Baseline Report Yala and Nzoia River Basins
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Sampling methods
Socio economic information is collected on a household level by the use of a questionnaire designed by KARI and ICRAF. The questionnaire contains 63 questions regarding various socio economic parameters such as household size and economy, livestock, soil and water conservation, agroforestry, etc. Three enumerators carry out the survey. They interview 10 households per cluster and collect one soil sample per household, (i.e. sample size is 160 households). A soil sample is collected to i) assess topsoil fertility at farm level and to ii) increase the number of soil samples collected per block to enhance the modeling of soil parameters. The soil samples are dried, crushed, and sieved through a 2mm sieve before being sent to ICRAF Nairobi for further analyses. See section below for more detailed description of analyses for soil samples. The information from the questionnaire is then entered into a Microsoft Access database created by ICRAF, which enables easy queries of data. The questionnaire is attached in Annex 2.
Biophysical information is collected for each of the 10 sampling plots for the 16 clusters. The biophysical team collects information on soil infiltration capacity, land forms and land cover, and soil characteristics. Before sampling can begin, the sample plot needs to be laid out.
Upon reaching the sampling plot, the radial arm plot method is used in setting up the plot layout as described on p.5 in Annex 1. This method allows soil and vegetation to be sampled and classified for an area of 1000m2. After identifying the centre point (point no. 1) an additional three points are set up in the following order: sample point no. 2 is placed 12.2 m up-slope from the centre point, where point no. 3 and 4 are off-set 120o and 240o, respectively from the centre point in the down slope direction. Once the plot layout is set-up, sampling can begin.
The field data recording sheet is given on p.10 in Annex 1. The recording sheet is divided into six sections, A-F: Section A: First, the centre point location is geo-referenced using a GPS unit. Thereafter, slope is measured both up and down slope using a clinometer. Section B: Second, the major land forms and the topographic position are described. To do this, the surrounding area is inspected and the appropriate categories, provided on the field data recording sheet, are selected. Section C: Thereafter, the land cover for all four points is recorded using the FAO Land Cover Classification System (LCCS). This classification system recognizes 8 primary land cover types of which 5 are present in the study areas of WKIEMP: Cultivated and managed terrestrial areas, natural and semi-natural vegetation, cultivated aquatic or regularly flooded areas, natural or semi-natural aquatic or regularly flooded vegetation, and bare areas. The LCCS classification system allows the identification of different land cover types on the basis of the dominant vegetation type (tree, shrubs, herbaceous). The questions in the field data recording sheet are designed to guide one through the classification process. Section D: In section D, we collect information is regarding land use and land ownership. Section E: Section E is for characterization of the soil surface. The first questions are on erosion and conservation. Thereafter, soil sampling at the four points is carried out. Topsoil is sampled for the 0-20 cm depth and subsoil for the 20-50 cm depth by using a soil auger. The soil samples are bulked for the two depths in separate bags. Soil depth is measured until a depth of 120 cm at 5 cm increments and the depth of restriction is indicated on the field recording sheet. Soil texture is assessed by using the ribbon method. The method is widely used for quick assessment of texture and is also the recommended method by the Australian Gas office. Instructions for this method can be found on p. 6 in Annex 1. Section F: Woody vegetation is measured in this section using the T-square sampling method. This method is one of the most robust methods for sampling woody plant communities. It can be used to estimate stand parameters such as density, basal area, bio-volume, and biomass. The advantage of this method is that it is less prone to bias where plants are not randomly distributed, such as in managed landscapes. In this sampling scheme, trees and shrubs are sampled separately. See the guide given on p. 7 in Annex 1 for a more detailed description of the woody vegetation measurements.
Infiltration measurements are carried out at 3 of the 10 sampling plots for each of the 16 clusters. Infiltration rings measuring 12 inches in diameter are placed at the centre point (point no. 1) and infiltration rates are measured after the soil has been pre-wetted with approx. 2-3 liters of water. The data sheet is given on p. 12 in Annex 1. The infiltration data is then entered into the Microsoft Access database designed for the biophysical baseline survey and infiltration curves are fitted using the Hortonian infiltration function.
The soil samples collected from both baseline surveys are air dried for a minimum of 3 days at the ICRAF Kisumu soils laboratory. The dried soil samples are crushed and sieved through a 2mm sieve and sent to Nairobi for further analyses. Samples are first analyzed using infrared spectroscopy and a subset of samples is sent to the lab for further analysis to permit calibration of the spectral data to soil properties of interest. After completing the data collection, data is entered into the Access database designed for the bio physical baseline survey. This data together with the entered data from the socioeconomic survey is the basis of this report.
In the Nyando river basin, the collection of baseline data is nearing completion. The lower block has been sampled and a draft baseline report has been written and shared with KARI (Dec. 2006). As for the two other blocks, the socio economic survey hav been completed for the middle block and the survey is taking place for the upper block. The biophysical team is collecting data for middle block and will thereafter move into the upper block. |