Download Analysing soil moisture

Analysing soil moisture
10/15/2013
In vineyards – utilizing the Sentek Enviroscan Probe
Analysing soil moisture
OVERVIEW
This Document is just a brief overview on the benefits of using a soil moisture probe in your daily
decision making process – in the management of your vineyard.
Please note – the information your probe generates is greatly affected by many factors inc:
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SITE SELECTION
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TYPE OF CROP
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SOIL TYPE
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INSTALLATION TECHNIQUE
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TOPOGRAPHY
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LOCATION AND ASSOCIATED WEATHER FACTORS
THE LOCATION
This installation is located in a Shiraz vineyard in the McLaren Vale grape growing region of South
Australia.
ABSTRACT
The information outlined in this document is intended to demonstrate how from analyzing soil
moisture graphs you can determine different factors including:
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WATER HOLDING CAPACITIY
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ON SET OF STRESS
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SOIL TYPES
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SOIL DRAINAGE VS CROP WATER USAGE
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Analysing soil moisture
Contents
MOISTURE DATA – manual vs. continuous ........................................................................................... 3
Seasonal comparison .............................................................................................................................. 4
Saturation to stress .................................................................................................................................. 5
Stacked irrigation investigation ............................................................................................................ 6
Soil classification ...................................................................................................................................... 7
Please Note: the information within this document is based on observations only, based on the response of soil
moisture in the soil profile. IPV recommends that independent 3rd party advice is required prior to changing
vineyard management strategies.
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Analysing soil moisture
MOISTURE DATA – manual vs. continuous
The image below shows the same data however the information on the top graph is continuous and shows irrigation
events along with the ability to show the Start time, stop time, duration, infiltration rate, active root zone, crop water
usage and critical points like onset of stress, full and saturation point. The lower graph is basically a trend only at
best it will verify an event and overtime you would pick up stress.
In summary the point data provides a more “Reactive Management tool” – hopefully allowing you to avoid making
an error again, where Continuous is a “Proactive Management tool” allowing you to change the outcome in time for
the next irrigation or in some cases during the current irrigation.
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Analysing soil moisture
Seasonal comparison
“THOSE WHO DO NOT REMEMBER THE PAST ARE CONDEMNED TO REPEAT IT.”
G EORGE S ANTAYANA
You can start making decisions and changing irrigation strategies from your first few weeks of data – however the real power of
the technology comes 12 months later.
After 12 months you have enough information to set your critical data points – like “Onset of Stress”, “Refill Points” and “Full
Points”
You can also take a snap shot and compare a point in time this year to a previous year – this could help greatly in determining
when to do strategies like a “Flushing Irrigation” or estimating how many weeks before you need to apply your first irrigation.
After you have a full 6-8 years data there is a good chance that you have an example of each season (Hot Dry, Hot
Wet, Cool Dry and Cool Wet) having this information can help greatly in forward planning strategies for the coming
or current season.
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Analysing soil moisture
Saturation to stress
Knowing at any given time where the moisture levels are in your soil is critical when planning for a heat wave or
period of high heat and wind, a large number of vineyards run very tight irrigation schedules – in some cases its not
so much the availability of water it the ability to deliver it when and where you need to.
Knowing at a glance how many days you have before the “Onset of Stress” can help quickly in providing and
distributing water on a priority basis.
Maximizing the water efficiency is also – critical in ensuring irrigation strategies are effective, the image below shows
that over the first 48 hrs that 30-40% of the water is not utilized by the plant but more likely drainage in the profile,
by employing strategies like mulching, irrigating with additives that improve water holding characteristics e.g.
AquaBoost™ will keep the water in the root zone which will reduce the need for such regular irrigations.
If through monitoring soil moisture and integrating water efficient strategies you can reduce the frequency and
duration of irrigation – this will intern give you more opportunities to customize irrigation during high demand periods
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Analysing soil moisture
Stacked irrigation investigation
This is where all the questions can be investigated and answers generated.
In the Stacked view many factors relating to you irrigation, soil types and vines can be examined.
Irrigation:
The graph below clearly shows when the irrigation started, when it stopped, the duration and how effective it was, a
quick look shows that most irrigations made it to the 60cm zone however even with the same duration and interval as
the season progressed the penetration reduced.
Vines:
Looking at the graph – you can see at the end of December that there was good root activity in the 80cm Zone –
however the irrigation strategy was setup for the 0-60cm zone. If you look closely you can clearly see the daily crop
water usage as shown in the stepping in the graph – the Flat zones show “night time” little or no water use, the
downward slope shows water use.
Soil:
By looking closely after irrigation is applied you can get a good idea of the soil type – by looking at the time frame
between when an irrigation event occurs and how long it takes to get to each of the following sensors, the water will
move quickly thru sand and very slowly thru clays. – (see Soil Classification for more information)
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Analysing soil moisture
Soil classification
The best way to determine your soil type, texture and nutrients is by collecting a soil core or soil sample and getting it
tested, failing this the Soil moisture graph can tell you allot about the soil type and texture, there are three main
factors of the soil moisture graph that can do this.
Soil Moisture Level:
Looking over a period of time – from one irrigation to the next or ideally from summer through to winter and back to
summer, we can see what the moisture range is at a given sensor. If you look at the graph below around December
12th was the first irrigation for the season – prior to it you could see that Sensor 1 was holding around 13% moisture
– if it was really sandy it would possibly be only 3-5% if it was heavy clay 25-30%.
Infiltration rate:
Once water is applied (providing it’s a good installation) the time it takes to move thru the profile is another good
indicator of the soil type – in this case it took between 15 – 30 minutes (based on sample rate) this would suggest it’s
a sandy loam – the water holding and pre irrigation moisture level help validate this further.
Soil Drainage rate:
After irrigation – both the maximum saturation level and the speed in which the water drains from the profile
(surrounding the sensor) also helps determine the soil structure. For example – a sandy soil would hold a maximum of
6-10% moisture after removing the water source you could expect a level of 4-6 within 30-60 minutes (depending on
the underlying soil profile) likewise a light clay loam could hold as much 25-35% and drain to 20-25% then hold the
rest allowing the plant to draw on the water as required.
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