Ringing changes in lime & analysis trims inputs
Albrecht analysis
The ISS soil cation exchange audit, developed by Prof Albrecht in the 1920s, measures amounts of calcium, magnesium, potassium and sodium, hydrogen and other trace elements (all cations) present in the rhizosphere. "Thats the top 6.5in where 90% of nutrient uptake occurs." says Mr Chapman.
The cation exchange capacity effectively shows the soils ability to hold nutrients. "Its all about balance. For optimum plant growth you need a calcium: magnesium ratio of 7:1.
"The true definition of pH is, in French, the power of hydrogen." In correcting soil acidity hydrogen, a cation, is replaced by other cations. But in this respect magnesium has one and a half times the strength of calcium.
Even though a soil may seem quite alkaline, if there is too much of any one cation around, growth may be impaired as one element prevents others from being taken up.
On organic soils excessive calcium can create magnesium and potassium deficiencies and cut yields.
"Although gypsum is often recommended, there are many instances where soils with high pH need ordinary calcium lime, for example where calcium levels are extremely low because they have been replaced by magnesium." The result will, perhaps surprisingly, be a drop in pH, he says.
Ringing changes in lime & analysis trims inputs
By Andrew Blake
A SWITCH in liming material, prompted by a change in soil analysis method, is helping a North Yorks grower trim fertiliser costs and improve the structure of his land.
Mark Hinton long used locally quarried magnesium limestone to correct soil pH on his 200ha (500 acre) West Low Field Farm, Kirkby Fleetham, Northallerton. But having gained a deeper insight into the nutrient content of his fields four years ago through Norfolk-based Independent Soil Services, he used gypsum instead.
"Nothing is instant and there is nothing new in using gypsum as a soil conditioner," says Mr Hinton. "But we are beginning to see a difference. The soil is certainly draining better."
Fertiliser inputs have also been cut with no apparent reduction in output. "We have stopped using phosphate altogether and reduced our nitrogen dressings by up to 15%.
"We have seen a small yield improvement, but some of that could be tied up with our use of strobilurin fungicides and new varieties.
"We are not on particularly strong wheat land, but we are averaging 3.75-4t/acre. Five years ago we were getting 3.25-3.5 and I have a feeling quite a lot of it is to do with the improved workability of the soil."
Compared with the cost of a routine soil analysis for pH, phosphate, potash and magnesium, the US-originated Albrecht cation exchange method he uses through ISS seems expensive.
"But it gives us a tremendous amount of information and the £250 one-off cost can be spread over several years."
Any later check tests cost a lot less."
"I am quite happy with the cation soil testing system and using gypsum," says agronomist Rachael Webster of Yorkshire Arable Advice, who advises Mr Hinton on all other inputs. "Gypsum liming does seem to be doing a lot of good in this area," adds colleague Andrew Fisher.
WESTLOWFIELDFARM
• Soils naturally high in magnesium.
• Extra Mg locking up calcium.
• Albrecht analysis undertaken.
• Gypsum used to restore balance.
Digging for a better insight into liming requirements. David Chapman (right), with penetrometer, reminds Mark Hinton how excessive magnesium can lead to hard-to-work soils.