This article is a part of the NASA DEVELOP’s Spring 2017 Article Session. For more articles like these, click here
NASA DEVELOP team uses NASA Earth observations to map winter cover crop conservation performance in the Chesapeake Bay watershed to improve agricultural management strategies.
NASA Landsat 5, Landsat 8, and Sentinel-2 imagery were used to quantify winter cover crop performance in the Chesapeake Bay watershed, by estimating biomass and nitrogen uptake. The methods developed in this project automate acquisition of annual satellite imagery and calculation of winter cover crop metrics.
NASA DEVELOP is part of the agencyÛªs Applied Sciences Program. This project exemplified the DEVELOP programÛªs goal of using Earth observations to address environmental and public policy issues through interdisciplinary research projects. The end user for the project was the Maryland Department of Agriculture (MDA), and the two collaborating agencies were the US Geological Survey (USGS) and the US Department of Agriculture ÛÒ Agricultural Research Service (USDA-ARS).
The Chesapeake Bay is a diverse ecosystem supporting a wide variety of plants and animals. It is the largest estuary in North America, covering a watershed of roughly 167,000 square kilometers which is roughly the size of California (1). Migratory birds use the bay as a stop-over point and the fisheries are some of the most productive in the country (2). In addition, the bay is home to large metropolitan areas with high population densities. The size of its watershed makes the Chesapeake Bay very sensitive to changes in regional land use. Intensive land uses such as urban development and agriculture have a great impact on the ecosystem, often leading to excess nutrients in the water and overall habitat degradation (3).
Excessive nutrients flow downstream into the bay and can lead to algal blooms and eventual depletion of dissolved oxygen through the process of eutrophication. According to 2015 estimates from the Chesapeake Bay Program, agriculture contributes 42 percent of the nitrogen, 55 percent of the phosphorous and 60 percent of the sediment entering the bay (4). Water quality degradation is accelerated due to increased sedimentation that reduces sunlight and limits primary productivity within the water column as well as by benthic plants. The resulting oxygen-poor environments caused by sedimentation and algal blooms adversely affect Chesapeake Bay fauna such as fish and oysters (5). Because the Chesapeake Bay is an important economic source for tourism and fisheries, this ecosystem degradation also has a negative economic impact.
Planting cover crops during winter months reduces nutrient and sediment runoff, and increases yields for cash crops by reducing opportunistic weeds and insect pathogens. The Maryland Agricultural Water Quality Cost-Share (MACS) program by the MDA began providing cash incentives in 2005 for farmers to grow winter cover crops (6). The program offers a variety of incentives based on factors that influence nutrient uptake; furthermore, farmers have flexibility in choosing the specific crops and methods for their individual farms and fields. Generally, farmers are paid higher cash amounts for planting crop species that retain more nutrients. For example, rye is paid at a higher rate than lower-performing species like wheat because it has been shown to capture greater quantities of excess nitrogen (6, 10). Similarly, planting early and using more effective planting methods lead to higher biomass and thus higher payments (9). However, performance of winter cover crops can vary based on factors that are not explicitly included in the payment scheme. Field preparation, local and annual climate variability, or previous crop species can all affect performance (8, 9).
Winter cover crop performance is measured using metrics including biomass, percent ground cover, and nutrient uptake. As biomass is strongly associated with nutrient uptake, it is critical to accurately calculate biomass to understand the impacts of winter cover crops on agricultural systems (9). Planting winter cover crops early results in higher biomass accumulation, because of a longer growing period, which in turn reduces nitrogen runoff (8). The MDAÛªs MACS program records data for participating fields which includes the specific locations of the fields, species of crop planted, date of planting, and planting method.
This project focused on winter cover crop performance during the fall and spring seasons from 2006ÛÒ2016, coinciding with the span of the cost-share program. The fall period was used to assess maximal growth before winter dormancy while the spring assessment determined total aboveground biomass accumulation prior to harvest. NASA Earth-observing satellite Landsat 5 provided historical imagery of participating fields for 2006ÛÒ2012 that was collected at the same time as in-situ field data collected by the USDA-ARS and the USGS Eastern Geographic Science Center (EGSC). Aboveground biomass is often estimated from remote sensing indices derived from plant greenness reflectance data from satellite imagery (8). Similarly, because nitrogen content has a close association with plant chlorophyll content for different species, plant nitrogen content can be estimated from multi-spectral data when such information is combined with agronomic field data (9, 10). In this study, the Normalized Difference Vegetation Index (NDVI) was used to quantify the relationship between aboveground biomass and nitrogen content of the cover crops as sampled in the field and that observed from satellite imagery. Regression models built on this relationship were then applied to subsequent years to calculate aboveground biomass and nitrogen content.
After creating models defining the relationship between satellite imagery and field data, the DEVELOP team used images from NASAÛªs Landsat 8 and the European Space AgencyÛªs Sentinel-2 satellites to evaluate winter cover crops from 2014ÛÒ2017. The team focused on three counties on the Eastern Shore of Maryland (Talbot, Somerset and Queen AnneÛªs), in addition to Washington County in western Maryland, as these counties participated in a MACS pilot project that collected spatial data on the fields. These four counties also served as a starting point for automating the evaluation of winter cover crop performance, using aboveground biomass and nitrogen content, for participating farms in Maryland. Timely, calibrated Earth-observing data facilitates the calculation of winter cover crop effectiveness. Automating the process in Google Earth Engine will expedite and enhance key conservation management practices at the MDA and will enable researchers to integrate near real-time monitoring into the winter cover crop program.
