Some effects of lime and molybdenum on the growth of white clover in autea clay

Abstract

Abstract Results are reported of the effects of different rates of lime and molybdenum on the yield and composition of white clover grown under glass-house conditions on a molybdenum-deficient strongly leached clay soil of low pH. Molybdenum alone at 1 oz/acre caused a rise in yield, which was greatly increased by lime, but amounts of molybdenum above 1 oz/acre produced no additional effect in the presence of lime, and no consistently significant yield increase in its absence. Lime alone at the 1 ton rate gave yield responses of the same order as molybdenum, and each successive increment of lime gave a further increase. At the 1 ton and 2 ton rates of lime molybdenum gave a further increase, but not at the 4 ton rate. Plant manganese levels ranged from 150-286 p.p.m. in the treatments without lime, but progressively decreased with each increment of lime. The level of manganese associated with adverse effects on growth not corrected by molybdenum was in excess of 100 p.p.m., and this was independent of the Mn:Mo ratio in the tops. High N levels were produced by 4 tons of lime and by lower rates of lime combined with molybdenum, but lower rates of lime without molybdenum gave reduced N levels. Molybdenum alone gave very low N levels in the initial cut, but levels were high in a later cut. Maximum yields were associated with high N levels in the foliage and with Mo levels of 0.1-4.7 p.p.m. Levels of molybdenum of 2 p.p.m. and over were compatible with both low and maximum yields but where yields were low there was evidence that adverse factors associated with high manganese levels were operating. Where these. factors were not operating low Mo levels of 0.4 p.p.m. or less were associated with low yields only when N levels were low.