30 Jun 2008

Drip versus Flood

I'm neither farmer nor hydrologist, but I thought drip irrigation was always better than flood irrigation for growing crops. (See also yesterday's post on not-so-wasteful "wasteful" water management.) But that's not the case according to this email:
I find that the garden I do use drip on, I have to water a lot of more often and I don't think the plants seem as strong. Right now from the stage of planting seeds, I am watering every 10 days and from this stage on I can get away with irrigating every 21 days and go into 30 or more days in August and September) without watering (although I am growing in clayey loam). On drip I need to water once a week, and that is with row covers, which hold in moisture and create a cooler environment. Part of my theory is that the plants tend to be deep rooted with flood irrigation and thus more drought tolerant, while drip irrigation encourages shallow root systems.


I think soil type plays a significant role in the efficiency or lack of drip. For instance because I grow in clay/clay loam soil percolation is slow, and even on the drip, I need to apply water 24 hrs for deep soil percolation to occur and even then I don't get the same kind of root depth as on flood. (The flood irrigated fields cannot have too steep a slope or the water will move across too quickly and not enough downward flow to the root zone will occur.)

Also soil cultivation is very difficult with drip and for my heavy clay it is critical for plant health to be able to get in cultivate aerating the soil and preventing soil compaction.

Weed control is also more difficult because it makes it difficult for mechanized weeding and so requires tremendous hand weeding, manual labor.

Then there is the issue of salt accumulation. And when dealing with high TDS water, drip lines quickly clog and sometimes have to be replaced within a season.

Gophers also love to munch into a drip tape, don't know if that's by accident or what. I don't get gopher activity in the flood irrigated fields, I think because of mechanized cultivation and the fact that they get flooded out.
Bottom Line: It's all about cost and benefit. When water is cheaper, it's not too important to conserve it, but expensive water doesn't necessarily mean that the "best" irrigation method is the one that uses the least water. (Although drip-irrigated rice uses less water, it also has a lower yield.)