Potassium Source and Biofertilizer Influence K Release and Fruit Yield of Mango ( Mangifera indica L.): A Three-Year Field Study in Sandy Soils

Arid degraded soils have a coarse texture and poor organic matter content, which reduces the activity of microorganisms and soil enzymes, and thus the soil quality, plant yield and quality decrease. Potassium solubilizing bacteria (KSB) have been suggested to increase the activity of soil enzymes and increase the release of potassium from natural K-feldspar in the arid degraded soil, and thus potentially reduce the rates of the application of chemical fertilizers. Field studies were conducted for three successive growing seasons in an organic farming system to investigate the effects of K-feldspar and KSB ( Bacillus cereus ) on K release, soil fertility, and fruit yield of mango plants ( Mangifera indica L.). The maximum growth of mango plants was found in the treatments inoculated with KSB. KSB increased soil available N, P, K, and the activity of dehydrogenase and alkaline phosphatase enzymes by 10, 7, 18, 54, and 52%, respectively. KSB increased the fruit yield of mango by 23, 27, and 23% in the first, second, and third growing seasons, respectively. The partial (up to 50%) substitution of chemical K-fertilizer with K-feldspar gave fruit yield and quality very close to that fertilized with the full chemical K-fertilizer. The release rate of K (over all the treatments) varied between 0.18 and 0.64 mg kg −1 of soil per day. KSB significantly increased the K release rate. The application of chemical K-fertilizer gave the highest K release, while substitution with K-feldspar reduced the release of K. Natural K-feldspar contains 8.2% K but is poorly soluble when applied alone. KSB increased the soil quality parameters and enhanced the growth and quality of mango fruit. The fruit yield of mango, under KSB inoculation and fertilization with different K sources, ranged between 9.14 to 17.14 t ha −1 . The replacement of 50% of chemical K-fertilizer with natural K-feldspar caused a decrease in the fruit yield by 17, 8, and 2.7% in the first, second, and third years, respectively. The substitution of chemical K-fertilizer with K-feldspar up to 50% with KSB is a good strategy to reduce the excessive use of chemical K-fertilizer. B. cereus and natural K-feldspar have the potential to improve soil health and mango plant productivity in low fertile arid soils.