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September 12, 2022
Rocco Falconer

SOA Application Makes Soil Correction More Important Than Ever This Year

SOA Application Makes Soil Correction More Important Than Ever This Year
“Don’t let Nitrogen acidify your soil.”

— Government of Australia

The dramatic increase in global energy prices as well as the Russian invasion of Ukraine have caused major shocks to the global fertiliser market, leading prices to increase over 300% since 2020. Farmers in Ghana are feeling the impacts of this more than ever with reduced availability and high price of fertilisers in the market.

One of the major shifts this has created in Ghana is farmers shifting from the use of Urea as the major source of Nitrogen fertiliser to the use of Sulphate of Ammonia (SOA) as nitrogen. Whilst SOA is considerably cheaper, it brings along with it significant additional challenges.

SOA is cheaper for a reason. It contains less Nitrogen than Urea (urea contains 46% nitrogen, whilst SOA contains 21% nitrogen). More importantly, the form of the nitrogen is sulphate, not nitrate: that means that for the nitrogen to become available to plants, a chemical reaction must occur.

Although this is a little complex, it is very important. In warm soils, microbes will rapidly begin to convert ammonium to nitrate in the process of nitrification [2 NH₄⁺ + 3O₂ → 2NO₃⁻ + 2H₂O + 4H⁺]. During this microbial reaction, acidity [H⁺] is released, which will ultimately decrease soil pH. Ammonium sulfate has an acidifying effect on soil due to the nitrification process. The acid-producing potential of ammonium sulfate is greater than the same N application from ammonium nitrate, for example, since all of the N in ammonium sulfate converts to nitrate, compared with only half of the N from ammonium nitrate that converts to nitrate. More information is available here.

What this means is: SOA will increase soil acidity in your field. As you can see from our other blogs, soil acidity is a major barrier to yield and to efficient use of fertilisers. Also important to note is that the amount it will increase the acidity is also dependent on the heaviness of the rainfall and the amount of leaching: if heavy rainfall leaches the nitrates away, then the soil becomes more acid. So controversially, the application of too much Nitrogen fertiliser can actually slow down plant growth, depending on the weather conditions.

Remember also that the acidity of soil reduces the uptake of all nutrients, reducing efficiency of fertilisers:

Fertiliser efficiency at acidic pH

So the use of acidifying fertilisers, if not managed well, can cause a downward spiral on yields by increasing acidity, reducing efficiency of fertilisers, and locking up nutrients that all farmers need to pay attention to.

As soil gets more acidic with every application of acidifying fertiliser, then you can see how the conditions of farms and the yield over years can decline. This can cause major challenges, with these impacts are observable already in the more sparsely fertile soils of the Northern regions of Ghana. Over time, yields will go down and more fertiliser will be needed to have the same results – which is actually making the problem of soil acidity worse. Ultimately, over time it will cause increasing problems for farmers as costs go up (as more fertiliser is needed to have the same effect) and fertiliser efficiency, soil health, and ultimately yield go down.

The good news is that these twin issues of soil acidification and inefficiency of fertiliser application are very easy to solve. Of course, the acidifying impact of fertiliser is nothing new: SOA was first used in Europe in the 1800s and farmers then had to find ways to counteract the impacts it had on yield.

The simple thing to do to counteract the impact of this acidity is simply to neutralise the acidity. This is easily done with the application of Calciprill®, which is available from Demeter Ghana Ltd.

When either Urea or SOA is used, Calciprill® should be used. In fact, in other markets such as Europe, USA, and Australia, the government issues guidelines for the use of neutralising substances (lime) when any acidifying nitrogenous product is applied. It is important to note that usually the recommendations suggest that for every 1kg of SOA that is applied, up to 6kgs of lime should be applied. For example, please see Don't let nitrogen acidify your soil ( from the Australian government (please note that the bag weights they are using is 40kgs / bag).

So given the shift in Ghana from Urea to SOA in the last few years given the high price of the former and the wider availability of the latter, it is imperative for farmers to correct their soil acidity early, before it is too late. If you have applied SOA this year, please call Demeter Ghana Ltd on 0245297047 to get your Calciprill® to correct soil acidity. Even if you haven’t applied any you should still test your soil and see what treatments are required, so call us or get in touch now.

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