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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Serie: ACSESS Books
- Sprache: Englisch
Cover Crops and Soil Ecosystem Services A comprehensive resource on cover crops and their role in soil ecosystems Cover crops are a reemerging strategy to improve and maintain the services that soils provide. They can have an enormous affect on agricultural outcomes, preventing soil erosion, restoring vital soil nutrients, sequestering C from the atmosphere, and more. The successful management and use of cover crops is therefore critical to ensure soil ecosystem services are maintained or improved not only to meet our demands for food, fuel, fiber, and feed but also to reduce pollution and improve the soil. Cover Crops and Soil Ecosystem Services provides a heavily researched and highly readable introduction to cover crops and their role in soil ecosystems. It ranges from a detailed discussion of cover crop biomass production to a thorough treatment of soil ecosystems and their vulnerabilities. The result is an essential guide to a critical area of agricultural science. Cover Crops and Soil Ecosystem Services readers will also find: * Detailed treatment of cover crop biomass production, soil erosion, greenhouse gas fluxes, nitrate leaching, soil C sequestration, and more * Discussion of emerging issues, including extreme weather events and the economics of cover crop farming * Wide-ranging summaries of interdisciplinary soil and cover crop research Cover Crops and Soil Ecosystem Services is a useful reference for students and researchers at all levels of study relating to cover crop agriculture.
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Table of Contents
Cover
Title Page
Copyright Page
Preface
1 Cover Crops and Soil Ecosystem Services
1.1 Cover Crops
1.2 Soil Ecosystem Services
1.3 Cover Crops and Soil Ecosystem Services
1.4 Summary
References
2 Cover Crop Biomass Production
2.1 Cover Crops and Biomass
2.2 Aboveground Biomass Production
2.3 Belowground Biomass Production
2.4 Threshold Level of Biomass Production
2.5 Management Practices that Affect Biomass Production
2.6 Summary
References
3 Soil Health
3.1 Soil Health
3.2 Cover Crops and Soil Health
3.3 Interconnectedness of Soil Health Parameters
3.4 Managing Soil Health
3.5 Summary
References
4 Water Erosion
4.1 Overview
4.2 Runoff
4.3 Sediment Loss
4.4 Nutrient Loss
4.5 Soil Carbon Loss
4.6 A Leading Factor of Water Erosion: Biomass Production
4.7 Cover Crops and Erosion‐Prone Systems
4.8 Summary
References
5 Wind Erosion
5.1 Extent of Wind Erosion
5.2 Soil Loss
5.3 Soil Erodibility
5.4 Managing Wind Erosion
5.5 Summary
References
6 Nutrient Losses
6.1 Implications of Nutrient Losses
6.2 Nutrient Leaching
6.3 Dissolved Nutrients in Runoff
6.4 Nutrient Release from Cover Crops
6.5 Management Implications
6.6 Nutrient Stratification
6.7 Summary
References
7 Soil Gas Emissions
7.1 Carbon and Nitrogen Emissions
7.2 Carbon Dioxide
7.3 Nitrous Oxide
7.4 Methane
7.5 Factors Affecting Soil Gas Emissions
7.6 Summary
References
8 Carbon Sequestration
8.1 The Need for Carbon Sequestration
8.2 Rates of Carbon Sequestration
8.3 Topsoil Versus Subsoil Carbon Sequestration
8.4 Managing Carbon Sequestration
8.5 Cropping System Carbon Footprint
8.6 Strategies to Enhance Cover Crop Potential to Sequester Carbon
8.7 Summary
References
9 Soil Water
9.1 Soil Water Management
9.2 High Precipitation Regions
9.3 Low Precipitation Regions
9.4 Mechanisms of Soil Water Storage with Cover Crops
9.5 Water Management
9.6 Summary
References
10 Weed Management
10.1 Cover Crops and Weeds
10.2 Weed Suppression
10.3 Managing Weeds
10.4 Summary
References
11 Soil Fertility
11.1 Soil Fertility Management
11.2 Organic Matter
11.3 Phosphorus
11.4 Other Nutrients
11.5 Soil pH
11.6 Cation Exchange Capacity
11.7 Carbon to Nitrogen Ratio
11.8 Summary
References
12 Crop Yields
12.1 Multi‐functionality of Cover Crops
12.2 Crop Yields
12.3 Climate
12.4 Factors Affecting Crop Production
12.5 Summary
References
13 Grazing and Harvesting
13.1 Cover Crop Biomass Removal
13.2 Grazing
13.3 Minimizing Potential Grazing Impacts
13.4 Harvesting
13.5 Grazing and Harvesting: An Added Benefit from Cover Crops?
13.6 Summary
References
14 Economics
14.1 Cover Crops and Farm Profits
14.2 Economic Analysis
14.3 Site‐Specificity of Economic Benefits
14.4 Summary
References
15 Adaptation to Extreme Weather
15.1 Extreme Weather Events
15.2 Droughts
15.3 Floods
15.4 Precipitation Extremes
15.5 Dust Storms
15.6 Temperature Extremes
15.7 Soil Resilience
15.8 Summary
References
16 Opportunities, Challenges, and Future of Cover Crops
16.1 Opportunities
16.2 Challenges
16.3 Remaining Questions
16.4 The Future of Cover Crops
16.5 Summary
References
Appendix I: Common and Scientific Names Used in the Book
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Some of the Current Signs Showing Soil Ecosystem Services Have De...
Chapter 2
Table 2.1 Case Studies of Low Cover Crop Biomass Production When Cover Crop...
Table 2.2 Mean (± Standard Deviation) Cover Crop Biomass Production for Dif...
Table 2.3 Examples of Cover Crop Biomass Production Averaged Across Various...
Table 2.4 Some of the Potential Strategies to Increase Cover Crop Biomass P...
Table 2.5 Examples of Cover Crop Biomass Production When Interseeded into S...
