Some physical and chemical properties of soil in organic and conventional farms for a semi-arid ecosystem of New Mexico

Farming practices involving less intense chemical use are becoming popular in the U.S. primarily due to the environmental concerns related to the use of chemicals in conventional farming systems. This study was undertaken to: (1) evaluate the effect of organic farming on soil physical and chemical properties in three organic farms, and (2) contrast them to that of a nearby conventional farm. Four farms located in Anthony, Dona Ana County of southern New Mexico, were selected for this study. Dominant soil was of Harkey series (coarse-silty, mixed, calcareous, thermic typic Torrifluvents). Three of the farms were under organic farming system for three (OF3), six (OF6), and nine (OF9) years, and the fourth was under a conventional farming system. Core and bulk soil samples were collected in triplicate at each of the 0-10, 10-20, and 20-30 cm depths from all farms during September 2005. Soil properties measured include: soil bulk density (pb), particle size classification, saturated hydraulic conductivity (Ks), soil moisture characteristics, effective porosity (6e), available water capacity (AWC), volume of transmission (VTP) and storage pores (VSP), pH, electrical conductivity (EC), total carbon (TC) concentration, ammonium-N, and nitrate-N. The analysis on interdependence of soil properties showed that EC and nitrate-N were positively correlated (r2 = 0.82). A significant negative correlation was obtained among pb and VSP (r2 = -0.45) and pb and AWC (r2 = -0.41), and a positive among 6 at 6 kpa, and AWC (r2 = 0.90) and VSP (r2 = 0.88), respectively. In general, sand content did not vary among organic farms at any of the three depths but clay content varied as OF3 OF6 OF9 at 0-10 and 10-20 cm depths. The VTP decreased and soil pH and EC increased with increasing amount of time under organic farming primarily at 10-20 and 20-30 cm depths. Inorganic-N was higher in organic than conventional farm indicating a greater yield potential of organic farms. However, no differences in AWC and VSP among organic and conventional farm showed the negative influence of tillage on soil water storage. Soil water storage is important for crop growth and yield and due to the low rainfall and deficit irrigation practiced in the arid ecosystem of southern New Mexico; management practice involving less tillage could enhance the soil water-holding capacity.