The reclamation of acidic colliery spoil. III. Problems associated with the use of high rates of limestone.
Growth of Trifolium repens in acidic colliery spoil (pH 2.5) was suppressed by >90% when agricultural ground calcitic limestone was applied at >5 t/ha, whereas Lolium perenne was unaffected at rates up to 100t/ha. The inhibitory effect of ground limestone on T. repens was reduced by high P fertilization and disappeared within 34 wk of treatment. There was some evidence that high liming caused imbalance in Ca:Mg ratio in freshly limed spoil, contributing to growth inhibition. Growth of L. perenne was improved and the inhibitory effect on T. repens was alleviated by substituting magnesian limestone (dolomite) for calcitic limestone. P adsorption of spoil was similar after low and very high limestone applications but increased by 100% after liming at 25 t/ha to pH 5.1. It is suggested that P adsorption at pH 5.1 is caused by freshly precipitated amorphous aluminium hydroxide. The practical implications of the results are discussed.