Resilience of Nitrogen Availability and Retention in Soils of Kentucky Certified Organic Farms

Project Overview

GS00-003
Project Type: Graduate Student
Funds awarded in 2000: $6,900.00
Projected End Date: 12/31/2003
Region: Southern
State: Kentucky
Graduate Student:
Major Professor:
Mark Coyne
University of Kentucky

Annual Reports

Commodities

  • Agronomic: grass (misc. perennial), hay
  • Vegetables: beans
  • Additional Plants: herbs

Practices

  • Animal Production: feed/forage
  • Crop Production: cover crops, fallow, no-till, nutrient cycling, organic fertilizers, conservation tillage
  • Education and Training: on-farm/ranch research
  • Farm Business Management: new enterprise development
  • Natural Resources/Environment: indicators, soil stabilization
  • Production Systems: holistic management
  • Soil Management: green manures, organic matter, soil analysis, nutrient mineralization, soil quality/health
  • Sustainable Communities: new business opportunities

    Abstract:

    Organic farm management requires soil building practices such as cover cropping and does not allow chemical fertilizers. Enhanced soil biological activity is a goal of many organic farmers. The ability of three organically managed soils to resist change in or to recover biological functions after perturbation (soil resilience) was related to properties affected by management. Managing nitrogen (N) in organic farm systems is challenging. Partitioning of N among various forms was quantified. Because organic farmers’ soil management practices are directed by knowledge and beliefs about soil, Kentucky organic farmers were interviewed.

    Undisturbed soils on two organic farms had higher soil quality than cropped soils on those farms, as measured by organic matter content, light fraction organic matter, and selected physical properties. Cropped and undisturbed soils were similar in resilience to perturbation for soil enzymes measured. Organically cropped soils on a research farm did not differ in soil quality characteristics or resilience from undisturbed soil on that farm.
    Cropped soils had more N in mineral forms at all times than undisturbed soils, but undisturbed soil had more potentially mineralizable N. Added N was not fully assimilated into organic forms over a brief incubation in any soil. Gross N-mineralization rates were similar for cropped and undisturbed soils over a 6-d incubation. If N-retention is a goal, management attention should be paid to light fraction organic matter, a strong sink for N.
    Organic farmers are likely to concentrate on building soil organic matter rather than on managing N. They do not consider N-loss a problem. Organic matter is difficult to increase because most organic management practices are land- and labor-intensive. Attention to N-management as well as organic matter could benefit organic farms. The land grant university could best help organic farmers by encouraging the creation of markets and infrastructure appropriate to organic farming.

    Introduction

    This project investigated soils under certified organic management. Organic management practices such as cover cropping, compost or manure usage, and intensive mechanical weed control can affect some soil characteristics (e.g. cation exchange capacity, water-holding capacity, microbial diversity and activity, and pH) that influence soil biological behavior.

    Soil resilience, the ability of the soils to resist change or to recover biological functioning after environmental disturbance, was related to properties affected by management. Soil resilience is an aspect of soil quality, in that soils of “higher” quality are expected to display more resilient behavior and to be less susceptible to permanent degradation. Long-term organic management may increase soil resilience. The measurement of soil resilience is challenging; a widely agreed-upon dataset or protocol for describing soil resilience does not yet exist.

    Partitioning of N among various forms in soil was quantified and related to properties affected by management. The relationship of organic farm practices to N is a particular concern because of the necessity of N for crop production, its instability and easy loss from soil, and its expense and possible off-site environmental impacts. The main difficulty in managing N organically is to match temporal N availability and crop demand. The complementary processes of N mineralization and immobilization are key soil functions; adding active organic matter, as occurs in organic farming, may change mineralization and immobilization rates.

    The project focused on describing soils in certified organic management systems, rather than comparing organically managed soils to conventionally managed soils. Because undisturbed natural soils, such as those under forest or grassland, generally have higher SOM and microbial activity than cultivated soils, comparisons were drawn between cultivated organic farm soils and undisturbed soils on the same farms.

    The lack of basic research in certified organic agriculture means that perceptions about organic N-management practices may or may not be supported by data. Farm decisions are often made on the basis of personal observation, personal belief, and consultation with other farmers. Kentucky organic farmers’ typical N-management practices, the information on which they base their decisions, and the reasons why they believe their practices are effective and beneficial were investigated. The object was to identify areas for research and extension helpful for organic farmers.

    Project objectives:

    Describe organic practices used on two organic Kentucky farms, plus the Kentucky State University (KSU) research farm.

    Investigate N-transformations in these soils.

    Quantify the ability of the soils to recover N-transforming functions after disturbance, relating results to fundamental soil properties.

    Describe common N-management practices used by Kentucky certified organic farmers and describe the beliefs and knowledge supporting management choices.

    Identify research and extension topics that would benefit organic farms.

    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.