Charles K.K. Gachene

Effects of soil management practices and tillage systems on surface soil water conservation and crust formation on a sandy loam in semi-arid Kenya

Abstract The effect of different soil management practices on crust strength and thickness, soil water conservation and crop performance was investigated on a ferric lixisol in a semi-arid environment of eastern Kenya. The study proved that manure and mulching with minimum tillage have a greater effect on the water balance of crusted soils and maize emergence. There was increase in steady infiltration rates, amount of soil water stored in the soil and better drainage. The physical effect of mulch was less important in the rehabilitation of crusted soils in the study site when it was incorporated into the soil. Manure and surface mulch with minimum tillage should therefore be taken into account in land management and water conservation in the semi-arid areas of Kenya. The response of crops to the improved water availability due to manure with minimum and with conventional tillage and surface mulch was very clear. These management practices should be recommended when considering the effectiveness of soil and water management techniques in the study area.

Impact Of Enclosure Management On Soil Properties And Microbial Biomass In A Restored Semi-arid Rangeland, Kenya

Rangeland degradation is a serious problem throughout sub-Saharan Africa and its restoration is a challenge for the management of arid and semi-arid areas. In Lake Baringo Basin of Kenya, communities and individual farmers are restoring indigenous vegetation inside enclosures in an effort to combat severe land degradation and address their livelihood problems. This study evaluated the impact of enclosure management on soil properties and microbial biomass, being key indicators of soil ecosystem health. Six reseeded communal enclosures using soil embankments as water-harvesting structures and strictly regulated access were selected, varying in age from 13 to 23 years. In six private enclosures, ranging from 3 to 17 years in age, individual farmers emulated the communal enclosure strategy and restored areas for their exclusive use. Significant decreases in bulk density, and increases in the soil organic carbon, total nitrogen and microbial biomass contents and stocks were found in the enclosures as compared with the degraded open rangeland. In the private enclosures, the impact of rehabilitation on the soil quality was variable, and soil quality was in general lower than that obtained under communal management. The significant increase of absolute stocks of carbon, nitrogen and microbial biomass compared to the degraded open rangeland indicates the potential for the restoration of soil quality through range rehabilitation. Over-sowing with indigenous legume fodder species could improve total nitrogen content in the soil and nutritional value of the pastures as well.

Decomposition rates of biomass obtained from six month-old Tephrosia vogelii, Tithonia diversifolia and natural fallow vegetation at Maseno, Kenya

ABSTRACT Organic residues incorporated into soil release their nutrients through decomposition. This process may be slow or rapid depending on the biomass quality and environmental conditions. For a period of 8 months, an incubation study with litterbags was carried out in field conditions to determine the decomposition rate of Tephrosia vogelii Hook F., Tithonia diversifolia (Hemsley) A. Gray and natural vegetation fallows. Leaves, stems and roots of Tephrosia, Tithonia and natural fallow had high decomposition rates and less than 30% of the biomass remained undecomposed after 8 months of incubation. Tithonia leaves decayed within 1 month after incubation and Tithonia mixture released most of its N in mineral form during the first month. Tephrosia roots and leaves had a halflife (bo) of about 2 months, which is lower than that for Tithonia roots. Tephrosia stems and natural fallow roots were both low in N and decomposed slowly. Decomposition and nutrient release patterns were influenced by the quality of the material, in particular the N content, lignin and polyphenols.

Nitrogen Fixation by Natural Populations of Acacia Senegal in the Drylands of Kenya Using 15N Natural Abundance

Nitrogen (N) fixation was estimated for three Acacia senegal (L.) (A. senegal) Willd. varieties (A. senegal var. senegal, kerensis, and leiorhachis) growing naturally in different sites in the dryland areas of Kenya. The quantities of N2 fixed were estimated by the 15N natural abundance method, using leaves as the sampling material. Balanites aegyptiaca (B. aegyptiaca) was selected as the reference species growing in the same area. Soil samples were also collected under A. senegal trees for nodule assessment. Leaf 15N natural abundance values (δ15N) were significantly different between A. senegal and B. aegyptiaca. These values averaged 6.35, 4.67, and 3.03% for A. senegal var. kerensis, leiorhachis, and senegal, respectively, and were lower than those of the adjacent reference species. There were also significant differences in the amount of N2 fixed (%Ndfa) among the varieties. A. senegal var. senegal showed the highest levels of N2 fixation with a mean of 36% while A. senegal var. kerensis and leiorhachis had equal estimates of 25%. However, no nodules were observed in the collected soil samples. Leaf N values were significantly different among the varieties with a mean of 2.73, 2.46, and 4.03% for A. senegal var. kerensis, leiorhachis, and senegal, respectively. This study shows that the three varieties of A. senegal are able to fix N2 in their natural ecosystems and the differences could probably be due to soil properties and nutrient availability under the different environments. The species can hence be utilized as plantations in agriculture and land rehabilitation programs.

Participatory Evaluation of Residue Management Effects of Green Manure Legumes on Maize Yield in the Central Kenya Highlands

ABSTRACT An on-farm study to evaluate three methods of applying legume residues in maize-based cropping systems in the central Kenya highlands was initiated in 1997 and conducted for three years. The legumes involved in the study were velvet bean (Mucuna pruriens (L.) DC) and crotalaria (Crotalaria ochroleuca G. Don), which were planted between maize (Zea mays L.) rows, two weeks after planting maize. The legumes were left growing in the field after maize harvest, until land preparation for the next maize crop. The legume forage was harvested and was either incorporated into the soil, left on the surface as mulch, or removed from the field before planting maize. The first cropping season when green manure legumes were establishing, maize grain yields were depressed by an average of 33% compared to the non legume control treatment. The legume treatments increased maize grain yields from a mean of 1.0 t ha−1 in the controls to a mean of 1.6 t ha−1 during the 1998 and 1999 long rains cropping seasons. Over the two cropping seasons, incorporation of legume residue into the soil gave a higher maize yield (2.1t ha−1) compared to leaving the legume biomass on the surface as mulch (1.4t ha−1). The effects of below-ground biomass on maize yields were minimal. The legume treatments did not significantly affect soil N, P, K, and organic carbon. During the study, farmers were able to identify characteristics of suitable green manure legumes and also identify possible niches for green manure legume technologies.

