Watch: sub-optimal soil fertility on Dairylink farms

Over half of the land soil sampled on Dairylink Ireland farms during the winter analysed at sub-optimal levels for either pH, phosphorus (P) or potassium (K). In the two programme farmers profiled below, only 45% of soils had optimal soil fertility on average.

The results from these farms are significantly better than recent widescale soil analysis schemes carried out across NI. However, it still shows that soil remains an under-utilised resource on Dairylink farms so addressing soil nutrient deficiencies has become an important focus for programme participants.

It can be a worthwhile exercise after receiving soil analysis results to calculate how much land is at optimal levels. A quick scan through the results often doesn’t highlight the true extent of a soil fertility problem.

When analysing results on Dairylink farms, programme adviser Conail Keown deemed optimal pH to be 6.2 or above. The general advice on grassland farms is for soil pH between 6.0 and 6.3, with some targeting 6.5 to allow for slow changes in pH and the gradual loss of lime after applications. On Dairylink farms in NI, the Olsen soil test is used and the recommendation for intensive grassland soils is to have a P index of 2 and a K index of 2-. Deficiencies in P and K on grazing blocks is being addressed by early applications of slurry and/or compound fertilisers throughout the year.

Applications will also be needed for maintenance in paddocks that are at optimal levels. At stocking rates of 2.5 to 3.0 LU/ha, 18 units of P and 32 units of K are needed per acre for maintenance annually. At above 3.0LU/ha, this rises to 22 units of P and 36 units of K per acre and below 2.5LU/ha it is 15 units and 28 units respectively. Paddocks that are above optimal levels for P and K will only receive nitrogen fertiliser.

Results from soil samples taken from the grazing block on James King’s farm near Ballymena show that 39% of the grazing block is at optimal levels or above for pH, P and K.

The main soil fertility issue is pH as only 3% of the grazing block is deficient in P and no paddocks were low in K. That said, 59% of the grazing block was just slightly sub-optimal between pH 5.9 to 6.1 and only 5% was below pH 5.8.

The plan is to get lime applied to paddocks with sub-optimal pH levels throughout the year. Paddocks with the lowest pH levels will get lime first at 2t/acre in May or June and the rest will be applied at a lower rate in late summer or autumn.

A high stocking rate of over 4.5LU/ha and spreading of slurry with an umbilical system in the spring most years pushed P and K levels up on the grazing block. Slurry has not been spread on any land around the farmyard this year and was instead used on outlying silage blocks.

Nitrogen will only be used on paddocks with above optimal P and K indices this year and other areas of the grazing block will get some compound fertilisers applied for maintenance. Urea was spread at three-quarters of a bag per acre last month and grass has responded well. Covers were low at the time and cows did not get out. However, James is now ready to begin grazing once ground conditions allow.

On Richard Marshall’s farm near Omagh, 47% of soils are at pH 6.2, P index 2 and K index 2- or above. Results from soil analysis conducted during the winter show that 58% of soils have a pH at 6.2 or more, 20% are between pH 5.9 and 6.1 and 22% are below 5.8. The figures indicate 27% of land is at P index 1 or 2- and 21% is K index 1.

The soil nutrient situation is slightly more complicated on the Marshall farm and could require use of diammonium phosphate (18-46-0) and muriate of potash (0-0-60). This is because some land is deficient in P and above optimal for K, and vice versa. Ground lime will be spread throughout the year and will be initially applied to where it is needed most.

Slurry was spread on silage ground at around 3,000 gallons/acre in February. On the grazing block, paddocks with low covers and low P indices got around 2,000 gallons/acre, with everywhere else receiving half a bag of urea per acre. There has been a response to the slurry and urea, with covers greening up, but cold temperatures are holding growth back.

Later-lactation cows were out at grass for around 10 days before ground conditions deteriorated. Richard has got more cows scanned in calf since this and so has more cows ready to get to grass once conditions improve again. The aim is to have the whole herd out grazing from around mid-April.

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