Table 2.6 Some Examples of Cover Crop Biomass Production When Cover Crops a...
Table 2.7 Examples of Cover Crop Biomass Production When Cover Crops are Se...
Table 2.8 Examples of How Termination Timing Affects Cover Crop Biomass Pro...
Chapter 3
Table 3.1 Review Results on the Impacts of Cover Crop on Soil Physical Prop...
Table 3.2 Results from Two Meta‐Analyses of Studies on Cover Crop Impacts o...
Table 3.3 Cover Crop (CC) Impacts on Earthworm Abundance
Chapter 4
Table 4.1 Cover Crop Impacts on Runoff and Sediment Loss Based on Recent St...
Table 4.2 Cover Crop Impacts on Time to Runoff Initiation
Chapter 5
Table 5.1 Impact of Cover Crops on Wind Erosion
Table 5.2 Cover Crop Impacts on Soil Wind Erodible Fraction (<0.84 mm Dry A...
Chapter 6
Table 6.1 Factors that can Affect Cover Crop Impacts on Nitrate Leaching
Table 6.2 Cover Crop Impacts on Dissolved Nutrients in Runoff
Chapter 7
Table 7.1 Potential Impacts of Different Factors on CO
2
and N
2
O Emissions a...
Chapter 8
Table 8.1 Some Case Studies on Cover Crops and Soil C from the U.S. Midwest...
Table 8.2 Potential Factors Affecting Soil C Sequestration with Cover Crops...
Chapter 9
Table 9.1 Case Studies on Cover Crops and Soil Water Content Under Rainfed ...
Chapter 11
Table 11.1 Cover Crop Impacts on Soil Organic Matter and Cation Exchange Ca...
Table 11.2 Cover Crop Impacts on Soil pH Across Different Environments in t...
Chapter 12
Table 12.1 Synthesis of Review Papers on Cover Crops and Crop Yields on Reg...
Table 12.2 Some Case Studies of Interseeding Cover Crops and Crop Yield Res...
Chapter 13
Table 13.1 Case Studies Reporting Impacts of Grazing Cover Crops on Soil Pe...
Table 13.2 A Few Case Studies on the Impacts of Grazing Cover Crops on Wate...
Table 13.3 Case Studies on The Impacts of Grazing Cover Crops on Soil Organ...
Table 13.4 Crop Yield Response to Cover Crop Grazing Under Different Locati...
Chapter 14
Table 14.1 Impact of Grazing and Harvesting Cover Crops on Annual Net Retur...
Chapter 15
Table 15.1 Cover Crops can be Effective at Reducing Runoff and Losses of Se...
Table 15.2 Mechanisms by which Cover Crops can Enable Agricultural Soils to...
Chapter 16
Table 16.1 Opportunities and Challenges of Cover Crops for the Management o...
List of Illustrations
Chapter 1
Figure 1.1 The number of publications on cover crops has increased exponenti...
Figure 1.2 No‐till sunn hemp (left) and late‐maturing soybean (right) summer...
Figure 1.3 Soils provide numerous essential services.
Chapter 2
Figure 2.1 Interconnectedness among cover crop biomass production, soil prop...
Figure 2.2 Early‐terminated (~30 days before planting corn) winter rye cover...
Figure 2.3 Corn without cover crop interseeded (left) and corn with aerially...
Chapter 3
Figure 3.1 Changes in soil physical, chemical, and biological properties as ...
Figure 3.2 Tap‐rooted cover crops can penetrate 20 cm or deeper into the soi...
Figure 3.3 Winter triticale cover crop effect on geometric mean diameter of ...
Chapter 4
Figure 4.1 Winter rye cover crops can reduce water erosion in sloping cropla...
Figure 4.2 Cover crops reduce sediment loss and runoff in most cases but may...
Figure 4.3 Oat cover crop planted in late summer and terminated in late fall...
Chapter 5
Figure 5.1 Winter rye cover crop planted to manage wind erosion in the weste...
Figure 5.2 Soil surface exposed to water and wind erosion in early spring wh...
Chapter 6
Figure 6.1 Some potential strategies for enhancing the potential of cover cr...
Chapter 7
Figure 7.1 Some strategies that can enhance cover crop potential to reduce s...
Chapter 8
Figure 8.1 Published reviews on cover crop impacts on soil C sequestration....
Figure 8.2 Early‐terminated cover crop (top) may not increase organic soil C...
Figure 8.3 Some potential strategies to promote C sequestration with cover c...
Chapter 9
Figure 9.1 Cover crop growing during fallow period in winter wheat‐fallow sy...
Figure 9.2 Cover crops contribute to precipitation capture and water storage...
Figure 9.3 Positive, neutral, and negative impacts of cover crops on soil wa...
Chapter 10
Figure 10.1 Winter rye cover crop can be effective at suppressing weeds (lef...
Figure 10.2 Some potential strategies that can enhance the effectiveness of ...
Chapter 13
Figure 13.1 Grazing cover crops can support livestock production while maint...
Figure 13.2 Grazing cover crops can cause pugging and compaction especially ...
Figure 13.3 Strategies for alleviating grazing cover crop impacts on soil co...
Figure 13.4 Winter rye cover crop planted after corn silage and harvested as...
Chapter 14
Figure 14.1 Simplified balance of input and output costs following cover cro...
Chapter 15
Figure 15.1 Flooded cropland under intense rainstorms in the spring near Cla...
Chapter 16
Figure 16.1 Cover crops can be multi‐functional systems for managing soil he...
Figure 16.2 Cover crops can have more positive than negative impacts.
