Joshua O. Minai – Masters Defense Announcement

Assessing the Spatial Variability of Soils in Uganda

Major Professor: Darrell G. Schulze

Friday, March 13, 2015

2:00 p.m.                   LILY 2-425

Ecological Sciences and Engineering Interdisciplinary Graduate Program

Department of Agronomy

Everyone is Welcome!

Abstract

Uganda’s soils were once considered the most fertile in Africa, but soil erosion and soil nutrient mining have led to soil degradation and declining agricultural productivity. Lack of environmental awareness among farmers, traditional agricultural practices, minimal inorganic fertilizer use, and little to no use of improved crop varieties all contribute to continued soil degradation. The objective of this study was: (1) to quantify and characterize the spatial distribution of selected soil properties in Uganda and (2) to identify the driving factors and processes for soil spatial variability and soil degradation at the national scale using biophysical and socioeconomic variables.

This study used a 2003 Uganda National Household Survey dataset that included analyses for 2,144 soil samples that covered western, southwestern and northwestern Uganda, representing ~50% of the country. Variables include pH, organic matter, total N, available K, total K, total P, and soil texture (Nkonya et al., 2008, IFPRI Research Report 159). Ordinary kriging was used for spatial analysis, while a generalized linear model was used to identify the most dominant factors influencing soil variability. ANOVA results found significant variation among soil properties, as one would expect. Strong spatial correlation (< 25% nugget to sill ratio) was observed in available K, pH, sand, total N, and silt, while moderate spatial correlation (25% to 75% nugget to sill ratio) was observed for total K, clay, total P, and organic matter. Distances where spatial correlation occurred ranged between 69 and 230 km. Interpolated soil quality maps identified the Mt. Elgon and the southwestern highlands regions as having soils above the critical soil chemical and physical thresholds, indicating that these are the most favorable agricultural areas in the country. The remaining areas of the country had numerous constraints such as acidity, very sandy soils, low N and/or low organic matter, making these areas less optimal for agricultural production.

Climate had the strongest effect on the variability of total N, with higher soil N in the cooler, higher elevations around Mt. Elgon and in the southwestern highlands. Geology and land use / land use management were the second most dominant factors influencing the variability of soil properties at the national scale. This study showed that geostatistical approaches can be used to evaluate spatial diversity of natural resources at larger scales. Policy makers can use this information to implement region-specific soil management approaches to address soil quality degradation. For example, programs to increase the soil pH of acid soils should be focus on the southwestern region where soils are generally more acid than other parts of the country.

Christal Musser

Program Coordinator

Ecological Sciences and Engineering

Office of Interdisciplinary Graduate Programs

The Purdue University Graduate School | Purdue University

Ernest C. Young Hall, Room B-40 | 155 S. Grant Street | West Lafayette, IN 47907

Email: musser@purdue.edu | Web: www.purdue.edu/ese

Phone: 765-494-2102 | Fax: 765-496-6271

Like us on Facebook