditionally, it is sown in spring as a rainfed crop in the region, which has highly variable and often insufficient rainfall. It is, therefore, largely raised on residual moisture, which results in low and variable yields and discourages farmers from investing inputs in its production. In the early 1990s, a winter-sown chickpea technology was developed that outweighs spring-sown chickpea in terms of productivity, water use efficiency and other traits. Limited supplemental irrigation can, however, play a major role in boosting and stabilizing the productivity of both spring-sown and winter-sown chickpea. Therefore, we investigated the effect of supplemental irrigation and sowing date on yield and water use efficiency in winter-sown chickpea. An experiment was carried out over four cropping seasons (1997–2001) at ICARDA’s main station at Tel Hadya, Aleppo, northern Syria (mean annual rainfall 330 mm). A cold-tolerant chickpea cultivar with improved resistance to ascochyta blight (ILC 3279, released as Ghab 2 in Syria) was grown in rotation with wheat. The experiment included three sowing dates (late November, mid-January, and late February) and four levels of supplemental irrigation (SI): full SI, 2/3 SI, 1/3 SI, and no SI, i.e. rainfed. The plots were replicated three times in a split-plot design, with date of sowing being the main plot treatment. Soil water content was monitored at approximately at 7–14-day intervals using a neutron probe. Crop evapotranspiration was determined for each subplot during each time interval, from sowing to harvest, using the soil-water balance equation. Water use efficiency was determined as the ratio of crop yield per unit area to seasonal evapotranspiration. The results showed that chickpea yield per unit area increases with both earlier sowing and increased SI. However, water use efficiency under supplemental irrigation decreases with earlier sowing, due to the relatively large increase that occurs in the amount of evapotranspiration at early sowing dates. The study’s results indicated that a 2/3 SI level gives the optimum water use efficiency for chickpea under supplemental irrigation. Under rainfed conditions, however, it was found that sowing chickpea around mid-January resulted in the highest WUE. The analysis also proposed a function, based on regression, which relates winter-sown chickpea yield to water use and which is applicable under both supplemental and rainfed conditions.

Supplemental irrigation for dry-spell mitigation of rainfed agriculture in the Sahel

Unreliable and erratic rainfall combined with inherent low soil fertility in crust prone soils affect crop growth in the Sahel. Past efforts of agricultural water management have primarily focused on maximising rainfall infiltration through soil and water conservation. The challenge of how to cope with dry-spells, short periods of water stress during crop growth, remains largely unsolved. Small-scale water harvesting (WH) for supplemental irrigation may be a tool for small-holder farmers to stabilise crop water supply and thereby increase yields and create incentives for increased investments in fertilisation. Results are presented on the effects on Sorghum ( Sorghum Bicolor (L.)) yields under supplemental irrigation and soil nutrient application in an on-farm experiment in northern Burkina Faso. Focus is on dry-spell bridging and water and nutrient interactions on biomass productivity. The water harvesting system consisted of a low-cost manually dug farm pond with a storage volume of 150 m 3, collecting surface runoff as rill and small gully flow from a 1.8 ha catchment area. The on-farm experiment involved five repetitions of two levels of nutrient application (non-fertilised and fertilised) and two levels of supplemental irrigation (non-irrigated and irrigated) including: farmers’ traditional practices (TC), supplemental irrigation (I), fertiliser application (F) and supplemental irrigation combined with fertilisation (IF). This paper presents field results from three rainy seasons (1998–2000), receiving a cumulative seasonal rainfall ranging from 418 to 667 mm. Supplemental irrigation ranging from 60 to 90 mm per season was applied based on actual occurrence of dry-spell induced crop water stress. Supplemental irrigation had a significant effect on grain yield over the three crop seasons ( ∗∗ P<0.001). Similarly, fertiliser application (46.5 kg N ha −1) resulted in a significantly higher grain yield ( ∗∗∗ P<0.0001). Analysis of variance for interactions between supplemental irrigation and fertiliser application showed significant differences between treatments when analysing the 3 years together ( ∗∗∗ P<0.0001). The control grain yield’s (TC) average over the 3 years was 455 kg ha −1. Supplemental irrigation alone resulted in an average grain yield of 712 kg ha −1, while fertiliser application alone gave an average grain yield of 975 kg ha −1. Supplemental irrigation combined with fertiliser application resulted in an average grain yield of 1403 kg ha −1, which is higher than the farmer’s normal practice by a factor of three. Total above ground biomass yields followed the same pattern as the grain yields for respective years. All three seasons provided data systematically supporting supplemental irrigation as a dry-spell mitigating and yield gap reducing technology.

