3. The use of agricultural wastes in soils

diameter, and root mass were observed to decrease after an increase in BD [41]. However, the interpretation of BD with respect to soil functions depends on soil type, especially soil texture

One of the properties most directly related to the structure and movement of water in the soil is hydraulic conductivity. It is known that water movement in soils occurs both vertically and horizontally, depending on the humidity conditions. In saturated conditions, which occur below the groundwater level, the movement is predominantly horizontal and in a lesser proportion in a vertical direction. In conditions of non-saturation, when the large pores are filled with air, the flow is preferably vertical. The ability of soil to transmit water depends on

The saturated hydraulic conductivity (Ksat) of soil is a function of soil texture, soil particle packing, clay content, organic matter content, soil aggregation, bioturbation, shrink-swelling, and overall soil structure [43–46]. The Ksat is one of the main physical properties that aids in predicting complex water movement and retention pathways through the soil profile [47, 48],

Water holding capacity is the ability of a soil to storage water. Thus, the importance of this storage is that water can be available for plants. Environmental conditions such rain, temperature, and isolation join to the soil properties of soil organic matter, texture, and structure and

In rainfed agriculture of arid and semiarid environments, the capacity of the soil to store water plays an important role in the success of crops. Infiltration and evaporation are the most important processes that determine the storage of water in the soil. Surface conditions play an important role in determining the infiltration and evaporation rates of water in the soil. Tillage is the most effective way to modify the characteristics of the soil surface due to its effect on the

The roughness of the soil surface is another property of the soil that influences the balance of water, since it increases the storage capacity in soil depressions [50, 51]. In agricultural soils, the roughness of the surface is influenced by tillage, vegetation, soil type, and rainfall intensity [51]. The use of waste as surface cover has been shown to be effective in reducing the evaporation of water from bare soil, which translates into a greater potential availability of water for plants [16]. This reduction is due to the isolation of the soil from the sun's rays and the temperature of the air and the increase in the resistance to the flow of water vapor by reducing the wind speed [52, 53]. However, it is also necessary to determine the influence on the movement of water in the soil profile. In the arable layer, it is determinant for the proper functioning of agricultural soils. Therefore, the determination of hydraulic conductivity becomes very relevant information to predict the proper behavior of water against infiltration and storage capacity or loss by the soil.

and soil organic matter (SOM) content [21].

the presence of interlinked pores and their size and geometry [42].

and it is also widely used as a metric of soil physical quality [49].

2.6. Hydraulic conductivity

14 Agricultural Waste and Residues

2.7. Water holding capacity

determine the capacity of a soil to retain water.

porous space (shape, volume, and continuity of the pores).

Agricultural residues used as soil amendments or fertilizers may represent an excellent recycling strategy [54]. They are important to improve soil physical (e.g., structure, infiltration rate, plant available water capacity), chemical (e.g., nutrient cycling, cation exchange capacity, soil reaction), and biological (e.g., SOC sequestration, microbial biomass C, activity, and species diversity of soil biota) properties as organic soil conditioners [55–58]. Cultivating crops that produce substantial amounts of residues can increase SOC in the soil profile, depending on the tillage practices used [29]. Incorporated residue can beneficially influence soil chemical and physical properties, especially in non-flooded soils [57].

Organic residues can contribute to the development of soil structure with a binding agent in the formation of aggregates. The application of organic wastes to soils reduces bulk density; increases total pore space, mineralization, available nutrient elements, and electrical conductivity of soils; and increase microbial activity [26, 59, 60].

Crop residue application offers several environmental and ecological benefits for the soilwater-plant system, including improved soil structural quality, which ensures optimum soil functions. Generally, the incorporation of crop residues increases soil porosity (especially the large pores) and reduces soil bulk density, regardless of tillage operations. Large pores are particularly favored because organic matter is much less dense than mineral particles. The application rate can affect the extent of compaction. The effect of crop residues in a given tillage practice also depends on soil type and depth. When they are mechanically incorporated, crop residues can reduce the bulk density at depth. Conservation tillage with the incorporation of crop residues increases SOC content near the soil surface, whereas in conventional tillage, soil C is distributed throughout the plowed area. Soils with higher organic matter content tend to have higher aggregate stability and therefore less risk of compaction and soil erosion [29].

With regard to soil hydraulic properties, the presence of crop residues on the soil surface tends to increase hydraulic conductivity at the surface, whereas tillage affects soil hydraulic properties both at the soil surface and below it because of the destabilization of soil aggregates [61]. The influence of residue management on crop production is complex and variable and results from direct and indirect effects and interactions. A direct effect is, for example, the presence of residues on the soil surface, which constitutes a direct obstacle to crop emergence. Indirect effects include residue mineralization, which leads to more nutrients available for the plants or the presence of organic matter from residues modifying the soil structure and therefore modifying the root system development [29].

Incorporation of vegetable crop residues affects soil quality not only in terms of nutrient supply but also by influencing soil food web organisms and improving soil physicochemical properties, resulting in a better environment for crop growth and improved productivity [62–69]. The application of organic residues on carbon and nitrogen mineralization and biochemical properties in an agricultural soil led to a significant increase in soil microbial biomass size and activity [54].

Poppy waste, a suitable seed-free, inexpensive source of non-animal-based organic carbon, was used to evaluate its effect on soil organic carbon content and production of Bocane spinach (Spinacia oleracea) [70]. Application of poppy waste at 200 m3 /ha increased soil organic carbon content, soil pH, and soil salinity.

Soil porosity is the property that, due to the effect of compaction, is being altered largely in the European Union (and developing countries), together with the loss of organic matter from soils [77], and, for this reason, our management of the soils should allow maintaining this

Physical Properties of Soils Affected by the Use of Agricultural Waste

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

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The use of plant residues as soil amendments is a sustainable alternative to improve the physical properties [28], although we must take into account the characteristics of the waste to ensure its efficiency. Once incorporated into the soil, the waste can be mineralized more or less rapidly, depending on characteristics such as its degree of lignification, its C/N ratio, and environmental conditions [78]. Fresh vegetable residues, such as tomato (C/N = 12) and onion (C/N = 15) residues [79], with high water content, decompose quickly [80] modifying the composition of soil organic matter [9]. However, there are residues with high C/N ratios, such as wheat or rice wastes (C/N = 105), more lignified, which degrade more slowly [81], lasting for

In this second type of waste, we can consider the cereal straw and the palm tree leaves (Figure 1). Both, with high lignin composition and after a conditioning process (drying and crushing), can be used to modify the physical properties of the soil such as bulk density, porosity, and hydraulic

These agricultural wastes have a similar total organic matter (determined by loss on ignition)

) 84 29

Organic matter (%) 93.2 94.8

) 870 405

Palm tree leaves Hay straw

more time the modifications they produce on certain physical properties of the soil.

content but a different density, bulk, and particle density (Table 1).

property at adequate levels.

conductivity.

Figure 1. Palm tree leaves.

Bulk density (kg/m3

Particle density (kg/m<sup>3</sup>

Table 1. Density and total organic matter in the wastes.

Wheat stalk, cotton stalk, millet stalk, and soybean stalk were used as the main material, and oven-dried lentil straw was used as an additive material in 100:10, 100:15, and 100:20 w:w ratios for 100 g of main material (70% moisture content) to cultivate Pleurotus ostreatus and try to improve the total harvest amount [71].