“By incorporating NASA Earth observations into the management of Maryland’s Cover Crop Program, the Maryland Department of Agriculture now has the ability to analyze program performance at a field scale. The collaboration with the DEVELOP program not only provided an objective review of state investments within Maryland’s Cover Crop Program, but also reduces the amount of time staff spend in the field performing verification spot-checks.Û
– Jason Keppler, Watershed Implementation Program manager, Maryland Department of Agriculture, Office of Resource Conservation
The NASA DEVELOP team created a tool that finds satellite imagery of winter cover crop fields for both the fall and spring growing seasons to capture maximal growth during these periods. By comparing in-situ samples to satellite-derived vegetation indices, the team then determined crop performance by modeling the relationship between vegetation indices and crop metrics (i.e., biomass and nitrogen content). This analysis will help determine if winter cover crops are absorbing nutrients. Fields that exhibit greater accumulated biomass represent higher nutrient uptake, thus decreasing excess nutrient runoff into waterways. This tool will be used by MDA for participating fields across Maryland in the 2017ÛÒ2018 program as they scale-up efforts to record spatial data for all MACS participating fields. The long-term goal is to employ this tool across the entire Chesapeake Bay region, in partnership with organizations like the EPA Chesapeake Bay Program.
 D. F. Boesch, R. B. Brinsfield, and R. E. Magnien, ÛÏChesapeake bay eutrophication,Û Journal of Environmental Quality, vol. 30, no. 2, pp. 303ÛÒ320, 2001.
 C. E. Council, ÛÏChesapeake Bay waterfowl policy and management plan,Û Chesapeake Bay Program, Environmental Protection Agency, Annapolis, Maryland, 1990.
 J. Talberth, M. Selman, S. Walker, and E. Gray, ÛÏPay for Performance: Optimizing public investments in agricultural best management practices in the Chesapeake Bay Watershed,Û Ecological Economics, vol. 118, pp. 252ÛÒ261, 2015.
 ÛÏAgriculture – Chesapeake Bay Program.Û [Online]. Available: http://www.chesapeakebay.net/issues/issue/agriculture#inline. [Accessed: 30-Jan-2017].
 W. M. Kemp et al., ÛÏEutrophication of Chesapeake Bay: historical trends and ecological interactions,Û Marine Ecology Progress Series, vol. 303, pp. 1ÛÒ29, 2005.
 J. J. Meisinger, W. L. Hargrove, R. L. Mikkelsen, J. R. Williams, and V. W. Benson, ÛÏEffects of cover crops on groundwater quality,Û Cover Crops for Clean Water. Soil and Water Conservation Society. Ankeny, Iowa, vol. 266, pp. 793ÛÒ799, 1991.
 ÛÏMarylandÛªs 2014-15 Cover Crop Sign Up. – Maryland Department of AgricultureÛ [Online]. Available: http://mda.maryland.gov/resource_conservation/Pages/cover_crop.aspx. [Accessed: 10-Feb-2017].
 W. D. Hively, M. Lang, G. W. McCarty, J. Keppler, A. Sadeghi, and L. L. McConnell, ÛÏUsing satellite remote sensing to estimate winter cover crop nutrient uptake efficiency,Û Journal of Soil and Water Conservation, vol. 64, no. 5, pp. 303ÛÒ313, Sep. 2009.
 K. Prabhakara, W. D. Hively, and G. W. McCarty, ÛÏEvaluating the relationship between biomass, percent groundcover and remote sensing indices across six winter cover crop fields in Maryland, United States,Û International Journal of Applied Earth Observation and Geoinformation, vol. 39, pp. 88ÛÒ102, Jul. 2015.
 S. Lee, I. Y. Yeo, A. M. Sadeghi, G. W. McCarty, W. D. Hively, M. W. Lang. Impacts of watershed characteristics and crop rotations on winter cover crop nitrate-nitrogen uptake capacity within agricultural watersheds in the Chesapeake Bay region. PloS One, 11(6). Jun. 2016.
Sunita Yadav, Ph.D. is a project lead at NASA DEVELOP, Goddard Space Flight Center, working on the Chesapeake Bay Agriculture project. She has a Ph.D. in biological sciences from the University of Cincinnati.
John Fitz is a NASA DEVELOP participant at Goddard Space Flight Center working on the Chesapeake Bay Agriculture project. He also is completing a masterÛªs degree at the University of Maryland in Geospatial Information Sciences (GIS).
Sean McCartney is the center lead for the NASA DEVELOP National Program at Goddard Space Flight Center and contributed to the Chesapeake Bay Agriculture project. He holds a masterÛªs degree in GIS for Development and Environment from Clark University.
Perry Oddo is a NASA DEVELOP participant at Goddard Space Flight Center working on the Chesapeake Bay Agriculture project. He has a masterÛªs degree in geoscience from Penn State University.
Alison Thieme is the assistant center lead and Geoinformatics Fellow for NASA DEVELOP at Goddard Space Flight Center, as well as an investigator on the Chesapeake Bay Agriculture project. Follow Alison Thieme on Twitter @alisonthieme.