Soil Management Practices to Mitigate Nitrous Oxide Emissions and Inform Emission Factors in Arid Irrigated Specialty Crop Systems

Mary Carlson,Mark Easter,Lucas Thompson,Xia Zhu-Barker,Kerri L. Steenwerth,William R. Horwath,Amy Swan,Keith Paustian

doi:10.3390/soilsystems3040076

Abstract

Greenhouse gas (GHG) emissions from arid irrigated agricultural soil in California have been predicted to represent 8% of the state’s total GHG emissions. Although specialty crops compose the majority of the state’s crops in both economic value and land area, the portion of GHG emissions contributed by them is still highly uncertain. Current and emerging soil management practices affect the mitigation of those emissions. Herein, we review the scientific literature on the impact of soil management practices in California specialty crop systems on GHG nitrous oxide emissions. As such studies from most major specialty crop systems in California are limited, we focus on two annual and two perennial crops with the most data from the state: tomato, lettuce, wine grapes and almond. Nitrous oxide emission factors were developed and compared to Intergovernmental Panel on Climate Change (IPCC) emission factors, and state-wide emissions for these four crops were calculated for specific soil management practices. Dependent on crop systems and specific management practices, the emission factors developed in this study were either higher, lower or comparable to IPCC emission factors. Uncertainties caused by low gas sampling frequency in these studies were identified and discussed. These uncertainties can be remediated by robust and standardized estimates of nitrous oxide emissions from changes in soil management practices in California specialty crop systems. Promising practices to reduce nitrous oxide emissions and meet crop production goals, pertinent gaps in knowledge on this topic and limitations of this approach are discussed.

Highlights

Irrigated agriculture, producing nearly 40% of food and agricultural commodities globally, is recognized as a source of considerable greenhouse gas (GHG) emissions [1,2]
That the Greenhouse gas (GHG) nitrous oxide (N2 O), with a global warming potential 298 times greater than carbon dioxide (CO2), is primarily emitted by agriculture when soil processes respond to management dioxide (CO2 ), is primarily emitted by agriculture when soil processes respond to management practices practices is well known [5]
Studies on N2 O emissions from California specialty crop systems were identified through an initial literature search in August 2017 and an update in September 2018 using the Web of Science and Google Scholar and through personal communications with experts researching this topic

Summary

Introduction

Irrigated agriculture, producing nearly 40% of food and agricultural commodities globally, is recognized as a source of considerable greenhouse gas (GHG) emissions [1,2]. The outcome of process-based models like DayCent [44] can be used to calculate EFs of N fertilizer under specific management practices, but this approach is limited by lack of available empirical data from many specialty crop systems to parameterize and calibrate the model [45,46,47]. We summarize management practices that influence N2 O emissions from specialty crop systems, including fertilization, irrigation, cover crops and tillage, and characterize the implementation of these practices within tomatoes, lettuce, grapes and almonds. These empirical studies will be leveraged to calculate EFs based on practice and crop, and the resultant. We identify limitations of this approach and gaps where further efforts will bolster the capacity to determine practice-based emissions from the state’s specialty crops

Literature Review—Approach

Brief Overview of Four Specialty Crops

Estimating EF and State-Wide Emissions by Crop and Management Practice

Fertilization

Fertilizer Rate

Fertilizer Efficiency Enhancers

Method Derived

Tomatoes and Fertilization

Lettuce and Fertilization

Wine Grapes and Fertilization

Almonds and Fertilization

Irrigation