This study assessed how small-scale farmers in Tanzania manage soil fertility and livestock manure. The researchers found that most farmers do not handle manure effectively before applying it to crops. Regression analysis showed that applying both mineral fertilizer and livestock manure had positive effects on crop productivity, though fertilizer effects were greater. Households using manure had smaller herds and farms but higher crop values per acre. The study suggests building farmer capacity on proper manure handling and application to improve soil fertility where mineral fertilizers are limited.

1. Importance of livestock manure in crop
production in Tanzania
Luke Korir, Nils Teufel and Henry Kiara
International Livestock Research Institute
,
Tropentag 2020: Food and Nutrition Security and its Resilience to
Global Crises, Virtual Conference, 9–11 September 2020

2. INTRODUCTON - 1
• Soil nitrogen depletion is an important constraint to
crop productivity in Sub Saharan Africa
• Farmers cannot afford to apply recommended levels of
mineral fertilizer
• With increasing importance of livestock to livelihoods
of poor famers, livestock manure offers a potential
solution to soil fertility loss in mixed farming-systems

3. INTRODUCTON - 2
• The positive effects of manure application on crops
are well known,
but depend on practices of handling manure
• Aims of the study are to assess
 how small-scale farmers in Tanzania manage
soil fertility and manure,
 how their use of manure affects crop
productivity and
 which farmers benefit most from manure use

4. METHODS
Data
• Cross sectional survey of livestock keeping farmers in Tanzania, 2017
• Survey covered variety of topics relevant to small-scale mixed farming:
demographics, livestock and crop production, income, food security
• A total of 994 farmers were interviewed
Econometric analysis
• OLS regression model for factors influencing crop productivity
• Dependent variable
• Crop productivity: Value of crop products produced per acre
• Independent variables
• Herd, farm & household characteristics: household size, hh head (age,
education, gender), off-farm income, land and herd resources, mineral
fertiliser, manure

5. Distribution of farmers interviewed

6. Manure and soil fertility management practices
• Most farmers do not handle manure in
any special way before use on crops
• Disposed includes burnt
• Most farmers apply manure to crops
• 22 % use both manure & mineral fertilizer
• 56 % use only manure alone and
1% use mineral fertilizer alone
n = 994 n = 994

7. Crops receiving fertilizer and manure
Mineral fertilizer (334 responses)
• Manure applied to a wider range of crops
(on average 2 crops per household)
n = 994
Manure (1,899 responses)
• Mineral fertilizer applied mainly to maize
(on average 1 crop per household)

8. Descriptive statistics of variables used in OLS model
Variable No manure Applied manure p-value*
Household size
(male adult equivalent)
7.8 (5.1) 7.0 (4.9) 0.041
Age of household head 50.2 (12.5) 51.4 (12.1) 0.194
Total land owned (acres) 71.1 (250.5) 23.2 (59.7) 0.006
Total livestock owned (TLU) 105.8 (121.6) 44.5 (78.9) <0.001
Value of crops produced/acre (USD) 167.9 (380.1) 668.6 (4738.8) 0.004
Standard deviation in brackets;
* t-test of mean difference

9. Descriptive statistics of variables used
Variable Label No manure Applied manure Chi-
square
P-value
Education level of
household head
primary or low 173 (79.4) 605 (78.0) 0.728
post_primary 45 (20.6) 171 (22.0)
Gender of household
head
female 7 (3.2) 66 (8.5) 0.012
male 211 (96.8) 710 (91.5)
Whether received off-
farm income
No 143 (65.6) 495 (63.8) 0.680
Yes 75 (34.4) 281 (36.2)
Whether applied
mineral fertilizer to
crops
No 206 (94.5) 555 (71.5) <0.001
Yes 12 (5.5) 221 (28.5)
Share (%) in brackets

10. Descriptive statistics - highlights
Households applying manure
(compared to those not applying manure)
• had significantly smaller herd, farm and household sizes
• produced a higher value of crops/acre
• included a higher proportion of female headed
households
• were more likely to use mineral fertiliser

11. Regression results – crop productivity
N=986, R squared=0.16, F statistic=18.79, *** p < 0.01, ** p < 0.05, * p < 0.1, ¥ Refers to log transformed
Dependent variable:
Value of crops produced (USD/acre) ¥
coefficient SE
Household size (male adult equivalent)¥ 0.51 *** (0.13)
Age of household head (years) ¥ -0.46 ** (0.22)
Total land owned (acres) ¥ -0.001** (0.0005)
Total livestock owned (TLU) ¥ -0.12 ** (0.05)
Gender of household head - male 0.17 (0.25)
Education level of household head - primary or lower 0.22 (0.16)
Received off-farm income - yes -0.04 (0.14)
Mineral fertilizer on crops - yes 2.56 *** (0.59)
Livestock manure on crops - yes 1.72 *** (0.17)
Interaction mineral fertilizer*livestock manure -2.31 *** (0.61)
(Intercept) 4.11 *** (0.92)

12. Crop productivity regression highlights
• Both fertilizer and manure application have positive
effects, but fertilizer effects are greater
• Interaction term between manure and fertilizer is negative
=> Effect of manure reduces when fertilizer is introduced
and vice versa, though overall effect still greater than 0
• Higher livestock and land ownership (acres) as well as age
of household head have negative associations with crop
productivity

13. Conclusions
• Many farmers utilise manure, but hardly any effectively
• Farmers with more livestock and land are less likely to
intensify crop production through soil fertilisation
• Benefits of manure use are greater for farmers who
currently apply none
• This suggests building farmer capacity on effective
livestock manure handling and application
• Especially where soil fertility is threatened and access to
mineral fertiliser is constrained
• Study limitation: only binary variables for manure and
fertilizer use, quantities would provide more insights

14. This presentation is licensed for use under the Creative Commons Attribution 4.0 International Licence.
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