Effects of Nitrogen Fertilization and Grass Species on Soil Physical Condition in Some Tropical Pastures

Abstract

The effect of intensive grazing on compaction of Catalina clay and of Santa Isabel silty clay loam as influenced by four grass species and the rate of nitrogen fertilization was determined. Although both soils were compacted to some extent by grazing animals, the effect was not important and did not extend below the surface 3-inch layer. Nitrogen fertilization reduced surface-soil compaction in Catalina clay under Pangola, Para, and Napier grasses, but not under Guinea grass, and resulted in increased percolation rates and volume of large pores in the 3-6-inch soil layer with all four grasses. Surface-soil compaction by livestock was apparently less with Pangola grass than with Guinea or Napier. However, animal traffic is concentrated on the bare soil between clumps of the latter two grasses where the soil cores must be taken, and the untrampled surface under the clumps would have a compensating effect. Soil compaction by trampling does not appear to be a serious problem with well-fertilized pastures on the typical latosols of Puerto Rico's mountains, even at high stocking rates and with clump grasses.