When it comes to nutrients, plants can be like Goldilocks. For healthy growth and reproduction, nutrient levels have to be just right. Plants can suffer from both nutrient deficiencies and nutrient toxicity. Each species of plants has its own nutrient requirements. The balance between enough and too much of a given nutrient can also be a moving target. Plant nutrient needs and tolerances can change as a plant reaches different stages of development or reproduction. To complicate matters even more, any environmental variable that influences nutrient mobility through soil, nutrient uptake by the plant, or nutrient mobility within the plant will complicate matters. For example, different substances can “compete” with each other for opportunities to either acquire or donate electrons. If a “better competitor” is present in the soil surrounding a plant, it will “interfere” with a nutrient moving into a plant’s roots. When such competition is present, knowing the concentration of a nutrient is the soil relative to the plants needs won’t be enough information.
As it is, professional recommendations for nutrient levels in soil or plant tissue are calibrated and based on research that is specific to, at a minimum, the following: plant species, stage of growth, and analytical method used for soil and plant tissue analysis. There are consultants who will be happy to take your money and give you advise for plant species that have not been researched or by using analytical methods that have not been calibrated. My Dad happens to be one of the professionals who is a stickler about the limitations of analysis for plant nutrition. When faced with a situation where the assumptions of analysis methods are not met, he relies on his extensive experience and training. Ok, there it is. I have a bias. I happen to find that it is a handy bias. Additionally, I have a dad who expects me to do my own homework before calling him.
I also have a budget with no expectations of making money off of my plants. Good consulting and analytical work tends to cost money (In my case the question is will it be my money or Dad’s money. The older I get, the less likely it will be Dad’s money.) Getting to a library with good resources on plant nutrition roughly translates to putting gas into the gas tank. That takes money, so I start with what I can do for free. I go online. The posts linked to this page include online sources that I found and summary notes that I have taken from my reading. Each post is likely to be directed reading in response to something that is going on in my garden.