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

Abstract

The relationship between topdressing rate and Cu concentration in lucerne grown on Hinemaiaia sand was investigated using dressings of 0, 0.5, 1, 1.5, 2, and 4 kg Cu/ha. The changes in Cu concentration in the foliage over two years, with three harvests in each, are reported. Differences between years, and among treatments, were significant. In the first year, 4 kg Cu/ha increased the average harvest concentration from 3.6 to 6.7 ppm Cu. In the second year, the effect from 4 kg Cu/ha applied only in year 1, was as good as that from 2 and from 4 kg Cu/ha applied in both years. Cu application did not increase yield. The annual DM production was 11 960 kg/ha in year 1, and 11 780 kg/ha in year 2.

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

“…Since there is no proven mcthod for mcasuring "availablc" soil Cu in these soils, thc Cu conccntration in luccrne is relatcd to an index of the Cu accumulated from topdrcssing. Forbes (1976) showed that the quantities of EDTAextractablc Cu in the 0--7.5 cm and 7.5-15 cm soil dcpths under "Cu free" pasture on thcse soils were virtually the same. Any concentration above 1 ppm Cu indicates applicd Cu.…”

“…The sequence of events in this survey and the field trial of Part II (Forbes 1978) are given in Fig. 1.…”

“…The increases in soil Cu resulting from topdressing are shown in Table 2 and Fig 3. The range of EDT A-extractable Cu is 1-23 ppm Cu in the 0-7.5 cm depth where 1 ppm Cu indicates no applied Cu (Forbes 1976). Although some samples had slightly higher values (see inset Fig.…”

“…Whole shoots of lucerne, at the early flower stage, were collected at random from each area for a representative sample. The quantity and fate of the applied Cu was determined by analysis of the 0--7.5 cm and 7.5-15 cm soil depths using the EDT A and HCIOol extraction methods reported by Forbes (1976) . These measurements were based on samples composed of 15 "one inch" cores collected in each area.…”

“…Cobalt and copper have been applied annually to yellowbrown pumice soils in the region, the former to pasture and lucerne, and the latter to lucerne alone. Most of the Co (Forbes 1976) and, it is suspected, Cu accumulates in the topsoil. An increase in concentration may eventually lead to less frequent applications.…”