Mm Of Irrigation Research Articles

Water and Nitrogen Use of Winter Wheat under Different Supplemental Irrigation Regimes

Winter wheat (Triticum aestivum L.) production in the Huang‐Huai‐Hai plain of China has been threatened by drought. This study was conducted to determine the water and N use of wheat under quantifying irrigation (W1, 60 mm of irrigation each at jointing and anthesis) and supplemental irrigation, determined by measuring the water content in the 0‐ to 20‐cm (W2), 0‐ to 40‐cm (W3), and 0‐ to 60‐cm (W4) soil layers. The highest grain yields of 9177 kg ha−1 in 2012 to 2013 and 9460 kg ha−1 in 2013 to 2014 were obtained in W3, which exhibited greater soil water consumption in the 60‐ to 140‐cm soil layers. Soil nitrate N uptake in the 40‐ to 160‐cm soil layers was higher than in W1, W2, and W4 treatments. Compared with the W1, W2, and W4, the total N uptake in W3 was higher by 9.4, 27.1, and 7.7%, respectively, and the grain N content was higher by 13.3, 33.0, and 11.2%. The water use efficiency, partial factor productivity of applied fertilizer and N harvest index were the highest in W3, which also showed high N utilization efficiency. Quadratic relationships of the amount of irrigation with soil water consumption, grain yield, water use efficiency, total N uptake, N translocation amount, N uptake for grain postanthesis, partial factor productivity of applied fertilizer, and N harvest index were also observed. Optimizing the supplemental irrigation regime improved uptake water and N uptake from the soil and increased the grain yield and water and N use.

Irrigation Requirements for Seed Production of Five Lomatium Species in a Semiarid Environment

Seeds of native plants are needed for rangeland restoration in the Intermountain West. Many of these plants are rarely cultivated and relatively little is known about the cultural practices required for their seed production. Irrigation trials were conducted for five perennial Lomatium species over multiple years. Lomatium species grown at the Oregon State University Malheur Experiment Station, Ontario, OR received 0, 100, or 200 mm of irrigation per year. Seed yield responses to irrigation were evaluated by linear and quadratic regression. In general, seed yields from the three species grown for 10 years responded linearly or quadratically to irrigation. To improve the accuracy of estimated irrigation water requirements, regressions were also run on seed yield responses to irrigation plus precipitation during the previous spring; spring and winter; and spring, winter, and fall. Over multiple years, Lomatium dissectum (Nutt.) Mathias & Constance and L. triternatum (Pursh) J.M. Coult. & Rose seed yields were best estimated by a quadratic response to irrigation plus spring precipitation with highest yields at 243 and 255 mm, respectively. Lomatium grayi (J.M. Coult. & Rose) J.M. Coult. & Rose seed yields were best estimated by a quadratic response to irrigation plus precipitation during the fall, winter, and spring with highest yields at 358 mm. Two of the Lomatium species were grown for the last 6 years. The seed yields of L. nudicaule (Pursh) J.M. Coult. & Rose did not respond to irrigation. Seed yields of Lomatium suksdorfii (S. Watson) J.M. Coult. & Rose responded linearly to irrigation in 2015.

Impact of Irrigation Volume on PRE Herbicide Activity

The importance of PRE herbicide applications in cotton has increased since the evolution of glyphosate-resistant (GR) Palmer amaranth. Cotton producers are relying on residual herbicides for control of Palmer amaranth, as POST options are limited or ineffective.S-Metolachlor, acetochlor, fomesafen, and dicamba all provide PRE control of Palmer amaranth; however, little is known about the effect of irrigation rate on incorporation and herbicidal efficacy. In 2015, an experiment was conducted on fine sand and loamy sand soils to evaluate the influence of irrigation volume (0.0 to 12.7 mm ha−1) on Palmer amaranth control with PRE herbicides. Irrigation volume after herbicide application was significant for bothS-metolachlor and acetochlor. Efficacy ofS-metolachlor was greatest in plots receiving 6.4 and 12.7 mm of irrigation where Palmer amaranth biomass was reduced to 4 and 2% of a nontreated control (NTC), respectively, compared with 61% in plots with the 0-mm irrigation treatment. Palmer amaranth control by acetochlor incorporated at 3.2- to 12.7-mm irrigation did not differ but did reduce Palmer amaranth biomass compared with the 1.6-mm irrigation rate. Irrigation volume was not significant for the soil incorporation of fomesafen or dicamba. Across all herbicides, fomesafen-treated plots provided the most consistent control of Palmer amaranth, reducing its biomass to < 3% of NTC at all irrigation rates. Dicamba provided the least and most inconsistent control of Palmer amaranth, producing 17 to 51% of NTC biomass.