Guide
Cover Page
Title Page
Copyright Page
Preface
Table of Contents
Begin Reading
Appendix I Common and Scientific Names Used in the Book
WILEY END USER LICENSE AGREEMENT
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Cover Crops and Soil Ecosystem Services
Humberto Blanco
Department of Agronomy and Horticulture
University of Nebraska
Lincoln, NE, USA
Copyright © 2023 American Society of Agronomy, Inc. / Crop Science Society of America, Inc. / Soil Science Society of America, Inc. All rights reserved.
Copublication by American Society of Agronomy, Inc. / Crop Science Society of America, Inc. / Soil Science Society of America, Inc. and John Wiley & Sons, Inc.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted by law. Advice on how to reuse material from this title is available at http://wiley.com/go/permissions.
The right of Humberto Blanco to be identified as the author of this work has been asserted in accordance with law.
Limit of Liability/Disclaimer of WarrantyWhile the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy of completeness of the contents of this book and specifically disclaim any implied warranties or merchantability of fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The publisher is not providing legal, medical, or other professional services. Any reference herein to any specific commercial products, procedures, or services by trade name, trademark, manufacturer, or otherwise does not constitute or imply endorsement, recommendation, or favored status by the ASA, CSSA and SSSA. The views and opinions of the author(s) expressed in this publication do not necessarily state or reflect those of ASA, CSSA and SSSA, and they shall not be used to advertise or endorse any product.
Editorial Correspondence:American Society of Agronomy, Inc.Crop Science Society of America, Inc.Soil Science Society of America, Inc.5585 Guilford Road, Madison, WI 53711‐58011, USA
agronomy.org • crops.org • soils.org
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Wiley also publishes its books in a variety of electronic formats and by print‐on‐demand. Some content that appears in standard print versions of this book may not be available in other formats.
Library of Congress Cataloging‐in‐Publication DataNames: Blanco, Humberto, 1961‐ author. | American Society of Agronomy, issuing body. | Crop Science Society of America, issuing body. | Soil Science Society of America, issuing body.Title: Cover crops and soil ecosystem services / Humberto Blanco.Description: First edition. | Hoboken, NJ, USA : Wiley‐ACSESS, 2023. | Includes bibliographical references.Identifiers: LCCN 2023002570 (print) | LCCN 2023002571 (ebook) | ISBN 9780891186397 (hardback) | ISBN 9780891186427 (adobe pdf) | ISBN 9780891186410 (epub)Subjects: LCSH: Cover crops. | Soil protection. | Soil conservation.Classification: LCC SB284 .B536 2023 (print) | LCC SB284 (ebook) | DDC 631.4/52–dc23/eng/20230215LC record available at https://lccn.loc.gov/2023002570LC ebook record available at https://lccn.loc.gov/2023002571
Cover Design: WileyCover Image: Courtesy of Humberto Blanco
Preface
Literature is replete with peer‐reviewed and non‐peer‐reviewed information on cover crops. Indeed, the number of publications on cover crops has exponentially increased in recent years. However, a book that integrates the potential soil ecosystem services provided by cover crops based on peer‐reviewed research information is difficult to find in the midst of the abundant literature. Such integration can be helpful to better understand the ability of cover crops for maintaining or improving soil ecosystem services. Thus, the purpose of this book is to present readers with science‐based information on cover crop implications on soil ecosystem services.
The positive or negative impacts of cover crops on soil ecosystem services are often overgeneralized in non‐peer‐reviewed literature and during general conversations. Also, cover crop experience from one location or region is often extrapolated to other agroecozones with different soil types, cover crop management scenarios, and climatic conditions without consideration of potential site‐specific soil and crop response to cover crops. Discussion based on the research on both benefits and barriers surrounding cover crops can help with making informed decisions regarding cover crop adoption and management.
The discussion of cover crop impacts on soil ecosystem services in this book is based on published reviews, meta‐analyses, and individual studies. When no reviews or meta‐analyses are available for in‐depth understanding of a given topic, the book cites relevant case studies or reports summaries of recent studies to support discussions and conclusions. Because most research work on cover crops has been conducted in temperate regions such as the U.S., most of the conclusions in this book are based on studies from these regions.
This book covers these topics: cover crop biomass production, soil properties, soil erosion, nutrient losses, soil gas emissions, soil C sequestration, soil water, weed management, nutrient management, crop production, and cover crop grazing and harvesting. It also includes some discussion on cover crop economics, cover crop potential for adaptation to extreme weather events, and opportunities and challenges of cover crop management. Factors that can affect cover crop impacts on soil ecosystem services are emphasized in each chapter. This book emphasizes ‘soil’ because understanding soils is critical to understand cover crops and their services.
This book is written for researchers, soil conservationists, crop consultants, students, and others interested in exploring the complex system changes that happen when cover crops are used in a cropping system. However, this book is not a guideline for cover crop establishment and management. The intention is to discuss cover crops and relevant soil ecosystem services based on experimental research information that advances our understanding of the potential of cover crops for addressing the declining soil ecosystem services and increasing concerns about weather extremes. It is my hope this book will further stimulate the discussion on the role of cover crops in the changing face of agriculture.
1Cover Crops and Soil Ecosystem Services
1.1 Cover Crops
According to the Soil Science Society of America, cover crops are defined as a “close‐growing crop that provides soil protection, seeding protection, and soil improvement between periods of normal crop production, or between trees in orchards and vines in vineyards. When plowed under and incorporated into the soil, cover crops may be referred to as green manure crops” (SSSA, 2022). Cover crops are not entirely new. Their use dates back over several millennia or probably to the origins of agriculture. Literature indicates that cover crops were used as green manure by civilizations in eastern Asia and ancient Rome approximately 3000 years ago (Groff, 2015; Lipman, 1912). Ancient civilizations used cover crops such as legumes as a source of essential nutrients to support soil fertility and productivity. In early times, cover crops were normally incorporated into soil to accelerate decomposition and improve soil fertility and thus were synonymous to green manure. In the U.S., Native Americans often used a mix of crops to improve crop diversity, which portrayed cover crop mixes (Groff, 2015). In the late 1700s, the first U.S. president, George Washington, was one of the first promoters of using cover crops to conserve soil in the Americas, and he often planted clover, grass, and buckwheat as cover crops (Groff, 2015). At the time, cover crops were mostly used in nutrient‐depleted soils including monocultures of cotton in the southern U.S. and in other crops with limited residue input.
