As soon as a block is harvested, each vine in the block gets at least 12gal of water – some years twice that. The idea is two-fold: 1) relieve any deficit post-veraison irrigation stress, and 2) flush out as much accumulated salts in the root zone as possible (Mother Nature really does the best job of this – assuming we get decent rainfall). In terms of the growing season, this is the next to last irrigation that I perform.
The final irrigation is part of what I call the ‘winterizing’ phase of the year’s growing season: the harvest is complete and it’s time to prepare the vines for dormancy with a view towards pruning in late January or early February and then bud-break in early April.
The colder nights and shorter days are doing their job to lower the vines average root temperature and slowing down the plant’s function. While the vines are still somewhat active I apply a dose of nitrogen & potassium (8-0-9) to the root zone via the irrigation system. My goal is that these nutrients be available to the vines systemically when they come out of dormancy in April.
In addition the application of nitrogen through the irrigation system, I also use a leguminous cover crop (a barley-big-bean mix) that pulls nitrogen from the atmosphere and makes it available to the vines via the soil. That’s a topic for another post!
I guess this is the first time I’ve brought up fertigation (fertilizing via the irrigation system) so let me digress and explain it a bit…
My system is simple: a 250 gallon plastic tank, a pump, and a simple injection nozzle into the source of the vineyard irrigation.
It’s a completely manual timer-paper-and-tape-measure system. Each fertigation has a specific gallons-per-acre recommendation, while the pump always seems to be adjusted to a different gallon-per-minute setting. I’ve got to figure it out new each time, but it’s not that difficult.
The tank is a cylinder and gets filled with the appropriate total number of gallons for the entire vineyard (ie, 10 gal/acres X 14 acres = 140 gallons).
The tank is semi-transparent and it’s easy to see the starting level. I use a tape measure to determine that starting level in inches (measured from the bottom of the tank) and then divide by the number of acres total (for instance, 32” div 14 total acres = 2.25” per acre).
A 3 acre block would then get 3 x 2.25” = 6.75” of fertilizer as measured from the starting level on the side of the tank. In this example, the first block to be fertilized would begin with the tank level at 32” and end when the tank level dropped to 25.25”; this level is now the start level for the next block. This process repeated for all blocks in the vineyard.
Interesting story: a few years ago, before I had a permanent tank, I rented a (cylindrical) tank that was delivered to me on its side. While this would have presented no problem if I were injecting just a single block, I went a bit cross-eyed trying to figure out (in a timely fashion, as all things during the growing season are!) how to inject the correct amount into each of my four blocks.
Full and empty are easy, as is 50%. But how do you measure 3/14?? Obviously a job for some integral calculas! Jayne looked at me like I had two heads when I pulled out the dusty text book from college (yes, I still have almost all of them).
Ironically, I just recently heard a similar story on NPR’s Car Talk: a caller’s big rig fuel gauge didn’t work, so he stuck a stick into the (side saddle) tank to gauge how full it was.
Obviously, the full, half and empty points are easy to determine… but what about 25%? 33%? I think the caller was most interested in the 25% level (running out of diesel in a big rig is really something to be avoided). No clue why he just didn’t get the gauge fixed…
In any case, the Car Talk guys at first thought it was trivial but after a few moments decided that there was no way they could solve the problem while on the air and put the answer off for a week. There was one listener that came up with a fun and elegant solution. It was optimized to find the 25% mark, but could conceivably be extended for many other points as well:
- go to the fridge and pull out a can of beer.
- get four glasses, all the same size
- pour the beer into all four glasses, equal amounts of beer in each one
- drink three of the four glasses of beer
- pour the remaining glass of beer back into the can and seal the opening
- lay the can on its side
- punch a hole into the side of the can, large enough to accommodate a straw
- stick a straw into the can, pull it out and measure the level from the bottom of the straw that was wet with beer (if the can had a transparent bottom you could just measure the level from the bottom of the can).
- knowing the level on the stick and the diameter of the can bottom, you can now ratio that up to the diameter of the truck’s tank
For those of us less creative, and actually needing to know where the 3/14 level is here’s the more general solution: http://mathworld.wolfram.com/CircularSegment.html