“Mine”ding your Phosphorus

03 Apr 2017, Posted by Kevin Thompson in Archived

So we asked Kevin to do up a blog for the website.  He decided after pouring over soil tests all winter that this was a recurring theme.  Yes TJ did the same topic a couple of years ago when we were on a blog roll.  (This is not a coincidence, again this is from going through our customers soil tests.)  Have a read.

Yields have come a long way in my lifetime…. Wheat from 40 bu/ac and canola from low 20s up to averages of 52 and 41 respectively in 2016. Lots has changed in 27 years! But, what about phosphate? In MB close to half of all fields are testing low to very low, less than 10ppm, and trending in the wrong direction. Our P fertilization practices haven’t changed since MAFRD came out with recommendations in the early 90’s!

Times have changed.  There are several reasons to the decline in our soil test P levels.

  1. Growing crops that use more P, yet are more sensitive to seed-placed P(canola, soybeans instead of cereals)
  2. A shift to drills with a smaller seedbed utilization
  3. Growers farming more non-owned land
  4. Most importantly…… Bigger Yields!

These low soil test levels pose a problem not only for future generations but it affects your bottom line today. Crops need both a solid P base and proper fertilization to achieve maximum yield. A soil with 15ppm will out yield a soil with 5ppm regardless of added fertilizer!

The table below shows typical phosphorus fertilizer application for provincial wide average yields and the resulting deficit.

Yield Lbs  P205 removed Applied Net P205
Wheat 55 36 30 -6
Canola 40 45 25 -20
Soybeans 40 35 20* -15
Net -41

*some growers aren’t applying any P on soybean crops.

Keep in mind these are removal rates only, and when setting yield targets we should be using soil test data along with total uptake numbers to be sure we are meeting the crops needs.  Also, these are pretty modest yield goals for our area. So, if you have canola yielding 60bu/ac you are removing 68 lbs P205!

So, where do we go from here? We already have low P, and we’re growing bigger crops than ever. How do we increase our P levels? Unfortunately, the only answer is more fertilizer, applied away from the seed either through a SB, MRB, or broadcast. It will take some time to get back up to the magical 15ppm. It can take as much as 40 lbs of P205 to move soil test levels by 1 ppm, so, economically it can be impossible. But if we can focus on zones within the field that need it, we will ensure we are not only make economical decisions, but environmental ones as well. And as we near that magical 15ppm, we will grow better crops and ensure the land will produce for many years to come.