Abstract:

In order to determine the appropriate nitrogen application level and irrigation mode for rice production in Hunan double cropping rice area,a randomized block design was adopted.Lingliangyou 942 and Lingyouhuazhan were used as early and late rice materials respectively.Three nitrogen application levels of N1-N3(150,120,0 kg/ha for early and late rice respectively)and three irrigation modes of W1-W3(water layer irrigation,wet irrigation and dry wet alternating irrigation for early and late rice respectively)were set.The effects of different water and fertilizer synergistic treatments on agronomic characters and yield of Double-cropping Hybrid rice were studied.The results were as follows:The increase of nitrogen fertilizer could significantly improve the SPAD value of rice, but the SPAD values of N1 and N2 were similar in early and late rice as a whole, while the irrigation method was W3, which could not only maintain a high SPAD in early and late rice, but also avoided late green and late ripening. Rice leaf area index (LAI) was directly proportional to the amount of nitrogen applied to a certain extent. The LAI values between N1 and N2 were similar in the whole growth period of early rice and the early growth stage of late rice, but N1 was higher than N2 in the late growth stage of late rice, while irrigation methods had little effect on the LAI value of early and late rice, mainly W3 was slightly higher. The increase of nitrogen fertilizer could significantly promote the accumulation of dry matter mass of rice. Except that the dry matter mass per plant of early rice at milk stage was N2 higher than N1 and the dry matter mass per plant of late rice at full heading stage was N1 higher than N2, the dry matter mass per plant of early and late rice at other stages was N1 and N2 similar, which showed that nitrogen reduction would not significantly have reduced the dry matter mass per plant of paddy rice on the whole. The irrigation method had little impacted on early rice and great impacted on late rice. The overall dry matter mass per plant of early and late rice increases better with W3, W2 followed. Increasing nitrogen fertilizer application could significantly improve the theoretical, actual yield and effective panicle number of rice, but they were similar in N1 and N2. Compared with the control group N3, the actual yield of early and late rice N1 and N2 increased by 53.21%-59.64% and 21.65%-32.68% respectively, indicated that the effect of nitrogen reduction and yield increase in early rice was obvious, and the poor effect of nitrogen reduction and yield increase in late rice was mainly because high nitrogen was not the nitrogen application level of conventional late rice.There was no significant difference between irrigation methods and yield and yield components. Under the cooperation of water and fertilizer,N2W2,N2W3 treatment could make early and late rice obtain higher leaf SPAD and LAI. Under the factors of dry matter accumulation, yield and yield components, the effect of N2W3 treatment was better for early rice, and N1W3 treatment was better for late rice. In conclusion, N2W3 treatment of early rice could not only met high yield, but also saved fertilizer and water;although N2W3 treatment of late rice performed better in SPAD and LAI, its dry matter accumulation and yield performance were lower than N1W3 treatment, so N1W3 treatment of late rice had obvious yield increasing effect. Therefore, from the perspective of economic and ecological benefits, under the alternative mode of dry and wet, the nitrogen application rate of early rice was 120 kg/ha and that of late rice was 150 kg/ha, which could give full play to the interaction effect of water and fertilizer. They had good yield increasing potential, which was more conducive to the growth and development of rice and increased yield.

Key words: Double-cropping hybrid rice, Water-fertilizer synergy, Agronomic characters, Yield