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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Date
2004
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Publisher
Sokoine University of Agriculture.
Abstract
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.
Description
Keywords
Rice (Oryza sativa), Green manure, Soil fertility, Inorganic fertilizer, Striga asiatica, Upland rice, Kyela District, Tanzania