Emergence and early growth of Lotononis bainesii cv. Miles on a cracking clay soil compared with four other tropical legumes

Abstract

The effects of soil type (sand, loam and cracking clay), treatment with Terra-sorb, sowing depth and watering regime on the emergence and early growth of Lotononis bainesii (DC.) Eckl and Zeyh. cv. Miles were examined in 4 glasshouse experiments. We also compared the effects of sowing depth, watering regime, and early growth on the establishment of L. bainesii and 4 other tropical legumes (Macroptilium atropurpureum cv. Siratro, Rhynchosia minima CPI 32963, and Stylosanthes hamata (CPI 75171 and Indigofera schimperi CPI 73608). Lotononis germination was greatest when surface sown on a well watered cracking clay soil but emergence was similar for all soils at other depths. Seed sown deeper than 10 mm did not emerge. Siratro and Rhynchosia were able to emerge equally well from 40 mm as from 2 mm. Stylosanthes hamata showed a steady decline in emergence to zero at 40 mm. Emergence of Lotononis and Stylosanthes was greatest under the most lenient watering regime, whereas Rhynchosia emergence was greatest under the harshest watering regime. Coating seeds with a moisture seeking polymer, Terra-sorb, did not significantly improve the emergence of these legumes. Two weeks after sowing, top and root dry weight were related to seed size; Lotononis and Indigofera compensated for small seed size with high relative growth rates so that by week 6 there were no differences in total dry weight. Siratro and Rhynchosia had the highest and Lotononis the lowest rootlshoot ratio. Small seed size, an inability to emerge from depth and a low root/shoot ratio are all factors contributing to the poor establishment of L. bainesii, particularly on cracking clay soils.