The aim of this study was to determine the reliability of DRAINMOD-S for simulating water management in irrigated land and to simulate drainage system design criteria to ensure high crop yields for the western part of the Central Kızılırmak Basin in Turkey. The model was tested under arid conditions using field data for winter wheat and corn. Daily water-table depth, drain outflows and drainage water salinity were monitored throughout the growing season. Soil salinities were measured to a depth of 1.00 m from the soil surface. The reliability of the model was evaluated by comparing measured and predicted values of the daily ground water table depth, drain outflows, drainage water and soil salinity during each season, and relative crop yield. Good agreement was found between the measured and predicted values. Absolute deviation was 5.68 cm for water table depth, 10.13 mm for drain outflows, 0.66 dS m -1 for drainage water salinity, and ranged from 0.51 to 0.96 dS m -1 for soil salinity. The corresponding coefficients of efficiency (E) were between 0.48 and 0.95. The results also showed that DRAINMOD-S can be recommended as a useful tool for design and evaluation of irrigation and drainage systems in salt-affected soils under arid and semi-arid climates.Additional key words: corn; drainage system; water table management modeling; wheat. ResumenEvaluación de terreno de DRAINMOD-S para prever la salinidad de la tierra y del agua de drenaje bajo condiciones áridas en Turquía El objeto de este estudio fue determinar la fiabilidad de DRAINMOD-S para simular la gestión del agua en suelos regados y el criterio de diseño del sistema de drenaje a fin de asegurar el rendimiento de las cosechas en la parte oeste de la Cuenca Central de Kizilirmak, Turquía. El modelo fue comprobado bajo condiciones áridas, utilizando datos de campo relativos al trigo de invierno y maíz. Se observaron diariamente, a lo largo de la temporada de crecimiento, la profundidad del nivel freático, el flujo y la salinidad del agua de drenaje. La salinidad del suelo se midió a la profundidad de 1,00 m. Se evaluó la fiabilidad del modelo comparando los valores diarios medidos y simulados y se encontró un buen ajuste entre ambos valores. La desviación absoluta fue de 5,68 cm para la profundidad del nivel freático; 10,13 cm para el flujo de drenaje; 0,66 dS m -1 para la salinidad del agua de drenaje; y entre 0,51 y 0,96 dS m -1 para la salinidad del suelo. Los correspondientes coeficientes de eficiencia (E) estuvieron entre 0,48 y 0,95. Según los resultados de la simulación, son necesarios un espaciamiento entre drenajes de 125 m y una profundidad de drenaje de 160 cm para asegurar una buena cosecha e impedir la degradación del suelo y del agua en esta zona. Los resultados demuestran que DRAINMOD-S puede ser una herramienta útil para el diseño y la evaluación de los sistemas del riego y de drenaje en suelos salinos bajo climas áridos y semiáridos.Palabras clave adicionales: gestión del nivel freático; maíz; sistema de drenaje; trigo.
Farming winter wheat in Central Anatolia of Turkey traditionally is rainfed. Crop yields are frequently affected in this region because of the drought events of varying severity. There is apparent necessary for an aim appraisal of the effect of dryness on this critical crop, to answer the contradiction whether irrigation is essential or not. For this reason the FAO-AquaCrop (Ver.5.0) crop water productivity model was preferred to predict attainable yields of winter wheat (Triticum durum L.) under four different irrigation regimes. Field experiment was conducted under four different irrigation treatments in Central Anatolia Region of Turkey during 2008-2010. The AquaCrop was calibrated with 2008-2009 field data and model validation was performed using 2009-2010 data. Model simulation results showed that model simulates soil water content in root zone (SWC), canopy cover (CC), grain yield (GY) and aboveground biomass (BM) of wheat reasonably well. The average root mean square error (RMSE) between simulated and observed SWC, CC, GY and BM were 21.1 mm, 7.1%, 0.32 t ha-1 and 0.34 t ha-1. Nash-Sutcliffe efficiency (EF) and index of Willmott (d) also were obtained 0.89 and 0.98 for CC, 0.74 and 0.93 for SWC, 0.98 and 0.92 for BM, 0.95 and 0.82 for GY. Model predicted canopy cover, grain yields and biomass with high accuracy while soil water content at 90 cm soil depth was estimated in the moderate accuracy. The results presented that AquaCrop model can be suggested as a convenient model for decisionmaking whether irrigating wheat is in the priority or not at the limited water resources areas.
Agriculture is the main consumer (75%-80%) of available water resources in many countries (Baris and Karadag, 2007). Generally, crop productivity where there is sufficient soil water is higher than in dry soil conditions (Misra et al., 2010). In semiarid regions such as Central Anatolia in Turkey water scarcity is a serious problem for sustainable crop production (Oweis and Ilbeyi, 2001). Efficient use of water by plants plays a crucial role especially in arid regions. Regulation of water productivity is particularly important in arid ecosystems where plants are sporadically exposed to water stress (Tanner and Sinclair, 1983). As reported by Molden et al. (2003), productivity of irrigation water can be evaluated at the plant, field, farm, system, and basin level. The irrigation water productivity at the field level is the ratio between evapotranspiration and total diverted irrigation water for crop production (Kijne et al., 2003).In recent decades important progress has been made using isotopic techniques of water management in agriculture (Heng et al., 2005). Oxygen, hydrogen, carbon, and nitrogen abundance measurements in soil, water, and plant components can be useful in identifying the sources of water and nutrients used by plants (Bazza, 1993;IAEA, 2006). Several studies have shown that carbon isotope discrimination is highly correlated with plant water status (Xu et al., 2007;Misra et al., 2010;Wahbi and Shaaban, 2011).Two parameters are currently used to characterize carbon isotope ratio in plants: carbon isotope composition (δ) and carbon isotope discrimination (∆). Carbon isotope composition is calculated as δ 13 C(∆) =
The purpose of this study was to determine the comparison of salt accumulation in soil profile and crop yields under drained and un-drained conditions. Current field conditions were used to represent poorly drained conditions where drainage system was not installed yet. Simulations were performed to illustrate well drained condition using the water management simulation model while controlling soil salinity in root zone. To put forward drainage system impacts; soil salinity and relative crop yields for well drained conditions were compared to poorly drained conditions. Soil, crop and site parameters were obtained from coordinated 40 soil sampling locations where dry bean, winter wheat and fallow crop rotations were applied. Results of the study showed that water table decreased rapidly after installing proper drainage system. Percentage of salt decreases in soil profile occurred by 24.1, 37.9 and 14.4% for wheat, bean and fallow locations respectively with adequate drainage conditions. On the drained soils, the relative yield of the winter wheat was higher by 11.2%, on the average, whereas that of bean was higher by 24.7%. Overall the net impact of yield enhancement due to drainage was about 36%. This shows the positive impact of drainage system on crop yields in this area.
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