Are you happy with the quality of your lime?

Written by James Warne from Soil First Farming

A word of warning to all of you who buy bulk lime products. There appears to be nobody in the supply chain fighting your corner to ensure the quality of the lime you buy meets the legal requirements as laid down in the Fertiliser Regulations 1991. 100% of the bulk lime products we see tipped on farm does not meet these specifications in terms of particle size. Even if it’s being sold as screened lime it fails to make the specification. This low quality lime will not be able to neutralise soil acidity as quickly, or for as long, resulting in declining crop performance. I encourage everyone buying bulk lime products to take a sample from the delivered pile before spreading and get it tested for Neutralising Value (NV) and particle size distribution to make sure it meets to specifications of the product. The correct specification is given in the table below. If the analysis results show substandard product, talk to your supplier and send the results to the Aglime Association. It’s only by collective effort that we can encourage change. Always request ground agricultural lime from your supplier and put it in writing.

The Aglime Association, which represents lime producers, has launched its own assurance standard to ensure product consistency from the quarries. But why do we need another assurance standard when the supply requirements are laid down in law? I mention this topic regularly for good reason. Farmers are paying for sub-standard inputs which can be very costly, not only in the purchase and spreading price, but also the knockon effects of reduced output. Low soil pH can negatively affect nitrogen use efficiency. With urea trading at ~£700/per tonne you need to ensure that you are maximizing its efficiency.

All ag-lime sold in the UK must meet the requirements of the Fertiliser Regulations 1991 to be sold as lime, for the purposes of this article I will look at limestone only, but these regulations also apply to dolomitic limestone, chalk and many other types of lime. The table below is taken from the Fertiliser Regulations.

Don’t just buy on neutralising value, the particle size distribution is critical, almost more so. To put it in context, Lincoln Cathedral has a neutralising value, it’s built of limestone after all, but it won’t neutralise very mush due to the low surface area to volume ratio. Grind the stone to 150 micron and it will neutralise acid, provide plant available calcium and react well.

Once the levels start to decline the effectiveness of inputs also starts to decline and the return on investment declines alongside. The health of the crop suffers which results in an increase in inputs which are already under pressure. You can see this becomes an ever-decreasing circle of increased cost and decreasing output.

As mentioned above we now know that grind size is as important as neutralising value in determining whether the lime will actually do as intended. This is where the fertiliser Regulations 1991 become relevant because they set out the standards for lime quality as a fertiliser. If we consider these regulations for a moment it is clear that both the neutralising value and the specific material name must be given, in addition the percentage by weight passing through a 150 micron sieve must also be declared (the grind size). A limit of variation (tolerence) of 5% is allowed.

By grinding the rock finer we are increasing the surface area of the product. It is this increase in surface area which allows the lime to react faster and bring about quick reductions in soil acidity. If we calculate the degree of grinding and surface area

Name of material Meaning Declarations

Ground limestone Sedimentary rock consisting largely of calcium carbonate and containing not more than 15% of magnesium expressed as MgO and of which 100% will pass through a sieve of 5 mm, not less than 95% will pass through a sieve of 3.35 mm and not less than 40% will pass through a 150 micron sieve

Sedimentary rock consisting largely of calcium carbonate and containing not more than 15% of magnesium expressed as MgO and of which 100% will pass through a sieve of 5 mm, not less than 95% will pass through a sieve of 3.35 mm and not less than 20% will pass through a 150 micron sieve. Neutralising value Amount of material as a percentage by weight that will pass through a 150 micron sieve

Neutralising value Amount of material as a percentage by weight that will pass through a 150 micron sieve Limit of variation (percentage by weight) 5.0% of amount

5.0% of amount stated

Name of material Prilled Lime Ground Limestone Screened Limestone Sieve size

5mm 100

3.35mm 100 100

95 100

95

0.15mm 100 40 70

Surface area (m2) per metric tonne 44776 19476 11528

we can see from the table above that ground limestone has a surface area nearly twice that of screened limestone, while prilled lime products can be four times the surface area of screened limstone. This increase will give greater reaction and therefore faster pH reduction.

So how fine does the rock need to be ground to be effective? The aglime website states that “coarser material requires a heavier application” and “There is a considerable reduction in the effectiveness of liming materials containing particles above 600 microns (0.60mm, 60 mesh) unless the material is easily broken down”. The finer the lime is ground, the more effective it becomes.

