The wealth of a farm rests in the health of its soil. So, it is vital that farmers address the three main foundation blocks for soil health, Kevin Havekes of Kilwaughter Lime told viewers during a recent industry webinar last week.

According to Havekes, the first thing that impacts on soil health is drainage and compaction.

“Heavily compacted and poorly drained soils will hold water and become anaerobic, which cam be identified by a distinct musty smell.

“Plant roots cannot migrate downward and tap in to the nutrients present, so fertilisers are less effective and yields will be lower.

“Improve drains where needed and sub-soiling will open up soils, improving aeration, removing water and is money well spent,” said Kevin.

Liming

The second foundation block is soil pH. Mineral soils should be between pH 6.3 to 6.5 for optimum crop growth. As soils become more acidic, the availability of nutrients decreases.

Havekes stressed the importance of understanding soil pH, as the indices follow a logarithmic scale.

“Some farmers are happy to stop liming soils once they reach pH 6.0. But this is not an optimum pH and soil nutrients will still be locked up.

“The thing to remember is that at pH 6, soils are 10 times more acidic than pH 7. At pH 5, soils are 100 times more acidic than pH 7.

“If a farmer with soils around pH 6.0 can increase levels to 6.5, it will have a huge bearing on nutrient availability.

“At pH 6.5, 100% of soil nutrients are available to the plant. At pH 6, only 89% of nitrogen (N) and 52% of phosphorous (P) is available for plant growth. That means if we spread one bag per acre of 27-4-4, costing £600/t, to soils at pH 6, the farmer is wasting £90/t because of the N and P locked up in the soil.

“At pH 5.5, spreading fertiliser becomes even less effective. Only 77% of N, 48% of P and 77% of potash (K) is available for plant growth. If using our 27-4-4 fertiliser costing £600/t, £150 is wasted.”

Macro nutrients

The final aspect to soil health is the level of macro-nutrients. Sulphur is a crucial element that is often neglected when purchasing fertiliser, usually because it increases the price by £15 to £20/t.

But where soils are lacking sulphur, yields will be significantly reduced, costing farmers a lot more in the long run due to reduced output.

Magnesium, selenium and calcium are other macro-nutrients that get overlooked, but will impact on soil health, soil biology and crop performance.

“Calcium is the king of all nutrients and has greater interaction with soil biology than any other element.

“It is a major component of plant cell walls, strengthening the stem and reducing lodging. It also makes the plant more resistant to fungal disease and pest damage, reducing the reliance on chemical fungicides,” said Havekes.

Negative cycle

Industry analysts estimate around 17% of UK soils are at optimum pH levels. Part of the problem is down to increased use of chemical fertilisers.

According to Havekes, liming was traditionally carried out on farms every year. But as chemical fertilisers became more widely available in the 1980s, farmers saw immediate growth responses from applying nitrogen.

Over time, more money was spent on fertiliser to increase yields and less investment was made on lime. But consequently, as fertiliser levels increased, soil pH began to fall.

In order to maintain yields, farmers began to increase fertiliser use and it is only in more recent years that farmers have started to address soil pH again.

Addressing soil pH

Soil pH measures the hydrogen level in the soil and it is hydrogen that creates acidity. Lime is normally calcium carbonate or magnesium carbonate.

Calcium binds to the hydrogen ions, forming water which then drains off through the soil pores. There is also CO2 produced, which is released to the atmosphere, replaced by oxygen in the soil.

Not all liming products condition soil in the same manner. Some have a faster effect, some have a slower release and application rates differ depending on the calcium content.

Granulated lime is readily dissolved and effective inside six weeks from application

“The important thing is choosing a quality liming product with fine particles and a high neutralizing value, rather than focus on the merits of one type of lime over another.

“Lime is measured on neutralizing value and the size of the particles. The smaller the liming particles, the faster they condition the soil.

“Farmers should be asking their lime supplier for a certificate of neutralizing value. The EU passed regulation that at least 70% of lime particles should be smaller than 1mm in size,” Havekes stated.

Conventional lime

There is a place for both conventional and granulated lime on-farm. Choosing a product comes down to the timing of application and how low soil pH is. With conventional ground lime, Havekes recommended using it on acidic soils around pH 5.5 or below, or on fields being ploughed for an arable crop or new grass ley.

This will lift soil pH to a level that can then be easily maintained each year using a granulated liming product. However, the downside with ground lime is that 50% of particles are greater than 0.5mm and 30% greater than 1mm in size.

According to Havekes, these particles can take anywhere from six to 18 months to fully break down and give the full lift in soil pH.

Granulated lime

For soils at pH 5.7 and above, Havekes recommended using granulated lime over a three to four year period to reach pH 6.5, then maintain with a smaller, annual dressing.

“Granulated lime is readily dissolved and effective inside six weeks from application. This makes it much more suited to grassland applications compared to coarser, ground lime.”

Compromise

There is a happy medium to be found between both forms of lime. Havekes outlined an example of farmer applying 2t/ac of ground lime to raise soil pH.

Around two to three years after this application, pH will begin to fall at a rate of 0.1 to 0.2 units per year.

Rather than opting for a follow up dressing of 2t/ac, his advice was an annual maintenance dressing of 100kg/ac of granulated lime through the growing season from year two onwards.

Economics

Havekes concluded with an economic comparison of different liming strategies and maintained that a granulated product was the cheaper option in the long term.

“If you cost out applying 2t/ac of ground lime every five years on soils at pH 5.7, it will cost £40/ac more compared to spreading 250kg/ac of granulated lime in year one, 200kg/ac in year two, 150kg/ac in year three and 100kg/ac from year four to year 20.

“There are also yield benefits as the soil will spend 48% longer at the optimum pH level using the annual maintenance little and often approach,” he said.

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