The Study On Yield,water And Nitrogen Utilization Of 1-yr Alfalfa-Winter Wheat Rotation System In The Loess Plateau

Alfalfa-winter wheat rotation is one of the common rotation patterns of crop-forage rotation.Alfalfa is a perennial leguminous plant.Due to the characteristics of its deep root,it has an impact on the growth and water use of the subsequent crops.The yield,water utilization and nitrogen utilization of the following crops have been the focus of academic community and practical attention.It is of great significance to explore the effect of short-term alfalfa growth on growth and water utilization of the subsequent crops under dryland farming conditions.This study was conducted in Qingyang Loess Plateau,Gansu Province from August 2018 to September 2020,with alfalfa’Zhongmu 1’（Medicago sativa L.）and winter wheat’Longyu 4’（Trticum aestivums L.）as the research object,three cropping patterns were constructed,continuous cropping of winter wheat（W-W）,alfalfa-winter wheat rotation（A-W）and alfalfa grassland system（A-A）.The yield,water and nitrogen use efficiency of 1-yr-old alfalfa-winter wheat rotation system were studied under two nitrogen application levels(normal nitrogen application(150 kg·N·hm^-2)and half nitrogen application(75kg·N·hm^-2).The main results are as follows:（1）In the continuous cropping system of winter wheat（W-W）and 1-yr-old alfalfa-winter wheat rotation（A-W）,the leaf area index（LAI）of the whole growing season of the subsequent winter wheat showed a‘unimodal’dynamic pattern,with the peak values of 5.12,which appeared at filling period.The LAI increased fastest from the regreening period to the jointing period.The normalized difference vegetation index（NDVI）of winter wheat in the whole growing season of W-W and A-W system showed a downward trend,with the highest values were 0.88 and 0.85 respectively.The growth rate of LAI and NDVI of alfalfa get the highest at branching period,and reached the peak value of 5.75 and 0.95 at flowering period,respectively.（2）In the two-year rotation cycle,W-W system harvested winter wheat grain7.03 t·hm^-2 and winter wheat straw 13.19 t·hm^-2,A-W system harvested alfalfa hay yield 11.69 t·hm^-2,winter wheat grain 3.83 t·hm^-2 and winter wheat straw 7.55 t·hm^-2.Compared with the W-W system,the grain yield of winter wheat increased by 9.4%and8.6%under the normal nitrogen application(W₁₅₀)and half nitrogen application(W₇₅).A-A system harvested 24.04 t·hm^-2 alfalfa hay.（3）The water evapotranspiration（ET）of alfalfa grassland system（A-A）was the highest,which was 13.8%and 27.1%higher than that of A-W system and W-W system,respectively.The WUE of the subsequent winter wheat grains were 9.06 and 10.52kg?hm^-2?mm^-1 under continuous cropping of winter wheat,1-yr-old alfalfa-winter wheat rotation.（4）Under the condition of half nitrogen application,the content of NO₃^--N in 0-10 cm soil decreased by 54.7%,and the nitrogen uptake efficiency of winter wheat increased by 12.4%,which was 16.6%higher than that of continuous cropping of winter wheat.In conclusion,under the condition of Loess Plateau,1-yr-old alfalfa can guarantee the soil water requirement for the growth of the subsequent winter wheat,reduce the amount of nitrogen application by half,still maintain the grain productivity of the subsequent winter wheat,and enhance the absorption and utilization of nitrogen in the subsequent winter wheat.In practice,1-yr-old alfalfa-winter wheat rotation can ensure the productivity,save water and reduce nitrogen input and realize the improvement of quality and efficiency.