Determination of the crop coefficient for grafted ‘Tahiti’ lime trees and soil evaporation coefficient of Rhodic Kandiudalf clay soil in Sao Paulo,Brazil

The expansion of permanent trickle irrigation systems in Sao Paulo (Brazil) citrus has changed the focus of irrigation scheduling from determining irrigation timing to quantifying irrigation amounts. The water requirements of citrus orchards are difficult to estimate, since they are influenced by heterogeneous factors such as age, planting density and irrigation system. In this study, we estimated the water requirements of young ‘Tahiti’ lime orchards, considering the independent contributions from soil evaporation and crop transpiration by splitting the crop coefficient (Kc = ETc/ETo) into two separate coefficients; Ke, a soil evaporation coefficient and Kcb, a crop transpiration coefficient. Hence, the water requirement in young ‘Tahiti’ lime (ET_y) is ET_y = (Ke + Kcb) · ETo, where ETo is the reference crop evapotranspiration. Mature tree water requirement (ET_m) is ET_m = Kcb · ETo, assuming no soil water evaporation. Two lysimeters were used; one was 1.6 m in diameter and 0.7 m deep, and the other was 2.7 m in diameter and 0.8-m deep. The first one was used to calculate evaporation and the second one was used for transpiration. ETo was estimated by the Penman–Monteith method (FAO-56). The measurements were conducted during a period between August 2002 and April 2005 in Piracicaba, Sao Paulo state, Brazil. The lysimeters were installed at the center of a 1.0-ha plot planted with ‘Tahiti’ lime trees grafted on ‘Swingle’ citrumelo rootstock. The trees were 1-year old at planting, spaced 7 × 4 m, and were irrigated by a drip irrigation system. During the study period, Kc varied between 0.6 and 1.22, and Kcb varied between 0.4 and 1.0. The results suggested that for young lime trees, the volume of water per tree calculated by Ke + Kcb is about 80% higher than the volume calculated using Kc. For mature trees, the volume of water per tree calculated using just Kcb can be 10% less than using Kc. The independent influence of soil evaporation and transpiration is important to better understand the water consumption of young lime trees during growth compared to mature lime trees.     

Single and dual crop coefficients and water requirements for onion (Allium cepa L.) under semiarid conditions

The objectives of this study were to determine onion water requirements with a sprinkler irrigation system, the most usual irrigation method in Spain. A weighing lysimeter was used to measure single (Kc) and dual (Kcb + Ke) crop coefficient curves and obtain the relationship between Kc-ground cover (GC) and Kcb-GC. Experimental work was carried out in 2005 at “Las Tiesas” farm, located in Albacete (Central Spain). To determine actual onion evapotranspiration (ETc), we used a weighing lysimeter with continuous electronic data recording. Daily measured ETc values obtained by the lysimeter were compared to calculated ETc values obtained through the standard FAO methodology [Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. FAO Irrig. and Drain. Paper 56. Rome, Italy]. Seasonal evapotranspiration measured in the lysimeter (893.34 mm) was higher than the seasonal ETc calculated by FAO-56 method (832.90 mm). The percentage of GC was found through the supervised classification technique of digital photographic images with the maximum probability algorithm [Calera, A., Martínez, C., Melia, J., 2001. A procedure for obtaining green plant cover: relation to NDVI in a case study for barley. Int. J. Remote Sensing, 22, 3357-3362]. The values derived from lysimetric measurements are Kc ini: 0.65, Kc mid: 1.20 and Kc end: 0.75, similar to values given in FAO-56. Lysimetric measurements showed that the evaporative component was high during the growing season, due to the high frequency of irrigation and the fact that the onion crop does not completely cover the ground; maximum GC was 72%. Therefore, the dual crop coefficient was calculated, which allowed differentiation between crop transpiration (basal crop coefficient, Kcb) and evaporation from the soil (evaporation coefficient, Ke). With the aim of facilitating extrapolation of the results to other areas, Kc and Kcb were linearly correlated to fractional GC.     

