Abstract:

The flowering and boll stages are the most critical periods for the formation of cotton. To explore the compensation effect of nitrogen fertilizer backward shift on the yield of water-deficient cotton at the flowering and boll stages, Xinluzao No. 45 was used as the test material and a split-plot test design was adopted. The drip irrigation amount in two flowering and boll stages was determined as follows: a conventional irrigation amount of 2410 m³·hm^-2 (W1) was the control and the deficit irrigation amount was 1668 m³·hm^-2 (W2). N1 (flowering period fertilizer: boll period fertilizer 3:3), N2 (flowering period fertilizer: boll period fertilizer 2:4) and N3 (flowering period fertilizer: boll period fertilizer 4:2) was explored. Results showed that under the same nitrogen fertilizer conditions, the leaf area index (LAI) and net photosynthetic rate (Pn) of the water deficit were significantly lower than those of the normal irrigation treatment; was prolonged and the accumulation and proportion of dry matter in reproductive organs decreased significantly; the number and weight of bolls per plant decreased by an average of 11.7% and 45.6%, respectively, compared with normal irrigation; and the yield of seed cotton decreased by an average of 17.3%. The water consumption and partial productivity of nitrogen fertilizer decreased by 35.49% and 15.97% on average, respectively, and water use efficiency increased by an average of 16.77%. Compared with normal irrigation and under a water deficit condition at the flowering and boll stages, the LAI and Pn of cotton treated with nitrogen fertilizer (N2) increased compared with that of N1 and N3 and the expression was N2 > N1 > N3. The dry matter accumulation, Δt, and Vm performed best under fertilization, GT was the most coordinated, and the transfer rate from vegetative growth to reproductive growth of cotton was the highest at 68.25%. The number of bolls per plant and weight of single bolls increased by 10.40%, 16.02%, 8.41%, and 11.61%, respectively, and the yield of seed cotton increased by 7.32% and 13.88%, respectively. Water consumption, water use efficiency, and partial nitrogen fertilizer productivity were as follows: N2 > N1 > N3. In summary, a backward shift in nitrogen fertilizer can increase the LAI and Pn of cotton in the flowering stage, slow down the decline of LAI and Pn in the late boll stage, increase dry matter accumulation in the aerial part and increase the proportion of reproductive organs, and regulate the yield and its components to reduce the impact of water stress.

Key words: cotton, nitrogen fertilizer back, flowering and boll stage, water deficit, nitrogen fertilizer management