HOW AGRICULTURAL PRACTICES EFFECT SOIL HEALTH?

Present-day agricultural practices with their sole aim of maximizing yields pose a serious threat to soil health. With this aim, the dramatic agricultural changes that have been taking place in recent years constitute the predominant change of the century, intensive production in terms of “increased use of agrochemicals and commercial seeds being the major trends” (Tomich et ah, 2011). This major change of the century has manifested itself in the form of massive expansion and intensification of agriculture over just a span of few years. This is a predominant change and a predominating cause of environmental degradation through its impact on soil. All these production maximizing agricultural practices alter soil mainly negatively by changing the essence of soil health—the key indicators. Among these practices that lead to mismanagement and ultimately degradation of soil are tillage, short rotation, irrigation (leading to soil salinization) and a tendency to adopt monoculture rather than crop diversity (Montgomery, 2007; Ponting, 2007). Today, the abandonment of traditional techniques with modem hallmark techniques of agriculture - the intensive-based production management ones has led to major soil degradation. These techniques have the capability to change soil profiles from inherent to anthropogenic (Zalidis et al., 2002; Borselli et al., 2006). Modem agriculture especially the current agricultural practices followed intensively to maximize yields has certain main features like selection of specific crop varieties (involving genetic modifications and hybrids), maintenance of nutrients and fertility of soils to desired levels through use of chemical fertilizers, effective control of pests by use of chemicals. These features increase agricultural production today which from an environmental perspective are main polluters of soil disturbing overall soil health. On reviewing various studies, the main practices currently in use that significantly impact the health of agricultural soils were found to be tillage involving use of machinery, mono-cropping, excessive use of agrochemicals and various irrigation practices. These agricultural practices impact soil through processes like compaction, erosion, and salinization.

PROCESSES INVOLVED IN THE IMPACT

TILLAGE EROSION

The main agricultural practices that degrade soil health operating through acceleration of soil erosion include tillage and certain cropping practices. These practices disturb soil structure cause soil redistribution and soil compaction contributing to increased soil erodibility. Studies have identified tillage erosion “as a major process of soil redistribution on agricultural land, as a result increasing soil susceptibility to agents of erosion like water leading to net soil loss” (Lindstrom et al., 1992; Lobb et al., 1995). Therefore, agricultural tillage is capable of causing soil erosion by action of water. Further evidence is available in literature about the escalation of this tillage induced erosion in soils through mechanized agriculture which makes use of heavy and large sized tilling tools increasing tillage depth and speed so causing more losses to soil (Van Muysen et al., 2002; Van Oost et al., 2005). On one hand, it becomes clear that modem mechanized agriculture with heavy machinery tillage involvement accelerates soil erosion. On the other hand, it has also been established that minimum till or no till practices reduces soil erosion effectively. Tillage erosion has gained importance in recent years (Czubaszek and Czubaszek, 2014) in terms of being the major operating system of soil erosion by water as it concentrates surface water runoff in certain convergent areas or patches of the field due to redistribution of soil. Through all this tillage erosion ultimately impacts agricultural soils and hence crop yield and development (Heckrath et al., 2005). Related to tillage erosion in agriculture studies have concluded that “shifting cultivation to more permanent highland cropping system leads to an increase in tillage erosion and intensity” (Turkelboom et al., 1999; Rybicki et al., 2016; Nguyen and Pham, 2018).

SOIL SALINIZATION

The process of salinization leading to agricultural soil losses and limiting productivity of crops is a serious problem arising from improper irrigational practices in agricultural fields. Arid and semi-arid soils of world are more susceptible to degradation through salinization. Salinization associated with increasing soil conductivity is a negative effect which irrigated agriculture has on soil health. Salinization process in agriculture is related to “build-up of excessive salts in the soil due to its inherent saline nature or because of improper or insufficient drainage condition of soil” (Singh, 2015). Recently, Machado, and Serralheiro (2017) reported that “process of soil salinization has accelerated because of large scale intensive fanning associated with extensive irrigation of fields.” However, present times necessitate the extensive development of irrigated agriculture, due to pollution and scarcity of water sources, along with population pressure. However, the use of improper high salt concentration wastewater for this purpose impacts soil negatively by risking it to salinization. This irr igation-induced soil salinization has negatively affected crop yields by deteriorating soil health ultimately decreasing overall agricultural productivity (Houk et al., 2006; Endo et al., 2011; Singh, 2015; Machado and Serralheiro, 2017). Estimates regarding area of irrigated agricultural lands salinized range from 30% to 50% in various parts of world (Flowers, 1999; Hillel, 2000; Ngigi, 2002; Gulzar et al., 2005).