Survival and regeneration of four legumes oversown into native grasslands in northeast Thailand.
The survival and regeneration of Stylosanthes humilis cv. Lawson, S. hamata cv. Verano, S. guianensis cv. Endeavour and Macroptilium atropurpureum cv. Siratro oversown into Arundinaria ciliata grassland and grazed by steers at stocking rates of 2.5, 3.5, 4.5, 5.5 and 6.5 animal units/ha over the wet season were studied at Khon Kaen during 1977-80. M. atropurpureum displayed the highest level of perennation with 40% of plants surviving from the 1st year to the next and 2% surviving into the 4th year. A density of at least 6 crowns/m2 was maintained at the lowest stocking rate but loss of persistence occurred at higher stocking rates. M. atropurpureum had the highest seed reserves (74 kg/ha) and a high initial seedling density after the 1st year. S. hamata and S. guianensis performed as weak biennials with a mean survival of 17 and 9%, resp., from the 1st year to the next. Both spp. relied predominantly on seedling recruitment for persistence and in S. hamata this was 60-125 seedlings/m2 for the first 3 years. However, this decreased in the 4th year as stresses during the growing season reduced mature plant density and seed formation. S. guianensis had almost disappeared by the 3rd year mainly because of late flowering during the dry season. S. humilis performed as an annual and disappeared after the 3rd year due primarily to a severe attack of anthracnose disease (Colletotrichum gloeosporioides).