ASSESSING CLIMATE, SOIL AND LANDSCAPE PROCESSES AFFECTING AGRICULTURAL ECOSYSTEMS
Title: Using satellite remote sensing to estimate winter cover crop nutrient uptake efficiency
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2009
Publication Date: December 15, 2009
Citation: Hively, W.D., Lang, M.W., McCarty, G.W., Keppler, J., Sadeghi, A.M., McConnell, L.L. 2009. Using satellite remote sensing to estimate winter cover crop nutrient uptake efficiency. Journal of Soil and Water Conservation. 64:303-313.
Interpretive Summary: The use of winter cover crops can reduce the potential for leaching of residual agricultural nitrogen to groundwater following the summer growing season. Accordingly, they play a central role in efforts to reduce agricultural non-point source pollution inputs to the Chesapeake Bay. Cover crops can also provide additional benefits to the cropping system, including erosion prevention, carbon sequestration, bioenergy production, and nutrient contribution to the following crop. This study used a combination of satellite remote sensing, on-farm sampling, and acquisition of agronomic data from cost-share program implementation records to estimate cover crop nitrogen uptake efficiencies at the landscape scale. Results revealed trends in biomass production and nutrient uptake that were linked to cover crop species choice (rye>barley>wheat) and planting methods (drilled>broadcast), and confirmed that early-planted cover crops are most effective at fall nutrient sequestration. This innovative methodology allowed the direct evaluation of cover crop performance using real-time observation of practices employed by participating farms. Continued efforts to combine remote sensing tools with farm program data will provide important information to scientists and regulators working to improve conservation programs. Results can be used to more effectively utilize scarce conservation resources and derive the maximum water quality protection benefits.
The practice of planting winter cover crops following summer row crops is recognized as an important agricultural conservation measure with potential to reduce nitrogen losses to groundwater. Sequestration of residual soil nitrogen in growing cover crop biomass can significantly reduce wintertime nutrient leaching potential. Accordingly, state cost-share programs have been established to promote the cultivation of winter cover crops on farms throughout the Chesapeake Bay watershed. However, current estimates of cover crop nutrient uptake are generally based on plot studies extrapolated to the watershed scale based solely on enrollment acreage. Remote sensing provides a tool for real-time estimation of cover crop biomass production on working farms throughout the landscape. This project combined cover crop cost-share program enrollment data with satellite imagery and on-farm sampling to evaluate cover crop nitrogen uptake on 136 fields distributed within the Choptank River watershed. Agronomic factors influencing cover crop biomass production and nutrient uptake included cover crop species (rye > barley > wheat), planting date (September > November), and planting method (drilled > broadcast > aerial). Overall, early-planted drilled rye outperformed other methods. The average autumnal nutrient accumulation for rye, barley, and wheat crops, respectively, was 24, 21, and 8 kg ha-1, corresponding to biomass production rates of 1275, 1120, and 410 kg ha-1. Springtime residual nitrate concentrations were reduced from a high of 14 mg kg-1 on sampled fields with low cover crop biomass to < 4 mg kg-1 on fields with biomass greater than 1000 kg ha-1. By utilizing remotely sensed data, cover crop efficiencies can be derived at the landscape scale, accounting for the effects of spatial variability (watershed position, soil type, hydrology) as well as agronomic factors. Study results, although they must be replicated over several growing seasons to account for climate variability, have strong implications for evaluating and improving the success of the cover crop programs and promoting effective water quality protection strategies. Continued efforts to combine remote sensing tools with farm program data will provide important information to scientists and regulators working to improve conservation programs. Results can be used to more effectively utilize scarce conservation resources and derive the maximum water quality protection benefit.