The influence of organic and mineral fertilisation on vegetable growth andN availability in soil: Preliminary results

The dynamics of mineral N in soil as affected by either organic or mineral N fertilisation during cabbage (from April to July 1997) and spinach (from September 1997 to May 1998) cultivation were observed in a field trial in L jubljana. Farmyard manure (FYM) and compost from chicken deep layer manure and bark were compared to mineral fertilisation (NPK) and to non-fertilised control plots. The amount of added fertiliser was adjusted to a total N su pply of 200 kg ha(-1) for cabbage production and 100 kg ha(-1) for the foll owing spinach production. Soil samples taken from 0-30 cm, 30-60 cm and occasionally 60-90 cm, were a nalyzed for mineral N content several times during the growing season. Trea tments with NPK application had the highest soil mineral N content througho ut the experiment and the N uptake was closely related to the cabbage yield (R-2 = 94%). Plants grown under mineral fertilisers were higher, heavier a nd larger than organically grown plants. The highest yield (8500 kg dry mat ter ha(-1)) was obtained with mineral fertilisation where N was supplied tw ice (before transplanting and during head formation), followed by mineral f ertilisation in which the whole amount of N was added at transplanting time (7900 kg d.m.ha(-1)), then the treatment fertilised with FYM (6000 kg d.m. ha(-1)), compost (4200 kg d.m.ha(-1)) and, finally, the control (3700 kg d. m.ha(-1)). Compost induced N immobilization during cabbage and spinach cultivation, de spite its relatively low C/N ratio (C/N = 17). However, spinach that was so wn in September 1997 on the same field showed better emergence on the organ ically manured plots and, although the survival rate during winter was bett er on the NPK treatment, the yield (821 kg d.m.ha(-1)) was not significantl y higher.