Determination of growth-stage-specific crop coefficients (Kc) of cotton and wheat

Development of crop coefficient (Kc), the ratio of crop evapotranspiration (ETc) to reference evapotranspiration (ETo), can enhance ETc estimates in relation to specific crop phenological development. This research was conducted to determine growth-stage-specific Kc and crop water use for cotton (Gossypium hirsutum) and wheat (Triticum aestivum) at the Texas AgriLife Research field at Uvalde, TX, USA from 2005 to 2008. Weighing lysimeters were used to measure crop water use and local weather data were used to determine the reference evapotranspiration (ETo). Seven lysimeters, weighing about 14 Mg, consisted of undisturbed 1.5 m × 2.0 m × 2.2 m deep soil monoliths. Six lysimeters were located in the center of a 1-ha field beneath a linear-move sprinkler system equipped with low energy precision application (LEPA) and a seventh lysimeter was established to measure reference grass ETo. Crop water requirements, Kc determination, and comparison to existing FAO Kc values were determined over a 2-year period on cotton and a 3-year period on wheat. Seasonal total amounts of crop water use ranged from 689 to 830 mm for cotton and from 483 to 505 mm for wheat. The Kc values determined over the growing seasons varied from 0.2 to 1.5 for cotton and 0.1 to 1.7 for wheat. Some of the values corresponded and some did not correspond to those from FAO-56 and from the Texas High Plains and elsewhere in other states. We assume that the development of regionally based and growth-stage-specific Kc helps in irrigation management and provides precise water applications for this region.     

Irrigation requirements and transpiration coupling to the atmosphere of a citrus orchard in Southern Brazil

Crop evapotranspiration (ETc) was measured as evaporative heat flux from an irrigated acid lime orchard (Citrus latifolia Tanaka) using the aerodynamic method. Crop transpiration (T) was determined by a stem heat balance method. The irrigation requirements were determined by comparing the orchard evapotranspiration (ETc) and T with the reference evapotranspiration (ETo) derived from the Penman-Monteith equation, and the irrigation requirements were expressed as ETc/ETo (Kc) and T/ETo (Kcb) ratios. The influence of inter-row vegetation on the ETc was analyzed because the measurements were taken during the summer and winter, which are periods with different regional soil water content. In this study, the average Kc values obtained were 0.65 and 0.24 for the summer and winter, respectively. The strong coupling of citrus trees to the atmosphere and the sensitivity of citrus plants to large vapor pressure deficits and air/leaf temperatures caused variations in the Kcb in relation to the ETo ranges. During the summer, the Kcb value ranged from 0.34 when the ETo exceeded 5 mm d⁻¹ to 0.46 when the ETo was less than 3 mm d⁻¹.     

水分胁迫条件下羊草群落生育期双作物系数计算方法的验证

基于浑善达克沙地2005-2006两个不同水文年对羊草、拂子茅、冰草构成的羊草群落生育期中气象因子及生理因子野外观测试验数据,用联合国粮农组织FAO-56分册中介绍的方法计算了羊草群落生育期基本作物系数和土壤蒸发系数,并对基本作物系数进行了地区气象因素和牧草单叶气孔阻力校正。用校正后的作物系数模拟计算的蒸腾、蒸发量与实际观测值间进行了拟合相关图、拟合优度参数法的有效性检验。结果表明:计算的蒸发、蒸腾量与实测结果基本接近。考虑水分胁迫时,有条件的地区应该对作物系数进行地区气象因素和单叶气孔阻力校正。     

Using a subsurface drip irrigation system to measure crop water use

Procedures are presented for determining crop water use and crop coefficients for a row crop, using a neutron scattering probe with an efficient subsurface drip irrigation system. One procedure is called the slope-projection method, and the other is called a covariance procedure. Field tests were conducted with full-season, narrow-row cotton (Gossypium hirsutum L.) on a well-drained, sandy soil in a semiarid environment over a 5-year period. The goal was to improve automated irrigation scheduling, by relating evapotranspiration (ET) to growing degree days (GDD). The result, using a Penman–Monteith reference ET, was an average midseason crop coefficient of 1.11, with a standard error of 0.056. With class A pan evaporation as the reference ET, the average midseason crop coefficient was 0.877, with a standard error of 0.029. A fifth-order polynomial for the pan-based crop coefficient as a function of GDD was programmed into a controller and used successfully to irrigate a field automatically for one season.Communicated by A. Kassam     

