Lucerne (Medicago sativa L.) yields were unaffected by phosphorus fertility level under grazing in a dryland farmlet experiment

Abstract

Phosphorus (P) is a key nutrient recommended for optimal nitrogen fixation by legumes in New Zealand pastoral systems. However, few field studies have examined the response of legume monocultures to soil P levels. This experiment measured lucerne yield under grazing in the field when grown under two P fertiliser regimes for the first three years of the dryland farmlet experiment at Lincoln University. The ‘High’ phosphorus treatment aimed for an Olsen P of ∼20 compared with ∼10 for the ‘Low’ treatment. Lucerne shoot biomass showed no effect of treatment at any time. This was consistent with no differences observed for lucerne mean daily growth rates and canopy light interception. Additionally linear regression analysis showed no relationship (R² = 0.01) between soil Olsen P and any of the measured variables. These results suggest that the critical Olsen P may be <10 for dryland lucerne monocultures measured to a soil depth of 75 mm, which is consistent with previous recommendations.