2 Materials and Methods
An annual time-step model for estimating SOM dynamics was developed and
tested [8, 9] in a 22-year time frame. Indeed, C stock changes are generally calculated in a duration longer than 20 years. The model takes into account the main
soil characteristics, annual mean temperature, and management of cropping systems
and in particular organic fertilizers and crop residues. The analysed agricultural
system consists in a not irrigated 8-years rotation repeated until 22 years: 6-year
cardoon, one-year durum wheat (Triticum durum Desf.) one year field bean (Vicia
faba cv Minor) and so on.
The model implements the Hénin-Dupuis equation [10–12] which apply two
different kinetic constants (k 1 and k 2 ) on annual step in the above complex cropping
system.
DSOM ¼ k 1 Ã M À k 2 Ã SOM
ð1Þ
where M (dry matter, Mg/ha) stands for raw OM, exogenous OM and/or crop
residues, k 1 (% w/w) as the humification constant (i.e. the organic matter that arrive
to become humus) and k 2 (% w/w) as the mineralisation constant (i.e. how much
humus is mineralised in CO 2 ). Soil type did not affect significantly the mineralisation behaviour of M according to Noirot-Cosson et al. [13], rather constant k 1 is
specific for each M, and it is correlated to specific biological stability index (BSI, %
w/w), calculated after a laboratory measurement of biochemical fractions [14], and
OM, calculated as M without ashes content, by Eq. (2)
k 1 ¼ BSI Ã OM/M
ð2Þ
One gross estimate of the mineralisation constant k 2 depends on agricultural
practices (P, i.e. tillage frequency and depth, irrigation, crop residues and organic
fertilizer frequency), clay content (A, g/kg), total carbonates (g/kg CaCO 3 ), site
mean annual air temperature (T, °C):
k 2 ¼
1200 Ã 0:2 Ã ðT À 5Þ
200 þ A
ð
ÞÃð 200 Ã 0:3 Ã CaCO 3 Þ
ð3Þ
In addition, specific residual biomasses, agricultural practices (i.e. tillage frequency and depth, irrigation, crop residues and organic fertilizer frequency), were
considered [8]. The SOM stock (SOMS, Mg/ha) in 30 cm topsoil (h, m) were
estimated taking into account soil organic carbon (SOC, % w/w), bulk density (BD,
Mg/m
3 ), coarse materials (CM, % v/v):
SOMS ¼
SOC
0:58
à BD à ð1 À CMÞ Ã h
ð4Þ
The Role of Compost in Bio-waste Management …
135
An annual time-step model for estimating SOM dynamics was developed and
tested [8, 9] in a 22-year time frame. Indeed, C stock changes are generally calculated in a duration longer than 20 years. The model takes into account the main
soil characteristics, annual mean temperature, and management of cropping systems
and in particular organic fertilizers and crop residues. The analysed agricultural
system consists in a not irrigated 8-years rotation repeated until 22 years: 6-year
cardoon, one-year durum wheat (Triticum durum Desf.) one year field bean (Vicia
faba cv Minor) and so on.
The model implements the Hénin-Dupuis equation [10–12] which apply two
different kinetic constants (k 1 and k 2 ) on annual step in the above complex cropping
system.
DSOM ¼ k 1 Ã M À k 2 Ã SOM
ð1Þ
where M (dry matter, Mg/ha) stands for raw OM, exogenous OM and/or crop
residues, k 1 (% w/w) as the humification constant (i.e. the organic matter that arrive
to become humus) and k 2 (% w/w) as the mineralisation constant (i.e. how much
humus is mineralised in CO 2 ). Soil type did not affect significantly the mineralisation behaviour of M according to Noirot-Cosson et al. [13], rather constant k 1 is
specific for each M, and it is correlated to specific biological stability index (BSI, %
w/w), calculated after a laboratory measurement of biochemical fractions [14], and
OM, calculated as M without ashes content, by Eq. (2)
k 1 ¼ BSI Ã OM/M
ð2Þ
One gross estimate of the mineralisation constant k 2 depends on agricultural
practices (P, i.e. tillage frequency and depth, irrigation, crop residues and organic
fertilizer frequency), clay content (A, g/kg), total carbonates (g/kg CaCO 3 ), site
mean annual air temperature (T, °C):
k 2 ¼
1200 Ã 0:2 Ã ðT À 5Þ
200 þ A
ð
ÞÃð 200 Ã 0:3 Ã CaCO 3 Þ
ð3Þ
In addition, specific residual biomasses, agricultural practices (i.e. tillage frequency and depth, irrigation, crop residues and organic fertilizer frequency), were
considered [8]. The SOM stock (SOMS, Mg/ha) in 30 cm topsoil (h, m) were
estimated taking into account soil organic carbon (SOC, % w/w), bulk density (BD,
Mg/m
3 ), coarse materials (CM, % v/v):
SOMS ¼
SOC
0:58
à BD à ð1 À CMÞ Ã h
ð4Þ
The Role of Compost in Bio-waste Management …
135