Brassicas
Ground Preparation
Forage brassicas are a small seed and are best sown into cultivated soil, devoid of large clods. It can be direct drilled into the ground but with varying success. The use of a roller will improve the soil to seed contact and therefore increases the speed of germination.
Soil Fertility
Yield potential of the forage brassica is strongly correlated with the level of fertility in the soil. It is recommended that before sowing a brassica, a soil test is taken to determine any deficiencies or restraints such deficient phosphorus or low pH (acidic). Soil pH between 4.8 and 7.5 will ensure the crop can achieve its potential yield. Once the soil fertility is known, any deficiencies can be rectified before sowing commences.
Weeds
Reducing weeds in the seed bed reduces competition for the establishing brassica. A knock-down herbicide can be used prior to sowing. If weeds emerge during the establishment of the brassica, there are several selective herbicide options available to control certain weeds. Ensure herbicide label guidelines are strictly adhered to.
Fertiliser
At sowing, it is important to apply a sowing fertiliser such as MAP or DAP, which contains both phosphorus (essential for root development) and nitrogen (essential for leaf growth). Sowing fertiliser provides the forage brassica with sufficient nutrition to establish successfully. After initial grazing the use of nitrogen fertiliser such as Urea can be used to increase recovery rates on the forage brassica. Ensure safe grazing intervals are adhered to (see animal health section).
Pests
Insects, specifically diamond back moths, can cause significant damage to newly sown brassica crops. It is essential to monitor for insects prior and immediately after the germination of the pasture. If pests are present in large numbers, it may be necessary to apply an insecticide. The use of insecticide coated seed can also help with the prevention of insect damage from sap sucking insects. Ensure insecticide label guidelines are followed specifically regarding grazing withholding periods.
Sowing Depth
Brassicas are a small seed and therefore should not be sown too deep as this will hinder emergence of the shoot. Forage brassicas should be sown no deeper than 20mm.
Grazing Management
Before grazing use the ‘pull test’ whereby you attempt to pull the plant up, if it pulls from the soil easily it is best to wait until it is well anchored before allowing livestock to graze. Brassicas are suited to either strip grazing or rotational grazing. Graze down to approximately 5cm, leaving some leaf if possible as this allows for quicker recovery.
Animal Health
Forage brassicas can be very lush feed and highly digestible, caution should be taken when introducing hungry livestock or changing livestock diets rapidly. Ensure roughage is provided until livestock have adjusted to the brassica. The use of nitrogen fertiliser to increase growth of the brassica can also cause animal health issues such as nitrate poisoning. If the crop has not had sufficient time or sunlight to convert nitrate (from urea) into proteins, livestock eating the brassica can suffer from poisoning effects. After urea has been spread it is good practice to wait three to four weeks before grazing again. This will allow time for the nitrates to assimilate into proteins, but also the leaves will grow larger in this time and dilute the nitrates which are often found in high concentration in young fresh leaves. Provide roughage upon re-introduction this will also help combat any nitrate issues in the rumen.
