Evaluation of the potential of green manure and plant extracts for the control of witchweed (strig a asiatica l. kuntze) in upland rice (oryza saliva l.) in Kyela, Tanzania

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Sokoine University of Agriculture.


Striga asiatica is a serious problem in upland rice in Kyela Tanzania. The use of inorganic nitrogen fertilizer urea assures control of the weed. Resource poor farmers cannot adopt the technology due to unavailability and higher prices of inorganic fertilizers. Therefore, the use of green manure available in upland rice fields will be a plausable alternative. Three experiments were conducted to evaluate the potential of green manure and plant extracts for the control of Striga asiatica (L.) Kuntze on upland rice (Oryza sativa L). These experiments aimed at evaluating the decomposition of the green manure, determining the effect of the green manure and inorganic fertilizer on Striga and rice yield and determining the influence of green manure and plant extracts on the germination of Striga. Decomposition of roots and shoots of Crotolaria ochlroleuca G. (sunhemp), Mimosa invisa L.(CoIla), and Cassia obtusifolia L.(Sicklepod) was determined. Results showed that by the 2nd week shoots had lost 51% of the biomass while by the 6lh week roots had lost 50% of the biomass. Then inorganic fertilizer urea at 0 N, 25 kg N ha'1 and 50 kg N ha'1 was superimposed in green manure plots. Generally, it was found that Striga infestation was reduced by 100% while the yield of rice increased from 1238 kg ha’ to 2846 kg ha'1. However, the residual effect of green manures did not reduce Striga but increased rice yield. High benefit per unit cost was realised on when C. ochlroleuca was combined with 50 kg N ha'1). Green manure application methods (ploughing under, mulch) was also superimposed with inorganic fertiliser urea (0 N, 25 kg N ha' 1 and 50 kg N ha '). Results showed that there was no significant difference between mulch and ploughing under on Striga except for rice grain yield. Mulch was found toiii be more economical than ploughing under. The potential of green manure to stimulate Striga germination, plant extracts to suppress Striga germination and application methods was also determined in the laboratory and field. Striga germination was found to be in the order C. ochlroleuca C. obtusifolia > M. in visa (both field and laboratory). Plant extracts were collected from C. ochlroleuca, M. invisa, C. obtusifolia, Vernonia amygdalina Del. (bitter leal), Neuritania niitis, Dolichos kilimandcharis and Gnidia kraussiana Mcisn. (yellow heads). It was found that Striga seed germination was reduced where D. kilimandcharis and G. kraussiana were found to be effective in suppressing Striga seeds germination. Seed hardening was selected as a good application method. Crotalaria ochroleuca and C. obtusifolia were recommended for Striga control and improvement of soil fertility in Kyela.



Rice (Oryza sativa), Green manure, Soil fertility, Inorganic fertilizer, Striga asiatica, Upland rice, Kyela District, Tanzania