There are big differences in the nutrient requirement between brassica types to produce a unit of yield; the ratio of the nutrients which are taken up by the plants; and the amount which is removed from the field by harvest.
This level of removal has a significant impact on the nutrition of the following crop. This needs to be taken into account when devising fertiliser programmes in the field, both for the brassica and also the following crop.
Nitrogen is fundamental to achieving high yields. Total nitrogen requirements vary according to brassica type and range between 1.6 kg/t to 4.7 kg/t of total plant material respectively in Chinese cabbage and Brussels sprouts. The key need for nitrogen in broccoli happens during intensive leaf production
Phosphorus is required early on in the plant’s development to ensure good root growth and to boost establishment.
Potassium and calcium are needed in large quantities – often at levels above those for nitrogen.
Peak potassium - demand is during intensive leaf production, but crop’s need doesn’t decline as much as that for nitrogen, with high quantities also needed during maturation and bulking of the produce.
Magnesium and sulphur increase photosynthetic activity maintaining good growth for high yields.
Relatively high levels of sulphur are utilized in broccoli, and around 20% is removed in the harvested crop. Magnesium is required at lower levels than in other crops and removals are between 0.1 - 0.3 kg/t depending on crop.
While much lower levels of micronutrients are needed to satisfy yield, the correct balance of these trace elements is essential. The key micronutrients needed in greatest quantities are iron, boron, zinc, and manganese.