Sprinkler irrigation scheduling of winter wheat in the North China Plain using a 20 cm standard pan

Based on evaporation from a 20 cm diameter pan placed above the crop canopy, sprinkler irrigation scheduling of winter wheat was studied in the North China Plain (NCP) in the 2001–2004 winter wheat seasons. Results showed that pan evaporation (E _pan,C) was closely related to actual evapotranspiration (ET) measured using weighing lysimeters. The combined pan–crop coefficient (K _c,pan), the ratio of ET to E _pan,C, was closely related to leaf area index (LAI ) and plant height. Data from the 2002–2003 season were used to establish the relationships between K _c,pan and LAI (method A) or plant height (method B), and used to determine the crop coefficient (method C). ET computed by the three methods was compared with measured ET using lysimeters in the 2001–2002 and 2003–2004 seasons. Mean relative error of estimated daily ET by the three methods ranged from 20 to 30%, and the relative error in cumulative ET in the experimental periods ranged from 1 to 19%. Among the three methods, results from methods A and B were not significantly different from each other (P > 0.01), and were closer to the lysimeter data than results from method C (P < 0.001). Method B, being easier to measure, was recommended for ET estimation in NCP.     

The dual crop coefficient approach using a density factor to simulate the evapotranspiration of a peach orchard: SIMDualKc model versus eddy covariance measurements

The dual crop coefficient approach accounts separately for plant transpiration and soil evaporation by using the basal crop coefficient and the evaporation coefficient, respectively. The SIMDualKc model, which performs the soil water balance simulation with estimation of the actual crop evapotranspiration (ET) with the dual crop coefficient approach, was applied to a drip-irrigated peach orchard under Mediterranean conditions. Orchard ET was obtained with the eddy covariance technique, which was subsequently correlated with tree transpiration estimated from sap flow measurements and soil evaporation determined with microlysimeters, thus providing ET for the whole irrigation season. Two years of field observations were used for model calibration and validation using those ET measurements and taking into account the fraction of ground covered by trees through a density factor which adjusts the basal crop coefficient. Model fitting relative to ET observations during calibration and validation provided indices of agreement averaging 0.90, coefficients of regression close to 1.0, root mean square errors around 0.41 mm and average absolute errors of 0.32 mm. Model fitting relative to transpiration and to soil evaporation produced similar results, so showing the adequateness of modelling.     

Sprinkler evaporation losses in alfalfa during solid-set sprinkler irrigation in semiarid areas

Gross sprinkler evaporation losses (SEL_g) can be large and decrease irrigation application efficiency. However, it is not universally established how much of the SEL_g contributes to decrease the crop evapotranspiration during the sprinkler irrigation and how much are the net sprinkler losses (SEL_n). The components of SEL were the wind drift and evaporation losses (WDEL) and the water intercepted by the crop (IL). The gross WDEL (WDEL_g) and evapotranspiration (ET) were measured simultaneously in two alfalfa (Medicago sativa L.) plots, one being irrigated (moist, MT) and the other one not being irrigated (dry, DT). Catch can measurements, mass gains, and losses in the lysimeters and micrometeorological measurements were performed to establish net WDEL (WDEL_n) during the irrigation and net IL (IL_n) after the irrigation as the difference between ET_MT and ET_DT. Also, equations to estimate IL_n and net sprinkler evaporation losses (SEL_n) were developed. IL_n was strongly related to vapor pressure deficit (VPD). SEL_n were 8.3 % of the total applied water. During daytime irrigations, SEL_n was 9.8 % of the irrigation water and slightly less than WDEL_g (10.9 %). During nighttime irrigations, SEL_n were slightly greater than WDEL_g (5.4 and 3.7 %, respectively). SEL_n was mainly a function of wind speed.     

