| Nitrogen fertilizer occupies the important position in agriculture. Nitrogen fertilizer is great importance of increasing grain production and ensuring food security, but the excess of nitrogen input also brings serious ecological environment problems and is not conducive to the sustainable development of agriculture. Therefore, reducing nitrogen input technology development has become a research hot spot for agricultural experts and scholars. In recent years, in the southwest of China, maize-soybean relay strip intercropping system has developed rapidly, and its cultivation system has already been matured, which had some great contribution to the local agriculture production and farmers’income. However the fertilization technology is still following the traditional pattern of maize-sweet potato intercropping, or the sole cropping to maize and soybean, which leds to large nitrogen input, complex technology, low nitrogen use efficiency, serious loss, and limits the further applying of maize-soybean relay strip intercropping. Therefore, several years field experiments was conducted, combined with the 15N isotope tracer of soil pool, to study the yield, N uptake and use efficiency, N residue and loss and soil N transformation in maize-soybean relay intercropping system. Three planting patterns were used in the research including maize monoculture (MM), soybean monoculture (SS) and maize-soybean relay strip intercropping (IMS), combined with three N levels, no N application (NN), reduced N application (RN:180 kg N.hm-2) and conventional N application (CN:240 kg N.hm-2).This study were to evaluate the N uptake features between crops in the relay strip maize-soybean intercropping system, and reveal the efficient N utilization mechanism under reduced N application condition. The results were as follows:1. Compared with MM (SS), maize of IMS stem biomass was no significant change, but the grain yield was decreased by 3.49%;Soybean of IMS stem biomass decreased significantly, while the grain yield increased significantly by 9.71%; compared with no N input, applying N improved both stem biomass of maize and soybean and grain yield of maize. As in MM (SS) pattern, under the N treatment, maize grain yield in CN was highest, and soybean in RN was highest; when in the IMS, applying N relative to no N increased stem biomass and grain yield of maize and soybean, and RN treatment was the highest with the N input.2. Compared with MM (SS), maize stem N uptake was increased in IMS, while the grain N uptake was decreased; soybean stem N uptake was declined, but grain N uptake increased in IMS. In the RN treatment. N fertilizer utilization ratio of IMS was 99.87% higher than MM. but soil N contribution rate is low 18.12% than MM. and N fertilizer utilization rate of agronomy of IMS was higher than MM and SS,21.77% and 138.67% respectively. Applying N compared with no N input significantly increased maize and soybean plant N uptake under the MMã€SS and IMS. RN compared with CN, maize and soybean plant total N uptake increased by 12.17% and 12.17% respectively; N fertilizer use efficiency and N fertilizer agriculture utilization increased by 100.95%and95.09% respectively, the soil N contribution rate was decreased by 10.94%in IMS.3. With the increase of soil layers, soil NO3--N accumulation and 15N residue of maize and soybean was decreased gradually, and the residual nitrogen were mainly concentrated in the 0 to 40 cm soil layer. In IMS, compared with MM (SS), maize soil NO3--N accumulation and 15N residue were increased, soybean soil NO3--N accumulation was decreased, while 15N residue was increased. With the RN-NH4 15NO3 treatment,15N residue of maize and soybean were significantly higher than treated by RN-15 NH4NO3 under the IMS, MM and SS. Ammonia volatilization accumulation in IMS was no significant difference than MM, but its loss rate was significantly decreased. N2O emissions and loss rate in IMS were lower than the MM and SS. Compared with CN treatment, Ammonia volatilization accumulation in RN treatment was significantly decreased similar with the Ammonia volatilization loss rate and N2O emissions and N2O loss rate under the IMS.4. Compared with the MM (SS), maize soil NO3-N, NH4+-N and total N content were increased in IMS, and soybean soil NO3--N and total N content was decreased, while soil NH4+-N content were increased. Compared with MM (SS), maize and soybean soil nitrifying capacities and ammonifying capacities were increased, the nitrogen-fixing capacities of soybean was decreased in IMS. Compared with CN, nitrifying capacities of soybean soil was increased by 12.69%; soil ammonifying capacities of maize and soybean were decreased by 23.69%,7.93%, and soil nitrogen-fixing capacities of maize and soybean were increased by 26.31% and 32.53% in IMS with RN treatment.5. Compared with the MM (SS), IMS increased maize total N content of stem,15N% abundance and 15N uptake of stem and grain, and soybean total N content of stem,15N% abundance and 15N uptake of pod and grain. Compared with the RN-NH415NO3,15N% abundance and 15N uptake of maize and soybean increased significantly in RN-15NH4NO3, among them, the total 15N absorption of maize and soybean increased by 15.79% and 15.79% respectively in IMS. Compared with SS, biological nitrogen fixation volume of soybean increased significantly in IMS. |
