Monitoring Soil Moisture At Depth?

[TheWaterbug]

At first I worried that I was under-watering my corn, because I'd read some articles suggesting they need anywhere from 1 inch to 1.5 inches or even more of water per week, but without any mention of adjustments for plant density.

I'd been watering significantly less than 1" per week. I have thinned to one plant every 12", in rows 3' apart, and my plants are currently about 3' tall, or approximately stage VE7.

Last week a few of my plants looked a little dry, and the top 3-4" of soil was dry to the touch, so I left my drip hose on for an hour, which should provide about 1/3 of an inch, if my math is correct (1 GPH every 18" on each hose, and the hoses are set 3' apart).

Then the next morning I dug down in a spot that didn't have a corn plant, and it was very wet all the way down to a foot or more.

I have very heavy clay soil. I till manure into the top layer as far down as my tiller will go, but it won't go down a foot.

I've turned off the watering to let it dry out a bit over the last 3 days, and the plants do not show any signs of overwatering, but now I'm curious about how to monitor soil moisture way below the surface.

I'm a bit skeptical about a regular soil temp/moisture probe, because those measure just at the tip, and I'm not sure how accurate it will be if I'm attempting to take multiple readings while moving it up and down through 6 - 24" of soil.

One option would be to buy a much more expensive soil sampling probe, pull up a series of samples every 6", and lay them out for inspection.

How does everyone else do this? Or do you just watch the plants and react accordingly?

[TheWaterbug]

I planted on Father's Day, about 5.5 weeks ago. Here's how it looked yesterday, 3 days after I found out how wet the soil had been.

[imafan26]

I do have a soil moisture probe. It was not that expensive. It does light, moisture, and approx. pH. My friend is a soil scientist so she regularly keeps records of soil moisture in the garden. While I have this meter, because my old happiness meter finally died, it is less fun to use. Most of the time I just use a trowel or my hand and dig down look and feel the soil. The plants dying of thirst is also a good indicator. Because the garden likes to cut off water arbitrarily based on the water bill and not on plant needs, we keep records to justify our need to have adequate water and we are able to adjust our watering system to make sure the plants get enough water but not too much. It was how we justified getting the drip tape changed to drip emitters because they were running the drip tape for 3 minutes 3 times a day.Which is not how you run a drip system. It calculated that the 167 ft row got a total of 15 gallons of water a day. It made a puddle about 3 inches and usually no where near the plant. We were able to negotiate for one more minute and instead of three times a day of shallow watering. We asked for 10 minutes of watering at 6 am so we could maximize deep watering and minimize losses to evaporation from shallow watering in the heat of the day. Switching to the emitters which delivered more water in the same time we were able to lose fewer plants and we were able to adjust some emitters downward because they did not need as much water.

[applestar]

Though not as scientific, sometimes other plants around the garden and including weeds growing among the crops are good indicator of soil moisture.

Some crops like cucurbits have visible physiological leaf reaction when hot and/or dry.

Some weeds wilt faster and you think oh, it looks like they’ll need water soon, and others have longer tap roots but if THOSE are looking water stressed, it’s DEFINITELY time to water TODAY.

[imafan26]

We lose plants every year. Mainly because there is no regular monitoring of the irrigation system and when something breaks, the water gets turned off, but the leaks don't always get a priority for repair.

I have an irrigation system at home, but it needs new valves, new low voltage lines and probably a new timer since it is already over 10 years old. I have fixed only 2 valves. I hate working with pvc and glue. Some of the drip lines are also clogged or damaged, so need to be replaced as well. For several years now, I hand water my yard and only rarely will I use a spot sprinkler. It takes an hour to water my small yard every day.

Wilting of the plants in midday is a protective mechanism against heat stress. The plants usually perk up by the end of the day. The plants that have the most problems are the plants that are pot bound. Smaller pots can't wait as long as larger containers and the type of media and if the plants are mulched or grouped also matters.

If watering intervals are gradually increased some plants can be trained to go a little longer, sometimes it is only half a day longer, but even that helps since it means I would only water twice in three days. I have also experimented with watering tubes to give water directly to the root zone and use less water. I did not do it on a large scale, it seemed to work, but it took longer to water that way because I had to un cap the tube and use a funnel to water and it ended up taking more time. I could only do it with new plantings. Retrofitting watering tubes wase hard to do around existing roots. It was actually easier to drill the drain holes in buckets 2 inches above the bottom. It created a muddy reservoir in the bottom of the pot so the pot would not dry out as fast.