Agriculture Reference
In-Depth Information
plex interaction could result in nutrients sequestration (robbing) or availability or
leaching. The soluble fractions of nutrients are released by microorganisms in the
soil-water solution resulting in easily available forms ready for plant uptake. Nu-
trient concentration in soil solution is a very dynamic process over time; it can be
higher or lower than plant demand affecting plant growth in terms of quality and
quantity. From an environmental perspective, higher concentration of plant nutri-
ents in soil solution might result in nutrients leaching below the root zone leaving
less-soluble nutrients forms in the soil surface layers and leading to groundwater
contamination on the long run. Soil incorporation of unbalanced, in terms of C/N
ratio, organic residues or amendments facilitates nutrients leaching (residues C/N
much lower than soil C/N) or nutrients sequestration (residues C/N much higher
than soil C/N) from soil pools. Removal of crop residues and appropriately timed
application of soil amendment are the most used practices to reduce nutrients 'rob-
bing' and/or leaching.
1.4.2
Crop Residues: Incorporated or Composted?
A remarkable question for farmers and composters is whether to incorporate crop/
farm residues directly into soil or use them as a compost substrate. To answer this
question many aspects should be considered: (i) raw materials availability in quan-
tity, place and season; (ii) the easiness of the processes; (iii) the cost of the opera-
tions; and (iv) the potential benefits and constraints on the yield.
The total amount of crop residues produced globally was estimated in 2001 at
~ 4 × 10
9
mg year
−1
in which about 75 % came from cereals (e.g., corn, rice, wheat,
sorghum, barley, rye), those crop residues are mainly constituted of cellulose, hemi-
cellulose and lignin (Barreveld
1989
). Crop residues application into soil provides
many benefits to the soil ecosystem such as enhanced soil physical (e.g., structure,
plant-available water capacity), chemical (e.g., nutrient cycling, cation exchange
capacity and soil pH) and biological properties (e.g., microbial biomass C and soil
biotic diversity). Crop residues promote sustainable land as a result of its positive
impact on the environment and ecosystem services (Lal
2005
). Recycling of crop
residues through leaving them on soil, incorporating them into soil and/or com-
posts has been practiced in different agricultural systems. Benefits of crop residues
recycling include soil protection against wind and water erosion, enrichment with
organic matter, enhanced water retention and the principle benefits of nutrient re-
cycling (Smil
1999
).
Decomposition of crop residues depends mainly on their chemical and physical
characteristic together with the surrounding environmental conditions. The quick-
ness of the decomposition of a crop residue is based on the simplicity of the residues
chemical composition. Simple compounds, e.g., sugars, amino acids and low mo-
lecular weight organic acids are quickly decomposed while complex polymers and
high molecular weight compounds will take longer time to be decomposed (Berg
and McClaugherty
2003
). Usually, the decomposition of the crop residues in open
field is faster at the beginning as the simple compounds decomposed first by large
