html xmlns="" xml:lang="en" lang="en"> From the archives: End the hating!

Tuesday, October 30, 2007

End the hating!

OK, look. Flood and furrow irrigation is not necessarily a primitive, wasteful irrigation technique. It can get distribution uniformities up in the eighties, which is about as good as a decent irrigation foreman should expect*. Of course, getting furrow irrigation that high takes an unusual amount of management.

To do a good job on furrows, in addition to annually shaping the furrows and beds, you would torpedo every furrow. (Drag a heavy, torpedo-shaped weight the length of every furrow, to smooth the run and get rid of clods. You can attach several of these to the bar behind your tractor, so you get several rows done at once.) You would also keep track of your wheel rows. Those are the furrows that your tractor wheels went down. The soil in wheel rows is compacted; the water will run down those faster. You have to match them to smaller siphons. You would use surge flows, to push the water to the tail of the furrow faster, so that water sits on the tail of the field for about as long as it sits on the head of the field. You constantly monitor your soil moisture, so that you don't start your irrigation event before the soil is dry enough to hold the water you put on. Every irrigation event changes the furrows (compacts and slicks them down), so you manage each one differently from the last. You keep a notebook, every year, noting daily soil moisture, date of irrigation events, size of siphons in each run, duration of event, and when the water reached the quarter, half, three-quarters and full length of field. You MANAGE your furrow irrigation system.

That said, flood or furrow** can be very sloppy and has the potential to let huge amounts of water run off the field. It is what you'd do if you have more water than management capacity, or if water is cheap and your drainage is good. The image of wasteful flood and furrow irrigation is well-founded.

So where do you see flood and furrow irrigation? You see it where water is so cheap that you don't need to do careful applications. You also see it where the grower is constrained by the irrigation district. Some districts deliver water on rotation. They don't keep all their lateral canals full all the time; you take your water when your canal is full, once every three weeks. If your district is on rotation, you have to use flood irrigation. You can't put down enough water to last you for three weeks through some pansy little sprinklers***. You also see flood and furrow in modern irrigation districts, where the grower chose the method. Maybe the grower prefers labor costs to capital costs. Maybe the grower is experienced with furrow and wants to stay with his expertise.

My whole point is that flood and furrow irrigation are not themselves proof of wasting water. If you're in a real old-school atmosphere, where the growers are contemptuous of water management, yeah, furrows are a strong signal of waste. But in a district where the manager and growers are alert to the modern ways of conservation, furrow and flood irrigation can be very good.

*An irrigation fanatic gets them in the very low nineties, but that is astonishing. That indicates a lot of interest and maintenance. If you saw irrigation efficiencies in the nineties in nature, you would wonder what was motivating the grower.

**Furrow irrigation is, like, furrows. Flood irrigation is in border checks.

***Everyone is always all "ooooh, switch to drip! Drip irrigation is Teh Cool!", but for drip irrigation, you have to have a constant, clean supply, preferably with some head on it. You can re-create that on your farm, by building a small reservoir, pumping and filtering. That takes space and capital and maintenance. Drip isn't a good solution for everyone. Resist the peer pressure!


Anonymous margie said...

hey, megan! What do you know about groundwater recharge using flood irrigation? Is that an accepted technique in school? If so, how do you implement and monitor it to make sure you aren't wasting water? I guess in general I'm curious what needs a farmer has for water once evapo-transpiration has decreased for the winter season and also once periodic rains start occurring. Frost protection for orchards, etc.

12:06 PM  
Blogger jens said...

Usually your water engineering posts are my least favorite (I prefer the human interest ones), but this one was interesting enough to make me chase the links.

The only place you lost me was with "surge flows", and I think I figured that one out.

I would think with the flood method illustrated (especially in a dry climate like much of California) you would lose a lot to evaporation (although I'm only conjecturing that soil would bind to the water tighter than exposed water would).

I'm guessing with "head" you mean pressure (no innuendo there - I've heard the term before in connection with steam engine, but had to think about it, and connect it to the reservoir - I'm guessing the reservoir would be elevated?).

12:31 PM  
Anonymous Anonymous said...

That Kevin Drum article certainly reinforces the "commenters are like their hosts" argument...


2:12 PM  
Anonymous swissarmyd said...

mmm, I'd be curious to see numbers on the size of the farmstead that uses furrow irrigation... since they may be so small that efficiency is relative. For a single person, or one with a couple hired hands, lots of testing isn't do-able, so I'm going to guess that this would be aimed at the larger businesses. I guess I'm naively assuming that center pivot would be more efficient for them, since they would likely be able to run cost/benefit analysis, and decide where to spend any capital they have...

One of the interesting things I was finding in the links was how people tend to think of things in states instead of basins/watersheds. I guess that works OK sometimes, and eventually you have to tink it that way because of the water laws involved... It's just that a state like mine [CO] actually drains 3 different ways... Colorado River west, Rio Grande River South, and everything else east [Platte, Arkansas, etc...]

The Colorado is actually not going through the largest of the Ag areas, since it's running west... Where the Rio runs through the San Luis valley, and everything on the plains, like hay corn wheat etc. is run off the Platte and Arkansas.

Dunno if any of that makes a difference in the long run, but the diversity of sources is also in how the water happens. Ala on the plains people tend to be looking to the Ogallalla aquifer, rather than snowmelt, where the ColoR, and the Rio are snowmelt... So that is much more a show of snowmelt being affected by climate change. The BIG however, is that the Oga aquifer ISN"T replenishable, and we are using it like there is no tomorrow, and someday... there won't be. ASFAIK this will affect more farming in the US than any water issue in the west.

Heh, is that enough tangents for 'ya? I, know... this isn't anything to do with y'all in CA, except in that fundamentally interconnected way...

2:33 PM  
Anonymous Anonymous said...

What crops can be flood irrigated? I'm thinking it's the ones that don't grow in rows, but the only ones I've seen are alfalfa, tree crops, and rice. Safflower, maybe? I don't remember if that is planted in rows or not. Maybe small grains, depending on how you seed them?


8:23 PM  
Blogger Megan said...

Safflower, winter wheat. Trees, definitely. Cotton. The Boswells grow their cotton in great big border checks.

8:47 PM  
Blogger jens said...

I believe I have gone my whole life, getting near 50 years, without EVER hearing drip irrigation mentioned - and now it pops up twice in two days! (in the comments of this entry)

10:07 AM  
Anonymous Anonymous said...

I'll have to learn a little bit about which crops need furrows, as opposed to just being planted in rows. I guess it's the ones that need beds need furrows.

Hey, I checked the EWG database for the Boswells: $0 in subsidy payments in 2004 and 2005!

A "Only $16 million over the whole 1995-2005 period! Hmm." 4

1:46 PM  

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