Seed pelleting to improve nodulation of tropical and subtropical legumes. 4. The effects of various mineral dusts on nodulation of Desmodium uncinatum

Abstract

In field experiments at Beerwah, Queensland, in two successive seasons lime and Florida rock phosphate were compared as seed pelleting materials with 18 other mineral dusts. Desmodium uncinatum was used as the test legume, strains CB627 and CB1517 as the test inoculant strains, and methyl cellulose (4 per cent) and gum arabic (40 per cent) as the stickers. Seed was planted after storage for two days and again after 28 days to separate immediate effects of materials on nodulation from effects of storage on survival of bacteria on the seed. The nodulation resulting from the various pellets was assessed by comparison with inoculation done with the sticker alone. Lime pelleting in both seasons gave a stimulation of nodulation at the first planting followed by a severe decline, both absolute and relative to sticker alone, after storage for 28 days, which was attributed to a faster death rate of the inoculant bacteria. Rock phosphate on average gave the best nodulation and the bacteria apparently survived well also under a bauxite pellet. On the basis of nodulation performance combined with ready availability and ease of grinding, the two most promising materials for further test were indicated to be Christmas Island 'c' grade calcined rock phosphate and bauxite. Rhizobium CB627 was a superior inoculant to CB1517, and there was no important difference between the performance of the two stickers Methofas and gum arabic.