Resilience of Nitrogen Availability and Retention in Soils of Kentucky Certified Organic Farms
Certified organic farms use production methods to build soil organic matter (SOM) and microbial activity. Soils so managed may retain nitrogen (N) in organic and inorganic forms, releasing N to plants over long periods with little N loss to leaching or volatilization. These soils may also be quite resilient; that is, they may be able to recover biological functioning quickly and completely after environmental disturbances such as drought, flood, or heavy nutrient inputs.
1.) Quantify the ability of cropped vs undisturbed woodlot soils of two certified organic Kentucky farms to retain N in organic, microbial, and inorganic forms and to release N in mineralized forms to plants. Relate N-cycling in the soils to soil parameters that may respond to farming practices intended to build and retain soil organic matter. Repeat the objective for soils in a replicated vegetable production trial at the Kentucky State University research farm.
2.) Quantify the ability of these soils to regain their N-retention and transformation functions after environmental perturbation. Relate soil resilience to soil parameters that may respond to farming practices intended to build and retain soil organic matter.
Samples will be collected throughout the year after large additions of nitrogenous or carbonaceous matter. Soil total carbon (C) and N, microbial C and N, potentially mineralizable N, and mineralized N will be measured. Nitrate and ammonium movement below 30 cm will be measured in the field by ion-exchange resins. In a greenhouse study, soils will be perturbed by drought, flood, and heavy N application. Soil processes mentioned above will be measured at intervals to determine the rate and extent of the soils’ recovery from perturbation. Soil processes will be related to soil properties changed by farming practices intended to build SOM and microbial processes.
So far, soil type or level of SOM rather than management practice seems to be most influential in producing soil resilience, with high SOM soils more resilient than low SOM soils. Farmers have been identified and one year of data collected for N-movement below 30 cm.
A pilot experiment for soil resilience has been completed. Greenhouse studies have been designed.
This project will benefit organic farmers by providing information on the potential of organically managed soils to supply N, an expensive and unpredictable input in cropping systems. Since such information will be related to basic soil parameters such as organic matter fractions, results should be generalizable beyond the farms on which the work is conducted.
Graduate Research Assistant
University of Kentucky
500 South Limestone St
Ag. North, N106R
Lexington, KY 40546-0091
Office Phone: 8592572103