Effect of tillage, farmyard manure and potassium rates on the perfomance and profitability of cassava in selected districts of Kagera, Tanzania
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Date
2022
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Publisher
Sokoine University of Agriculture
Abstract
In Tanzania cassava (Manihot esculenta, Crantz) is the second most important food
security crop after maize. Its roots produce at least 30% of starch on dry weight basis,
which is the major source of dietary energy, different industrial products like sugar,
pharmaceutics, alcohol, textile products and animal feeds. In the Lake zone of Tanzania,
cassava is grown in all regions, which account for 23.7% of the total cassava production in
the country. Despite the importance of cassava in food systems there is decreasing yield.
For example, the national average root yield is 10 MT ha -1 compared to the potential yields
of 25 - 80 MT ha -1 , whereas in Kagera region, average yield in farmers’ fields is about 7.80
MT ha -1 .
The low yield is due to, among others, increased susceptibility of the crop to cassava
mosaic disease (CMD) and cassava brown steak disease (CBSD), declining soil fertility
and poor agronomic practices. In the Lake zone, cassava is planted on ridges or on flat
tillage but little information exists on the performance of cassava when planted on ridges
or on flat tillage. In addition, cassava responds well to farmyard manure and inorganic
fertilizers. But scant information exists on the performance of cassava upon use of different
rates of FYM and potassium fertilizer, specifically based on Kagera region climate and
soils. This study, therefore, aimed to determine the effects of tillage methods and
application of different rates of FYM and potassium fertilizers on the performance and
profitability of cassava in Bukoba, Missenyi and Biharamulo districts of Kagera region.
The specific objectives of this study were to: (i) characterize and classify the soils of the
study area and assess their suitability for cassava production, (ii) assess the current soil
fertility status of farmers’ fields in the study sites, (iii) determine the effects of tillage
methods, farmyard manure and potassium rates on soil moisture conservation and relationship with cassava root yield, (iv) determine the effects of tillage methods, FYM and
potassium rates on cassava growth, yields and root quality, and (v) evaluate the economics
of using farmyard manure and potassium fertilizer rates in cassava production in the study
area.
To achieve objective i, pedological characterization, which involved reconnaissance field
survey in Bukoba, Missenyi and Biharamulo Districts was carried out. Soil profile
description and soil sampling for laboratory analysis were done according to the FAO
Guidelines for Soil Description. The soils of the study sites were classified to the family
level of the USDA Soil Taxonomy and to tier-2 of the FAO World Reference Base for Soil
Resources. Soil suitability assessment of the experimental sites was done using a simple
limitation method based on the FAO Framework for Land Evaluation. The results revealed
that the soils of Bukoba and Biharamulo sites had similar morphological properties, which
were different from Missenyi site. But all differed in their physical, chemical and generic
properties. Based on the USDA Soil Taxonomy, Bukoba and Biharamulo sites were
classified as “Typic Kandiudults”.and as “Haplic Ferralic Acrisols”, and “Chromic
Ferralic Acrisols” respectively according to FAO World Reference Base for Soil
Resources. Missenyi site was classified as “Typic Endoaquolls” and “Fluvic Gleyic
Phaeozems” according to USDA Soil Taxonomy and FAO World Reference Base for Soil
Resources, respectively. Moreover, Missenyi and Biharamulo sites were evaluated as
marginally suitable and the Bukoba site as moderately suitable for cassava production.
Therefore, soil fertility management strategies are recommended in each studied site for
optimum cassava yields.
To achieve objective ii, two wards and one village in each ward were selected in Bukoba,
Missenyi and Biharamulo districts. A total of thirty-three fields were selected (five farmers' fields in each village and one experimental field in each district). Composite soil samples
at 0- 20 cm depth were taken using a using a zigzag pattern over the whole field's area and
analyzed. Correlation analyses among soil chemical properties were performed using IBM
SPSS Statistic 20 statistical package. Soil fertility index (SFI) and identification of limiting
nutrients were used to assess the fertility status of selected farmers’ the fields. Results
indicate that the studied fields had poor fertility to good fertility. Phosphorus and
potassium deficiencies were widely spread in Bukoba district while N and S deficiencies
were widely spread in Missenyi district and N, P and K deficiencies were widely spread in
Biharamulo district. There were positive and negative and significant (p≤ 0.05) and highly
significant (p≤ 0.01) correlations among the soil chemical properties in each district.
