Proxy quantification and mapping of seasonal rangeland herbage using grass cover in the cattle corridor of Uganda

Abstract

This study aimed at estimating herbage mass functional relationship with rainfall and selected soil morphological properties using Geographic Information Systems (GIS). Herbage mass as dry matter (DM) measurements from quadrat harvesting method and estimations based on grass cover were done. Herbage on 1 × 1 m quadrats was harvested and oven dried at 60 • C until constant weight. Grass cover data collection was based on spectral strata of vegetation cover types obtained from Landsat image. Rainfall data were collected from 14 rain gauge stations. Soil profiles were described and their drainage was determined. A multi-linear regression analysis was performed to determine the relationship among DM, grass cover, rainfall effectiveness and soil drainage. The relationships among the variables were integrated using ModelBuilder in ArcGIS 9.3 to come up with spatial and seasonal herbage distribution. Results showed a strong relationship among the above variables and DM (R 2 = 0.76; p < 0.001). Grass cover was found to be the important variable for herbage DM determination (R 2 = 0.73; p < 0.001). A correlation analysis of estimated and harvested DM resulted in a positive relationship (R 2 = 0.85). Estimated DM ranged between 895 and 1923 kg/ha with the highest DM during March-May and the lowest during September-November. This study demonstrated that grass is an important proxy measure of spatial and seasonal patterns of rangeland herbage mass. Therefore, rangeland herbage can in reality be monitored based on grass cover measurements to avoid or at least minimize the cost, destruction and information timeliness implications that are known to be associated with harvesting methods.