Biological Soil Testing vs NPK testing vs No Testing

[Susan BBPM]

NPK testing is very usefull if you use chemical fertilizers - it lets you know the current NPK condition of your soil so that you can, if required, add precise amounts of fertilizer to get your ideal growing condition. This makes a lot of sense.

However, people are moving away from 'feeding the plants' with fertilizer to 'feeding the soil' - the idea being that the soil life will take care of feeding the plants.

So, should we assume that well fed soil life will produce perfect amounts of NPK? It seems not.

Ultimately the goal is to grow great vegetables. So your primary guide should be the health, quality and size of your plants.

What then will you do if your soil is producing absolutely amazing harvests but an NPK soil test tells you that you need to add huge amounts of fertilizer? It's this situation that's caused many no dig gardeners to be very wary of NPK testing. It seems that there are too many other factors at play - the quality of the plants and harvest is the most reliable guide.

Maybe NPK testing is a red herring - a throw back to the days when fertilier companies were king?

You can get biological testing done - here's a UK site that does it. It would be interesting to see what various things (adding compost vs green manure vs cow manure, or dig vs no dig) has on soil life. And of course on NPK.

But ultimately your guide to soil quality is the veg and flowers that you grow. If NPK OR biological test results say your soil is bad, and your crops say otherwise - believe your crops. The whole process isn't yet fully understood and tests could well be looking at entirely the wrong thing.

https://www.laverstokepark.co.uk/about-us/we-believe/microbiology/

 

[Oliver Buckle]

I'm with no testing, firstly I have got enough to do, second I am poor. Most deficiencies show up in particular ways in the growth of the plant. "What's wrong with that? Could be ...? put on a bit of wood ash/manure/seaweed concentrate/blood fish and bone as seems appropriate and see if it works.

 

[redback]

NPK soil testing begins with fumigation of the soil to kill all that is living in it. Correct me if I'm wrong. Then the soil is chemically tested for the presence of minerals and salts. However, the plant roots cannot 'chelate' these minerals and therefore cannot use them.
In a living soil plant roots excrete glucose to seduce microbes to come around and feed. Then the root absorbs the mineral carrying microbes it requires and strips them of their usable minerals and expels their DNA from root hairs. The DNA reforms a microbe and repeats the process.
Refer to Dr. Christine Jones uTube videos. The best soil test for beneficial soil microbes is to pull up a plant/weed/grass in the area of concern and look at its roots. If there is a thick covering of soil on the healthy-looking roots this is called a 'sheath'. This sheath indicates the presence of sticky glucose and an oxygen exclusion zone where the plant extracts nitrogen from the air.
This is a simplified version of the soil science carried out by Dr. Jones and Dr. White. Their research is telling everyone to keep their soil alive and stop using chemical fertilizers, herbicides and insecticides.