Nitrogen Modifies the Leaf Anatomy and the Antioxidant System of Cotton in Irrigated and Rainfed Cultivation

The nitrogen (N) used as a nutritional source for the irrigated and rainfed systems are factors that can influence the physiology, anatomy, and yield of cotton. The objective of this study was to investigate the influence of N rates and sources on cotton cultivation in irrigated and rainfed systems. The trial was conducted in the field in the 2017/2018 cropping season, in a 4 × 2x2 factorial scheme, the first factor was the rates of N 0, 40, 80, and 150 kg ha−1, the second factor the sources of N (Urea and Ammonium nitrate), and the third factor the irrigated and rainfed cropping systems. Significant effect (p ≤ 0.05) of the cultivation system was observed and the irrigated system provided an increase in plant height, number of branches, shoots dry mass, leaf area, boll mass, boll number, yield, net photosynthesis rate, stomatal conductance, transpiration, intracellular CO2, thickness of palisade and spongy parenchyma, number of stomata in abaxial leaf face, and total thickness of cotton leaf. However, in the rainfed system a significant increase (p ≤ 0.05) was observed in the higher activity of the superoxide dismutase enzyme, catalase, adaxial and abaxial epidermis thickness, intrinsic water use efficiency, and root dry mass. The N rates 40, 80, and 150 kg ha−1 significantly (p ≤ 0.05) increased plant height, catalase activity, leaf N, leaf proline, number of abaxial stomata, and adaxial epidermis compared to the control (0 kg ha−1). The use of urea as source of N gave significantly higher thickness of the adaxial and abaxial epidermis, whereas ammonium nitrate significantly increased the number of adaxial stomata and the thickness of the palisade parenchyma compared to the urea. The increase in N supply favored the activity of the antioxidant system, photosynthesis, leaf blade thickness, and protection against stress (proline). Irrigation benefited the physiological system, leaf anatomy, and productive components.