Soil Management for Sustaining Ecosystem Services - Principles of Sustainable Soil Management in Agroecosystems - page 528

from paired site surveys, especially when soils are dissimilar. Thus, it is pertinent to
assess periodically SOC pool changes in agroecosystems (e.g., cropland) at a national
level (Sleutel et al. 2003). In addition to SOC, national inventories are also needed for
emission of NT 2 O (Li et al. 2001) and CH 4 . While NT farming can be a source of NT 2 O,
it can be a sink for CH 4 (Lal 2004a). Long-term adoption of NT farming increased
SOC concentration in the top 0.2-m layer by 21.4% in some soils of Inner Mongolia,
China (He et al. 2009). Furthermore, 10-year crop yields increased by 14.0% and
water use efficiency (WUE) by 13.5% compared with traditional tillage. Despite
numerous advantages of an NT system in soil and water conservation and improving
the SOC pool in the surface layer, producers are reluctant to adopt NT in semiarid
Mediterranean soils (and elsewhere) because of a potential increase in soil compac-
tion as indicated by high bulk density and strong penetration resistance (Imaz et al.
2010). Adoption of appropriate rotations and use of cover crops can reduce the risks
of soil compaction. In the rainfed farmlands of Northeast China, a soybean ( Glycine
max L.) - cor n ( Zea mays ) rotation is recommended for SQ enhancement and agro-
nomic productivity improvement (Kou et al. 2012). An integrated soil-crop system
management approach can increase the productivity (Chen et al. 2011). Adoption of
agroforestry systems also enhances earthworm activity and reduces loss of the SOC
pool (Fonte et al. 2010). Use of integrated nutrient management (INM), through a
judicious combination of inorganic fertilizers and organic amendments, is needed to
enhance the SOC pool and sustain SQ.
19.5.2 p aStureland S oilS
Globally, pasture soils represent a large managed ecosystem and have a strong
impact on the global C cycle and emissions of greenhouse gases (GHGs). In the
Amazon region, expansion of pastureland is the principal cause of tropical defores-
tation. Conversion of forests to pastures increases bulk density and exacerbates soil
compaction (Martinez and Zinck 2003). Soil compaction hazard increases with the
increase in the stocking rate, due to the trampling effects of animals (Houlbrooke
et al. 2009). Intensive grazing on wet soils can severely degrade soil structure and
adversely impact soil physical quality. In comparison with forests, pasture soils may
have a lower CH 4 uptake and lower N 2 O flux (do Carmo et al. 2012). In New South
Wales, Australia, Wilson et al. (2011) reported that C, N, and C/N ratio in the surface
layer were in the following order: woodland > unimproved pastures = improved pas-
tures > cultivated soil, and soil bulk density observed an opposite trend. Wilson and
colleagues observed that conversion from croplands to pastures would sequester C in
soil at the rate of 0.06 to 0.15 Mg/ha/year. In Coshocton, Ohio, Owens and Shipitalo
(2011) reported that sediments from a watershed under pasture had a C enrichment
ratio of 1.2 to 1.5 compared with the 0 to 2.5 cm layer and that pasture sediment C
concentrations were more than twice the concentration on sediments from a nearby
row crop watershed.
Conversion of pasture to croplands can deplete the SOC pool. Experiments con-
ducted in a southern Mediterranean highland of Turkey indicated that conversion
of pasture into cropland reduced SOC concentration of the 0 to 20 cm layer by
49%, increased soil bulk density from 1.19 to 1.33 Mg/m 3 , and decreased the mean