Solar Saturation

In my research and wanderings, I've repeatedly heard of "solar saturation", the concept that in full sun, photosynthesis shuts down and plants stop growing. Solar saturation is presented as one of the reasons that forest gardening is so productive- multiple layers of vegetation shade each other so that no plants get solar-saturated and shut down, allowing for more complete photosynthesis. I've commonly heard that "a field of corn stops growing for four hours in the middle of the day due to solar saturation."

I have been searching for more information on the subject. I found mentions at David Blume's site, and Mark Shepard's youtube presentations, but I looked on Wikipedia and Google and haven't found anything. What I have found, is "the Saturation Point" which is the point at which light is no longer the limiting factor for photosynthesis, and ambient CO2 level becomes the limiting factor. This doesn't mean that photosynthesis "shuts down", though- just that it levels off.

Can anyone provide some thoughts or resources about this? I'm wondering if Solar Saturation is a misinterpretation of the Saturation Point, and has been repeated so often that it has become canon.

nathan luedtke wrote:In my research and wanderings, I've repeatedly heard of "solar saturation", the concept that in full sun, photosynthesis shuts down and plants stop growing. Solar saturation is presented as one of the reasons that forest gardening is so productive- multiple layers of vegetation shade each other so that no plants get solar-saturated and shut down, allowing for more complete photosynthesis. I've commonly heard that "a field of corn stops growing for four hours in the middle of the day due to solar saturation."

I have been searching for more information on the subject. I found mentions at David Blume's site, and Mark Shepard's youtube presentations, but I looked on Wikipedia and Google and haven't found anything. What I have found, is "the Saturation Point" which is the point at which light is no longer the limiting factor for photosynthesis, and ambient CO2 level becomes the limiting factor. This doesn't mean that photosynthesis "shuts down", though- just that it levels off.

Can anyone provide some thoughts or resources about this? I'm wondering if Solar Saturation is a misinterpretation of the Saturation Point, and has been repeated so often that it has become canon.

Commercially we use shade netting upto 75 percent to get far better results than growing in full sun. Once your into using shade netting there is a lot you can do to affect plant growth just by changing the colour of the netting. Have a look at the well documented research carried out in Israel for a better understanding of the benefits of shading.

Great topic! I have heard specifically of peppers benefiting from shade and have talked to one farmer who stated explicitly that he achieved higher yields and bigger plants when shading his peppers with shade cloth. In a Permaculture setting I think one of the best plants to accomplish this shading is with large sunflowers but other tall plants can work well too. Sunflowers are good additions to almost any poly-culture especially if you mix them with some pole beans.

Yet another thing learned from this forum. That would explain the benefits of the edges for growing.

Has anybody found any research on solar saturation? The anecdotal evidence is great, but I want to present this idea of solar saturation to a university farming group and it'd be great to have some evidence that shows it is true. Any help here would be greatly appreciated. Perhaps Paul knows of some resources, as I heard him mention the idea of solar saturation in his making the big bucks with permaculture podcast.

I think the tall grass prairie and most other natural ecosystems deal with this on their own.

 I saw some beautiful hay fields in Canada's Yukon territory that grow very fast with 22 hours of daylight in June. The sun is at more of an angle at that latitude and it is never extremely hot. It could be that overheating has as much to do with growth shutting down, as too much sunlight does.

I don't have handy links, but remember seeing some reasearch about photosynthetic activity in wine grapes slowing to nearly zero when leaf temperature is in the mid 80s F. At that point, water is too precious to waste by opening stomata, so the plant can't get carbon dioxide either. That study was from Washingtom State University.

Mark Shepard says something about the specific temperature at which photosynthesis shuts down - don't recall off the top of my head what the temperature was. But I don't recall him saying it was a function of time in sunlight, but rather of getting too hot.