Agriculture Reference
In-Depth Information
C/N ratio of 14.3 ± 0.5 and the overall soil microbial biomass C/N ratio of 8.6 ± 0.3.
Accordingly, it is possible to have estimation, from both ecological and biochemi-
cal viewpoints, of a C/N range for the biomass to be incorporated in soil feasible to
reduce nutrients loss and to maximize microbial growth. This optimum C/N ratio
should be higher than soil C/N and lower than 20-25, which has been empirically
considered as the transition point in organic matter decomposition from N immo-
bilization to mineralization (Berg and McClaugherty
2003
). Values under soil C/N
ratio might provide easily available nutrients without keeping SOC depletion. On
the other hand, it must be considered that a fertility management strategy based on
the organic matter implicates the supply of an amount of nutrients, over time, much
higher than the crops demand. For instance, 10 t ha
−1
of production can be obtained
providing a supply of 100 unit of N ha
−1
of easily soluble fertilizer applied in the
appropriate way according to crop requirements. To provide a similar amount of N
by compost, assuming 25 % of N mineralization occurs during the cropping period,
a compost dosage of about 400 unit of N ha
−1
has to be provided. It means that the
N use efficiency (NUE = Yield/N supply) decreases from 100 kg of production per
each kilogram of fertilizers to 25 kg of yield per each kilogram of compost (Dober-
mann
2005
). Indeed, NUE should be evaluated in field condition to have precise
values, especially in case of simultaneous incorporation of green manure and/or
of residues of the previous crop, as herewith suggested. Moreover, on a medium
term the residual effect of mineralization should be accounted to the successive
years. Nonetheless, it seems to be in contrast with the ecological intensification
assumption of higher resources efficiency, as reported above. A similar example
could be done for other nutrients such as P and K (Goulding et al.
2008
) and for
the crop recovery efficiency of applied nutrients (Dobermann
2005
). A reasonable
alternative calculation might exclude from the efficiency index calculation the per-
centage of nutrients which have been provided from an on-farm origin, as follow:
NUE = Yield/(N supply-N on-farm). Consequently, more suitable nutrients use ef-
ficiency indices must be considered and measured in field conditions to quantify, in
terms of nutrients supply, the ecological services provided by on-farm composting
and internal resources recycling (Cassman et al.
2002
).
1.6
Conclusion
Crop residues recycling and composting has been deeply described to highlight the
linkage among starting mixture, process factors and potential use and benefit for
the soil, and so for crop production. These practices are fundamental to recycle re-
sources at farm level, improve nutrients use efficiency and to decrease the off-farm
input needs. In the organic farming system, a balanced combination of compost ap-
plication and crop residues incorporation increases the microbial C use efficiency,
which regulates the SOM decomposition and the nutrients mineralization resulting
in better crops productions. Agroecological fertility management practices contrib-
ute both to yield increasing and to reduction of the adverse environmental impacts.