Determination of growth-stage-specific crop coefficients (KC) of maize and sorghum

A ratio of crop evapotranspiration (ET_C) to reference evapotranspiration (ET_O) determines a crop coefficient (K_C) value, which is related to specific crop phenological development to improve transferability of the K_C values. Development of K_C can assist in predicting crop irrigation needs using meteorological data from weather stations. The objective of the research was conducted to determine growth-stage-specific K_C and crop water use for maize (Zea Mays) and sorghum (Sorghum bicolor) at Texas AgriLife Research field in Uvalde, TX, USA from 2002 to 2008. Seven lysimeters, weighing about 14 Mg, consisted of undisturbed 1.5 m × 2.0 m × 2.2 m deep soil monoliths. Six lysimeters were located in the center of a 1-ha field beneath a linear-move sprinkler system equipped with low energy precision application (LEPA). A seventh lysimeter was established to measure reference grass ET_O. Crop water requirements, K_C determination, and comparison to existing FAO K_C values were determined over a 3-year period for both maize and sorghum. Accumulated seasonal crop water use ranged between 441 and 641 mm for maize and between 491 and 533 mm for sorghum. The K_C values determined during the growing seasons varied from 0.2 to 1.2 for maize and 0.2 to 1.0 for sorghum. Some of the values corresponded and some did not correspond to those from FAO-56 and from the Texas High Plains and elsewhere in other states. We assume that the development of regionally based and growth-stage-specific K_C helps in irrigation management and provides precise water applications for this region.     

冬小麦蒸发系数变化规律研究

作物蒸发蒸腾量(ET)是进行合理灌溉和水资源配置的重要依据。为了更方便地估算作物蒸发蒸腾量,以大型称重式蒸渗仪实测的冬小麦蒸发蒸腾量(ET)为依据,分析了水面蒸发量(E0)与实测蒸发蒸腾量(ET)的相关性,并研究了蒸发系数的变化规律。结果表明:水面蒸发量(E0)和蒸渗仪实测值(ET)呈线性关系,冬小麦全生育期内二者的相关系数R2=0.7708,蒸发系数α=1.37。在冬小麦的整个生育期内α先是由大变小,接着再增大直到在抽穗—灌浆期达到最大值,之后再慢慢减小。     

Water use of spring wheat to raise water productivity

In semi-arid environments with a shortage of water resources and a risk of overexplotation of water supplies, spring wheat (Triticum aestivum L.) is a crop that can reduce water use and increase water productivity, because it takes advantage of spring rainfall and is harvested before the evaporative demands of summer. We carried out an experiment in 2003 at “Las Tiesas” farm, located between Barrax and Albacete (Central Spain), to improve accuracy in the estimation of wheat evapotranspiration (ETc) by using a weighing lysimeter. The measured seasonal ETc averages (5.63 mm day⁻¹) measured in the lysimeter was 417 mm compared to the calculated ETc values (5.31 mm day⁻¹) calculated with the standard FAO methodology of 393 mm. The evapotranspiration crop coefficient (Kc) derived from lysimetric measurements was Kc-mid: 1.20 and Kc-end: 0.15. The daily lysimeter Kc values were fit to the evolution linearly related to the green cover fraction (fc), which follows the crop development pattern. Seasonal soil evaporation was estimated as 135 mm and the basal crop coefficient approach was calculated in this study, Kcb which separates crop transpiration from soil evaporation (evaporation coefficient, Ke) was calculated and related to the green cover fraction (fc) and the Normalized Difference Vegetation Index (NDVI) obtained by field radiometry in case of wheat. The results obtained by this research will permit the reduction of water use and improvement of water productivity for wheat, which is of vital importance in areas of limited water resources.     

Peach orchard evapotranspiration in a sandy soil: Comparison between eddy covariance measurements and estimates by the FAO 56 approach

The evapotranspiration from a 3 to 4 years old drip irrigated peach orchard, located in central Portugal, was measured using the eddy covariance technique during two irrigation seasons, allowing the determination of crop coefficients. These crop coefficient values differed from those tabled in FAO Irrigation and Drainage Paper 56. In order to improve evapotranspiration estimates obtained from FAO tabled crop coefficients, a dual crop coefficient methodology was adopted, following the same guidelines. This approach includes a separation between the plant and soil components of the crop coefficient as well as an adjustment for the sparse nature of the vegetation. Soil evaporation was measured with microlysimeters and compared with soil evaporation estimates obtained by the FAO 56 approach. The FAO 56 method, using the dual crop coefficient methodology, was also found to overestimate crop evapotranspiration. During 2 consecutive years, measured and estimated crop coefficients were around 0.5 and 0.7, respectively. The estimated and measured soil evaporation components of the crop coefficient were similar. Therefore, the overestimation in evapotranspiration seems to result from an incorrect estimate of the plant transpiration component of the crop coefficient. A modified parameter to estimate plant transpiration for young, yet attaining full production, drip irrigated orchards is proposed based on field measurements. The method decreases the value of basal crop coefficient for fully developed vegetation. As a result, estimates of evapotranspiration were greatly improved. Therefore, the new approach seems adequate to estimate basal crop coefficients for orchards attaining maturity established on sandy soils and possibly for other sparse crops under drip irrigation conditions.     

