Hi Robert! How far will roots go for water?

For some reason, I think that roots of annuals and perennials will 'go' beyond their normal 'length' to get water .... that they can actually 'sense' where water is, and go in that direction, rather than just waiting for water to get to them. I'm thinking of a well-draining, sandy soil, with water holding 'caches', such as a 'well' filled with organic material, clay material, biochar, etc.... will roots travel to them? In a perfect world, there would be enough of this material to be perfectly distributed through all of the growing area, but ... in an imperfect world?

Do some annuals / perennials have 'traveling' long roots? Can plants with typically short roots, onions, etc. extend their length to reach lower levels of hydrated soil?

I think in drip irrigation, clay and sandy soils have different 'profiles' of subsurface water 'spread', and plants have to be placed closer or father from the dripped water... but do the roots also 'reach' to get a drink?

This may be a stupid question, but I haven't found any real answers in my searching... and I've been wondering about it for a long time ;)

Alas Nancy, It is my opinion, backed up by tree scientists, that roots don't sense water. A plant is constantly send roots out to explore the soil. When they find moisture and nutrients they "sprout" root hairs and roots to take advantage of the resource. Remember roots usually travel .5 to 3 times the width of the canopy. So a large cubic footage of soil will be explored. See my Drip Irrigation book for a detailed discussion of the subsurface spread of moisture depending on the soil type and emitter .

Robert, I often wonder if sufficient mycorhizae are present, could they lead the roots to water?

Not that I know of Bill.

My observations while working for a market-gardening company last year are fully consistent with the view that plants only expand existing roots that have found water, not actually "sniff out" water. One of our garden sites was in sandy soil, and we were using drip tape under black plastic "mulch" for the crops. We pulled huge quantities of pigweed out of the dirt paths between rows, as well as the margins of the field, and there were some interesting differences in the various plants. If the pigweed was growing at the edge of the field and if it was over a certain size, it would quite consistently have a normal taproot for about 3" and then have one or two giant secondary roots that turned abruptly and grew horizontally straight toward the rows with the drip tape. Smaller plants had normal root systems. It appeared, therefore, that the plants started out growing normally, but as they got bigger, the secondary roots would eventually explore a large enough circle around the taproot that they would run into the moister soil near the drip tape. As soon as this happened, the plants appeared to put all of their energy into further developing the roots that had found water, so these roots quickly grew much bigger while the others basically stopped growing. If the plants were actually sensing water, I would have expected their taproots to bend toward the water. As it was, the taproots kept merrily growing straight down, until they were rendered obsolete by other roots that found water closer to the surface.

Jonathan

Excellent observation Jonathan.