Mineral fertilizer and manure effects on leached inorganic nitrogen, nitrate isotopic composition, phosphorus, and dissolved organic carbon under furrow irrigation

Authors: Lentz, Rodrick; Lehrsch, Gary

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2017
Publication Date: 3/8/2018
Citation: Lentz, R.D., Lehrsch, G.A. 2018. Mineral fertilizer and manure effects on leached inorganic nitrogen, nitrate isotopic composition, phosphorus, and dissolved organic carbon under furrow irrigation. Journal of Environmental Quality. 47:287-296. https://doi.org/10.2134/jeq2017.09.0384.
DOI: https://doi.org/10.2134/jeq2017.09.0384

Interpretive Summary: To improve nitrogen (N) use efficiency in high-yielding, furrow-irrigated agricultural fields, a better understanding is needed of mineral fertilizer and manure effects on nutrient leaching. Substantial mineral or organic (dairy manure) fertilizer applications are needed to achieve high yields, but these may produce accumulations of nitrate-N and dissolved phosphorus in the soil and increase nutrient losses in water draining below the soil rooting zone. Leached nutrients contaminate groundwater, which subsequently seeps into surface waters. The excess nitrate-N and dissolved phosphorus promote algal growth and deplete dissolved oxygen content in surface waters, and promote development of dead zones in downstream waters, which have dramatically reduced aquatic production. Impacts of agriculture on groundwater quality are difficult to ascertain, but this knowledge is crucial for protecting and preserving Earth’s water supply. This four-year field study, measured deep percolation at 1.2-m depth and associated nutrient concentrations and mass losses for dairy manure-N- or mineral-N-amended soils (372 kg available N/ha in four years) and non-amended controls. In study plots, mineral and manure fertilizer had opposite effects on leaching of nitrate-N and dissolved phosphorus. For individual 2-wk periods following each irrigation, mean leachate nitrate-N concentrations or mass losses for mineral fertilizer were either equal to, or greater than, those of manure and non-amended treatments. Yet for mean dissolved phosphorus, mass losses for manure and non-amended treatments were greater than, or equal to, mineral fertilizer values. In light of the potential negative effects associated with either fertilizer type, and because even non-amended soils produced substantial amounts of leached nitrate-N (69.5 kg ha-1 Yr-1), an important management key for limiting nutrient losses in these fertilized, furrow-irrigated soils is to minimize percolation water losses. An increased knowledge of soil N balance and transport in these irrigated agricultural soils can lead to improved nutrient management, cropping efficiency, and water quality in the region.

Technical Abstract: To improve nitrogen (N) use efficiency in irrigated agriculture, a better understanding is needed of mineral fertilizer and manure effects on nutrient leaching in a furrow irrigated silt loam in southern Idaho. In this 2003-to-2006 field study, we measured deep percolation fluxes at 1.2-m depth and associated nutrient concentrations and mass losses for dairy manure-N or mineral-N (urea, sodium nitrate [NaNO3]) amended soils (372 kg available N/ha in four years) and non-amended controls, and determined the 2H-H2O and 18O-H2O isotope ratios in the leached nitrate. Flow-weighted concentration means for individual irrigations varied widely, from near zero to as much as 250 mg/L for NO3-N, 480 µg/ L for dissolved reactive phosphorus (DRP), 43 mg/L for dissolved organic C (DOC), and 390 mg/L for chloride (Cl). Relative to other treatments, mineral fertilizer increased NO3-N (3.3x) and Cl (4.4x) concentrations in deep leachate, particularly when NaNO3 was applied in 2004, and produced maximum mean season-long NO3-N and Cl losses. Manure and control treatments produced similar leachate nutrient mass losses, and for some irrigation periods, mineral fertilizer produced 85% and 97% lesser DRP losses and 2x greater Cl losses compared to manure and control treatments. Four-year cumulative losses among treatments differed only for Cl. Isotopic composition of deep leached nitrate indicate that both transformation and biologic cycling of mineral and manure N are rapid in these soils, which, with percolation volume, influence the amounts of NO3-N and DOC leached. In light of the potential negative effects associated with either fertilizer type, and because even non-amended soils produced substantial amounts of leached NO3-N (69.5 kg ha-1 Yr-1), an important management key for limiting nutrient losses in these fertilized, furrow-irrigated soils is to minimize percolation water losses.