Farmers need to reconsider their view on practice of soil testing

Soil testing is the most cost effective tool to optimise the use of fertiliser and slurry and farm production.

Yet it is one of the most neglected practices on Irish farms. A number of accredited laboratories for soil testing have been set up in recent years.

Co-ops and merchants handing out soil corers to farmers to take the samples themselves is a good idea to cut costs — but it can also be a recipe for disaster if used wrongly.

Bad soil sampling is worse than no sampling because it can give misleading results. For example if samples from areas that have been treated differently in the past regarding slurry applications, silage cutting, etc., are sampled together the results might indicate that the area is ok for lime, P and K but the reality would be quite different.

Fertiliser recommendations are based on samples taken tofour inches deep. Samples taken to any other depth are misleading because most of the nutrients are in the top layers.

At least 25 cores should be taken in a W pattern in the area to be sampled.

Avoid sampling for P and K within ten weeks of fertilizing with P and K and within 12 weeks of slurry application or within 18 months of liming. You should also avoid any sampling around gaps or areas where cattle gather for shelter or other purposes.

Farmers using the soil corers should get good advice on proper soil sampling and recording methods.

A lot of bad soil sampling has been done in the past as a result of the corers being handed out in offices without any instructions.

Ideally testing laboratories should have a well trained person to take the samples. This should not cost very much extra if there was a reasonable minimum number of samples per farm.

Soil Fertility

Proper soil fertility is the basis for profitable and environmentally friendly farming. Based on the low level of soil testing and the deficiencies that are showing up it is clear that this basic and essential element of profitable and good farming is not getting the attention it deserves.

Proper soil fertility is more important than ever in order to optimise the returns from very expensive fertiliser and lime.

Over 80% of the recent soil samples are showing up serious deficiencies in P, K or lime and to make matters worse these samples are probably from the better farms.

Because of the Nitrate Directive restrictions on fertiliser use, particularly P, it is also very important that fertiliser is distributed properly throughout the farm.

Indeed the Nitrate Directive restrictions on P applications have been found to be too restrictive resulting in a slight increase in P application allowances in certain situations.

In the past few years some farmers who have applied the maximum P allowance have found their soils slipping back into index 1 or 2.

This is not only bad for grass production but also bad for the environment as it will require extra N fertiliser.

Cut Back in P, K and Lime Effecting Pasture Production and Animals

Fertiliser and / or lime deficiencies can reduce grass production by up to 50% and based on available information, deficiencies are widespread.

According to official figures, lime usage has been cut back by 45% since 2003.

This has had a serious effect on grass production and Teagasc estimates that the present average pH of Irish mineral soil is only 5.4 (far too low) while around 6.4 is ideal for grass growth in most situations.

Low pH (lime deficiency) reduces the effectiveness of P and K and in turn this reduces the effectiveness of N.

It also results in ryegrass reduction — in favour of less productive grasses as well as a reduction in the percentage of P content in pastures.

Official figures indicate the usage of fertiliser P and K in recent years is the lowest since the1950s and the lowest usage of N since 1983.

The average usage of N, P and K on grassland has been estimated at 52 units, 2.5 units and seven units per acre respectively. These figures represent a reduction of 38% in N usage, 63% in P usage and 50% in K usage since 2003.

The average usage of N, P and K for silage was estimated to be 80 units N, 5.5 units P and 20 units K. This represents a decrease in usage of 16% N, 46% P and 41% K.Some of these reductions are due to the Nitrate Directive but are also due to economic reasons and in some cases due to over use in the past when fertilisers were very cheap.


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