Growth and development of soybean roots according to planting management systems and irrigation in lowland areas

ABSTRACT: The presence of a compacted soil layer near the ground surface in paddy fields may limit the growth and development of soybean roots. The objective of this study was to evaluate different planting management systems and irrigation on growth and development of soybean root systems in lowland area. The experiment was carried out in 2013/14 and 2014/15 crop seasons in randomized complete block design with factorial treatment (3x2), with four replications. The treatments consisted of different planting management systems: sowing with double disc (A1); sowing with shank (A2) and deep tillage + sowing with double disc (A3), and irrigation: irrigated (D1) and non irrigated (D2). Planting management systems and irrigation influenced the growth of soybean roots. When double disc was used, roots have lower growth and increase in diameter. Use of shanks and deep tillage provide increased growth and development of soybean roots and greater depth distribution. An additional 55mm of irrigation during the V4 soybean development stage provides increased surface area and root volume in when the soil moisture reaches values below 60% of field capacity.

Interactions among hydraulic conductivity distributions, subsurface topography, and transport thresholds revealed by a multitracer hillslope irrigation experiment

AbstractInteractions among hydraulic conductivity distributions, subsurface topography, and lateral flow are poorly understood. We applied 407 mm of water and a suite of tracers over 51 h to a 12 by 16.5 m forested hillslope segment to determine interflow thresholds, preferential pathway pore velocities, large‐scale conductivities, the time series of event water fractions, and the fate of dissolved nutrients. The 12% hillslope featured loamy sand A and E horizons overlying a sandy clay loam Bt at 1.25 m average depth. Interflow measured from two drains within an interception trench commenced after 131 and 208 mm of irrigation. Cumulative interflow equaled 49% of applied water. Conservative tracer differences between the collection drains indicated differences in flow paths and storages within the plot. Event water fractions rose steadily throughout irrigation, peaking at 50% sixteen h after irrigation ceased. Data implied that tightly held water exchanged with event water throughout the experiment and a substantial portion of preevent water was released from the argillic layer. Surface‐applied dye tracers bypassed the matrix, with peak concentrations measured shortly after flow commencement, indicating preferential network conductivities of 864–2240 mm/h, yet no macropore flow was observed. Near steady‐state flow conditions indicated average conductivities of 460 mm/h and 2.5 mm/h for topsoils and the Bt horizon, respectively. Low ammonium and phosphorus concentrations in the interflow suggested rapid uptake or sorption, while higher nitrate concentrations suggested more conservative transport. These results reveal how hydraulic conductivity variation and subsurface topographic complexity explain otherwise paradoxical solute and flow behaviors.

Modeling Cotton Lint Yield and Water Use Efficiency Responses to Irrigation Scheduling Using Cotton2K

