Productivity and profitability of mechanized deep nitrogen fertilization in mechanical pot-seedling transplanting rice in South China

The deep nitrogen (N) fertilization coupled with mechanical pot-seedling transplanting rice (DNF-MPT) is an effective alternative to traditional transplanted rice (Oryza sativa L.) with broadcasting fertilizer; however, little is known about its effects on grain yield, nutrient accumulation, and economic profitability. In present study, a 2-yr field experiment was conducted in early seasons (Mar.-July) of 2019 and 2020. All seedlings were transplanted by DNF-MPT, whereas four treatments were designed as mechanized deep placement of all fertilizers as basal fertilizer (MD); mechanized deep placement of 70% basal fertilizer and 30% broadcasting fertilizers at panicle initiation (MDB); manual broadcasting of 40, 30, and 30% fertilizers at the transplanting, tillering, and panicle initiation stages, respectively (MB); and no fertilizer (CK). The results indicated that the MD treatment substantially improved the grain yield by 33.48-36.35%, total N accumulation by 26.38-44.15%, total phosphorus (P) accumulation by 28.72-30.23%, and total potassium (K) accumulation by 25.61-37.33% compared with MB. Deep placement of N fertilization treatments, that is, MD and MDB, remarkably promoted root morphological indexes including total root volume, total root length, and root superficial area. Furthermore, nitrate reductase, glutamine synthetase activities, and total chlorophyll content of leaves were also enhanced under deep placement of N fertilizer. Overall, the MD treatment had the highest benefit/cost ratio due to high gross returns and low input costs. Therefore, deep placement of N fertilizer coupled with mechanical pot-seedling transplanting rice could be better alternative to conventional rice production system with more economic benefits.

Automated summary

The use of deep nitrogen fertilization coupled with mechanical pot-seedling transplanting rice significantly improved grain yield, nutrient accumulation, and economic profitability compared to traditional broadcasting fertilizer methods. Deep placement of nitrogen fertilization also promoted root morphological indexes and leaf physiological activities, leading to higher benefit/cost ratio and making it a better alternative for conventional rice production systems.