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Old 09-06-2007, 12:56 PM
Kiril Kiril is offline
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Join Date: Jun 2007
Location: District 9 CA
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Originally Posted by lawnsbytim View Post
Everything I read says that there is nutrient uptake by the roots after the blade growth stops. I will see earlier green up in the spring even with lawns I winterized late with organics. If it gets late in October, consider a bridge fertilizer as the temps may be too low for microbial release of a straight organic.
That would be more or less correct. Nutrient uptake is primarily a function of gradients (diffusion, mass flow) and root interception. Diffusion (concentration) and mass flow (transpiration is one mechanism) being the most important.

I believe the primary reason for a late season fertilize (with respect to roots) is because soil temperatures are more conducive to root growth, which is one reason why you see a quicker response in the spring (greater root density).

Carbohydrate storage is also an important factor, which is directly related to transpiration/photosynthesis.

Therefore you want to promote late season root growth and carbohydrate storage, both of which require the plant to be actively photosynthesizing.

When utilizing a Sept. and Oct. fertilizing practice I would apply N in the nitrate form in Sept. and Ammonium form in Oct. This is primarily because transpiration gradients are more likely to be a stronger factor in Sept. than in Oct.

Water management following any fertilizer application is also extremely important, so make whatever adjustments necessary to promote efficient uptake of nutrients. Also be sure to aerate (if needed) early enough for it to be a factor.

If your interested in nutrient modeling, check out the following (be sure to check out the references as well):

Environmental Control on Root Water and Nutrient Uptake
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