The importance of using lime

The Importance of Lime   

The importance of adding lime to our plots cannot be over emphasised. Apart from its ability to break up heavy clay soil – a serious consideration on my ground, its influence on the pH (acidity/alkalinity) of our soil is crucial. It must be said, heavy clay soils are more likely to be acid rather than alkaline. I’ve talked about the addition of lime with many of my allotment neighbours over the last year – it seems very few people now apply this essential ingredient. We keep adding cow manure, horse manure, green manure, etc., but fail to take into account the affect these have on the pH of our ground. We look at our crops – some doing well, some doing okay and some failing, although we keep adding manure – what can we be doing wrong? Do have a look at the tables below:-

The most important nutrients for our plants are :- N – Nitrogen – for leaf growth P – Phosphorus (phosphates) – for root growth K – Potassium ( potash) – for fruit and flowers The essential trace elements are probably already present in our soil and are:- S – Sulphur Ca – Calcium Mg – Magnesium Fe - Iron Mn - Manganese B - Boron Cu & Zn – Copper and Zinc Mo – Molybdenum

Check out – www.hydroponics.co.nz/images/large/pH_chart.gif

I hope the chart above makes sense – the thickness of the shaded lines indicates the optimum uptake of each the essential plant nutrients. For my soil it should be around 6.3 – 6.5. Where the pH is below 5 the plants’ uptake of nutrients tails off significantly and the ground can become toxic. Although the nutrients may be present the plants are unable to use them. The word ‘toxic’ seemed to me to be a somewhat dramatic statement. When I asked why ‘toxic’? I was told that in very acidic conditions, minerals such as aluminium can increase in the soil to toxic levels. Even acid loving plants like heathers are not so happy when it is very acid. I do know that pH of 7 is neutral. Someone was very quick to point out to me that 7 is neutral and not 6.3 - 6.5. However, neutral is not necessarily the best pH for your plants

A pH meter is inexpensive and easy to use. ( if you want to be really sure, it's probably worth investing in a proper kit). It will tell you almost instantly where lime should be added but, don’t add it to the ground before planting, for example - potatoes ( check out the soil conditions needed for individual vegetables), and don’t apply at the same time as manure. It is not a good idea to apply a lot of lime in one dressing. If the pH of your ground is very low, ( in some patches on my plot it has been as low as 3! ! - really!),  it is best to apply a light dressing over several years to bring the pH up to a reasonable level. It must be said that a high alkaline soil will have a similar effect as acidic, although it is likely to take some time to build it up to toxic levels.