Effect of different incorporation of Chinese milk vetch coupled with urea or controlled release urea on yield and nitrogen and potassium nutrient use efficiency in double-cropping rice system

Objective In order to develop scientific strategy to improve the efficiency of chemical fertilizer usage, a study of different proportion ofAstragalussincus and urea or controlled release urea (CRU) under the condition of reduced nitrogen and potassium fertilizer application rate on rice yield in south China during double rice season was conducted.

Method The 6-year field trial was conducted to study the effects of combined applying ofAstragalussincus with urea or controlled release urea (CRU) on double rice yield, content of nitrogen and potassium in rice plant, accumulation of nitrogen and potassium in rice plant, nitrogen and potassium use efficiency and status of soil nitrogen and potassium fertility.

Results Results showed that CF60 + A40, CRU60 + A40 and CRU40 + A60 treatments could increase both early rice yield and late rice yield compared with CF100 treatment and the yield increasing effect was the most obvious in CRU60 + A40 treatment. Both CF60 + A40 and CRU60 + A40 treatments increased nitrogen and potassium nutrients accumulation in rice grain, rice straw in early and late rice compared with CF100 treatment. The increasing effect in CRU60 + A40 was more significant than CF60 + A40. Combined applying ofAstragalussincus with urea or CRU could increase nitrogen and potassium nutrient use efficiency. The nitrogen recovery efficiency, potassium recovery efficiency, nitrogen agronomic efficiency, potassium agronomic efficiency, nitrogen partial factor efficiency and potassium partial factor efficiency were all higher in CF60 + A40, CF40 + 60A, CRU60 + A40 and CRU40 + A60 treatments than in CF100 treatment. The increasing effect of nutrient use efficiency was higher with combinedAstragalussincus with CRU than with urea under the same substitution proportion ofAstragalussincus and the same fertilizer rate. After six years (twelve rice seasons), contents of total N, alkalytic N and available K all increased in all the treatments combinedAstragalussincus with urea or CRU compared with CF100 treatment.

Conclusions Considering the crop yield response, efficient use of nutrient and soil fertility cultivation, recommended fertilization practice was that in early rice season, nitrogen chemical fertilizer can be cut down by 40% and substituted byAstragalussincus, potassium chemical fertilizer can be cut down by 20% and substituted byAstragalussincus, and in late rice season, nitrogen chemical fertilizer can be cut down by 40% and potassium fertilizer can be cut down by 20% associated with the usage of urea or CRU. When CRU was adopted, the substitute proportion ofAstragalussincus in early rice and the fertilizer reduction ratio in late rice can be properly raised.