Effects of nitrogen management on rice growth and grain yield under conservation tillage in rice-wheat cropping system

In rice-wheat cropping system, conservation tillage technology is widely used in wheat cultivation. Because seedling standing and high yield cultivation technology under the conservation tillage condition is not perfect, rotary tillage with no straw returning is also playing a dominant role in rice cultivation. From 2006 to 2008, the effects of nitrogen management on rice growth and grain yield under the conservation tillages were studied in Guanghan, Sichuan province. The results may be helpful to promote conservation tillage applying in rice cultivation. There were three wheat straw application rates (0, 6000 and 12000 kg/ha), three nitrogen fertilizer rates (N 0, 150 and 210 kg/ha) and different ratios of basic, tillering and spike fertilizer (6∶2∶2, 6∶3∶1, 8∶2) in the experiment. Wheat straw was returned with mulching treatment and rice seedlings were transplanted with digging-hole method. The results showed that the nitrogen fertilization is an important limiting factor for rice growth and yield improving under the conservation tillage condition. Compared with the 150 kg/ha nitrogen application during rice growth, the tillering ability, amount of dry matter accumulation, individual and population qualities at the flowering stage, and dry matter exported from stem and sheath and photosynthate accumulation after flowering are all increased under the 210 kg/ha nitrogen application and the yield are increased by 7.3%. Compared with the rotary tillage, the zero tillage has little effects on dynamics of stems and tillers, dry matter accumulation and grain yield whether wheat straw is returned under the 150 kg/ha nitrogen and application ratio of 6∶2∶2. However, the proportion of photosynthate from flowering to yielding is increased. Under the 210 kg/ha nitrogen and application ratio of 6∶3∶1, the tillering ability is enhanced, the individual and population qualities at the flowering stage and the panicles and filled grains per panicle are increased, and grain yield is increased by 4.1% when the amounts of wheat straw are applied from 6000 kg/ha to 12000 kg/ha. Increasing nitrogen application before transplanting and decreasing application at the panicle initiation stage can induce panicles, number of filled grains and yield. These results suggest that sufficient application of nitrogen is an important practice for high yielding of rice under the conservation tillage condition, and increasing wheat straw returning and nitrogen supplement at the middle and later growth stages has promoting effect on high-stable yield.