Therefore, site specific soil fertility management practices are recommended based on
limiting nutrients.
To achieve objective iii, one cassava field trial was established in each selected district
(Bukoba, Missenyi and Biharamulo) during 2018/19 and 2019/20 cropping seasons using
the split-plot design. The treatments were arranged in Randomized Complete Block Design
(RCBD) with three replications. Tillage methods (flat tillage, open ridging and tied
ridging) were the main plots and fertilizer types and rates [farmyard manure (FYM) alone
at 4 MT ha -1 or FYM alone at 8 MT ha -1 , nitrogen (40 kg N ha -1 ) + phosphorus (30 kg P ha -
1
) + potassium at 40, 80 or 120 kg K ha -1 and the combination of FYM alone at 4 MT ha -1
or FYM alone 8 MT ha -1 + potassium at 40, 80 or 120 kg K ha -1 ] were the sub-plots. Soil
moisture was monitored starting from 1 week after the last rain event at an interval of 2
weeks up to the first rain event of the following season. The soil samples in cores were
weighed and placed in the drying oven at 105 o C to constant weight. The soil moisture
content (%) in each soil sample was determined gravimetrically. The results showed that
tie and open ridges conserved significantly (p≤0.05) more soil moisture ranging from 24 to 58% (Bukoba district), 10 to 45% (Missenyi district) and 10 to 32% (Biharamulo district)
than flat tillage ranging from 22 to 43% (Bukoba district), 8 to 37% (Missenyi district) and
7 to 27% (Biharamulo district) in both cropping seasons. However, tied ridges conserved
significantly (p≤0.05) more (11 to 58%) soil moisture than open ridges (10 to 47%) in the
medium and high rainfall areas as opposed to the low rainfall area. The results also indicate
that the use of FYM significantly (p≤0.05) conserved more soil moisture (16.54 to 63.48%)
than inorganic N, P and K fertilizers (12.27 to 53.60%). In addition, use of FYM alone at 8
MT ha -1 conserved significantly (p≤0.05) more soil moisture (19.94 to 62.16%) than FYM
alone at 4 MT ha -1 (16.80 to 58.33%). Moreover, there was a significant (p≤0.05)
association between soil moisture conservation and changes in cassava root yields.
Therefore, planting cassava on ridges together with use of high rates of FYM (8 MT ha -1 ) is
indispensable for adequate soil moisture conservation and improving cassava root yields.
To achieve objective iv, data on daily rainfall (mm) were collected in each experimental
site. Data on root and biomass yields (MT ha -1 ) were collected from the net plot from
established trials described in objective ii above. About 500 g of cassava roots from each
treatment were peeled and oven dried at 105 o C to constant weight for determining dry
matter content gravimetrically and root starch content in each treatment was determined. In
addition, the post-harvest soil samples and cassava leaf samples were collected from the
control plots and the plots that received the combination of FYM at 8 MT ha -1 and
potassium (K) at 40 or 120 kg ha -1 for determining the concentration of Nitrogen,
phosphorus and K and soil pH. The results indicate that planting cassava on ridges gave
significantly (p≤0.05) higher (18.98 - 34.84 MT ha -1 ) cassava fish root yield than on flat
tillage (16.86 - 29.74 MT ha -1 ). However, use of ridges or flat tillage did not show
significant (p≤0.05) difference in starch and dry matter contents in cassava roots, soil pH,
and concentration of N, P and K in the soil and cassava leaves and sprouting of cassava plant. Combined use of FYM at 4 MT ha -1 or FYM at 8 MT ha -1 and potassium at 40, 80 or
120 kg K ha -1 significantly (p≤0.05) improved cassava growth and increased cassava fresh
root yields (14.56 - 39.94 MT ha -1 ). Also, combined use of FYM at 4 MT ha -1 or FYM at 8
MT ha -1 and potassium at 40, 80 or 120 kg K ha -1 ; significantly (p≤0.05) improved cassava
growth and increased cassava fresh biomass yields (9.36 - 32.86 MT ha -1 ). Combined use
of FYM at 8 MT ha -1 and potassium at 120 kg K ha -1 or FYM at 8 MT ha -1 and potassium
at 40 kg K ha -1 increased the concentration N, P and K in the soil and N and K in cassava
leaves. Therefore, planting cassava on ridges and combined use of FYM at 4 MT ha -1 and
potassium at 80 or 120 kg K ha -1 is desirable for improving cassava growth, increasing
biomass and root yields and increasing root quality. Combined use of farmyard manure at
8 MT ha -1 and potassium at 120 kg K ha -1 is desirable for increasing the concentration of N
and K in the soil and in cassava leaves. However, for the resource-poor farmers who
cannot afford the high rate of K, combined use of farmyard manure at 8 MT ha -1 and
potassium at 40 kg K ha -1 can be used.
