Investigations into the availability to lucerne (Medicago saliva) of copper applied to yellow-brown pumice soils

Abstract

Cu concentration in lucerne at the hay stage was related (R² = 0.84) to the soil Cu level in 28 stands where Cu was topdressed commercially. Plant values ranged from 2.6 ppm Cu (deficient for stock) to 13.2 ppm Cu. The extractant, 0.02m EDTA/0.1m NH₄Cl, dissolved 67% of the accumulated Cu and established a range in soil Cu from 1 to 23 ppm Cu. On average the CV for the soil measurement was twice that for the plant. Lucerne Cu concentrations differed considerably between harvests within the growing season. Harvest 1 consistently gave the lowest values. Neither changes in growth rate nor soil moisture could account for this. It is postulated that lower insolation and temperature during the first growth period caused the low harvest 1 values. The plant Cu values measured in 14 stands over 3 years revealed that for stock health a useful residual effect exists for at least 3 years after topdressing.