Managing Soil Organic Carbon Concentration by Cropping Systems and Fertilizers in the North China Plain - Principles of Sustainable Soil Management in Agroecosystems - page 196

TABLE 8.6
Descriptive Statistics of SOC Concentrations in Different Cropping
System in 1999 and 2006

SOC Concentration (g kg -1 )

Cropping System Statistics 1999 2006

Wheat-maize N 59 10

Mean 6.84 7.34

Minimum 3.39 4.84

Maximum 9.69 10.34

S.D. 1.37 1.57

CV (%) 20.0 21.4

Cotton N 2 56

Mean 4.07 6.72

Minimum 3.42 2.73

Maximum 4.72 11.12

S.D. 0.91 1.80

CV (%) 22.0 26.8

TABLE 8.7
Change in SOC Concentrations in Same Cropping System in 1999 and 2006
Cropping System

Year Sample SOC Concentration (g kg -1 )

Wheat-maize 1999 59 6.84

2006 10 7.34

Cotton 1999 2 4.07

2006 56 6.72

CV of SOC concentration ranged from 20.0% to 26.8% in different cropping systems
(Table 8.6). This change was probably related to conversion of cropping system and
fertilizer application rates, since the soils were relatively uniform.
An increase in biomass accumulation was the main reason for the observed
increase in the SOC concentration when similar crops were cultivated. Compared
to the cotton-based system, more crop residues were returned to soil during the
wheat-maize cultivation. The decrease in SOC concentration under the cotton-
based system, converted from wheat-maize system, was attributed to low quantity
of crop residues. For example, 85% of the family farms returned residues of wheat
and maize to the soil, while only 15% of cotton residues were returned to the soil.
Similar results were reported by Peterson et al. (1998).
Many studies have reported that stable SOC concentration is generally achieved
after several years depending on the crop management system, soil type, climate,
and other environmental factors (Hendrix et al. 1998). Lal (2004) hypothesized that