Benefits of mechanized deep placement of nitrogen fertilizer in direct-seeded rice in South China

Abstract

Mechanical hill direct-seeded rice synchronous with deep placement of N fertilizer (MHDSR-NF) is an efficient alternative to conventional transplanted-flooded rice (CTFR), however, little is known about the effects of MHDSR-NF on grain yield, nitrogen use efficiency (NUE), and economic profitability. In present study, two types of N fertilizer viz., commercial compound fertilizer (CF) and ammonia bicarbonate (AB), placed mechanically at 10cm of soil depth (M) or broadcasted manually (B), (written as CFM, CFB, ABM and ABB, respectively) in two rice cultivars viz., Tianyou998 and Yuxiangyouzhan which were grown in both early and late seasons of 2014 in double rice cropping system of South China. Plants without N fertilizer application were taken as control (N0).Compared to surface broadcasting, mechanically deep placement of N fertilizer enhanced NUE and grain yield significantly while improved nitrogen recovery efficiency (NRE) by 32.52–50.79%, 21.51–32.68%, and nitrogen agronomy efficiency (NAE) by 32.10–50.43%, 19.47–38.78%, of Tianyou 998 and Yuxiangyouzhan, respectively, in both seasons. Compared to surface broadcasting, the grain yields of Tianyou 998 and Yuxiangyouzhan under mechanically deep placement of N fertilizer were also increased by 6.31–8.03% and 4.70–6.78%, respectively, which were ascribed to the increased spikelet number per panicle. Furthermore, the lower production cost and the higher total return in CFM led to the highest benefit-cost ratio (BCR) in CFM, followed by CFB and ABM, whereas the lowest BCR was recorded for ABB. In addition, significant improvements were also observed in leaf area index, total aboveground biomass, and photosynthesis rate in CFM at the heading stage. Catalase (CAT) and Peroxidase (POD) activities of the uppermost leaves were significantly higher under deep placement of N fertilizer than surface broadcasting. Hence, mechanized deep placement of commercial compound fertilizer can be taken as an efficient fertilization method in mechanical hill direct-seeded rice in South China.