College of Agriculture

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    Agronomic performance of local and improved rice (Oryza Sativa l.) cultivars under weed pressure in Malinyi District, Morogoro, Tanzania
    (Sokoine University of Agriculture, 2024) Ilumbi, Halifa Ally
    Weeds significantly reduce the quantity and quality of the rice harvest and raise the cost of production. More than half of the world's population relies primarily on rice (Oryza sativa L.), which accounts for more than 20% of all calories consumed. African continent is the third-most rice producer, after Asia and America. After maize, rice is Tanzania's second-most significant food and commercial crop, where the principal rice-producing regions are Morogoro, Mbeya, Rukwa, Tabora, Shinyanga and Mwanza. Rice is the primary crop planted in Malinyi District, Morogoro region, followed by maize. Local rice cultivars comprise more than 95% of the cultivated land area, while improved rice varieties occupy less than 5%. Compared to the national average yield of 2.5 t/ha, the rice productivity in Malinyi district is low at an average of 1.5 t/ha caused by both abiotic and biotic factors, including weeds as a key barrier. Farmers do weeding up to four times per season. Weedscan result in losses of up to 48 to 100%. In Tanzania, little is known about the cultivars of rice used by farmers to combat weeds in terms of their competitive ability and critical period for weed competition.Thus experiment was conducted at Malinyi district from January to July 2021 in which the main objective of the study was to boost the productivity of a few farmer-preferred rice cultivars in Malinyi district, Morongo, Tanzania, through weed-competitive cultivars and effective weeding regime.Specific objectives of the study were (i) assess weed diversity and abundance in rice growing areas in Malinyi District, Morogoro and (ii) identify weed- competitive rice cultivars under natural weed pressure in Malinyi District, Morogoro. For specific objective 1; Survey was conducted in 70 rice fields, each 0.4ha to identify weeds. Systematic quadrat sampling technique in diagonal pattern used. Ten samples from each field by using 1m2 quadrat were recorded. Weeds in each field were identified, counted by species and the data were used to calculate frequency, uniformity, density, abundance of each species. Weed species diversity in each village was measure by Shannon weinner and Simpson indices while similarity of floristic composition between pairs of villages was obtained by Sorensen index. For objective 2, the experiment was laid out in Randomized Complete Block Design (RCBD) with 20 treatment combinations replicated three times. Factor A contained four rice cultivars and factor B had five weeding regimes as treatments. Subplots had 9 m2. Space between replications was 1 meter. An alley of 0.5 m separated subplots and 1m separated main plots and 1.5 m border space. Sowing Space was 25 cm by 20 cm for inter and intra row. Four rice cultivars were randomly assigned with five weeding regimes. Data were collected for crop and weed plant growth and yield parameters. Summed dominance ratio and relative yield loss were computed by formulae. Two- way mode of analysis of varience usedin data analysis and Turkey's honest and least significance difference test at 5% level used in mean separation. The present survey identified 35 weed species from 13 families; 19 were annual, 16 perennial; 15 grassy, 3 sedges and 17 broad leaved weeds. This study revealed high relative abundance in grass weeds; Paspalum scrobiculatum (36.7%), sedges; Fimbristylis miliacea (26.0%) and broad leaved; Ageratum conyzoides (22.5%) The results indicated Paspalum scrobiculatum was more dominant than other weeds. Number of weed species count in villages ranged from 15 to 29 species. Shannon Wienner and Simpson index had the highest values (2.68, 1.95) and lowest value (0.92, 0.79), respectively; Indicating there is medium weed species diversity due to uneven distribution. Similarity index between pairs of villages ranged from 50% which low to 89% which is high. Results revealed, out of six weed species, Paspalum scrobiculatum with summed dominant ratio (43.60), indicated that had greater contribution in competition. The results had statistical significance differences (p<.001) in relative yield loss ranging from 39.54% to 63.84%, Karimata cultivar with lowest value, demonstrated high tolerance to weeds while SARO 5 with high value had less tolerance. At least two weeding had positive effect (p <.001) on rice grain yield in all cultivar tested. Correlation between weed drymater and grain yield had significant negative relationship (p<.001, R2 = 0.2691). This study revealed that Paspalum scrobiculatum, Fimbristylis miliacea and Ageratum conyzoides were the most prevalent and abundant grass, sedge and broadleaf groups, respectively. This may be they are highly adapted to the environment which favors reproduction and survival. These weeds need special attention to reduce their populations. This study also concludes that weed species in Malinyi district were moderately diverse and most similar between villages. The study concluded that Karimata contained weed competitiveness and high yield. Weedingat 15 and 45 DAE had no statistical significance difference of grain yield with weeding more than two. This study recommends; regular survey is needed to identify possible problematic weed and weed population shifts, sequential cropping system proposed to rice farmers in order to minimize weed pressure, furtherresearch toward new or enhanced weed control measures, evaluation of karimata weed competitive ability and control methods of Paspalum scrobiculatum and Ischaemum rugosum weed species, and farmers are adviced do weeding at 15 and 45 DAE, as the optimal weeding.