Water Drives EverythingPosted in: Farming By Elston Solberg June 22 2016
OK, I’ve been harping on this for a long time and I will continue to do so until I quit breathing. After CO2, water (H2O) is the most limiting ‘nutrient’ (H and O are both nutrients) to crop production, whether there is too little or too much.
So here’s the question, “On average, how many lbs of water does it take to grow a bushel of corn, soybeans, wheat or canola? Over the past 5 years, I’ve asked this question of 1,000’s of growers, students, consultants, advisors, experts and professors, and never had a guess closer than 1 order of magnitude low. Typically, the first answer will be somewhere between 20 and 200 lbs when the real answer is somewhere between 34,000 and 69,000 (depending on the crop).
For those that don’t believe, here’s my rough napkin math:
In Alberta, an average canola yield is just under 40bu/ac with about 11 inch of crop available water.
- 1 inch of rain/acre weighs 227,000 lbs
- 227,000 lbs x 11 inches = 2,500,000 lbs
- 40 bu canola weighs 2,000 lbs
- 2,500,000 lbs / 2,000 lbs = 1,250 lbs of water per lb of canola
- 50 lbs per bushel of canola x 1,250 lbs = 62,500 lbs per bushel
That this is not commonly known is a problem!
Now here’s the point. If we don’t know how much water it takes to grow anything, how do we start to connect all the thoughts that would lead us to better and better water use efficiency (WUE) and by default, to ever improving nutrient use efficiency (NUE) and environmental sustainability/enhancement (ESE).
So while most don’t know, there are some that will say, “Of course we know how much H2O it takes, we have sophisticated models that integrate available soil water with precipitation, irrigation, evapotranspiration and topography etc, etc, that are crop/geography specific. We just can’t get anyone to use them!” It’s true, there are numerous moisture driven yield models out there and farmers aren’t using them.
Well my theory is that the models are too complex to be communicated effectively. We need to initially speak in lbs H2O/bu, not mm H2O/kg and right now, we just need models that are easy to conceptualize and use to get us close – into Section P of the Yield Stadium not section P, row 9, seat 13.
Let me explain with an example from western Canada. We grow primarily spring crops and we know, plus or minus a small hand grenade that it takes 4" of crop available water to grow the crop factory and then every inch after that goes to yield. We know a good grower with good land can easily grow 6-7 bu of canola per inch of H2O after the factory is built. Bushels per inch of water will vary with the crop and a grower’s management practices.
If you know how much crop available water is in the soil and how precipitation and/or irrigation has/will fall prior to crop bolting (elongation), then you can calculate water driven Yield Potential. Once we know our Yield Potential, we can set a Yield Goal and by tracking moisture and its deviation from historical norms we can make better agronomic decisions.
Farmer Brown is a dryland grower who has a yield goal of 52 bu/ac on Grandpa’s field; because the spring soil samples to Agri-Trend Analytics, he knows there is 5.5" of crop available water in the soil. He also knows that his average growing season rainfall is 11.5” (most growers don’t know this number) and on June 15 (crop is fully cabbaged) he has already received 5.5" of this total, which is slightly ahead of schedule.
So that’s 5.5" (soil water) + 5.5" of precipitation for a total of 11 inches. The first 4" goes to the factory leaving 7" of yield creating water. On June 15, he knows he is already on track to grow 42-49 bu/ac canola with no more rain and there should be another 6” coming. If he was conservative and figured only 50% will fall during the remainder of the growing season, then he could confidently add 18-21 bu/ac yield potential to the total meaning he is now at 60-70 bu/ac. WOW!!
Knowing that he had a 60-70 bu/ac yield potential, now he can start making informed decisions. Like tissue sampling while scouting for pests to determine if nutrients are in short supply, relative to yield potential, and they likely will be. Then broadcasting or streaming on mobile nutrients like N, S, B, Cl while checking on what micros may need attention over the remainder of the season. Booking the fungicide as canopy density will be such that sclerotinia will be a concern.
