Wednesday, November 15, 2006

Profile Distribution of Soil Moisture, Electrical Conductivity, and Soil Temperature under Various Organic-Farming Treatments.

Phillip P. Defoe and K. Kpomblekou-A. Tuskegee University, 210 Campbell Hall, Tuskegee, AL 36088

Over the past decade, sales of organic produce have shown an annual increase of at least 20%. Organic farming is the fastest growing sector of agriculture. In 2005, retail sales of organic food and beverages were approximately $12.8 billion. Advances in data monitoring and network communications enabled us to successfully monitor profile distribution of soil moisture, electrical conductivity and soil temperature on a continuous basis. Soil temperature affects plant growth indirectly by affecting water and nutrient uptake as well as root growth, while soil moisture and electrical conductivity affect inorganic plant nutrient solubility and availability. An organic farming research plot was instrumented at the George Washington Carver Agricultural Experimental Station, at Tuskegee University. The experimental design was a randomized complete block design consisting of four replications and four treatments (broiler litter, NPK, crimson clover, and control-no fertilizer). Time-Domain Reflectometry (TDR) probes in a 3-rod design were installed horizontally at 30, 60, and 90 cm depths.  The TDR probes recorded soil volumetric water content and electrical conductivity. A change in volumetric water content of the medium surrounding the probe causes a change in the dielectric constant.  This change seen as probe impedance affects the shape of the reflection which contains information used to determine water content. Four EnviroSMART (Sentek, Inc.) probes with sensors attached at different depths were also installed for measurement of water content profile distribution between 10 and 200 cm depth. The TDR and the EnviroSMART probes were connected to a CR23X micrologger (Campbell Scientific, Inc.). A wireless connection to the station enabled data retrieval using a cellular phone. The volumetric water content of the control plot during the growing season was low (<0.4%) while the EC increased (0–0.6 dsm-1) with increasing depths except in the control plot.