The EM Surveying Calendar

We have had another successful EM year so far and our clients have used their surveys for many different uses. I will go into that in more detail in a future blog. Today I will cover the EM and the four seasons. I often get asked when the best time to conduct a survey is, the answer is any time from late autumn through winter into the spring right up to late November.

For an autumn survey, natural moisture is our deciding factor on start dates.  Once the irrigation on farm has finished and we have had at least a good 50mm of rain to balance out any irrigation affects, we can start EM surveying. This year we held off until the end of April and in some areas south of Oamaru and north of Canterbury later still, as we didn’t get the 50mm+ for quite a while. So we concentrated on the areas that once they got too wet we knew we would not be able to get on again! Getting this sort of information from our client’s knowledge of the land is very useful to help with the logistics and completing the survey with as little fuss as possible. Once on site we are self-sufficient and conduct the survey without the client having to get involved, but we rely on good information on the conditions to manage the logistics before we arrive!

Getting ready to start a survey in Ellesmere, early May.

Winter is ideal for surveying and the concerns here are not getting stuck and being able to get along without making a mess especially in cropping situations. We can juggle between all grassland projects and cropping regimes as the weather fluctuates between torrential rain and drying enough so we can travel on it! It involves shifting jobs around depending on the conditions to ensure we get all the projects conducted in a timely manner, not making a mess or damaging crops and without too much to-ing and fro-ing, to ensure all data is collected as efficiently as possible. On some farms we have to leave a few paddocks if they have winter feed crops in or crops in the ground still to be harvested, in that situation we can come back in the spring and drive some transects over the rest of the project and tie all the data in together. Ponded surface water is not an issue and does not interfere with the EM readings and results. If there is a big rain event between starting and finishing a project we can tie the data together be driving transects and using our robust protocols to ensure data quality is not compromised. The only weather that stops us is snow! Mainly because we can’t see the ground and any potential hazards are covered up, as well as getting to and from the site can be tricky, we had a few close calls getting in and out of regions this winter but we managed to keep ahead of the snow!

Surveying near Staveley in July once the snow had thawed.

In the spring we also get good results, the temperature is a little warmer and we can get along very well in most cases, the only issue comes in the cropping situation when the crops start to get too tall. Generally we are fine in a cereal crop until stem elongation. Again it is a matter of logistics and knowing the clients requirements, timing limitations and concerns, as long as there is good communication this is not an issue. We can and have EM surveyed right through to early December before in dryland situations where there has not been any irrigation and good natural moisture. Once clients start irrigating the influence of the irrigation pattern will start to show through in the data. In the summer itself the ground is too dry, the variation in your soil textures is still there but the low moisture levels means the range in EM units is reduced and the EM profile compressed so outside influences start to creep in and have more of an effect on the readings so reducing the quality of data – which is the main reason we make a conscious decision to stop as quality data is of paramount importance. In situations where we are just looking to gauge salinity issues then we can go later as the very high EM values (150-600 mS/m) are not affected by moisture, but for general EM work we stop and concentrate on the other areas of precision agriculture until the following autumn. 

Surveying in late August on a freshly drilled spring barley paddock near Blenheim.

Now we are getting to the end of August if you are still interested in getting a survey conducted this year please let us know as soon as possible otherwise you may have to wait until next autumn.

Chris Smith

Field Manager Agri Optics NZ Ltd

A guide to S-Map

What is S-Map?

S-Map is a map containing information of the soils across the country. It is being developed by Landcare Research and information is continually being added to it. The project was started to collaborate and update information on New Zealand’s soils into one easily accessible map of the whole country with different layers of information for different applications and to support land management at different scales.

Anyone can access the information freely. Mapping is carried out by Landcare scientists who either use old soil maps or go to the area and undertake traditional soil surveying. This is where soil core samples are taken to determine the soil type and this information, alongside the history of the area, is used to present what they think the pattern of soils will look like. The most detailed information available is currently on the lowlands while the uplands of the country are being mapped using digital modelling based on the soils having similar characteristics to other known soil types.

