Up to 2012, 96 commercially released super rice varieties were grown on over 80 million ha in China. However, there was little increase in terms of large-scale rice production due to unreasonable agronomic practices. Therefore, understanding the yield responses of super rice to various agronomic practices, such as nitrogen (N) - rates or planting methods, is of great importance to fully realize the potential of the newly released super rice varieties.

A two-year experiment was conducted by China National Rice Research Institute (CNRRI) to evaluate the responses of super rice to different planting methods for grain yield and N-use efficiency in the single cropping season. A total of 17 rice varieties, including 13 super rice [8 Hybrid Indica rice & 5 Japonica rice] and four non-super checks (CK), were grown under three N levels [0 (N0), 150 (N150), and 225 (N225) kg ha^-1] and two planting methods [transplanting (TP) and direct-seeding in wet conditions (WDS)].

This research was partly supported by grants from the ‘Five-twelfth’ National Science and Technology Support Program (2012BAD04B00), the National Natural Science Foundation of China (31301255&3117150156), and the MOA Special Fund for Agro-Scientific Research in the Public Interest of China (201203096). The research finding has been published on PLoS ONE on August 11^th, 2014.

Grain yield under WDS (7.69 t ha^-1) was generally lower than TP (8.58 t ha^-1). However, grain yield under different planting methods was affected by N rates as well as variety groups. In both years, there was no difference in grain yield between super and CK varieties at N150, irrespective of planting methods. However, grain yield difference was dramatic in Japonica groups at N225, that is, there was an 11.3% and 14.1% average increase in super rice than in CK varieties in WDS and TP, respectively. This suggests that high N input contributes to narrowing the yield gap in super rice varieties, which also indicates that super rice was bred for high fertility conditions.

Effect of nitrogen (N) rates and planting methods on N agronomic efficiency (NAE) in 2011 (A) and 2012 (B). WDS, wet direct-seeded rice; TP, transplanting rice; N0, 0 kg N ha^-1; N150, 150 kg N ha^-1; N225, 225 kg N ha^-1. The vertical bars stands for standard error of means.

In the Japonica group, more N was accumulated in super rice than in CK at N225, but no difference was found between super and CK varieties at N0 and N150. Similar results were also found for N agronomic efficiency. The results suggest that super rice varieties have an advantage for N-use efficiency when high N is applied. The response of super rice was greater under TP than under WDS. The results suggest that the need to further improve agronomic and other management practices to achieve high yield and N-use efficiency for super rice varieties in WDS.

More details are available on PLoS ONE on the links bellow:

http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104950