Potassium Management in Custard Apple Agri-Horticulture: Enhancing Potassium Availability and Plant Uptake Through Quantity/Intensity Relationships

Abstract

ABSTRACT The study examines the impact of potassium management on the sustainability of custard apple agri-horticulture, focusing on the Quantity/Intensity relationship which is crucial for soil fertility and potassium availability to plants. A long-term field experiment with a custard apple-based agri system was started in the wet season of 2009 with seven different intercrops and one custard apple mono-crop at the University of Agricultural Sciences, Bangalore, within the Eastern Dry Zone of Karnataka. The soil, classified as Typic Kandiustalf, was analyzed for its physical and chemical properties, revealing a sandy clay loam texture with low organic carbon and moderate levels of available potassium. The study found that custard apple yields were highest when grown alone, particularly with finger millet and chili intercrops, and lowest with foxtail millet. Soil analysis showed minor differences in particle size and bulk density, with variations linked to crop type and depth. Chemical analysis indicated that custard apple affects cation exchange capacity, especially when combined with field bean, enhancing soil nutrients. Surface soils had more water-soluble and exchangeable potassium with cowpea, and more non-exchangeable potassium with finger millet. Potassium decreased with depth, except for lattice and total potassium. The results Q/I relationship of K showed that CRe 0K values ranged from 16 to 32 × 10−3 (mol litre−1)1/2 whereas, PBCK ranged from 10.4 to 14.1 (cmol kg−1)/(mol L−1)1/2. Studies indicate that for custard apple farms, especially in rainfed zones, legume intercropping with frequent potassium application is advantageous to maintain the sustainable long-term yield of custard apple.