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

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

Summary

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. We are conducting a field experiment to assess the impact of cover crop mixtures on N retention in both above- and below-ground biomass. Cover crop treatments planted in fall 2011 include eight monocultures, seven four species mixtures, one eight species mixture, and a no cover crop control. This design will allow us to 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.”

Objectives/Performance Targets

Objective 1: To quantify the effect of cover crop mixtures on the quantity of N in aboveground cover crop biomass.
Progress to date: Aboveground cover crop biomass was collected in October 2011 and will be analyzed for N content in February 2012.

Objective 2: To assess the effects of cover crop mixtures on microbial N uptake.
Progress to date: Soils were collected for biological analysis in November 2011. Soil microbial biomass and N will be determined from soil extracts in January 2011. Microbial activity was assessed through a community level physiological profile, the statistical analysis of which is in process.

Objective 3: To measure the effects of cover crop mixtures on nitrate leaching during the cover crop season.
Progress to date: Anion resin membranes were placed in the field in September and collected in November to measure potentially leachable nitrate in the fall; membranes were extracted and extracts will be analyzed for nitrate in February 2012. Following membrane removal, anion resin beads were placed in the field and will be removed for nitrate analysis in spring 2012.

Objective 4: To determine the effect of cover crop mixtures on nitrogen supply to a subsequent cash crop.
Progress to date: We will address this objective during the 2012 corn growing season.

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.
Progress to date: This objective will be met through synthesis of all data collected during the course of this two year project.

Accomplishments/Milestones

All field activities planned for August through December 2011 were completed as proposed and there have been no changes to the plan of work. Our proposal highlighted that seeding rates and planting date were potential limitations of this study, as best management practices for mixtures are not yet determined. Visual observation suggested that seeding rates for the majority of species was appropriate, and we will analyze cover crop stand count and biomass data to confirm this observation. Of the six winter kill species included, four established poorly or not at all (sorghum sudangrass, sunn hemp, foxtail millet, and soybean). This outcome is likely due to climatic conditions following planting; we are considering moving the planting data forward and/or substituting species to improve establishment next year. Another issue related to planting was selection of appropriate equipment to plant cover crop mixtures that contain seeds of varying size, a challenge also faced by growers. We had originally proposed using a Brillion seeder equipped with a small and a large seedbox, however, we opted to use a drill equipped with a cone seeder and were satisfied with its performance. As indicated above, laboratory analyses of plant and soil samples will be conducted in winter 2012. Fall planted cover crops will be terminated in spring 2012 prior to corn planting.

• 2011 Project Activities

Impacts and Contributions/Outcomes

Farmers throughout the Northeast have demonstrated interest in cover crops and cover crop mixtures to enhance agricultural productivity and sustainability. One of the goals of my project is to provide farmers and other agricultural professional with research-based information on the management and benefits of cover crop mixtures. To this end, I have led than 80 farmers, students, and agricultural professionals on tours of my research plots this fall. One tour was part of the Cover Crop Innovations Field Day supported by the Northeast SARE Pennsylvania State Program (http://extension.psu.edu/cover-crops/events/oct27-field-day). More than fifty percent of participants (17 of 30) reported that their knowledge of cover crop mixtures had increased as a result of this field day. Seventeen of 30 participants also indicated that they were likely to adopt and/or recommend cover crop mixtures after the field day.

• Field Day Brochure

Collaborators: