The effect of the incubation period for the short-term assessment of nitrification rates of soils in the laboratory

EnglishThe present work studied the effect of the incubation time forthe evaluation of the actual nitrification rate, alterna- tively to the soil potential nitrification rate described by the international standard procedure ISO 15685. In this work, both actual and potential soil nitrification rates were determined by monitoring the N-NO2 - production kinet- ics over a 72-h period. It was observed, that the N-NO2 - (nitrite) production has a linear increase with the incubation time (R2 = 0.998) during the first 10-h of incubation for both alternatives. Notwithstanding, a non-proportional relation of N-NO2 - production with incubation time was verified, complying a logistic function (R2 = 0.983), which cannot be attributed to substrate limitation. On opposition to the method described in literature (24-h incubation), the results indicate that the evaluation of the actual nitrification rate of the soil should be performed based on a 5-h incubation period, similar to that used when assessing the potential nitrification rate. portuguesFoi estudado o efeito do tempo de incubacao para a avaliacao da taxa efetiva de nitrificacao do solo, em alterna- tiva a determinacao do potencial de nitrificacao, metodo descrito na norma ISO 15685. Para tal, foram determi- nadas a cinetica de nitrificacao e o potencial de nitrificacao pela monitorizacao da cinetica de producao de de N- NO2 - por um periodo de 72 h. Em ambas as alternativas, a producao de N-NO2 -durante as primeiras 10 h de incubacao apresentou um aumen- to linear em funcao do tempo (R2 = 0,998). Apos este periodo, a relacao da producao de N-NO2 - com o tempo passa a ser menos proporcional, obedecendo a uma funcao logistica (R2 = 0,983), nao se podendo atribuir esta quebra de proporcionalidade a limitacao de substrato. Ao contrario do indicado na literatura (24 h), os resultados obtidos indicam que a avaliacao da taxa efetiva de nitrificacao de um solo devera ser realizada com base num periodo de incubacao de 5 h, semelhante ao utilizado para o potencial de nitrificacao