Some changes in the soil during natural succession of vegetation after abandonment in western Nebraska

A study was undertaken on cultivated land, native grass land, and land abandoned for various periods of time in Kimball County, Nebraska, for the purpose of discovering the changes that occur in the soil during the process of revegetation. Determinations were made of the rate of infiltration of water in the field and of percolation in the laboratory, the volume-weight, the state of aggregation, and the quantity of plant roots, organic matter, and nitrogen in the soil. The rate of infiltration of water in the field was considerably greater under wheat stubble than under native vegetation. It was relatively low after 1 year of abandonment, but after several years became approximately equal to that of the wheat stubble land. Bare areas in the abandoned land generally had a low infiltration rate. The rate of percolation of water through a 6-inch column of topsoil showed about the same relationships as the infiltration rate. Percolation in the soil from the native grassland and the bare areas of the abandoned land was much slower than in that from the stubble field and the abandoned areas under vegetative cover. The volume-weight and the state of aggregation of the soils were very closely correlated. The volume-weight and the percentage of large aggregates (larger than 0.5 mm) were highest in the soils having the lowest infiltration and percolation rates and were generally lowest in the soils permitting the fastest infiltration and percolation. The root content of the soil of the cultivated fields, determined shortly after wheat harvest, was found to be one-fourth to one-third of that under native grassland vegetation. After several years of abandonment, the root content of the soil was greater than in cultivated fields and was approximately half of that under native grasses. The organic matter and nitrogen content of the soil of cultivated and abandoned fields tended to be lower than in the native grasslands, but the difference was not statistically significant for the number of samples taken. Under the native grasses 7.3% of the soil organic matter in the surface 6 inches and 2.2% of that in the second 6 inches was found to consist of plant roots. Under cultivation or abandonment, the percentage of root material was much smaller.