ORGANIC FARMING RESEARCH FOUNDATION

RESEARCH GRANT APPLICATION

 

THE EFFECTS OF GREEN MANURE, COMPOST, AND FEATHER MEAL ON SOIL NITROGEN DYNAMICS, BENEFICIAL SOIL MICROORGANISMS, AND BELL PEPPER YIELD

 

PRINCIPAL INVESTIGATORS:

 

Mark Gaskell, Farm Advisor University of California Cooperative Extension 624 West Foster Rd. Santa Maria, CA 93455 Tel: (805)‑ 934‑6240 Fax: (805)‑ 934‑6333 E‑mail: mlgaskell@ucdavis.edu

 

Carolee T. Bull, Ph.D., Research Plant Pathologist, USDA‑ARS 1636 E. Alisal St. Salinas, CA 93905 Telephone: (831)755‑2889. Fax: (831)755‑2814. E‑mail: CTBull@aol.com

 

RESEARCH COLLABORATORS:

 

Helmut Klauer, General Manager Nojoqui Farm P.O. Box 327 Buellton, CA 93427 Tel: (805) ‑ 686‑0194 Fax: (805) ‑ 6861254 E‑mail: nojoqui@utech.net

 

Organic Farmer Laison Committee USDA Experiment Station Salinas, CA

 

SUMMARY

 

Green manure cover crops are an important part of an organic soil fertility program that may contribute a significant proportion. of the nitrogen (N) requirements of a succeeding crop. The special nutritional needs of vegetable crops may indicate N uptake needs that do not match the availability of N from a green manure. Early or late market options and other farm management decisions may also restrict green manure use on some organic vegetable farms. Studies have shown that compost and other organic N sources can supplement or replace a green manure for the short‑term N needs of vegetables but the results are variable. More research is needed to develop specific information on rates and timing of compost and organic fertilizers for vegetable production.

 

Organic farmers have relied on cultural practices to build soil tilth and to avoid or suppress soil borne plant pathogens. Biological control of many soil‑born plant pathogens has been achieved by applying bacterial populations that inhibit plant pathogens. Application of larger numbers of purified bacteria may be beneficial as a strategy for conventional producers where the soil microbial community may be altered. In stable microbial communities, this "augmentation" may not be a productive strategy. Cultural conditions may alter the populations of organisms which could potentially inhibit plant pathogens. In this study, we will evaluate the effect of cultural practices on the soil bacterial community. In particular we will test the hypothesis that some cultural methods promote the growth and occurrence of bacterial populations associated with disease suppression.

 

This study proposes to collect critically needed data on soil nitrogen dynamics, soil microbial populations, and vegetable crop yield response following application of different rates of preplant incorporated compost combined with subsequent sidedressing treatments of either compost or feather meal. These treatment variables will be applied as subplots in plots that have or have not had a prior green manure crop. We propose to compare preplant compost applications of 0, 4, and 8 tons per acre and within each of these rates compare subsequent sidedress applications of either compost or feather meal. The data collected in this study will allow us to quantify the effects of green manure alone and in combination with rates of compost or compost plus feather meal equal to 70, 158, and 245 lb. N per acre. The data will also show the effects of substituting compost or compost plus feather meal for a green manure in those situations where a green manure is not part of the production system.

 

PROBLEM

 

Nitrogen Management

 

Cover crops are an economical source of organic nitrogen, which provide additional potential benefits for succeeding crops. The N provided by green manure cover crops has been shown to provide adequate N for subsequent crops in many circumstances but results are variable. The availability of N from a green manure many not coincide with N uptake requirements of certain vegetable crops and crop yield or quality may be adversely affected by short-term N shortages. Because of short‑term nutrient needs of vegetable crops, there may also be benefits of applying compost or other organic fertilizer materials so that N availability more closely matches the needs of the crop. Additionally, time or market constraints and the need to intensively farm high value land may also restrict the use of cover crops on some organic farms and increase the need to utilize compost and other economical organic fertilizer sources.

 

Compost is often the most economical source of pre‑plant applied N fertilizer, but compost is quite variable and little information is available to guide vegetable growers on the most efficient rates and timing for the application of compost (Roe, 1998). Other organic fertilizer sources may be more convenient or efficient than compost for subsequent side dress or fertigation application. Several types of commercially available nitrogen fertilizer materials are approved for organic, certification but little information exists on optimal management of these materials. Previous studies have also shown that of the materials other than compost that are generally available as sources of N in organic production systems, feather meal is one of the more efficient and cost effective (Gaskell and Klauer, 1999.)

 

This study proposes to collect critically needed data on soil nitrogen and vegetable crop response following application of different rates of N application with or without a prior green manure crop incorporation. The different rates of N will be applied as either preplant plus sidedressed compost or preplant compost and subsequent sidedressed feather meal.