The Effect of Surface Mulches on Water Conservation and Forage Production in Some Semidesert Grassland Soils 1

TUDIES of the effects of surface mulches, condition of soil surS face, and different types of plant cover on runoff and soil loss have received considerable attention in various parts of the country during the last few years. The benefits of mulches to infiltration have been demonstrated especially in agricultural lands of the Great Plains, where successful growth of many farm crops depends on conservation of as much as possible of the rather limited rainfall. In recent work in Ohio, Borst and Woodburn3 have analyzed the mechanics of the action of mulches in controlling erosion and determined the relative importance of raindrop impact and overland flow. The pore-clogging effect of rain-dispersed soil particles has been known for some time, although details of just how this action takes place were not fully investigated until recently. Obviously, the approach to this problem differs between soils that are cultivated and those that comprise range lands which are used for grazing. The benefits of natural plant litters have been observed by soil conservation workers and range ecologists. Little work has been done in the past, however, to determine their actual effectiveness in promoting infiltration of water into range-land soils and the part they may play in restoring vegetation in areas which have suffered from poor land use and accelerated erosion. It is fairly clear that a cover of vegetation tends to retard the rate of surface runoff and provides stability against erosion. It is not generally recognized, however, how plants and soils under natural conditions are dependent upon one another to maintain this condition. Stripping the protective cover from the soil apparently brings about other changes than simply removing a mechanical surface and sub-surface obstruction to accelerated runoff and erosion. In most soils (the very sandy and gravelly ones being not so greatly affected), when the surface is laid bare to the influence of torrential rains through lack of permanent cover, it is not long before the natural vegetal litter, mulch, and organic matter disappear. This removes the buffer protection and the soil then seals over so that water penetrates with difficulty, thus giving rise to a more or less permanent droughty condition. Unless this surface condition is changed, it is not surprising that natural revegetation is very slow, even when grazing pressure or other detrimental factors are removed.