In the early 1900s, Hugh Hammond Bennett, known as the Father of Soil Conservation, vehemently advocated for the use of cover crops to reduce soil erosion, reduce nutrient leaching, and improve soil productivity during and in the aftermath of the Dust Bowl in his influential book “Soil Conservation” (Bennett, 1939). He considered cover crops as an integral piece to conserve soil and halt soil degradation. Indeed, Hugh Hammond Bennett was testifying before Congress in spring 1935 on the need to implement better soil conservation practices, such as cover crops, as a dust storm approached Washington, D.C. at the peak of the Dust Bowl. His testimony, coinciding with the dramatic arrival of the dust storm to the Capitol, facilitated the passage of the Soil Conservation Act by Congress and subsequent signing by President Roosevelt on April 27, 1935 (The National Agricultural Law Center, 1935). The Act specifically called for the implementation of soil erosion prevention measures such as growing vegetation (e.g., cover crops).
Cover crops were often used before World War II (1939–1945). Common cover crop species used by early adopters included crimson clover, field pea, crotalaria, sudangrass, millet, sweet clover, alfalfa, hairy vetch, winter rye, buckwheat, and others (Bennett, 1939; Lipman, 1912). Legume cover crops were used as sources of nutrients (e.g., N, C), while grass cover crops were used for erosion control. Following World War II, the rapid production and vast availability of commercial pesticides, herbicides, and synthetic fertilizers led to a slowed interest in the use of cover crops. Cover crop use was relatively minimal between 1940 and 1980 although organic farmers used cover crops throughout this period. However, increasing concerns over soil C losses, soil degradation, nutrient runoff, and nitrate leaching from agricultural lands contributed to reemergence of interest in cover crops in the 1980s.
Figure 1.1 The number of publications on cover crops has increased exponentially in the past few decades.
Web of Science.
The heightened interest in using cover crops in the past few decades resulted in an exponential increase in the number of publications (Figure 1.1). A search in Web of Science using the phrase “cover crops” up to December 2021, shows the number of publications was only 35 prior to 1980, 613 between 1980 and 2000, and 5967 between 2001 and 2021 (Figure 1.1). Most articles published before 1980 discussed the use of cover crops in low‐biomass producing crops (e.g., cotton), orchards (e.g., cover crops planted under or between trees), and vegetable gardens for pest suppression (e.g., nematodes). Between 1980 and 2000, the main reasons for the use of cover crops were water and wind erosion control, soil fertility improvement, and the suppression of pests and diseases, while between 2000 and 2010, there was greater discussion of cover crops for sequestering soil C and improving soil quality.
Research on cover crops during the last decade (2010–2020) has expanded beyond the on‐farm benefits from cover crop use. Now, most publications focus on ecosystem services or multi‐functionality of cover crops, climate mitigation potential, agricultural intensification, soil biological environment, soil water management, and the challenges and opportunities of cover crop management. Also, several publications have recently emerged regarding the potential of cover crops to support livestock production via grazing or haying while improving farm economics and maintaining soil ecosystem services.
The above chronology indicates that while the use of cover crops is nothing new, interest in the multi‐functionality of cover crops has increased in recent years (Figure 1.2). Most research on cover crops has been conducted in the U.S. Many studies are also evaluating management strategies to make cover crops work in water‐limited environments where cover crop success can be restricted due to limited precipitation. Despite abundant literature, the adoption rate of cover crops is still slow. For example, in the U.S., cover crops are used in less than 5% of croplands although the adoption rate depends on the region. In some regions, cover crops are used in approximately 20% of croplands (Yoder et al., 2021).
Figure 1.2 No‐till sunn hemp (left) and late‐maturing soybean (right) summer cover crops in winter wheat‐grain sorghum systems for enhancing soil ecosystem services.
Blanco‐Canqui et al., 2011; Photo by H. Blanco.
1.2 Soil Ecosystem Services
Soils provide many invaluable services to humans (Figure 1.3). Not only do soils support food crops, but soils also support biomass as fiber for the textile industry, feedstock for biofuel production, and forage for animals (Hatfield et al., 2017). Soils capture precipitation and irrigation water, clean water, degrade pollutants, sequester atmospheric C, adsorb and retain nutrients, moderate temperature, provide habitat for billions of soil organisms, and deliver many other services. These essential soil services can be grouped into four categories: supporting, provisioning, regulating, and cultural services (Figure 1.3; MEA, 2005; Dominati et al., 2010; Comerford et al., 2013). Supporting services refer to C, nutrient, and water cycling as well as primary production, soil formation, and microbial habitat, while provisioning services refer to the products we obtain from soil including water, food, fiber, feed, and fuel (MEA, 2005). Soils do not simply support and deliver products but also mediate and regulate many processes, which are vital to plants, animals, and humans (Hatfield et al., 2017). Such services are considered as regulating services and include climate regulation, air quality regulation, water movement and purification, prevention of floods, and management of pests and diseases (MEA, 2005). Also, soils have aesthetic, spiritual, educational, and recreational value, and these are grouped as cultural services (MEA, 2005).
Figure 1.3 Soils provide numerous essential services.
MEA, 2005; Dominati et al., 2010; Comerford et al., 2013.
