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Monday 5 December 2016

Apply fertilisers to encourage growth of shoot numbers

Michael Hennessy

Published 02/03/2010 | 05:00

The early risers such as snow drops, crocuses and daffodils are the only plants which are pointing the way to spring. The combination of a cold airflow and cold soil temperatures has prevented any growth over the past few weeks. Grass has gone backwards and it has become visibly yellow, which is probably because of leaf death from all the frosts over the past couple of months.

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Cereal crops are also showing signs of stress, with winter oat crops -- affected by frost heave -- particularly hard hit. Growers who make use of information from UK publications are aware of soil nitrogen testing to give growers an idea of the level of residual nitrogen left in the soil after the winter. Some success using this method is claimed, especially from commercial interests, but it's hard to find consistent scientific data supporting the widespread use of this technique.

The area of nitrogen release from the soil relates to ploughing and soil organic matter. When soil is moved, air is introduced and the process of breaking down the organic matter begins. This breakdown releases nitrogen, CO2 and water among other compounds. The speed of breakdown is affected by soil temperature and the degree of disturbance.

Testing soil nitrogen involves taking samples to different depths and analysing the soils in a lab. Difficulties with the test arise not because the test is faulty; it's more to do with the treatment of the soil from the time of sampling to the time of testing. Differences may occur due to the time between sampling and testing, transport method, temperature of the sample after testing etc.

To date, previous cropping history has been used to determine the potential of nitrogen release of soils under Irish conditions. Based on the weather since last year's harvest -- heavy rainfall in November followed by rapid cooling of soils -- it's safe to say reserves of available soil nitrogen are low at present.

Winter crops are struggling at the moment. Winter barley and most winter wheat will need nitrogen over the coming week. Winter barleys sown in September are looking well with plenty of tillers (shoots). However, later-sown crops are thin and in need of attention to increase tiller numbers before stem extension. It can't be overstated enough how important high shoot numbers are for high-yielding winter barleys. For the next month to six weeks, growers with thin crops should try to do everything they can to increase and hold on to shoots. The two tools in the armoury are nitrogen and growth regulators.

As nitrogen levels in soils are low, an immediate application of somewhere in the order of 60kg/ha of nitrogen is needed to thin crops. For the thicker crops, 40kg/ha should be enough at this stage.

Close monitoring of growth and weather conditions are essential to make sure the second split is applied and taken up before the start of stem extension. This will ensure the maximum survival of shoot numbers. Phosphate (P) and potash (K) should also be applied now. The application of a growth regulator such as CCC will also benefit the maintenance of shoot numbers. Rates of between 750-900g/ai chlormequat chloride/ha (CCC 750 1.0-1.2 litres/ha) will be required. As this week is forecast to be cold, delaying the growth regulator until some growth returns would be a good idea. Adding an adjuvant to CCC or using K2, etc, will help in cold conditions, but growth is necessary for good efficacy.

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Similarly, crops of winter wheat need nitrogen over the coming week or so -- rates of 25-45kg/ha are necessary. Increase these rates to 60kg/ha on backward crops, second wheats or crops susceptible to take-all. Top up the P and K in these crops as soon as you can.

Irish Independent