Regulation of density and nitrogen fertilizer on physiological characteristics, yield, and quality of silage maize using a ridge-furrow rainfall harvesting system in Longdong Region, China

To determine the suitable planting density and nitrogen level of silage maize under furrow and ridge rainwater harvesting in the Longdong area of China, field experiments were conducted at the Huan County Grassland Agricultural Experimental Station of Lanzhou University. Four planting densities of 6 × 10⁴ (D₁), 7.5 × 10⁴ (D₂), 9 × 10⁴ (D₃), and 10.5 × 10⁴ (D₄) plant·hm⁻², and four nitrogen treatments of 0 (N₀), 120 (N₁), 240 (N₂), and 360 (N₃) kg·hm⁻² were established to investigate the effects of planting density and nitrogen application on the physiological characteristics, yield, and quality of silage maize. Under D₂, D₃, and D₄ densities in 2019 and four densities in 2020, the net photosynthetic rate (P_n) of the N₂ and N₃ treatments was significantly higher than that of the N₀ treatment (P < 0.05). Under the same fertilization conditions, there were no significant differences in P_n among density treatments at the 6-leaf stage in two years (P > 0.05). However, P_n decreased with increasing density at the silking, grain filling, and wax ripening stages. The content of malondialdehyde (MDA) in the N₂ and N₃ treatments was significantly lower than that in N₀ (P < 0.05). In contrast, the content of soluble protein and the activities of ribose diphosphate (RuBP) and phosphoenolpyruvate (PEP) carboxylase were significantly higher than those in N₀ (P < 0.05). The activities of RuBP and PEP carboxylase in the N₂ and N₃ treatments were significantly higher than those in the N0 treatment (P < 0.05). In two years, D₃N₂ treatment resulted in higher hay, crude protein, and starch yields. At the same density, the crude protein content and relative feed value (RFV) of the N₂ and N₃ treatments were significantly higher than those of the N₀ treatment (P < 0.05). With an increase in density, the crude protein, crude fat, and RFV contents decreased, while the neutral detergent fiber and acid detergent fiber contents increased. The collective findings demonstrate that the D₃N₂ treatment is a suitable cultivation model for silage maize under furrow and ridge rainwater harvesting in the Longdong area.