Effects of land use changes on kinetics of potassium release in sweetpotato garden soils of the highlands, Papua New Guinea

Abstract

Abstract. The present study attempts to employ K release parameters to identify soil quality degradation due to changed land use pattern in sweetpotato (Ipomoea batatas (L.) Lam) gardens of Highlands of Papua New Guinea. Soils with widely differing exchangeable and non-exchangeable K contents were successively extracted 569 h in 0.01 M CaCl2 and K release data was fitted to four mathematical models: first order, power, parabolic diffusion and Elovich equations. Results showed two distinct parts in the K release curves and 58–80% of total K were released to solution phase within 76 h (first 5 extractions) with 20–42% K released in the later parts (after 76 h). Soils from older gardens which were subjected to intensive and prolonged land use showed significantly (P < 0.05) lower cumulative K release potential than the gardens which are recently brought to cultivation (new gardens). Among four equations, first order and power equations best described the K release pattern and the constant b, an index of K+ release rates, ranged from 0.005–0.008 mg kg−1h−1 in first order model, and was between 0.14 and 0.83 mg kg−1h−1 in power model for the soils. In the non-volcanic soils, model constant b values were significantly (P < 0.05) higher than the volcanic soils thus indicative of vulnerability of volcanic soils to K deficiency. The food garden soils need management interventions either through improved fallow management or through mineral fertilizers plus animal manures to sustain productivity.