Decreasing groundwater supplies and increasing variability in weather challenge profitable cotton (Gossypium hirsutum L.) production in the Texas Rolling Plains. A modeling study was conducted using the Cotton2K model using weather data from 1980 to 2010 (31 yr) from the Texas Rolling Plains. Our objective was to study cotton yield, water use efficiency (WUE), and economic returns responses to irrigation, which included a combination of six evapotranspiration (ET) replacement levels (40, 60, 80, 100, 120, and 140% ET) and four irrigation durations (4, 6, 8, and 10 wk). The model was initially calibrated and validated using field data. Calibrated model was then used to run simulation scenarios. Maximum lint yield of 1838 kg ha−1 was obtained by irrigating at 111% ET for 10 wk while maximum WUE of 2.65 kg ha−1 mm−1 was obtained by irrigating at 85% ET for 8 wk or 96% ET for 10 wk. This maximum lint yield required 530 mm of irrigation and 880 mm of total water. Maximum economic returns of US$1610 ha−1 was obtained with 516 mm of irrigation water. However, if this amount of water is not available for irrigation, deficit irrigation at 85% ET for 8 wk is a good alternative strategy as it produced 1560 kg lint ha−1 and $1240 ha−1 economic returns with improved WUE. Our results indicate that scheduling irrigation by considering cotton ET demand could increase lint yield, WUE, and profit in the Texas Rolling Plains.Core Ideas Core IdeasCrop models can be used for agronomic and economic assessments. Core IdeasCotton2K can be used to simulate the yield of cotton in semi‐arid regions. Core Ideas85% ET replacement is a promising deficit irrigation strategy for the Texas Rolling Plains.

Planting pattern and irrigation effects on water status of winter wheat

SUMMARYThe effects of planting pattern and irrigation on the soil water content, stomatal conductance, leaf relative water content, leaf water potential and leaf water use efficiency of winter wheat were investigated in North China during the 2008/09 and 2009/10 growing seasons. A field experiment was conducted using a randomized complete block design that consisted of three planting patterns: (i) a uniform row spacing of 25 cm, and alternating wide–narrow row spacing of 40 and 20 cm tested as (ii) flat and (iii) furrow–ridge seedbeds. In addition, irrigation treatments of 90, 135 and 180 mm were used. The planting pattern, irrigation treatments and interactions between them significantly affected soil water content, stomatal conductance, leaf relative water content, leaf water potential and leaf water use efficiency. The soil water content, stomatal conductance, leaf relative water content, leaf water potential, grains/spike, thousand grain weight, leaf water use efficiency and yield were highest in the furrow–ridge seedbed planting pattern and increased with increasing irrigation (except for the leaf water use efficiency). The leaf water use efficiency in the 135 mm irrigation treatment was significantly greater than in the other treatments. In addition, soil water content, stomatal conductance, leaf relative water content, leaf water potential, grains/spike and thousand grain weight were positively correlated with leaf water use efficiency and yield of winter wheat. The interaction between the furrow–ridge seedbed planting pattern and 135 mm irrigation increased soil water content, leaf water indices, grains/spike, thousand grain weight, leaf water use efficiency and yield. These results indicated that a beneficial response occurred for wheat yield. The furrow–ridge seedbed planting pattern combined with 135 mm of irrigation improved the soil and leaf water status and could increase wheat yield while using less water.

Water Interception by Crop Mulch Avena strigosa in Irrigated No-Tillage System

One of the difficulties of the irrigation management is determining the effective rainfall, that is, the water that is indeed available to the crops, due to the influence of the climatic factors and the soil characteristics, as the surface roughness, the composition and the amount of mulch. Objectifying the quantification of the interception and the water storage through mulching in an irrigated no-tillage crop system this work was conducted on a Ultisol in Santa Maria, RS, Brazil; in the agricultural year of 2013/2014 with Avena strigosa crop waste. The period of the evaluations was from 60 days, numbering nine events; in which three levels of mulch, (bare soil, 2 and 4 t ha-1 of dry matter - DM) under three irrigation levels (4, 8 e 16 mm) in a micro sprinkler system, with a bi-factorial distribution scheme in three repetitions. The water content in the mulching were quantified before, 3; 6 and 24 h after the irrigations, collecting the mulch, randomly in the experimental units, with the assistance of a sampling board of 0.09 m² and the content of water in the soil, with sensors FDR installed in depths 0.00-0.10; 0.10 -0.25; 0.25-0.55 e 0.55-0.85 m. The content of water in soil from different levels of mulch, which received 4mm of irrigation, didn’t diverge, suggesting a bigger specification of the soil profile when small doses of irrigation are evaluated. In relation to the water in the mulch, it is observed that three hours after the irrigation, the mulch has the same content of water it had before the irrigation, not having difference between the two mulches levels in the whole period evaluated. The water interception through the mulch drifted from 0.5 to 1 mm, in the treatments 2 and 4 t ha-1 of DM, tending to reduce with time, considering the collections done thereupon the irrigations. The water interception through the mulch must be offset in an irrigation crop system in irrigated no-tillage, particularly as it is worked with low irrigation volume.

