1. Introduction

The major environmental problems all over the world are the production and accumulation of wastes. Many considerations should be taken into account but, especially, those from the targets given by the European Union (EU). These problems related to wastes, together with the exhaustion of many resources, direct the European Union (EU) toward a strategy of zero waste through the circular economy. The transition to a more circular economy, where the value of products, materials, and resources is maintained in the economy for as long as possible, and the generation of waste minimized is an essential contribution to the EU's efforts to develop a sustainable, low-carbon, resource-efficient, and competitive economy [1].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In the EU plan action for the circular economy, we can find targeted actions for various types of waste. Agricultural wastes can be reflected in two aspects of this plan: recycling of nutrients and biomaterials.

This chapter pays attention to the physical properties of the soil due to their importance in plant growth and soil stability and the possibilities associated to the use of agricultural wastes. Moreover, it is centered in applying the circular economy concept and zero waste in agricul-

Physical Properties of Soils Affected by the Use of Agricultural Waste

http://dx.doi.org/10.5772/intechopen.77993

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Agricultural wastes can be used as a source of organic matter and nutrients for soils and influence the physical properties of soils. They can also be easily applied as mulching, providing numerous advantages [16]. So, this chapter gives an overview of the positive effects of

The physical properties of the soil are very important for agricultural production and the sustainable use of soil. The amount and rate of water, oxygen, and nutrient absorption by plants depend on the ability of the roots to absorb the soil solution as well as the ability of the soil to supply it to the roots. Some soil properties, such as low hydraulic conductivity, can limit the free supply of water and oxygen to the roots and affect negatively to the agricultural yield.

Soil structure is one of the most important soil's physical factors controlling or modulating the flow and retention of water, solutes, gases, and biota in agricultural and natural ecosystems [17, 18]. Soil structure is very important in soil productivity and is a limiting factor of crop yield [19, 20]. Soil structure controls many processes in soils. It regulates water retention and infiltration, gaseous exchanges, soil organic matter (SOM) and nutrient dynamics, root penetration, and susceptibility to erosion [21]. For these reasons, soil structure stands out among the physical properties of the

The term "structure" of a granular medium refers to the spatial arrangement of solid particles (texture) and void spaces. Most soils tend to exhibit a hierarchical structure. That is, primary mineral particles, usually in association with organic materials, form small clusters or "firstorder aggregates." These form larger clusters or "second-order aggregates" [22]. Aggregate hierarchy in soils is reflected in increasing aggregate size with each successive level. However, the term "structure" in soil cience generally carries a connotation of bonding mechanisms in addition to geometrical configuration of particles [22]. Organic matter acts as a cement that can

Without hierarchical structure, medium- and fine-textured soils such as loams and clays would be nearly impermeable to fluids and gases [22]. Moreover, the soil organic carbon has a greater effect on aggregation especially in coarse-textured soils [23]. Thus, structure plays a crucial role in the transport of water, gases, and solutes in the environment and in transforming soil into a

soil, since it exerts an important influence on the edaphic conditions and the environment.

help the formation of aggregates and, therefore, the soil structure.

suitable growth medium for plants and other biological organisms [22].

tural systems that can be able to reuse their own wastes.

recycling vegetable wastes and soil physical properties.

2.1. Soil structure

2. Importance of the physical properties of the soil

Recycled nutrients are a distinct and important category of secondary raw materials, for which the development of quality standards is necessary. They are present in organic waste and can be returned to soils as fertilizers. Their sustainable use in agriculture reduces the need for mineral-based fertilizers, the production of which has negative environmental impacts, and depends on imports, e.g., phosphate rock, a limited resource [1].

Bio-based materials, e.g., those based on biological resources (such as wood, crops, or fibers), can be used for a wide range of products (construction, furniture, paper, food, textile, chemicals, etc.) and energy uses (e.g., biofuels). The bioeconomy hence provides alternatives to fossil-based products and energy and can contribute to the circular economy. Bio-based materials can also present advantages linked to their renewability, biodegradability, or compostability. On the other hand, using biological resources requires attention to their life cycle environmental impacts and sustainable sourcing. The multiple possibilities for their use can also generate competition for them and create pressure on land use [1].

Agriculture is one of the major activities that produces wastes and consumes space, the agricultural soils. It is important to find a synergy between this activity and the soil. In this sense and following the considerations of the EU, crop residues are an important source of plant nutrients and organic matter [2]. Reuse of organic materials is desirable in order to reduce waste streams and to take advantage of the soil benefits associated with added organic matter and associated plant nutrients [3].

Nowadays, it is well known that the application to the soil of organic amendments derived from urban, agricultural, industrial, or municipal activity has several agronomic and environmental effects [4]. This addition can be a good strategy to maintain or even increase the levels of organic carbon in the soil [5]; to improve physical properties such as stability of aggregates and soil porosity [6–8]; to incorporate nutrients such as N, P, and K, thus avoiding the high fossil energy costs and therefore the impact on global warming due to the production and the use of synthetic fertilizers [9]; and to help cushion climate change through the sequestration of atmospheric CO2 by the organic compounds of the soil [10].

Considering the physical properties and the soil organic carbon (SOC), organic matter amendments can increase water holding capacity, soil porosity, water infiltration, and percolation while decreasing soil crusting and bulk density [11–13]. One of the main measurable effects of the repeated application in the soil of organic wastes is the increase of soil porosity and, therefore, the decrease in the bulk density of the soil [8, 14]. It is also expected to be beneficial for the work of tilling the soil, thus reducing the draft force and, consequently, a possible decrease in tractor fuel [15]. The energy saved due to the lower resistance that the soil offers when being worked if we apply waste is being ignored from the waste treatments that imply the application to the soil of this in the environmental evaluations. However, reducing greenhouse gas emissions can be important [15].

This chapter pays attention to the physical properties of the soil due to their importance in plant growth and soil stability and the possibilities associated to the use of agricultural wastes. Moreover, it is centered in applying the circular economy concept and zero waste in agricultural systems that can be able to reuse their own wastes.

Agricultural wastes can be used as a source of organic matter and nutrients for soils and influence the physical properties of soils. They can also be easily applied as mulching, providing numerous advantages [16]. So, this chapter gives an overview of the positive effects of recycling vegetable wastes and soil physical properties.
