Studies On Mechanized Cultivation Technology For Rice Harvested Twice A Year

Rice （Oryza sativa L.） harvested twice a year is also called rice rationing, which possesses great potentials in rice growing region as the production of a second rice crop from the stubble left behind after the first seasonal rice harvest. Ratooning can largely improve resources use efficiency by fully using natural resources like light, temperature, land, and water and reduce the inputs by saving seeds, labor force, and pesticide. Additionally, ratooning rice planting is of great potential in southern China for its low production cost, short growth period and good rice quality. However, traditional cultivation technologies are hardly suitable to the scale and mechanized ratoon rice production. Therefore, the field experiment was carried out to explore mechanized cultivation technologies for ratooning rice in the region along the Yangtze River based on rice varieties, cutting height and nitrogen management. The main results as follows.1. The studies clarified the general principles of ratoon rice varieties screening, and selected two rice varieties adapted to the region along the Yangtze River in Anhui Province. There were significant yield differences between the main and ratoon crops, and no significant correlations between them. Zhunliangyou608 was the prior ratoon rice variety with the ratoon yield of 5.27 t.hm^-2 and total grain yield （main crop plus ratoon） of 13.59 t.hm^-2 in this region. Fengliangyouxiangl was second with total grain yield （main crop plus ratoon） of 11.86 t.hm^-2. Zhunliangyou608 had the stronger ratoon ability causing the significant increased effective panicles and spikelets per panicle, and finally realizing the high yield in second crops. Given the temperature resource, light resource, production system and requires of rice safe development, this study revealed that the suitable ratoon rice varieties should have the properties of a adaptive, one high, one strong and three resistances. Zhunliangyou608 and fengliangyouxiangl were recommended as candidate varieties for higher grain yield in rice production.2. The study revealed the appropriate stubble height for mechanized cultivation in the main crop. Ratoon rice showed increased leaf area index, dry matter accumulation after booting stage and increased grain yield with the increase of stubble height. The analysis of yield components indicated that the raised effective panicles as well seed setting were responsible for ratoon yield increase under high stubble height. The optimal cutting height for Zhunliangyou608 is 40 cm in the main crops, which could reconcile rice safe production and grain yield increase.3. The study ascertained the nitrogen management for ratooning rice. Nitrogen fertilizer facilitated bud germination can significant advance rice grain yield. The application of nitrogen fertilizer facilitated bud germination and effectively decreased the bud mortality. Early fertilized or increased the nitrogen dose can significant increase the effective panicles and hence the grain yield. The proper nitrogen fertilizer facilitated bud germination was applicated 138.0 kg·hm^-2 at 20^-25 days after heading in the main crop under the mechanized cultivation condition,.4. The mechanized cultivation technologies for rice harvested twice a year showed good demonstration effects in the region along the Yangtze River. The demonstration fields planted Zhunliangyou608 produced the yield of 8.18 t·hm^-2in the main crop,5.55 t·hm^-2 in second crops, and total grain yield （main crop plus ratoon） of 13.73 t.hm^-2 using the technology of mechanized transplanted in the main crop +mechanized harvested in main and second crops. The mode of mechanized cultivation technologies of rice harvested twice a year showed the higher increase in revenues than the mode of "medium indica hybrid rice+wheat" and "double cropping rice".