Strategies that obeyed this threshold value on a long-term scale can con-
tribute to avoid nitrogen losses of agro-ecosystems.
To evaluate these fertilizer strategies, their effects on total yield and
produce quality have to be taken into account. Therefore a long-term
box plot experiment was carried out by the Grossbeeren Institute. Dur-
ing the 24-year period of the experiment three levels of mineral nitro-
gen fertilizer were combined with different organic fertilizers that were
applied annually to each of the plots.
In 1998 carrots (‘Nanthya F1’) were harvested from those plots in
July. They received 0 kg N/ha, 40 kg N/ha from organic (farmyard ma-
nure), 120 kg N/ha from mineral or 160 kg N/ha from a combination of
organic and mineral fertilizers. The increase of N-fertilization led to a
significant linear increase of the yield, and some increase in the enzy-
matically measured sugar content was recorded (Table 15.1). The per-
centage of juice extractable by a household press did not change
significantly.
288 INTEGRATING PROBLEM-ORIENTED RESEARCH
FIGURE 15.2Effect of nitrogen supply from mineral fertilizer and farmyard manure
on the nitrogen uptake of vegetable crops. Institute for Vegetable and Ornamental Crops,
Grossbeeren, Germany, means 1989–1997.