Assessment of Properties of a Harkey Soil under Organic and Conventional Farming Systems

Farming practices involving less intense chemical use are becoming popular in the United States primarily because of environmental concerns related to the use of chemicals in conventional farming systems. Physical and chemical soil properties were assessed on four farms, one conventional farm and three organic farms 3 (OF3), 6 (OF6), and 9 (OF9) years after certification. All farms were located in Doña Ana County of southern New Mexico, sited on Harkey soil (coarse silty, mixed, calcareous, thermic typic Torrifluvents). OF3, OF6, and OF9 were planted to cotton (Gossypium arboreum L.), chile (Capsicum annuum), and alfalfa (Medicago sativa) in 2006, respectively, and the conventional farm was planted to cotton. Core and bulk soil samples were collected from each farm at three different locations and three depths during September 2005, June 2006, and November 2006. Clay content was positively correlated with field capacity, wilting point, and available water capacity (AWC) and negatively correlated with transmission pore volume (VTP) and sand content at most depths. The one-way analysis of means of soil physical and chemical properties separately by depth showed that bulk density (ρ_b) was greater in November 2006 samples than in September 2005 and June 2006 samples in OF9 and was lowest in the conventional farm. In general, saturated hydraulic conductivity (K_s), volume of storage pores, effective porosity, AWC, and VTP showed little variation and were not related to the amount of time under organic farming. Soil pH and electrical conductivity (EC) were greater in the organic farms, and EC values mostly increased with increasing amount of time under organic farming. The greatest EC (2.6 dS m^?1) in OF9 indicated that 9 years of manure application has raised soil salinity only slightly. Although no evidence on significant improvement of soil quality due to organic farming was observed, with regard to soil storage and transport properties and soil salinity, the organic farming system is sustainable for this region.