The effects of liming on the availability of soil potassium, phosphorus, and sulfur

This discussion has dealt with the important work touching the effects of liming on the availability of soil potassium, phosphate, and sulfur. The more recent research, embodying laboratory extractions with weak solvents, pot studies using a variety of plants as indicators of the concentration of the soil solution in potassium and the analyses of their ash, lysimeter experiments from which the outgo of potassium has been measured, and field tests, have failed to show that basic compounds of calcium and magnesium increase, by chemical action, to any practical extent, the availability of the soil store of native potassium. More research needs to be carried out before we can say that additions of lime will reduced the necessity of applying soluble phosphates to the soil. As measured by yields, phosphates of iron and aluminum seem to be as available as calcium phosphates. It is very probably true that fixation of phosphatic fertilizers by colloidal absorption induced by iron and aluminum oxids is responsible for the failure of some crops to respond to phosphorus additions. Additions of lime on such soils undoubtedly flocculate some of these colloids, which gives the soil a better physical condition for plant growth. Additions of lime, before or after applications of soluble phosphates, have greatly increased the efficiency of the phosphatic fertilizer. When insoluble calcium phosphate has been applied, it seems that applications of lime have reduced the effectiveness of the phosphate in a majority of cases. The scant data of lysimeter experiments only, which deal with the question of sulfate availability or conservation, seem to show that liming, with small amounts of CaO, both small and large amounts of MgO, MgCO3, limestone, dolomite, and magnesite, increases the solubility of native soil sulfate. Heavy applications of CaO, for a few years at least, apparently reduce this loss of sulfur from the soil.