126. There are specific principles of sustainable management of soil resources (Lal, 2009b) that are relevant to the choice of SLM options for site-specific situations (Figure 17).
(i) Soil Resources Are Finite, Fragile and Unequally Distributed: Soil resources are unequally distributed among biomes and geographic regions. Highly productive soils in favorable climates are finite and often located in regions of high population density, and have already been converted to managed ecosystems (e.g., cropland, grazing land and pasture, forest and energy plantations).
(ii) Soil Degradation is Caused by Land Misuse and Soil Mismanagement: Most soils are prone to degradation through inappropriate land use. Anthropogenic factors leading to soil degradation are driven by desperate situations and helplessness in the case of resource-poor farmers and smaller landholders; and greed, short sightedness, poor planning/policies and inappropriate incentives for quick economic returns in the case of large scale farmers and commercial farming enterprises.
(iii) Soil Degradation Depends on “How” Rather Than “What” is the “Land Use:” Accelerated soil erosion and decline in soil quality by other degradation processes depend more on “how” rather than on “what” crops are grown. The productive potential of farming systems can only be realized when implemented in conjunction with restorative and recommended soil and water management practices. Sustainable use of soil depends on the judicious management of both on-site and off-site inputs. Indiscriminate and excessive use of tillage, irrigation and fertilizers can lead to as much as or even more degradation than none or minimal use of these technologies.
(iv) Harsh Climate Plays an Important Role in Soil Degradation: The rate and susceptibility of soil to degradation processes increases with the increase in mean annual temperature and the decrease in mean annual precipitation. All other factors remaining constant, soils in hot and arid climates are more prone to degradation and desertification than those in cool and humid ecoregions. However, mismanagement can lead to desertification even in arctic climates (e.g., some parts of Iceland).
(v) Soils and Terrestrial Ecosystems Can Be Either a Source or Sink of Greenhouse Gases: Soil can be a source or sink of greenhouse gases (e.g., CO2, CH4, and N2O) depending on land use and management. Soils are a source of radiatively-active gases with extractive farming practices which create a negative nutrient budget and degrade soil quality, and a sink with restorative SLM practices which create positive C and nutrient budgets and conserve soil and water while improving soil structure and tilth.
(vi) Rate of New Soil Formation is Extremely Slow: While soils are non-renewable resources over a human time frame of decadal or generational scales, they are renewable on a geological time scale (centennial/millennial). This implies that with the increase in human population of 70 to 80 millions per year and projected to be 10 billion by 2100, restoring degraded and desertified soils over a centennial-millennial scale is not an option. Hence, because of the heavy demands on finite resources, soils are essentially a non-renewable resource, and must not be taken for granted.
(vii) Soil Resilience Depends on Land Use and Management: Soil’s resilience to natural and anthropogenic perturbations depends on its physical, chemical and biological processes. Favorable chemical and biological processes enhance resilience only under optimal soil physical properties (e.g., soil structure and tilth), processes (e.g., aeration, water retention and transmission), and edaphological environments (e.g., soil temperature).
(viii) Build up of Soil C Pool is a slow Process: The rate of restoration of the SOM pool is extremely slow, while that of its depletion through extractive farming and soil degradation is often very rapid. The rate of restoration and degradation processes may differ by an order of magnitude.
(ix) Soil Structure, like Photosynthesis is Nature’s Gift: Processes governing soil structure are as important to NPP as those affecting photosynthesis, but are much less understood. Soil structure, similar to an architectural design of a functional building, depends on stability and continuity of macro-, meso- and micropores which are the sites of physical, chemical and biological processes that support the soil’s life support functions. Site-specific sustainable land management practices tend to enhance stability and continuity of pores and voids over time and under diverse land uses.
(x) Sustainability implies Positive Trends: Sustainable land management implies an increasing trend in NPP per unit input of off-farm resources along with improvement in soil quality and ancillary ecosystem services such as increase in the ecosystem C pool, improvement in quality and quantity of renewable fresh water resources, and an increase in biodiversity. However, positive trends cannot be maintained indefinitely (Bartlett, 2005), and emphasis must be given to ecosystem resilience.
127. The importance of SLM is appropriately highlighted by the fact that if soils are not restored, crops will fail even when rains do not (Lal, 2008). Hence knowledge and information on land management is essential to the well-being of societies. But understanding the significance of land degradation is constrained by many uncertainties. It is therefore critical for all stakeholders to deepen, better coordinate and integrate ongoing efforts aimed at gathering policy relevant and action-oriented data on various aspects of land management. Only then can there be effective SLM interventions that demonstrate impact at large scales.
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