| In this study, a field experiment was conducted, three nitrogen levels and three kinds of cropping patterns were set, and physiological index, dry matter accumulation and N, P and K accumulation and yield of soybeans and corn in the soybean/maize mixed cropping system were studied. Results show that:1. Effects of mixed cropping of soybean and corn on physiology index:In the soybean/corn mixed cropping system, SPAD value and chlorophyll content of intercropped soybean leaves, N03-N and dissolved protein content of intercropped soybean plants were lower than monoculture soybean; SPAD value and chlorophyll content of intercropped corn leaves, N03-N and dissolved protein content of intercropped soybean plants were lower than monoculture corn;During the whole growth period, SPAD value and chlorophyll content of soybean and corn increased with the increase of the amount of nitrogen; N03-N and dissolved protein content of corn plants were increased; N03-N and dissolved protein content of soybean plants were increased in the beginning, and then became lower. There was a very significant linear correlation between SPAD value of leaves and yield of soybean at podding period; There was a very significant linear correlation between SPAD value of leaves and yield of corn at the tassel period.There was a very significant difference between NO3-N, dissolved protein content and dry matter accumulation, N accumulation of soybean and corn plants.Therefore, NO3-N and dissolved protein content could be used to estimate enrichment or deficiency level of plant N nutrition for the reference index of the crop nitrogen application.2.Effects of mixed cropping of soybean and corn on nutrition absorbtion and utilization:The overall trend of dry matter accumulation was similar to NPK accumulation. In the soybean/maize mixed cropping system, dry matter accumulation and NPK accumulation of soybean intercropped at each growth period were slightly lower than that of the monoculture soybean; Dry matter accumulation and NPK accumulation of corn intercropped at each growth period were higher than that of the monoculture corn; the mixed cropping system showed advantages of mixed cropping on nutrient absorption. In the mixed cropping system, soybean played a significant role in promoting corn absorption and utilization of NPK nutrition. During the whole growth period, the dry matter accumulation and NPK accumulation of soybean plants were increased in the beginning, and then became lower with the increase of the amount of nitrogen. Dry matter accumulation and NPK accumulation of corn plants were increased.3. Effects of mixed cropping of soybean and corn on yield:In the soybean/corn mixed cropping system, when nitrogen fertilization was the same, yield of intercropped corn was higher than that of monoculture corn, and yield of intercropped soybean was lower than that of monoculture soybean,but total yield of mixed cropping was higher than that of monoculture corn and soybean, respectively. The mixed cropping system showed advantages of mixed cropping on yield. Total yield of mixed cropping increased with increase of nitrogen amount.4. Effects of mixed cropping of soybean and corn on soil inorganic nitrogen:During the whole growth period, soil nitrate content of mixed cropping soybean field was lower than that of monoculture soybean field. Soil ammonium content of mixed cropping soybean field was higher than that of monoculture soybean field. Soil nitrate and ammonium content of mixed cropping corn field was higher than that of monoculture corn field. In the soybean/corn mixed cropping system, Soil inorganic nitrogen of mixed cropping field was higher than that of monoculture soybean and corn field, respectively. Soil nitrate, ammonium and inorganic nitrogen content of soybean and corn field increased with increase of nitrogen amount. There was a significant linear correlation between soil nitrate and ammonium nitrogen content of soybean and corn field; No matter what mixed cropping or monoculture, there was a significant linear correlation between soil nitrate of soybean and corn field and plant nitrate content, respectively, which would provide a theoretical basis for the rational application of nitrogen fertilizer.5. Effects of mixed cropping of soybean and corn on nitrogen utilization:Soybean/maize mixed cropping could improve the nitrogen use efficiency of soybean and corn. Nitrogen use efficiency of mixed cropping soybean decreased, but that of intercropped corn increased slightly, and total nitrogen use efficiency of mixed cropping was higher than that of monoculture corn and soybean, respectively.Therefore, the mixed cropping system showed advantages of mixed cropping. Agronomic nitrogen use efficiency of mixed cropping soybean was lower than that of monoculture soybean. Agronomic nitrogen use efficiency of mixed cropping corn was higher than that of monoculture corn. Total nitrogen use efficiency of mixed cropping was higher than that of monoculture corn and soybean, respectively.Therefore, mixed cropping could increase both of crop nitrogen use efficiency and agronomic nitrogen use efficiency. |
