Effects of nitrogen fertilizer levels and application stages on nitrogen utilization of strip-relay-intercropping wheat in Sichuan Hilly Areas

【Objectives】Strip-relay-intercropping is a classic wheat production pattern in Sichuan, which mainly distributes in upland of hilly areas, with corn constituting as wheat/corn complex planting system. In this study, a two-year field experiment was carried out to study effects of nitrogen(N) fertilizer levels and application stage on N accumulation, distribution and transportation, N usage and its residual in soil, providing scientifical support for the wheat production in the tested area. 【Methods】Chuanmai 42, a major wheat cultivar in local production, was used as material, a two-year field experiment was carried out inRenshou county, Sichuan Province.Spilt-plot experiment was designed, the main-plot was N application rate in four levels (90, 135, 180 and 225 kg/ha), and the sub-plot was N distribution with the ratio of base fertilizer, seedling fertilizer, jointing fertilizer and booting fertilizer in four levels (10:0:0:0, 7:3:0:0, 7:0:3:0, 5:1:2:2), and no fertilizer (CK) as control. 【Results】1) The total N accumulation of aboveground plants at the maturity are increased significantly with the application of nitrogen fertilizer. The N accumulation amounts in vegetative organs at the flowering as well as in leaves and stems at the maturity are increased with the increase of N levels, and the contribution rate of translocated N to grain exhibits the same tendency. The N assimilation and the contribution rate to grain at the post-anthesis are increased first and then declined with the increase of N levels, peaking at the N rate of 135 kg/ha. Simultaneously, the N assimilation at the post-anthesis and the contribution rate to grain are improved effectively by the dressing ratio of 7:3(base fertilizer: jointing fertilizer). On other hand, the N application with dressing ratio of 5:1:2:2(base fertilizer: seedling fertilizer: jointing fertilizer: earing fertilizer) effectively promotes the translocation of storage nitrogen before the anthesis from vegetative organs to grain, increases the residual nitrogen in vegetative organs at the maturity, and decreases the allocation proportion of nitrogen in grain. 2) With the increase of nitrogen levels, the N use efficiency and N productivity of wheat are decreased, while the contents of total N, NO-3-N and NH+4-N in soil are increased.Total basal application or top dressing at the elongation stage significantly raise N residues in soil when N application rates are N 180-225 kg/ha, whereas the split dressing and higher dressing ratio could mediate this problem. 3) The relationship between the N application rate and grain yield can be illustrated by a quadratic fitting, i.e. per 100 kg grain needs 3.6 kg nitrogen in average. The highest grain yield of 4800 kg/ha (The following year, 4706 kg/ha) is obtained under this nitrogen strategy in which nitrogen level is 180 kg/ha with the dressing ratio of 7:3 (base fertilizer: jointing fertilizer), which could bring 25.6% additional yield compared with control. 【Conclusions】Comprehensively ansidering the grain yield, N use characteristics and N residues in soil, under the prerequisite of over 4650 kg/ha yield guaranteed, N application rate should be properly decreased and adopt backward and split application pattern. In our case, N application rate of 135-180 kg/ha, basal to devessing at the elongation stage of 7:3 is the recommended.