This is supported by work taken from North Carolina University in the US shown to the right;

This graph clearly demonstrates that lime in the range of 0.177 – 0.150mm (177-150 micron or 80-100 mesh) gave the quickest pH rise and most sustained pH rise. The larger particle size 0.841mm and above gave a very limited pH increase and took 18 months to achieve it.

Focus on the detail of the basics and the output and profitability will follow. My advice to you is avoid buying bulk lime altogether because you cannot guarantee what you are going to receive and instead buy a guaranteed quality product such as a prilled lime which will work for you every time.

The Rezult stubble rake evens out previous crop residue and promotes a flush of weeds and volunteers ahead of drilling

Fitted with a seeder box, the Rezult becomes a cost-effective means of establishing cover crops The Rehab has been designed to lift and aerate the soil profile whilst minimising surface disturbance

As we say on our own farm, ‘It starts with the combine’.

The first step in direct drilling a typical field is combining the previous crop, so it is only right that this step sets up the field for effective drilling and makes best use of any remaining crop residue.

That’s why we like to use the Rezult stubble rake to even out any combine mishaps and ensure an even coverage of straw across the field. Fitted with leading discs, these make an invaluable addition to any rake for chopping surface straw and mixing it with surface tilth to accelerate decomposition.

This tilth also makes it easy to create stale seedbeds and encourages a flush of weeds and volunteers ahead of drilling. A couple of passes of the Rezult, a few weeks apart can make best use of chemistry for an effective weed kill.

By opting for a stubble rake with leading discs, it also gives operators the added flexibility to use as a means of establishing low-cost cover crops when fitted with a seeder box.

The Rezult rake is also an ideal tool for cutting slug activity, particularly in OSR stubbles, where disrupting slug habitats and exposing eggs to the midday heat has huge advantages for reducing slug populations in the following crop. For Rezult’s fitted with a seeder box, slug bait can be applied at the same time to pack an even bigger punch.

Whether it forms part of the transition to direct drilling, or used periodically for fields requiring remedial care, a low disturbance subsoiler is a great addition to the direct driller’s arsenal.

Our Rehab low disturbance subsoiler has been redesigned for 2021 featuring leading discs, shearbolt protected legs and heavy-duty V-shaped roller packer.

As direct drillers turn to less disturbance, some growers report experiencing compaction issues at depths of 6”-8” as a result of machinery passes or long periods of heavy rainfall. The Rehab has been designed to alleviate this type of compaction whilst staying true to growers’ requirements for low disturbance.

The Rehab features spring loaded pivoting discs which act to slice through topsoil and crop residue, allowing the following leg to lift and aerate the soil profile whilst minimising disturbance to the field surface. A generous leg spacing of 500mm and a stagger of 750mm promotes an excellent flow

of crop residue through the implement to reduce the risk of blocking up in high-residue environments - something which is important to maintain for many direct drillers.

Operators can determine the level of fracture through the soil profile by choosing from three wing widths including 55mm, 115mm and 135mm. The legs are protected by ‘hammer-thru’ shearbolts rather than hydraulically pressurised to maintain maximum draft control and the correct draft angle of the wing for more efficient use and lower disturbance.

When designing the Rehab, it was important to create an implement that would leave the field with a weatherproof finish, perfect for direct drilling. The Rehab achieves this by incorporating a V-shaped packer roller which is designed to consolidate either side of the leg and leave an even finish.

By minimising surface disturbance and working with previous crop residue, the Rehab achieves better moisture retention whilst ensuring sufficient lifting of the soil profile, complimenting direct crop establishment.

1. Cutting: Pivoting serrated discs mounted on spring - loaded arms slice through the surface residue, ensuringa lower disturbance to the topsoil. Consistent contact with the ground is achieved across field contours. 2. Shattering: Shearbolt protected legs maintain an accurate draft angle of the ground engaging parts for better control of shatter action. Each leg is fitted with a two sectioned replaceable point and wing, with a choice of wing width depending on the level of fracture required. 3. Consolidating: A steel V-shaped packer directly consolidates either side of the cultivated area and closes the opening behind the leg, leaving a weatherproof soil structure without the risk of drying out.

• Soil potential investigation • Visual soil structure analysis • Comprehensive chemical, physical and biological analysis and interpretation • Farm soil organic matter and carbon analysis • Farm machinery review • Detailed Report with practical

DIRECT DRILLER MAGAZINE recommendations “Our platinum soil health analysis will help take your understanding of soils to the next level”