IRRIGATION OF CHICKPEA (CICER ARIETINUML.) INCREASES YIELD BUT NOT WATER PRODUCTIVITY

SUMMARYThe depth to ground water is increasing in several regions of the world due to use of high-yielding, but also high water-requiring crops such as rice (Oryza sativa) and wheat (Triticum aestivum), in order to maintain food security for an ever increasing world population. There is a need not only to increase the water productivity of food crops, but also to find less water-requiring crops. Irrigated chickpea (Cicer arietinumL.), traditionally grown without irrigation, may provide an alternative crop to irrigated wheat in some regions. Two field experiments were conducted to determine the effects of irrigation on chickpea yields, yield components and grain and biomass water productivity (based on irrigation (WPI) and irrigation + rainfall (WPI+R)) grown in a loamy sand soil. In the first year, 75 mm of irrigation at the vegetative stage and at the vegetative plus podding stages resulted in a 59% and a 73% increase in grain yield, respectively, compared to no irrigation, but with little change in WPI+R. Overall yields in the second year were significantly higher due to warmer temperatures and fewer frosts during flowering and podding. Compared to no irrigation, 75 mm of irrigation at flowering or at podding resulted in a 7% and a 27% increase in grain yield, but a decrease in grain and biomass water productivity (WPI+R). Irrigation had a significant effect on the number of pods plant−1in both the years and on 100-seed weight in the first year. We conclude that application of a single irrigation during podding to chickpea grown in a loamy sand soil will reliably increase yields and may provide a water-saving alternative to wheat in water-scarce environments.

Irrigation to Enhance Native Seed Production for Great Basin Restoration

Native shrublands and their associated grasses and forbs have been disappearing from the Great Basin as a result of grazing practices, exotic weed invasions, altered fire regimes, climate change and other human impacts. Native forb seed is needed to restore these areas. The irrigation requirements for maximum seed production of four key native forb species (Eriogonum umbellatum, Lomatium dissectum, Penstemon speciosus, and Sphaeralcea grossulariifolia) were studied at the Oregon State University Malheur Experiment Station beginning in 2005. Species plots were supplied with 0, 100, or 200 mm of subsurface drip irrigation per year using a randomized complete block design with four replications. Irrigation in each plot was divided into four equal increments applied between bud and seed set with timing dependent upon the flowering and seed set phenology of each species. Seed was harvested in each year of production through 2011, and the optimal irrigation rate was determined by regression. The four native forb species differed in their responses to irrigation. Lomatium dissectum seed yields were optimized with 140 mm of irrigation. Eriogonum umbellatum seed yields were optimized with 173 to 200 mm of irrigation in dry years and progressively less to no irrigation in the wettest year. Penstemon speciosus seed yields were optimized with 107 mm of irrigation in dry years and were reduced by irrigation in wet years. Sphaeralcea grossulariifolia seed yields did not respond to irrigation. Water requirements of these species are low, and these results can be used by seed growers to produce native forb seed more economically.

