Influence of weed control options on growth and yield of cassava in Eastern zone of Tanzania.
Loading...
Date
2022
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Sokoine University of Agriculture.
Abstract
Cassava (Manihot esculenta Crantz) is an important crop in sub-Saharan Africa as it has
been used as staple food by most of tropical Africans, it is averaged to be used as food on
over 24 countries in Tropical Africa. Despite of the importance of cassava as food and
cash crop in Tanzania, its production is affected by several factors, weed being one of
those and it has been estimated that weed reduce cassava yields by almost fifty percent. In
the Eastern zone of Tanzania, adoption of the best integrated weed control options on
cassava production has not been clearly done, thus farmers still face challenges in terms
of efficiency, timeliness and effectiveness in weed control as they mostly relay on a single
weed control option. Also, weed control cost has been very high leading to inappropriate
weed control as it has been estimated that the annual cost of weed control been almost $
4.3 billion in Africa. This study aimed at developing the best integrated weed control
combination for improved cassava productivity. Specifically, the study sought to: (1) to
identify common weeds found in the selected cassava farms in Eastern zone of Tanzania,
(2) to determine the effect of tillage, pre-emergence and post-emergence weed control
options on weed growth, cassava yield and soil quality and (3) to conduct cost benefit
analysis of the selected weed control options in cassava farms. The first chapter contain
general introduction, the second, third and fourth in the dissertation comprise
manuscripts in the form of publishable papers which cover the first, second and third
specific objectives while chapter five covers general conclusion and recommendations.
The effects of different weed control treatment combinations were studied during the
2019/2020 planting season at Ilonga village, Kilosa district and Kiimbwanindi village,
Mkuranga district. For the first objective, a study was carried out from November 2019 to
April 2020 in which a field survey was done to identify common weeds found in cassava
fields in two sites. A total of 24 random 1 m × 1 m quadrat were placed in each cassava
field whereby all weed species found in each quadrat were identified to a species level.
During weed identification, weed density, uniformity and frequency were calculated
according to Thomas methodology and used to determine relative abundance. The effect
of different weed control treatment combinations on weed growth and cassava yield, soil
quality and cassava profitability were studied for the objectives two and three,
respectively. Till only and till + Ridge, pre-emergence herbicides (Primagram Gold a.i
290 g/L S-metolachlor + 370 g/L atrazine and Oxfen a.i Oxyfluorfen 24% EC), post
emergence herbicides (Force up a.i 480 g/L of Glyphosate-Isopropylamine salt and back
pack weeder with modified tines) were tested on Cassava variety Kiroba in a factorial
experiment arranged in a randomized complete block design (RCBD) replicated three
times. Data on the number of days for the weed reemergence, cassava plant height and
cassava stem girth at five months after planting, cassava fresh root weight, cassava
biomass and cassava dry matter content were collected. Also, a random composite soil
samples were collected from each field at a depth of 0-30 cm before land preparation and
after harvesting, and analyzed in the laboratory to determine the soil pH, total N, P, K, Ca
and Mg nutrients content. Data obtained were subjected to analysis of variance (ANOVA)
at P≤0.05 using R statistical package version 3.5.2. The treatment means were compared
using Tukey’s honestly significance test at alpha 5% for objective two. For the objective
three, data collected were all variable costs for the inputs applied on each weed control
treatment combination, costs of cassava harvesting and the price of cassava per kilogram,
and data were subjected to benefit-cost ratio analysis.
Results revealed that, there were 22 weeds species belonging to 16 families identified in
the cassava fields, whereby out of those species, 14 were broad leaved weeds, 6 grassy
weeds, 1 sedged weed and 1 mushroom belonging to 10 perennial and 12 annual weediv
plants. During weed identification, Cyperus rotundus and Echinochloa colona were the
most abundantly weed species while Dactyloctenium aegyptium, Portulaca oleracea,
Agaricus sp and Bidens pilosa were the least abundant weed species at both sites. Results
showed, a combination of tillage practices and pre-emergence herbicides application (S-
metolachlor + atrazine at 3.0 lts a.i/ha and Oxyfluorfen at 3.0 lts a.i/ha) increased number
of days weeds took to emerge in both sites. Also, the correlation analysis showed a non-
significant positive relationship, r = 0.389, p > 0.05 and r = 0.055, p > 0.05 between
cassava stem height and cassava fresh root weight, and cassava stem girth and cassava
fresh root weight, respectively at Kiimbwanindi site and highly significant strong positive
relationship, r = 0.925, p < 0.001 and r = 0.781, p < 0.05 between cassava stem height and
cassava fresh root weight, and cassava stem girth and cassava fresh root weight,
respectively at Ilonga site. Combination of weed control treatments significantly affected
cassava fresh root weight and biomass, (p = 0.019 and p = 0.026, respectively) at
Kiimbwanindi while at Ilonga, combination of weed control treatments did not
significantly affected the cassava fresh root weight, (p = 0.514) and cassava biomass (p =
0.732). Further findings indicated that, the selected weed control treatment combinations
had not significantly affected soil pH, amount of total N, P, K, Ca and Mg nutrients at
Ilonga and Kiimbwanindi sites. The highest profit at Kiimbwanindi site was recorded on
till × Oxfen × Force up and till × Primagram × Force up treatment combinations which
had the benefit cost ratio of 2.39 and 2.04, respectively while at Ilonga site, only Till and
Rigde × Oxfen × Force up treatment combination had the benefit cost ratio of 2.31 and
high cassava root yield of 25.58 t ha -1 .
We conclude that, perennial weeds Cyperus rotundus, Echinochloa colona, Trichodesma
zeylanicum, Reissantia sp, Mucuna pruriens and Commelina benghalensis were the most
and abundant occurred weed species due to their ability to adapt into various soil typesv
and their ability to reproduce as compared to other weeds. The combination of till +
ridges, application of pre-emergence herbicide (S-metolachlor + atrazine) and post
emergence herbicides (glyphosate) provided favorable environment for cassava growth
and root formation as compared to other treatment combinations. Also, these results
proved that, proper use of weed control methods have had minimum effects on the soil
quality while having positive impacts on the cassava performance. However, its
recommended that, for the positive nutrient balance in cassava production, it is important
to apply fertilizers that contain high N and K nutrients because cassava responds
effectively on these nutrients. Also, good farm preparation, the use of Oxyfluorfen 24%
EC herbicides as pre-emergence herbicide and 480 g/L of Glyphosate-Isopropylamine salt
as post emergence weed control treatments should be encouraged in cassava production as
they lead to maximum profit.
For maximum cassava productivity, proper tillage and ridging before cassava planting,
use of pre-emergence herbicide made of S-metolachlor and atrazine and proper use of
glyphosate as post emergence herbicide could highly help keeping cassava farms free
from weed for a longer period of time as compared to other treatment combinations. Also,
more research is recommended on a regular basis to identify possible weed population
shifts for improved control measures needed.
Description
Masters Dissertation
Keywords
weed control, Cassava, Tanzania, Cassava Production