Bad weather and dung spreading
The weather in 2012 has upset slurry plans on most farms.
A higher than normal proportion of slurry was applied for first cut, but very little during the summer.
This has resulted in a lot of slurry having to be applied over the autumn.
The extension of the Oct 15 EU deadline for spreading until Oct 31 will be helpful, but won’t fully solve the problem because slurry should not be spread on good grass covers.
The extension for chemical fertiliser spreading is of little benefit, because all nitrogen should be spread as soon as possible.
Based on the current price of fertiliser, Teagasc puts a value of well over €20 on 1,000 gallons of good quality slurry, if used efficiently. Pig slurry and cattle slurry have similar total values, but have very different levels of nutrients.
Average cattle slurry contains 15% N (of dry matter), 17% P, and 68% K, but these will vary with the level of nutrients being fed to cattle. Good quality pig slurry contains 43% N, 22% P and 35% K.
Remember that 75% of the N, 71% of the P and over 90% of the K consumed by animals is excreted in the slurry.
Teagasc estimates that the total nutrients excreted by the national cattle herd are 146,000 tonnes of N, 22,450 tonnes of P and 126,000 tonnes of K.
Spring is the time of the year that most spreading of slurry should take place. However, due to weather and ground conditions, this is not the situation on many farms. It is estimated that only one third is usually spread in spring, half in summer (mostly after first cut silage) and the remainder in autumn. Due to the better utilisation of N from spring applications it increases the value of 1,000 gallons slurry by €5.
Slurry should generally be spread on silage areas, thereby returning most of the nutrients in silage to where they came from.
Each 1,000 gallons of good quality cattle slurry is approximately equivalent to one bag of 0.7.30 plus some valuable nitrogen.
In order to make the best use of slurry, and save on fertiliser spending, it is absolutely essential to know the P, K and lime status of each separate area of your farm. This involves having a proper slurry and fertiliser plan for the entire farm which necessitates proper soil testing.
How many farmers have a map of their farm showing the nutrient levels of different areas? There are very few.
Due to this lack of knowledge, and because most slurry is not spread at the optimum time in the spring for N utilisation, Irish farmers are not making optimum use of slurry.
Results from thousands of samples tested in recent years indicated that 60% of land was below the lime status level which can make best use of nutrients from slurry and fertiliser.
Results also indicated that up to 50% of soils are deficient in P and/or K.
Even within farms, there are deficiencies and surpluses in different areas.
P and K Availability
The P and K in slurry is almost 100% available to grass in normal soils.
Once the P and K levels are brought up to standard (based on a soil test), P and K levels can be more easily maintained by applying all the slurry in the silage areas, and very little fertiliser P and K on the grazing area.
The availability of slurry N varies widely with factors such as timing and methods of application.
About half the slurry N is in organic form, and is not available to crops in the year of application, but can be released gradually over time. The other half of the N is in the form of ammonium which is readily available to crops, under certain circumstances.
By spreading slurry in early spring by traditional methods, it is estimated that 25% of the N can be utilised, but if is spread during the summer, only 5% is available, because it generally goes away in the air in hot and dry summer conditions.
Developments in spreading techniques, such as the trailing shoe or band spreading or even the dribble bar, increase availability.
The target should be to apply at least 75% to 80% of slurry in spring before closing up for silage and the remainder before mid-June, in cool moist conditions if possible.
This will significantly cut the cost of fertiliser N for silage. New research has shown that diluting slurry with soiled water makes its nutrients more available to grass.
Generally, less than one third of slurry is applied in spring. About half is applied in summer, mostly after first cut silage when it is most convenient to do so, but with a loss of very valuable N fertiliser. A considerable amount of slurry is spread in autumn, and this should be carried out as soon as possible.
The reason for so little slurry being applied in spring is because of a very narrow window of opportunity. Ground and weather conditions are often a problem.
Ideally slurry should be spread between early grazing and closing for first cut silage. This will not only give optimum use of slurry but also minimise disease risks.
The development of band spreading and the trailing shoe method of application (which separates the grass and applies the slurry in lines at the base of the sward) has overcome many of the constraints to spring slurry spreading. Not only will these methods of slurry application avoid grass contamination, they also reduce odour emissions and losses of N to the air. They will allow farmers to apply slurry later in silage swards, when trafficability has improved.
By switching the application of 3,000 gallons of cattle slurry from summer to spring, there is an economic advantage of €15 per acre in terms of extra N.