Response Of Crop Growth To Water Saving Practices And Optimizing Of Irrigation Scheduling In An Arid Region Of Northwest China

The shortage of water resources and the deterioration of the ecological environment in the arid Northwest China have been the limiting factors for its sustainable development of agriculture. In recent years, reducing the planting area of highly water consumptive crops and increasing the planting proportion of cash crops which are water saving is becoming one of the important strategies to relieve the contradiction between supply and demand of water resources, as well as increase ingatherings of the peasantry. Therefore, study the response of cash crops’growth to water saving practices and establish the irrigation schedules with high water use efficiency is scientifically and practically significant for promoting the sustainable utilization of water resources, and guaranting the ecological security and agricultural sustainable development in this arid region. In this research, field experiments’data analysis and model simulation were combined to study the responses of soil water content, crop ecological and physiological characteristics, crop evapotranspiration, yield and its quality as well as water use efficiency to water deficit, and the irrigation schedules for three cash crops, i.e., onion, pepper and tomato, were established. The field experiments were conducted at the Wuwei Experimental Station of Crop Water Use, Ministry of Agriculture, located in Gansu Province of northwest China in2008-2011. The soil-water-nitrogen-crop growth model (SWNCM) was adopted to predict the dynamics of soil water content and crop growth, as well as optimizing the irrigation schedules. The main results are as follows:(1) Deficit irrigation experiment on onion under border irrigation with plastic mulch were carried out in2008and2009, nine weighing lysimeters were used to estimate onion evapotranspiration. The effects of water deficit on onion yield and water use efficiency (WUE) were investigated, and the crop coefficient was obtained. The seasonal evapotranspiration of onion was up to358mm, water consumption rate and percentage at different growth stages ranked as bulbification stage>development stage>establishment stage>ripening stage. Onion yield can be up to62.12t hm-2, water deficit during bulbification stage can significantly reduce onion yield. The crop coefficients of onion at initial, mid-season and late season stage were0.73,1.28and0.70, respectively.(2) Regulated deficit irrigation experiment on onion under drip irrigation with plastic mulch were conducted in2009and2010, the response of crop growth and physiological indexes to different water saving practices were analysed. The results showed that onion growth indexes (i.e., plant height, neck thickness, number of leaves, leaf area index and dry matter of different parts) and physiological characteristics (i.e., photosynthesis, transpiration and stomatal conductance) were significantlty affected by water deficit when irrigation depth less than0.8ETC. Water deficit at the establishment stage can restrain the crop growth of onion in a certain degree, but the effect was not remarkable. Water stress significantly reduced the growth and physiological indexes when water deficit imposed at the development stage. Water deficit occurred at the bulbification stage can remarkably reduce the dry matter of different parts and the physiological indexes. No significant effects were found in crop growth indexes when water deificit imposed at the ripening stage.(3) Seasonal evapotranspiration of onion can be up to414mm under mulched drip irrigation. Onion yield increased with the increase of irrigation depth significantly when irrigation depth less than0.8ETc. Water deficit during the development and bulbification sages reduced bulb yield significantly, while during establishment and ripening stages, the effects of water deficit on bulb yiled were not well marked. All water deficit treatments improved the water use efficiency of onion. Higher total soluable solids and protein content in onion bulb can be obtained under treatment with irrigation depth of0.8ETc, and water deficit can improve the vitamine C content. The water sensiticity indexes of water production function indicated that bulbification stage is the most critical stage for onion irrigation.(4) The SWNCM model was calibrated and validated by the observed soil water content and crop growth data. The results indicated that the model can be used to simulate the effects of deficit irrigation on the soil water dynamics, crop growth processes, crop yield and evapotranspiration of onion, chili pepper and tomato in this study area. And then, the appropriate irrigation management for the cash crop can be evaluated by the model.(5) Based on the calibrated model, various scenarios of different irrigation amounts and frequencies were studied on the water balance, crop yield and water productivity. With the consideration of water saving, high crop yield and water productivity, the appropriate irrigation schedules for onion, chili pepper and tomato are irrigating with intervals of5,5,7days and the irrigation quota are0.65ETc,0.73ETc and0.72～0.74ETc, respectively, under mulched drip irrigation.