Green manure and inorganic fertiliser as management strategies for witchweed and upland rice.

Abstract

Weed infestation, especially the Witchweed (Striga asiatica) is a serious problem in fertility-depleted soils of Tanzania. The use of urea fertiliser is known to control weed but resource-poor farmers cannot afford this technology due to high costs involved. To alleviate the problem of Striga and soil fertility, green-manure applications could be an alternative strategy. Ths study was conducted to (a) evaluate the potential of green manure against Striga, and (b) determine the potential of inducing Striga suicidal germination by selected green manures. For the first part of the study, treatments included three green manure species, Crotolaria ochlroleuca G. (sunhemp), Mimosa invisa L.(Colla) and Cassia obtusifolia L.(Sicklepod) superimposed with three fertiliser rates 0, 25 and 50 kg N ha-1. The treatments were laid out in a randomised complete block design (RCBD). In the second study part, the 3 green manure species were evaluated for their potential to stimulate Striga seed germination in the laboratory and the field. Results showed that green manure applications significantly reduce Striga infestation, resulting in significant rice yield increases. Green manure exhibited potential to induce suicidal germination of Striga. Based on these findings, green manure applications should be promoted especially among smallholder resource-poor farmers as a strategy for control of Striga infestation in rice fields. Additionally, crop rotation using rice and C. ochlroleuca is the best option since it reduces Striga infestation and increases yield of rice.