Agronomic performance of local and improved rice (Oryza Sativa l.) cultivars under weed pressure in Malinyi District, Morogoro, Tanzania
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Date
2024
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Publisher
Sokoine University of Agriculture
Abstract
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.
Description
Dissertation
Keywords
Rice, Weeding, Weeds, Broadleaf, Grass, Sedges, Yield, Research, Biotic, Abiotic, Family