Compost Analyses

The Dairy Compost Utilization Project helped the dairy compost producers become members in the Seal of Testing Assurance (STA) Program. Compost facilities in the STA Program must follow a regular testing schedule and utilize laboratories in the STA Program for compost analysis.

Texas Cooperative Extension and Texas Water Resources Institute also worked with the dairy compost facilities to ensure the facilities produced a high quality consistent composted product.

To analyze the material, dairy compost samples were submitted to the Soil, Water and Forage Testing Laboratory at Texas A&M University (Non-STA Laboratory) and to Soil Control Laboratory in Watsonville, CA (STA Laboratory) throughout the project. Laboratory analysis is provided below. The samples analyzed by the Soil, Water and Forage Testing Laboratory were collected in 2003. The samples analyzed by the Soil Control Laboratory were collected in 2005.

Dairy manure compost analysis - Non-STA Laboratory (2003)
Dairy manure compost analysis - STA Laboratory (2005)

Compost Standards

The Texas Department of Transportation (TxDOT) demonstrated that by adding organic matter in the form of compost, poor soils can be amended, revegetation can occur, erosion can be avoided, and time and money can be saved. In FY 2002, TxDOT specified over 300,000 cubic yards of compost and continues to utilize composted material on Texas roadsides.

Compost facilities supplying compost to TxDOT must meet the following criteria:

• All compost must be Seal of Testing Assurance (STA) certified.
• Producers must present a STA certified lab analysis proving that their compost has met the physical requirements listed below.
• More information on compost use by TxDOT is found in the TxDOT 2004 Specifications Book. Specifically, Special Specification 1001 addresses compost quality, type and its use.

Improving Dairy Compost

Modification of Low Quality Dairy Manure Compost with Organic Amendments

Abstract: Composts produced with dairy manure from that area tend to contain high levels of inorganic components (50 to 75%, mainly quartz sand and limestone fragments) and often fail to meet the pH and organic matter standards set by TX DOT and other users. Addition of high carbon amendments to finished composts is being employed as a means to adjust these parameters to meet the TxDOT standards. Four “low quality” compost products were amended with three high carbon by-products (peanut hulls, sawdust and wood chips) by physically mixing the amendments (10% and 30% v/v basis) with the composts.

TMECC have been adopted as the industry standards for compost testing but due to strict QA/QC requirements, analytical costs tend to be relatively high. Service laboratories that do not use TMECC or are not STA certified often offer “analytical packages” for lower costs. A comparison of compost test results provided by Soil Control Laboratory (an STA certified laboratory) and the Texas Cooperative Extension Soil, Water Forage Testing Laboratory (a service laboratory) showed that values for selected nutrients (total N, P, Ca, and Na), pH and soluble salts varied significantly between the two laboratories but there were no differences in organic matter levels.

Results: The full report presents the methodology, data and analysis of this compost improvement study.