Wednesday 26 August 2015

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