Effect of repeated manure application on potassium, calcium and magnesium in soil and cereal crops in Saskatchewan

Increasing use of animal manures in Saskatchewan requires information on the effect of manure addition on the availability of soil K, Ca and Mg and their concentrations in plant tissue. To address these issues, we examined the effects of repeated application of liquid swine and solid cattle manure at low and high rates on extractable K, Ca and Mg in soils from three different long-term field trials in Saskatchewan, and on plant K, Ca and Mg concentrations in cereal straw grown on the soils. After 5 to 7 yr of manure application, extractable potassium in the soils was significantly increased, while extractable Ca and Mg tended to remain similar, or was decreased with swine manure addition. In the cereal straw, concentrations of K, Ca, and Mg were all increased by repeated swine manure application, such that there was no significant increase in the K/(Ca + Mg) ratio. However, the K/(Ca + Mg) ratio in the cereal straw grown on soil amended with the high rate of cattle manure was increased. These findings suggest that increased risk of tetany potential from manure application would mainly be associated with excessive application rates of cattle manure in these soils, but should be monitored in feeds grown on all manured soils.Key words:Soil extractable K, Ca, Mg and Na; cereal K, Ca and Mg concentrations, K/(Ca + Mg) ratio, tetany potential, urea, swine manure, cattle manure