Farm Ireland

Saturday 24 March 2018

Keep an eye out for compaction

Michael Hennessy

Yet another week has passed with little or no growth and crops appear to have retreated into the ground rather than increasing leaf mass.

Conditions have improved with some good drying by day, but ground is still very sticky and soft in many places.

Over the past week, I have been looking intensively at soils to determine if this resource is proving to be a blockage to high yields. Blockage may be a strong word as soils are the key building block to yields. But it must be asked if there is anything we can do to increase the soil's capacity for crops to deliver yield.

Many of us can focus on the conditions close to the surface and modify machinery and practices to achieve the result.

Soils have taken a hammering from harvesting in the wet weather to planting and operating machinery in less-than-ideal conditions during cultivations. Soils have indeed suffered but can we ignore the problems and hope soils will repair themselves? All good tillage farmers know the answer to this.

Repairing this damage is not easy. A compaction layer (cultivation/plough pan) can exist at relatively shallow (7-8 inches) depths but equally can be as deep as 14 inches. In many cases a plough will not be capable of breaking this compacted layer.

In fact, ploughing land when wet (watch for smearing as the sod is turned over) will also cause smearing at the ploughing depth and this will only add to a pan/ compacted layer, if present.

Assessing problem fields and identifying the exact cause of lower yields may not be as difficult as you might think. Digging test holes with a spade, or possibly with a digger, will allow assessment and identification of the depth of a compacted layer in the soil profile. It can also give an insight into the structure of the top soil.

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If there is a problem with a compacted layer, how is it solved? Unfortunately, there are no simple remedies. Sub-soiling in dry conditions is the only real answer. All research points to the necessity of subsoiling when the soil is dry. The opportunity to subsoil in these conditions comes around about once every four or five years in Ireland due to our wet summers.


Sub-soiling in wet conditions will not achieve the aim of breaking a pan as movement of soils will be limited to just behind the sub-soiler legs. Keep sub-soiling on the back burner for the moment and attack problem fields after the harvest this year if conditions allow.

Some growers have forward bought fertilisers earlier in the year and taken advantage of the lower prices at that stage. Since the beginning of the season fertiliser prices, nitrogen in particular, have increased by €15-€30/t depending on the part of the country you are in. Forward buying at this stage may seem attractive to many people as the indications, from some within the industry, suggest that retail prices may increase further. Whether you are buying your requirement now or purchasing as you go through the season you will still need to know the total quantity (or maximum usage) of nitrogen and phosphate for the year.

Sit down as soon as possible, with your advisor if necessary, and work out your requirements rather than exceeding limits.

Current soil tests, cropping history and historic yields will give the information needed to calculate N and P requirements on tillage farms. Of course, if livestock is on the holding or organic manures are being imported then allowances should be made for these.

Irish Independent