While the nitrogen (N) value obtained from slurry is at its greatest when applied in spring, slurry applied to land after silage has been cut can also make a valuable contribution to the nutrient requirement of the next cut. In addition to this, generally speaking, more favourable field and weather conditions are likely to exist when compared to those often found in spring or autumn in the run up to the closed spreading period.
Summer pollution control requires extra vigilance
Over the years some of the most serious agricultural pollution incidents have occurred during the summer months, with many occurring when field and weather conditions were perfect for slurry spreading. There are a number of reasons why this is the case. Dissolved oxygen is essential for a wide range of aquatic life including fish and one of the most common causes of a fish kill is a reduced oxygen supply in the water. The amount of oxygen dissolved in water decreases at higher summer temperatures. Reduced oxygen carrying capacity often coincides with low summer flows which effectively reduces the potential of a waterway to dilute any pollutants. In these conditions pollution control on the land and farmyards even remotely connected to a waterway must be of the very highest standard to minimise the risk of a pollution incident.
The breakdown of most farm pollutants requires oxygen and the Biochemical Oxygen Demand (BOD) is a measure of the amount of oxygen needed by micro-organisms to break down organic material. A material with a high BOD value means high pollution potential if it makes its way to a waterway.
|BOD mg/l of oxygen
|Dilute dairy and parlour washings
|1000 - 2000
|Raw domestic sewage
Carry out those seasonal checks
The table above illustrates that silage effluent is one of the most potent sources of pollution on the farm. Therefore, it is important to ensure that none of it escapes to a waterway, no matter how minor. Remember that it can continue to flow for a long time after grass has been ensiled and for this reason you should regularly check the level of effluent in your tanks. Also ensure that effluent channels can flow freely and are clear of obstruction. Look for signs of effluent escape as often grass will appear scorched if effluent leakage is occurring.
Don’t forget the drains and other farm waterways
No matter how thoroughly silos, channels and tanks have been examined it is essential to check beyond the farmyard. Check all waterways on the farm on a regular basis for signs of contamination. Indications of pollution include an unpleasant odour, discolouration or the presence of froth, foam or fungus. Pay particular attention to the appearance of the waterway above and below all discharge points as any change may indicate pollution.
By Alan Morrow, Countryside Management Delivery Branch
Notes to editors:
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