Water Use Efficiency of Rainfed and Irrigated Bread Wheat in a Mediterranean Environment

In West Asia and North Africa, shortage of water limits wheat (Triticum aestivum L.) production. Current irrigation practices aim at maximizing grain yield, but achieve lower return for the water consumed. Maximizing water use efficiency (WUE) may be more suitable in areas where water, not land, is the most limiting factor. We examined the effects of various levels of supplemental irrigation (SI) (rainfed, 1/3 SI, 2/3 SI, full SI), N (0, 5, 10, 15 g N m−2), and sowing time (Nov., Dec., Jan.) on evapotranspiration (ET) and WUE of wheat. WUE was calculated for rain (WUEr), for total water (gross: rain + irrigation) (WUEg), and for SI water only (WUESI). ET ranged from 246 to 328 mm for rainfed crops, with grain yield ranging from 130 to 270 g m−2 and total dry matter from 380 to 1370 g m−2. Irrigated crops had ET of 304 to 485 mm, with grain yield of 170 to 500 g m−2. The degree to which water supply limits grain yield was indicated by the ratio of pre‐ to post‐anthesis ET (2.1–2.4:1). The SI treatments significantly increased WUEg: from 0.77 to 0.83 to 0.92 kg m−3 in November and December sowings for 1/3 SI and from 0.77 to 0.92 kg m−3 in November sowing for 2/3 SI. The highest WUEg and WUESI were achieved at 1/3 to 2/3 SI. WUE was substantially improved by applying 5 and 10 g N m−2, with little increase for higher rates. Delaying sowing had a negative effect on WUE for both irrigation and rainfed conditions. In this rainfed Mediterranean environment, WUE can be substantially improved by adopting deficit SI to satisfy up to 2/3 of irrigation requirements, along with early sowing and appropriate levels of N.

Soil Management and Supplemental Irrigation Effects on Potato: II. Root Growth

AbstractThis study was conducted to determine if supplemental irrigation and/or application of soil amendments rich in organic matter can improve root growth of potato (Solanum tuberosum L.). Root length density (RLD) and root dry matter production of potato were studied under two levels of supplemental irrigation (nonirrigated check vs. moderate irrigation) and two levels of soil amendments [none vs. amended with compost and manure from beef cattle (Bos taurus L.)] during 1993 and 1994. Amendments significantly increased RLD during both growing seasons and these increases occurred consistently throughout each growing season. Irrigation effects were not observed in 1993, while irrigation significantly increased RLD during 1994. Approximately 85% of the root length was concentrated in the upper 30‐cm layer of the soil. The supplemental irrigation and soil amendment treatments did not affect the proportional distribution of roots among the soil layers. Root‐to‐shoot ratio was not affected by irrigation or amendment during either growing season. The RLD and leaf area index (LAI) at all four sample dates during 1994 were significantly correlated with final tuber yields, indicating that growth patterns early in the season were important in establishing the productivity of the potato crop. Root length density tended to have a higher correlation with yields than did LAI (r = 0.58* to 0.80** vs. 0.51* to 0.68**).

Nitrogen Leaching as Influenced by Nitrogen Management and Supplemental Irrigation Level

AbstractCorn (Zea mays L.) management systems involving two nitrogen (N) fertilization methods and two supplemental irrigation levels were evaluated for soil water percolation and N leaching losses in west central Minnesota. Nonweighing lysimeters were used to collect soil water and the accompanying nutrients that moved below the root zone of the droughty Estherville sandy loam soil studied. Nitrogen was applied either as granules broadcast and disked in before planting or in liquid form through the irrigation system four times during the growing season. Supplemental irrigation was applied as either a partial replenishment (2.5 cm) or full replenishment (5 cm) irrigation each time the available soil water decreased to about 5 cm (50% depletion).Annual soil water percolation from spring thaw to fall freezeup averaged about 7.1, 11.2, and 18.0 cm for nonirrigated corn, 2.5‐cm irrigated corn, and 5‐cm irrigated corn, respectively, during the 5‐year period studied. Average annual NO3‐N leaching losses ranged from about 29 (for nonfertilized, nonirrigated corn) to 112 kg ha−1, and the combination of variable rainfall, soil NO3‐N content, and low soil water‐holding capacity caused great variation within and among years. Compared with values for fertilized nonirrigated corn, annual NO3‐N leaching losses increased an average of 17 and 53%, respectively, for the partial and full replenishment irrigations. The periodic application of liquid N through the irrigation system reduced average annual NO3‐N leaching loss by about 12 kg ha−1 at the 5‐cm irrigation level, but no difference resulting from N management was observed at the 2.5‐cm level.