Abstract:
Investigations conducted during 2003-2007 at the Podu-Iloaiei Agricultural
Research Station have studied the influence of different sewage sludge, manure and crop
residues on yield quality and quantity and soil agrochemical characteristics. Experiments were
set up in a five year-crop rotation (soybean-wheat-maize-sunflower-wheat). Sewage sludge
was applied annually at rates of 20, 40 and 60 t/ha, together with mineral fertilizer,
differentiated according to the growing plant. The Cambic Chernozem used for experiments
had a clayey-loam texture (415 g clay, 305 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 24.6 t/ha DM sewage sludge resulted in the accumulation of mobile
phosphate stock in soil of 49 ppm and the microelements content (mobile forms from soil) was
of 12.4 ppm at Cu, 0.47 ppm at B, 142 ppm at Zn and 382 ppm at manganese. The combined
use of mean rates of mineral fertilizers (N70P70), together with 40 t/ha manure or 6 t/ha crop
residues from wheat and maize crops, has resulted in improving soil physical and chemical
characteristics and getting yield increases in wheat of 2313-2214 kg/ha (136-130 %), on
weakly eroded lands, and 2074-2001 kg/ha (178-172 %) on highly eroded lands, compared to
the unfertilized control. Both on weakly and highly eroded lands, the mineral fertilization with
lower rates than N140P100 kg/ha has determined the decrease in humus content from soil until
2.49- 3.05 %. On highly eroded lands, the humus content was kept at values of 3.42-3.49%
only by the annual application of the rate of 60 t/ha manure or N70P70+ 60 t/ha manure.