Effect of seasonal water stress imposed on drip irrigated second crop watermelon grown in semi-arid climatic conditions

A study was conducted to determine the water stress effect on yield and some physiological parameters including crop water stress index for drip irrigated second crop watermelon. Irrigations were scheduled based on replenishment of 100, 75, 50, 25, and 0% soil water depletion from 90 cm soil depth with 3-day irrigation interval. Seasonal crop evapotranspiration (ET) for I₁₀₀, I₇₅, I₅₀, I₂₅, and I₀ were 660, 525, 396, 210, and 70 mm in 2003 and 677, 529, 405, 221, and 75 mm in 2004. Fruit yield was significantly lowered by irrigation water stress. Average water-yield response factor for both of the years was 1.14. The highest yield was obtained from full irrigated treatment as 34.5 and 38.2 t ha⁻¹ in 2003 and 2004, respectively. Lower ET rates and irrigation amounts in water stress treatments resulted in reductions in all measured parameters, except water-soluble dry matter concentrations (SDM). Canopy dry weights, leaf relative water content, and total leaf chlorophyll content were significantly lowered by water stress. Yield and seasonal ET were linearly correlated with mean CWSI values. An average threshold CWSI value of 0.17 before irrigation produced the maximum yield and it could be used to initiate the irrigation for watermelon.     

Crop evapotranspiration of processing tomato in the San Joaquin Valley of California, USA

Yield of processing tomato has increased by 53% over the past 35 years. Thus, concerns exist about the current seasonal crop evapotranspiration requirements of processing tomato compared to the past published requirements, which were about 645 mm. Also, the mid-season crop coefficient for processing tomato developed 35 years ago with sprinkler irrigation was 1.25, while a mid-season coefficient developed 20 years ago with subsurface drip irrigation was 1.05. Because of the age and variability of crop coefficients and the long-term yield increase, a study was conducted to determine the seasonal crop evapotranspiration and crop coefficients of processing tomatoes using the Bowen ratio energy balance method in eight commercial fields from 2001 to 2004. Measurements were made in both furrow- and drip-irrigated fields. Results showed seasonal crop evapotranspiration to range from 528 to 752 mm with an average of 648 mm. No statistical differences were found between furrow and drip irrigation. Mid-season crop coefficients varied between 0.96 and 1.09 with statistically similar values between furrow- and drip-irrigation for a given year. Current evapotranspiration rates were similar to those of the early 1970s, indicating that the water use efficiency of processing tomato increased substantially with time during the past 35 years.     

Evapotranspiration and responses to irrigation of broccoli

In cold, semi-arid areas, the options for crop diversification are limited by climate and by the water supply available. Growing irrigated crops outside the main season is not easy, because of climatic and market constraints. We carried out an experiment in Albacete, Central Spain, to measure the water use (evapotranspiration, ET) of broccoli (Brassica oleracea L. var. italica Plenck) planted in late summer and harvested at the end of fall. A weighing lysimeter was used to measure the seasonal ET under sprinkler irrigation. Consumptive use reached 359 mm for a period of 109 days after transplanting. The crop coefficient (K_c) for broccoli was obtained and compared to the standard recommendations for normal planting dates. Dual crop coefficient computations of the lysimeter ET data indicated that evaporation represented 31% of seasonal ET. An analysis of the variation in daily K_c values at a time of full cover suggested that the use of a grass lysimeter as a reference ET (ET_o) was superior to using the ASCE Penman-Monteith (ASCE PM) equation at hourly time steps, which in turn caused less variability in K_c than when using the FAO-56 Penman-Monteith (FAO-56 PM) equation at daily time steps for the ET_o calculation. An additional experiment aimed at evaluating the yield response to applied irrigation water by the drip method (seven treatments, from 59 to 108% of ET_c) generated a production function that gave maximum yields of near 12 t ha⁻¹ at an irrigation level of 345 mm, and a water use efficiency of 3.37 kg m⁻³. It is concluded that growing broccoli in the fall season is a viable alternative for crop diversification, as the lower yields obtained here may be more than compensated for by the higher produce prices in autumn, at a time of the year where irrigation water demand for other crops is very low.     

