Deforestation and land-use effects on soil degradation and rehabilitation in western Nigeria. III. Runoff, soil erosion and nutrient loss

Abstract

Runoff and soil erosion were measured in a two‐phase experiment for seven consecutive years from 1979 through 1986 on a 44·3 watershed comprising 12 sub‐watersheds of 2–4 ha each. These experiments were conducted at Ibadan, Nigeria, which is characterized by two growing seasons per year. The first season lasts from mid‐March through mid‐July, and the second season from mid‐August to early November. Experiments were conducted in two phases comprising different treatments. The six treatments during Phase I (1979–1981), involving different combinations of land clearing and tillage methods, were: (1) manual clearing (MC) with plough‐till (PT); (2) MC with no till (NT); (3) shear‐blade (SB) clearing with NT; (4) tree‐pusher (TP) clearing with PT; (5) TP clearing with NT; (6) traditional clearing and farming (TF). The five farming‐system treatments during Phase II (1982–1987) were: (A) alley cropping with Leucaena leucocephala planted on the contour at 4 m intervals, (B) fallowing with mucuna (Mucuna utilis) on severely degraded soils; (C) fallowing with mucuna on moderately degraded soils; (D) ley farming on severely degraded soils; (E) ley farming on moderately degraded soils. The traditional farming treatment of Phase I was discontinued in 1982 at the beginning of Phase II and the land was returned to natural fallowing. Runoff, soil erosion, and nutrient losses in runoff were monitored using a 4·5 feet H‐Flume, FW‐1 waterstage recorder and Coshocton Wheel sampler. From the mean annual rainfall of 1320 mm, mean annual runoff amounts for the 3‐year period from 1979 through 1981 during Phase I were 5·6 mm (0·42 per cent of rainfall) for MC‐NT, 5·7 mm (0·43 per cent) for TF, 43·2 mm (3·27 per cent) for SB‐NT, 43·5 mm (3·30 per cent) for MC‐PT, 68·3 mm (5·17 per cent) for TP‐NT, and. 113·1 mm (8·57 per cent) for TP‐PT treatments. Runoff losses were consistently more during the first compared with the second growing season. Trends in soil erosion were similar to those of runoff, and annual soil erosion amounts were 0·1 Mg ha−1 for MC‐NT, 0·2 Mg ha−1 for TF, 1·5 Mg ha−1 for SB‐NT, 3·6 Mg ha−1 for MC‐PT, 5·1 Mg ha−1 for TP‐NT, and 8·3 Mg ha−1 for TP‐PT treatments. Measurements made during Phase II showed that there were no significant differences in runoff or soil erosion among the restorative farming systems adopted. Nutrient concentrations in runoff and nutrient loss were generally high in uncropped treatments, e.g. mucuna fallow during the fallowing phase and ley farming during the grazing phase.

The Exotic Legume Tree Species Acacia holosericea Alters Microbial Soil Functionalities and the Structure of the Arbuscular Mycorrhizal Community

“…Degraded soils are characterized by loss or disturbance of the vegetation cover, increased soil erosion, decreased in-water infiltration, loss of available nutrients and organic matter, loss of microbial propagules, and/or diminution in microbial activity (25,35,44). Restoration of ecosystem health and productivity was traditionally achieved via abandonment of land and subsequent natural forest succession.…”

Soil Organic Carbon in Alley Cropping Systems: A Meta-Analysis

“…Salicaceae species are fast-growing tree species cultivated for biomass feedstock for bioenergy production [47]. In general, Fabaceae trees are used when the purpose of alley cropping is soil improvement and regeneration [13,48,49]. Juglandaceae trees are grown to diversify agricultural production and, at the same time, reduce further degradation of soil.…”

“…For example, in only 11 years, the SOC doubled in alley cropping systems compared to sole cropping systems on poor soil in Southern Malawi [34]. Introducing alley cropping on degraded soils positively affects soil chemical and physical properties while also reducing risks of runoff and soil erosion [13,48,49]. The Fabaceae family has a beneficial effect on microbial biomass and SOC [45,60].…”

Soil erosion and sediment transport in Tanzania: Part I – sediment source tracing in three neighbouring river catchments

“…Third, overgrazing in the region prohibits natural vegetation recovery, leading to a higher vulnerability to soil erosion and runoff generation (Hein, 2006). Finally, the high contribution of 'open rangelands' could also be partly explained by their clearance for conversion into 'maize croplands', wherein land clearance increases erosion and thereby also the contribution of soil from the cleared land use to the sediment (Lal, 1996). The high contribution of 'maize croplands' is also not surprising given its high vulnerability to soil erosion.…”