TOWARDS SOUND STRATEGIES FOR SOIL-WATER AND NUTRIENT RETENTIONA CAWT CASE STUDY OF KIBWEZI

Kalinda Mhosi Chester

SupervisorsProf Kamau

Ngamau (JKUAT)Dr John Kihoro

(JKUAT)Maimbo Malesu

( ICRAF)

Presentation LayoutIntroductionApproach -Experimental -StatisticalResultsRecommendations and Conclusion

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

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

Methodology Two way experimental designFour tillage practices Minimum tillage (Mt)Zero tillage (Zt)Farmer Innovation(FI)Conventional tillage was used as a control (Ct)Three tree speciesFaidherbia albidaGliricidia sepiumTephrosia candida

Tree species used

Faidherbia albidaTephrosia Candida Gliricidia sepium

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

Collecting sample for Bulk density and moisture characteristic determination

Gypsum blocks and a Moisture content reader Double ring infiltrometer

Results 10 rain days the

whole season

160.3mm total rainfall received

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

Benefits of water harvesting

Conventional tillage plot

Farmer Innovation plot

Water harvesting ponds

Effects of tillage on soil water content (SWc) (%)

Tillage Practice

Depth0-20cm

Depth20-30cm

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%

Influence of tree species on SWc (%)

Tree species SWc

F. albida 8.15b

G. sepium 9.01a

T. candida 6.85c

LSD 0.95

Effect of tillage on soil TOC

Tillage practice Mean

factorZero

tillage1.35a

Minimum tillage 1.25a

Farmer innovation 1.10b

Conventional tillage 0.61c

LSD 0.127

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 <.001Residual 84 18.74125 0.22311 8.17

Effect of tillage on soil CEC

Tillage Practice Mean

factor

Zero tillage 19.16a

Minimum tillage 18.46a

Farmer innovation 16.47b

Conventional tillage 8.52c

LSD 2.10

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 0.001Residual 84 11042.2 131.454 39.44

Effects of tree species on soil organic carbon (%)

Tree species

Mean factor

G. sepium 1.26ab

T.candida 1.13b

F.albida 1.31a

LSD 0.137

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 0.032Residual 76 20.05688 0.26391 9.41

Influence of Tree species on soil CEC

Tree Species

TOC (%) CEC

G. sepium 1.26ab 19.53a

T. candida 1.13b 16.34b

F. albida 1.31a 20.24a

LSD 0.137 3.14

Fertilizer trees produce sufficient biomass to maintain or increase SOC

This SOC creates more exchangeable site for cation

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%.)

Tillage practice influence on Infiltration

Tillage practices

Bd (g/cm3)

TOC (%)

CEC

Zt1.31 1.35 19.16

Mt1.45 1.25 18.46

FI1.51 1.10 16.47

Ct1.60 0.61 8.59

Soil Compaction

Bulk density of the soil Hard pan

Tillage

Bulk density(0-20cm) (g/cm3 )

Bulk density (20-30cm) (g/cm3 )

Mt 1.45 1.53

Zt 1.31 1.64

FI 1.51 1.56

Ct 1.60 1.72

Impact of soil hardpan on crop development

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

Moisture Characteristic curves

Tree performance and survival

Tree species Survival

rateTOC

%CEC

(Cmol/kg)

F.albida44.3 1.31 20.24

G. sepium43.5 1.26 19.53

T.candida29.1 1.13 16.34

SWc under CAWT plots was 2.2 to 2.9 times more than that in bare conventional tillage plots

Increase in the amount of SOC due to fertilizer trees biomass

These type of trees that can be established depending on water harvesting technologies which can be easily adapted in an area

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

Thank you all for coming