Evaluation And Optimization Of Winter Wheat Cultivation Management Measures On The Loess Plateau Based On RZWQM2

Global warming has significantly impacted the dryland winter wheat growth and its development and aggravated the local soil water deficit in the agro-ecosystem. The frequent extreme climate events have significantly increased the fluctuation of agricultural production. Climate change has altered crop cultivation patterns and planting regions, increased the agriculture production cost, and even considerably decreased the crop yields on the Loess Plateau. Thus, the climate change would have reduced crop production and bring greatly challenge to the local food security. In the present study, two experiments were conducted, including a continuous crop rotation experiment of winter wheat(Triticum aestivum L.)–spring maize(Zea mays L.) from 2004 to 2012 and a winter wheat experiment using different fertilizer management(2010-2012) to calibrate and validate RZWQM2(Root Zone Water Quality Model-version 2). The objectives of this study were to(1) study the reliability of RZWQM2 on the Loess Plateau;(2) study the optimal sowing date of winter wheat under consideration of precipitation patterns under global warming;(3) explore the applicability of later-maturing cultivars of winter wheat under climate warming, and study impacts of later-maturing cultivars of winter wheat on the soil water deficit on the Loess Plateau;(4) establish a quantitative relationship between precipitation and optimal N application strategies for dryland winter wheat. Results showed that:(1) RZWQM2 can efficiently simulate crop development, soil water movement, and final crop yields on the Loess Plateau. RZWQM2 could also efficiently simulate yield factors, N uptake of shoot and grain, and the soil N-NO3 content using different N fertilizer management practices on the Loess Plateau. RZWQM2 is a reliable tool for predicting the dryland winter winter development, production, and soil water dynamic change on the semiarid Loess Plateau.(2) Temperature and the available growing degree days from September through next June increased significantly in the study site with time going, even more significantly increased since 1980 s. The average precipitation decreased with time going. The total growth duration of winter wheat have significantly decreased, and meanwhile, the yield exhibited a decreasing trend due to global warming over the past decades. Due to the more significant decreasing trend of wheat yield than evapotranspiration(ET), the water use efficiency(WUE) showed a decreasing trend.(3) The delayed sowing date could delay the winter wheat growth development, and improve the soil water condition in the vegetative growthphase, which may indirectly improved the soil fertility. In this way, the vegetative growth was greatly promoted by the delayed sowing date, which provided a stable material basis for an efficient reallocation of photosynthates to the grain. Then the delayed sowing date can optimize the contribution of post-anthesis dry matter and N accumulation to grain dry matter and N yields, respectively. Finally, the delayed sowing date effectively increased the wheat yield, decreased the ET, consequently improved the WUE under global warming. The sowing date of winter wheat could be delayed by 10-20 days in the wet and medium years and by approximately 20-25 days in the dry year than the current sowing date of 20 Sept. to maintain a high level of yield under global warming on the Loess Plateau.(4) The later-maturing cultivars of winter wheat can fit its development to the characteristics of local climate change and environment on the Loess Plateau. The downward trend of wheat growth duration was effectively counteracted, and even reversed by later-maturing cultivars. The increase in precipitation during wheat growth duration could partly compensate some additional water consumption, and maintain, or even reduce soil water deficit. This modification improved the soil water conditions at the stage of yield formation. The adapted varieties adequately utilized abundant sunlight-heat resources, and significantly improved the wheat yield, WUE, and water balance in the dryland farming.(5) Wheat turning green and jointing stages were found to be the optimal topdressing stages for winter wheat on the Loess Plateau. Split application of N when topdressing at turning green stage can increase soil mineral N in the key periods of N uptake, which can modify the contribution of post-anthesis dry matter and N accumulation to grain dry matter and N yields, respectively. Split application of N was contributed to the synchrony between N fertilizer supply and crop demand, and significantly increase the wheat yield compared with single basal dressing. The maximum potential of N fertilizer saving using split application mainly fall in the precipitation ranging from 320 to 400 mm compared with single basal dressing on the Loess Plateau.