Environmental Engineering Reference
In-Depth Information
organic matter depletion. On the other hand surplus carbon is emitted into the atmo-
sphere as GHG. Current waste-streaming must be changed to redirect carbon into the
soil by applying a carbon sequestration method which can support soil to resist anthro-
pogenic and meteorological stress and hinder nutrient and organic matter depletion.
Integrating waste management into soil amelioration can sequester carbon in an eco-
friendly way. This can improve soil functioning and crop production, soil properties
such as water and nutrient retention, and the use of waste as a soil amending product.
Research and development prove that closing material cycles and reinstating healthy
balance, e.g. by utilizing waste on soil, is a much desired solution (SOILUTIL Project,
2013) both for soils and wastes.
The following example of sulfur demonstrates the beneficial use of sulfur-
containing wastes on soil in a feasible way. Sulfur is one of the most important elements
of mineral origin in the human body. It plays a role in detoxifying and regenerating
deteriorated tissues. Historically, food contained a sufficient amount of sulfur. Since
produced quantity is the primary target of industrialized agriculture, soils have been
depleted of sulfur no matter if the food has been organically grown or not. Several
diseases such as obesity, heart disease, Alzheimer's and chronic fatigue syndrome are
associated with sulfur deficiency (Seneff, 2010). Anticancer agents show higher effi-
ciency and fewer side effects when sulfur is consumed at the same time. A team from
Reading University, UK has discovered that wheat grown on sulfur-deprived soils yields
flour with high levels of acrylamide (a cancer-causing chemical). Many crops contain
equal amounts of sulfur and phosphorous. Sulfur deficiency is much more frequently
reported in legumes, cereals and tree crops. Sweet potato may also be exposed to sulfur
deficiency. The highest deficiencies are reported in alfalfa crops. The signs of sulfur
deficiency are pale-green leaves. An easy field test can be performed by supplementing
sulfur to a test plot within the suspected large area. When the leaves are greener and
exhibit better growth, S-deficiency in the area has been proven.
Agricultural crops extract an average 5-15 kg/ha sulfur from soil. The requirement
of grain is on average 5 kg/ha, alfalfa has a higher need of 10-25 kg/ha, being the
highest in the year of seeding. There is an input of 2-10 kg/ha by acid rain. The subsoil
is able to supply 5-10 kg/ha depending on its mobilizable mineral content. In addition
to harvesting, leaching also removes a significant amount of sulfur from the soil and
from the S-cycle (see also Chapter 1). Sulfur (dissolved as sulfate) is readily leached
from the soil; that is why weathered and sandy soils in high rainfall areas frequently
have a low sulfur concentration. Burning of vegetation results in gaseous losses of
sulfur (as SO 2 ). Regular high levels of phosphorus application may displace sulfur
from the soil matrix and contribute to sulfur depletion. Due to intensive leaching,
sandy soil may need yearly sulfur supply.
Sulfur's form used for supplementation can be the very soluble ammonium, potas-
sium or magnesium sulfate, the highly insoluble elemental sulfur and the best form is
the moderately soluble gypsum. Gypsum cannot be easily leached from soil. Elemental
sulfur or sulfide should be oxidized by soil bacteria to convert them to sulfate, which
is accessible by plants.
Sulfur and its compounds are available in wastes in large quantities. Phosphogyp-
sum is the primary waste by-product of the wet-acid process to produce phosphoric
acid. Phosphogypsum has little market value and is hauled off as slurry to huge waste
piles, so-called stacks. There are hundreds of stacks all over the world. The greatest
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