Residual nitrogen from preceding garlic crops is important for double-cropped rice

Abstract

Rice alternated with upland crops has become increasingly popular in recent years. To investigate the residual effects of nitrogen from the previous upland crop on rice growth, two cropping systems, garlic-rice and wheat-rice, were studied from 2014 to 2017 under field conditions and from 2016 to 2017 under pot conditions. The results showed that the total nitrogen content in the 0–0.2 m soil was higher for the garlic-rice cropping system than for the wheat-rice cropping system and the 15N isotope abundance of the soil after harvesting garlic was 63% higher than that after harvesting wheat. Residual nitrogen from the preceding crops was one of the main nitrogen sources for rice growth. The contribution of residual nitrogen accounted for 17% to 60% of the total nitrogen accumulation by rice plants during the vegetative stage, which gradually decreased after the rice jointing stage. Most of the residual nitrogen absorbed by rice plants was transported to the reproductive organs for grain growth. Therefore, the growth of vegetative organs, viz., tillers and leaves, was more vigorous under the garlic-rice cropping system than under the wheat-rice cropping system. This led to a significant increase in total nitrogen accumulation in rice plants and an increase in rice yield by 8% to 16%, even under identical management of rice under upland crop–paddy rice systems. Thus, under upland crop–paddy rice systems, high-yield and high-efficiency rice production can be achieved by utilizing residual nitrogen from the preceding crops and decreasing the application of base and tiller nitrogen.