Developing an adaptive management framework for promoting agroecosystem services through cover crops

Developing an adaptive management framework for promoting agroecosystem services through cover crops

Summary

Given the environmental impact of conventional agriculture and its vulnerability to increasingly extreme climate variation, it is necessary to explore and develop alternative, more environmentally sensitive, and resilient agricultural systems. By relying more heavily on natural ecosystem processes, or management practices that mimic these processes, we can establish progressively more sustainable production systems. In order to do this, we must better understand the plant-environment feedbacks in agroecosystems and develop a framework for converting this knowledge into effective management practices.  

Cover crops are a key tool as we work to manage ecosystem processes with more precision in sustainable agriculture. Cover crops have been used extensively in the past, and are increasingly used today, especially in organic farming. Cover crops serve many purposes in agricultural systems, and promote different ecosystem functions. This project is focusing on three specific desirable outcomes from cover crops; biomass production (productivity), nitrogen fixation, and weed suppression. Based on current ecological theory, this project tests if increased diversity in cover crop mixtures can increase the ecosystem functions of productivity, biological nitrogen fixation (BNF), and weed suppression. If so, it would be a valuable tool to improve the multifunctionality of agroecosystems and decrease environmental impact from agriculture. Practically, this work will lead to recommendations for farmers for how to select and manage cover crops. From a broader perspective, by observing this ecological phenomenon in contrasting agroecosystems, the underlying basis of this diversity-function relationship may become clearer. Additionally, we can more easily see how it changes with key environmental conditions like soil fertility and management history. While both diversity and ecosystem function are currently discussed in the agricultural field, we are only just beginning to tie them together and understand how they interact in agroecosystems.

Objectives/Performance Targets

1. 1. Assess the relationship between diversity and the ecosystem functions of productivity, weed suppression, and biologic nitrogen fixation (BNF).
      1. 1. We are still in the process of analyzing the first field season data with regard to these three ecosystem functions. Initial indications show that our experimental design will allow us to make these assessments through data analysis and another field season (currently in progress).

1. 1. Rank legumes and non-legumes in terms of complementarity in mixtures on a relative scale.
      1. 1. Similar to the status for #1 above, I believe we will be able to provide results with regards to the general mixing ability of the different cover crops. However, we won’t have significant conclusions until we have analyzed more of the first season data, and we have harvested the second season.

1. 1. Evaluate the BNF rates of different legumes in monocultures and mixtures.
      1. 1. Because the BNF determination analysis is specialized, we have not yet prepared all the samples for shipment. This will be done soon and will allow us to make some initial comparisons of BNF rate between the different species and their response to mixtures.

1. 1. Develop and refine simple plant-based and visual metrics for BNF and biomass production.
      1. 1. We collected visual data from this first field season for comparison to the actual BNF and biomass data collected. Once we have final measurements for those two variables we will be able to compare them to our simple plant-based and visual metrics, and evaluate effectiveness.

Accomplishments/Milestones

While we managed to protect the research plots from deer with an electric fence, we couldn’t protect the seedlings from the extremely cold winter we had in the northeast. While this will allow us to examine the response of these more diverse mixtures to extreme environmental conditions (we would hypothesize the mixtures would be more resilient to these extremes), we did have significant mortality in the peas and clover plots. Due to this, we did density counts for each species in each plot (~350 plots), so that we can account for this loss in the data analysis. The slow, cold spring gave us some additional time to collect this count data before we finally harvested the biomass in the middle of June (50% flowering vetch plants). The full biomass harvest was no small feat and took approximately 200 person hours over 4 days. We all felt very satisfied at the end! I also feel much better prepared to do this same task again next year, when it will hopefully run even smoother and faster. We also took soil samples before the biomass collection to examine changes in soil nitrogen (N mineralization and total inorganic N). This data will also be shared with a collaborating graduate student and lab to examine the effect of these different cover crop treatments on nitrous oxide (N2O) emissions, a major agricultural contributor to greenhouse gas emissions. We are continuing this collaboration next year, and are very excited about the potential results after this initial year. Through the summer we weighed the dried plant samples and started grinding the samples in order to analyze the nitrogen fixation in the legumes. We are continuing this work through the fall and winter.

In early September we planted the second field season of this experiment. While the main design is the same, we made a few tweaks that will improve the conclusions we can make next spring. We also added four on-farm sites through collaborations with very cooperative farmers. These on-farm sites will show how stable a subset of these cover crop treatments are in terms exposure to different environmental conditions. They will also demonstrate the effectiveness of these cover crop options in a real farm setting using typical farm equipment and practices. This spring will be very busy with the data collection at the main research site along with all the on-farm sites. With six site-years total, the data we will have collected through this experiment will be very powerful in helping to address our objectives (above).

Impacts and Contributions/Outcomes

While still in the preliminary data analysis stage, one of the most exciting results we’ve found is that weeds are suppressed more in mixtures of two or more cultivars of the same cover crop species compared to just one cultivar. For example, when all five cultivars of hairy vetch were mixed together, they suppressed more weeds than any one cultivar when it was planted alone. This suggests that a simple management change such as increasing the cultivars in a cover crop, can provide additional weed suppression capacity in a cover crop. This result was consistent across all six cover crop species we used (hairy vetch, winter pea, crimson clover, wheat, rye, and ryegrass). This could increase the effectiveness of cover crops, further reducing the need for herbicides to control weeds in the growing season. I’m excited to continue to analyze the data for more results like this, ones that could have a direct impact on farmer practices and agricultural sustainability. I am continuing to update my blog (http://blogs.cornell.edu/soho/), though I am a little behind posting about this fall’s field work. It’s a great way to easily share what the project is about, and the progress we’re making.

Collaborators: