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Side dressings essential for good crop yield

22 December 2009

Side dressings essential for good crop yield

Winter and all that goes with it may seem like a long way off, but a bit of planning now will ensure that your forage crops will see you and your stock through the colder months.

Farmers planning to utilise brassicas as a source of supplementary feed this coming winter should be thinking about a side dressing nitrogen application to increase dry matter yields.

Ballance Technical Consultant Jeff Morton explains that management of brassicas after planting is one of the key factors that contribute to the success of any brassica crop.

‘Selection and preparation of the paddock(s), the selection of the brassica crop, and the management of the brassica crop once planted will give you the best chance of producing a good yield. Taking short-cuts or making poor decisions at any of these stages will impact on the return on investment and the absolute value of any brassica crop.

‘To ensure brassica crops reach their yield potential, the importance of using nitrogen at six to 12 weeks cannot be underestimated.’

The amount of fertiliser nitrogen that will be of benefit to a brassica crop will depend on the amount of available nitrogen already in the soil. At low levels of soil available N (e.g. around 50 kg N/ha), fertiliser nitrogen gives very strong yield responses, with economic crop yield responses likely to rates of N in excess of 200 kg N/ha). However, at medium levels of soil available N (e.g. 100-150 kg N/ha) the response to fertiliser N is much reduced, and economic responses are likely to occur to lighter rates of fertiliser N (e.g. 100 kg N/ha).

‘Nitrogen inputs should be reduced when growth conditions are adverse and can be increased when growth rates are high. You can also minimise losses through leaching by splitting applications if rates are greater than 80 kg N/ha,’ advises Mr Morton.

‘Splitting nitrogen applications gives flexibility and avoids wastage if conditions turn dry. There is no point applying all nitrogen at sowing for a 15 tonne DM/ha crop if the growing season dictates that the crop will only yield 10 tonne DM/ha.’
Nitrogen can also be used on multi-grazed crops, such as Pasja, which can be grazed up to five times. The N stimulates the development and growth of new shoots, converting the plant back to a producer of high-quality leafy forage after grazing and helps to re-establish and drive yield. Potash may also be required after grazing.
‘Care should also be taken to ensure that crops have adequate supplies of trace elements, especially boron. Boron helps to stabilise plant cell walls and membranes, and without sufficient boron brassicas develop disorders such brown heart and hollow stem,’ says Mr Morton.

‘Brassica crops also tend to have low levels of copper, selenium and cobalt – if brassica crops are becoming a larger percentage of annual stock dietary intake, stock should be monitored to ensure they are getting sufficient intake of these micronutrients to prevent animal health problems.’

The Ballance Brassica Test has been designed to give farmers all the information they need to determine their crop’s nutrient requirements. Soil samples are taken and analysed for pH, phosphorus, potassium, sulphur, magnesium, calcium, sodium, boron and available nitrogen.

‘The Ballance Brassica Test will enable your Ballance representative to develop a fertiliser strategy that meets your crop’s needs,’ says Mr Morton.

Once plants are established, plant tissue testing (a leaf test) gives an indication of nutrient levels mid-growth. A cross-section of recently matured leaves is taken and tested so that side-dressing fertiliser applications can be targeted to counter nutrient and mineral deficiencies.

In addition to testing, farmers should look out for visual signs of poor performance throughout the life-cycle of their crop. Nitrogen deficiency can appear as a pale green to yellow crop, often accompanied by a purple to pink coloration in the older foliage. This symptom can also be induced by other factors such as cold weather, root damage from nematodes, drought stress and water logging. Urine patches in the crop is another visually obvious indication that the crop is nitrogen limited.

‘Farmers should be out checking their crops regularly,’ Mr Morton suggests. ‘If the crop shows signs that it may be struggling, then the quicker you pick this up, the sooner the cause can be isolated and the problem corrected.’

Contact your Ballance Technical Sales Representative on 0800 222 090 for advice specific to your crop.


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