A map of soil moisture at freeze-up can give you a good indication of your yield potential
Water in the bank is a certainty; rainfall is a probability. Much of what we do in farming is based on probabilities — a game of chance.
What are the chances we will get timely rains to keep a crop from withering away to a low yield? What are the chances we will suffer disease or insect damage? What are the chances of good harvest weather? And the list goes on and on.
But, what could we do if we could be certain about an important factor determining yield?
Flashback to 1978
In the 1970s I was busy pounding pavement all around the province supervising fertilizer field tests. About that time the Backsaver soil probe came along and it was easy to inspect soil moisture. Along about September we would be checking out the wetting front as fall rains started to replenish water sucked up by the crop.
We must remember that fall rains are usually system rains rather than thundershowers so not as variable over large areas. We came to realize that when checking the wetting front, one probe in a quarter section was as good as a dozen. We then learned that we could often go for miles and miles and get the same answer. And, we also learned that a rainfall map for the time since crop water use had ceased was huge. But, the rain map had to be based on hundreds of stations. The Saskatchewan Agriculture Crop Reporting Service provided the needed maps, and still does. Rainfall cannot be modelled — it can only be measured.
By and by, we realized that we could make a map of soil moisture as of freeze-up, around November 1. We established a legend that showed soil moisture in terms of the wetting front for light, medium and heavy soils and expressed it as inches of available moisture. Inches of available water can easily be converted to bushels of grain.
One October morning in 1978 I took my rough, hand-coloured map to my boss, Don Rennie. Many will remember Rennie as the guy who badmouthed summerfallow when it was a sacred practice. His response: “Les, if you can make a map like that we will find the money to print it and and have it posted on every elevator wall.” By afternoon coffee break he came to me and said the money was in place so “get on with it.” And it was done! In today’s world it would take that long to form the committee to see if it should be done.
Soil moisture as of freeze-up
If subsoil is full of water at freeze-up, it will still be full when a crop root comes looking for it in June. The idea behind a freeze-up map is to be certain about a base level yield for the five months when most cropping and input decisions are made.
We were never so naive as to think the map would be 100 per cent accurate for every quarter section. But, it does provide a standard for comparison and a recipe for using the data to predict yield possibilities.
It has always been a frustration to me that out of the many agros now helping farmers with information and decisions, so few have provided farm clients with simple soil moisture mapping as of freeze-up.
Fast forward to 2005 and beyond
I have very good water well evidence for a 30-year cumulative net drought from 1975 to 2005. Sloughs went dry, water tables dropped and shallow-bored wells started to dry up.
The big snow of 2004-05 was followed by more years of snow and good rains. Lo and behold, the water tables rose sharply. By 2012 water tables were high enough to give us sub-irrigation compliments of Mother Nature, no pivot required. A new category of soil moisture was established (superwet) to deal with high water table situations. High water tables resulted in parts of fields too wet to farm, combines getting stuck and general mud farming.
In the past few years we have seen situations where very good yields were produced on very stingy rainfalls. Some have concluded that we can grow crops on just a bit of water. Not so. We can grow crops on very little rain, if Mother Nature gives us a soil full of water and a water table to deliver water to deep roots.
2018: Finally someone measuring soil moisture
About a year ago I had communications with Kendall Gee about interesting work her group, South Country Equipment Ltd., was doing with soil moisture. They were installing soil moisture capacitance probes to get a continuous soil water use record by crops to a depth of one metre. Their data showed evidence of deep water use and of yields beyond expectation based on rain plus soil water to one metre. The invisible angel was most likely a high water table.
In late June, 2018 it was my great pleasure to take part in a field day at Imperial, Sask., about a 90-minute drive southeast of Saskatoon. It was organized by South Country Equipment Ltd. In the morning the Trevor Lewis farm quonset was used as the lecture hall and after lunch we took to the field. They had installed weather stations and soil capacitance probes. In the field they dug soil pits and dug out roots to confirm that roots extend to considerable depth.
At the first pit I could soon see from the soil samples that the water table was not far down. The Dutch augers were summoned and after a short demonstration by an old fossil, a young, strong chap took over the serious work. In no time he was turning up samples that showed the water table was well within the reach of canola roots.
We then had a peek at the weather station and the site where the soil moisture probe was installed. These smart young kids can take their cell phone and find data that is pivotal to final crop yield, and access it from anywhere in the world. Truly amazing!
Water drives everything: Water-driven yield
The game-changing meeting at Imperial was aided in no small part by Elston Solberg. Elston and I have passed ideas back and forth for many years. Many will know Elston from his days at Alberta Agriculture and many productive years with Agri-Trend.
At Agri-Trend he often emphasized that “water drives everything.” When he read my Grainews piece titled “Water in the Ground is a Certainty” he quickly grasped the implications and came up with “Water-Driven Yield.” The idea is to make sure a farmer provides a crop with what it needs to meet the potential that Mother Nature is providing.
A sincere thank you to Elston, the South Country people and to farmer Trevor Lewis for a day with the most fun I have had in a long time. Thanks also to Ryan Hutchison and Bonnie Mandziak for their contributions and the very touching keepsake they left me with — a poster that summarizes the day.
For the past decade we have been cascaded with fancy new technology that is too often peddled because it is new, fancy and magical. In many cases the fancy technology has come up wanting when the application to a farmer’s bottom line is considered.
The soil moisture work in progress by South Country Equipment Ltd. will only get better as they learn more about what happens underground and the application of that knowledge to further a farmer’s profit. Hopefully, others will jump on the bandwagon and do the same.
40 Years Later
Communication is a complicated business. To be understood and used, an idea has to be communicated with clear terminology that can be understood by the user. For years we have said, “Water in the ground is like money in the bank.” A nice idea but there are many steps missing in making the link between the cause and the end result. Certainty is easy to comprehend. It is going to happen.
Forty years after we made the first Stubble Soil Moisture Map I can now see where young, smart tech savvy kids will carry the idea to heights I could not imagine.
Keep tuned for the Soil Moisture Map as of November 1, 2018. I hope that I will finally be able to pension off my coloured pencils and leave it to the young folks to make maps much better than mine.
By: Les Henry
January 15, 2019