Soil Moisture Terms

In the last article we focused on soil moisture and how it is stored in the soil; adhesion, cohesion and capillarity. But how does this relate to the terms: saturation, field capacity and permanent wilting point?

When soil moisture is stored in the soil it is possible to measure both the amount (content V%) and the tension. The soil tension forms the basis of the following soil moisture parameters: saturation, field capacity and permanent wilting point.

Saturation

A soil is saturated when all pores (micro and macro) are filled with water and no air remains in the soil. At saturation there is free water in the soil profile. Gravity will cause water to drain from macro pores and saturation is therefore a temporary state.

Figure 1: Example of a soil reaching saturation point and the subsequent drainage period. 

This is how it appears on AquaCheck soil moisture plots. 

Field Capacity

When a soil is at field capacity, water is held by adhesion to soil particles and capillarity in micro pores. Field capacity is reached when rapid drainage decreases (Figure 1).

On your Vantage NZ soil moisture plots the field capacity is determined for each sensor depth, then summed to determine the l field capacity for the active root zone. This allows for soil texture changes throughout the profile and provides you with a field capacity unique to the sensor site.

Permanent Wilting Point

Evapotranspiration and drainage (to a much lesser extent) will cause the soil to dry below field capacity. During this process water is removed from all but the smallest micro pores. The permanent wilting point (PWP) varies depending on plant conditions, plant type and soil texture (Figure 2). Nevertheless, the soil water potential at which permanent wilting occurs is considered to be 1500 cba.

Figure 2: Illustration of saturation, field capacity and permanent wilting point for three different soil types. 

Available Water 

Available water (AW) is the amount of water held in the soil between field capacity and wilting point for a defined depth of soil and is expressed as V% or millimetres (mm). 

AW = FC - PWP

Readily Available Water

Not all the available water is equally (readily) available to plants. Water becomes more difficult for plants to extract the closer the water potential comes to permanent wilting point. This is because the reminding water is bound to the soil at increased tension.

Plants need to take up enough water to satisfy their transpirational demand and sustain optimum growth rates. For every kilogram of dry matter (DM) produced, a plant must transpire between 200 – 500 litres of water.[1] For plants to obtain this quantity of water from the soil, water needs to be readily available. Water is said to be readily available when plant growth is not restricted by water availability. Stress point is the point at which plants can no longer extract water at potential rates. On a soil moisture plot this will be demonstrated by a change in water use, i.e. a change in slope of the soil moisture trace (Figure 3).

Figure 3: A change in slope indicates a change in water use. This is how it appears on AquaCheck soil moisture plots. 

As water below the stress point is not readily available and not sufficient to meet potential daily plant demands, yield is lost. Water between the stress point and permanent wilting point is available to plants, but growth is adversely affected.

The key soil moisture parameters described above are essential in irrigation management. At Vantage NZ we strive to clearly determine and label these on your soil moisture plots (Figure 4) so you can make good irrigation management decisions. 

Figure 4: AquaCheck soil moisture plots clear labelling of key soil moisture parameters. 

---

[1] McLaren, R.G. and Cameron, K. C. (2000). ‘Soil Science’, Sustainable production and environmental protection. Second edition, Oxford University Press. Page 99.

So, What is Soil Moisture

 

I recently heard a gardening segment on a NZ radio station. The gardening commentator was answering questions and providing advice on ‘how to irrigate your garden’. Her advice was: “Deep watering will encourage the roots to grow into the water table below. This is desirable as it allows the plants to be self-sufficient in accessing water.”

We all have our own perception of water and how it is stored in the soil, but the gardening commentator’s description isn’t an accurate description of what actually happens within the soil or what we are aiming to achieve through irrigation.

There are several processes at play when water is “stored” in the soil: 

·        cohesion - the attraction of water molecules (H₂O) to one another it causes water molecules to stick to one another and form water droplets;

·        adhesion – the attraction between water molecules and solid surfaces, in this case soil particles;

·        surface tension – as a result of the cohesive properties of water molecules and their attraction to other water molecules, a water surface behaves like an expandable film; and

·        capillarity – is a combination of cohesion/adhesion and surface tension forces and is the primary force that enables the soil to retain water and to regulate its movement.

In this article we will take a closer look at these terms and and apply the concepts to soil moisture storage.

To demonstrate or understand adhesion and cohesion, pick up a rock or stone, dip it into a pool of water, pull it out again. The water dripping off the rock is free water (lost to gravity, same as free water will be lost to drainage when soil is at saturation point). If you give the rock a shake you will free it of more water - this is the water “stored” by cohesion. The rock is still wet even after the shaking - the water left on the rock is “stored” by adhesion (Figure 1). Water is stored in this way on all soil particle surfaces, whether it be a clay, silt, sand or gravel particle.

Figure 1: Soil moisture is stored on soil particles like a film via adhesion. On this stone adhesion is demonstrated by dipping it into water solution containing blue dye.

Capillarity is the key to storage of water in the soil. It allows water to move upward (and through) soil pores against the force of gravity. The finer-textured the soil (silts and clays) the greater the ability to hold and retain water in the soil in the spaces between particles. The pores between small silt (less than 0.02mm diameter) and tiny clay (less than 0.002mm diameter) particles are known as micropores. Compare these to the larger pore spacing between larger particles, such as sand (0.2-2mm) and stones (larger than 2mm) which are called macropores. Micropores enable greater capillarity rise.

Capillarity can also be simply demonstrated by placing a dry sponge into water – it will progressively wet upwards through the sponge (Figure 2). The finer the sponge material the higher the water will wet the sponge.

Figure 2: Fine sponge placed into a dish with water solution containing blue dye demonstrating capillarity.

When we irrigate, we want the water to have the opportunity for adhesion and capillarity to take place; i.e. “coat” the soil particle surfaces with water and be retained in the micro pores by capillarity this is best achieved through low application rates and by matching the applied depth to soil moisture deficit.

Back to the garden commentator’s recommendation to practice deep watering and aim to push roots into a water table. Very few farmers/growers/irrigators will have a water table shallow enough for roots to reach the water table. When roots explore the soil profile, they form perfect contact with soil particles, via this contact they can extract the moisture stored on particle surfaces. Deep watering is accurate to an extent. We want roots to explore as much soil as possible as this allows them to access more water and nutrients. Roots will only grow in moist soil, so they’ll only explore the soil profile if it’s been wetted. However, it is unusual for the subsoil not to be moist enough for root growth as the plant advances through its growth stages. Irrigation should therefore only be aimed at wetting the soil within the active root zone.

Aquacheck sensors measure soil moisture at several depths. This depth profile is a very useful tool in managing your irrigation. It allows you to see if you are wetting the active root zone and whether the subsoil is wet enough to allow for root growth.

Jane Robb 

Vantage NZ Customer Support Specialist

It's starting to get dry...

Other than this slightly cooler snap we've had over the last couple of days you'd have to say spring is well and truly here! And with these nor-west winds (in Canterbury anyway) and warmer days things are starting to dry out and there's not much rain on the horizon. The seasonal weather outlook from NIWA suggests that we're in for a dryer than average season in most places (https://www.niwa.co.nz/climate/seasonal-climate-outlook/seasonal-climate-outlook-september-november-2018) and at this point I'd have to say they're about on the money. 

The joys of being a farmer or in the ag industry is that everything you do hinges on the weather, so we get really good (for the most-part) at managing timings and inputs and reading the signs to optimise what we do on farm. Now is no different. Whether you're an irrigated farmer or a dryland one now is the time to be installing your soil moisture probes if you haven't done so already so that you can accurately measure and manage your soil moisture and timings of related inputs on farm. 

Soil moisture probes allow you to know whats going on under your feet and make accurate and timely decisions to set yourself, your farm, your crops and your livestock up to perform to the best of their ability for the coming season. Soil moisture is one of the key drivers for plant growth so it's important that we know where we're currently sitting in terms of soil moisture levels so we can react to it accordingly. Decisions around fertiliser (and other input) timings, timing and amount of irrigation, stock carrying-capacity decisions etc can all be driven by more accurate information regarding soil moisture levels. 

If you want to find out more about some of the leading soil moisture probes in the NZ market have a look here: https://bit.ly/2OyeVj1 

And if you're wanting to get some installed for the coming season please pick up the phone and give the Agri Optics team a call now before you run out of time and you're left carrying a spade in the back of your ute or ruining the tip of your good pocket knife for the upcoming summer. 

All the best for an upcoming and prosperous season ahead! 

Cheers, 

Jemma

The Irrigation, Grazing Game - Digging Deeper

Following on from last week our guest contributor Nicole Mesman digs a little deeper into the findings from her research that looked at the effect of grazing and irrigation on soil porosity.

Soil natural capital and soil health may seem like unnecessary concepts, names that you already know the meaning of without having to learn them. However I will outline them briefly and how they relate to my findings so that you are, in turn, able to relate to them if you come across them in environmental plans, legislation or elsewhere in the future.

Soils are referred to as a stock of properties or natural capital which yield a flow of valuable ecosystem goods or services into the future. Both soil health/ quality and natural capital are similar in that they use soil indicators and parameters to determine the state or function of a soil system. However soil natural capital provides a more holistic analysis of the resource as it takes into account not only the state of the soil itself (through soil indicators) but also the effect of this state on the products and services that soils provide and the human needs that are catered for by soils.

In the soil natural capital framework macroporosity is identified as the key physical attribute. This is because macroporosity determines: water flow, solute transport and drainage through soil. As a result macroporosity influences ecosystem services such as flood mitigation and filtering of nutrients. Macroporosity and associated soil physical properties provide important services and it is important for land managers to be aware of the potential to change these properties and the ecosystem services they provide.

Research has been carried out to determine the effect of land use practices on other soil physical properties such as bulk density, aggregate stability, soil carbon and water holding capacity however macroporosity remains the main indicator of soil physical natural capital and health because of its sensitivity to intensification.

My research found that on average for the 0-30 cm increment macroporosity was significantly lower on the Dairy site (9 ± 1%) than both the Sheep farm (19 ± 1%) and the Control site (15 ± 1%). This suggests that intensification is having a significant effect on the Dairy site. Furthermore on the Dairy site the 0-10 cm and 10-20 cm depth increments both have values for macroporosity < 10%. Other researchers have proposed that macroporosity values of > 10% are needed to maintain pasture production near optimum.

Target ranges for macroporosity are given in Table 1 as part of the National Soil Quality Indicator Programme. Here, for soils under pasture, macroporosity values < 8% are considered low and could restrict pasture growth. Macroporosity for the 10-20 cm depth increment on the Dairy site was 7 ± 1%, a level where less than optimum production could be expected. Results from an AgResearch trial found similar values for and changes of macroporosity with stocking intensity.

