Calcium, Magnesium, Sodium, and Potassium Release during Decomposition of Some Organic Residues

The use of organic residues might be appropriate in maintaining long-term nutrient requirements of crops. We investigated under laboratory conditions the dynamics of calcium (Ca2+), magnesium (Mg2+), sodium (Na+), and potassium (K+) release during decomposition of eight plant residues and two manures over 12 weeks of incubation at 25 ○C. During the processes of decomposition, these nutrients were extracted by 0.1 M sulfuric acid (H2SO4). The release rate of nutrients for residues was best estimated by the exponential model. There were differences in the rates at which release took place between residues and nutrients. In general, release patterns of nutrients with time for all residues were similar in shape, and two regions could be distinguished: a first one during the first 4 weeks of incubation, corresponding to faster release of nutrients, and a second for longer incubation times (weeks 5–12), when the release of nutrients was slower. A 71% loss of K+ was found after 1 week for vegetable waste and only 43% loss of Na+ for rape. Generally, based on release rate (% week–1), nutrient release from residues was in the order K+ (–0.363) > Na+ (–0.344) > Mg2+ (–0.327) > Ca2+ (–0.280). The release rate of nutrients was significantly correlated with their residue content. Our results suggest that the use of organic residues as a source for short- and long-term nutrients supply for crops should be encouraged. The quick release of K+ and Na+ may pose a high risk of K+ and Na+ losses in sandy soils with low cation exchange capacity.