Abstract:
Investigations conducted at
the Podu-Iloaiei Agricultural Research
Station, Iaşi County, have studied the
influence of different sewage sludge rates
on yield quality and quantity and soil
agrochemical characteristics. Trials were set
up in a five year-crop rotation, winter rapewheat-
maize-sunflower-wheat. Sewage
sludge was applied every 2 years at rates of
20, 30, 40 and 60 t/ha, with different
mineral fertilizer rates, differentiated
according to the growing plant. The Cambic
Chernozem used for experiments had a
clayey-loam texture (410 g clay, 310 g loam
and 280 g sand), a weakly acid reaction and
a mean supply with mobile phosphorus and
a very good one with mobile potassium.
Applying rates of 30 t/ha sewage sludge has
resulted in the accumulation of mobile
phosphate stock in soil of 57 mg/kg and the
microelement content, mobile forms from
soil, was of 7.9 mg/kg at Cu, 1.4 mg/kg at
B, 6.8 mg/kg at Zn and 186 mg/kg at
manganese. The combined use of mean
rates of mineral fertilizers (N100P80),
together with 40 t/ha sewage sludge has
resulted in improving soil chemical
characteristics and getting yield increases in
winter rape of 1854 kg/ha (108 %). After 8
years since the application of a rate of 30
t/ha sewage sludge, soil pH has increased
0.4 units, while phosphorus and potassium
content from soil has increased by 30 and 52
mg/ kg soil, respectively. Sewage sludge
from the Iaşi Water Treatment Station,
which was applied every two years at rates
of 20 and 30 t/ha, has determined the
increase in the organic carbon content from
soil by 2.9 g/kg (18%) and 4.4 g/kg (28%),
respectively, compared to the unfertilized
variant. The copper and zinc content from
grains in wheat and maize crops, fertilized
with 30 t/ha sewage sludge, was by two-four
times higher, compared to the unfertilized
control.
