Changes in soil physical health indicators of an eroded land as influenced by integrated use of narrow grass strips and mulch

Soil erosion remains a major threat to sustainable use of soil and water resources, and often leads to degradation of soil physical health. An erosion study was conducted on a sloping (7% slope) Rhodic kandiudult land at Ikenne (6° 51'N, 3° 42'E), Nigeria, to assess changes in soil physical health index (SHphy) following integrated use of vetiver grass strips (VGS) and vetiver mulch (VM). The VGS spaced at 10 m (10VGS) and 20 m (20VGS) intervals were integrated with VM of 2 (VM2) and 4 (VM4) t/ha as: 10VGS + VM2, 10VGS + VM4, 20VGS + VM2 and 20VGS + VM4. The four integrated treatments and 10VGS, 20VGS, VM2, VM4, VM6 and no vetiver (NV) were assessed for their effectiveness in reducing soil loss and improving SHphy with NV served as a control. Soil physical health indicators (particle-size distribution, bulk density, water stable aggregates (WSA), mean-weight-diameter, moisture retention, pore-size distribution, saturated hydraulic conductivity, soil strength and soil organic carbon) were determined and integrated to form data set for SHphy, using the soil management assessment framework. The aggregate-associated carbon (Agg-C) in <2000 μm and 2000-1000 μm classes accounted for 55-73% variation in soil organic carbon stock among the treatments. The transmission and storage pores (0.5-300 μm pore size) together constituted 52.5-63.1% of the total pore space with the largest pores obtained under 10VGS + VM4. The mean SHphy varied significantly (p ≤ 0.05) among the treatments, and it was highest for 10VGS + VM4 (0.79) and least for NV (0.49). Changes in SHphy over 3 years ranged from -10.9% to 33.1%. The highest maize grain yield was obtained under 10VGS + VM4 (1.82 t/ha), closely followed by VM6 (1.79 t/ha), and the least yield recorded under NV (0.89 t/ha). Positive and significant relationship (r = 0.93; p < 0.01) was established between SHphy and maize grain yield. However, the significant beneficial of vetiver mulch alone in improving soil physical health was dwarfed by the potential danger of high soil loss beneath the mulch cover in the absence of vegetative strips.