Keep an eye on your pH levels – soil acidity can cost yield
NRM
Agriculture
Most basic soil tests for phosphate, potash and magnesium will also give a guide to the soil’s pH status. However, there is a risk of more localised acid patches in many fields. Expanding testing to each hectare or spot checking with an in-field test kit will help determine the lime requirement necessary to correct low pH levels. The opportunity for variable rate application and the availability of granular liming products means both the background pH levels and acid patches within the field can be treated.
Lime use has dramatically declined in recent years, increasing the likelihood of soils with low pH and acidic patches. In arable situations it has been shown that when soil pH falls to 5.5, wheat yields can be reduced by as much as 25%. Even if only part of a field was below pH 5.5, average yields and margins would be reduced.
Optimal pH levels for crop production
Potatoes 5 to 6.5
Oats 5.5 to 7
Wheat 6 to 7
Ryegrass 6 to 7.2
Barley 6.4 to 7.5
Sugar beet 6.5 to 7.8
There are a number of key reasons why low pH will impact yield. Crops depend on good levels of biological activity to solubilise and mineralise nutrients, but microbial activity is significantly reduced in acid soils. Optimal uptake of all nutrients is essential for good yields, but nutrient availability is influenced by pH, with some nutrients (especially phosphate) restricted at high and low pH levels. Acid soils also increase the solubility of plant toxic metals such as aluminium, which again leads to restricted growth.
Optimum pH for nutrient availability
There is a wide range of liming products available, generally containing either calcium or magnesium carbonate. The carbonate (CO3) reacts with hydrogen ions in the soil to make water and carbon dioxide. This reduces the hydrogen concentration and enables more beneficial cations such as potassium, calcium and magnesium to be held on the clay colloid and therefore accessible to the growing crop.
With the potential for yield loss in acid soils due to poor nutrient uptake and crop growth, regular monitoring of soil pH is essential. Variable rate application is strongly recommended for all liming products, using good pH map data, to avoid over-liming which can also restrict nutrient availability.
This spring, take note of any problem areas, backward crops or areas of poor crop growth, and check these for low pH so you can correct them at the earliest opportunity. Ask your agronomist, soil sampling provider or lime supplier to arrange for sampling to be done, or contact NRM directly for sample kits on 01344 886338.
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