Table 1 – target values for macroporosity for pasture, cropping & horticulture and forestry

I did not find any changes in water holding capacity within the plant available range with increasing land use intensification. This result in itself was interesting as it shows that intensifying land use practices did not have a measureable impact on the readily available water (RAW, that available to plants) of the soil. In comparison other studies have found that there is a significant decrease in RAW with irrigation and increased compaction.

Finally my study did find that there was an increase in small micropores holding water at suctions too great for the plant to overcome. These findings all highlight the importance of on farm soil testing to determine the RAW of the specific soil textures and under different land uses to increase management efficiency.

Bulk density values were found to be significantly higher on the Dairy site (1.40 ± 0.02 g cm^-3) than both the Sheep farm (1.26 gcm-3± 0.02) and the Control site (1.31 ± 0.02 g cm^-3), indicating increased compaction on the DF in agreement with macroporosity values. Bulk density is not as sensitive an indicator of compaction as macroporosity and this can be seen by the large target range 0.7–1.4 gcm^-3 that has been identified for Pallic soils (Table 2). Therefore it is not recommended as an indicator for determining the effect of land use intensification on soils.

Table 2 – target ranges for bulk density are large indicating that this is not as sensitive an indicator as macroporosity for determining the effect of land use intensification on soils.

Landcare Research has developed a tool which can be used by everyone to determine the quality of their soil based on a number of indicators.

sindi.landcareresearch.co.nz

The tool allows you to measure your soil against current understanding of optimal values for: Macroporosity, bulk density, Total N, Total C, Mineraliseable N, pH and Olsen P

It will tell you about the effect each indicator has on soil quality alongside some general management practices that can be used to improve your soil.

In addition to thinking about the effect of these indicators on your soil quality I encourage you to take a step back and also think about the long term effect of the state of these indicators/ properties on your farm’s functions and the importance of each of these functions to your profitability. 

Thanks to Nicole Mesman (BSc (Hons) Soil Science) for the content of this post!

Rain gauges – why they're a powerful tool for your operation

Do you know how much rain has fallen on your farm?  Or on your block of land down the road?  Do you sometimes forget to tip out the rain gauge?  Accurate rainfall figures for farm records are becoming more and more important in this age of transparency.  Knowing how much rain fell on any given day on your own farm or on a particular crop will give you the ability to make more accurate decisions.  Telemetered rain gauges save you the hassle of manually reading the rain gauge and provide up to date data straight to your phone or computer. 

Rain gauges can be installed along with your soil moisture probe and positioned under the irrigator or installed in a dryland area.  Positioning the rain gauge under the irrigator enables you to monitor exactly what application depth the irrigator is applying.  Application depths can change as a result of adding extra irrigators to the system, blocked or broken nozzles and changes to system pressures to name a few.  Excessive application depths are expected to account for on average 10% of water losses on an average irrigation system, that’s wasted power, water and most importantly money.  Not applying enough water may result in yield losses and shallow rooted plants.    

A telemetered rain gauge installed under the irrigator will also enable you to see the application rate applied.  If it is above the rates described for your situation in the table below you may be wasting water.  

Agri Optics can add a rain gauge to your soil moisture system to help your decision making.  Ring us today to talk about the options for your farm. 

Agri Optics office: (03) 302 9227

Cindy Lowe 021 796 834 or cindy@agrioptics.co.nz

Email: info@agrioptics.co.nz

Tips, Tools and Technology for Efficient Farming - Part 1

During winter the H2Grow team ran a series of workshops throughout the South Island titled ‘Tips, Tools and Technology for Efficient Farming’. These workshops were very well attended and the team thoroughly enjoyed meeting everyone and the wide-ranging discussions that were had.

For those that were unable to attend we do not want you to miss out, so over the next few blog posts we will be posting notes of the key messages from each of the presentations. These are only condensed versions of the main points so if you would like further information or have any questions then please do feel free to contact the contributors directly by either clicking on the photo widgets to the right of this blog, or use the links provided.

The first set of presentation notes briefly cover the following topics:

1. Why should we care about farming efficiently?
• Nutrient management - why are we doing this?
• Irrigation and nutrient management - how to they fit together?
2. Soil moisture and water use efficiency

You will see there are two copies of the notes, one for Canterbury and the other for Otago as the notes relating to the regulations between these two areas differs.

Nutrient Management and Soil Moisture - Canterbury

Nutrient Management and Soil Moisture - Otago

Both topics were presented by Irricon Resource Solutions, so for more information please fee free to contact Keri Johnston or a member of the Irricon Team.

The irrigation season is just around the corner…

With the days getting longer and the weather getting warmer (I’m sure it’s too good to be true!) spring growth will soon be kicking into gear and irrigation season will be just around the corner. Now is the time to be ensuring that you’re as prepared as you can be for the irrigation season.

If you’re an irrigated farmer now is the time to be thinking about how you’re going to schedule your irrigation throughout the upcoming season. The days of scuffing the dirt with your boot and having a dig with a spade are fast coming to their end with the need for on-farm soil moisture monitors such as the AquaCheck probe, to give some more accurate numbers to the soil moisture levels than a scuff of your boot on the soil. Having soil moisture probes installed on farm not only helps you make better irrigation decisions but it also gives you some hard and fast data to have when it comes to Farm Environment Plan (or the likes) auditing.

Soil moisture probes for use this coming season should be being installed now or over the next few weeks ideally. All continuous soil moisture measurement devices take a period of a few weeks to ‘settle down’ and give accurate readings post installation.

At Agri Optics we have a great soil moisture probe in the AquaCheck probe as part of our suite.

