Split application improving sweetpotato yield by enhancing photosynthetic and sink capacity under reduced nitrogen condition

Abstract

Injudicious nitrogen (N) fertilizer application has increased the risk of environmental pollution and decreased sweetpotato yield as well as farm profits in China. Appropriate N fertilizer management is beneficial for improving growth, and yield attributes of field crops. Field experiments were conducted to determine the effects of application methods [three N treatments-conventional basal application 100 kg N ha−1 as control (100:0) and two treatments which received a total of 80 kg N ha−1 applied either 100% at basal application (80:0), 50% at basal application and 50% at tuber initiation stage (35 days after transplanting, 40:40)] on the sweetpotato growth and yield formation for the first time during growing season 2015 and 2016. Two sweetpotato cultivars, Xushu 22 (XS22) and Shangshu 19 (SS19), were used in three N treatments. Although a reduced N rate decreased initiation biomass accumulated, splitting N relatively delayed late-season leaf senescence as indicated by the increased chlorophyll content, LAD, NAR and biomass accumulated during the intermediate and final growth phases compared to conventional basal application of 100 kg N ha-1. Compared to 100:0, sweetpotato yields were significantly lowered by the reduced applications of 80:0 (relative yield of 95.3% for XS22 and 94.3% for SS19, respectively) but were significantly increased by the split applications of 40:40 (relative yield of 117.2% and 118.9% for XS22 and SS19, respectively). The improved yield by split N was due to both enhanced canopy photosynthetic capacity with higher biomass products and increased sink with greater tuberous root numbers, higher biomass partition ratio to storage root and larger storage root weight. This indicates that split application of N was more beneficial in terms of better growth, balanced sink–source ratio and higher storage root yield under reduced N condition. Outcomes of this research will help producers schedule fertilization to maximize yield and nutrition use efficiency.