Designing Nitrogen Efficient Agroecosystems
Current research compares cover crop monocultures to diverse mixtures like the soybean, rye grass, red clover mix shown here.
We are working on a variety of projects that evaluate N pollution losses from agroecosystems. In all of these experiments, the goal is to design systems that have low pollution outputs but retain high yield and economic viability. When possible, we take advantage of long-term cropping systems trials that account for cumulative treatment effects over many crop rotations.
One recent study took place at the Hunter Rotation Experiment at Penn State's experimental farm. This replicated experiment compared several crop rotation systems since 1969, and since 1982 there have been experimental manipulations of N inputs from fertilizer and manure. Such long-term experiments are rare, and it provided a unique opportunity to assess the effects of N source (synthetic fertilizer, legume crops, manure) on soil processes. We quantified soil-atmosphere emissions of CO2, N2O, and NH3 from these plots (see Adviento-Borbe et al. 2010), and are currently assessing the depth distribution of soil organic matter from 1-m soil cores.
A second major emphasis in our group has been to increase understanding of nutrient cycling in organic agricultural systems. Organic farmers often use cultivation to manage weeds, but some cultivation practices can diminish soil quality and promote nitrogen leaching and losses of soil organic carbon. We have been working with weed scientists and entomologists to design organic agricultural systems that balance soil health with weed suppression. See Schipanski et al. 2014 for an example, and visit the organic forage website for more details.
In 2011, we established a new organic agriculture experiment to determine whether diverse cover crop mixtures, as opposed to single-species cover cropping, can enhance ecosystem functions in a corn-soybean-wheat cash crop rotation that produces organic feed and forage. We are designing cover crop mixtures that target nutrient supply, nutrient retention, weed suppression, and management ease, and testing the idea that diverse mixtures provide these functions better than cover crops in monoculture. Another innovative part of our work is that we are interested in quantifying a suite of ecosystem functions that arise from cover crop use (e.g. Schipanski et al. 2014). Most studies focus on one function, but we will monitor: nutrient supply, nutrient retention, weed suppression, insect pest regulation, soil quality, erosion control, yield, and short-term profitability.