Effect of Supplementary Irrigation on Agronomical and Physiological Traits in Durum Wheat (Triticum durum Desf.) Genotypes

Drought, one of the abiotic stresses, is the most significant factor restricting crop production in large agricultural fields of the world. Wheat is generally grown on arid-agricultural fields. Drought often causes serious problems in wheat production. Ten durum wheat (Triticum durum Desf.) genotypes were tested under rain-fed (T0) and three irrigated treatments (T1 = 50 mm at Booting stage, T2 = 50 mm at Booting and 15 mm at heading stages and T3 = 50 mm at Booting and 30 mm at heading stages) in semi-arid conditions of Eastern Algeria. Grain Yield, components of yield, heading evolution, leaf relative water content, leaf specific weight, grain filling rate and duration and chlorophyll content were measured. The irrigation treatments affect significantly all characters. Application of 50 mm of irrigation at booting stage increased significantly grain yield by 23%, compared to rain-fed treatment. Another supplementary irrigation of 15 or 30 mm, at heading, increased significantly grain yield by 45 and 61%, respectively. Stressed condition affects negatively thousand kernel weights (105%). In addition, combined analysis of variance showed high genetic variation for all parameters measured, excepted leaf relative water content and leaf specific weight, when measured at heading stage suggesting the possibility of selecting tolerant genotypes for drought tolerance under semi arid condition.

Long‐term irrigation effects on soil organic matter under temperate grazed pasture

SummaryIrrigation of grazed pasture significantly increases plant and animal production, which may in turn increase soil organic carbon (SOC), depending on the balance between primary production and below‐ground allocation of C on the one hand, and the decomposition and export of C from the soil on the other. To evaluate the effect of irrigation on SOC we sampled a grazed pasture field experiment maintained under different irrigation treatments for 62 years. The dry‐land treatment in this experiment only received rainfall at an average of 740 mm year−1. The 10 and 20% irrigation treatments involved application of 100 mm of irrigation when the soil reached 10 and 20% gravimetric moisture content, respectively. The 10 and 20% irrigation treatments received average total annual irrigation inputs of 260 and 770 mm year−1, respectively. The 10 and 20% irrigation treatments increased pasture production by 44 and 74%, respectively, compared with that from the dry‐land. Analysis of soils taken to 1‐m depth revealed that amounts of SOC were not significantly different between the dry‐land (125.5 Mg ha−1) and 10% irrigation (117.8 Mg ha−1) treatments, but these were significantly greater than the 20% irrigation treatment (93.0 Mg ha−1). At 50–100 cm, SOC was also less (34%) for the 20% irrigation treatment than for the 10% irrigation treatment. The relative quantities of carbon (C) and nitrogen (N) in the light fraction (LF) at all soil depths decreased successively from dry‐land to the 20% irrigation treatment, suggesting that wetter soil conditions accelerated decomposition of the LF fraction, a comparatively labile SOC fraction. The C‐to‐N ratio of the bulk soil was also less for the 20% irrigation treatment, indicating more decomposed SOM in the irrigated than in the dry‐land treatment. There were no significant differences in the microbial biomass between the three different irrigation treatments, but the respiration rate (CO2 production) of soil organisms in the 20% irrigation treatment was consistently greater than in the other two treatments. It was concluded that large increases in plant productivity as a result of irrigation had either no effect or significantly reduced SOC stocks under grazed pasture. The reduced SOC content observed in the 20% irrigation treatment was attributed to a combination of increased C losses in animal products and drainage associated with greater stocking, together with accelerated decomposition of organic C resulting from elevated soil moisture maintained throughout the growing season.

Irrigation of Residential Landscapes Using the Toro Intelli-Sense Controller in Southwest Florida

The objective of the research reported in this paper was to determine the potential water-savings effectiveness of Toro Intelli-Sense evapotranspiration (ET)-based irrigation controllers in single-family homes. Of the 36 cooperators selected, 21 cooperators were outfitted with Toro Intelli-Sense TIS-612 (the ET group) and the remaining 15 were used as comparisons. The ET group reduced irrigation compared to the gross irrigation requirement by 23–41% and the 9-year historical average by 23–34%. Results varied based on the relationship between historical irrigation and the gross irrigation requirement, with water savings of 24%, no difference, and an increase of 54% when the historical value exceeded, approximated, and was less than the gross irrigation requirement, respectively. Turfgrass quality was maintained above an acceptable threshold for both treatments. In southwest Florida, a properly programmed Intelli-Sense controller is recommended when irrigation exceeds the gross irrigation requirement and at least 696 mm of irrigation is applied annually. Other smart-irrigation technologies would be more appropriate in locations for which the irrigation rate is less than the gross irrigation requirement.

Alfalfa Response to Irrigation from Limited Water Supplies

<abstract><title><italic>Abstract.</italic></title> A five-year field study (2007-2011) of irrigated alfalfa production with a limited water supply was conducted in southwest Kansas with two years of above-average precipitation, one year of average precipitation, and two years of below-average precipitation. The irrigation treatments were designed to reflect the declining ability of the aquifer to supply water for irrigation, the constraints of water rights, and irrigation management that either distributed water over the growing season or withheld water during the most stressful part of the growing season. Dry matter yields, averaged over irrigation treatments, declined from 1.68 kg m^-2 in the first year to 0.41 kg m^-2 in the final year because stored soil water contributed to crop evapotranspiration (ET_c) in the first year, but precipitation could not replenish soil water in the following years, and stand densities declined over time. Annual yields, averaged over years, declined from 1.53 kg m^-2 with 610 mm of irrigation to 0.43 kg m^-2 for rainfed production. Annual yields were the same when irrigation was distributed over the growing season or withheld between the second and third cuttings. Crop productivity (water use efficiency) and plant stand decreased significantly as irrigation decreased and from the first through the final year of production. A linear regression of alfalfa dry matter yields with respect to evapotranspiration (ET_c) produced an R² equal to 0.90. Yield response to irrigation was influenced by irrigation amount, precipitation, and the depletion of stored soil water from the beginning to ending years. Yields were highest in the first year, and the marginal yields decreased as irrigation decreased that year. Yield response to irrigation was nearly linear during the second through fourth years and linear during the fifth year with drought, indicating that alfalfa efficiently utilized irrigation and precipitation. Regression of yield-irrigation data from the middle three years of this study overlapped the results from a ten-year field study conducted at the same location from 1921 through 1930, demonstrating that similar alfalfa dry matter was produced with presumably similar atmospheric energy. Because the same irrigation treatment was in the same plot location for all years, available soil water (ASW) at the end of the previous growing season influenced the next year’s starting soil water content (θ_v). All plant-available water was depleted during the first growing season to a depth of at least 2.4 m, and it was partially restored in only one other dormant season. In all years, θ_v diminished to a value of 0.1 in the rainfed treatment, which was less than 0.15, the assumed wilting point for corn, grain sorghum, and sunflower in this soil. These results can be used to evaluate the economic viability of alfalfa production compared with other annual crops where limited water supplies lead to crop water stress.

Performance of Zoysia matrella ‘Zeon’ in Shallow Green Roof Substrates under Moisture Deficit Conditions

The use of turfgrasses might provide an additional solution for establishing green roofs in urban environments. The aim of the present study was to determine Manilagrass [Zoysia matrella (L.) Merr. ‘Zeon’] drought tolerance when grown under green roof conditions and under two different irrigation regimes. Treatments included: 1) two extensive green roof substrates {locally produced substrate [3 sandy loam soil:8 pumice:4 perlite:4 compost:1 zeolite (by volume)] and a commercially available substrate based on crushed tiles}; 2) two substrate depths (7.5 cm or 15 cm); and 3) two irrigation regimes (3 mm or 6 mm of irrigation every 3 days). Substrate characteristics (particle size distribution, saturated and dry bulk density, total porosity, water potential curves, in situ substrate moisture, pH, electrical conductivity, and nutrient analysis), turfgrass growth, and physiological status [green turf cover (GTC), normalized difference vegetation index (NDVI), and leaf relative water content (RWC)] were determined. During moisture deficit periods, GTC, NDVI, and RWC were most affected by substrate depth; moderately affected by irrigation regime; and, to a lesser extent, by substrate type. Turfgrass growth and physiological status were best during moisture deficit conditions in the deeper profile (15 cm) using the higher amount of irrigation (6 mm) and the locally mixed substrate.

Mitigation of ammonia losses from urea applied to a pastoral system: The effect of nBTPT and timing and amount of irrigation

To investigate the effect of applying urea with or without the urease inhibitor (UI) N-(n-butyl) thiophosphoric triamide (nBTPT - trade name Agrotain®) and to assess impact of the amount and timing of irrigation on subsequent ammonia (NH3) emission, a field trial was set up on a research farm at Massey University, Palmerston North, New Zealand in December 2012. Measurements of the daily NH3 emission showed that majority of NH3 losses occurred during the first 1-3 days following urea application. Delaying irrigation for 48 hr post urea application resulted in high average NH3-N losses, at 23% and 28.3% for urea applied at 30 and 60 kg N ha-1, respectively. However, even when 5 or 10 mm of irrigation was applied 8 hours after urea application, average NH3 losses were still 11.3% and 14.4% of the N applied at 30 and 60 kg N ha-1, respectively. Our results suggest that 5 to 10 mm of irrigation/rainfall is needed very soon (

Sunflower Response to Irrigation from Limited Water Supplies with No-Till Management

Limited irrigation necessitates maximizing economic returns by rotating crops, so we conducted a field study during 2005-2009 in southwest Kansas to determine the yield response of sunflower to irrigation and evapotranspiration (ETc) and to measure plant growth parameters and soil water use. Sunflowers were grown in a five-year rotation of corn-corn-wheat-sorghum-sunflower. Six irrigation treatments were imposed by applying 25 mm of irrigation every 4 to 18 days. When sunflowers were planted, sorghum stubble covered 59% to 53% of the surface as irrigation decreased. Similarly, sunflower residue covered 46% to 40% of the surface after planting the following corn crop. The rate at which sunflowers reached growth stages was not affected by irrigation amount. Seed yield (SY) averaged over five years did not differ significantly among the irrigation treatments; however, oil content increased significantly as irrigation decreased. Average annual crop evapotranspiration (ETc) decreased significantly from 481 to 414 mm as irrigation decreased. Because measured ETc for the driest treatment was 86% of fully irrigated ETc, a linear regression of SY data with respect to ETc was not realistic until a threshold value of ETc (ETc required to produce the first increment of seed) from prior field research was added to the dataset. Sunflower SY did not increase with added irrigation, which did not follow the normal pattern of diminishing yield returns as irrigation increases. Sunflowers, traditionally a dryland crop in the region, were able to utilize stored soil water at greater depths than other crops, which contributed to ETc and compensated for decreased irrigation. The soil stored more dormant season precipitation in the lowest irrigation treatment compared with the highest irrigation treatment (116 to 69 mm), and sunflowers receiving the least irrigation were able to use 63 mm more stored soil water during the following growing season. Small year-to-year variations in SY across irrigation treatments indicate that sunflowers can substitute for a crop that uses more water over the whole field or part of a field when water is very limited, which can reduce potential income risk from year to year.

Effects of Limited Supplemental Irrigation with Catchment Rainfall on Rain-fed Potato in Semi-arid Areas on the Western Loess Plateau, China

In semi-arid areas on the Western Loess Plateau, China, crop growth has been greatly limited by water supply. The comparative wet season in the region runs from July through September, and about 60 % of the yearly precipitation total falls within this period. Rainfall is very sparse from November of the preceding year through June of the following year. Water harvesting agriculture has been shown to be one of the most efficient ways to increase water use efficiency (WUE) and crop productivity for wheat, corn, broccoli etc. however, research on WUE in potato (Solanum tuberosum L.), one of the dominant crops in the area, is sparse. Field experiments on supplemental irrigation (amount and timing) using catchment rainfall were carried out in both 2008 and 2009 in Dingxi, a typical potato growing area, for the purpose of determining effective utilization of the limited supplemental irrigation water for potatoes. Soil water storage, evapotranspiration (ET), WUE, irrigation water use efficiency (IWUE), tuber yield and size and starch and protein contents were determined in this research. The results showed that both ET and tuber yield increased with supplemental irrigation, consequently WUE was improved. IWUE appeared to be better with 45 mm of irrigation applied at the vegetative growth stage and tuber yield was increased by 7–18 % compared to the treatment without irrigation (T1), and WUE and IWUE were significantly higher than other treatments in both years. Compared to the control, WUE with 45 mm of irrigation at the vegetative growth stage increased by 1.28 % and 2.17 % in 2008 and 2009, respectively. In addition, 45 mm of irrigation at the vegetative growth stage also increased the percentage of large tubers, and the sum of large and medium tubers. Tubers under such practice were of acceptable size and had the highest protein content. Therefore, we conclude, 45 mm of supplemental irrigation at the vegetative growth stage is the best way to use the limited available supplemental irrigation water from catchment rainfall for rain-fed potatoes grown in semi-arid areas on the Western Loess Plateau of China. Applying more water, or at a later growth stage of potato, was less effective.

