The growth of grasses and legumes on a sequence of acid soils as affected by liming and phosphate fertiliser

The causes of differential growth of lucerne, lotus, ryegrass and brown top on a range of three acid soils were investigated by means of pot trials carried out in the glasshouse. Of the four species, lucerne was affected strongly by the factors of soil acidity particularly in Craigieburn and Katrine soils. The growth of this species was almost completely restricted on the untreated soils. In contrast, there seemed little problem with the growth of browntop even in the Katrine soil. In general, grasses yielded more dry matter than did legumes. The average yields of lucerne were the smallest on all soils. For all species, yields on Craigieburn soil were the lowest. Both grasses produced their highest dry matter in Katrine soil whereas the highest yield of lucerne was in Mesopotamia soil. All plant species responded strongly to P on all soils suggesting acute P deficiency. Responses of the legumes to P were more marked than those of the grasses. In Mesopotamia soil, liming strongly depressed dry matter yields of all species except lucerne where the effect of lime was not significant. There appeared no problem with acidity factors in this soil where plants could be grown without liming if P, N and other essential nutrients were not limiting. In Craigieburn soil lucerne and ryegrass responded strongly to lime whereas lotus showed no response. The net effect of lime on yields of browntop was negative. In Katrine soil liming strongly increased yields of all species except browntop where the effect was not significant. The strong positive effects of lime on dry matter and close relationships between yields and A1 and Mn contents of dry matter, and yields and exchangeable A1 and Mn in soil strongly suggest that the restriction of the growth of lucerne on Craigieburn and Katrine soils was due mainly to A1 and Mn toxicities and that the beneficial effects of lime was through reduction of the concentration of these elements. Similarly the growth of ryegrass was affected by A1 toxicity in these two soils. Aluminium toxicity might also be one of the factors responsible for the variation in growth of lotus in Katrine soil. On the other hand browntop stood out as an extremely tolerant species and was not affected by any of the toxicity factors even in this extremely acidic Katrine soil