MINERALIZAÇÃO DO NITROGÊNIO NO SOLO SOB FLORESTA OMBRÓFILA DENSA DAS TERRAS BAIXAS, EM PARANAGUÁ, PR- BRASIL

O objetivo deste trabalho foi compreender a dinâmica da mineralizacao do nitrogenio (N) do solo, nas diferentes estacoes do ano, em Espodossolo sob Floresta Ombrofila Densa das Terras Baixas, no litoral do Parana. Foram feitos dois ensaios de mineralizacao do nitrogenio, um aerobico e outro anaerobico, com amostras de solo coletadas nas profundidades 0-5 e 5-10 centimetros (cm). No anaerobico as amostras de solo foram submetidas ao processo de incubacao/extracao em periodo sequencial de 0, 15, 30, 45, 60 e 75 dias, sendo a incubacao feita com solucao nutritiva, em estufa a 30 graus Celsius (o C) a extracao de nitrogenio inorgânico com solucoes de Cloreto de Potassio (KCl) e as determinacoes de N inorgânico por leitura em espectrofotometro ultra violeta visivel (UV-VIS) a 210 nanometros (nm) para (nitrato) e pelo metodo do endofenol (amonio) descrito por Waring e Bremner (1964); APHA (1995). No aerobico as amostras foram secas a 30o C, sendo feita uma primeira extracao de N inorgânico com solucoes de KCl. Depois disso, as amostras foram umedecidas a 30 porcento (%) e incubadas a 19,8 oC em câmara fitoclimatica por 15 dias. Diariamente foi feita leitura de respiracao do solo e, ao final, foi feita nova extracao com KCl. Aliquotas dos dois extratos obtidos foram entao transferidas para microplacas para leitura de nitrato e amonio (Rodriguez et al., 2009). A analise estatistica foi realizada com teste parametrico com teste de Duncan (p<0,10) para os resultados de mineralizacao anaerobica. A mineralizacao do N no solo mostrou-se influenciada pelas estacoes do ano e suas variaveis meteorologicas, alem da umidade do solo. As temperaturas mais elevadas favoreceram a atividade microbiologica, a umidade do solo quando excessiva resulta em menor nitrificacao e maior amonificacao. Os ensaios de mineralizacao anaerobico e aerobico mostraram-se como ferramentas importantes para a identificacao do efeito estacional e na profundidade de coleta sobre a mineralizacao de N no solo. Palavras-chave: carbono; respiracao do solo; amonificacao; nitrificacao; processo de mineralizacao.   MINERALIZATION OF NITROGEN IN THE SOIL UNDER ATLANTIC RAINFOREST DENSE OMBROPHYLOUS OF THE LOWLAND, IN PARANAGUA, PR – BRAZIL   ABSTRACT:  The objective of this work was to understand the dynamics of soil nitrogen mineralization in the different seasons of the year in Spodosol under Atlantic Rainforest Dense Ombrophylous of the Lowland in the Parana state coast. Two nitrogen mineralization tests, one aerobic and one anaerobic, were performed at depths 0-5 and 5-10 centimetros (cm) in Spodosol under Dense Ombrophylous Lowland. The anaerobic test, soil samples were subjected to the incubation /extraction process in a sequential period of 0, 15, 30, 45, 60 and 75 days, with incubation being carried out with nutrient solution, in an oven at 30 degrees Celsius (o C) the extraction of inorganic nitrogen with solutions of Potassium Chloride (KCl) and the determination of inorganic N by reading in a visible ultra violet spectrophotometer (UV-VIS) at 210 nanometers (nm) for (nitrate) and by the endophenol (ammonium) method described by Waring and Bremner (1964); APHA (1995). The aerobic test, the samples were dried at 30o C, with a first extraction of inorganic N with KCl solutions. After that, the samples were moistened at 30 percent (%) and incubated at 19.8 oC in a phytoclimatic chamber for 15 days. The soil breath was read daily and, at the end, a new extraction was done with KCl. Aliquots of the two extracts obtained were then transferred to microplates for reading nitrate and ammonium (Rodriguez et al., 2009). Statistical analysis was performed with parametric test with Duncan's test (p <0.10) for the results of anaerobic mineralization. The mineralization of N in the soil was shown to be influenced by the seasons and its meteorological variables, in addition to soil moisture. Higher temperatures favored microbiological activity, and excessive soil moisture results in less nitrification and greater ammonification. The anaerobic and aerobic mineralization tests proved to be important tools for the identification of the seasonal effect and the depth of collection in the mineralization of N in the soil. Keywords: carbon; soil respiration; ammonification; nitrification; mineralization process.