The above table demonstrates the importance of early sowing to maximise returns per hectare on forage brassicas.
This trial was run in a very dry spring year with rainfall well below average from September to February and higher than average temperatures. This highlights the importance of sowing early with available moisture for both forage yield, carrying capacity and subsequently gross returns.
*Stocking rate – based on 50 days grazing; lambs turned off average 40kg lwt, with feed on offer of 2.5kg/head/day and averaged 270g/head/day growth rates.
**Total value – assumption dressing out 46%. The early sowing produced an additional $621/ha over the later sowing.
Note: Market price example of 650c/kg cwt the early sowing would produce an additional $807/ha.
Brassicas will respond to high levels of fertility and are particularly responsive to phosphorus (P).
As a guide, crops should have at least 30-40kg P/ha available to them at sowing. However, care is needed to choose fertiliser with minimal sulphate to help avoid potential animal health disorders. Crop rotations prior to the brassica crop should be considered so low soil sulphur levels are achieved.
Leafy brassica crops will respond well to nitrogen (N), especially if they follow cereals and if adequate moisture is present. When these crops have been grazed, an application of nitrogen will greatly increase yields of subsequent regrowth. Care should be taken with potential nitrate toxicity on regrowth following a nitrogen application.
Brassicas prefer moderately acidic soils (pHCaCl2 5.5–6.5) but they can grow well in soils ranging from (pHCaCl2 4.5-8.6).
Brassicas do best in a rotation following grass but may be sown after any crop. If sowing after a crop, consideration should be given to herbicides applied during the cropping phase.
Forage brassicas are small seeded and therefore must be sown into a fine, firm seedbed to ensure good seed to soil contact. Seed should be sown to an approximate depth of 10-15mm to ensure maximum germination. Sowing should occur when the soil temperature is 10°C and rising, and moisture levels are adequate for germination.
The seed should be drilled or broadcast and rolled into a cultivated seed bed. Avoid broadcasting seed if the soil is dry. Seed on a dry surface will not germinate until substantial rain (at least 20mm) has fallen. Depending on farm practices, direct drilling can also be successful for sowing a brassica crop.
Brassicas are sensitive to water deficit, especially at establishment. Shallow-rooted crops (leafy turnips, turnips) are more sensitive while deep-rooted crops (kale, rape) tolerate drought conditions better. Forage brassicas can produce between 20-40kgDM/mm of water used.
Ensure adequate time is given when applying knockdown herbicides to allow for full weed kill while conserving soil moisture prior to sowing forage brassica.