The key things to note on these probes compared others (other than their great price) are as follows:

·         They’re fully telemetered, giving you access to view up-to-date soil moisture data and make timely decisions based on current, actual data

·         They’re a vertical oriented probe that has multiple soil moisture sensors down their length, giving you a total soil moisture trace and soil moisture traces at each different sensor depth. This means that you can see how the soil moisture moves down through the soil profile and how effective you’re being with your irrigation management. The bottom sensor is also a good ‘check’ for drainage leaving the root zone

·         The AquaCheck probe has built-in soil temperature sensors – a good gauge to be able to better manage irrigation and fertiliser timings in the shoulders of the season in particular

·         They have the option of connecting to rain gauges to give accurate records of rainfall and irrigation at each soil moisture probe site

·         They have a short ‘settling’ time post install compared to most of their competitors, meaning that you’ll get useful data to make decisions off in a short time frame

·         They’re easy to install and uninstall, making them great for seasonal cropping situations

·         They’re very competitively priced

·         There are multiple depth option so that the depth of the probe installed can be matched to your farming system and requirements

·         In NZ they’ve got Agri Optics behind them, to help you, the farmer understand and interpret soil moisture readings and get the most out of soil moisture probes for irrigation scheduling

You can also view more information on the AquaCheck probes on our website: http://www.agrioptics.co.nz/portfolio/aquacheck/

If you’re interested in the AquaCheck probes or need a soil moisture solution for this season please don’t hesitate to contact one of the Agri Optics Team for some more information and a quote.  

All the best for an upcoming irrigation season & year ahead!

Cheers,

Jemma

The Finance of Farm Environmental Improvement

There has long been the perception that good environmental management comes to the detriment of the overall farming business.  I’d like to think we’ve got beyond that, but with nutrient regulations coming into play, I suspect that this perception if running rife again!  But, it doesn’t have to be that way, and in fact, it can be positive financially for the farm.  In this post I’m going to show you examples of where environmental and financial gains can be made for farms, and that the two objectives don’t have to be at logger heads.

Resource consents held by a farm is the obvious place to start.  Quite often, consents were obtained, shoved in a draw and never looked at again.  But consents are a valuable asset to a farm, and having the right consents is critical.  The three questions that need to be asked is:

1. Are they correct?  For example, is my rate of take correct, is my effluent discharge area actually right, are my cow numbers to be milked right?
2. Could they be better?  For example, does my effluent consent cover my whole farm to give me flexibility?  
3. Are they even needed?   With Canterbury having changed its plan twice in the last 10 years, there are now consents that were needed under the old plan that are not needed under the new plan, for example consents to store dairy effluent.  

As an example, a consent audit was undertaken on a farm which had six consents to take and use water, and a dairy effluent consent.  This means:

• Seven lots of monitoring charges.
• Old take consents that no longer reflected what was happening on farm, including that none of the consents specified whole of farm for irrigation or effluent, and had horrible 14 day volumes that didn’t fit with newly installed pivot irrigation.  

The six take consents were merged into one consent, 14 day volumes removed and replaced with one annual volume for the farm, and the whole farm was also be irrigated with any source.  This means:

• Better use of the water – the farm was no longer restricted by horrible 14 day volumes, so is able to irrigate when needed.
• Easier to comply with – One consent versus six…..
• Flexibility – The water can be used anywhere it’s needed, rather than from a certain point on a certain area.  

The paperwork is now sorted, so next it’s time to look on farm.

Is your infrastructure up to scratch?  This can encompass all types of things, but common examples include having effluent storage that’s big enough, or your control box says that the pivot is putting on 10mm, but how do you know that’s what actually coming out the sprinklers?  Right the way through to the question “is your pump and mainline adequate and not costing you more to run than they need to be?”  Has it been looked after?  Things like sprinklers broken or not turning, or missing altogether!  Remember that an irrigator has moving parts – how often are these checked and serviced?
And finally, how do you make the decision to start irrigating or when to discharge effluent?  The neighbor is not generally the most reliable tool to use, and if it’s too early, then its water wasted, effluent and therefore nutrient wasted, and production lost.

Now let’s take a look at lost production due to infrastructure.  We’ve got a farm with an intake that required frequent rehabilitation, and cleaning and clearing of weed despite it having a screen which resulted in reductions in flow.  It also had a mainline configuration resulting in substantial system losses, and pumps not performing at their optimum efficiency.  The farm needed 4.5 mm per hectare per day for optimal growth.  Because of the intake and mainline issues, it was constantly only getting 2.5 mm per hectare per day.  This resulted in a shortfall for the farm of 2650 cubic metres per hectare.  The impact on production from this shortfall is 10% or 1.5 tonnes of dry matter per hectare of average annual growth loss.  If this additional growth is worth 28 cents per kg of dry matter, this this is $420 per hectare.  And all this because the infrastructure was not doing what is supposed to be doing!

Now let’s compare a farm with soil moisture monitoring to one without it, both located within 1km of each other, of similar area, lay of the land, and irrigation systems.  For the 2013/14 irrigation season, the farm with soil moisture monitoring used 3213 cubic metres per hectare.  The farm without soil moisture monitoring used 5389 cubic metres per hectare.

• Energy Cost to farm with soil moisture monitoring = $321.30 per hectare
• Energy Cost to farm without soil moisture monitoring = $538.90 per hectare

And let’s not forget that less water applied = less nutrient loss.

