html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> From the archives: The few of you who care will be happy to get an answer to this.

Tuesday, July 11, 2006

The few of you who care will be happy to get an answer to this.

No, it is not ridiculous for Valley growers to be running their sprinkler systems during a spring rainstorm.

Soils have a moisture holding capacity. Crops, depending on their size, have a certain depth their roots can reach to. The soil moisture reservoir for a field is the (volume of soil crop roots can access) times (the moisture holding capacity of the soil).

Vsoil * Moisture Holding Capacitysoil = Soil Moisture Reservoir.

During the summer, a grower has to schedule irrigations. Some systems, like furrows, can entirely re-fill the soil moisture reservoir very quickly. Sprinklers, on the other hand, deliver water relatively slowly. Hand-move sprinkler lines are set far apart. Each line waters a portion of the field for a couple days before an irrigation crew breaks it apart and moves it to the edge of its spray radius. In the heat of the summer, it is entirely possible that the crop sucked more water out of the soil than the sprinkler line was able to replenish in that position.

When that happens, the grower is depending on a slowly depleting soil moisture reservoir. He or she is trying to keep wet soils wet and losing that battle throughout the summer. If she times it perfectly, her soil moisture reservoir will be empty when it is time for drydown. If she mis-times it and the soil dries out first, she’ll lose her crop. She doesn’t have an irrigation system that can deliver enough water fast enough to save it.

It is crucial that growers with hand-move sprinklers enter the summer with a full soil moisture reservoir. That’s why they are running their sprinkler systems over an empty field in the late spring. A rainstorm is great, but it could be too short to deliver the full amount of water. She can’t take that chance. She must irrigate a known amount of water to be sure the soil moisture reservoir is full. She could monitor her soil moisture profile during the rainstorm/irrigation event to see if the combination fills the soil moisture reservoir faster than the sprinklers would alone. If she does adapt to the rainstorm, she would move the sprinkler line down to its next position sooner. You would still see sprinklers on during the rain. That is cautious behavior on her part, not wastefulness.

13 Comments:

Anonymous Anonymous said...

That's exactly why I leave the shower running even when I'm not in it at times. I'm trying to reach the moisture holding capacity of the dirt, and mold, and mildew in my shower. I want to keep it healthy, it's the only plants I keep in my apartment.

12:45 PM  
Anonymous UnderwearNinja said...

I love when you talk irrigation to me.

1:23 PM  
Blogger R2K said...

: )

2:07 PM  
Blogger Jason said...

Please, slide seamlessly into your take on aerial application... (pesticides, fertilizers, sulfur dust, urea...)

10:24 PM  
Blogger Megan said...

I don't know much about it. All I know is two things. When farmers heard cropdusters, they would roll up their car windows, which told me I should do that too. And growers in the Sac Valley plant rice aerially, release the seed over flooded paddies for a more even distribution.

That's all I got.

10:43 PM  
Blogger Sweet Coalminer said...

what about lawn sprinklers during a storm?

11:11 PM  
Blogger Jason said...

Bummer. On the rare occasion that I find someone I consider "Reasonably Green" and not prone to knee jerk responses to honest questions, I like to check my facts with them. I was a cropduster in the mid/late 90s in the Dixon/Davis area. Mainly, dusting sulfur on tomatoes and sugarbeets (miticide) and, later, planting rice up north.
Many folks suggest that farmers only care about profits. That, in some cases, may be true, but that economic incentive is exactly what keeps farmers worried about drift claims and over application. And you've never met a bunch of guys more worried about the wind, the inversion layer and humidity than a group of ag pilots with 10,000 acres on the books...

I'm enjoying this tangent you're on.

11:18 PM  
Blogger matt said...

This new tangent is fun. Mmm, water.

5:17 AM  
Blogger Megan said...

Sweet Coalminer,

Completely irresponsible. Lawn roots only go down a few inches and most rains will deliver enough water for that. Turn your personal sprinklers off during the rain, people. (I know you would, of course, Sweet.)

8:24 AM  
Anonymous Anonymous said...

What if you have trees in your yard? Is it ok to run your lawn sprinklers in the rain then?

9:46 AM  
Blogger Megan said...

Trees should get a long soaking from a hose so they develop deep roots. Frequent shallow irrigations, like sprinklers apply, will give them shallow, less stable roots.

Don't water in the rain, y'all. You aren't in danger of losing a crop and your income for a year. Wait for the rain to pass and see if anything still looks wilted.

You can't possibly be this interested for real. Are you just seeing if you can get a response from me? I can't not answer irrigation questions.

10:18 AM  
Anonymous UnderwearNinja said...

Will long soaks help all manner of trees, or just certain varieties? Here in Sacramento we have hardpan, wouldn't you run the risk of the water sitting on the roots and damaging the tree? Or is that something I made up?

(What is with the hardpan here anyway?)

12:58 PM  
Anonymous jens said...

If you didn't get enough nibbles on your personal ad, THIS should definitely have you warding them off with a flyswatter!

11:36 AM  

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