Silly irrigation question from a dryland guy - Page 2 - The Combine Forum
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post #11 of 42 (permalink) Old 04-07-2007, 07:56 PM Thread Starter
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Re: Silly irrigation question from a dryland guy

I completely didn't think about water table limitations and over-pumping one area. That would explain why it isn't physically possible to put a pivot on every quarter in an area, even if the land would allow for it.

As for running a half-mile pivot on 180 degrees, and then mentioning not having enough capacity to do all 360 degrees, shouldn't the system be sized correctly to be able do all 360 degrees on a 3 day rotation or whatever. Excluding water pumping limitations of course.

I like learning, thanks for the knowledge guys.

-Lance

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post #12 of 42 (permalink) Old 04-08-2007, 02:41 AM
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Re: Silly irrigation question from a dryland guy

Even though I am on the other side of the globe, I fully endorse what you have said here farmboy

Without irrigation, the land here where I live in Northern Tasmania (Australia) would be just grazing land (sheep & some cattle). With irrigation our farmers produce over 20 different crops including potatoes, poppies, processing peas, cereals, pasture seeds & lucerne (alfalfa).

The majority of our water in this area comes from runoff, through rivers & on farm dams & from a large Hydro dam in the highlands. When we have seasons of low rainfall (such as the current one), our irrigation farmers struggle to get the required water, so have to plant smaller areas of crop.

The government is looking at building another 2-3 big dams to drought proof farmers which would help allieviate this problem but of course we need rain to fill these dams. They are also encouraging farmers to put in more on farm storage.

Underground water tends to be salty here, so isnt really an issue for farmers looking to irrigate at this stage. With seasons getting drier, maybe this will be looked into further.

Regards,

TC.

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post #13 of 42 (permalink) Old 04-08-2007, 07:52 PM
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Re: Silly irrigation question from a dryland guy

you guys who work with irrigation have taught me a lot about irrigation equipment and how it works thanks
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post #14 of 42 (permalink) Old 04-09-2007, 01:10 PM
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Re: Silly irrigation question from a dryland guy

The one big thing I've noticed is that a whole section pivot (480 ac. under water) 160 dryland corners, is that if you have one crop on that 480 acres, the pivot runs almost constantly. It seems very inefficient to run a pivot constantly. You figure it's covering 120* every day it'll make a complete rotation but when it gets back to the starting point it would have to run again if it didn't rain. Am I wrong here in my assumptions and from what I've seen? Or is it just a bad farmer?

Also the corn on that one pivot was about 20-30bpa less than when the pivot was 4 (120 ac.) pivots instead of the one big one.

Alex
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post #15 of 42 (permalink) Old 04-09-2007, 04:37 PM
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Re: Silly irrigation question from a dryland guy

Alex,

In my area, a regular 1/4 mile pivot will run continuous on corn or beans from around the middle of June until August only shutting down about a day for 1 inch of rain.

This is drawing back on some agronomy from college 15 years ago, but I believe that corn during its peak water usage time (around tasseling) can use as much as .5 inches of water a day depending on temperature etc. Most 1/4 mile pivots around here are only capable of about 1" of water on a 3 day pass, or .33 inches per day on a 800-1000 GPM well. (These are approximate numbers, you could calculate the acre-inches of water for 1000GPM times 72 hours etc, but that would be too much work ) This means there is an amount of time in which you can not physically put enough water on to keep up with the corn, but if you have a full soil profile, it will be able to make up the difference. Any help from Mother Nature is a bonus, but that is why you turn immediately back on after a day, even after a 1" rain.

Now, I have not run a 1/2 mile pivot, but in order to apply the same amount of water to 4 times the area, one could assume you would need to either apply 4 times the volume for the same amount of time (3200-4000GPM on 3 day revolution), or slow down the pivot and take more time to make a revolution. There aren't any wells capable of pumping at those rates here, so I suspect that it is very difficult to be as effective watering with a 1/2 mile pivot.

Now, the advantage might be that there are way less tires, engines, gearboxes, nozzles, etc. etc. on one 1/2 mile pivot than on 4 1/4 mile pivots.
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post #16 of 42 (permalink) Old 04-09-2007, 06:44 PM
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Re: Silly irrigation question from a dryland guy

We farmed some 350 acre circles back in the early 80's and the corn was curling before the sprink made it around. If something made the sprink stop you were in real trouble. Quarter section circles seem to be the most efficient in our area, run continuously all summer except for maybe a 2" rain which happens rarely.

We nozzle our quarter section circles for 600 to 800 gpm and get along good at that. Had 249 average yield last year over 2300 acres, no hail and the year was nearly perfect.

The only difference between 1/2 mile and a 1/4 mile pivot is you have 2 center towers on the 1/4, and one less tower. Same # of tires and gear boxes except for the one less tower.
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post #17 of 42 (permalink) Old 04-09-2007, 07:44 PM
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Re: Silly irrigation question from a dryland guy

Harsh,

The 1/2 milers that I've seen cover a whole section but end up getting roughly 500 acres under the sprinkler, taking the place of 4 1/4 milers. You can find some on Google Earth west of Meade. On some of them if the resolution is good enough, you can see the tracks, I counted 18 towers on them. (which makes sense, a 1/4 miler has 9 usually, so twice as long, twice as many towers)

Like you said, I can't see any way you could get them around fast enough, heck we have a 1/4 miler running on just over 700 GPM, and during 110 degrees in July with corn we can't stand for it to be down more than a 1/2 a day or we are in trouble.
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post #18 of 42 (permalink) Old 04-10-2007, 10:49 PM Thread Starter
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Re: Silly irrigation question from a dryland guy

You bought a new pivot to replace an old one? Since they gave you some trade-in value, that means it must have some life left in it yet. Do they just start to break down too much to deal with?

Man would I like to see a well that can pump 3000 GPM. We can't even fill our sprayer at anywhere close to that rate of flow. How much HP does that take to run?

-Lance
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post #19 of 42 (permalink) Old 04-10-2007, 11:24 PM
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Re: Silly irrigation question from a dryland guy

Pivots aren't that hard to move just unhook the wires or hoses remove a boot and some bolts and hook it up to the pickup and put the tires on other end on an old pickup or something that you can steer and away you go. that is if it is within a reasonable distance 50 miles or so. they are easier to move than a descent size bin.
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post #20 of 42 (permalink) Old 04-10-2007, 11:37 PM
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Re: Silly irrigation question from a dryland guy

If I had a choice I would use 4 1\4 milers and a 5 tower one in the middle with a line burried to it that drops down from one of the other machines. At 800 gpm or so it would probably only take 24-30 hours or so to make it around.that would be about another 40 acres or so watered and if you put a used machine on it it would probably last 20 years or so if it is taken care of and is in good shape to start out with.

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