Nitrogen balance during growth of cauliflower

The potential for loss of nitrogen to the environment during growth of cauliflower was investigated. A comparison was made between cauliflower growth and nitrogen uptake without, and with, nitrogen application of the recommended amount (=225 kg ha-1 minus mineral nitrogen in the soil layer 0–60 cm, applied at planting) on sandy clay soils under natural rainfall conditions. In two experiments, with low mineral nitrogen availability at planting, the quality and yield were reduced when no nitrogen was applied. The rate of nitrogen uptake by the crop rapidly increased from about four weeks after planting. Concurrently the amount of mineral nitrogen in the soil started to decrease. Most of the nitrogen was taken up from the 0–30 cm soil layer. The amount of nitrogen in the crop at harvest with the recommended amount of nitrogen applied ranged from 170 to 250 kg ha-1, while 7–100 kg ha-1 mineral nitrogen remained in the soil (0–60 cm layer). Crop residues contained about 95–140 kg ha-1 nitrogen. No evidence was found for leaching of fertilizer nitrogen during crop growth. With the recommended amount of nitrogen applied, during crop growth the measured amount of nitrogen in the crop and soil (0–60 cm), generally, was lower than the amount of available nitrogen (calculated as the amount of nitrogen in the crop and soil without nitrogen application plus the amount of fertilizer nitrogen applied). No period could be indicated in which there was a particularly great difference between the measured and calculated amount of nitrogen in the crop + soil system. It is concluded that the potential for loss of nitrogen to the environment is greater after crop harvest, when nitrogen may be lost from crop residues and soil, than during growth. Perspectives to reduce nitrogen fertilizer input by split application are discussed.