So why look at all of this stuff I hear you ask?  The reality is that the use of resources on farm cost money:  Water, energy, fertiliser and/or effluent…. Increased production tends to not only cost money, but it is also considered to have environmental impacts.    In my view, it is really important that farmers don’t view the two as being incompatible.  A Farm Environment Plan and the process involved in preparing one, is a place to assess the risk of your farming business to the environment.  But you should take it as an opportunity to look at your business as a whole, and use it as a way to not only achieve good environmental management, but good “full stop”.    Don’t view the process as a hindrance, and just another regulation box to tick. Take the positive approach.

So, my final comments!

This has been a snapshot of the opportunities that exist on farm where being environmentally responsible can also be financially beneficial. So, use what’s coming from a regulation point of view to take a look at your whole business.  You might be just pleasantly surprised at what you find, and be able to make positive changes to your business all round.

Keri Johnston, Irricon Resource Solutions Limited.
Phone: (027) 2202425
E-mail: keri@irricon.co.nz

Keri’s expertise is in the field of natural resources engineering and resource management, primarily in water resources, irrigation and nutrient management. As well as doing this, she farms with her husband and two girls at Geraldine.  

Why my soil moisture sensor might be lying to me?

After choosing the type of moisture sensor you are going to invest in, the most crucial thing is to get the installation correct. It goes back to the old adage; rubbish in rubbish out, if you don’t get the installation correct everything that follows will at best be very marginal data.

Most probes are measuring a very small volume of soil within 10-20mm of the sensor itself, so good soil contact is imperative as well as a crop cover around the probe that is representative of the rest of the field being monitored.

If you are looking at installing a probe for next season or looking at maintenance on an existing probe then read on! These few basic does and don’ts will be of good use!

Don’t!

• Don't leave the excess cables on the ground – it is an accident waiting to happen!
• Don’t leave exposed cables for wildlife that want to see how tasty it is!
• Don’t site the probe on a ridge or in a hollow!
• Don’t site the probe in bare soil. Is there a crop growing over the probe site to give you a true representation of what is happening in the rest of the field? 
• Don’t site under the fence line

Don't leave cables on the ground

Do!

• Ensure you use good consistency of slurry around the probe to ensure good soil contact.
• Ensure you know the soil type your moisture sensor is located in and how that compares to the rest of the area you are monitoring.
• Make sure any tramlines or irrigation tracks miss the probe site by metres rather than millimetres!
• If your probe is near an electric fence, do ensure any metalwork is earthed.
• Do install the probe as early in the season as you can, so it has time to bed in and the crop over the top of it time to establish like the rest of the field.
• Do ensure a competent and trained person installs the probe with the right equipment to do so!
• If checking an old installation make sure there are no cracks around the probe site, the soil around the probe hasn’t sunk and the wires are in good order.

AquaLINK telemetry unit, away from AquaCheck probe out in the paddock

If you have any doubts about the site or installation of your probe, by installing it as early in the season as you can means that it can be moved and still have the winter to bed in again.

AquaCheck WEB, induvial sensor graph responding to irrigation and rain events.

Monitor your probe data and its response to rain or irrigation events, the beauty of the capacitance probes is that moving them is not an issue.

This article contains information from a post previously written by HydroServices but has been updated to include the experience from the Agri Optics team installing AquaCheck probes.

A Guide to Making Sense of Soil Moisture Data

With an increasing amount of soil moisture monitoring sensors on offer in the market today there is growing importance on not only having sensors installed but actually understanding the information they provide. This blog is written to give some insight into the data they you might receive from one of these devices. The following traces are the output of an AquaCheck soil moisture sensor with 3G telemetry. The sensors measure soil moisture and temperature every 30 minutes. The data is available to Agri Optics clients from the AquaCheckWeb platform. For more info see our website http://www.agrioptics.co.nz/portfolio/aquacheck/

The key to getting the most out of your soil moisture sensor is to have an accurate field capacity (FC) and refill point for the probe site calculated. The most convenient way of identifying Field Capacity is to have the probe installed prior to the winter period. Typically there will be enough precipitation to allow the profile to recharge to FC. FC can also be identified by saturating the profile manually with a large quantity of water. The key points we are looking for when identifying FC is a repeated filling to saturation then drainage of the profile. The point where drainage ceases can be identified as FC. Night time events are more accurate as ET is not a factor.

Fig 1. Identifying field capacity

The next key feature to identify is drainage. Drainage is classified as the loss of soil water past the effective rooting zone. The effective rooting zone varies dependent on the crop. Once the depth of plant roots has been identified we can identify any drainage. For the graph below if the crop has a rooting depth of 600mm. The bottom pink line represents the sensor at 600mm. We can see the lift and subsequent drainage of soil water past the effective rooting zone of 600mm.

Fig 2. Drainage events

The third key piece of information that the AquaCheck package provides is the ability to set variable management allowable deficit (MAD) lines. These lines create the target “Green Zone” typically between 85% and 15% of readily available water (RAW). Using MAD lines leaves room for any rain so that any free rain water is not wasted as drainage. It also gives an indication when soil moisture is approaching stress point. The MAD is able to be adjusted to give a desired target soil moisture zone for crop and pasture growth stages e.g. establishment or harvest.

Fig 3. MAD Lines

The final bit of information that becomes available once the crop starts growing is the daily soil water usage. The staircase like moisture trace is showing us evapotranspiration and it allows us to see the impact that increasing crop biomass and increasing temperatures are having on crop or pasture water usage. Crop rooting depth can be identified by seeing how far down the water usage is occurring. In fig 2. above below the roots are drawing moisture down to 600mm vs a later spring sown wheat in fig 4. which is only drawing water to 400. Note the size of the usages. This relates to the root mass at the given depths.

