Wheat straw returned combined with nitrogen as base fertilizers and topdressing at tiller stage improving the tiller emergency, earbearing traits and yield for machine-transplanted super japonica rice

Abstract: The tiller emergency and ear bearing traits of super rice have important influence on actual yield. With the transfer of rural labor and the integration of farming machine and agronomy, rice planting mechanization has become a dominated developing direction and key technology for modern agriculture in China. Rice-wheat rotation is the main mode in farming system of China, every year large amount of straw is produced by wheat planting, and the returning of straw has become the most direct and sustainable technical method to the comprehensive utilization of straw. The application of nitrogen is an important measure in improving rice yield, however, the unreasonable application is unfavorable for the growth of rice and the utilization efficiency of nitrogen. At present, the research about the tiller emergency and ear bearing traits of machine-transplanted super rice under the growing condition of straw returning and nitrogen management is still scare. In order to analyze the effects of different amount of returned wheat straw treatments and different ratio of basic and tiller nitrogen on tiller emergency, ear bearing and yield composition of machine-transplanted super rice, the experiment took the super rice Nanjing 9108 as experimental materials, and designed 5 treatments with different ratios of basic and tiller nitrogen and 3 treatments with different wheat straw returned amounts. Under the condition that the total nitrogen application amount was 300 kg/hm2 and the panicle nitrogen was 120 kg/hm2, the ratios of basic and tiller nitrogen were 0:180, 45:135, 90:90, 135:45 and 180 :0 respectively (unit: kg/hm2), and the amounts of the returned straw were 0, 3 000 and 6 000 kg/hm2. The study was done in a field plot experiment to survey the tiller traits and the yield composition at mature stage of machine-planted super rice in 2013 and 2014. The result showed that the tiller starting position of the primary tiller emergency for main stems of non-straw returned machine-transplanted super rice was 3/0, the main tiller positions were 4/0, 5/0, 6/0 and 7/0, and the emergency rates were over 73.17%; the tiller starting position of the primary tiller emergency for main stems of straw returned machine-transplanted super rice was 4/0, and the main tiller positions were 5/0, 6/0 and 7/0, which indicated that the wheat straw returned treatment decreased the emergency rate of lower position tiller of machine-transplanted super rice. The tiller emergency rate of machine-transplanted rice was 100% when the tiller positions were 5/0 and 6/0 and wouldn't be influenced by the ratio of basic and tiller nitrogen. With the increasing application of basic nitrogen and the decreasing application of tiller nitrogen, the tiller emergency rate of other tiller positions decreased. Wheat straw returned treatments reduced the tiller ear bearing rate and therefore further reduced the effective panicle number at mature stage, but grain number, setting rate, thousand seed weight, panicle weight and actual yield increased. The increased ratio of basic nitrogen reduced the tiller ear bearing rate, but promoted the grain number per panicle and the panicle weight of single tiller. In the experiment, the highest yield was achieved when the ratio of basic and tiller nitrogen was 45 kg/hm2:135 kg/hm2. Contrasting the experiments in 2013 and 2014, both the effective accumulated temperature at rice tillering stage and the tiller emergency rate under the same treatments in 2013 were higher than those in 2014, and hence the final effective panicle number and the yield in 2013 were improved. The research revealed the law of tiller emergency and ear bearing traits and the reasonable nitrogen management of super japonica rice, and provided the technical base for the high-efficiency and high-yield cultivation of machine-transplanted super japonica rice planted in large area. In conclusion, the research results of the experiment are as follows: 1) Wheat straw returned treatment postpones one tiller position in tiller emergency stage for machine-transplanted super rice, and leads to the reduction of effective panicle number, but improves grain number per panicle, seeding rate, thousand seed weight and actual yield. 2) With the increasing application ratio of basic nitrogen, the effective panicle number decreases, and the super rice has the highest yield when the ratio of basic and tiller nitrogen is 45 kg/hm2:135 kg/hm2. 3) When the amount of the returned straw increases, the appropriate improvement of the ratio of basic and tiller nitrogen can improve the yield of super rice. 4) Under the temperature range appropriate for rice growth, the increase of air temperature or soil temperature can promote the tiller emergency of super rice and the tiller emergency rate has a significantly positive correlation to temperature, which can further improve the effective panicle number and the final yield.