Effects of Excessive Natural Mulch on Development, Yield, and Structure of Native Grassland

Abstract

The authors studied an upland area of True Prairie near Lincoln, undisturbed by mowing, grazing, or burning for 15 yrs. Mapping revealed that Andropogon gerardi, Panicum virgatum, and Sporobolus heterolepis occupied 78, 8, and 9% of the area, respectively, each in nearly pure stands. A natural mulch 4.5-8 in. deep, and weighing 6-9 tons per acre, covered the deep loam soil. It intercepted much precipitation but promoted rapid infiltration and greatly retarded evaporation. It increased the organic matter of the surface soil 1.5-2% and N content 0.1% of its oven-dry wt. Pore space was 61.7% and volume-wt. was 0.97. Soil temps, were decreased 22[degree]-28[degree]F in May and renewal of growth in spring was delayed 3 weeks. Production of flower stalks was considerably later than in unmulched controls and also less in Andropogon. Yields in June, July, and Aug. were 53, 26, and 29% less than those from unmulched stands of Andropogon. and 57, 55, and 26% le.ss in Panicum. Consequences of the effects of the mulch upon the environment were the production of a nearly pure, but thinner than normal, stand of Andropogon. The understory of low-growing plants had disappeared, mid grasses were few or none, and only the taller forbs remained. Forbs under Panicum were those characteristic of very moist sites. Between the large bunches of Sporobolus the deeply mulched soil was usually free of vegetation.