Cover Crops' Effect on Soil Quality and Soil Health

Introduction

Soil quality is one of the three primary components of environmental quality, along with water and air quality (Islam and Weil, 2000; Andrews et al, 2002). The tenn ‘soil quality’ is often confused with ‘soil health’. Scientifically, soil quality refers to the integration of soil’s quantifiable biological, chemical and physical properties to perform functions. In contrast, soil health is a popular tenn portraying soil as a complex living system that acts holistically to perform functions, rather than as a mixture of sand, silt and clay. While soil quality is defined as the soil’s capacity to function within an ecosystem and land-use boundaries to sustain biological productivity, maintain environmental quality and to promote plant and annual health (Doran and Parkin, 1994), soil health describes the integrated condition of the soil system in a holistic manner.

Soil health functions include support for economic crop production, recycling of applied nutrients, improving air and water quality and sustaining animal nutrition and health, as well as food quality and public health. Soil health (or quality) has been defined in many ways and usually includes an integration of soil biological, chemical and physical properties (Fig. 1).

Soil is a very complex multifunctional polydisperse system, of which its health or quality depends on variations in natural and anthropogenic factors, such as parent material, climate and topography and management practices. These factors determine and regulate the biological, physical and chemical properties of the soil. While soil quality cannot be measured directly, its assessment

Soil health (quality) and its relationship with physical, chemical, and biological properties

Fig. 1 Soil health (quality) and its relationship with physical, chemical, and biological properties.

The Ohio State University, Columbus, Ohio, USA.

relies oil selected soil indicators or properties to quantify the management-induced changes in soils (Karlen et al„ 1997; Islam and Weil, 2000; Weil et ah, 2003).

A range of soil-quality indicators has been identified to estimate soil quality; some of the most important are those which are responsive to changes in soil management and these include soil structure, porosity, infiltration, soil rooting characteristics, plant available water, soil cover, soil acidity, electrical conductivity, plant nutrients, soil organic matter (SOM), microbial biomass and microbial diversity (Allen et al„ 2011). Various smdies have been conducted to evaluate soil-quality indicators under different land use types (Abbasi et al., 2007; Ishaq et al., 2014; Kalu et al., 2015). However, the most popular chemical indicators used to assess soil quality are soil organic carbon (OC), total nitrogen (TN) and soil acidity (pH). Increasing the amount of OC improves soil quality, as it contributes to many beneficial physical, chemical and biological processes in the soil ecosystem (Carson, 2013). Therefore, soil quality related to soil health is crucial because only healthy soil can ensure high crop yields. To determine the effects of management practices on soil quality, it is essential to identify easily measurable, sensitive and early and key indicators of soil’s functionality in response to management practices (Table 1).

Cover cropping is one of the important components of sustainable agricultural practices that has received attention as a means of improving soil quality and is directly related to crop productivity and enhanced ecosystem sendees (Fig. 2). Cover crops are defined as the crops used to cover the ground as a living mulch or surface mulch to protect the soil and enhance soil productivity (Kaye

Table 1 Key indicators of soil functionality across agricultural management practices (Source: Islam and Well, 2000).

Ephemeral

Changes within Days/weeks (Very dynamic)

Intermediate

Subject to management Over several years (Dynamic)

Permanent

Inherent to profile or site (Inherent)

Moisture content

Microbes biodiversity

Depth slope

Field respiration

Enzymes/basal respuation

Texture

pH and salts

Earthworm/nematode

Climate

Available nutrients

Organic carbon (C)

Stoimiess

Bulk density

Total nitrogen

Fragipan

Cone mdex

Aggregate stability'

Mineralogy

Available water capacity

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Increasing Permanence

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Sustainable management practices and soil health quality

Fig. 2 Sustainable management practices and soil health quality.

and Quemada, 2017). Cover crops are either annual or perennial in nature and are planted between main crops (fallow) to improve soil quality and agricultural productivity by supporting biodiversity and efficiency, chemical buffering by accumulating SOM, regulating nutrient cycling, conserving soil moisture, reducing compaction with an associated increase in water filtration and adding soil physical stability (Hobbs et al., 2008).

Cover crops are grown to maintain soil quality by providing protection against soil erosion and nutrient leaching or runoff (Reeves, 1994), suppressing weeds, carbon sequestration, decreasing soil- bome pests and diseases, conserving soil moisture, reducing non-point source pollution, increasing water quality, etc. (Lai, 2015; Dabney et ah, 2001).

Cover crops improve soil physical, chemical and biological properties by providing organic carbon content, cation exchange capacity, aggregate stability and water infiltration (Dabney et ah,

2001). The schematic diagram for stepwise improvement of soil quality use of crops is presented in Fig. 3. Cover crops have been suggested to potentially improve soil nutrient nitrogen (N). Cover crops conserve nitrogen (N) by converting mobile nitrate into immobile plant protein (Weerasekara et ah, 2017). Legume cover crops fix atmospheric N2 and build up soil N, which benefits productivity and yield of subsequent cash crops while reducing N fertiliser requirements (Debney et ah, 2010). Legume cover crops (e.g., alfalfa, vetches, clover) can fix nitrogen (N) biologically and increase SOM content (Ltischer et ah, 2014). Non-legume cover crops (spinach, canola, flax) can absorb excess nitrate from the soil, increase crop biomass and improve soil quality (Finney et ah, 2016; White et ah, 2016). The SOM is a very important soil-quality indicator as cover crops have the potential to maintain higher levels of SOM, which might positively influence cation exchange capacity, water holding capacity, soil structure and microbial activity as well as might stabilise the soil (pH, which helps in plant nutrient uptake) (Sharnia et ah, 2018). In addition, SOM reduces compaction and crusting and binds soil particles together to reduce soil erosion.

Stepwise advantages of using cover crops and their effect on soil quality parameters (Source

Fig. 3 Stepwise advantages of using cover crops and their effect on soil quality parameters (Source: Blanco-Canqui

et al., 2015).

 
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