Scheduling water application on drip irrigated sugarcane

Irrigation is necessary in order to produce sugarcane in semiarid south Texas, but water supplies are becoming increasing limited. Drip and sprinkler irrigation systems offer more precise water control than conventional furrow irrigation, but are more expensive. This study was conducted to evaluate four different methods (pan evaporation (E_pan), evapotranspiration (ET), auto-tensiometers, manual tensiometers) for determining the amount of irrigation water to apply, and three different frequencies of water application on sugarcane, in order to make the most efficient use of available water using subsurface drip irrigation. The study was conducted over three sugarcane seasons: the plant crop and two ratoon crops. The amount of water applied based on the different methods varied from year to year, with the ET method prescribing the most water in the first ratoon crop but the least amount in the second ratoon. This was probably caused mostly by differences in annual weather conditions. The more frequently water was applied, the larger amount any method tended to prescribe, since more frequent applications resulted in keeping the soil profile fuller, therefore providing less capacity to store rainfall when it occurred. Number of stress days as determined by calculating a stress coefficient based on ET and soil water balance indicated a large amount of stress in the first ratoon but almost none in the second ratoon crop. Direct soil water monitoring indicated much less stress than the calculated levels. Growth measurements and sugarcane yields showed that the highest water applications resulted in the best responses, regardless of the scheduling method used. All irrigation scheduling methods were effective, prescribing similar amounts of water for a given season. Direct measurement using tensiometers gives the most accurate assessment of field conditions, but is expensive and labor intensive. Automated tensiometers were not very reliable. Pan evaporation and ET are effective once they are properly calibrated by developing appropriate coefficients for a particular region. Pan evaporation has been used for a long time, but it is more difficult to obtain reliable data compared to ET data from automated weather stations.     

Comparison of drip and sprinkler irrigation strategies on sunflower seed and oil yield and quality under Mediterranean climatic conditions

This study compares the effects of different irrigation regimes on seed yield and oil yield quality and water productivity of sprinkler and drip irrigated sunflower (Helianthus annus L.) on silty-clay-loam soils in 2006 and 2007 in the Mediterranean region of Turkey. In sprinkler irrigation a line-source system was used in order to create gradually varying irrigation levels. Irrigation regimes consisted of full irrigation (I₁) and three deficit irrigation treatments (I₂, I₃ and I₄), and rain-fed treatment (I₅). In the drip system, irrigation regimes included full irrigation (FI-100), three deficit irrigation treatments (DI-25, DI-50, DI-75), partial root zone drying (PRD-50) and rain-fed treatment (RF). Irrigations were scheduled at weekly intervals both in sprinkler and drip irrigation, based on soil water depletion within a 0.90 m root zone in FI-100 and I₁ plots. Irrigation treatments influenced significantly (P < 0.01) sunflower seed and oil yields, and oil quality both with sprinkler and drip systems. Seed yields decreased with increasing water stress levels under drip and sprinkler irrigation in both experimental years. Seed yield response to irrigation varied considerably due to differences in soil water contents and spring rainfall distribution in the experimental years. Although PRD-50 received about 36% less irrigation water as compared to FI-100, sunflower yield was reduced by an average of 15%. PRD-50 produced greater seed and oil yields than DI-50 in the drip irrigation system. Yield reduction was mainly due to less number of seeds per head and lower seed mass. Soil water deficits significantly reduced crop evapotranspiration (ET), which mainly depends on irrigation amounts. Significant linear relationships (R² = 0.96) between ET and oil yield (Y) were obtained in each season. The seed yield response factors (ky_seed) were 1.24 and 0.86 for the sprinkler and 1.19 and 1.06 for the drip system in 2006 and 2007, respectively. The oil yield response factor (ky_oil) for sunflower was found to be 1.08 and 1.49 for both growing seasons for the sprinkler and 1.36 and 1.25 for the drip systems, respectively. Oil content decreased with decreasing irrigation amount. Consistently greater values of oil content were obtained from the full irrigation treatment plots. The saturated (palmitic and stearic acid) and unsaturated (oleic and linoleic acid) fatty acid contents were significantly affected by water stress. Water stress caused an increase in oleic acid with a decrease in linoleic acid contents. The palmitic and stearic acid concentrations decreased under drought conditions. Water productivity (WP) values were significantly affected by irrigation amounts and ranged from 0.40 to 0.71 kg m⁻³ in 2006, and from 0.69 to 0.91 kg m⁻³ in 2007. The PRD-50 treatment resulted in the greatest WP (1.0 kg m⁻³) and irrigation water productivity (IWP) (1.4 kg m⁻³) in both growing seasons. The results revealed that under water scarcity situation, PRD-50 in drip and I₂ in sprinkler system provide acceptable irrigation strategies to increase sunflower yield and quality.     

