[PureHarvest]

Absolutely on the leaf test.
We have a lab 20 minutes from me.
He is not offering leaf sampling for growers primarily like me. They do tons of in-soil crops including corn and tomatoes etc.
Doesn't replace an annual soil test but does give you a picture of "where am I right now".
Farmers take this and make adjustments to their crop based on what they see in the test matches with some symptoms they might see in the field.
We all want to believe we are leaf readers, and can to a degree, but NOBoDY can know what is going on in that unseen complex world underground regardless of above ground symptoms.
Leaf canopy looks like boron is lacking? Wrong, Potassium was low. N too low...nope, not enough zinc.
Those were examples from a farm where they saw symptoms above ground, guessed, but tissue sampled to be sure. Then found out what was really causing it, applied the material needed and got the response. These were guys I know that have been farming corn for 50 plus years. You can't always know the exact culprit. Sometimes you may be right and make an application that corrects it, or maybe you just got lucky. Sometimes your hunch was close but there was a secondary element that needed to be added to your first hunch. Tissue tests would tell you about your hunch and if your potential application made sense.
So there is a way to make an change in a soil grown crop in the middle of the season. Farmers around here can make the application based on a tissue test by airplane, through irrigation, or by spreading it on with a spread truck. They also do what's called a psnt (pre sidedress nitrogen test) to tell how much N is available in the soil when manure has been used. Based on that they decide how much, if any, N to put on that crop when it is about knee high.