Effect of Mesquite on Physical and Chemical Properties of the Soil

Abstract

Highlight: Soil under the crown of mesquite trees was compared to soil from adjacent openings at three depths for several physical and chemical properties near Tucson, Ariz. Bulk density was lower in soil under mesquite but increased with depth in that location. Organic matter, total nitrogen, total sulfur, and total soluble salts were up to three times greater in the surface 0 to 4.5 cm of mesquite soil than in open soil but declined with increasing depth to levels approximately the same as in open soil. Total potassium was higher under mesquite but increased with depth. Total phosphorus and hydrogen ion concentrations were the same in soil under mesquite as in soil from open areas. Results suggest that mesquite trees function to improve soil conditions under their canopies by redistribution of nutrient ions from areas beyond the canopy to areas beneath the canopy. This process helps to explain the greater abundance and improved growth of perennial grasses observed under mesquite. It also helps to explain grazing patterns and responses on desert grassland. Mesquite (Prosopis juliflora (Swartz.) DC.) is a native, deciduous, leguminous tree that has invaded vast areas of desert grassland range in the southwestern United States since the early 1900’s. Because of a lateral root system that spreads to distances of 10 m or more (Kearney and Peebles, 1960), mesquite competes with perennial grasses for moisture in natural openings. This results in reduced forage production and increased soil erosion. Effectiveness of mesquite in extraction of soil moisture and in competition with perennial grasses was demonstrated by Parker and Martin (1952). They found significant increases in moisture content of the upper 45 cm of soil at distances of 3, 6 and 10 m from killed mesquite trees compared with live trees. Also, soil moisture was available for a longer period of time where mesquite trees were killed than where they were alive. In comparison of surface soil properties between native desert grassland and invading mesquite stands, Paulsen (1950) found that native grassland soil had a more favorable physical regime and a higher nutrient capital than soil from the mesquite stands. However, an aspect of competition between mesquite trees and perennial grasses that has not been examined is the role of mesquite in altering physical and chemical properties of the