Effect of exchangeable calcium and magnesium as essential for soil chemistry and plant nutrition in organic manures- treated soils for sustainable agriculture.

Calcium and magnesium are important secondary nutrients that contribute to soil fertility, nutrient balance, and sustainable crop production. This study evaluated the mineralization of soil exchangeable Ca2+ and Mg2+. The study was conducted at the Teaching and Research Farm of the Federal University of Agriculture, Abeokuta. The experiment was a randomized complete block design with three replications. Cured cattle, goat and poultry manures were applied at 5, 10, 20, 40, 60, 80, 120 and 150 t ha-1 once at first cycle and N15P15K15 at 0.4 t ha-1 per cycle. At two weeks intervals, soil samples were collected and analyzed for exchangeable calcium and magnesium. Pretreatment soil and manures were analyzed for Electrical Conductivity (EC), pH, ammonium-nitrogen, nitrate-nitrogen, total phosphorus, potassium, sodium, calcium and magnesium, using standard procedures. Across cycles, soil Ca2+ and Mg2+ values were not increase consistently according to increase in manures rates. High Mg2+ contents were observed between 8 – 10 WAI for cattle and poultry manure treatments while goat manure treatment was between 10 - 14 WAI during the experiment at first, second and third cycles of planting, respectively. Addition of cattle, goat and poultry manures at 6 WAP improved the soil Ca2+ and Mg2+ with highest values during first and second cycles and 4 WAP during third cycle which could be due to solubilization. The lowest values of Ca2+ and Mg2+ during third cycle could suggest uptake by plant and leaching.