A quick ROI calculation – To capture an additional 13 bu (staying very conservative) the crop may need an additional 39 lbs of N and 6 lbs of S. This will cost roughly $34/ac applied. Thirteen bushels of additional canola is worth $143, which is an ROI of 4.2 and there is opportunity for MUCH more.
If on this same farm, Grandma’s field, which is 9 miles away on sandier ground, only had 3" of soil crop available water and had received only 3.5" of an expected 11.5 inches, the Yield Potential, decisions and risk are far different. He may choose to re-allocate resources from Grandma’s field to Grandpa’s because of this. If Grandma’s field had irrigation, water should have been flowing yesterday.
So you see, water driven yield potential drives lots of decisions that can capture huge ROIs with just a little critical information and a really simple formula.
Now I can hear the chorus of “yah but” questions…how about runoff? How about evapotranspiration? How about topography? How about varietal differences? How about a bunch of stuff that the complex models have built in? And my answer is…wait for it…EXACTLY!! That’s exactly where we need to get but not yet. For now, let’s get started and figure out how to get into the Yield Stadium, section P for profit and a really good start toward NUE and ESE.
I’m also hearing other growers saying something like, “Elston, you just don’t understand, we always get too much rain. This whole concept simply does not work! Look, water drives yield especially when there is too much, our considerations/responses are different. In high rainfall environments/circumstances (they happen in dryland too), there is concern with leached nutrients, saturation, denitrification, increased disease pressure, etc., etc. AND if you think about it, is it always to wet in these environments? Every year, every season? Really? Why are ‘wet’ areas experiencing rapid irrigation development? Does soil NO3-N always leach and/or denitrify? Do you discount ENR (mineralized N) for the same reason?
So again, if Grandpa’s field has 5.5" of spring soil water in a high rainfall area, what does this tell us?? Watch out for leaching if the soil is prone. Soil sample deeper and don’t discount NO3-N every year/season. Connect weather to leaching potential, use tissue samples to confirm. Consider multiple applications, or use of control release forms of mobile nutrients such as Elemental Sulphur and ESN throughout the growing season. Watch out for denitrification and saturation, if soil texture does not allow leaching. Can we limit/eliminate saturation? Consider surface/tile drainage. Investigate the benefits of ripping to minimize ponding. Use carefully irrigation prior to/during wet periods.
Now consider the Grandma’s field scenario – different starting point with different soil requiring different management.
Here’s the kicker for the future. Where water driven yield potential meets the future is when it intersects with VR precision management. Many are beginning to utilize PowerZone to manage different parts of fields differently based on yield potentials supported by soil samples to depth, tissue analysis and VR nutrition, fungicide, etc. Precision management is the new norm. Water driven yield potential is foundational to wide adoption.
So, how do we start?
- Measure rainfall with a rain gauge or start playing with weather stations – they’re cheap, reliable and telematics is not usually the problem it used to be. Larger farms may need several stations. Agri-Trend’s Premium Weather provides accumulated rainfall plus the historical average.
- Determine crop available water in the soil either directly as described earlier or indirectly with moisture probes over the course of the growing season.
- Understand how your management practices may affect water use efficiency and constantly strive to improve. For instance, a direct seeder in Rolla, BC may use 3" for the factory while a tillage fiend in Havre, MT may use 4.5 inches.
- Use the simple formula to determine Water Driven Yield Potential realizing that the goal is to keep fine-tuning into the future. Fine-tuning can include any change in practice that keeps more water in the soil and available to the plant such as fertilizer practices that encourage roots to go deep and explore more volume or encourages seedlings to emerge quickly, creating a strong solar panel that reduces evaporation from the soil surface.
- Your Agri-Coach can help you improve your ROI by understanding your Water Driven Yield Potential and matching it with solid agronomic decisions.
Water Driven Yield Potential =
Soil Available Water +Observed Rainfall + Expected Rain/Irrigation – 4 in (the factory) X bu/In of Water
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