Tillage Effects on Soil Health and Crop Productivity: A Review

Abstract

The greatest challenge to the world in the years to come is to provide food to burgeoning population, which would likely to rise 8,909 million in 2050. The scenario would be more terrible, when we visualize per capita availability of arable land (Fig 1). The growth rate in agriculture has been the major detriment in world food production. It has been declining since past three decades.The cultivation of agricultural soils has until recently predominantly been achieved by inverting the soil using tools such as the plough. Soil tillage is one of the basic and important components of agricultural production technology. Various forms of tillage are practised throughout the world, ranging from the use of simple stick or jab to the sophisticated para-plough. The practices developed, with whatever equipment used, can be broadly classified into no tillage, minimum tillage, conservation tillage and conventional tillage. Energy plays a key role in the various tillage systems. Soil tillage is defined as physical, chemical or biological soil manipulation to optimize conditions for germination, seedling establishment and crop growth (Lal, 1979a, 1983). Ahn and Hintze (1990), however, defined it as any physical loosening of the soil carried out in a range of cultivation operations, either by hand or mechanized. For any given location, the choice of a tillage practice will depend on one or more of the following factors (Lal 1980; Unger 1984): i) Soil factors includes Relief, Erodibility, Erosivity, Rooting depth, Texture and structure, Organic-matter content & Mineralogy ; ii) Climatic factors includes Rainfall amount and distribution, Water balance, Length of growing season, Temperature (ambient and soil), Length of rainless period; iii) Crop factors includes Growing duration, Rooting characteristics, Water requirements, Seed ; Socio-economic factors includes Farm size, Availability of a power source, Family structure and composition, Labour situation. Tillage is a labour-intensive activity in low-resource agriculture practised by small land- holders, and a capital and energy-intensive activity in large-scale mechanized farming (Lal 1991). Continual soil inversion can in some situations lead to a degradation of soil structure leading to a compacted soil composed of fine particles with low levels of soil organic matter (SOM). Such soils are more prone to soil loss through water and wind erosion eventually resulting in desertification, as experienced in USA in the 1930s (Biswas, 1984). This process can directly and indirectly cause a wide range of environmental problems. The conventional soil management practices resulted in losses of soil, water and nutrients in the field, and degraded the soil with low organic matter content and a fragile physical structure, which in turn led to low crop yields and low water and fertilizer use efficiency (Wang et al. 2007). Therefore, scientists and policy makers put emphasis on conservation tillage systems. Compared to conventional tillage, there are several benefits from conservation tillage such as economic benefits to labor, cost and time saved, erosion protection, soil and water conservation, and increases of soil fertility (Uri et al. 1998, Wang and Gao 2004)Conservation tillage (reduced tillage) can lead to important improvements in the water storage in the soil profile (Pelegrín, 1990; Moreno et al., 1997, 2001). Tillage operations generally loosens the soil, decreases soil bulk density and penetration resistance by increasing soil macroporosity. Under these conditions, improvements were also obtained in crop development and yield, especially in very dry years (Pelegrín et al., 1990; Murillo et al., 1998, 2001). Mahboubi et al (1993) in a 28 years long term experiment found that no-tillage resulted in higher saturated hydraulic conductivity compared with conventional tillage on a silt loam soil in Ohio. Whereas, Chang and Landwell (1989) did not observe any changes in saturated hydraulic conductivity after 20 years of tillage in a clay loam soil in Alberta. Saturated hydraulic conductivity of silt clay loam soil was higher when subject to 10 years of tillage than no-tillage in Indiana (Heard et al., 1988). They attributed the higher hydraulic conductivity of tilled soil to greater number of voids and abundance soil macropores caused by the tillage implementation. Studies comparing no-tillage with conventional tillage systems have given different results for soil bulk density. (Osunbitan et al., 2005) found that soil bulk density was greater in no-till in the 5 to 10 cm soil depth however Logsdon et al., (1999) reported no differences in bulk density between tillage systems. The ambiguous nature of these research findings call for additional studies of the effect of long-term tillage on soil properties under various tillage practices in order to optimize productivity and maintain sustainability of soils.Since tillage strongly influences the soil health, it is important to apply that type of technology that will make it feasible to sustain soil properties at a level suitable for normal growth of agriculture crop. Appropriate tillage practices are those that avoid the degradation of soil properties but maintain crop yields as well as ecosystem stability (Lal 1981b, c, 1984b, 1985a; Greenland 1981). The best management practices usually involve the least amount of tillage necessary to grow the desired crop. This not only involves a substantial saving in energy costs, but also ensures that a resource base, namely the soil, is maintained to produce on a sustainable basis.