Spring slurry key for soil fertility as new season commences

The period in which farmers are not allowed to spread slurry came to an end for farmers in the south east of the country yesterday. Farmers nationwide will get the go ahead in the coming weeks.

With this in mind Agriland spoke to Stan Lalor of Teagasc, based in Johnstown Castle, Wexford on some advice for farmers on how to make the most of their slurry.

Lalor noted: “Farmers normally like to get slurry out at this time of year to allow flexibility in tanks for the remainder of the spring. The good weather last autumn would have increased the chance to get slurry out on dry ground, but the good grass growth would have meant that some farmers didn’t get a chance to spread slurry in some fields because of high grass covers.”

He added: “Applying slurry in spring is a good way of ensuring that the nitrogen (N) value of the slurry is maximised. Farmers should aim to use dry spells in early spring for slurry application, to avoid having slurry left in tanks in the summer and autumn when the fertiliser value of the slurry will be lower.”

When asked the true value of spreading slurry in the spring, he said: “Research in Johnstown Castle has shown that spreading slurry in spring makes the slurry worth three units of extra N per 1000 gallons compared with spreading in summer. This is because the cooler weather conditions means that less N is lost to the air as ammonia.”

“However, more than 85 per cent of the fertiliser value of slurry is in the Phosphate (P) and Potash (K), so the key thing is to apply slurry on fields that are low in P and K. Soil testing is the best way of finding what parts of the farm needs P and K. Slurry should be applied to these fields as a cost-effective way to improve soil fertility.”

Due to the impact of wet weather over the past few weeks and with more forecast for this week Lalor commented: “Soil moisture conditions have been estimated by Met Eireann to be wetter than what would normally be required for slurry application. It is therefore important to avoid slurry application where soil conditions are wet in order to avoid soil compaction damage and run-off of slurry nutrients.”

This being the case he cited: “Farmers should try to target drier fields and but should not apply slurry close to watercourses where soil conditions are marginal. The size and inflation of the tyres on the tractor and tanker are also important to reduce soil damage.”

Lalor highlighted: “Umbilical systems are also a very effective way of reducing soil damage, and work very well where spreadlands are close to the slurry tank.”

He advised farmers to target the fields now that will not be grazed in the next four to six weeks, and then target the other fields after grazing for the remainder of the spring. He stressed that by getting slurry out now or in March and April, after closing for silage, it will reduce the pressure to apply slurry next autumn before the closing date in October.

In terms of different methods of application, he said: “The trailing shoe injection and bandspreader methods have been shown to improve N uptake from slurry, and can also increase the opportunity to apply slurry into taller grass swards with reduced risk of sward contamination with slurry.

“However, they are expensive, and the N fertiliser savings are unlikely to fully make up for the extra cost. For this reason, splash plate application remains the dominant method. However, irrespective of the method, application in spring and in weather conditions that are cooler and overcast is a good way of getting good response to slurry as a fertiliser.”

Application rates

Lalor had some key advice for farmers on application rates at this time of the year. He said: “Normally application rates of up to 3000 gallons per acre (33 m3/ha) are recommended, depending on the soil test and whether the fields are used for grazing and silage. 1000 gallons of cattle slurry is equal to a 50kg bag of 6-5-38, and 1000 gallons of pig slurry is equal to a 50kg bag of 19-7-20.

“So if you are considering what rate to apply, think of it in terms of the chemical P and K that the field might receive. In reality 3000 gallons of cattle slurry per acre should provide enough P and K for first cut silage.”

On pig slurry applications, he said: “It is better balanced for cattle slurry for grazed swards, as the K content is lower. Again 2000-3000 gallons per acre of pig slurry is a good application for grazing.”

However he stressed: “It is important not to over apply slurry as it may reduce grass regrowth rates, especially if applied on taller grass covers. Note that P and K contents will be lower in more watery slurries.”

Please be considerate of others when commenting. All comments posted are subject to our commenting policy. Comments violating this policy will be removed without notice.