Seed pelleting to improve nodulation of tropical and sub-tropical legumes. 2. The variable response to lime and rock phosphate pelleting of eight legumes in the field

Abstract

To determine whether a lime oy rock phosphate pellet has any beneficial effect on nodulation of tropical legumes two field experiments were done using Centrosema pubescens, Dolichos lab lab, Desmodium intortum, D. uncinatm, Lotononis angolensis, and Glycine wightii cvs. Cooper, Clarence and Tinaroo. At one site the experiment was sod-seeded into a Paspalum-Axonopus sward, at the other it was sown into cultivated soil. The second site was acid and calcium-deficient and lime was deliberately withheld to introduce bias towards a lime pellet response. At both sites each legume was tried separately with two effective Rhizobium strains and the effect of lime or phosphate pelleting was assessed by comparison with inoculation done with Cellofas sticker without pellet. Nodulation was assessed on 100 plants of each species at ages from seven to twelve weeks. At the sod-seeding site Lotononis and D. intortum did not establish, but the remaining twelve legume-Rhizobium combinations showed no benefit in nodulation from lime pelleting. At the calcium-deficient site lime pelleting in comparison with Cellofas inoculation improved nodulation with eight legume-Rhizobium combinations, had no effect with six combinations, and depressed nodulation with two combinations. Rock phosphate pelleting showed no benefit in nodulation in twelve combinations under sod-seeding. At the calcium-deficient site four combinations showed improved nodulation and 12 combinations no effect, but there were no negative effects. Good nodulation resulted from simple Cellofas inoculation at both sites, with the exception of D. uncinatum at Beerwah. Pelleting treatments gave no yield increases with the exception of D. uncinatum at Beerwah where yield was significantly increased by lime pelleting. No evidence in favour of routine pelleting with either lime or phosphate was provided bv these experiments. The superiority of certain rhizobial strains as field inoculants was demonstrated.