Effects of irrigation management and watertable depth on growth and yield of field-grown Sultana grapevines in south eastern Australia

The influence of irrigation amount and frequency of application on growth and yield of Sultana grapevines was studied in a field trial carried out over four years in the Murray Valley irrigation area of Australia. Treatments included low (280mm of irrigation and rainfall), medium (780mm) and high (1300mm) application amounts, each with frequencies of 1, 2 and 4-weekly. Despite artificial drainage, there was a watertable of variable depth: its effect was evaluated by grouping plots into those with shallow (<2.2m depth) or deep (>2.2m depth) watertables. Treatments were applied to grapevines with Sultana scions grafted to Ramsey rootstocks and own-rooted Sultana vines. Yields from vines grafted to Ramsey were largely unchanged by irrigation treatments even where shallow watertables resulted in high soil salinities (ECe>3.0dSm−1), probably because of the capacity of Ramsey rootstock to exclude chloride ions. For vines on their own roots, there were interactions between irrigation frequency and watertable depth for soil salinity and yield, with the fortnightly frequency offering the best compromise where there was a shallow watertable. The response to irrigation amount also depended on watertable depth; the low amount reduced yield relative to that in the medium and high amounts in areas where the watertable was deep but not in areas where it was shallow. Yield in the medium and high amounts tended to be lower in areas where the water table was shallow compared with areas where it was deep. The results suggest that where shallow watertables are present irrigation management should be modified for both own-rooted and Ramsey grafted Sultanas to apply no more than moderate amounts of irrigation and preferably at not less than fortnightly intervals.

Simulation of nitrate leaching in Yala season in Batticaloa - A modeling approach

The leaching behaviour of NO3--N was evaluated through field experiments with those predicted by LEACHM-N, a uni-dimensional, water flow, solute transport and plant uptake model. Therefore, the objective of this study was to evaluate the application of LEACHM-N for predicting nitrate leaching in Batticaloa during Yala 2005. Field experiments were carried out from April 12th 2005 to June 30th 2005. The experimental treatments were 3 nitrogen rates (0, 70 and 140 kg N/ha) together with 3 irrigation rates (7, 14 and 30 mm) which resulted in 9 treatment combinations. The treatments were arranged in a split plot design in 3 replicates. Twenty seven cylindrical lysimeters with 1 m height and 50 cm diameter were built in at the experimental site. Outlets from each lysimeters were fixed with outflow pipes, directed to an underground sampling point, from where the water samples were collected. Red onion (Allium cepa; var. Vethalan) was planted in the lysimeters. Nitrogen fertilizer was applied 3 times during the cropping season. Irrigation water was delivered using a micro sprinkler system. Leachates from individual outlets were collected separately and NO3--N was determined spectrophotometrically by the Cadmium reduction method. A moderately good agreement has been found out in between the measured and the predicted NO3--N losses, but the model overestimated the losses. The treatment combination 140 kg N/ha with 30 mm of irrigation showed better simulation accuracy. It was also found out that the model was unable to predict preferential flow.Keywords: LEACHM-N, leaching, sandy regosols,Yala, lysimeter, preferential flowDOI: http://dx.doi.org/10.4038/josuk.v5i0.4089 J Sci.Univ.Kelaniya 5 (2010): 33-45