Mineralização de N após incorporação de adubos orgânicos em um Neossolo Regolítico cultivado com milho

Farms within the Agreste region of Paraiba often do not have sufficient animal manure to maintain the fertility of the soil and green manures, such as prunings of Gliricidia sepium, are an alternative to increase nutrient supply. The objectives of this work were to compare N mineralization dynamics following additions of cattle manure or Gliricidia sepium prunings to a Entisol, under field and laboratory conditions. In the field experiment, three treatments were established: addition of 20 t ha-1 of cattle manure; addition of 15 t ha-1 of green branches of Gliricidia, or a control without any addition. Maize was sown immediately after the additions. Soil N mineralization in the field was measured in situ during 120 days, in the 0-15 cm layer. Nitrogen uptake by corn was also recorded. Soil N mineralized in the laboratory was followed during 56 days in samples from the 0-15, 15-30 e 30-60 cm layers. Samples from the 0-15 cm layer received manure and Gliricidia at rates equivalent to those in the field. An average of 74 kg ha-1 of N were mineralized in the field until harvest (120 days). In the laboratory, Gliricidia additions hastened net N mineralization while cattle manure induced net N immobilization during 14 days.