The supporting, provisioning, regulating, and cultural services are all interconnected and subject to feedbacks among services. As an example, a soil may not be able to produce food and biomass if it cannot effectively cycle and recycle water and nutrients. Perhaps the leading service from the soil is the supporting service, which directly affects the capacity of the soil to produce food, fiber, feed, and fuel (provisioning services), buffer or moderate temperature, and contribute to water flow and storage (regulating services), improve landscape esthetics, and serve as recreational, educational, and spiritual space (cultural services).
The concept of soil ecosystem services is often implied but not entirely valued (Pires‐Marques et al., 2021; Yee et al., 2021). Any service in society has a value. Thus, the services that soils provide have a value. Assigning a monetary value on different soil ecosystem services has been the topic of recent publications (Comerford et al., 2013; Mikhailova et al., 2021; Pires‐Marques et al., 2021). Provisioning services such as food and biomass production can be easily valued because these products are marketable, but how about the rest of soil ecosystem services? For example, what is the monetary value of clean water, clean air, reduced C losses, reduced sediment losses, and other services?
Some have quantified the value of select soil ecosystem services by considering the “avoided cost” of soil erosion (Pires‐Marques et al., 2021) and CO2 emissions (Mikhailova et al., 2021), while others considered natural capita and flow of ecosystem services for the economic valuation of such services (Comerford et al., 2013; Yee et al., 2021). Comerford et al. (2013) reported some estimates of economic values for different ecosystem services including nitrate leaching, sediment loss, nutrient cycling, soil formation, salinization, contamination, and others. Most of these estimates are for supporting services. Also, available approaches often value a single service such as C sequestration or reduced losses of C as CO2 (Mikhailova et al., 2021). However, linkages of a given service with related ecosystem service indicators need further consideration (Comerford et al., 2013). For instance, if a soil sequesters C or reduces CO2 emissions, then soil aggregation or the amount of stable soil aggregates that contribute to the protection of C within aggregates should be considered during the valuation of services. This and other similar inter‐related processes complicate the valuation.
Qualitative valuation of ecosystem services is relatively simple but quantitative valuation (monetary value) of ecosystem services is complex, especially when processes are interconnected or not directly marketable. A more comprehensive economic assessment of all indirectly marketable soil ecosystem services can help with decision‐making process for the management of natural resources and thus ecosystem services. Indirectly marketable soil ecosystem services including recreation, spiritual fulfillment, landscape esthetics (e.g., year‐round growing vegetation), mental and overall plant, animal, human health are often subtle but these soil services can be as valuable as marketable soil ecosystem services (Comerford et al., 2013; Yee et al., 2021).
The consideration of benefits from soil within the framework of ecosystem services is a holistic approach to view the soil as a service provider and one that deserves attention and care. Process‐based models or quantitative frameworks are being developed to account for multiple soil processes contributing to a given service, although more refinement of such models is needed to fully quantify and value soil ecosystem services at farm‐scales (Yee et al., 2021). It is clear that an understanding of the value of soil will be incomplete until we fully assign a quantitative value to each ecosystem service that soils provide. However, a value cannot be assigned until the impacts of cover crops on each soil service is quantified and understood.
1.3 Cover Crops and Soil Ecosystem Services
The concept of soil ecosystem services emerged in recent decades due to declining services from the soil and the need to improve, maintain, and restore such services (Figure 1.3). The fate and downfall of many past civilizations depended on the ability of soils to continuously deliver vital services to plants, animals, and humans (Bennett, 1939). Increased erosion (Thaler et al., 2021), increased water pollution (Haque, 2021), development of hypoxic zones (Anderson et al., 2021), and other environmental problems are current signs of accelerated loss of ecosystem services from soils (Table 1.1). This is particularly true under increasing extreme weather events with intense rainstorms, frequent droughts, extreme temperatures, and heat waves. Thus, the challenge of this century is to ensure that soil ecosystem services are maintained or improved not only to meet the demands for food, fuel, fiber, and feed but also to reduce water pollution, air pollution, soil C loss, soil erosion, and others. Soil ecosystem services are finite and exhaustible as the soil is highly dynamic and susceptible to rapid degradation when not managed properly. Management determines the ability or inability of the soils to provide the essential provisioning, regulating, supporting, and cultural ecosystem services.
Table 1.1 Some of the Current Signs Showing Soil Ecosystem Services Have Declined
Decline in soil ecosystem services
Source
Increased losses of soil C via erosion, leaching, and as C emissions
Minasny et al.,
2017
; Jian et al.,
2020
Reduced water quality or increased water pollution
Blanco‐Canqui,
2018
; Haque,
2021
Increased hypoxic and anoxic events in lakes and coastal areas
Fennel and Testa,
2019
; Anderson et al.,
2021
Increased susceptibility to water erosion (increased runoff and sediment loss)
Fenta et al.,
2020
; Thaler et al.,
2021
Increased minimum and maximum temperature or temperature extremes
Kaye and Quemada,
2017
; Zscheischler and Fischer,
2020
Increased susceptibility to prolonged and frequent flooding
Kaye and Quemada,
2017
; Wright et al.,
2017
Reduced soil and agroecosystem resilience against droughts
Vogel et al.,
2019
; Zscheischler and Fischer,
2020
Overall reduced health of soils against extreme events
Lehmann et al.,
2020
One of the reemerging biological strategies that has potential to improve and maintain soil ecosystem services from agricultural lands is the inclusion of cover crops into current cropping systems (Figure 1.2). Unlike other management practices such as the introduction of perennial vegetation (e.g., grass hedges) to croplands, cover crops would not compete with land for food production as they are often grown during times when no crops are growing in the field. Even when cover crops are interseeded along main crops or before the main crop harvest, cover crops do not appear to compete with the main crops nor reduce crop yields under proper management. Interseeding cover crops via aerial broadcasting or drilling with improved high clearance equipment when main crops are in the field is a subject of current research (Blanco‐Canqui et al., 2017).