Fig 4. Crop water usage

I hope these tips are useful when interpreting your soil moisture data and that it results in more efficient scheduling of your irrigation this summer. Irrigation New Zealand also has some more tips and info on their website http://irrigationnz.co.nz/news-resources/irrigation-resources/

Post By Nick

Know your Soil Better than your Bank Manager - Continued

Identifying Soil Texture

Soils are made up of particles of different sizes, the largest sand, followed by silt, to the smallest clays. Together these make up the soil’s texture. Soil texture has a direct impact on soil physical properties: porosity, water holding capacity and bulk density. Furthermore soil clay content determines soil chemical properties and the soil’s ability to hold onto nutrients.

This blog will discuss hands on ways to determine your soil texture, how texture relates to key soil physical properties and the role of clays in the soil. You can determine your soil texture at the same time as you carry out the VSA described in the previous blog post and together these practices will improve the quality of your information.

The change in a soil with depth, the cross section down through the soil, is referred to as the soil profile. It normally consists of a number of soil horizons (layers) each with different characteristics (texture and/or stone content). The picture below shows a soil profile with six distinct soil horizons. When scheduling irrigation you need to know information about the hydraulic (water) properties of each soil horizon that plant roots occupy within the soil profile to determine the amount of water available to the plant. This determines how frequently you need to irrigate (return period) and the maximum irrigation you can apply in one application (irrigation depth).

Example soil profile

Soil texture is an important characteristic because it gives a good indication of other soil properties such as water storage, drainage and nutrient supply. It is a stable soil property and is not likely to change with normal soil management. Soil texture can be estimated in the field by some practical tests involving the feel of the soil and these are outlined below. To determine the textures and get an idea for the ability of your soil to hold water it is beneficial to dig a pit and expose an open face on the soil profile so you can determine the different horizons visible down the profile. You should identify the soil texture of each of the horizons that plant roots are found to grow in, or down to about 60 cm.

Hands on method to determine your soil texture.
Found in the joint Irrigation NZ and Plant and Food resource - Click here to visit the webpage.

The graph below shows typical soil water holding capacities (WHC) for different soil textures in % or mm of water per 100 mm of soil depth. It also shows their typical permanent wilting points (WP) and field capacities (FC). The relationship between WHC, porosity and bulk density is straightforward. Sand has the largest particles, the lowest WHC and therefore the lowest porosity. This translates into the highest bulk density because less space is occupied by air. As shown by the WHC of silt and clay below, silt has a higher porosity and lower bulk density which is very similar to clay soils although clays tend to have the highest porosity. This is because clay is made up of lots of small particles which create lots of air spaces between them. Therefore clay also has the lowest values for bulk density.

Relationship between soil texture and soil water content.
Found in the joint Irrigation NZ and Plant and Food resource.

Another role of clay in the soil is in terms of nutrient management. The structure of clay's means that they tend to become negatively charged around the surface. This means that positively charged nutrients are attracted to the surface of the clay and, depending on the conditions, can move between this surface and the soil solution from where they can be taken up by plants. It is helpful to have an idea of how much clay your soil has because this will determine its ability to store positively charged nutrients such as potassium, calcium, magnesium, sodium and resist changes in pH. Clay also holds phosphorus by allowing it to be adsorbed into the clay structure; some clay's allow this more than others. This is important to note because when phosphate is adsorbed it is less likely to become available to the plant and more phosphate will need to be applied to the soil to avoid deficiency in plants.

For more information on soil texture and water holding capacity you will find a great resource by following this link.

Once you have an idea of your soil texture and water holding capacity mapping tools can be used to get an idea of the representation of this soil type across your whole farm. Simple mapping such as Google Earth images (see the Ground Truthing your Soil Variability blog) and S-Map (which will be discussed in a future blog post) are helpful resources. It is important to be aware that these are tools to increase your understanding but to provide the detail required for efficient farm management tools such as EM mapping and determining exact water holding capacity are greatly beneficial.

Blog post written by Nicole Mesman - BSc (Hons) Soil Science.

Know your Soil Better than your Bank Manager

A Practical Guide to Assessing your Soil Quality

The soil’s physical properties are vital to the ecological and economic sustainability of land. They control the movement of water and air through the soil, and the ease with which roots penetrate the soil. Damage to the soil can change these properties and reduce plant growth, regardless of nutrient status. Decline in soil physical properties takes considerable expense and many years to correct, and can increase the risk of soil erosion by water or wind.

The primary functions of the soil are to provide plants with air, water, nutrients and a rooting medium for growth and physical support (image sourced from the Landcare Research website) 

The Visual Soil Assessment (VSA) was developed by Landcare Research to give cropping and pastoral farmers a straight forward and time efficient checklist to use in the field to assess the state of their soil, primarily the physical soil quality.

The VSA can be found online here -> Visual Soil Assessment (VSA)

The VSA aims to help farmers identify changes occurring to soil physical properties so that they can assess the effect that these changes will have on their soil quality and the sustainability of their land management and long term profit.

Pictures in the VSA guide can be helpful when carrying out the assessment in the field (image sourced from: VSA Volume 1).

The assessment can be carried out quickly, reliably and cheaply with little equipment, training or technical skills. The scorecard below is to record those visual soil indicators used to assess soil quality. There is a similar scorecard for recording plant indicators. You are then able to compare the two sets of indicators to see if you have similar scores for both and if not why. For instance, is damage to soil quality not being seen in crops yet or are crops struggling to recover from previous soil damage?

