Improving grain yield, nitrogen use efficiency and radiation use efficiency by dense planting, with delayed and reduced nitrogen application, in double cropping rice in South China oleh You-qiang FU, Xu-hua ZHONG, Jia-huan ZENG, Kai-ming LIANG, Jun-feng PAN, Ying-feng XIN, Yan-zhuo LIU, Xiang-yu HU, Bi-lin PENG, Rong-bing CHEN, Rui HU, Nong-rong HUANG