Effect of Low Nitrogen Rate Combined with High Plant Density on Yield and Nitrogen Use Efficiency of Machine-transplanted Early-late Season Double Cropping Rice

Abstract

In order to alleviate the contradictions of growth period mating problem of machine-transplanted double cropping rice in Changjiang Rive regions, a field experiment with three nitrogen rates (0, 110-140, and 176-189 kg N ha -1 ) and three plant den- sities (36.4, 28.6, and 19.0 hill m -2 ) was conducted using conventional early variety Zhongjiazao 17 in both early and late sea- sons to explore the effects of machine transplanting densities and N application on yield and N recovery efficiency (REN) in 2014-2015. Adopting the same conventional early variety was able to reach the high yield in machine-transplanted early-late sea- son double cropping rice. The treatment of high density (36.4 hills m -2 ) with high nitrogen rate (176 kg ha -1 in early season, 189 kg ha -1 in late season) had the highest yield of 16.94 t ha -1 in 2014 and 16.99 t ha -1 in 2015, but not significantly higher than the treatment of high density with low nitrogen rate (110 kg ha -1 in early season, 140 kg ha -1 in late season). REN declined with in- creasing N application and improved with increasing density. The treatment of high density with low nitrogen rate showed the highest REN of 62.77%, 55.75%, 65.82%, 64.37% in early and later season 2014 and 2015, which are 12.11%, 9.01%, 8.49%, and 2.14% higher than the treatment of high density with high nitrogen rate, respectively. The treatment of high density with low ni- trogen rate displayed certain advantages of dry matter accumulation and radiation use efficiency compared with the treatment of low density (19.0 hills m -2 ) with high nitrogen rate. As a result, adopting high planting density and low nitrogen fertilizer could not only achieve high yield, but also significantly improve REN in early-late season double cropping rice. The key technology provided in the study would be available for machine-transplanted double cropping rice cultivation in the Yangtze River regions.