Nitrogen Mineralization Potential in a Calcareous Soil Treated with Two Organic Fertilizer

Organic fertilization has been practiced in Iran due to the shortage of soil organic matter. In recent years, attention has been payed to the organic fertilizers because their commercial production has recently started and demands for their application have increased. The objectives of this study were to investigate the effects of organic fertilizer type, rates and times of application on the N mineralization potential (NMP) in a calcareous soil (fine loamy, mixed, thermic, Typic Haplargid) in Isfahan region. The soil samples were collected from a previousely established field experiment. The experiment design was split plot with three replications. Each main plot was split into subplots receiving 1, 2 and 3 annual consecutive applications of cow manure and sewage sludge at the rates of 0, 25 and 100 Mg ha-1. The soil samples were taken from 0-15 cm depth, 6 months after the third application of the organic fertilizers. Nitrogen mineralization potential was measured by a long-term leaching-incubation procedure. Results indicated that NMP was similarly affected by cow manure and sewage sludge. Nitrogen mineralization potential in the treatments which received 100 Mg ha-1 organic fertilizers, was 4 and 1.7 times greater than that of control and 25 Mg ha-1 treatments, respectively. A significant increase was also observed in NMP in the treatments which received different times of application. The NMP in the three-year applied treatments was 5, 2.5 and 2.1 times greater than that of control, two- and one-year applied soils. Significant correlations were observed between NMP and corn yield (r=0.531**) and corn N uptake (r=0.568***). The product of NMP and N mineralization rate constant was also significantly correlated with corn yield (r=0.710***) and corn N uptake (r=0.734***). Different patterns were observed between the responses of total N and NMP in the treated soils.