A. Name:

Organic Nitrogen Decomposition Study

 B. Goals:

 To determine mineralization rates from organic amendments such as biosolids, composts, and manures one year following application. Knowledge of mineralization rates are key if nitrate pollution of groundwater is to be avoided while assuring sufficient nutrients to optimize crop production. This project will provide CE personnel with information to help regulators develop the TMDL’s (Total Maximum Daily Loads) when required by the Clean Water Act. It will also serve as a basis for suggestion biosolids application rates as required under 40 CFR Part 503.

C. Plan:

This will require a statewide effort. Dr. Crohn will coordinate the project but all workgroup members should be considered as participants. Our study will emphasize decomposition in a great many agricultural environments located throughout the state. All potentially interested workgroup members will be asked to participate.

Our approach as a Workgroup will combine massive scope with procedural simplicity. We will select three products (anaerobically digested biosolids, dried dairy manure, and a green waste compost). These amendments will be partially aerated to remove ammonia nitrogen prior to the mixing with soils. Participants will be asked to send soil samples representative of their area to David Crohn’s laboratory in Riverside where they will be analyzed for initial bulk density as well as total carbon and nitrogen, and then mixed with the organic amendments, and placed into litter bags. (The nitrogen and carbon introduced with the organic amendments will known and recorded.)  The filled bags will be shipped back to the participants who will install them in the field four inches from below the soil surface. Nine bags will be installed at each site, or three of each type of material. These will be collected after one year and returned to Riverside for analysis of total nitrogen and carbon using a Carlo Erba C-N-S analyzer. We anticipate the development of 200 sites for this study for a total of 1800 litter bags. Mineralization rates will be determined by difference. Participants will be asked to describe the climate and irrigation patterns experienced at the study sites for incorporation into a final report.

 This is a very simple protocol conducted over a short time interval. Because of its very ambitious scope, it concentrates funds and labor on issues critical to determining the appropriate use of organic amendments. For example, measuring total nitrogen is much less expensive than estimating organic nitrogen which requires measurement of and subtraction of inorganic nitrogen forms such as ammonium and nitrate. The concentrations of ammonium and nitrate a low in soils relative to the total soil nitrogen pool and may be neglected when studying the behavior of the organic nitrogen pool. This assumption will be tested by random inorganic nitrogen assays.

Upon completion of this study, we will have a solid data base of the mineralization potential of different organic materials under California’s many diverse soil and climatic conditions. A “mineralization potential” map of the state will be prepared from the research results to give guidance to regulators and agronomists. Attention will also be paid to the influence of different soil texture and to the influence of moisture management.

 D. Budget:..