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Soil pH Measurement.

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Laboratory Report For Soil pH Measurement Introduction Soil pH can be tested in a number of ways. The measurement of pH is the most common chemical measurement in soil, biology and aqueous solutions (Bohn et al.). The most common ways are either using an electrochemical tester, where electrodes that are capable of detecting hydrogen ions, are placed in the solution to be tested and the pH displayed on a digital display. The other method, BDH, involves creating a suspension and comparing its colour to a chart with known pH levels. The electrochemical method provides an accurate reading in the laboratory, but is relatively immoveable, BDH, on the other hand provides a rapid assessment that may be used in the field, but may not be as accurate or precise. It is important to know the pH of the soil as it provides a useful indication as to its general state of health. It shows if the soil has good structure, nutrient availability status and indicates soil organism activity. ...read more.


The tube was then shaken until all of the contents was wetted and thoroughly mixed after a stopper had been placed in the other end of the tube. If necessary remove the stopper and top-up the de-ionised water to the first mark. Indicator was then added to the second mark, the stopper replaced and then shaken well again. The suspension was allowed to settle for a few minuets before the clear solution at the top of the tube was compared to the reference card, with the nearest colour match being the pH reading. Results The results obtained from both methods are shown in the table below. Soil Type pH BDH pH Electrochemical Danbury 5.5 3.97 Danbury 5.5 4.03 Alluvium 6.5-7 6.2 Alluvium 5.6-7 6.4 Hornbeam 6.5 6.29 Hornbeam 6.5 6.27 Bengeo 7 7.3 Bengeo 7 7.3 Hamble 6.5 6.02 Hamble 6.5 2.12 Hanslope 7.5-8 7.66 Hanslope 7.5-8 7.79 Chart 1. Discussion As can be seen from the chart above the differences between the two methods are fairly low, this indicates that both methods are relatively accurate. ...read more.


Other nutrients such as manganese can be released into the soil water at toxic rates below pH 5.5. At low pH levels, conditions also become unfavourable for certain micro-organisms, slowing decomposition or nitrogen fixation. High soil pH levels lead to the low availability of many nutrients such as Phosphorus, Iron and Manganese. Soils with low pH are more common than soils with high pH, this is due to several reasons. When organic matter is mineralised nutrients are released along with hydrogen ions. These hydrogen ions lead to a pH drop and an acidic soil, hydrogen ions are also released when ammonium is converted into nitrate. The leeching of calcium, magnesium and potassium as well as heavy cropping that also removes these nutrients leads to a drop in soil pH. Conclusion This experiment shows that while laboratory methods for testing pH are more accurate, in most circumstances the BDH method of testing is more suitable. This method provides a quick, reasonably accurate way of finding the soil pH level, allowing decisions to be made on the nutrient and soil structure status. ...read more.

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