How to use it

In the previous blog (identifying soil textures) you see how the content of sand, silt and clay determines soil physical properties such as WHC, porosity and bulk density and how there are different horizons in a soil profile with different quantities of these three particle sizes. S-Map also uses soil horizons to determine soil characteristics.

You can search for your location on S-Map and select to see polygon layers to view the soil types present on your farm as shown below for Methven, Canterbury.

S-Map Online is freely accessible for anyone; smap.landcareresearch.co.nz

You can then select the ‘Soil information’ tab at the top of the screen and click on a point on the map. S-Map will show you the percentage of each soil type present around this point and you can select to view the factsheet of the dominant soil type (and the other soil types present). In the figure below the Greenvale farm near Methven is shown by S-Map to have three dominant soil types: 50% is a shallow, well drained Eyre, 25% is a shallow Darnley and the final 25% is a moderately deep Mayfield.

The soil will have been given a series of names using the New Zealand Soil Classification System however don’t worry about this too much, the information contained further down in the factsheet has more practical applications. The fact sheet tells you:

• ·         How stony the soil is which relates to its drainage class
• ·         The amount of water expected to be held at different depth increments
• ·         The clay content
• ·         Potential rooting depth
• ·         Soil phosphorus retention
• ·         Water management such as the potential for waterlogging and drought
• ·         Nutrient management such as nitrogen and phosphorus leaching vulnerability. 

Page 1 of an S-Map report for an Eyre soil, downloaded from smap.landcareresearch.co.nz

You can also select different layers to view on the map, on the left hand side of the screen: soil drainage, depth to hard soil/ gravel/ rock and soil moisture. The map will then update using the colour scheme from the legend for this layer which is shown on the right hand side of the screen. The figure below shows that for the Greenvale farm the soil drainage depth layer has been selected and on the right hand side the legend explains what each drainage class means.

Positives

S-Map brings all information on NZ soils into one database that can be easily accessed and used by all land users and interested parties. It is the largest national resources on soils that NZ has and it contains a range of information that is relevant and useful for all scales of management. However there are also aspects to S-Map that limit its usefulness, especially to farmers.

Drawbacks

According to S-Map the Greenvale farm, shown in the S-Map figures above is a mix of mainly three soil types. However an Electromagnetic map carried out alongside soil sampling showed that there was, in fact, a much more complex pattern of soils present on the farm. The picture below and top is the Electromagnetic map of the property and the different colours represent different textures while the picture below and bottom uses the patterns from the EM map alongside soil sampling to identify the pattern of soil types (families) on the property. 

Top, EM map by Agri Optics Ltd. Bottom map of soil types developed from soil sampling.

These maps provide a substantial amount more information than the map of the farm from S-Map (discussed above). The soil information used by Overseer to determine nitrate leaching is supplied by S-Map and this can result in inaccuracies in N leaching figures when S-Map believes the soil pattern on a farm is more simple or different than it actually is. Furthermore using soil information from S-Map for irrigation scheduling could mean over or under irrigating areas which can decrease yields as well as creating inefficiencies in water and power use. 

Temperature – How cold is too cold?

Following on the theme of soil (moisture) sensors, this blog is concentrating on soil temperature.  At this time of the year (mid-August) soil temperature is or has become the most important factor influencing irrigation (and to a lesser degree fertiliser application).  Just like soil moisture, if you don’t get the installation or measurement point this right you will never get any decent data and never be able to utilise the soil temperature measurements with any confidence.  There are three key requirements for soil temperature measurement:

a)     Ensure any sensor is centred at 10cm depth or the measurement is taken at 10cm;

b)     Ensure the sensor or measurement taken is under the crop/pasture (not in a bare patch for example); and

c)     Temperature is measured at 9am (and not 9am daylight saving time).

Why is 10cm depth and 9am so important?  Crop production models use the 9am 10cm soil temperature as a key input parameter.  If the soil temperature is not above the base temperature at 9am then production will be affected.

It is imperative you measure soil temperature on your farm and in the paddocks of interest.  As at mid-August there is a wide range in soil temperature.  On the east coast of both islands the temperature gradient is large – warm enough for pasture growth in the North Island and too cold in the South Island.

