Effects Of Maize-soybean Intercropping Systems With Different Belt Types On Nitrogen Transfer And Utilization

Crop intercropping is an important planting method to realize efficient utilization of agricultural resources.Crop spatial layout and nitrogen management in intercropping system are particularly important for improving ecological benefits of crop production.However,the transfer and utilization of legume source nitrogen during the current growing season and its contribution to the nitrogen utilization of later crops under different intercropping belt configurations are still unclear.Therefore,in this paper,two independent and closely related field trials were carried out in the double-cropping area of wheat and maize in Guanzhong from 2021 to 2022 using a single factor randomized block design and¹⁵N isotope in situ labeling and tracer technique.In the first season（summer maize growing season）,five different belt types of maize and soybean intercropping patterns were set:The transfer of legume source nitrogen in the current growing season and its effect on the nitrogen utilization of maize were studied firstly,including 2-row maize and 4-row soybean intercropping（M2S4）,4-row maize and 4-row soybean intercropping（M4S4）,6-row maize and 4-row soybean intercropping（M6S4）,soybean single cropping（CKS）and maize single cropping（CKM）.In the second season（winter wheat growing season）,the in situ plot division of the previous season was maintained,and M2S4,M4S4,M6S4 and CKS were retained to explore the effects of maize and soybean intercropping on nitrogen utilization of the later wheat,in order to provide scientific basis for the scientific design of the compound cropping system and efficient nitrogen management in the double-cropping area of Guanzhong.The main findings are as follows:（1）In situ labeling results of ¹⁵N confirmed the transfer of source nitrogen from soybean to intercropped maize plants.The proportion of nitrogen deposited in rhizosphere of M6S4 at V6 stage and R2 stage was the highest（11.35%and 19.39%,respectively）,and the proportion transferred to intercropped maize grains under this treatment was also the highest,which is 4.03%.Soybean intercropping decreased nitrogen use efficiency（△NUE）,but increased nitrogen uptake（△NU）,nitrogen harvest index（NHI）and nitrogen uptake efficiency（NUPE）.The total nitrogen accumulation of intercropped soybean was increased by 32.97%compared with that of soybean monocropping,and the total nitrogen accumulation of intercropped maize was increased by 11.27%compared with that of maize monocropping.In all treatments,the N production efficiency（NPE）of soybean and maize in M4S4 was the highest.The land equivalent ratio（LER）of the three intercropping belts is all greater than 1.The yield of soybean and maize under M4S4 treatment was the highest,and the yield of soybean and maize under M4S4 treatment was increased by 25.29%and10.29%,respectively,compared with monocropping.Soybean and maize showed different marginal effects,soybean intercropping yield was higher than the side row yield under the same treatment,but maize side row yield under each treatment was higher than the side row yield under the same treatment.（2）The ¹⁵N isotope tracer confirmed that the ¹⁵N from soybean was transferred to the stems,leaves and grains of wheat in the next season through rhizosphere deposition and straw returning.The nitrogen transferred from the previous season was the highest in the stems,leaves and grains of wheat in M6S4,which were 9.50%and 8.76%,respectively.Maize and soybean intercropping had more positive effects on nitrogen accumulation and utilization and yield of later winter wheat than soybean monoculture.The effect of maize intercropping on grain nitrogen content was significantly higher than that of soybean mono-cropping.Compared with soybean mono-cropping,maize intercropping increased grain nitrogen content by 6.70%and NUPE by 25.78%on average.The total nitrogen accumulation,NHI,NUPE and NPE of M4S4 treatment were the highest among all treatments.The yield of wheat treated with intercropping last season was higher than that of wheat treated with soybean mono-cropping last season,and the yield of M4S4 treatment continued the advantage of last season,increasing by 12.81%compared with that of soybean mono-cropping previous season.In conclusion,the positive effects of maize and soybean intercropping on crop nitrogen use were not only reflected in the current growing season,but also the subsequent crop effect.Among them,the intercropping of four rows of maize and four rows of soybean not only improved the nitrogen absorption efficiency and grain yield of maize in the current season,but also improved the nitrogen productivity of later wheat,which could be regarded as the optimal allocation belt type suitable for Guanzhong region.