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Fertiliser: Make soil samples the first step in fertiliser budget decisions


Taking soil samples is essential to establish baseline fertility

Taking soil samples is essential to establish baseline fertility

Taking soil samples is essential to establish baseline fertility

As we head towards the spring, longer days and, hopefully, higher temperatures will force our temperate plants out of their wintertime slumber.

This growth is the very essence of what we live off as farmers and it has to be encouraged and maximised wherever possible.

In order to encourage growth, the number one tool we have at our disposal is fertiliser, whether chemical or organic. The application of fertiliser on to our crops stimulates growth and increases the rate of growth over and above what would otherwise occur.

Before any discussion of fertiliser source can take place, the first thing to address is the soil pH level. Where lime is required, any manure applied, whether slurry or chemical fertiliser, will not work efficiently and therefore wastage occurs. Lime is so important to fertility that if the budget is so limited and lime levels are low, all monies should be spent on lime and none on any other manure - it's that important.

Lime application has the effect of releasing previously applied nutrients that were unavailable as they couldn't be 'activated' as the soil pH wouldn't allow for it. So in the absence of applying other nutrients, lime application can result in the soil temporarily supplying other nutrients to the crop from soil reserves.

Once the soil pH has been addressed, for the purposes of this discussion, manure comes in three forms: organic manure being recycled from within the farm, organic manure being imported from external sources, and inorganic manure or chemical fertilisers. In terms of importance, they can be considered in the above order. Every year, as soon as the prohibited period from applying spreading slurry starts, as sure as the clock turns back, the bleating starts for the 'end-of-calendar farming', accompanied by the perennial 'bureaucracy gone mad' statements.

The purpose of these calls are to allow farmers to spread slurry whenever and wherever they want. This attitude is perplexing. One of the most valuable resources a farm produces is slurry. It contains vast amounts of phosphorus, potassium and nitrogen, the three elements that are most scarce on the farm and the most expensive to replace.

Yet there are those who continually wish to treat slurry as a waste, something to be disposed of rather than managed to best effect.

The timings to get the most from slurry have been well established - in springtime, as growth commences, after cuts of silage, or before sowing a spring cereal or maize crop.

Careful application of slurry is recycling at its best. Where silage and animal growth depletes the soil of reserves, slurry returns the nutrients back on to the soil from where it came.

When deciding where to close off for silage production, it is of real benefit to a farm to rotate the area cut for silage with the grazed area. Too often, fields are classified as 'silage fields' or 'grazing fields', whereas alternating the fields from year to year can have huge benefits. Grazing a field for a season that is normally cut for silage can replenish nutrients, and give the field a 'break' for a season.


Taking silage from a grazed sward can deplete nutrient levels where they have accumulated to excess. There may be implications on fencing and water access, and it can be a bit of hassle, but as we are beginning to relearn in the tillage arena, rotations can bring huge benefits over and above the effort involved in implementing them.

Another issue regarding spreading slurry is to start spreading from the extremities of the farm and work towards home. Far too often, slurry is spread in the handiest and nearest fields possible.

The second most important source of nutrient is organic manure produced on other farms like heavily-stocked dairy and beef units; pig/ poultry units or businesses such as mushroom producers, meat factories, dairy processing facilities and municipal waste management. These nutrients are normally applied on to tillage soils where off-take is usually greatest. However, importation of organic manures on to grassland can also be very effective. It can be hassle to import organic nutrients, with significant regulatory oversight involved. However, there are opportunities to significantly cut fertiliser costs and increase soil fertility levels by importing manure.

Given that grain and straw produced on tillage soils can end up as excess nutrients produced on pig, poultry and mushroom units, land spreading organic manures can be viewed as recycling in its broadest sense. The one issue to be aware of with regard to organic nutrients is that they may not be as balanced as chemical fertilisers.

Most land that is fertilised will be fertilised using inorganic or chemical fertiliser. There is good reason for this. Chemical fertiliser is effective, is clean with consistent quality and can be easily controlled.

Analysis of soil sample results show that soil P and K levels are in continual decline. It has been well established that low P and K soil reserves cannot produce maximum yields. While it is a very expensive process to build up soil reserves, in many instances, that is what is required to increase output on a farm. Before any fertiliser programme can be reasonably planned, an up-to-date soil sample is necessary as a basis on which to make decisions.

Richard Hackett is an agronomist based in north Co Dublin and is a member of the ITCA and ACA.

Indo Farming