Influence of some perennial grasses on the organic matter content and structure of an eastern Nebraska fine-textured soil

The effects of various perennial grasses on the chemical and physical properties of a fine-textured eastern Nebraska soil were investigated. Measurements of total nitrogen and readily oxidizable organic matter content were made as indicators of soil organic matter content. The percentage of soil aggregates greater than 0.25 mm, the percentage saturation of pore space at a tension of 40 cm of water, and the volume weight were physical measurements used to characterize the soil. There was a highly significant difference in total nitrogen and readily oxidizable organic matter content of the soil under various grass covers for the 0 to 6-inch depth. The differences between grass covers were not significant for the readily oxidizable material at 6 to 12 inches. No distinct differences in total nitrogen content and readily oxidizable material were observed in relation to seasonal growth habits of the several grasses. Blue grama, buffalo grass, bromegrass, blue grass, and orchard grass were grasses maintaining the highest organic matter content. A highly significant difference in the percentage of soil aggregates greater than 0.25 mm diameter was obtained between soils under the various grasses for the 1- to 3-inch depth. The difference was significant at 5 to 7 inches and highly significant at 11 to 13 inches. Side-oats grama, blue grama, bluegrass, and bromegrass were grasses imparting the greatest stability to the soil aggregates. No significant difference between sods was found for measurements of pore-space saturation or volume weight. It is thought that insufficient samples were taken to establish any relationships. The regression coefficient for nitrogen content as related to the percentage of stable aggregates was significant at the 5% level. The regression coefficient for readily oxidizable material compared with stability was highly significant at the 1% level. In all determinations, organic matter content and favorable physical conditions were maintained relatively higher under a grass cover than in an adjoining cultivated field. In comparison with a weedy check plot, the grass-covered plots were nearly all significantly higher in matter content. Grasses apparently differ in their ability to stabilize soil aggregates. This stabilizing ability is correlated with total nitrogen content, or with readily oxidizable material. It is not closely related to the vegetative production of the various grasses. Seemingly it then must be a function of the differential root development of the individual perennial grasses. The results obtained indicate that well-adapted perennial grasses in the cropping systems of fine-textured soils of eastern Nebraska will conserve the organic matter content and may provide increased structural stability to the soil granules. These factors are important items in the long range planning which will provide these soils with adequate protection against erosion and soil fertility depletion.