Effect of potassium humate on the yield and N, P, K content in soil and leaves of cv. Ligol apple in Central Chernozem region

Abstract

Nutrient management of high-density apple orchards remains to be a serious problem in central Russia. Enhancing apple productivity by applying higher fertilizer rates leads to an increased environmental burden and undesired consequences. Although the transition to organic farming may solve many horticultural problems, conventional methods still produce higher crop yields. One of the most pressing issues consists in reducing mineral fertilizer use by applying more organic substances. This approach allows soil fertility to be preserved while maintaining high levels of plantation productivity. In the present research, particular attention was paid to potassium nutrition of apple trees. During 2020 and 2021, we studied the effect of potassium fertilizers in various standard amounts and silicon-modified potassium humate on the state of apple trees cv. Ligol grafted on 62-396 rootstock in the experimental orchard of I.V. Michurin Federal Research Center. The orchard was planted in 2018 according to a 1.2×4.5 m pattern (1852 trees per hectare). The experimental design was as follows: control (irrigation); full standard amount of N20P6K28 fertilizers; ¾ standard amount of N15P4K21 mineral fertilizers + ½ standard amount of potassium humate, ½ standard amount of N10P3K14 mineral fertilizers + ½ standard amount of potassium humate; full standard potassium humate amount of 10 L/ha. In 2020, the introduction of potassium humate provided the maximum yield, although without significant differences compared to the use of mineral fertilizers. In 2021, the yield was also at the level achieved with mineral fertilizers. Potassium humate provided a higher nitrogen content in the leaves as compared to mineral fertilizers, largely due to a significant increase in the availability of nitrogen and potassium in the soil. The content of available phosphorus was not significantly affected. This assumes that the effectiveness of humates depends on the soil type. The combined application of reduced standard amounts of mineral fertilizers and potassium humate contributed to maintenance of high yields under with a less dramatic increase in soil acidity.