Valorização agrícola de lamas de ETAR: disponibilidade de azoto

With the aim to study nitrogen availability from sewage sludge, a pot trial was installed under greenhouse conditions, using maize (Zea mays L.) as plant test. The experimental design was a completely randomized blocks with three replications and thirteen experimental treatments: control; four levels of N from sludge; four levels of N from a salt (NH4NO3) and four levels of N resulted of the sludge and salt mixture in equal quantities. Increasing amounts of sludge gave significantly increased yields (p=0.05) causing the larger response to the equivalent application level of 60 t ha‑1. The combined application of nitrogen in the mineral and sludge form proved to be a viable technique to supply the nitrogen needs of the crops, and led to the higher yields of the aerial part of the plant test and to larger amounts of removed nitrogen. The nitrogen recovery from the mixture of sludge and ammonium nitrate was statistically higher than the observed quantities when only sludge was applied and at the highest application level of ammonium nitrate.