This study examined soil and water retention strategies using conservation agriculture with trees (CAWT) in Kibwezi, Kenya. Minimum and zero tillage increased soil organic carbon and cation exchange capacity compared to conventional tillage. Faidherbia albida, Gliricidia sepium and Tephrosia candida improved soil fertility when used in CAWT. Soil water content was highest under zero tillage and F. albida. The hardpan layer reduced infiltration. Overall, CAWT and water harvesting increased soil organic matter and water retention compared to conventional practices.

1. TOWARDS SOUND STRATEGIES FOR SOIL-
WATER AND NUTRIENT RETENTION
A CAWT CASE STUDY OF KIBWEZI
Kalinda Mhosi
Chester
Supervisors
Prof Kamau
Ngamau (JKUAT)
Dr John Kihoro
(JKUAT)
Maimbo Malesu
( ICRAF)

2. Presentation Layout
Introduction
Approach
-Experimental
-Statistical
Results
Recommendations and Conclusion

3. Introduction continued
 Study done in Kibwezi
 Rainfall is erratic, majority lost to runoff and evaporation
 Dominant soils are Lixisols and Acrisols
 Soils are shallow and low in fertility
 Soils low in organic carbon and exchangeable cations
 Soil have low water retention capacity and infiltration rate
due underlying hardpan

4. Objectives
Overall Objective
To determine whether the inclusion of trees in conservation
agriculture is an effective land management strategy in conserving
of soil water and nutrients.
Specific Objectives
To determine soil water-retention characteristics of CAWT fields
To determine soil fertility levels of CAWT fields
To examine the suitability of Faidherbia albida, Tephrosia candida
and Gliricidia sepium through performance for CAWT under the
semi-arid conditions of Kibwezi

5. Methodology
Two way experimental design
Four tillage practices
Minimum tillage (Mt)
Zero tillage (Zt)
Farmer Innovation(FI)
Conventional tillage was used as a control (Ct)
Three tree species
Faidherbia albida
Gliricidia sepium
Tephrosia candida

6. Tree species used
Tephrosia Candida Gliricidia sepium Faidherbia albida

7. Methodology Continued
 Gypsum blocks installed at two depths for moisture measurements
 Double ring infiltrometer to measure infiltration
 Measures for CEC, gravimetric moisture content, TOC and Ph taken
over time
 Four soil sampling times ( Feb, March, April and May)
Analysis Methods
 Using Genstat 13th ed and R 2.13.2 version
 Repeated measure analysis of variance
 Correlation and Regression analysis
 LSD used to separate means
 α of 0.05 used in the analysis

8. Collecting sample for Bulk density and
moisture characteristic determination
Gypsum blocks and a
Moisture content reader Double ring infiltrometer

9. Results
 10 rain days the whole
season
 160.3mm total rainfall
received

10. 13 years first season rain fall data
 Below mean rainfall
for past 13 years
(231.26mm)
 Cv 49.88%
 Rain water can be
harvested and used
to supplement crop
water requirements
or lost completely

11. Benefits of water harvesting
Farmer Innovation
plot
Conventional tillage plot Water harvesting ponds

12. Effects of tillage on soil water content (SWc)
(%)
Tillage Depth Depth
Practice 0-20cm 20-30cm
Zt 9.22a 6.01b
Mt 7.94b 6.92a
FI 6.92c 4.51c
Ct 3.49d 1.93d
LSD 1.02 0.89
Means with the same letter are not statistically different at 5%

13. Influence of tree species on SWc (%)
Tree species SWc
F. albida 8.15b
G. sepium 9.01a
T. candida 6.85c
LSD 0.95

14. Effect of tillage on soil TOC
Source of variation d.f. s.s. m.s. v.r. F pr.
Block stratum 2 3.41486 1.70743 7.65
Tillage 3 15.60944 5.20315 23.32 <.001
Residual 84 18.74125 0.22311 8.17
Tillage
practice Mean
factor
Zero tillage 1.35a
Minimum
tillage 1.25a
Farmer
innovation 1.10b
Conventiona
l tillage 0.61c
LSD 0.127

15. Effect of tillage on soil CEC
Source of variation d.f. s.s. m.s. v.r. F pr.
Block stratum 2 445.832 222.916 1.7
Tillage 3 3308.5 1102.83 8.39 0.001
Residual 84 11042.2 131.454 39.44
Tillage
Practice Mean factor
Zero tillage 19.16a
Minimum
tillage 18.46a
Farmer
innovation 16.47b
Conventional
tillage 8.52c
LSD 2.10

16. Effects of tree species on soil organic carbon
(%)
Source of variation d.f. s.s. m.s. v.r. F pr.
Tillage stratum 2 3.33841 1.6692 6.32
Tree_Species 2 1.89927 0.94964 3.6 0.032
Residual 76 20.05688 0.26391 9.41
Tree Mean
species factor
G. sepium 1.26ab
T.candida 1.13b
F.albida 1.31a
LSD 0.137

17. Influence of Tree species on soil CEC
 Fertilizer trees produce
Tree TOC (%) CEC sufficient biomass to
Species maintain or increase SOC
G. sepium 1.26ab 19.53a
 This SOC creates more
T. candida 1.13b 16.34b exchangeable site for cation
F. albida 1.31a 20.24a
LSD 0.137 3.14

18. Synergy between trees and tillage and
their effect on fertility
 The mean maximum TOC 1.40 % was noted in
Faidherbia albida plots prepared using Zero tillage
 1.33% under Gliricidia sepium plots prepared under
minimum tillage.
 SOC influences CEC
 Conventional tillage had the least amount of organic
carbon (0.61%.)

19. Tillage practice influence on Infiltration
Tillage Bd TOC CEC
practices (g/cm3) (%)
Zt
1.31 1.35 19.16
Mt
1.45 1.25 18.46
FI
1.51 1.10 16.47
Ct
1.60 0.61 8.59

20. Soil Compaction
Tillage Bulk density(0-20cm) Bulk density (20-
(g/cm3 ) 30cm) (g/cm3 )
Mt 1.45 1.53
Zt 1.31 1.64
FI 1.51 1.56
Ct 1.60 1.72
Hard pan
Bulk density of the soil

21. Impact of soil hardpan on crop
development

22. Correlation and Regression between IR
and some soil physical properties
Soil Property r r2 Regression line
Organic carbon 0.82 0.78 IR=35.5 + 143OC
Bulk density 0.67 0.62 IR=66-40.134Bd
Total porosity 0.73 0.7 IR=-159.56+24.7TP

23. Moisture Characteristic curves

24. Tree performance and
survival
 SWc under CAWT plots
was 2.2 to 2.9 times more
than that in bare
conventional tillage plots
Tree  Increase in the amount of
species Survival TOC % CEC SOC due to fertilizer trees
rate (Cmol/k
g) biomass
F.albida
44.3 1.31 20.24  These type of trees that
can be established
G. sepium
43.5 1.26 19.53 depending on water
harvesting technologies
T.candida
29.1 1.13 16.34
which can be easily
adapted in an area

25. Conclusions
 Encourage the use of reduced tillage practices and fertilizer
trees managed in sequential and simultaneous tree-crop systems
 Water harvesting will offer an opportunity for additional
cropping season
 The practices offer a wider scope for resource-stressed farmers to
produce sufficient food for consumption and market
 Hardpan need further research and attention as its influences
infiltration and soil water content
 It can be suggested that land that has a fragile structure and
other soil degradation problems invest in CAWT and water
harvesting for improved organic matter build-up and soil water
retention

26. Thank you all for coming