| Large portion of fertilizer often was used at earlier growth stages by traditional fertilization method. Nutrient supply with this fertilizer application can not meet the need of crops at different growing stages, which caused low fertilizer use efficiency. Split application of nitrogen was an effective technical measure at different growth stages. With the development of water-saving irrigation technology, the integration of irrigation and fertilization technology (fertigation) provided a convenient technical means to supply adequate nutrients to plants at middle-late growing stages. Split application of nitrogen by dripping fertigation method was an effective way to supply nutrient timely to crops based on plant needs, which dramatically changed the nitrogen fertilizer ratio of basal application and topdressing application. However, the related theory and technology about fertigation need further attention and study. Aiming at the technology development to supply nitrogen nutrient according to plant needs during the entire growing period, this study uses maize as testing crop and using drip irrigation technology. Pot and field experiments were performed to study the mechanisms and effects of splitting application of nitrogen by dripping fertigation with the goal to reduce fertilizer rate and to improve fertilizer use efficiency. The main conclusions are presented as follows:1. Nitrogen plays an important role in grain yield formation of maize. The grain yield could be improved by applying N fertilizer. With the increase of N fertilizer application rate, the grain yield was increased first, but with further increase in N fertilizer rate, the yield response to N decreased. Both total biomass and grain yield in N splitting application treatment were higher than those in conventional nitrogen application treatment under reasonable nitrogen application level, while little difference was observed at higher nitrogen application levels. The results demonstrated that by reasonably splitting application of nitrogen could realize the goal of reducing fertilizer application and increasing efficiency.Compared to CK treatment (no nitrogen application), the grain yield in all treatments with nitrogen application increased by11.7%to24.5%. Both total biomass and grain yield of treatments with5split application of nitrogen (A2) were higher than those in conventional nitrogen application treatment with two split applications (Al) with nitrogen application rate of150kg/hm2. Compared to CK, the grain yields in5split treatment and in2split treatment increased by21.8%and11.7%, respectively. Compared to CK, biomass yields in5split treatment and2split treatment increased by17.7%and6.8%, respectively.. At nitrogen application rates of150,300and450kg/hm2, compared to CK, grain yield in2split treatment increased by11.7%,24.5%and15.4%, respectively, while the5split treatment increased by21.8%,23.4%and17.0%, respectively. Compared to CK treatment, at nitrogen application rates of150,300and450kg/hm2, the biomass in2split treatment increased by6%、23.3%and13.9%, respectively, while that in5split treatment increased by17.7%,18.6%and9.2%, respectively. With5split application of N fertilizer under fertigation, application of N at150kg/hm2produced about the same yield with the2split application treatments at300kg/hm2, indicating that split application of N is an effective measure to improve N fertilizer efficiency.2. Both partial factor productivity from applied N (PFPN) and agronomic efficiency of applied N (AEN) were the important indexes about nitrogen use efficiency. Both PFPN and AEN in N splitting application treatment were higher than those in conventional nitrogen application treatment under reasonable nitrogen application level, while little difference was observed at higher nitrogen application levels. The results demonstrated that by reasonably splitting application of nitrogen could realize the goal of increasing nitrogen fertilizer efficiency.PFPN and AEN of treatments with5split application of nitrogen (A2) were101.77and18.22kg/kg N at nitrogen application rate of150kg/hm2, respectively, while the two split treatment (A1) were93.33and9.77kg/kg N, respectively. Compared to A1treatment, the grain yield in A2treatment was increased by8.45kg/kg N. PFPN and AEN of treatments with5split application of nitrogen (A2) were51.55and9.78kg/kg N at nitrogen application rate of300kg/hm2, respectively, and the same value was observed at the two split treatment (A1). PFPN and AEN of treatments with5split application of nitrogen (A2) were32.59and4.74kg/kg N at nitrogen application rate of450kg/hm2, and the same value was also observed at the two split treatment (A1).3. With increase of nitrogen application rate, nitrate nitrogen content in the soil was increased at maize maturity. There was a significant movement of nitrate nitrogen leaching down to the soil profile under high level of nitrogen application. Therefore, reducing input of nitrogen was the effective measures for reducing N nitrogen content at maize maturity. The nitrate nitrogen content in nitrogen split application for five times was significantly higher than that in nitrogen split application for two times. The soil nitrate nitrogen content decreased with the increasing of soil depths. By reasonably splitting application of nitrogen could realize the goal of reducing fertilizer application rate, increase grain yield and reduce the risk of environmental pollution.The average nitrate nitrogen content in0～100cm soil profile in CK treatment was4.83mg/kg. The nitrate nitrogen content in soils in the5split treatment under nitrogen application rate of150kg/hm2was20.83mg/kg, while that in2split treatment was6.11mg/kg. The nitrate nitrogen content in5split treatment under nitrogen application rate of300kg/hm2was30.67mg/kg, while that in2split treatment was19.80mg/kg. The nitrate nitrogen content in5split treatment under nitrogen application rate of450kg/hm2was268.94mg/kg, while that in2split treatment was20.82mg/kg.4. Dry matter yield, chlorophyll content, photosynthesis rate, nitrogen content and nitrogen uptake were significantly increased by nitrogen application under pot experiment condition. These indexes above in high fertility soil were all higher than those in low fertility soil. Results above showed that basic soil fertility was the foundation for plant growth and yield formation. Nitrogen fertilization is important in improving plant growth and yield formation.5. The photosynthetic capacity was improved by reasonable nitrogen application. Photosynthesis rate, stomatal conductance and transpiration rate in5split treatment in seedling and filling stages were higher than those in2split treatment. Reasonable nitrogen application could supply necessary nutrients for plants different growth stages and it was beneficial to obtain high yield.Results above showed that the synchronization between nitrogen supplying and plant nutrients need can be realized by the split application of nitrogen with fertigation, which is an effective way to improve nitrogen use efficiency in sustained high yield and high efficient maize production. |
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