Seed pelleting to improve nodulation of tropical and subtropical legumes. 3. A field evaluation of inoculant survival under lime and rock phosphate pellet on Dolichos lablab

Abstract

Use was made of a soil, in which the indigenous rhizobia are incapable of nodulating Dolichos lablab, to study nodulation of this species resulting from lime pelleted and rock phosphate pelleted seed after storage for one day and one, two, four, six, and eight weeks at 27¦C. Cellofas A was used as sticker and two strains of Rhizobium were compared. From each sowing plants were dug at eight weeks of age, and the treatments compared using the criteria : number of plants in row, per cent plants nodulated, number of nodules per plant, per cent of nodules on the crown and yield of dry matter per row. Rock phosphate pelleting was superior to lime pelleting in survival of inoculant on the seed, survival of plants in the row, and promotion of nodulation. Lime pelleting depressed yield at eight weeks of age but not at four months. Both strains of inoculant survived one month's storage satisfactorily when simply applied with sticker. Total nodule number fluctuated greatly with time of planting, and was inversely related to per cent crown nodulation, suggesting chat soil moisture at planting may have had a significant effect on nodulation. Strong interactions of inoculant strain with pelleting treatment and time of planting stressed the difficulty of interpreting nodulation effects resulting from pel!etinp treatments. Rhizobium strain CB756 was greatly superior to CB159 in survival on stored seed, nodulation criteria, onset of N fixation and yield.