Deforestation and land-use effects on soil degradation and rehabilitation in western Nigeria. I. Soil physical and hydrological properties

摘要: Assessments of the effects deforestation, post-clearance tillage methods and farming systems treatments on soil properties were made from 1978 through 1987 agricultural watersheds near Ibadan, southwestern Nigeria. These experiments conducted in two phases: Phase I 1981 II 1983 to 1987, with 1 year (1982) as a transition phase when all plots sown mucuna (Mucuna utilis). There six involving combinations land clearing methods: (1) manual no-till (MC-NT); (2) plough-till (MC-PT); (3) shear-blade (SB-NT); (4) tree-pusher/root rake (TP-NT); (5) tree-pusher/root-rake (TP-PT); (6) traditional (TF). The replicated twice completely randomized design. treatment was discontinued during II. five studied system were: alley cropping Leucaena leucocephala established contour at 4-m intervals; fallowing Mucuna utilis severely degraded moderately watersheds, respectively, for followed by maize-cowpea rotation another; ley establishment pasture first plots, controlled grazing second year, growing maize (Zea mays)-cowpea (Vigna unguiculata) third year. All treatments, imposed 2–4 ha each, twice. analyzed particle size distribution, total aggregation mean weight diameter aggregates, bulk density, penetrometer resistance, water retention characteristics, infiltration capacity saturated hydraulic conductivity. measured under forest cover 1978, once every dry season thereafter Phases Prior density 0·72 Mg m−3 1·30 m−3, penetration resistance 32·4 KPa 90·7 KPa, aggregates 3·7 mm 3·2 0–5 cm 5–10 depths, respectively. rate excessive (54–334 hr−1) conductivity rapid (166–499 cover. Furthermore, transmission varied significantly even over short distances about m. Deforestation cultivation increased but decreased aggregates. One after deforestation 1980, 1·41 depth 1·58 depth. Soil generally higher NT than PT methods, extremely high 1985. During II, cycle treatment. Sand content clay duration. Soon equilibrium cleared cultivated declined only 20–30 per cent that forest. Mean following 46·0 hr−1 53·7 Further, duration treatments. I, 115·8 20·9 1979, 17·4 1980 1981. 8·5 1982, 11·9 1983, 11·0 1984, 11·3 1985 5·3 1986. Infiltration Natural drastically improved 19·2 1982 193·2 1986, ten-fold increase within 5 years fallowing. High-energy characteristics affected those caused compaction mechanized systems. 0·01 MPa potential 1979 (gravimetrics) SB, 17·9 TP, 15·9 MC 17·8 TF methods. With regards tillage, compared 16·8 PT. not (average 4 years' data 1986) 16·6 cropping, 16·7 farming. 1·5 suction 9·3 8·7 fallowing, Water correlated organic carbon content.