pH in Soil Analysis: Influence on Soil Quality and Crop Growth
pH or acidity is an integral part of soil analysis. Too low a pH causes soil compaction, limits the activity of soil life and disturbs nutrient delivery. Acidity affects soil chemical quality and crop growth, via the availability of nutrients, (heavy) metals and acid particles (H+), but also via soil structure and soil life activity. pH is therefore a basic indicator of soil quality. For clay soils, a higher pH gives a more airy soil with more pores and less binding between soil particles.
A fertile, calcareous soil has a pH of 7, or just below. In lime-free soils, the pH can become too low (pH < 5). The type of crop and fertilisation influence the
pH level.
By liming, the pH of soils can be brought to the desired level. It is important to plan liming within the cropping plan and possibly spread it over several years.
When pH is below 5, the plant can absorb fewer nutrients. This results in lower yields and loss of quality. The most sensitive elements are nitrogen, phosphate, potash, magnesium, sulphur and calcium. This can lead to deficiency symptoms such as magnesium deficiency in potatoes (left) and maize (centre) and sulphur deficiency in sugar beet (right).
A high pH (pH-KCl > 7) limits the availability of certain nutrients, such as manganese.
For good crop growth, it is essential to maintain pH at an optimum level, between 6 and 7 in most soils.
For arable crops, the optimal pH depends on the cropping plan, as crops have different pH requirements. Beets, for instance, need a higher pH than potatoes. The proportion of beet or potatoes in the cropping plan therefore affects the level of optimum pH.
For grassland, a pH between 4.8 and 5.5 is assessed as good, but a grass-clover mixture requires a slightly higher pH (between 5.2 and 5.5) for the clover to perform well.
On sandy soils, pH values between 5 and 6 are maintained. On more acidic soils such as peat, a pH of 4.8 is advised.
Source:
Handboek bodem en bemesting www.handboekbodemenbemesting.nl
Kennisakker, adviesbasis voor de bemesting van akkerbouwgewassen. www.kennisakker.nl
Commissie Bemesting Grasland en Voedergewassen, (2011). Bemestingsadvies. p/a. Animal sciences Group, Wageningen. 186 p. www.bemestingsadvies.nl