Soils and soil parameters, such as nutrient levels, can vary within a field and from field to field. These variables can affect a wide range of management decisions. Western Colorado soils can include heavy clay to well-drained sandy soils encompassing many characteristics including being shallow or deep, deficient or adequate in organic matter content, or high in salts–to name a few.
Soils in river valleys and surrounding areas of Western Colorado were formed by sandstone from the Uncompahgre uplift, volcanic rock, and deposits left by the Mancos Sea, a prehistoric inland sea. The Mancos Sea advanced and retreated 29 times, laying down layers of salty soil each time, which compressed into Mancos Shale. When the sea finally withdrew from the area, deposits were as deep as two miles thick. Volcanic flows later capped parts of these salty deposits.
Mancos Shale decomposes into very productive soil with a high capacity to hold water and plant nutrients. By managing the area’s long growing season (up to 188 days) and utilizing highly-developed irrigation systems, the river valley can be excellent for crop production.
A soil testing program helps to manage the land and helps to answer the following questions:
- Are soil nutrients deficient or excessive?
- Which crop fertilizer program is best?
- Does the soil have a salinity problem, and what effect will the salt have on the crop?
- What is the pH and organic matter level, and can it be adjusted?
Annual field sampling and testing is recommended for accurate crop and nutrient management. Obtaining a representative soil sample from the planting area is critical for accurate results. To begin, divide the area into sites that are similar in soil type, slope, or other characteristics. For collection, use clean equipment, free of soil particles and rust. Collect 15-20 samples from the top eight to 12 inches of soil in a random or systematic pattern. You can do this in up to 40 acres of land. Mix the samples from a single sample area in a plastic bucket. Collect about two cups of the mixed sample to submit to the laboratory for analysis. Nitrogen recommendations for irrigated crops, should include subsoil samples (12 to 24 inches) as well as surface samples to account for the available nitrogen throughout the root zone.