VSA Scorecard (image sourced from: VSA Volume 1)

Below each indicator is a section in the online VSA booklet to refer to for assistance. Pictures are included so you can compare what you are viewing and refer to examples. You will need a spade, the score card, a surface to drop soil onto for a shatter test and a bin to contain soil. Each indicator is given a weighting and at the bottom of the scorecard you add the scores for the various indicators. Values falling within certain ranges are deemed “poor”, “moderate” and “good” quality. If your quality is poor or moderate it is suggested that you refer to Volume 2, also easily accessible from Landcare Research online. This volume contains tips on how to improve your soil quality or maintain it if it is already good.

Tips include:

• Cultivating at the correct moisture levels to avoid smearing of soil, formation of cultivation pans and reduced infiltration when the soils are too wet. 

  

  (image sourced from: VSA Volume 2)

• Use a sub-soiler to break cultivation pans and increase root growth
• Maintain soil organic matter levels to ensure porosity, drainage and root growth.

  

  (image sourced from: VSA Volume 2)

By utilising these resources, you will gain a better appreciation for the state of your soil and will be able to identify when changes are occurring and why. The VSA is a simple tool and when used regularly will help with building a picture of soil quality. There are a range of other resources that can continue from the VSA, further your knowledge of your soil and assist with management. SINDI, another resource for determining soil quality, will be discussed in a future blog post along with hands on ways to identify your soil type and S-Map, how its geomorphological (land formation) history can be used to assist your farming.

The blog post you have just read was written by Nicole Mesman - BSc (Hons) Soil Science.

Legumes + Efficient Water Use = Great Results at Omarama Station

Omarama Station recently played host to the "Legumes in the High Country" field day, organised by Lincoln University and Beef + Lamb NZ. There was a good turnout of farmers and industry professionals to the farm owned and run by Richard and Annabelle Subtil, 2015 winners of the South Island Farmer of the Year competition. The focus for the day was the use of legume species in the high country environment with a short session on the use of irrigation and soil moisture monitoring in the arid environment that is the Mackenzie Country.

Omarama Station (Courtesty of Richard Subtil)

Omarama Station covers 12,000ha with a mixture of dryland high country and irrigated flats. The property has had significant development work undertaken and a number of centre pivot irrigators installed that irrigate 560ha. A large water storage pond has been constructed to supply water to the irrigation system.

Dr MS Srinivasan from NIWA gave the first presentation for the day at the site of the lysimeter that has recently been installed on the station. The lysimeter is the first in the Waitaki catchment and aims to build knowledge around drainage and soil water under the developing soils at Omarama Station. The site contains three catchment sleeves one of which has soil moisture sensors installed. Any drainage water from the site is measured which gives an indication of the soil moisture status and how drainage from the soil profile is taking place.

From a soil moisture point of view the lysimeter is important as the soils at Omarama Station have exceptionally variable fertility, structure and water holding capacity. Irrigation is not new to the area however the shift from border-dyke irrigation to more efficient spray irrigation has seen a massive change in the water use efficiency on extensive properties such as Omarama Station. Soil development under irrigation is an interesting concept and soils mapped on Omarama Station have shown to have varying levels of water holding capacity based on how long they have been irrigated for in the past. Investigation has shown that the depth of soil and the water holding capacity has improved under 30 years of irrigation. 

Irrigation at Omarama Station (Courtesy of Richard Subtil)

Agri Optics has installed three sub-surface AquaCheck probes that will complement the work being undertaken at the lysimeter site. This information will flow into the decision making process that is used around timing and quantity of irrigation water applied by the team at Omarama Station. 

Derrick Moot spoke on how selection of species was important to maximising water use efficiency in moisture deficient environments such as the Mackenzie Basin. As we know lucerne is a great fit into dryland high country systems. It has the ability to maximise the water use efficiency and has a high water to dry matter conversion ratio (kg DM/mm/ha). The selection of species going forward and the development of novel species all points towards maximising the efficiency of water use in dry high country areas.

Write up by Nick Evans

Improving Irrigation Efficiency for Only $50 cont.

Here is the much anticipated second installment from the Improving Irrigation Efficiency field day run by The Waihao Wainono Group and Morven Glenavy Irrigation. Dr Anthony Davoren, renowned Irrigation Consultant with Hydroservices, shares how drainage through the soil profile can be measured. With this key piece of information we can improve our irrigation management, and know when to turn the irrigator on (or off) to ensure all irrigation that is being applied is going to benefit the grass or crops we are growing.

Thank you to Dr Anthony Davoren, Waihao Wainono Group and Morven Glenavy Irrigation.

Winter Is Coming! Tips for preparing AquaCheck soil moisture sensors for winter.

Preparation for winter is key when soil moisture is involved. Once soil moisture probes have been removed from the paddock the first thing to do is plan where they will be installed for the coming season. Choice of paddock, crop and location are all important.

 Re-installing the probe in a similar location for the following season will allow for the comparison of moisture management from year to year. It can also provide insights into how soil moisture is used by different crops in a rotation. Re-installing the probe in a different paddock will require some thought as to where the probe should be placed. Ideally a few key things should be considered as to the location:

Plan:

• Choosing a location that is representative of the paddock. If an EM survey has been done then a location can be selected from the results. If no EM survey has been conducted then a location that looks, or has anecdotally been, representative of the paddock should be identified.
• Make sure that the site is located in the middle third of a pivot, isn’t under any towers or under the end gun and that nozzles that pass over the probe aren’t blocked. Generally placing the probe in the middle of a span is optimal.

