Optimum combining rate of N and P fertilizer with 6-BA for highest photosynthetic efficiency and yield in foxtail millet

【Objectives】 Ninety percent of dry matter in millet is from photosynthesis. So it is important to maintain high and durable photosynthetic efficiency of the upper blades for the formation of high yield. The study of the appropriate application rate of N, P and plant growth stimulator for the highest photosynthetic efficiency in foxtail millet will provide a basis for rational fertilization in millet production. 【Methods】 Millet cultivar Zhangzagu 5 was used as test materials in a field experiment, two general rotating combination design was used for the experiment with 3 replications. Five N levels of 22, 69, 138, 207, 254 kg/hm2, and five P2O5 levels of 11, 36, 72, 108, 133 kg/hm2 were basal applied, and cytokinin 6-BA 0.5% (v/v) was foliar sprayed since the start of flowering period and the spray was conducted at 16:00pm in intervals of 4 days. The chlorophyll content, net photosynthetic rate, leaf area index of the flag leaves and the yield were measrued. 【Results】The single level of phosphate and cytokin 6-BA all have significant effects on leaf area index, net photosynthetic rate, chlorophyll contents, and yield of millet, and the four indices have a trend from rising to declining with phosphate and cytokin 6-BA all increasing. The nitrogen level has great effect on net photosynthetic rate, leaf area index and yield, and the three indices are increased at first and then decreased with the increase of nitrogen level. The levels of nitrogen, phosphate and cytokin 6-BA all showed significant effects on yield, and the yield was mainly affected by phosphate level, and less affected by nitrogen and cytokin 6-BA.The interactions between nitrogen and cytokin 6-BA level show significant effects on leaf area index, net photosynthetic rate, chlorophyll contents, and yield of millet. This combination of nitrogen and cytokin 6-BA could improve photosynthesis and yield, and exhibit great potentials for practical application. 【Conclusions】The appropriate nitrogen and phosphate levels combined with foliar spray of 6-BA show significant increase effect on leaf area index, photosynthetic efficiency and yield of millet, over the levels will lead to significant decrease effect. The regression relationship between the levels of nitrogen, phosphate, and cytokin 6-BA and the yield of Zhangzagu 5 can be used for production forecasts. The recommended level for Zhangzagu 5 is N 175 kg/hm2, P2O5 94.3 kg/hm2, cytokin 6-BA 11.8 mg/L under the experimental conditions with the expected yield of 6629 kg/hm2.