Effects Of Nitrogen Fertilizer Reduction On Maize Intercropping With Green Manure Root Returning To Field In Hexi Oasis Irrigation Area

Maize and leguminous green manure(GM)intercropping is a common planting system in Hexi oasis irrigation area of northwestern China.The aboveground parts of GM crops can be harvested as forage while their root residues can be returned to improve soil fertility.To reveal the impacts of fertilizer nitrogen(N)reduction on maize yield and N uptake,as well as soil fertility and N accumulation in soil profile,maize was intercropped with needle leaf pea(Pisum sativum)or hairy vetch(Vicia villosa)for 11 years with GM root resiude return.The main findings were as follows:(1)GM root residue return was effective to reduce chemical fertilizer N input while increase N-use efficiency in the maize and GM intercropping system.Compared with the conventional N application,10 to 20% reduction of N input in combination with root residue return maintained or increase maize grain yield,yield components,N,P and K uptake.Nitrogen partial factor productivity was increased by 10-11% in the treatment of pea root residue return with reduced N input,while the apparent N utilization was increased by 13% in the hairy vetch treatments with 10% reduction of N fertilizer.Nutrient-absorption related indicators were the dominant factors affecting maize grain yield,which was mainly act by apparent N accumulation.(2)Maize intercropped with GM root residue return substantially improved soil fertility.The results showed that pea root residue return with 20% N fertilizer reduction consistently enhanced the integrated soil fertility index by 38% to 41.7% when compared with the conventional N treatment.Under the simulated conditions,the capacity of soil N supply peaked at 10 days after incubation.The 10%-20% reduction of N fertilizer with GM root residue return outperformed the conventional fertilizer N treatment,and the most significant effects on soil fertility were achieved by the needle leaf pea with 20% N fertilizer reduction treatment.Fertilization treatments affected maize grain yield mainly through regulating the soil N storage.The soil inorganic N and dissolved organic N contributed the most to yield increase,accounting for 15% and 13%,respectively.(3)Maize intercropping with GM and root residue return increased soil N sequestration and reduced nitrate leaching.The continuous return of GM root residues under 10%-20% fertilizer N reduction could effectively maintain or increase the concentrations of different soil layers,among which the return of needle leaf pea root with20% reduced N fertilizer application treatment significantly increased the inorganic N concentrations of the top 20 cm layer by 34% and increased the total N and organic matter of the 80-100 cm soil layer,when compared with the conventional N application.The soil nitrate N concentrations under the treatments of GM root residue return and fertilizer N reduction was 27 % to 70% lower in the 40 to 100 cm soil layers than that in the conventional fertilizer treatment.Overall,the study suggested that in the maize and legume GM intercropping systems of Hexi oasis irrigation area,GM root residue return in combination with 20%reduction of fertilizer N input could simultaneously improve maize production,soil fertility and N utilization efficiency.