Prepare:

• Run the pivot or lateral over the paddock if possible so that wheel tracks are easily identifiable.
• Ensure that tramlines can be identified. This is to avoid installing too close to the tramline. 
• Generally installing after the first spray or fertiliser application is ideal.
• Winter provides the best time for soil moisture probes to bed in. Therefore it is important that probes are installed as early as possible. By installing early it allows for the soil profile to have time to rebuild structure around the probe which is key for accurate data capture. On top of this winter time will provide an opportunity to identify the soil moisture field capacity.

A recent install ready for winter. Tramlines are visible in the background.

If the probes are not being re-installed prior to winter then the following will apply:

• Disconnect the probe from the AquaLINK 3G telemetry unit. Store the probe in a safe place. Particularly away from anything that may chew on the cable.
• Place the AquaLINK 3G telemetry unit on a windowsill or in the garden, somewhere it will receive sunlight. This is to ensure that the battery remains charged up over the winter.
• If the probe is not going to be used for a whole calendar month contact Agri Optics to get the connection deactivated and save on the monthly bill.

Remember the 6 Ps. Prior Preparation Prevents Piss-Poor Performance. Ultimately your soil moisture management will be improved due to accurate and timely data from probes that are installed in the right place and as early as possible.

Inaugural PAANZ Conference - Summary

Precision Ag in New Zealand is finally starting to gain a bit of traction in NZ & this was seen last Friday by:

1)      the fact that the Precision Ag Association of NZ (PAANZ - www.precisionagriculture.org.nz) ran their first conference

2)      the  number of attendees that came from far and wide to attend & learn

Firstly, I’d like to congratulate the PAANZ committee on organising a well-run event with some thought provoking topics and speakers. I’m going to run through a bit of a summary of the day in terms of what was covered and some ideas to ponder.

Andy Macfarlane from Macfarlane Rural Business kicked the conference off to a start with a general overview of NZ ag and where we’re at in terms of water, nutrients and farming within limits. One of the key points from his presentation was that “Good Management Practice (GMP) is a given – everyone needs to get there NOW!” GMP will evolve and is not a fixed point. ‘Good’ will also not be good enough, farmers will need to be ‘great’ to keep ahead of the game and ensure long term farm viability. Precision Ag is going to be integral going forward to achieving this.

Some Key Principles for mitigating N leaching

1. Measure before you apply – need to know what you’re dealing with so you can make the right input decision.
2. Use nitrogen (& water) interceptors – roots, different crops etc
3. Smaller and often applications are better than large amounts and less often
4. Do not put nutrients where you don’t need them (use targeted application technology – Precision Ag)
5. Apply less urine or less nitrogen concentration in urine
6. Increase nitrogen utilisation in gut to decrease output of nitrogen
7. Less water drained = less nitrogen leached
8. Integrated farm systems approach required to achieve long term desired outcome
9. Validation of science needed both at research level and on farm

Keith Cameron, Professor of Soil Science at LincolnUniversity also posed a sound point that irrigation, even though it might be controversial in some areas and need better management allows increased N uptake as the plants are actively growing and not under stress, therefore less leaching of nitrogen results. Is there a case for environmental irrigation? Especially in summer dry areas? He also pointed out that we need to look at plant uptake as a mitigation strategy for decreasing nitrogen leaching. Catch crops following/during winter grazing is likely a good way to achieve this and studies have shown that this can be by between 20-40%.

While we all know that nitrogen itself is a key part to the nitrogen leaching discussion, in irrigated Canterbury and other parts of the South Island managing soil moisture is key to effective nitrogen management. Dr Tony Davoren from HydroServices spoke on this topic and highlighted the following:

• Measuring and understanding your soil moisture is key to good irrigation management and reduced leaching
• No drainage throughout the growing season from pivots if managed well – the same can’t be said of other irrigation systems with high application rates in particular
• You need to measure soil moisture at and below the root zone. Firstly to understand your plants requirements, and secondly to know and be able to prove that you aren't leaching and wasting water
• It’s also important to measure soil temperature as this is also a factor when scheduling irrigation and brings in the ‘farm systems approach’ that Andy talked about by looking at multiple factors.

As the focus of the day was mostly looking at how nitrogen leaching could be reduced using Precision Ag (PA) techniques there wasn't a lot of emphasis on other areas, however some were slightly touched on. These included Ian Yule (Massey University) talking about the economic impact of poor spreading pattern and that it could cost a farmer on average $45/ha if his spreading CV was at 20%, however CV was likely to be nearer 30% when out in the field. At costs like this we obviously need to get our spread pattern accurate before we start doing variable rate fert. Accuracy is key to everything in Precision Ag. The benefits of ‘All Paddock Soil Testing’ was highlighted for reducing paddock to paddock nutrient variation and pushing pasture yield along on dairy farms.

There were a vast array of topics covered during the day, stretching further than just nitrogen leaching and it was truly encouraging to see such a good turn-out of interested people to this inaugural event as well as the robust debates and discussion that went along with it. It’s truly heartening to see NZ farmers and industry pushing the boundaries and meeting NZ farming targets using tools and technologies that are already out there today. The future is very bright for NZ ag and coupled with all of the emerging technologies and the science to back these up I feel very encouraged about the position of the New Zealand farmer. Now to get everyone dabbling their toe in the water of Precision Ag…

~ Jemma