Abstract:

This experiment studied the effects on soil enzyme activities， nitrogen fertilizer use efficiency and wheat yield of straw return with nitrogen， in the wheat cultivar Luohan 22. A split field trial design was used with two factors， straw and nitrogen fertilizer. The main plot treatments were： Straw fully cleared （S₀） and straw return （S₁）. The split-plot treatments consisted of differing nitrogen fertilizer application rates： 0 （N₀），120 （N₁）， 180 （N₂）， 240 （N₃） and 300 kg·ha^-1 （N₄）. Soil urease， sucrase， catalase and protease activities of 0-20 cm and 20-40 cm horizons were determined and the wheat yield， the nitrogen fertilizer agricultural utilization rate， nitrogen fertilizer apparent recovery rate， nitrogen fertilizer partial productivity and nitrogen absorption efficiency were measured. It was found that： 1） Compared with nitrogen fertilization treatment alone， the soil enzyme activities， nitrogen fertilizer use efficiency and wheat yield were increased by straw return. The wheat yield under S₁N₃ was the highest， and was 36.92% greater than S₀N₀. 2） Soil enzyme activity showed a trend of initial increase and then decrease with increasing rate of nitrogen application. Urease and sucrase had the highest activities in N₂， while all other soil enzymes had the highest activity at N₃. The soil enzyme activities gradually decreased with increasing soil depth. 3） The agronomic efficiency and apparent recovery of nitrogen fertilizer initially increased and then decreased with successive increases in nitrogen application rate， with the highest values observed in N₂， while the partial nitrogen productivity and nitrogen absorption efficiency decreased gradually with increasing nitrogen application rate. 4） The soil enzyme activities were positively correlated with the wheat yield and the apparent recovery of nitrogen fertilizer. In each reproductive period， urease activity was positively correlated with nitrogen absorption efficiency and nitrogen fertilizer partial productivity during the jointing period， while activities of all other soil enzymes were negatively correlated. Straw return combined with 180-240 kg·ha^-1 nitrogen fertilizer was shown to reduce excess nitrogen loss， improve the soil environment and result in efficient utilization of nitrogen resources in rainfed wheat fields of western Henan Province.

Key words: straw returning, nitrogen fertilizer, soil enzyme activity, nitrogen fertilizer utilization rate, wheat yield