Diurnal nutrient flows and other things ...

I recently attended an excellent 4 day seminar on soil, plant and human health. One of the interesting parts of this seminar was an explanation of a plant's natural diurnal cycle of nutrient flow. During the day, much of a plant's nutrients (sugars, minerals etc) reside in the above ground part of the plant. During the night, a good proportion of the nutrients are pumped down into the root zone. This means that for maximum nutritive value as consumers, we should be harvesting late morning/early afternoon. It must also have an impact on the optimum time for taking cuttings. I suspect that cuttings are best taken at this time also to maximise the nutrients in the cutting, giving it the best chance of survival.
On a separate note, one of the interesting things we did was to test the nutrient content of hydroponic lettuce using a brix refractometer. A brix refractometer tells you the sugar level, the brix, and provides a measure of mineral content. The poor old hydroponic lettuce scored very poorly on both counts. In other words, it didn't have much nutrient value. It scored 1% for brix (12% or more is good) and the line reading was clear (the fuzzier the better), indicating little if any mineral content. I tested my pot grown lettuce. It only scored 3% but at least had a fuzzy line reading. Of course, given the diurnal nutrient flow, a proper test should have taken into account the time of harvest.

Interesting, Ray! I usually do my harvesting in the morning or late afternoon (just before cooking tea). Same with taking cuttings. Now I can back this up with your post!

Ps.: Aren't you off to distant lands soon?

Does this mean that we should be harvesting root vegies and the like late afternoon and leafy veg or fruiting crops in the morning and early afternoon?

Is this variation due to photosynthesis and respiration? Would the same changes in sugar levels also happen in dormant plants? I'm just thinking out loud. I'll have to do some research

Helen

Helen, I suspect it must have to do with photosynthesis. I didn't know there was a way to test this, so am interested in whether plants could be tested using moon phase/element criteria. Ain't science mindboggling! I tend to harvest early morning before the plants get too hot, but that's habit more than anything. I'd love to hear more about this. Are the seminars local or likely to be available elsewhere? I don't mind travelling to the big island. I was thinking of trying to hydroponic lettuce, but that's enough to put me off - I'd rather have the vitamins!

I'm not sure of the mechanism that triggers the movements to and from the roots but a light trigger would make perfect sense. Interestingly, a plant gives up some of its sugars as root exudates to feed the micro-organisms that live around the roots, the ones who live in symbiosis with the plant - fungi, protozoa, bacteria, beneficial nematodes and so on. For example, mycorrhyzal fungi insert their hyphae into the roots themselves to obtain food from the plants, who in turn receive various minerals from the fungi, whose hyphae can travel many metres further than the plant roots. In effect, they act as root extensions. Fungi, protozoa and bacteria are the mineral/nutrient conversion factories for the plants. It's fascinating just how complex this web of life is, each part dependent on the rest.

Helen, I suspect that you are dead right about harvesting root veggies. They would be at their densest nutrient-wise first thing in the morning whereas the leafy veggies and fruits would be better harvested later.

The course I attended is run by Nutri Tech Solutions ceo Graeme Sait, whose interest in human health led him to soil health. He calls it a course in sustainable agriculture but it covers three areas - soil, plant/animal and human, showing how the three are intimately linked.

Interesting - thanks Raymondo - confirms what I know as I live in a hot climate and lived in an even hotter, more arid climate before this. There is not often much moisture around in this climate but when there's dew I'm out there. Have always worked in the garden the coolest part of the day and know there's a world of difference between a lettuce picked midday and one picked first thing on a dewy morning. Through the summer I would water in the evening and pick next morning. Water content is important - don't understand the science but my own observations concur.

Just been reading about legumes and how they fix nitrogen with rhizobia - how rhizobia feeds the plant. Lot to it and I'm clueless but find it all fascinating when someone like you explains it - thanks

Ray, I went to their website but it seems there are no seminars coming up. I take it you did the 4 day certificate course. I think it is oriented more towards farmers than home gardeners which is a shame because soil technology and basic plant biology over 4 days would be right up many of our alleys. Long courses offered by TAFE and the like are just to long winded. Nice location too!

Yes Blossom. I did the four day certificate course. It is aimed at farmers but there's plenty in it for us home gardeners too.
Fran, it's a fascinating area, especially now as the boffins discover just how intertwined everything is.

The boffins know all this stuff, except many dont know how to apply the knowledge. It used to freak me out that they knew all the stuff and never used it. Luckily we have people like Bill Molleson and David Holmgrem that do.

Plant physiology was one of the subjects I did in third year uni. My lecturer for this was also my supervisor for my Honours. He was amazed that I used what I learned from this unit in my vegie patch. He grew vegies as well and never thought of applying it to the vegie patch. another plant scientist wondered why I had corn etc before he did. I didnt use hearsay, I used germination temperatures and planted the veg when the soil temperature is right. I now believe after living here in Tas I could grow tomatoes all year round in Perth, WA and I feel stupid that I pulled out my capsicums and eggplants after a years growth.