Manure decomposition in sandy soils fertilized with mineral nitrogen

Potato productivity has declined gradually over the last few years in the micro-region of agreste in Paraiba state due to incorrect soil fertility management, with empirical applications of bovine manure. To aim of supporting the appropriate management of this input, a study was carried out to evaluate the manure mineralization using three methods: CO2 emission in the field, soil incubation in the laboratory and dry matter loss in plastic net bags. The C-CO2 emitted on the soil surface was captured with NaOH solution, using chambers placed on the soil surface, in plots without and with the application of 11 Mg ha-1 of bovine manure. In the laboratory, soil incubation with manure addition (11 mg ha-1), combined or not with ammonium sulfate (60 kg N ha-1), was performed in hermetically sealed 2000 mL (68fl oz) containers containing NaOH for CO2 capture, for 180 days. Decomposition bags with manure addition (11 mg ha-1) with and without ammonium sulfate (60 kg N ha-1), buried at 15 cm depth, were followed for 110 days. In the laboratory assay, the decomposition, estimated by the accumulated C-CO2 emission, was very low, 5 and 3.5% for manure applied alone and with ammonium sulfate, respectively, in 180 days of incubation.