Soil, Runoff, and Nutrient Losses from Major Cropping Systems in the River Katonga Micro-Catchment of South-Central Uganda

This study determined the magnitude of soil, runoff, and nutrient losses under four major cropping systems, including annual crops, banana monocrop, coffee-banana intercrop, and grazing lands in the River Katonga Micro-Catchment, South-Central Uganda. Data were collected using the runoff plot approach. Runoff plots measuring 2 M × 20 m were installed on each cropping system in farmers’ gardens, equipped with dividers and collection tanks. Three soil erosion conservation practices, comprising trenches, mulches, and grass bunds, were tested for the experiment. Trenches and grass bunds were tested on annuals; trenches and mulches were tested on both banana and coffee-banana systems; and only trenches were tested on grazing land. The experiment included a control practice for each cropping system. Each treatment and control was replicated three times. Runoff and soil loss were estimated for each rainfall event and aggregated on a seasonal basis, while nutrient (nitrogen (N), phosphorus (P), and potassium (K)) losses were estimated per season. Results show that soil, runoff, and nutrient losses significantly depended on soil erosion conservation practices and rainfall seasons for all the cropping systems (p < 0.001). The magnitude of soil and runoff losses was in the order of annual crops > grazing lands > banana > coffee-banana. Soil losses ranged between 22.08 and 22.84 t/ha, while runoff losses varied from 84.15 to 97.05 m³ under annual cropping systems. In banana fields, soil losses ranged from 20.83 to 22.32 t/ha, while runoff losses were between 74.1 and 95.11 m³. Coffee-banana intercropping recorded soil losses ranging from 19.47 to 22.15 t/ha and runoff losses between 70.08 and 90.24 m³. For grazing lands, soil losses ranged from 20.53 to 21.75 t/ha, with runoff losses varying between 76.07 and 95.57 m³. Nutrient losses also varied across cropping systems. Under annual crops, nitrogen losses ranged from 21.23 to 41.53, phosphorus from 0 to 22.89, and potassium from 22.33 to 48.83 kg/ha. In banana cropping systems, nitrogen losses ranged from 10.17 to 32.71, phosphorus from 0 to 16.22, and potassium from 17.7 to 41.31 kg/ha. Coffee-banana systems recorded nitrogen losses between 0 and 40.46, phosphorus between 0 and 25.63, and potassium between 0 and 48.59 kg/ha. For grazing lands, nitrogen losses ranged from 13.37 to 24.4, phosphorus from 0 to 13.07, and potassium from 18.43 to 37.06 kg/ha. The study provides valuable data for sustainable agricultural land management in the Lake