AMELIORATION OF SOIL PHYSICAL PROPERTIES BY MUCUNA AFTER MECHANIZED LAND CLEARING OF A TROPICAL RAIN FOREST

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Abstract
We studied the effect of mucuna (Mucuna utilis) cover on the physical properties of an Oxic paleustalf in western Nigeria, previously cleared by four different methods. The methods used were manual clearing and clearing with a shearblade, a tree-pusher, and a treepusher/root rake. The soil physical properties measured total porosity, penetrometer resistance, infiltration, and soil water retention. In contrast to cropping, mucuna cover improved soil porosity, penetrometer resistance, and hydraulic properties in all treatments. Total porosity of the 0- to 100-mm depth increased with mucuna cover from 0.55 to 0.59, 0.54 to 0.57, and 0.57 to 0.59 m3 m-3 in the manual, shearblade, and treepusher clearing treatments, respectively. Porosity of the treepusher/root rake clearing method was unaffected by mucuna cover. Penetrometer resistance of the 50- to 70-mm depth decreased with mucuna from 426 to 409, 425 to 418, 436 to 398, and 412 to 403 kPa in the manual, shearblade, treepusher and treepusher/root rake methods, respectively. Cumulative infiltration amounts over 3 h of the plots sown to mucuna were 134.1, 55.2, 14.6, and 186.8% greater than the corresponding cropped plots for the manual, shearblade, treepusher, and treepusher/root rake treatments, respectively. Similar decreases were noted in soil water retention at a potential of 0 kPa. The beneficial effects of mucuna cover were greater in manually cleared and treepusher-cleared plots. It was indicated that where land clearing causes high soil compaction, mucuna cover for about 1 yr would be a useful practice to restore soil physical properties to favorable levels for arable farming.