the effect of sewage sludge and manures application on nitrogen mineralization and rhizosphere characteristics in corn and sunflower plants

abstract biological and chemical changes in rhizosphere following organic residues as well as manures application are important processes which influence nitrogen mineralization and nutrients bioavailibity in soils. this study was done to evaluation of organic residues effect on growth, nitrogen supply and rhizosphere characteristics of corn and sunflower plants in greenhouse experiment using sewage sludge (ss), poultry (pl), cattle (ct) and sheep (sh) manures. the results showed plants acquired significantly more n, p, k, ca, mg, fe, mn, zn and cu in ss treatment than other manures. sunflower in comparison with corn plants showed higher n, p, k, ca and cu uptake, which can be attributed to its higher nutrient-uptake efficiency. the highest mineralized nitrogen in rhizosphere and non-rhizosphere soil were achieved in pl (214.8 mg kg-1) and ss (227.5 mg kg-1), respectively. mineralized n in particular nitrate was observed at high concentration in rhizosphere compared to non-rhizosphere soil, which indicate higher microbial activity including nitrificators and high mineralization processes in sunflower rhizosphere. net nitrogen mineralization (nm) in rhizosphere was higher than that in non-rhizosphere which the microbial population in corn and sunflower rhizosphere were 3.7 and 2.3 times higher than non-rhizosphere soil, respectively . treatments applied with ss showed the highest microbial activity compared to other organic residues. at rhizosphere, net nitrogen mineralization was occurred in pl and ss treatments whereas ct and sh applied soil showed nitrogen net immobilization. except for ss, all applied residues showed net immobilization in non-rhizosphere soil. the highest total mineralized n (mineralized n exist in soil and absorbed n by plants) were as fallows in treatments: pl> ss> sh> ct.