Economic feasibility of growing capsicum crop under drip irrigation in West Bengal, India

Drip irrigation system has been one of the technical means to improve water use efficiency. In India, this system is gaining popularity among fruit growers and in water scarced area but a substantial area is being covered annually under vegetables crops. One of the major concerns raised by farmers about this system is its economic viability. In present study, the economic viability of drip irrigation system for growing capsicum crop based on discounted cash flow technique (Net present worth and Benefit cost ratio) was explored. Eight irrigation treatments were laid under drip with and without plastic mulch. The irrigation levels were taken as 1, 0.8 and 0.6 of the crop evapotranspiration. The pan evaporation method was used for estimation of reference evapotranspiration and Water Balance Approach was used for irrigation scheduling. The average amount of water supplied under treatment VD (100% irrigation requirement supplied with drip) was found to be 415 mm for whole growing season of the crop. Similarly the amount of water was found to be 332 mm and 249 mm for the treatment 0.8VD (80% irrigation requirement supplied with drip) and 0.6VD (60% irrigation requirement supplied with drip) respectively. Highest yield was recorded in case of treatment VD + PM (100% irrigation requirement supplied with drip plus plastic mulch) followed by VD. Yield under treatments 0.8VD, 0.6VD, 0.8VD + PM and 0.6VD + PM were significant while treatments VD, VF and VF + PM were at par with the treatment VD + PM. Net Present Worth (NPW) was found to be positive for all the treatments. The highest NPW was obtained under treatment VD as Rs. 309,734.90 and lowest was in case of 0.6VD + PM as Rs. 144,172.24. The yield per mm of water used was reported to be at higher side as 35 in both the treatments VD and VD + PM. But the yield per mm of water used was found to be lowest as 18.07 and 19 in case of VF and VF + PM respectively.     

A simple irrigation scheduling approach for pecans

Pecans are a major crop in New Mexico's Lower Rio Grande Valley (LRGV). It is estimated that New Mexico is responsible for about 21% of the world's pecan production (Lillywhite et al., 2007). Currently, approximately 12,000 ha of pecan orchards at various stages of growth consume 45% of the area's irrigation water. Pecan evapotranspiration (ET) varies with age, canopy cover, soil type, crop density and method of water management. Intense competition for the LRGV's limited water supply has created a serious need for better water management through improved irrigation scheduling. Annual pecan ET ranges from as low as 500 mm to as high as 1400 mm. Diversity of the pecan crop coefficient (K_c) and ET makes the task of irrigation scheduling for this crop very complicated. Using remote sensing technology and field ET measurements, a simple relationship was developed to relate crop coefficient and ET to canopy cover. This relationship is then used in combination with climate data to calculate daily and weekly water requirements for each orchard. The difference between annual ET values estimated from canopy cover and values measured with an eddy covariance flux tower ranged from 2 to 5%. The average ratio of estimated monthly ET values over measured ET values was 1.03 with the standard error of the estimate ranging from 10 to 20 mm/month. This methodology provides a simple tool that farmers can use to schedule irrigation of pecan orchards. Even though the methodology was developed for irrigation scheduling in the LRGV, it can be used in other locations by transferring the reference crop coefficients using K_c-GDD relationships.