Abstract
Feeding the world population, 7.3 billion in 2015 and projected to increase to 9.5 billion by 2050, necessitates an increase in agricultural production of ~70% between 2005 and 2050. Soil degradation, characterized by decline in quality and decrease in ecosystem goods and services, is a major constraint to achieving the required increase in agricultural production. Soil is a non-renewable resource on human time scales with its vulnerability to degradation depending on complex interactions between processes, factors and causes occurring at a range of spatial and temporal scales. Among the major soil degradation processes are accelerated erosion, depletion of the soil organic carbon (SOC) pool and loss in biodiversity, loss of soil fertility and elemental imbalance, acidification and salinization. Soil degradation trends can be reversed by conversion to a restorative land use and adoption of recommended management practices. The strategy is to minimize soil erosion, create positive SOC and N budgets, enhance activity and species diversity of soil biota (micro, meso, and macro), and improve structural stability and pore geometry. Improving soil quality (i.e., increasing SOC pool, improving soil structure, enhancing soil fertility) can reduce risks of soil degradation (physical, chemical, biological and ecological) while improving the environment. Increasing the SOC pool to above the critical level (10 to 15 g/kg) is essential to set-in-motion the restorative trends. Site-specific techniques of restoring soil quality include conservation agriculture, integrated nutrient management, continuous vegetative cover such as residue mulch and cover cropping, and controlled grazing at appropriate stocking rates. The strategy is to produce “more from less” by reducing losses and increasing soil, water, and nutrient use efficiency.
Highlights
Of the 5.5 billion people living in developing countries in 2014 [1], a large proportion of them depend on agriculture for their livelihood
Accelerated soil degradation has reportedly affected as much as 500 million hectare (Mha) in the tropics [4], and globally 33% of earth’s land surface is affected by some type of soil degradation [5]
Because of numerous ecosystem services provisioned through soils [11,12], soil quality must be protected or restored to enhance these services
Summary
Of the 5.5 billion people living in developing countries in 2014 [1], a large proportion of them depend on agriculture for their livelihood. In addition to negatively impacting agronomic production, soil degradation can dampen economic growth, especially in countries where agriculture is the engine for economic development [6]. Soil degradation implies a decline in soil quality [8] with an attendant reduction in ecosystem functions and services. There are four types of soil degradation: (i) physical; (ii) chemical; (iii) biological; and (iv) ecological (Figure 1). Soil biological degradation reflects depletion of the soil organic carbon (SOC) pool, loss in soil biodiversity, a reduction in soil C sink capacity, and increased greenhouse gas (GHG) emissions from soil into the atmosphere. Ecological degradation reflects a combination of other three, and leads to disruption in ecosystem functions such as elemental cycling, water infiltration and purification, perturbations of the hydrological cycle, and a decline in net biome productivity. The objectives of this review are to: (1) deliberate the role of soil resources in provisioning essential ecosystem services; (2) illustrate the impacts of soil degradation on decline in ecosystem services; and (3) identify strategies for improving soil quality to mitigate risks of soil degradation
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