Soil Management for Sustaining Ecosystem Services - Principles of Sustainable Soil Management in Agroecosystems - page 529

weight diameter of aggregates from a dominant size class of 4.0 to ≤0.5 mm (Celik
2005). However, conversion of croplands to pasture can enhance the SOC pool and
improve SQ (Breuer et al. 2006) and also influences the hydrological balance (Qiu
et al. 2011).
Understanding the processes and causes of pasture degradation is important,
especially in the neotropics of the Amazon and the cerrado/llanos of Brazil and
Columbia. Pasture degradation forces farmers to open new forest areas and may
alter the nutritional quality of forages without dramatically altering soil properties
(Muller et al. 2004). Numata et al. (2007) assessed soil physical and chemical prop-
erties of Oxisols and Alfisols under pastures in the southwest Amazon region of
Brazil. Pasture degradation caused more drastic changes in chemical properties of
Alfisols than those of Oxisols, with little change in those of Ultisols.
Therefore, judicious management of soils under pastures is needed for main-
taining productivity and reducing the risks of environmental degradation. On a
Southland dairy farm in New Zealand, Houlbrooke et al. (2009) indicated that
intrusive grazing when soil wetness is greater than the plastic limit contributed to
both soil trampling damage and severe compaction. In an alpine region of China, Li
et al. (2007a,b) observed that total SOC concentration decreased by 29% to 41% in
0 to 30 cm depth in annually cultivated pastures (oats). Both annual and perennial
pastures decreased soil WHC in comparison with the native pasture. Conversion
of dry forests into pasture (and cropland) in Mexico has increased the soil erosion
hazard (Cotler and Ortega-Larrocea 2000). Management of soil N content and the
stocking rate are key determinants of the quality of soil under pastoral land use
(Monaghan et al. 2005).
19.5.3 M anageMent of S oilS under f oreStland u Se
Forested ecosystems have a large SOC sink capacity (Lorenz and Lal 2010).
Afforestation and reforestation of marginal/degraded soils enhance the SOC pool
(Six et al. 2002) and strengthen numerous ESs. Soil and water conservation are
among the important ESs of forestlands. In St. Lucia, Cox et al. (2006) observed
that soil erosion from an extreme event was merely 0.2 Mg/ha from a forested site
compared with 3-78 Mg/ha from a cropland site. An afforestation study in Finland
on 220,000 ha of arable land indicated that bulk density of mineral soils tended to
be lower and SOC concentration higher than those of a soil under old forest sites
(Wall and Hytonen 2005). High variability in SOC concentration, however, limits
the precision of measurements of changes by land use conservation and management
practices (Conant et al. 2003). Therefore, the accuracy of measurements and under-
standing of the basic principles governing SOC dynamics in forested ecosystems
need to be improved (Six et al. 2002).
19.5.4 SQ and W ater S eCurity
Water scarcity and drought are serious constraints that need to be addressed. It is
widely recognized that as much as 60% of the world population may be vulnerable
to water scarcity by 2025 (Qadir et al. 2007). Further, water-scarce countries may