Effect of Fertilizer and Brush Control on Soil Fertility

Abstract

Seven years after herbicide application was applied to reduce woody vegetation and increase native grass, there was no change in total available soil N03-N, P, and K in the surface 15 cm. However, the area of native grass conversion had more soil K in the surface 5 cm and a higher pH in the surface 15 cm than the area supporting woody vegetation. Brush control followed by seeding of tall fescue (Festuca arundinacea) and annual fertilization with N, P, and K increased total available soil P and K in the surface 15 cm. Most of the P increase was in the surface 5 cm. Fertilizer applied to areas seeded to fescue appeared to reduce soil pH from that of native grass conversion. Eastern Oklahoma has several million hectares of rangeland presently dominated by woody vegetation. Over the past 30 years some of these lands have been cleared of brush by herbicide and mechanical means to increase grass production. McMurphy et al. (1976) described a method of converting such land to a tall fescue Festuca arundinacea) pasture through aerial herbicides, controlled burning and aerial seeding with fertilization. The objective of this study was to evaluate some of these fertilizer and herbicide effects upon soil fertility. Study Area and Methods The study site was near Lamar in eastern Hughes County, Okla., at the western edge of the Ouachita Highland resource area. The mean annual precipitation is approximately 105 cm and reasonably well distributed throughout the year with only the month of January receiving less than 5 cm. The soils are of the HectorHartsells association (Lithic Dystrochrepts and Typic Hapludults). The stony outcrops, low water holding capacity, and 5 to 30 percent slopes place it in Capability Class VII as a Shallow Savannah range site. The dominate overstory vegetation is blackjack oak (Quercus marilandica) and post oak (Q. stellata). Understory woody species are winged elm (Ulmus alata), hickory (Carya spp.), and tree huckleberry (Vaccinium arboreum). The major grasses are broomsedge (Andropogon virginicus) and little bluestem (Schizachyrium scoparium).