Effects of nitrogen reduction and water saving on the photosynthetic characteristics and yield of spring wheat in the Yellow River Irrigation Areas of Ningxia

Abstract: Excessive input of nitrogen fertilizer and low water use efficiency have posed a great threat to the spring wheat production in Yellow River Irrigation District of Ningxia Hui Autonomous Region, Western China. Therefore, this study aims to explore the effects of water-saving irrigation on the population dynamics, photosynthetic characteristics, and the yield of spring wheat under the background of nitrogen reduction. Taking the Ningchun No. 4 as the test material, a systematic field test was carried out at three nitrogen application levels: conventional nitrogen application (270 kg/hm2, NC), reduced nitrogen fertilizer 25% (202.5 kg/hm2, NJ), and no nitrogen fertilizer (0 kg/hm2, N0). Three irrigation scenarios were also set with the water quotas: conventional irrigation (400 mm, WC), water saving 20% (320 mm, W1), and water saving 40% (240 mm, W2). The results showed that: 1) There were no significant differences in the total number of stems in different irrigation treatment groups at the same nitrogen fertilizer level. Nevertheless, an outstanding increase was found in the total number of stems in the population with the conventional nitrogen application and nitrogen reduction level under the same irrigation quotas, compared with the non-nitrogen treatment. The nitrogen reduction and water-saving treatment also maintained a far higher total number of group stems, thereby improving the incidence of tillers. 2) There was no outstanding effect of 25% less nitrogen on the growth and development of spring wheat, compared with the conventional nitrogen application. More importantly, the 20% saving water greatly contributed to the plant height and leaf area of spring wheat for the higher accumulation of dry matter. 3) The 20% reduced nitrogen and saving water were also beneficial for the soil plant analysis development (SPAD) value and photosynthetic characteristics of the leaves, particularly significantly higher than that in the water saving by 40%. There was no significant difference between the nitrogen reduction level and the conventional nitrogen application in the SPAD value and photosynthetic index of spring wheat leaves. 4) The maximum number of grains per ear (42.87 grains) and 1 000-grain mass (54.28 g) were achieved by the saving 20% of water at the nitrogen reduction level among all the water and nitrogen treatments. The highest yield of spring wheat also reached 8 092.52 kg/hm2. The yield was not significantly decreased during the water saving of 20%, respectively, compared with the conventional nitrogen application and conventional irrigation treatment. Consequently, the 25% reduced nitrogen and 20% saving water can be expected to obtain a higher yield during spring wheat production with fewer nitrogen resources in the Ningxia Yellow River irrigation area. Therefore, it is suggested to be an effective local nitrogen irrigation scheme for the higher yield of spring wheat production.