Nitrogen availability in composted cork

Previous studies showed that plants grown in fresh cork (Quercus suberL. bark) had a reduced growth compared with peat and low rates of N. In
composted cork, however, plant growth was similar with those in peat,
but the N content of plants was still slightly lower.
The purpose of this study was to investigate N availability in fresh and
composted cork during 4, 5.5 and 7 months, using peat as control medium.
The substrates were also incubated at 25 degrees C during 60 days after
adding 0.25, 1.0, 1.75 or 3.0 g ammonium nitrate per 1 of substrate.
Samples were taken periodically to measure NO3-N, NH4-N and total N.
Also the Nitrogen Drawdown Index (NDI) for the addition of 75 mg.l(-1) N
and 150 mg.l(-1) N was measured after incubation at 25 degrees C.
N immobilization rates were well correlated to NDI. NH and soluble N
drawed down rapidly in cork substrates while total N stayed constant.
High rates of ammonium nitrate should be added to maintain a constant
level of available N to plants in cork.