Delving deeper into tackling soil variability – Farmers Guide
The start of the cropping year is an ideal time to assess soils to tailor management decisions over the next 12 months ...
The launch of Hutchinsons’ TerraMap Gold service earlier this year marks a step forward in the ability to analyse and map soils with even greater precision.
Hutchinsons head of soils, Ian Robertson believes the combination of TerraMap’s high-definition gamma ray scanning of key soil properties, with Hutchinsons comprehensive Gold analysis, gives growers and agronomists access to the most accurate and repeatable soil mapping service available.
Significant soil changes
“If you’re looking to make significant changes that affect the soil, such as reducing cultivations, or cutting fertiliser rates, you have to earn the right to do so,” he says.
“TerraMap Gold lets you fully understand the soil’s building blocks and why it behaves in a certain way. That performance may be good, or bad, but knowing exactly what is happening beneath the surface is the starting point for more effective decisions around cultivation strategy, organic matter applications, liming, or the amount and type fertiliser to apply.”
Mr Robertson says soil health is often considered on a macro-scale, but understanding soil chemistry and the microscopic interactions is key to ensuring physical and biological properties work effectively.
Employing the Gold soil sampling on top of TerraMap lets growers accurately measure soil variations in a raft of areas, such as biological activity, carbon:nitrogen ratios, available and unavailable nutrition, and structural variations caused by its chemical makeup.
TerraMap’s gamma-ray detection technology and algorithms are backed up by geo-referenced physical soil samples that together can accurately map more than 30 soil parameters within an individual field.
“If you’ve got variable soils, it allows you to understand where those variations are and make some really impactful decisions,” technical manager, Dick Neale adds. “That may include variable rate nutrition, or for applying lime for pH adjustment, or to correct soil structural issues through targeted use of something like gypsum.”
Ian Robertson, Head of Soils
Delving into detail
One key feature of TerraMap Gold is its ability to measure nutrient reserves and plant-available levels of macro elements, Mr Robertson notes. These sometimes differ significantly due to nutrient interactions within the soil, so understanding this helps manage soils and tailor fertiliser plans.
Being able to measure buffer pH is also useful, as this differs from normal water pH, providing an indicator of how much reserve acidity is in the soil, or the likely resting pH of the soil. Buffer pH influences cycling of nutrients, such as phosphorus, so understanding it allows plans to be implemented that optimise crop utilisation.
Mr Neale says pH variations are commonly detected by TerraMap scanning, and results can improve the understanding of pH and calcium content.
“For example, an alkaline soil with a pH of high 6 to 7+ does not necessarily have enough calcium. Soil pH is driven by a raft of nutrient and microbial interactions.”
Many growers recognise the role of applying calcium carbonate (chalk) on low pH soils to help neutralise acidity by displacing hydrogen ions, but the soil structure benefits from applying calcium in other forms to higher pH soils can be less well understood.
“Even in high pH soils, calcium content may be naturally too low which is affecting the structural components of the soil,” says Mr Neale. “A lack of calcium means clay particles do not flocculate, while higher magnesium means it will sit damp and wet. Applying calcium in gypsum form increases the calcium in the soil, allowing clay to flocculate and remove the excess magnesium from the seedbed area without affecting pH.”
Stowmarket farmer with a soil health focus
Suffolk farmer Brian Barker has been focusing on soil health for many years at his 513ha family-owned partnership near Stowmarket.
The farm is predominantly on medium- to heavy- bodied clay soil, and Mr Barker has long recognised the importance of understanding the soil’s chemical, physical and biological properties to get the most out of it through efficient and sustainable management practices.
Regular soil testing using the standard Gold test has been key to improving his understanding of soil conditions and has helped facilitate the adoption of strip tillage, direct drilling and cover cropping. He wants to take this understanding further by working with Farmacy agronomist Toby Clack to map the whole area with TerraMap Gold.
Mr Barker is particularly interested in better understanding how the relationship between the quantity of different elements affects nutrient availability and other soil properties; information that will help tailor fertiliser strategies through the season.
“Given the price of fertiliser, we have to be confident every pound spent is worthwhile. Doing something just because that’s what we’ve always done isn’t an option,” he says.
Standard soil testing has previously shown significant variations in the indices of certain nutrients, notably phosphate and potassium, with no obvious reason why. Phosphate, for example, varied from index 4 to 1 within one field.
“We therefore used TerraMap Gold to investigate what was going on,” Mr Clack explains. Results showed that while P and K indices were quite variable, levels of available nutrients looked quite different and did not necessarily correspond with the variations in the P or K index.
“It suggests nutrients were present in places, but were getting locked up in the soil, making them unavailable to plants. We looked to see what might be causing this, starting with calcium and magnesium.”
Magnesium and calcium levels were both relatively high in places, indicating they could be affecting phosphate availability and causing other structural issues.
“In areas where we’ve identified high calcium to be the issue, we will limit using nutritional products that are likely to get locked up by calcium, such as triple superphosphate, instead focussing more on using starter fertilisers in spring and autumn-sown crops.”
Where high magnesium is reducing workability of the clay soil, gypsum is being variably applied to improve the calcium/magnesium ratio, without affecting soil pH, thereby increasing the availability of other nutrients and improving structure.
“Unlike calcium carbonate, gypsum (calcium sulphate) is already acidified by the sulphur within it, so the neutralising ability of the calcium has already been balanced by the acidity of the sulphur,” explains Mr Neale.
“This allows the calcium to be purely used to shift magnesium off cation exchange sites without influencing pH.”
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