effect of wheat, alfalfa, corn, soybean and cotton residues on soil potassium content and its absorption by wheat (triticum aestivum l.)

crop residues management is one of the most important factors to sustain agro-ecosystems. application of plant residues as organic fertilizers has functional role on the amount of soil elements, their availability for crops and finally yield obtained. in order to investigate the effect of different crop residues and their management on providing wheat potassium requirement, a four-replicated field experiment was carried out as a completely randomized block design on wheat (triticum aestivum l.). five plant residues with different c:n ratio (including cotton، soybean, alfalfa, wheat and corn) in companion with pure urea and control treatment (without residue or fertilizer) were incorporated as<5 mm particles seze. the rate of residues and required nitrogen to avoid immobilization were calculated by determination of c:n ratio and nitrogen factor to provide 90 kg n.ha-1. soil extractable potassium was evicted by ammonium acetate extraction procedure after 49, 83, 99, 127, 165 and 175 days from beginning of experiment. the results showed that the effect of different residues on potassium release was significant just in booting growth stage. the highest concentration of k in booting stage belonged to alfalfa, wheat and corn residues (with corresponding values of 1663, 1637.6 and 1592.3 kg.ha-1 soil respectively) while the lowest values belonged to cotton residue, urea and control (1472.6, 1425.4 and 1215 kg.ha-1 soil, respectively). assessing trend of potassium (k) uptake showed that the most k uptake in plants (36.62 g.kg-1) occurred during the first 83 days (stem elongation) and in residue alfalfa treatment that the most k release (2375.7 kg.ha-1) was also from those residues. therefore, it seems that crop residues could be considered as potential internal inputs for agro-ecosystems with different capabilities. generally, our results revealed that alfalfa residue is the best option to provide potassium for wheat plants and corn and wheat (with not-significant difference) were ordered after alfalfa.