Arid soils are naturally low in organic matter. When land is cultivated, soil organic matter content approaches zero. Organic matter, especially the more stable component called humus, is largely responsible for many soil properties affecting soil quality, including soil structure and Cation Exchange Capacity (CEC). Soil structure is important because it affects the flow of air and water into and throughout the soil column. CEC affects water and nutrient holding capacities of the soil.
Soil Testing Includes:
1. Nutrient Content
2. Organic Matter Content
3. Moisture Content
4. Water Infiltration Rates
Plant Tissue Testing Includes: Nitrogen Content
At harvest, yield is be tested.
One reason Arnott Duncan became involved in the program was because of a phosphorus (P) problem. many of his crops were showing signs of P deficiency, however soil tests showed an abundance of P. Chemical fertilizers were not solving the problem, which was fixed P. This is a problem common in many western soils. These soils have high pH, due to high calcium content. The calcium compounds result in P being trapped in the soil matrix and therefore unavailable to plants.
Arnott applied 40 tons per acre (t/a) for the first application. The crops were not showing signs of P deficiency, where before they had. Following the harvest, the follow-up applications were 20 t/a and 40 t/a. In the field where 20 t/a was applied, germination rates were high, plant vigor was high, and no signs of P deficiencies were seen. In the field where 40 t/a was applied, germination rates were low. However, those that survived were vigorous and showed no signs of P deficiency. From this information, it can be inferred that an initial high application of compost with smaller follow-up applications is appropriate.
The application of compost addressed the problem of fixed P. Compost increases microorganism populations in the soil. There are two types of microorganisms that lead to increased available P. There are P-releasing microorganisms which release plant useable P during decomposition. In addition there are microorganisms, such as pseudomonads, that produce acids to solubilize the fixed compounds.
Beginning in spring 1997 a field trial was established at Sycamore Farms. The field trial had three treatments (no compost or control, 10 t/a, and 20 t/a). These three treatments were replicated three times on a 22 acre cotton field. In year one, the following measurements were taken:
1. soil organic matter (prior to compost application)
2. soil nutrient content (prior to compost application)
3. soil cantion exchange capacity (prior to compost application)
4. germination rates
5. nitrogen content of plants (5/28/97 and 7/23/97)
6. plant growth and development, specifically height to node ratio, number of fruiting sites and number of aborted fruits (5/28/97 and 7/23/97)
7. Yield (at harvest)
The soil organic matter content, soil nutrient content, and soil cation exchange capacity will also be sampled at the end of the field trial.