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

Abstract

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.

Keywords:

• calcareous soils
• exchangeable K
• K release
• kinetics
• plant residues

Acknowledgments

The author is grateful to Prof. Toth for critical review and perceptive comments on the manuscript. Two anonymous reviewers also made valuable comments on the manuscript. The author gratefully expresses his gratitude for their thoughtful and thorough reviews.

Notes

^a EC = Electrical conductivity; CCE = CaCO₃ equivalent (calcium carbonate in the soil based on the equivalent of pure calcium carbonate); CEC = cation exchange capacity; H₂O-K = extractable K with distilled water; NH₄OAc-K = extractable K with ammonium accetate; OM = organic matter.

^b I: Illite; S: Smectite; Ch: Chlorite; V: Vermiculite; K: Kaolinite.

*Not determined.

†Ash basis.

‡Dry basis according to Rowell (1994).

†Rowell (1994).

Values followed by the same lowercase and uppercase letter within a column and row, respectively are not significantly different at probability of α = 0.05 level, according to Duncan test.

†Calculated as: Cumulative K⁺ released from amended soil- cumulative K⁺ released from control soil/the amount of K⁺ added by amendement (the amount of K in organic residues determinied by nitric acid digestion).

Values followed by same lowercase and uppercase letter within a column and row, respectively are not significantly different at probability of α = 0.05 level, according to Duncan test.

Phase 1 (15–45 min) and phase 2 (45–150 min).

Elovich equation q_t = a + blnt, where q_t is the amount of released K, t, the time of release, a and b are constants.

Values followed by same letter within a row are not significantly different at probability of α = 0.05 level, according to Duncan test.

Phase 1 (15–45 min) and Phase 2 (45–150 min).

Elovich equation q_t = a +blnt, where q_t is the amount of released K, t, the time of release, a and b are constants.

Values followed by same letter for the same organic residue are not significantly different at probability of α = 0.05 level, according to Duncan test.