Comparison of Net Global Warming Potential and Greenhouse Gas Intensity Affected by Management Practices in Two Dryland Cropping Sites

Upendra M Sainju

doi:10.4236/jep.2015.69092

Abstract

Little is known about the effect of management practices on net global warming potential (GWP) and greenhouse gas intensity (GHGI) that account for all sources and sinks of greenhouse gas (GHG) emissions in dryland cropping systems. The objective of this study was to compare the effect of a combination of tillage, cropping system, and N fertilization on GWP and GHGI under dryland cropping systems with various soil and climatic conditions from 2008 to 2011 in western North Dakota and eastern Montana, USA. Treatments in western North Dakota with sandy loam soil and 373 mm annual precipitation were conventional till malt barley (Hordeum vulgarie L.) with 67 kg N ha-1 (CTB/N1), conventional till malt barley with 0 kg N ha-1 (CTB/N0), no-till malt barley-pea (Pisum sativum L.) with 67 kg N ha-1 (NTB-P/N1), no-till malt barley with 67 kg N ha-1 (NTB/N1), and no-till malt barley with 0 kg N ha-1 (NTB/N0). In eastern Montana with loam soil and 350 mm annual precipitation, treatments were conventional till malt barley-fallow with 80 kg N ha-1 (CTB-F/N1), conventional till malt barley-fallow with 0 kg N ha-1 (CTB-F/N0), no-till malt barley-pea with 80 kg N ha-1 (NTB-P/N1), no-till malt barley with 80 kg N ha-1 (NTB/N1), and no-till malt barley with 0 kg N ha-1 (NTB/N0). Carbon dioxide sink as soil C sequestration rate at the 0 - 10 cm depth was greater in NTB-P/N1 and NTB/N1 than the other treatments at both sites and greater in eastern Montana than western North Dakota. Carbon dioxide sources were greater with N fertilization than without and greater with conventional till than no-till. Soil total annual N2O and CH4 fluxes varied among treatments, years, and locations. Net GWP and GHGI were lower in NTB-P/N1 than the other treatments in western North Dakota and lower in NTB-P/N1 and NTB/N1 than the other treatments in eastern Montana. Net GWP across similar treatments was lower in eastern Montana than western North Dakota, but GHGI was similar. Annualized crop yield was greater in the treatments with N fertilization than without. Because of greater grain yield but lower GWP and GHGI, no-till malt barley-pea rotation with adequate N fertilization can be used as a robust management practice to mitigate net GHG emissions while sustaining dryland crop yields, regardless of soil and climatic conditions. Loam soil reduced GWP and crop yields compared with sandy loam soil.

Highlights

Agricultural practices produce three soil greenhouse gases (GHGs—CO2, N2O, and CH4) that significantly contribute to radiative forcing of earth’s atmosphere for global warming [1]-[3]
Carbon sequestration rate and crop yield were similar between NTB-P/N1 and NTB/N1 (Figure 2 and Figure 6). These results suggest that no-till with legume-nonlegume crop rotation with adequate rate of N fertilization can be recommended as a robust management option to mitigate net GHG emissions, improve soil quality, reduce chemical inputs, and sustain crop yields compared with the traditional systems under dryland cropping systems, regardless of soil and climatic conditions
Differences in CO2 contributions from farm operations, N fertilization rates, N2O and CH4 fluxes, and soil C sequestration rates as well as soil and climatic conditions resulted in variations in net global warming potential (GWP) and greenhouse gas intensity (GHGI) among treatments and study sites

Summary

Introduction

Agricultural practices produce three soil greenhouse gases (GHGs—CO2, N2O, and CH4) that significantly contribute to radiative forcing of earth’s atmosphere for global warming [1]-[3]. While soil C sequestration acts as the sink for GHGs, [1] [3] [4], chemical inputs used for increasing crop yields and residue returned to the soil, such as N, P, and K fertilizations and herbicide and pesticide applications, can produce CO2, thereby reducing the GHG mitigation potential [5]. Some of the novel management practices, such as no-till, diversified crop rotation, increased cropping intensity, and reduced N fertilization rate, can increase soil C sequestration and mitigate GHG emissions [3] [7] [8]. It is expected that a combination of management practices that includes no-till, diversified crop rotation, and reduced N fertilization rate might further enhance SOC sequestration and mitigate net GHG emissions without influencing crop yields compared with individual practices. Increased C sequestration helps to improve soil quality and productivity through enhanced soil water-nutrients-crop yield relationships [16] [17] and can serve as an additional source of income for farmers [18] [19]

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Conclusion