According to DairyNZ, Kale also has good tolerance to most insect pests and can be used as a second brassica crop, especially after swedes, because of its tolerance to club root and dry rot. It is usually sown in November or December.
The yield will vary depending on soil type, fertility, and available moisture. Soil moisture is usually the main cause of yield variation: in some areas it can be the lack of moisture during summer, while waterlogging can be a problem in wetter areas. Regardless of cultivar, yields as low as 6-8 t DM/ha can result if kale is grown on light, infertile soils or experiences water stress. Kale has no ripening requirements but maximum yield is about 150 to 220 days.
Kale leaves and the top third of the stems are generally high in energy, and will test at an ME of 12 MJ/kg DM or more. Lower portions of the kale stems have reduced ME, with feed quality dropping off as the stem gets closer to the ground. All stems will become increasingly hard and fibrous with time.
To maximise yield, a fine, firm, moist seed bed with good soil-seed contact and uniform plant population must be established. Full cultivation often produces the best seed bed for kale establishment, however if done correctly sowing method does not affect yield.
If spray and drill (direct drilling) is being used the sowing rate is 3-5kg seeds/ha, and if the seeds are being broadcast and rolled then the sowing rate is 5kg/ha. The optimum sowing depth is 1-1.5 cm.
Kale responds strongly to N application; it is advisable to do an available soil nitrogen test before sowing to determine how much fertiliser N will be needed. Depending on soil moisture levels and potential crop yield, a typical recommendation for kale is 250-350kg DAP/ha at sowing, followed by two topdressings of 100kg urea/ha at 4-6 and 8-12 weeks after emergence.
Too much N, or late applications can lead to nitrate poisoning and excess crude protein in the leaf and upper stem. Surplus crude protein during grazing will increase urinary N excretion and the risk of nitrate leaching.
While the requirement for P is quite low, sufficient P is vital for the establishment of seedlings. The P requirement for a second crop is likely to be higher. The ideal pH is 5.8 to 6.2; this should be corrected with lime a year before sowing. Kale seldom responds to S or K fertiliser.
Brassicas have a high boron requirement: applications of up to 400 grams B/ha can be required, but the amount should be adjusted depending on soil test results.
Keeping pests away
The main insect pests are springtails, diamondback moth, white butterfly and aphids.
Nysius fly can cause problems by allowing dry-rot (black leg) to enter; this causes weak bases in the plants.
Inspect young crops regularly by walking well into the paddock and if necessary, apply the appropriate insecticide. If the spray and drill method is being used, slug control and checks for grass grub and porina are recommended, as these pests can cause the death of new seedlings.
