Accelerated Incubation Protocols for Aglime Requirement Calibration.

Soil acidification in the Inland Pacific Northwest (IPNW) is an emerging issue.  Unlike most regions of North America, IPNW agricultural soils have not been calibrated for their pH response to increasing rates of aglime.  Plant nutrient availability and microbial activity are directly related to the pH of the soil. In modern agriculture, annual applications of ammonia-based fertilizers have contributed to the acidification of agricultural soils. Acid conditions can increase the solubility of aluminum and manganese to phytotoxic levels, and decrease the availability of many plant-essential nutrients. The most common method of acid soil remediation is by land application of aglime, pulverized calcitic and dolomitic limestone.  An aglime requirement is generally determined by soil testing that measures the relative quantity of exchangeable acid-forming cations that occupy cation exchange sites and the amount of base-forming cations needed to displace the acidity. Three-month CaCO3 incubation studies are customarily used to calibrate individual soils. Results of incubation studies are then calibrated to existing buffer pH algorithms. In the interest of accelerating the soil incubation and aglime calibration process, we tested four rapid incubation methods: 1) CaCO3 in DI water; 2) CaCO3 in 0.01 M CaCl; 3) Ca(OH)2 in DI water; and 4) Ca(OH)2 in 0.01 M CaCl.  We will present our findings illustrating calibration curves and time requirements to achieve pH plateaus under increasing lime concentrations for representative Palouse Region soils, and relate our findings to those performed under conventional incubation conditions.