A healthy, balanced soil will grow healthy balanced crops. When yields start to fall, identifying the cause of the problem is the the first step to resolving it. Here I look at the steps to work out what is deficient in this reader’s soil.
I had an interesting puzzle arrive in my inbox from Trevor
… I wonder if you can help me. I have been growing vegetables, with suitable rotation, for over 20 years on my patch. Over recent years whilst leaf vegetables, i.e. beans, peas, brassicas etc. are fine, root crop yields including potatoes are diminishing.
Any ideas what could be the cause?
Possible causes for the decline in crop yields
Well first of all, it seems the most likely reason will be a developing deficiency. Lack of water will cause a decline in potato yield but this year has been pretty wet so we can rule that out.
The leaf vegetables continuing to do well tells us that there isn’t a shortage of nitrogen which is necessary for leaf growth. It’s possible that too much nitrogen has been applied either as fertiliser or in manures. That would cause excessive leaf growth at the expense of tubers. It seems you can have too much of a good thing.
That leave phosphorus and potassium of the macro-nutrients. A shortage of potassium (potash) would be my feeling although phosphorus shortage would reduce yields on root crops.
There are other possible causes, a shortage of a micro-nutrient will have an effect even if there are plenty of macro-nutrients available.
The last suspect is the pH. If the soil is too acid or alkaline this will prevent nutrient uptake so mimicking a shortage. The ideal for potatoes is a pH between 5.5 and 6.5. Brassicas much prefer a high pH so possibly the soil is too alkaline.
Identifying The Soil Deficiency.
We need to identify the cause of the problem to rectify it so my advice is:
Check the pH of the soil. Testing kits are readily available, very cheap and easy to use. If necessary, rectify the pH.
Assuming the pH is within bounds then the next thing to look at is the macro-nutrients, Full test kits are a little more expensive than pH test kits but should show if there is a shortage to rectify.
Finally we have the micro-nutrients to consider. Testing for these is a job for a laboratory. The cost of professional testing is going to be higher than applying a trace element fertiliser like S-Chelate Cultiv-8. This will resolve any trace shortages. It’s organically approved and inexpensive.