The question is: Can cover crops under different scenarios of cover crop management improve or enhance all the ecosystem services that soils provide? If not, how can the potential of cover crops to deliver soil ecosystem services be enhanced? It is often considered that cover crops would improve soil properties, sequester C, and improve other ecosystem services. In some cases, this common belief may, however, contrast with field research data. Adoption and management of cover crops may not be free of challenges (Roesch‐McNally et al., 2018). A need exists to better understand the extent to which cover crops can maintain or enhance the multiple ecosystem services of agricultural lands based on experimental data.
Furthermore, many recent publications are emphasizing the multi‐functionality of cover crops (Schipanski et al., 2014; Blanco‐Canqui et al., 2015; Finney & Kaye, 2017). For instance, grazing or harvesting cover crops is generating interest (Franzluebbers & Stuedemann, 2008; Kelly et al., 2021). However, can cover crops be grazed or harvested and still be considered cover crops? The existing definition of cover crops does not appear to account for some of the potential multi‐functionality of cover crops such as supporting livestock production (SSSA, 2022).
This book discusses how cover crops affect the numerous ecosystem services that soils provide under different cover crop management scenarios and climatic conditions based on experimental data. It also highlights challenges and opportunities with cover crops to manage soil ecosystem services. The ecosystem services are discussed in terms of soil health, water erosion, wind erosion, greenhouse gas emissions, C sequestration, nutrient losses, soil water, weed management, soil fertility, crop yields, and economics, among others. It also includes discussion on how grazing or harvesting of cover crops could alter the main purpose of cover crops, which is soil conservation and management.
1.4 Summary
Interest in growing cover crops is reemerging as one of the options to address the decline in soil ecosystem services from agricultural lands. Soil ecosystem services refer to the numerous benefits we receive from soils. Soils not only produce food and biomass (marketable services) but also filter water, sequester C, recycle nutrients, suppress weeds and diseases, and moderate soil temperature, among other services. These services are grouped into four categories: supporting, provisioning, regulating, and cultural services.
Cover crops can be a strategy to restore, improve, and maintain these essential services from soil. The use of cover crops dates back over three millennia but slowed in the mid‐1900s due to the advent of inorganic fertilizers, herbicides, and pesticides after World War II. Interest rapidly increased after the 1980s due to heightened concerns of water pollution (e.g., hypoxia, anoxia), soil erosion, soil C losses, frequency of extreme weather events, and others. In early years, cover crops were primarily used for pest suppression and soil fertility improvement as green manure. Now, cover crops are being considered more and more as multi‐functional systems that can deliver multiple soil ecosystem services. However, the potential of cover crops to function as multi‐functional systems is not yet well understood. The question is: Can cover crop improve all soil ecosystem services? This book addresses this question based on experimental data on the impacts of cover crop management on soil environment, water quality, greenhouse gas emissions, C sequestration, soil water, weeds, crop yields, livestock production (e.g., grazing, haying), and other soil services.
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2Cover Crop Biomass Production
2.1 Cover Crops and Biomass
Can cover crops deliver numerous soil ecosystem services? One of the key drivers that determines the delivery of such services is the amount of cover crop biomass produced (Figure 2.1). Cover crop benefits may not be observed unless cover crop biomass production is high enough or reaches a threshold level that alters a service. Also, expanded uses of cover crops such as grazing and haying or harvesting for livestock or biofuel production depend on the amount of biomass produced to determine whether cover crops can be safely grazed or harvested without compromising the benefits of cover crops for other services.
A knowledge of both aboveground and belowground (root) biomass production is important to assess any changes in soil ecosystem services from cover crops. Indeed, some services such as soil C sequestration could depend more on belowground biomass production than on aboveground biomass production (Xu et al., 2021). Often, we focus on what we see in the field when cover crops are growing, which is aboveground biomass, and not on the “hidden” portion, which is belowground biomass. Also, interest in cover crop diversity or mixes is growing, but do multi‐species cover crop mixes produce more aboveground and belowground biomass than monocultures? Some hypothesize that diverse cover crop mixes could concomitantly translate into delivery of diverse and multiple ecosystems services.
This chapter discusses the amount of aboveground and belowground biomass that cover crops can produce. It also discusses how different cover crop management strategies including planting and termination timing, seeding rates, mixes and monocultures, and other factors affect cover crop biomass production.
Figure 2.1 Interconnectedness among cover crop biomass production, soil properties, and soil ecosystems services.
2.2 Aboveground Biomass Production
The amount of cover crop biomass produced is highly variable as there are numerous factors that affect cover crop biomass production. Perhaps the most critical factors for cover crop production are precipitation and temperature. Cover crop biomass production varies not only from location to location but also from year to year within the same location due to differences in precipitation amount and other factors. Reduced growing degree days, limited soil moisture for cover crop germination, delayed germination, and other challenges can result in reduced cover crop biomass production. In water‐limited regions, cover crop establishment is a major hindrance for biomass production.
2.2.1 Temperate Regions
Cover crops can produce, on average, 3.78 ± 3.08 Mg ha−1 of biomass in temperate regions (annual precipitation >750 mm; Ruis et al., 2019). Cover crops can produce lower amounts of biomass in colder temperate regions than in warmer temperate regions due to shorter growing cover crop seasons in colder regions. Within temperate regions, cover crop biomass production follows this order of warm > mild > cold. In cool temperate regions, cover crop biomass production may not exceed 1 Mg ha−1 if cover crops are planted late in fall and terminated early in spring, which limits the period of time for cover crop growth (Table 2.1). Winter cover crops such as rye are predominantly used in cold temperate regions (Table 2.1). These cover crops are often added to continuous corn or rotations with corn such as corn–soybean and corn–small grains. Cover crop biomass production among cover crop species does not significantly differ although grass cover crops tend to produce more biomass than other species (Table 2.2).
