I did a quick Google ... found a lot of hits http://edis.ifas.ufl.edu/cv004 it seems a good way to tell how much nutrient your plant is actually getting fromt the soil.
/// Taking the guess work out of farming
http://www.pikeagri.com/Frequently-Asked-Questions/6.-What-is-plant-sap-analysis.html

Didn't find the cost for a kit. Is it expensive?

I think Texas Plant and Soil Lab does that stuff.

Brix testing kits can be had for under 100.00, much more direct method of plant testing.

Dan

'morning, picked up a Brix refractometer from Sper Scientific no. 300001 last fall for 63 bucks with the shipping. A very nice kit. Interesing results.
I used tissue tests from Midwest labs and foriage tests from Dairyland Labs. Compare the results to your soil test, you may find that your soil is better than you think, or worse. Just my thoughts. No direct relationship with the above named companies. Best regards.

Barb: funny you should mention the work from the U of FL, I was deeply in involved in the work correlating plant tissue and sap as well as fertilizer rates and yield for numerous vegetables back in the 1990s there.

Dan: what are you using the refractometer to determine, analytically, I know what they measure. Are you using them on fruit?

Hey Michael, speaking of sap, here's a long shot. In your travels, have you come across reference sap data for the diagnosis of transient B deficiency in grapes? We would sing songs of you in my village for many moons.

Michael, I haven't done Brix testing in many years. I currently live in a McSuburb on a relatively small parcel. When the kid goes to another school, we'll likely move (if we don't run screaming from this place before then) and need to test again. But yes, you typically use them on fruit that depends strongly on sugar content for harvest.

Dan

Sorry gargwarb, never dealt with B issues. My only thought on the matter is that Hach may have a colorimetric method for B determination if you want to try to figure it out yourself. That would get expensive as you would have to correlate your sap results with those from other plant tissues analyzed in a lab. I have no doubt you can find sufficiency data at least for grape. Well suprise, I have a table here from the U of CA, Bulletin #1879 titled, "Soil and Plant Tissue Testing in California. It states for petioles collected opposite the flower cluster of full bloom, total B in ppm, deficient 300 in the leaf blade. These are not for petiole sap but for analyses carried out on dried petioles and the leaf blades in the case of the excess range.

The bulletin is at least 15 years old so it is quite possible that U of CA has done the work that would help you out already, Oregon may be another place to look.

I knew I kept that bulletin for something besides impressing my wife and friends.

Thanks Michael, but I got petiole data up the wazoo. (which makes it hard to sit). I was just hoping against hope you might have seen some sap data, which could possibly ferret out a transient B deficiency that won't show up in tissue. I can usually be pretty confident with the diagnosis based on symptoms and timing, but it would be nice to have some numbers to back it up with. Oh well, it was worth a shot.

gargwarb: I haven't bothered to look but, have no universities done any B sap research for grapes? Maybe they did but were unable to correlate the sap results to anything, in other words, a big fat NSD.

Michael

have no universities done any B sap research for grapes?

Surely UC Davis has, as there is high B in the well water there. I left before the Vit-Eno program went bonkers, so can't say what they are doing there these days.

Dan

Dan: one of these days my young 9 tree apple orchard will be in need of a refractometer as I am planning to make cider out of at least some of the pressings. From what I understand, measuring brix is a very important part of the blending process to make good ciders.

"To measure is to know", maybe that should have been, if you don't you'll be clueless.

Michael

Surely UC Davis has

Yeah, you'd think. Alas, no.