THE SOIL FERTILITY EFFECTS OF LEGUMINOUS LEY PASTURES IN NORTHEAST THAILAND .1. EFFECTS ON THE GROWTH OF RESELLE (HIBISCUS-SABDARRIFA CV ALTISSIMA) AND CASSAVA (MANIHOT-ESCULENTA)

The effect of ley treatments (mostly grazed) differing in legume speci es, duration of ley and non-nitrogenous fertilization on the growth of cassava and roselle is reported. Experiments were conducted in upland fields of farmers at Khon Kaen, Thialand. Soils at the experimental s ite range from paleustults to quartzipsamments with a loamy-sand surfa ce and are extremely infertile. Treatments included cassava and weed-f allow controls, and monospecific legume swards of Siratro (Macroptiliu m atropurpureum cv. Siratro), Verano (Stylosanthes hamata cv. Verano), mimosa (Mimosa invisa var. inermis) and crotalaria (Crotalaria juncea ) grown for 1, 2 or 3 years, or intercropped with cassava, or grown al one in alternate years with cassava followed by test crops of roselle and cassava. Treatments were with and without non-nitrogenous fertiliz er. Yields for the first test crop (roselle) in almost all fertilized legume plots were significantly higher than for the fertilized cassava control whereas in unfertilized plots there was no significant effect . Yields were highest in comparable fertilized plots following Verano or Siratro with crotalaria intermediate and mimosa the lowest. Yields were highest for fertilized two- and three-year Verano and Siratro plo ts and lower for fertilized one-year, alternating years or intercroppe d plots. Yields for the second test crop (cassava) again showed a subs tantial increase in most of the fertilized legume plots compared with the cassava control with results generally similar to those for the fi rst test crop. The test crop data show Verano and Siratro as the best ley species and suggest an optimum ley period in the range of one to t wo years with a cropping phase of approximately equivalent duration to the ley phase. The nitrogen fertilizer value of a Siratro ley in the first year of establishment was estimated to be 132 kg N ha-1. Land pr eparation treatments, following a Siratro ley, of mulching, incorporat ion and herbicide killing of the legume had no effect on subsequent yi eld of roselle whereas grazed plots resulted in a lower yield.