Seed pelleting to improve nodulation of tropical and sub-tropical legumes. 1. An examination of the validity of 'grow-out' nodulation tests in tubes

Abstract

Nodulation resulting from various seed pelleting treatments of Lotus pedunculatus, Desmodium intortum, and D. uncinatum was investigated by the 'grow-out technique', in which single treated seeds are dropped into seedling nutrient agar tubes which are assessed for presence or absence of nodules after a standard time. Two cellulosic stickers, Cellofas A and Methofas were used, and pelleting materials included lime, gypsum, kaolin, calcium silicate, and four rock phosphates. Calcium silicate was quickly lethal to rhizobia. Malt extract was included in the sticker in several experiments and had a protective action on rhizobia. Significant effects of pellet treatment were observed on both seed germination and amount of nodulation. Results indicate that the relative performance of different pelleting treatments can be influenced both by ambient environmental factors and by the type of mineral nutrient agar chosen for the performance of the test. It is suggested that such tests may be quite misleading, and that they provide no real guide to what may occur in the field.