Inhibition of Na⁺-containing foliar fertilizer on peanut growth under N deficiency stress and recovery effect by supplemental N spraying

ObjectivesSodium (Na⁺) is often contained as counterion in foliar fertilizers, so its effect on crop growth is least considered during fertilization. Na⁺plays both promotion and inhibition roles on crop growth, depending on the plant nutrition and physiology status. The inhibition role of Na⁺was studied on peanut exposure to Na⁺stress, and the recovery effect of supplemental spraying N to the inhibition was also investigated.

MethodsA pot experiment was conducted inside the growth chamber located in Shandong Peanut Research Institute. Three levels of Na⁺were designed in the foliar fertilizer:Na⁺0, 2.0 and 10.0 mg/pot, and recorded as T0, T1 and T2 in turn. The peanut photosynthesis, dry matter accumulation, root morphology, nutrient absorption were investigated in both N deficit stresses (T0, T1, T2) and later urea supplement (T0-N, T1-N, T2-N). The effect of Na absorption on the N, P and K absorption was analyzed.

Results1) Without N supplement, the net photosynthetic rates were significantly decreased from 11.4 CO₂ μM/(m²·s) to 6.7-7.5 CO₂ μM/(m²·s) in Na containing treatments, the dry weights of shoot and root were in order of T0 (6.4 and 2.4 g/pot) > T1 (5.7 and 1.9 g/pot) > T2 (5.3 and 1.5 g/pot). Total root length, surface area, and volume in T1 and T2 treatments were decreased by 7.8%-10.5% and 27.5%-31.8% compared with T0. 2) With later supplement of N, Na⁺inhibition in photosynthesis was recovered quickly. The shoot dry weights in T1-N and T2-N treatments were increased by 20.3%-25.8% compared with T0-N. The inhibition of Na⁺became promotion of N, P, K absorption. The shoot N, P, K absorptions in T1-N and T2-N treatments were respectively increased by 9.2%-19.2%, 20.0%-42.3%, 21.4%-24.0% compared with T0-N. The total dry weight of peanut and N, K absorptions were positively correlated with Na⁺(P < 0.05).

ConclusionsUnder N deficit, Na⁺shows inhibition effect on the growth and nutrient absorption of peanut and the effect will become exaggerated with the increased Na⁺contents in fertilizers.This inhibition will be remarkably correlated by later supplement of N, and the inhibition role will change to promotion role of Na⁺. Therefore, application of Na⁺containing fertilizer, especially those with high Na⁺concentration, should consider the N supply in order to relieve the possibly harmful effect of Na⁺.