| Excessive or irrational application of N-fertilizer is not conductive to the ecological security and agricultural sustainable development, in order to make full use of biological nitrogen fixation to reduce N-fertilizer input and improve N utilization efficiency, This experiment, combined with the field test, micro plot test and pool-culture test, conducted in 2012-2013 to study the N uptake, N utilization and nodule N fixation characteristic of maize-soybean relay strip intercropping, to explore the effect of reduced N application on nodule N fixation characteristic and the relationship between the it and N-fertilizerutilization efficiency in maize-soybean relay strip intercropping system, to provide theoretical and practical basis for the efficient N fertilization technique of this system. In 2012, three N application rates (0,180,240 N kg·hm-2) representing zero N application (NN), reduced N application (RN) and conventionalN application (CN), respectively and three planting patterns (maize monocropping, soybean monocropping and maize-soybean relay strip intercropping) was set up and studied the effect of different planting patterns and N application rates on soybean dry matter accumulation, yield, yield components, N uptake, N utilization and nodule N fixation; labeled 15N was used in micro plot test, studied the difference of maize and soybean in reduced N application (RN) and conventionalN application (CN) on N-fertilizer uptake and utilization. In 2013, pool-culture test further studied the effect of reduced N application (RN) on nodule N fixation characteristic in different planting patterns (soybean monocropping and maize-soybean relay strip intercropping). The results showed that:1. With the advance of growth stage, the dry matter accumulation of soybean showed a trend of increasing initially and then decreasing. The root, stem and total dry matter accumulation of intercropped soybean significantlydecreased compared with the monocroppingsoybean, while the dry matter accumulation of grain significantly increased, which was 12.84% higher than monocropping soybean. N application was beneficial to improving the dry matter accumulation of soybean. The intercopped soybean in the reduced N treatment (RN) got the highest root, stem and total dry matter accumulation during the reproductive stage, in which the grain dry matter accumulation increased by 42.61% and 10.15% compared with the zero N application treatment (NN) and conventional N application treatment (CN), respectively, and the grain dry matter accumulation was increased by 36.86% and 7.48%.2. Compared with monocropping soybean, the pods per plant,, grain yield and economic coefficient of intercropped soybean increased by 4.20%,12.84% and 7.78%, respectively. The annual total yield of maize-soybean relay strip intercropping system increased significantly. Under the intercropping plant pattern, the pods per plant of soybean in reduced N application treatment (RN) was 8.30% higher than that in conventional N application treatment(CN). The grain yield of maize and soybean in reduced N application treatment (RN) were 33.90% and 42.61% higher than zero N application treatment (NN), and 8.04% and 10.15% higher than the conventional N application treatment(CN)respectively. Compared with zero N application treatment (NN)and conventional N application treatment (CN), the total grain yield of maize-soybean intercropping system increased by 35.78% and 8.51%,and the economic coefficient and land equivalent ratio (LER) of the system were 0.49 and 2.17, respectively, the aggressivity and competition ratio of maize were lower than that of soybean(Acs<0, CRcS<1).3. The total N uptake of maize-soybean relay strip intercropping system was significantly higher than monocropping maize and monocropping soybean, N harvest index, AEN and UEN of the intercropping system were significantly higher than monocroppingand intercropping maize. In reduced N application treatment (RN), the grain N uptake of intercropped maize and soybean were significantly higher than that in the other two N application treatments, and compared with the zero N application treatment (NN) and conventional N application treatment (CN), the total N uptake of intercropped maize, intercropped soybean and maize-soybean intercroppingsystem in reduced N application treatment increased by 20.28% and 13.93%,58.16% and 11.28%,58.16% and 11.28%, respectively, and AEN and UEN of maize-soybean intercropping system were significantly higher than that in conventional nitrogen treatment (CN).4. Compared with monoculture, the soil 15N content of intercropped maize decreased, but grain 15N uptake per plant, total 15N uptake and 15N recovery rate content increased; the grain 15N uptake, total 15N uptake and 15N recovery rate of intercropped soybean increased, but soil 15N content decreased, in which, the grain 15N uptake and total 15N uptake of intercropped maize increased by 12.29% and 5.64%, and soybean increased by 254.81% and 334.98%, respectively. Under intercropping plant pattern, compared with conventional N application (CN), the grain 15N uptake and total 15N uptake of maize in reduced N application treatment increased by 17.29% and 14.38%, while those values of soybean decreased by 57.48% and 57.08%. In maize-soybean relay strip intercropping system, soil total N,NH4+-N,NO3--N and inorganic total N content of maize were increasing with the nitrogen fertilizer application rate increasing; and soybean in the reduced N treatment got the highest soil total N content and the minimum NH4+-N, inorganic total N content.5. With the advance of growth stage, soybean nodule nitrogenase number and nodules dry weight in monocropping showed a trend of increasing initially and decreasing afterwards, while those two values kept increasing in relay strip intercropping system, and got the highest value at R5 stage, which were 44.42% and 32.24% higher than that in monocropping. Under intercropping plant pattern, at R2 stage, soybean nodules number in reduced N application (RN) treatment increased by 20.28% and 13.93% compared with that in zero N application (NN) and conventional N application treatment (CN), still, the nodules dry weight and leghemoglobin content were 22.54% and 11.63% higher than that in zero N application treatment (NN); at R5 stage, soybean nodules number in reduced N application treatment (RN) increased by 32.94% and 19.75% compared with that in zero N application (NN) and conventional N application treatment (CN), besides, nodules dry weight and nitrogenase activityper plant were 17.34% and 16.70% higher than that in zero N application treatment (NN); at R8 stage, grain and total ureide content of soybean in reduced N application treatment increased by 18.63% and 14.19% compared with those in zero N application treatment (NN), respectively. |
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