Impact of nitrogen sources and rates under irrigated and rainfed systems on photosynthetic pigments, nitrogen and antioxidant metabolism and cotton yield

Abstract Background Irrigation has been a strategy used to reduce losses due to drought, which combined with a good supply of nitrogen (N), can improve the protective system of cotton plants. The objective of this study was to investigate the effects of irrigated and rainfed cotton cultivation using different rates and sources of N. Cotton cultivation was carried out in Selvíria-MS field in the 2017/2018 harvest. The experiment was conducted in randomized blocks, which were designed in a 4 × 2 × 2 factorial scheme. The factors were composed of 0, 40, 80, and 150 kg·hm −2 level of N, using two sources of N under rainfed and irrigated systems. Results The provision of irrigation provided an increase in the levels of chlorophylls (Chl) a, Chl b, total Chl, carotenoids, pheophytin, leaf chlorophyll index (LCI), N content, nitrate (NO 3 − ), sucrose (SUC), the number of vegetative and reproductive branches, boll mass, and seed cotton productivity. There was no effect of N sources on any of the characteristics evaluated. Application of 150 kg·hm −2 level of N increased in 11%, 59%, 22%, 15%, 15% and 17% in LCI, NO 3 − , N, total amino acids (TA), SUC, and proline concentration in leaves, compared with 0 kg·hm −2 of N, respectively. Application of 150 kg·hm −2 level of N improved the leaf catalase activity (CAT) under the irrigation system; however, in a rainfed system, the highest CAT was observed at rates of 0 and 150 kg·hm −2 level of N. Irrigation increased in 55%, 117%, 68%, 46%, 8%, 36%, 24%, 118%, 48%, 10%, 11% and 72% in Chl a, Chl b, total Chl, CAR, LCI, pheophytins (Pheo), SUC, NO 3 − , the number of vegetative branches, the number of reproductive branches, mass of 20 bolls and seed cotton yield compared with rainfed system, respectively, however, the antioxidant system and the ammonium content of plants was stimulated by rainfed cultivation. Conclusions Antioxidant responses increased during droughts in cotton farming, which may be connected to oxidative stress-related losses. Better N metabolism, photosynthetic pigments, and manufacturing components were all made possible by irrigated cultivation. The delivery of 150 kg·hm −2 of N in topdressing in cotton agriculture promoted the N metabolism, sucrose, total amino acids, and the plant’s defense mechanism against oxidative stress.