Agriculture Reference
In-Depth Information
nutrients mineralization and temporary storage of potentially leachable elements
(Araújo et al.
2008
). By time, compost application decrease the required amount
of mineral fertilizer needed to obtain a comparable yield. However, amendments
and raw materials incorporation with wider C/N affect microbial growth as more
C substrates has to be turned over to release enough N for microbial biosynthesis
(Ros et al.
2006
) which underlines that organic amendments including compost
has to be balanced in terms of C/N ratio. The effectiveness of the conversion of
organic amendment into microbial biomass is defined by C use efficiency which
controls: (i) the conversion of organic residues C into microbial products; (ii) the
rate of the agroecosystem C storage; and (iii) energy and material flow to plant
biosynthesis among the higher trophic levels (Miltner et al.
2012
). The C use ef-
ficiency is affected by environmental parameters such as temperature and moisture
but it could be decreased by agricultural practices which inhibit microbial growth,
like soil incorporation of inappropriate or unbalanced biomasses, or by nutrients
limiting conditions (Sinsabaugh et al.
2013
). However, microbial C use efficiency
increases with the increase in organic forms of soil nutrients (Manzoni et al.
2008
),
which is explained by the effect of inorganic nutrient availability on decomposer
metabolism. Further modeling studies showed a positive correlation between litter
decomposer efficiency and soil N content (d'Annunzio et al.
2008
). Moreover, C
use efficiency changes during the decomposition process (Moorhead et al.
2012
).
The quality of C degradability could also affect the decomposer C use efficiency,
which decreases with the degree of C substrate recalcitrance that is probably due to
the lower enzymes biosynthesis requirements to degrade the simple soluble sugars
than the more recalcitrant cellulose, hemicellulose, tannins, waxes, and lignin, pro-
gressively (Berg and McClaugherty
2003
).
1.5.2
Compost in the Turn of the 3
rd
Millennium
Organic farming agroecological practices aim to preserve, over long-term, soil qual-
ity and improve fertility levels through sustainable SOM management, which might
result from a synergic effect of livestock integration, on-farm nutrient production
and recycling through cover crops and plant residues management and composting.
Composting has the great potential to be a natural process that has certain regu-
latory parameters under human control. Noticeably, it is possible to supply sole
compost, or compost and crop residues or compost and green manure at different
rates. They could be used to achieve a target C/N ratio for the amendment before
its soil incorporation. The C/N ratio goal of the endogenous organic matter to be
incorporated should be calculated to have the highest C use efficiency for soil mi-
crobial communities. The threshold N ratio required for optimum microbial growth
is equal to the C/N ratio of the biomass divided by the C use efficiency and then
multiplied by the N assimilation efficiency (Bosatta and Staaf
1982
; Frost et al.
2006
), which has been evaluated as constant of 0.5 (Sinsabaugh et al.
2013
). It
means that an increase in the C use efficiency reduces the critical ratio of N for an
optimal microbial growth. Cleveland and Liptzin (
2007
) elaborated the overall soil
