Water Penetration

Meghan Sindelar Author

08/09/2016 Added

939 Plays

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This recording captures the author working calculations to determine how deep into a soil profile water will penetrate based on water content data.

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[00:00:01.481]Hello, this is Dr. Meghan Sindelar,
[00:00:03.887]and we have a soil physical properties calculation here
[00:00:08.634]looking at water penetration.
[00:00:11.671]This video kind of assumes
[00:00:14.281]that people understand water content and field capacity
[00:00:21.646]as being the upper limit of water storage,
[00:00:25.471]and that any water beyond that would freely drain away.
[00:00:29.179]So, the idea here is to calculate
[00:00:31.031]how deep will applied water drain?
[00:00:34.357]'Cause if it wets a certain depth up to saturation
[00:00:36.759]then it'll move down, so each depth will only be wetted
[00:00:39.647]up to field capacity and any excess water continues
[00:00:42.478]to move into the profile.
[00:00:44.731]This might be something you would want to calculate
[00:00:47.638]if you were trying to encourage deep rotting.
[00:00:50.721]You needed to get water to a certain depth for,
[00:00:55.241]you were planning to compact the top 12 inches say,
[00:00:59.235]or you had a fertilizer band you wanted
[00:01:02.330]to make sure was wetted.
[00:01:06.325]Various reasons.
[00:01:09.177]So, here would be the sorta input data we would use.
[00:01:12.309]Basically, we would need to know the water content
[00:01:14.971]at field capacity and then our current water content,
[00:01:20.608]so we will add water to go from the current
[00:01:22.693]up to field capacity and once that's reached,
[00:01:24.969]water will then move farther down into the profile.
[00:01:29.242]So for this example, we're going to add one inch of water
[00:01:35.364]to the soil.
[00:01:38.864]So, we'll start with this basic formula
[00:01:42.815]that we have used before, where you can calculate
[00:01:45.460]the depth of water in the soil profile
[00:01:48.741]using the water content and the soil depth,
[00:01:51.474]but we're gonna rethink about this formula
[00:01:53.981]from another perspective.
[00:01:56.266]So now, we wanna rework this so that we can think about
[00:01:59.621]what is the soil depth to which a given amount
[00:02:03.909]of water will move if we add, okay?
[00:02:08.221]So, we will know our depth of water.
[00:02:11.465]Okay, that's how much we add, so think of it
[00:02:14.344]as depth of water added.
[00:02:19.100]So, based on the water content, and so here let's think
[00:02:23.262]of this as volume room
[00:02:29.437]for more water,
[00:02:34.286]and that's gonna be the difference
[00:02:35.942]between current water content and field capacity, right?
[00:02:39.814]And then that will allow us to solve for a soil depth
[00:02:44.862]of penetration.
[00:02:48.344]Okay, so if we take our depth of water
[00:02:54.156]as water content times soil depth
[00:03:01.008]and now we just wanna solve,
[00:03:02.329]so we divide by water content both sides.
[00:03:11.057]Okay?
[00:03:12.764]So, here then is our formula to go.
[00:03:14.633]Soil depth on this side.
[00:03:16.603]Depth of water added divided by volume content
[00:03:22.896]for more water, so room for more water
[00:03:27.077]in this case will be field capacity minus current,
[00:03:33.277]so that's .4 minus 0.27 equals 0.13 centimeters cubed
[00:03:40.981]per centimeters cubed.
[00:03:43.160]So, our depth of penetration will be the one inch
[00:03:49.775]of water added divided by 0.13 volumetric room
[00:03:58.301]for more water.
[00:04:00.987]So, one divided by 0.13 is
[00:04:07.181]7.7 inches, all right?
[00:04:13.968]So for this soil, which can be wetted at field capacity
[00:04:20.292]up to 40% water is currently at 27% water.
[00:04:25.180]If we add one inch of water it will move 7.7 inches
[00:04:31.374]into the profile, okay?
[00:04:35.501]That is the depth at which the water will penetrate.

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Water Penetration

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