No abstract

The aim of the present study was to evaluate the efficiency of sewage sludge application on maize (Zea Mays L.) growth, yield and macroelements accumulation (N, P, K, Ca, Mg) when different doses of sewage were applied accompanied by mineral fertilization. The results indicated that sewage sludge fertilization produces significant increase of maize yield that are evident starting with 200 kg N/ha rate, and the highest increases were recorded in the rate of 400 kg N/ ha. The nitrogen content in the maize leaves increased significantly in the variants fertilized with sludge at a rate over 300 kg N/ha, meanwhile the potassium content of the maize leaves was significantly reduced as a result of sludge fertilization at a rate equivalent to 400 kg N/ha. Nitrogen and phosphorus contents in the maize kernels increased with sewage sludge loading, meanwhile in the case of potassium the data showed that there were no statistically significant changes in the potassium content of the maize kernels under the influence of sewage sludge fertilization. The application of sewage sludge caused a significant increase of the calcium and magnesium contents in the maize leaves at equivalent rates higher than 200 kg/N ha.

The aim of the present study was to evaluate the influence of sewage sludge application on metal accumulation (Cu, Mn, Zn, Cd, Ni, Pb) at maize (Zea Mays L.). It was applied different doses varying from 0-600 kg/ha of sewage sludge associated with mineral fertilization. The results indicated that copper and manganese contents increase with fertilization and rates equivalent to 200 kg N/ha resulted in statistically significant copper content in the maize leaves. The highest accumulation of manganese in the leaves was recorded at the sludge rate equivalent to 300 kg N/ha, meanwhile in the maize kernels after the increasing sludge rate, the manganese content recorded a decreasing tendency. The zinc content in the maize leaves significantly increased with the increasing rate of sludge, starting with a rate equivalent to 200 kg N/ha, sewage sludge application being a promoter of zinc accumulation but without becoming excessive. As concerns the zinc content in the maize kernels, sewage sludge rates higher than 300 kg N/ha resulted in statistically assured increases. The cadmium level in the maize leaves increased directly proportional with the rate applied and the values were statistically assured at rates higher than 200 kg N/ha. The cadmium content in the maize kernels was not affected by the treatments applied, as the very low values obtained were below the detection limit of the analytical method. The lead content in the maize leaves increased under the influence of sludge fertilization, but the accumulation was generally low, all values in leaves being under 10 mg/kg and in kernels under 1 mg/kg Pb.

Burning crop residues is frequently used by Romanian land users to clean agricultural fields after crop harvest for ease in postharvest soil tillage. Huge amounts of crop residues biomass, on very large areas, were burned in Romania in the last twenty years, as compared to other countries. There are several reasons (e.g. the lack of equipment to gather the crop residues and to transport and store them, the diminishing of the livestock after 1990, the absence of other alternatives, especially in the 1990s, but also the lack of information regarding the good practices) that are evocated to support the use of this method. However, this method is not a sustainable one since it can cause many environmental damages, especially related to soil properties (physical, chemical and biological), greenhouse gas emission and crop yields. Contrary to the above stated, crop residues' addition to the soil may restore damaged soil structure, improve aggregate stability, soil water retention, soil fertility, increase total organic carbon (TOC) and total nitrogen (TN) etc. The purpose of this paper is to make a multicriteria analyze of the effects of crop residue management on the soil, agricultural productivity and environment. At the same time, the use of crop residues biomass as a source of energy is presented as an alternative, given its potential ability to offset fossil fuels and reduce CO2 emissions.

The present paper illustrates the results obtained on oat (Avena sativa L.), Somesan variety, concerning growth, grains and straw yields and also of macroelements accumulation (N, P, K, Ca, Mg) when various doses of sewage sludge were applied associated or not with mineral fertilization. Sewage sludge application produced significant increase of plant height starting with equivalent dose of 100 kg N/ha, meanwhile the highest height was observed in the case of plants fertilized with doses equivalent with 300 and 400 kg N/ha. With the increase of sewage sludge dose it has been observed the straw yield increase, this being statistically assured starting with sewage sludge equivalent dose of 100 kg N/ha. Sewage sludge fertilization, accompanied or not by mineral fertilizers, evidenced that nitrogen contents in oat grains increases with applied sewage dose, being significant from an equivalent dose of 200 kg N/ha. Low sewage doses equivalent with 200-300 kg K/ha evidenced for potassium concentration in oat grains a significant decrease in comparison with untreated variant, meanwhile mineral fertilization generated a significant increase of potassium levels in oat grains. Calcium contents in oat grains present a significant increase after sewage sludge fertilization and at a dose equivalent with 600 kg N/ha, the calcium levels (0.24%) increased 3 times in comparison with untreated variant (0.08%). Sewage sludge fertilization, associated or not with mineral fertilizers, did not produced significant changes of magnesium levels in oat grains, found concentrations being considered as normal values.