Effects of water and nitrogen supply on parameters of root and leaf senescence in cotton plants grown under root restriction and with under-mulch drip irrigation

Abstract

Aim Our objective was to evaluate the influence of the water and nitrogen treatments on parameters of root and leaf senescence in cotton plants grown under root restriction and with under-mulch drip irrigation. Methods Our experimental materials were upland cotton cultivars ‘Xinluzao 13’ and ‘Xinluzao 33’, which are the main cultivars grown in the study region of northern Xinjiang, northwestern China. Treatments consisted of root restriction (RR), unrestricted root system (CK, control) and four levels of water and nitrogen supply: water and nitrogen deficiency (W0N0), water deficiency (W0N1), nitrogen deficiency (W1N0) and moderate supply of water and nitrogen (W1N1). The treatments were applied in a split-split plot design. Cotton plants were cultivated in soil columns to control the vertical depth of root growth and to regulate application of water and nitrogen. We measured the activity of antioxidant enzymes in the root and leaf and the accumulation and distribution of biomass at the yield-determining stages (from flowering to the full boll opening stage). Important findings The root biomass, activity of antioxidant enzymes (superoxide dismutase, guaiacol peroxidase and catalase) in the root and leaf, total plant biomass and the root/shoot ratio under root restriction decreased compared with the control. In contrast, aboveground biomass and cotton yield under root restriction were considerably higher than with the control. The supply of water and nitrogen effectively regulated root and leaf growth. With regard to their effects on antioxidant enzyme activity in the root and leaf, SPAD chlorophyll content, aboveground biomass and cotton yield, the water and nitrogen treatments were ranked as W1N1 W0N1 W1N0 W0N0 . In contrast and with regard to the shoot/root ratio and root biomass, the treatments were ranked as W0N0 W1N0 W0N1 W1N1 . Consequently, interaction between root restriction and the applied water and nitrogen regime had a marked effect on cotton growth and yield. Root restriction in conjunction with a moderate supply of water and nitrogen was the optimal treatment for aboveground biomass and cotton yield, whereas the root/shoot ratio was lowest in this treatment.