Cover crop cocktails: Harnessing diversity to enhance nitrogen retention in agroecosystems

Project Overview

Project Type: Graduate Student
Funds awarded in 2011: $14,998.00
Projected End Date: 12/31/2013
Grant Recipient: Pennsylvania State University
Region: Northeast
State: Pennsylvania
Graduate Student:
Faculty Advisor:
Dr. Jason Kaye
Pennsylvania State University

Annual Reports


  • Agronomic: corn


  • Crop Production: catch crops, cover crops, crop rotation, nutrient cycling, tissue analysis
  • Education and Training: demonstration, extension, networking, workshop
  • Production Systems: agroecosystems
  • Soil Management: nutrient mineralization, organic matter, soil analysis, soil chemistry, soil microbiology, soil quality/health

    Proposal abstract:

    Nitrogen loss from agroecosystems is a leading to contributor to non-point source pollution in the northeastern United States and an inefficiency that increases agricultural production costs. Cover cropping is an effective and widely promoted strategy that increases N retention to counter these negative impacts of production. In recent years, a growing number of farmers have expressed interest in the use of cover crop “cocktails” (species mixtures), though little research-based information is available on the management or ecosystem functions of mixtures. Mixtures are a promising strategy to augment N retention provided by cover crops, as plant diversity typically leads to increased productivity, and, consequently, increased N uptake. Further, a nascent understanding of linkages between aboveground diversity and belowground processes indicates that mixtures may also boost belowground activities that lead to increased N retention by soil microbes. We will conduct a field experiment to assess the impact of cover crop mixtures on N retention in both above- and below-ground biomass. The experiment will be designed to also evaluate how species number and the inclusion of functionally and temporally complementary species in a mix influence N dynamics, information that will assist farmers in selecting the “right mix.” This research dovetails with the goals of the SARE Pennsylvania State Program, and collaboration with PA-SARE will support timely and effective communication of results to extension and farmer audiences. Cover crop mixtures have the potential to support multiple ecosystem functions, and this project will contribute to our understanding of this underutilized approach to enhancing agroecosystem sustainability.

    Project objectives from proposal:

    The purpose of this project is to assess the potential of diverse cover crop mixtures to increase N retention in agroecosystems. To accomplish this, we will establish a two-year experiment at the Penn State agricultural research station with the following objectives:

    Objective 1: To quantify the effect of cover crop mixtures on the quantity of N in aboveground cover crop biomass. Expected outcome 1: We hypothesize that increased diversity will lead to increased uptake of soil N by non-leguminous cover crop species and an overall increase in aboveground biomass N.

    Objective 2: To assess the effects of cover crop mixtures on microbial N uptake. Expected outcome 2: We hypothesize that increased aboveground diversity will increase soil microbial biomass and activity and, therefore, microbial N assimilation during the cover crop growing season.

    Objective 3: To measure the effects of cover crop mixtures on nitrate leaching during the cover crop season. Expected outcome 3: We hypothesize that increased aboveground diversity will reduce the amount of nitrate leached through the soil profile during the cover crop growing season.

    Objective 4: To determine the effect of cover crop mixtures on nitrogen supply to a subsequent cash crop. Expected outcome 4: We hypothesize that increased aboveground diversity will lead to an increase in N available to a subsequent cash crop.

    Objective 5: To increase understanding of the mechanisms through which diversity influences N retention and supply in order to assist farmers in choosing species for cover crop mixtures. Expected outcome 5a: We hypothesize that increasing the number of species present in a cover crop stand will positively impact cover crop N content, microbial uptake, nitrate leaching, and N supply, but that effect size will diminish as the number of species increases (richness mechanism). Expected outcome 5b: We hypothesize that mixing species that perform different N functions (N-fixing versus N-scavenging) will lead to higher quantities of N in aboveground cover crop biomass, greater N uptake by N-scavengers, and reduced nitrate leaching than mixtures with only one N functional group (N functional diversity mechanism). Expected outcome 5c: We hypothesize that the greatest effects of increased diversity on cover crop biomass N, microbial N assimilation, nitrate leaching, and N supply will be observed in cover crop mixtures that include species exhibiting temporal complementarity (winter kill versus winter hardy; temporal complementarity mechanism).

    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.