Comparison of Potassium Release of Organic Residues in Five Calcareous Soils of Western Iran in Laboratory Incubation Test.

Nutrient cycling is an important part of integrated nutrient management. The effects of crop (potato, sunflower, rape) residues, weed residues, fruit waste, vegetables waste, tree leaves, sheep manure, and poultry manure on K release in five calcareous soils was investigated. The soils and plant residues were incubated for 4 weeks before initiating the kinetics study. In residue amended soils, the percentage of K released over 10 successive extractions with 0.01 M CaCl2 ranged from 28% of potato residues (average of five soils) and tree leaves to 75.8% of sheep manure. The kinetics of K release from amended soils and plant residues was analyzed by fitting the experimental data into four kinetic models (parabolic diffusion, power function, Elovich, and first order). The constant rate (mg kg-1 min-1) of K for amended soils was defined as the release rate (average of five soils) and decreased in the following order: vegetables waste (168.2) > sunflower (139.3) > poultry manure (137.9) > potato (146.9) > rape (122.3) > sheep manure (101) fruit waste (103.3) > tree leaves (78.3) > weeds residues (74.6). The release of K consisted of two phases. Phase 1 indicates the high rate of K release which can be considered to supply K to crop for short period. On the other hand, phase 2 indicates the slow release of K that will supply K to crop for longer period. The present study demonstrated that organic residues improved soil K fertility of calcareous soils by increasing NH4OAc-extractable K and release rate and could be an alternative indigenous source of K. [ABSTRACT FROM AUTHOR]