Table 2.1 Case Studies of Low Cover Crop Biomass Production When Cover Crops Are Seeded Late and Terminated Early Under Typical Corn and Soybean Systems in Cool Temperate Regions
Location
Crop
Cover crop
Planting time
Termination time
Cover crop biomass (Mg ha
−1
)
a
Iowa, U.S.
Soybean
Winter rye
Mid‐fall
Early spring
0.6
b
Nebraska, U.S.
Continuous corn
Winter rye
Mid‐fall
Early spring
0.8
c
Nebraska, U.S.
Corn–soybean
Winter rye
Mid‐fall
Early spring
1.1
d
Missouri, U.S.
Continuous corn
Winter rye
Mid‐fall
Mid‐spring
0.6
a Moore et al. (2014).
b Sindelar et al. (2019).
c Koehler‐Cole et al. (2020).
d Rankoth et al. (2019).
2.2.2 Semiarid Temperate Regions
The amount of cover crop biomass produced in water‐limited regions can be significant but is as variable as in regions with high precipitation. Cover crop biomass production in water‐limited regions with <750 mm of annual precipitation can average 2.50 ± 2.37 Mg ha−1 (Blanco‐Canqui et al., 2022; Ruis et al., 2019). This average across studies from semiarid regions suggests that cover crops can produce approximately 1 Mg ha−1 less biomass in water‐limited regions relative to the average in regions with >750 mm of annual precipitation. Data on cover crop biomass production from arid regions (<250 mm precipitation) are unavailable. Low precipitation limits cover crop adoption in arid regions. As in high‐precipitation regions, cover crop biomass production in low‐precipitation regions is management dependent.
Table 2.2 Mean (± Standard Deviation) Cover Crop Biomass Production for Different Cover Crop Species for Two Climatic Regions Within Temperate Regions
Climate
Cover crop species
Cover crop biomass (Mg ha
−1
)
Humid temperate regions
Grasses
4.02 ± 3.47
Legumes
3.58 ± 2.83
Brassicas
2.73 ± 1.90
Mixes
3.98 ± 2.83
Semiarid temperate regions
Grasses
3.37 ± 3.22
Legumes
2.19 ± 1.94
Brassicas
1.89 ± 1.22
Mixes
2.66 ± 2.09
Notes: Ruis et al. (2019).
The same factors that affect cover crop biomass production in high‐precipitation regions affect biomass production in low‐precipitation regions. Grass cover crops and grass–legume mix cover crops tend to produce more biomass than legumes in semiarid temperate regions (Table 2.2). Also, winter (e.g., rye, triticale, wheat) and summer (e.g., sorghum sudangrass) cover crops can produce relatively high amounts of biomass relative to other species (Holman et al., 2018; Kumar et al., 2020). It is important to note that when cover crops produce significant amounts of biomass in water‐limited regions, cover crops can reduce subsequent crop yields by reducing available water, especially in years when precipitation amount is below normal although improved soil physical properties after cover crop systems are introduced could lead to increased water retention in the long term (Holman et al., 2018; Nielsen et al., 2015). Improved cover crop management practices such as planting and/or terminating early can be options to reduce the negative impacts on subsequent crop yields. Well‐established cover crops can increase water infiltration and reduce evaporation via residue mulching, which can be valuable in low‐precipitation areas.
2.2.3 Tropical and Subtropical Regions
Cover crops generally produce greater amounts of biomass in subtropical and tropical regions than in temperate regions due to the longer growing window. For example, in a tropical region of Brazil, signal grass and jack bean produced approximately 9.32 Mg ha−1, while sunn hemp, crowngrass, and pearl millet produced between 3.98 and 5.24 Mg ha−1 during the first year (Teixeira et al., 2014). Case studies from humid subtropical regions show cover crops can produce as much 16 Mg ha−1 of biomass with an average of 6 Mg ha−1 (Table 2.3). As in other regions, the amount of biomass can be variable, depending on cover crop species and management. Legume cover crops (e.g., clover, sunn hemp, hairy vetch) are often used in subtropical and tropical regions as N sources for subsequent crops. High humidity and temperature in subtropical and subtropical regions can lead to rapid decomposition of cover crops, which can positively or negatively impact soil ecosystem services. For instance, the rapid decomposition of cover crop residues can release nutrients for the next crop, but it may reduce soil C accumulation. In particular, legume cover crop residues are subject to rapid turnover relative to grass cover crop residues.
Table 2.3 Examples of Cover Crop Biomass Production Averaged Across Various Years in Subtropical and Tropical Climates
Location
Cover crop
Biomass (Mg ha
−1
)
a
Parana, Brazil
Wheat
3.3
Radish
3.7
Vetch
3.7
Lupine
3.8
Oat
4.3
b
Parana, Brazil
Vetch
3.2
Radish
6.1
Ryegrass
5.1
Black oat
5.5
Clover
2.2
c
Georgia, U.S.
Rye
8.5
Austrian winter pea
4.6
Narrow‐leaf lupine
6.7
Cahaba vetch
2.8
Crimson clover
3.2
d
Rio Grande do Sul, Brazil
Oat
5.0
Vetch
4.0
e
Alabama, U.S.
Sunn hemp
7.6
f
Georgia, U.S.
Rye
4.0
Hairy vetch
4.2
a Tiecher et al. (2017).
b Pavinato et al. (2017).
c Webster et al. (2013).
d Gomes et al. (2009).
e Balkcom and Reeves (2005).
f Sainju et al. (2005).
2.3 Belowground Biomass Production
Belowground cover crop biomass production can influence soil ecosystem services more than aboveground biomass because roots are in closer contact with the soil (Qi et al., 2022; Xu et al., 2021). The ecosystem service benefits of cover crop roots are many, but the question here is: How much root biomass do cover crops produce? Experimental data on cover crop root biomass production are fewer than on aboveground biomass production. The available data indicate cover crop root biomass production can be 40–50% of the aboveground biomass production. While cover crop root biomass production can be lower than aboveground biomass production, addition of cover crops to existing cropping systems increases the total amount of root biomass produced by the system. For instance, cover crops can add, on average, 1.25 Mg ha−1 of root biomass to cropping systems in water‐limited regions considering the average aboveground cover crops biomass production in these regions is approximately 2.50 Mg ha−1 (Xu et al., 2021).
