CHANGES OF SOLUBLE NITROGEN AND CARBON IN THE SUBSOIL OF FIELDS GROWN WITH VEGETABLES

In the winter 1989/90 we examined 5 subsoils down to 10 m, cultivated with vegetables, and we found high contents of nitrate in most of the fields.
Input/ output calculations indicated that in some of the fields the N-input had decreased considerably in the years before, due to the use of the N_min method.
We expected a decrease in the nitrate content of the subsoil within the next years (Hähndel and Isermann, 1993).

A second sampling five years later in February 1995 indicated no major change in the amounts of soluble nitrogen (N_org NH₄-N, NO₃-N). Thus, the amount of inorganic nitrogen (NO₃-N + NH₄-N) ranged from 700 to 2 400 kg ha^-1 N, mostly as nitrate, compared to 500 – 2 300 kg ha^-1 N five years before.
Denitrification potentials, calculated from dissolvable organic carbon (DOC) were between 500 and 2 100 kg ha^-1 NO₃-N, in the same range as five years before.

In the years 1990 – 1994 the estimated yearly balances (N-fertilization minus N-export by marketable yield) did not change considerably compared to those in the eighties when the N_min method was used.

The expected decrease in the amounts of NO₃ in the subsoil did not occur within five years.
To reduce NO₃ amounts in the subsoil, further measures, e.g. better estimation of N-mineralisation during the vegetation period or intensive catch crop cultivation over winter, are necessary.

Ecological aspects of Vegetable Fertigation in Integrated crop Production in the Field

R. Hähndel, J. Dressel

N_min-method, nutrient balance, denitrification, ammonification, nitrate, subsoil

https://doi.org/10.17660/ActaHortic.1996.428.16