Water requirement and irrigation systems of winter wheat: CROPWAT-DSSAT model solution in Guanzhong District

Definitive regulation of winter wheat water requirement is critical for developing theoretical bases for rational irrigation systems with high agricultural water use efficiency in Guanzhong District. To develop time-variant optimal irrigation schemes, a simulation of seasonal characteristics of a range of variables (e.g., effective rainfall, crop water requirement, etc.) was conducted for the winter wheat growth seasons in the last 30 years in Guanzhong District. An integrated CROPWAT-DSSAT model was used to simultaneously simulate the changes in crop production and water stress under different irrigation schemes in different precipitation years. The optimal irrigation schemes were determined according to effects of irrigation on crop yield and economic benefits. Based on the results, the amount of effective rainfall was less than 50% of water requirement during winter wheat season. Seasonal characteristics were different across different precipitation years; which phenomenon induced severe water shortages during wintering, greening and jointing stages of winter wheat. Among the four investigated irrigation stages, which were wintering, greening, jointing stage and grain-filling stages, water for greening was most critical for winter wheat growth. This was followed by water for jointing, while grain-filling irrigation was least critical for winter wheat production. Abundance analysis suggested that optimal total irrigations in wet years, normal years and dry years were 75 mm, 125 mm and 150 mm, respectively. For detail, irrigation scheme suggested that water for wintering was the critical in wet years. For maximum yield and economic benefit of winter wheat, water for winter, greening and jointing were all noted to be no less than 25 mm in wet years. For normal years, waters for wintering, greening and jointing were 50 mm, 50 mm and 25 mm respectively. These water quotas gave the highest yields of winter wheat. However, halving the amount of water for wintering optimized the economic benefit of winter wheat. Similarly, waters for wintering, greening and jointing in dry years were 25 mm, 75 mm and 50 mm, respectively. These were the water quotas that produced the highest yields and economic benefits for winter wheat in Guanzhong District.