Nutrient and organic carbon losses by erosion, and their economic and environmental implications in the drylands of Kenya

Abstract

Erosion causes soil nutrients and financial losses, and negatively impacts the environment. We sought to assess the effects of integrated soil fertility and soil & water management practices on nutrient losses, their equivalent economic losses, and environmental disturbance in the drylands of Tharaka-Nithi County. An experiment was set in a randomized complete block design with four replications. Six treatments implemented included manure + fertilizer + tied ridging under 120 kg ha−1 and 30 kg ha−1 nitrogen (N) application rate, manure + fertilizer + minimum tillage with crop residue mulch under 120 N kg ha−1 and 30 N kg ha−1, Managing Beneficial Interactions in Legume Intercrops with 60 N kg ha−1, and conventional control. A two (120 N kg ha−1 and 30 N kg ha−1) by two (Minimum tillage with mulch and tied ridges) split-plot arrangement was used to evaluate the interaction effect of soil fertility, and soil & water conservation practices. Soil & water conservation and soil fertility management practices reduced soil nutrients and organic carbon losses, ecosystem disturbance, and monetary nutrient losses when isolated or integrated. Minimum tillage with mulch had a higher reduction in the nutrient loss by 20–165% compared to tied ridges. The 120 N kg ha−1 reduced nutrient loss by 16–19% more than 30 N kg ha−1. The enrichment ratio (ER) under all the treatments was above unity, which indicated ecosystem disturbance. Minimum tillage with mulch reduced ER more than the tied ridges, whereas 30 N kg ha−1 had lower ER than 120 N kg ha−1. The equivalent monetary losses of nutrients were as high as 30 US$ ha−1for soil organic carbon, 28 US$ ha−1 for nitrogen, 73 US$ ha−1 for phosphorus, and 140 US$ ha−1 for potassium per season. The combined treatment with the least economic losses was manure + fertilizer (120 N kg ha−1) + minimum tillage with mulch. Hence, the technology should be promoted for sustainable agricultural productivity.