To achieve objective v, yields data collected from the established trials as described in
objective iii above were used to perform partial budget analysis, whereby, the gross values
were estimated using the adjusted yields at market price for cassava and fertilizers. Costs
and benefits were calculated on a hectare basis. All variable costs were summed up to give
total variable cost (TVC). Thereafter, the net benefits (NB) ha -1 of the tested treatments
were calculated and used to assess the profitability of each treatment. In addition, benefit-
cost ratios (BCR) of the tested treatments were compared to the acceptable value of greater
than 2 for the technology to be adopted by farmers. The results indicate that in both
cropping seasons, and at all studied sites, all tested fertilizer rates gave acceptable BCR of
greater than 2, implying that all the fertilizer types and rates tested in this study could be
used in cassava production in the study areas. In addition, the results on net benefit indicate that use of combination of FYM at 8 MT ha -1 and potassium at 80 kg K ha -1 gave higher net
benefit than the other fertilizer types and rates, and is therefore, desirable for increasing
cassava root yield and economic benefit in the study area. However, for the resource-poor
farmers, combined use of farmyard manure at 8 MT ha -1 and potassium at 40 kg K ha -1 can
still be adopted in the study area because, for some reason, not all the famers can afford the
best treatment.
The major conclusions drawn from this study are that the soils of Bukoba and Biharamulo
sites have similar morphological properties, which are different from Missenyi site.
However, all soils differ in their physical, chemical and generic properties. According to
the USDA Soil Taxonomy, the soils of both Bukoba and Biharamulo sites were classified
as “Typic Kandiudults” and as “Haplic Ferralic Acrisols” and “Chromic Ferralic
Acrisols”, respectively, according to FAO World Reference Base for Soil Resources. The
soil of Missenyi site was classified as “Typic Endoaquolls” according to USDA Soil
Taxonomy and as “Fluvic Gleyic Phaeozems” according to FAO World Reference Base for
Soil Resources. Missenyi and Biharamulo sites were both evaluated as marginally suitable
while Maruku site was evaluated as moderately suitable for cassava production due to soil
fertility constraints and hence sustainable cassava production in these areas would need
interventions for soil fertility improvement.
The soil fertility status of the studied fields ranged from poor fertility to good fertility
whereas, P and K deficiencies were widely spread in Bukoba district while N and S
deficiencies were widely spread in Missenyi district and N, P and K deficiencies were
widely spread in Biharamulo district. Use of ridges conserved more soil moisture than use of flat tillage, and use of farmyard
manure at 8 MT ha -1 conserved more soil moisture than combined use of inorganic N, P
and K fertilizers or use of farmyard manure at 4 MT ha -1 . Moreover, plating cassava on
ridges together with combined use of FYM at 4 MT ha -1 and potassium at 40, 80 or 120 kg
K ha -1 improved cassava growth and increases cassava root and biomass yields than use of
flat tillage together with the same fertilizer rates.
Combined use FYM at 8 MT ha -1 and potassium at 80 or 120 kg K ha -1 or combined use of
inorganic N at 40 kg ha -1 , P at 30 kg ha -1 and K at 120 kg ha -1 increased the contents of
starch and dry matter in cassava roots and combined use of FYM at 8 MT ha -1 and
potassium at 40 80, or 120 kg K ha -1 increased concentration of N, and K in the soil and
cassava leaves.
In terms of profitability, combined use of FYM at 8 MT ha -1 and potassium at 80 kg K ha -1
gave higher net benefit than the other fertilizer types and rates tested in this study and is
therefore, desirable for increasing cassava root yield and economic benefit in the study
area. However, for the resource-poor farmers, who cannot afford the best treatment,
combined use of farmyard manure at 4 MT ha -1 and potassium at 80 kg K ha -1 can still be
adopted.
Description
Dissertation
Keywords
Farmyard manure, Potassium rates, Cassava, Tanzania, Kagera District, Tillage