In the northern east coast of the North Island (Gisborne area) temperatures have already peaked above the base temperature for pasture at 15°C and have been above 10°C for 6 days in August.

In the South Island (in the example mid Canterbury) temperatures have not even approached the 10°C base temperature.

So whether you have soil moisture sensors installed that also measure soil temperature or you use a $50 manual gauge, measure soil temperature from now to assist and guide the need to irrigate.

For more information on anything in this blog please contact HydroServices 

VRI & Irrigator Maintenance

In some areas it will not be long before pumps start up and irrigators are set in motion. So if you have not already done so you may want to consider a quick irrigator WOF check to make sure you get the best out of this critical piece of farm infrastructure. It may also be worthwhile evaluating if your irrigation system can be optimised or improved to save on costs such as water or energy.

Simple pre-season maintenance checks are able to be done by farm staff. A basic inspection while the irrigator is turned off can help assess if you will require service work to be carried out. It is recommended to park the pivot in an accessible position and ensure that the electrical isolator switch is tagged and locked to prevent accidental starting.

Every centre-pivot should be supplied with an operation manual which can come in handy, for most you will find this in the inside door of the main panel. Some manuals actually include recommended maintenance checks with instructions to show you how to carry them out. Whoever is carrying out the checks needs to be aware that centre-pivots are generally high voltage electrical systems, so leave all electrical checks to a qualified Service Technician. And if there is a need to work at heights make sure you have safe equipment to do so.

A walk up the length of the machine will allow you to assess any damage and parts requiring repair. Tighten, adjust or replace if possible, or note down so you can inform your Irrigation Dealer. Greasing of all the grease nipples as you go is highly recommended, important parts to maintain well-oiled are the pivot point, gear boxes and drive shafts. Checking that all moving parts around tower boxes are free and lubricated will help reduce problems for the upcoming season.

The uniformity of a centre pivot relies heavily on the correct sprinklers being fitted to each dropper, checking that the sprinklers installed match the sprinkler chart will allow your pivot to apply the specified application rates. Armed with a pole of some description you should be able to free any sprinklers that have become tangled over the truss rods.

It pays to check that the tyres are pumped up to their optimum pressure rating. As tyre pressure is critical not only for the life of the tyre, rim and gearboxes, but also the application rate of the sprinklers. Over or under-inflated tyres can apply higher or lower application depths than planned.

Once you have checked everything over with the pivot stationary, providing there are no required repairs, the next step is to run the pivot. This is ideally done when the soil is not too wet so that you don’t create big wheel ruts, or worsen those that need attention. Wheel ruts significantly increase the load and wear on the drive train so should be dealt with when possible. GrowSmart Precision VRI technology can be used to reduce the spray onto the wheel tracks to help minimise wheel rutting.

Obvious checks while running the pivot are leaks. Some of these can be fixed with simple repairs such as replacing droppers, but others may require a call to your Irrigation Dealer to sort out. While walking the length of the irrigator listen for excessive vibration or noise that may indicate issues on the towers motors, gear boxes and drive shafts.

Some component wear will depend on water quality as high concentrations of iron, suspended solids and effluent solids or grit can increase damage and degradation to parts. A general check is recommended every season to ensure that worn sprinklers and pressure regulators are replaced to maximise the efficiency of the pivot. Common causes to check for are blockages or damages from knocks during the previous season, missing sprinklers and spray plates.

At the end of the irrigator remove the sand trap cap (with the irrigator turned off) and flush the system to get rid of any sediment build up, this is very often common in the overhang. If your water supply has a high level of sediment than it is recommended that this is done regularly.

Reducing the risk of breakdowns during the irrigation season will help avoid production loses due to downtime for repairs. Long term water and energy cost savings are also possible through the installation of technology such as variable rate irrigation, which can reduce nutrient leaching as well. If you would like more information on recommended maintenance checks for your irrigator, system calibrations or technology to improve water use efficiency call your local GrowSmart by Lindsay Dealer.