Abstract:
Egypts population was projected to increase from 20 million in the 1960s to 67
million
by 2000. With this increase in the population, an increase in food production
of 200% to 300% is become
necessary to meet food demands. In addition to the
increasing demand for food, the population increase will result in increased amounts
of human wastes. This will, in tum, need to be disposed of in ways other than the
traditional
dumping in the nearest stream or the Nile River. It is therefore vitally
important to utilize as much as possible of this human waste (biosolids) as an organic
fertilizer and soil conditioner to increase
sandy soil productivity in Egypt.
Composting is recognized as a cost-effective environmentally sound process for
treatment of
biosolids, even though they may contain substances, which pose potential
hazard to the environment or food chain. The aim of this
study was therefore set out
to
develop a management strategy that used biosolids compost as a soil conditioner
and fertilizer to increase their
agronomic benefits and minimize their environmental
impacts when applied to newly reclaimed sandy soil. The agronomic benefits and the
environmental
impacts of applying biosolids compost to sandy soil were identified
through a series of glasshouse, pot, and incubation trials using tomatoes and grass
crop. Tomato was chosen as it represents a vegetable with a high potential for heavy
metals
uptake and because of its world-wide important as vegetable crop.
The results of this work showed that, compost application had the capacity to
stimulate
vigorous growth, nutritional status, production levels of tomato plants, 'and
to increase N
recovery by tomato plants compared to control. The major nutrient
concentrations of N, P, and K in tomato leaves taken from plants grown on compost
M.M. Abdel-azeim, Ph.D. Thesis, 2002.
The stem
radius of tomato
plants grown on the compost amended-plots were about twofold
thicker in the case of the
highest compost application rate (360 t/ha) than the plants
from control
plots. At 360 t/ha application rate, the tomatoes production level
response for the compost-treated plots was 13.3 kg/plot while it was 1.8 kg/plot for
the control. This
represents an increase of more than 700% over the control plots.
Nitrogen recovered by tomato crop following compost addition exceeded 20% of the
total
applied N after one and two compost applications. All these improvements in
growth quality parameters of tomato plants were not significantly different at the
higher compost application rates of 240 and 360 t/ha. This finding indicates that the
plant response due to the increasing of compost application rate is subject to
diminishing returns.
The
incorporation of biosolids compost into sandy soil has established sufficient grass
covering area and improved soil aggregate stability compared to mulched-applied
compost. The range in grass covering was a low of 7.9% for the control to 100% for
incorporated applied compost at all application rates. The grass covering ranged from
7.9% for the control to 70% for mulched
applied compost at the highest application
rate.
Incorporated-applied compost had more large aggregates and less small
aggregates and consequently the overall aggregate stability ranged from 25 to 30%
compared to 6 to 11% in the case of mulched-applied compost. The superiority of the
incorporated-applied compost to the mulched-applied compost on aggregate stability
was due to the
stabilizing effects of the organic matter. The N mineralization rate has
suggested that rapid and extensive N accumulated in the soil solution soon (60 days)
after
compost addition and the amount of N recovered was in excess of 20% of the
total
applied N. This value is higher than the 10% value reported elsewhere in the
literature. Soil
analysis of the compost treated plots revealed significant increases in
soil
pH, organic matter, CEC, soluble salts, and total heavy metals compared to
control.
Major considerations in recycling of biosolids compost on newly reclaimed sandy
soils are the increase in soluble
salts, the groundwater contamination by nitrate
M.M. Abdel-azeim, Ph.D. Thesis, 2002.
The increase in soluble salts
following compost addition was at a level that could reduce yields in sensitive crops.
High application rates of compost at high moisture status resulted in high levels of
nitrate in the soil solution
(> 50 mg/l). Another concern was the increased amounts of
heavy metal accumulation in the soil profile where more than 90% of the compost-
applied heavy metals were present in the top 20 cm of soil plots, but these increased
amounts were still far below the
plant toxicity levels. The results of this study clearly
indicated that
incorporated biosolids compost does increased agronomic benefits and
does not
pose the same environmental problems as mulched biosolids compost when
used as a fertilizer with
large-scale application rate.
Application of biosolids compost significantly increased the concentration of heavy
metals in tomato fruit
compared to control. Crop recovery of compost-applied Zn and
Cu
by tomato plants was less than 0.5% at all compost application rates regardless of
the method of
application, and was significantly greater by tomato plants grown on
compost-mulched plots than incorporated. Crop recovery of compost-applied Ni, Pb,
Cd, and Cr by tomato plants was less than 0.08% at all compost application rates. In
general, no health problems could be foreseen to humans or animals from food chain
movement of these
negligible amounts of heavy metals. With regard to heavy metal
concentrations in the soil
leachate, the data gave wide assurance that the environment
is
successfully protected.
From this
study, it could be concluded that high loading rates of good quality compost
to
sandy soils is ergonomically valuable with limited potential environmental risk if
managed properly. Under the conditions of this study, incorporation of biosolids
compost into sandy soil using drip irrigation system was the best management
strategy practice to reach optimum agronomic benefits while minimizing
environmental
impacts.
M.M. Abdel-azeim, Ph.D. Thesis, 2002.