Influence of soil degradation on development of aerial parts and roots of a legume-grass associated pasture

A study was conducted on the effects of two states of soil degradation (E1 more and E2 less) on the establishment of a pasture association of Festuca arundinacea and Mendicago sativa in an Argiudol vertic soil of Argentina. In the surface horizon the characteristics measured were organic carbon, structural instability (S index), apparent density, and mechanical resistance (penetrameter). Evolution of the structural variables of the pasture was studied and at 120 days postseeding, measurements were taken of ground cover represented by weeds and aerial forage phytomass; and in the roots of a sampling of 40 plants of each species, dry weight, length, and diameter. In soil E1 there was a significant reduction in the stand and plant height of alfalfa, whereas the number of fescue bunches increased, but total production of aerial dry matter declined (P<.05). In roots of the 40-test-plant samples there were differences between soils in the morphological characteristics, length, and distribution of diameters. Total root length was highly correlated with the S index and organic carbon content of the soil (r = -0.85, P<.07 and r = 0.75, P<.10, respectively). Apparent density of soil E1 was most closely associated with fescue roots of 2 mm diameter (r = 0.70, P<.15). The latter soil property and resistance to penetration correlated positively with area in weed cover (r = 0.45, P<.05 and r = 0.48, P<.001) in soil E1. Soil condition did affect establishment of the pasture, limiting the development of aerial parts and roots of the constituent species, especially alfalfa, under the most degraded conditions