Predictors of short-term nitrogen availability in organic farming systems that utilize warm season cover crops

Project Overview

Project Type: Graduate Student
Funds awarded in 2010: $10,000.00
Projected End Date: 12/31/2013
Grant Recipient: North Carolina State University
Region: Southern
State: North Carolina
Graduate Student:
Major Professor:
Dr. Nancy Creamer
North Carolina State University

Annual Reports


  • Agronomic: buckwheat, millet, peas (field, cowpeas), sorghum sudangrass


  • Crop Production: cover crops, crop rotation, organic fertilizers, tissue analysis
  • Natural Resources/Environment: carbon sequestration
  • Soil Management: green manures, nutrient mineralization, organic matter, soil analysis, soil chemistry, soil quality/health


    Both plant tissue quality and environmental conditions appeared to effect short-term N mineralization. All warm-season cover crops evaluated (C:N from 15-57:1) had net N mineralization during an incubation study. Legume-dominated crops had greater potential than grass cover crops. The incorporation of cover crop residues stimulated an increase of soil microbial biomass nitrogen as well as cellulase enzyme activity. The conservation of inorganic soil N in soils that supported cover crops compared to bare-ground controls was indicated. Selected cover crop residue qualities and the free, particulate organic matter (F-POM) C:N ratio were able to distinguish between legume-dominated and grass cover crops.


    Cover crops are utilized in many types of farming systems and multiple benefits have been attributed to them, including: decreased soil erosion, improved soil and water quality, weed suppression, nutrient contributions and recycling, pest and disease management, pollinator attraction, fertilizer input cost savings, and carbon sequestration (Hartwig and Ammon 2002; Janzen and Schaalje 1992; Lal et al. 1991; Shepard et al. 2002). Organic farmers in particular, rely on cover cropping (i.e., green manures) as a nitrogen (N) source for subsequent cash crops. Cover cropping itself is a highly encouraged practice under the USDA National Organic Program (NOP) which helps meet other requirements such as prohibition of synthetic inputs, crop rotation and the continual pursuit to improve overall soil quality (7 C.F.R. § 205.203 (rev. 2013)).

    One of the most challenging cover crop related issues is estimating the total plant available N and synchronizing N release with a subsequent cash crop from decomposing residues. The difficulty in estimation is due to the many variables that affect decomposition rates and N mineralization such as: residue quality, edaphic soil properties, environmental conditions, biological activity, and farm management activities (Baggie et al. 2004; Cambardella and Elliott 1993; Goh and Tutuna 2004; Johnson et al. 2007; Robertson and Groffman 2007). Improving our ability to predict N availability from cover crop residues requires further understanding of the interactions between biotic and abiotic variables as well as identifying measurable parameters that can reflect and/or predict N cycling in the soil. This knowledge will assist agricultural professionals in becoming more efficient nutrient managers by adopting and tailoring cover crop management practices to meet farm goals and environmental conditions.


    Baggie, I., D.L. Rowell, J.S. Robinson and G.P. Warren. 2004. Decomposition and phosphorus release from organic residues as affected by residue quality and added inorganic phosphorus. Agrofor. Sys. 63:125-131.

    Cambardella, C.A. and E.T. Elliott. 1993. Carbon and nitrogen mineralization in aggregates from cultivated and native grassland soils. Soil Sci. Soc. Am. J. 57:1071-1076.

    Goh, K.M. and S.S. Tutuna. 2004. Effects of organic and plant residue quality and orchard management practices on decomposition rates of residues. Commun. Soil Sci. Plant Anal. 35:441-460.

    Hartwig, N.L. and H.U. Ammon. 2002. Cover crops and living mulches. Weed Science. 50(6):688-699.

    Janzen H.H. and G.B. Schaalje 1992. Barley response to nitrogen and non-nutritional benefits of legume green manure. Plant Soil 142:19–30.

    Johnson, J. M-F., N.W. Barbour and S.L. Weyers. 2007. Chemical composition of crop biomass impacts its decomposition. Soil Sci. Soc. Am. J. 71(1):155-162.

    Lal. R.E., D.J. Eckert, W.M. Edwards and R. Hammond. 1991. Expectations of cover crops for sustainable agriculture. In: Cover crops for clean water. W.L.Hargrove (ed.). SWCW, Ankeny, IA, 15-21.

    Robertson, G. P. and P.M. Groffman. 2007. Nitrogen transformations. In: Soil Microbiology, Ecology, and Biochemistry (3rd Ed.). Elsevier Inc., Oxford, UK. p. 341-364.

    Shepherd M.A., R. Harrison and J. Webb. 2002. Managing soil organic matter implications for soil structure on organic farms. Soil Use & Mang. 18:284–292.

    Project objectives:

    1. Evaluate differences in short-term C and N mineralization among a selection of popular warm-season cover crops after soil incorporation

      Assess the utility of plant root simulator (PRS) probes as an in-situ indicator of inorganic soil N availability

      Explore whether free, particulate organic matter (F-POM) can serve as an indicator of short-term N mineralization

      Examine microbial biomass N and selected soil enzyme activities following incorporation of warm-season cover crops

      Evaluate whether soil enzyme activities are related to potential C and N mineralization

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.