Similar to aboveground biomass production, cover crop root biomass production is highly variable due to differences in climate, length of cover crop growing season, cover crop species, and years after cover crop introduction. For example, just letting cover crops grow for a few days or weeks longer than early‐terminated cover crops can significantly increase total root biomass production as well as aboveground biomass production. Selection of cover crop species can be important for increasing root biomass amount and the type of root biomass input. For example, species of brassicas have roots with larger diameter than grass and legume cover crops (Chen & Weil, 2010; Kemper et al., 2020). Differences in root biomass and characteristics among cover crops can determine differences in soil ecosystem services from cover crops.
How cover crop root biomass production varies with soil depth is unclear as most studies report root biomass data only for the upper 10 cm of soil depth. Cover crop roots that can penetrate deeper into the soil are important for deep C sequestration, nutrient scavenging, groundwater recharge, and other processes. In Germany, Kemper et al. (2020) found that root length density for seven select cover crop species was in this order: Oil radish, Winter turnip rape, and Phacelia > Bristle oat > Winter rye and Crimson clover. This order suggests that tap‐rooted cover crops can penetrate deeper into the soil compared with fibrous‐rooted cover crops. Planting a mix of both fibrous‐ and deep‐rooted cover crops could be a strategy for a uniform root distribution in the soil profile. Fibrous‐rooted cover crops primarily improve soil properties near the soil surface, while deep‐rooted cover crops can improve such properties in deeper depths. Overall, cover crops can produce significant amounts of root biomass (approximately 40–50% of aboveground biomass). Increasing the proportion of total cover crop biomass allocated to roots in deeper depths in the soil profile is critical to enhance soil ecosystem services.
2.4 Threshold Level of Biomass Production
Cover crops may not significantly improve soil ecosystem services unless biomass production exceeds a certain threshold level. The minimum level of cover crop biomass production needed to exert significant changes in soil ecosystem services could be approximately 1 Mg biomass ha−1 (Koehler‐Cole et al., 2020; Kaspar et al., 2001; Finney & Kaye, 2017). Various field experiments have shown that cover crops, particularly winter cover crops, in cool temperate regions often produce less than 1 Mg ha−1 due to the short growing window and thus do not significantly alter soil ecosystem services (Table 2.1). The threshold level of biomass production can vary with the soil ecosystem service. For example, a larger amount of cover crop biomass may be needed to change soil C stocks and suppress weeds than for other soil services such as erosion control or nitrate leaching reduction (Koehler‐Cole et al., 2020; Kaspar et al., 2001; Finney & Kaye, 2017). Also, the threshold level of cover crop biomass production to significantly suppress weeds can be approximately 4 Mg ha−1 (Finney & Kaye, 2017). Thus, developing management strategies that increase cover crop biomass production above the threshold level for different soils and climatic conditions is a priority to improve cover crop potential for maintaining or enhancing soil ecosystem services.
2.5 Management Practices that Affect Biomass Production
Cover crop biomass production not only depends on climate (e.g., precipitation and temperature) but also on cover crop management practices including planting and termination timing, seeding rates, cropping systems, irrigation, fertilization, and others (Table 2.4). In some cases, extending the cover crop growing season can increase cover crop biomass production if weather conditions are favorable. For instance, in cool temperate regions, winter cover crops such as winter rye are often planted late in fall after corn or soybean harvest and terminated early in spring before corn or soybean planting. Under this cover crop management scenario, the amount of biomass produced can be too low to exert significant changes in soil ecosystem services (Table 2.1). Planting cover crops early and terminating early, planting late and terminating late, and combining early planting with late termination can be strategies to extend the growing season and increase cover crop biomass production (Figure 2.2).
Table 2.4 Some of the Potential Strategies to Increase Cover Crop Biomass Production
Cover crop management strategies
Planting early via interseeding or drilling
Terminating late (at main crop planting)
Planting high‐biomass species
Planting after corn silage or short‐growing season crop
Increasing the seeding rate
Drilling rather than interseeding
Fertilizing at rates below main crop fertilization rates
Irrigating once or twice at establishment
Notes: Balkcom et al. (2018); Koehler‐Cole et al. (2020); Ruis et al. (2017); Antosh et al. (2020).
Figure 2.2 Early‐terminated (~30 days before planting corn) winter rye cover crop (left) can yield more biomass than late‐terminated (at corn planting) winter rye cover crop (right)
Photos by H. Blanco.
2.5.1 Planting Early
2.5.1.1 Interseeding
Planting cover crops into standing crops, known as interseeding, can be a potential opportunity to increase the length of the cover crop growing season (Figure 2.3). Methods of cover crop interseeding include broadcasting, drilling, and broadcasting followed by drilling. Aerial interseeding with an airplane or drone is an option to interseed cover crops at large scales. Concerns exist, however, that interseeded cover crops can compete like weeds with main crops to reduce crop yields. Research shows that competition and reduction in crop yields due to interseeding can be minimal if cover crops are interseeded after main crops are well established. Specifically, cover crops interseeded after certain vegetative stages (e.g., V2 in corn) may not adversely affect yields. In Michigan, U.S., ryegrass cover crop broadcast interseeded with a hand‐spreader at different corn growth stages from V2 to V7 for two years produced the highest amount of biomass of four treatments (ryegrass, crimson clover, oilseed radish, and three‐species mix) and generally had no negative effects on subsequent crop yields (Brooker et al., 2020).
Figure 2.3
