The samples can be air dried prior to sending them or they can be sent in a moist condition. Do not oven dry samples or expose them to extremely hot conditions. Keep samples in the shade or in a cooler with ice to prevent heat buildup if conditions are hot and dry. Western Colorado soils tend to be calcareous, which means that they contain residual or free lime (lime as small particles in the soil). The testing process should use lab procedures designed for these high lime type soils.
In Colorado, the analysis of soil samples should use ammonium bicarbonate-DPTA (AB-DTPA) to extract soil for analysis. AB-DTPA is a multi-use extractant for nitrate, phosphorus, potassium, and micronutrients and is used primarily by the Soil, Water, and Plant Testing Laboratory at Colorado State University. Other processes can be used to determine the nutrient levels in soils, however these are appropriate for more acidic pH levels. The AB-DPTA analysis provides the best results for high pH (alkaline) soils.
Western Colorado’s river valley soils typically have a pH of 7.5 to 8.5, a basic alkaline condition. Although soil pH can sometimes be reduced by using acidifying agents, such as elemental sulfur or sulfuric acid, Western Colorado soils are highly buffered with free lime (calcium carbonate). If sulfur is added to the soil, it combines with water and oxygen through bacterial activity, producing sulfuric acid. The sulfuric acid will neutralize calcium carbonate to produce water, carbon dioxide and calcium sulfate and, instead of changing the pH when this reaction occurs, salt levels may increase, due to the increase in concentration of the salt gypsum (calcium sulfate). “Alkaline” is not the same as “alkali.” “Alkali” refers to sodium salts, while “alkaline” refers to pH. Very few areas in Western Colorado have problems with sodium salt; our salts area typically calcium-based.
For more information on soil testing and specific recommendations for the area, contact your local Extension Office or the CSU Soil, Water, and Plant Testing Lab at 970-491-5061.