Mechanism of suitable nitrogen and mepiquat chloride combination rate on increasing the yield of cotton in the cotton-growing region of Yellow River valley

Objectives The mechanism of suitable nitrogen fertilizer and mepiquat chloride (DPC) combination rate on increasing cotton yield was studied to provide supporting theories for the practical application of nitrogen and DPC in cotton.

Methods Cotton field experiments were carried out from 2015 to 2017 in the Yellow River beach area of Zhengzhou City. A split-plot design was employed in this work. The main plots were assigned to N fertilizer rates, namely no N application (N0), normal N application (N1) and excessive N application (N2), with rates of N 0, 225 and 450 kg/hm², respectively. And the subplots to DPC dosages, namely no DPC application (D0), normal DPC application (D1) and excessive DPC application (D2), with dosages of 0, 75 and 150 g/hm², respectively. The SPAD value of leaves, dry matter weight and N content of different organs, the number of “four peach” and yield of cotton were determined.

Results The lint yield of cotton under different N rates was N1>N2>N0. The seed cotton yield and lint yield demonstrated an order with different DPC dosages of D1>D2>D0. The interaction of N and DPC combination reached 0.05 significant level on lint percentage and seed cotton yield, and 0.01 significant level on lint yield. Compared with N1D1, the N0D0 combination displayed lower SPAD value and higher dry matter and N accumulation in the stems and branches, resulting in reduced yield. Under N0 condition, D1 was recorded significantly higher SPAD value, total boll number, boll weight, and higher yield compared with D0. Among all the combinations, N1D1 showed optimal effect due to the highest proportion of dry matter and N distribution in the buds and bolls, more pre-summer and summer bolls, more bolls setting on the 1^st−10^th fruit branches, and synchronous boll number, boll weight and lint percentage. The lint yield of N1D1 combination was 1949.52 kg/hm², which was 106.75% and 20.36% higher than N0D0 and N2D2, respectively. Compared with N1D1, the SPAD value of leaves became higher with the combination of N2D2 while more dry matter and N distributed to leaves at this time.

Conclusions N and DPC exhibit a significant interaction on lint percentage, seed cotton yield and lint yield. The combination of normal N application rate and DPC dosage benefits the allocation of dry matter and N accumulation in the buds and bolls, as well as the reasonable spatial and temporal distribution of boll-setting, resulting in higher yield. Excessive application of N rate requires high DPC dosage to offset the adverse impact on yield caused by over vegetative growth.