Subsurface Drainage Nitrate and Total Reactive Phosphorus Losses in Bioenergy-Based Prairies and Corn Systems
2015
Daigh, Aaron L. M. | Zhou, Xiaobo | Helmers, Matthew J. | Pederson, Carl H. | Horton, Robert | Jarchow, Meghann | Liebman, Matt
We compare subsurface-drainage NO₃–N and total reactive phosphorus (TRP) concentrations and yields of select bioenergy cropping systems and their rotational phases. Cropping systems evaluated were grain-harvested corn–soybean rotations, grain- and stover-harvested continuous corn systems with and without a cover crop, and annually harvested reconstructed prairies with and without the addition of N fertilizer in an Iowa field. Drainage was monitored when soils were unfrozen during 2010 through 2013. The corn–soybean rotations without residue removal and continuous corn with residue removal produced similar mean annual flow-weighted NO₃–N concentrations, ranging from 6 to 18.5 mg N L⁻¹ during the 4-yr study. In contrast, continuous corn with residue removal and with a cover crop had significantly lower NO₃–N concentrations of 5.6 mg N L⁻¹ when mean annual flow-weighted values were averaged across the 4 yr. Prairies systems with or without N fertilization produced significantly lower concentrations below <1 mg NO₃–N L⁻¹ than all the row crop systems throughout the study. Mean annual flow-weighted TRP concentrations and annual yields were generally low, with values <0.04 mg TRP L⁻¹ and <0.14 kg TRP ha⁻¹, and were not significantly affected by any cropping systems or their rotational phases. Bioenergy-based prairies with or without N fertilization and continuous corn with stover removal and a cover crop have the potential to supply bioenergy feedstocks while minimizing NO₃–N losses to drainage waters. However, subsurface drainage TRP concentrations and yields in bioenergy systems will need further evaluation in areas prone to higher levels of P losses.
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