Abstract

Land use conversions into and out of agriculture may influence soil-atmosphere greenhouse gas fluxes for many years. We tested the legacy effects of land use on cumulative soil nitrous oxide (N2 O) fluxes for 5yr following conversion of 22-yr-old Conservation Reserve Program (CRP) grasslands and conventionally tilled agricultural fields (AGR) to continuous no-till corn, switchgrass, and restored prairie. An unconverted CRP field served as a reference. We assessed the labile soil C pool of the upper 10cm in 2009 (the conversion year) and in 2014 using short-term soil incubations. We also measured insitu soil N2 O fluxes biweekly from 2009 through 2014 using static chambers except when soils were frozen. The labile C pool was approximately twofold higher in soils previously in CRP than in those formerly in tilled cropland. Five-year cumulative soil N2 O emissions were approximately threefold higher in the corn system on former CRP than on former cropland despite similar fertilization rates (~184kg N·ha-1 ·yr-1 ). The lower cumulative emissions from corn on former cropland were similar to emissions from switchgrass that was fertilized less (~57kg N·ha-1 ·yr-1 ), regardless of former land use, and lowest emissions were observed from the unfertilized restored prairie and reference systems. Findings support the hypothesis that soil labile carbon levels modulate the response of soil N2 O emissions to nitrogen inputs, with soils higher in labile carbon but otherwise similar, in this case reflecting land use history, responding more strongly to added nitrogen.

Highlights

  • Land use change (LUC) due to agricultural conversion has greatly modified the Earth’s land surface, with ~38% of global land in agricultural production (World Bank 2016)

  • Soil N2O emissions were largely driven by N fertilizer input rate with the magnitude of response to N input rate modulated by labile soil C content, especially at high rates of N inputs

  • Highest emissions were observed from the corn system with both high N inputs and high labile soil C, which suggests that soil N2O emissions are modulated by the labile soil C content when N is in adequate supply

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Summary

Introduction

Land use change (LUC) due to agricultural conversion has greatly modified the Earth’s land surface, with ~38% of global land in agricultural production (World Bank 2016). Converting native ecosystems such as grasslands into agriculture increases soil erosion (Montgomery 2007), degrades water quality (Bennett et al 2001), and leads to habitat and biodiversity loss (Reidsma et al 2006, Lawler et al 2014, Werling et al 2014).

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