Influence of application of sewage sludges, and sludge and manure compostson plant Ca and Mg concentration and soil extractability in field experiments

Application of organic waste influences crop uptake of Ca and Mg and soil e xtractability, depending on the nature of the crop and the waste. Four orga nic wastes: (i) digested sewage sludge (DSS), (ii) irradiated sludge (DISS) , (iii) composted sludge (DICSS), and (iv) composted livestock manure (CLM) were applied for two years at rates of 10, 20, 30, and 40 Mg solid ha(-1) year(-1). Fertilizers N and K were applied to the control treatment (CT), a s well as to the waste treatments to supplement crop growth across all trea tments, so that these nutrients were not treatment variables. Calcium and M g concentrations in the tissue of lettuce, bean pods and petunias in 1990 a nd two cuts of lettuce in 1991, and the CH3COONH4-extractable soil Ca and M g were determined. Concentration of Ca and Mg in bean pods did not change t o the waste application. Calcium concentration in bean pods was less than h alf of that in other crops. Magnesium concentration in bean pods and petuni as was same, but was much lower than in lettuce. Application of DSS, in gen eral, increased Ca concentration in the crops more than did other wastes. T he extractable soil Ca was positively correlated with Ca applied with DISS (r=0.453, P < 0.05). Although only a limited amount of Ca was supplied with CLM at the rate of 10 Mg solid ha(-1) (40 kg Ca ha(-1)), Ca concentration in petunias increased significantly, then, decreased with increased Ca appl ication (r=0.453, P < 0.05). A similar pattern with CLM was found in the ex tractable soil Ca. The waste application from all the sources had no influe nce on crop Mg concentration in 1990, possibly due to low Mg concentration in the wastes. While continuously applied DSS and DISS in 1991 linearly inc reased Mg concentration in both cuts of lettuce (r=0.867, P < 0.01; r=0.670 , P < 0.01 and r=0.671, P < 0.01; r=0.665, P < 0.01 for first cut and secon d cut of lettuce with DSS and DISS application respectively), application o f CLM decreased Mg concentration in first cut lettuce. The patterns of extr actable soil Mg were opposite to crop Mg concentration, as the extractable soil Mg linearly increased with CLM, and decreased with the high rate of DS S application. The ability of wastes to supply N was an important factor in fluencing crop Sigma cations (K, Ca and Mg) uptake.