Climate Change and Crop Yield in Sub-Saharan Africa

Recent scientific evidence shows that crop yields in many Sub Saharan Africa (SSA) countries are likely to be severely affected by climate change. Reliance on rainfall in this region increases the vulnerability of cereal systems to climate change and variability. In large parts of SSA, maize (Zea mays L.) is the principal staple crop, covering a total of nearly 27 M ha, and yet maize yields remain the lowest in the world, stagnated at less than 2 Mg ha−1. Calculated and simulated analyses for SSA show that crop yields will decline by more than 10 % by 2055. The effect of climate change on crop yields is mainly attributed to: increased frequency of extreme events; effects of elevated CO2 (where studies project crop yield increases of 5–20 % at 550 ppm CO2); interactions of elevated CO2 with temperature and rainfall as well as with soil nutrients; and increased vulnerability to weed competition, insect pests, and diseases. However, several studies show that rainfall and water availability limit agricultural production more than temperature in SSA. The projected rainfall would increase by 2–4 % in Eastern Africa, but decrease by 5 % in Southern Africa during the main crop growing seasons. Temperatures are likely to increase throughout SSA by 2050, but the combination of increasing temperatures and low seasonal rainfall in Southern Africa suggest this region will be particularly vulnerable. Some of the crop models used for predicting the effect of climate change on yields are limited by their ability to predict effects of climatic events that lie outside the range of present-day variability. In addition, comparisons between models for the same setting have sometimes given differing results. This review paper shows that, for most of the SSA countries, the data required for assessing long-term effect of climate change on crop yield are lacking, that most of the models do not cater to assessment at the household level, and that no single approach can be considered as adequate. Therefore, a clear need exists for collaboration among different scientific disciplines for the development of agriculture in SSA in a changing climate.

Tillage Effects on Selected Soil Physical Properties in a Maize-Bean Intercropping System in Mwala District, Kenya

A field study was carried out to evaluate the effects of tillage practices on soil physical properties in Mwala district, Eastern Kenya, during the long rains (LR) and short rains (SR) of 2012/13. The treatments were disc ploughing (DP), disc ploughing and harrowing (DPH), ox-ploughing (OX), subsoiling-ripping (SSR), hand hoeing with tied ridges (HTR), hand hoeing only (H). These were investigated under three cropping systems of sole maize, sole bean, and maize-bean intercrop in a split-plot design with four replications. Soil physical properties were monitored at different weeks after planting (WAP) throughout the growing seasons. A four-season average shows that soil moisture content was significantly (P < 0.05) higher in OX > SSR > DPH > H > HTR > DP with values ranging from 13.1 to 14.1%. Soil surface roughness and crust strength varied significantly (P < 0.05) over time within the growing seasons, between the tillage practices, and across the different seasons with values ranging from 26 to 66% and 1.21 to 1.31 MPa, respectively. Tillage practices and cropping systems did not significantly affect bulk density, porosity, or K sat values. It is apparent that long term tillage experiment (>4 seasons) would be required to detect changes in soil physical properties as a result of the soil management practices.

Chapter 5:Agrobiodiversity and Potential Use for Enhancing Soil Health in Tropical Soils of Africa

a Department of Land Resource Management and Agricultural Technology, University of Nairobi, P.O Box 29053-00625, Nairobi, Kenya; b Department of Agricultural Economics, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya; c School of Biological Sciences, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya; d Department of Plant Sciences, University of Nairobi, P.O Box 30197-00100, Nairobi, Kenya; e World Agroforestry Centre, P.O Box 30677, Nairobi, Kenya*Corresponding author *E-mail: fredrick.ayuke@yahoo.com

Amendment of Tephrosia Improved Fallows with Inorganic Fertilizers Improves Soil Chemical Properties, N Uptake, and Maize Yield in Malawi

Maize production in Malawi is limited mainly by low soil N and P. Improved fallows of N-fixing legumes such as Tephrosia and Sesbania offer options for improving soil fertility particularly N supply. The interactions of Tephrosia fallows and inorganic fertilizers on soil properties, N uptake, and maize yields were evaluated at Chitedze Research Station in Malawi. The results indicated that the level of organic matter and pH increased in all the treatments except for the control. Total N remained almost unchanged while available P decreased in all plots amended with T. vogelii but increased in T. candida plots where inorganic P was applied. Exchangeable K increased in all the plots irrespective of the type of amendment. The interaction of N and P fertilizers with T. vogelii fallows significantly increased the grain yield. The treatment that received 45 kg N ha−1 and 20 kg P ha−1 produced significantly higher grain yields (6.8 t ha−1) than all the other treatments except where 68 kg N ha−1 and 30 kg P ha−1 were applied which gave 6.5 t ha−1 of maize grain. T. candida fallows alone or in combination with N and P fertilizers did not significantly affect grain yield. However, T. candida fallows alone can raise maize grain yield by 300% over the no-input control. Based on these results we conclude that high quality residues such as T. candida and T. vogelii can be used as sources of nutrients to improve crop yields and soil fertility in N-limited soils. However, inorganic P fertilizer is needed due to the low soil available P levels.