ZINC STUDIES IN ZIMBABWEAN SOILS - EFFECT OF LIME AND PHOSPHORUS ON GROWTH, YIELD, AND ZINC STATUS OF MAIZE

Greenhouse and field experiments were carried out to assess the effect of applying different levels of lime, phosphorus (P), and zinc on the growth, yield, and zinc status of maize. Liming was observed to impro ve yield when the soil pH was below 4.8 (0.01M CaCl2), but there was g enerally no yield benefit for liming when the soil pH was above pH 5.0 . In greenhouse experiments, applications of 120 to 240 kg P2O5/ha wer e observed to increase yield significantly. In the field experiments, yields were variable due mostly to weather stress. Yield response to z inc application was observed in soils which were either limed or had r ecieved 240 kg P2O5/ha. Liming and P applications reduced zinc concent ration in maize plants. The increase in CEC with P application was fou nd to be strongly correlated with the decrease in plant tissue zinc. T he ''dilution'' effect, often advanced as an explanation for reduced z inc concentration in plants where P application was made, was explored and did not explain the reduced zinc concentration in plants.