The combined effect of irrigation and potassium fertilization on the physiological characteristics and yield of peanut

This study clarified the combined effects of different levels of water and potassium supply on physiological characteristics and reproductive growth of peanut. To that end, a pot experiment was conducted to investigate the differences in leaf enzyme activities at late podding stage and reproductive growth. It was a random block design experiment with two factors and four levels for each factor — W₁: 35% field capacity; W₂: 50% field capacity; W₃: 65% field capacity ; W₄: 80% field capacity; K₀: 0 g(K₂O)·kg^-1(soil); K₁: 0.15 g(K₂O)·kg^-1(soil); K₂: 0.30 g(K₂O)·kg^-1(soil); K₃: 0.45 g(K₂O)·kg^-1(soil). The tested peanut cultivar was ‘Huayu 25’. The results showed that irrigation had an extremely significant (P < 0.01) effect on relative water content (RWC) and chlorophyll content of peanut leaves. Also leaf water had an obvious dilution effect on chlorophyll content. Thus, the RWC increased significantly (P < 0.01), while chlorophyll content decreased significantly (P < 0.01) with increasing irrigation amount. Moreover, interaction of water and potassium had an extremely positive effect on the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) (P < 0.05 or P < 0.01). The three enzymes had different responses to different adverse conditions. SOD activity increased obviously under deficient potassium (K₀) or high potassium (K₃) conditions. Also POD increased significantly (P < 0.01) under water stress (W1) or K₃, while CAT increased significantly (P < 0.05) in W₁ or K₀ conditions. With increasing soil water content, CAT activity decreased rapidly to match with the dynamics in chlorophyll content, which two processes had an extremely significant positive correlation (P < 0.01). These evidences indicated that CAT was a key element in reducing the degradation of chlorophyll and lengthening the functional period of peanut leaf at late podding stage. The effects of potassium fertilizer and irrigation on total flowering were significant or extremely significant. The application of potassium fertilizer significantly delayed the beginning of flowering, but reduced irrigation amount advanced termination of florescence. Under K₂ condition, fertile flower number and flower fertility rate of all the water treatments were relatively high. Under W₃ condition, potassium fertilizer had an enhancing-effect on single seed weight, which was also occurred under W₂ condition. The significant increase in single pod number and in dual kernel fruit rate enhanced the yield-increase effect of soil moisture. For all the treatments, W₃ and K₂ had the shortest florescence (25 days), the highest rate of fertile flowers (51%) and seed kernel yield in this experiment.