250-BUSHEL CORN USES ROUGHLY 128 POUNDS OF PHOSPHATE. 80-BUSHEL SOYBEANS ABSORB ABOUT 78 POUNDS. 90-BUSHEL WHEAT TAKES ABOUT 58 POUNDS. While you may say all the yields I just mentioned are higher than your field average, think about the very best spots on your farm. If your highest-yielding acres are pulling off lots of phosphorus, and your highest-yielding acres are probably making you good money, do you want to short those zones on fertility?

WHERE YOU PLACE IT IS WHERE IT STAYS, UNLESS YOU MOVE IT WITH TILLAGE. Laying phosphorus on the soil surface isn’t going to do this year’s crop much good. Worse yet, you could lose all your phosphorus that is surface-applied if there is soil erosion.

FOR EXAMPLE, WHEN CALCIUM BINDS WITH PHOSPHATE, IT FORMS CALCIUM PHOSPHATE, WHICH IS INSOLUBLE IN WATER. Keeping phosphorus available as long as possible is extremely helpful, which is part of the reason we talk so much about having soil pH in the 6’s as much as possible, since soil pH in the 8’s or the 5’s really restricts phosphorus availability.

If you go back to Mulder’s Chart that you may have learned about in college, if phosphorus levels in relation to zinc levels are excessive, you may get a lot of phosphorus into the plant, but zinc will be restricted, thereby hurting yield. This is just one example of why fertility balance is more important than simply looking at one nutrient alone without regard for anything else.

1. DON’T CUT BACK ON P IN YOUR HIGH-YIELD ZONES.

The place to potentially cut is in your low-yielding areas. Every lab and every type of soil test is a little different, not to mention how fields vary in terms of soil composition, rainfall, drainage, compaction, and other factors that affect nutrient availability. Therefore, I can’t give you a set number in terms of a critical level of P you shouldn’t drop below. I will, however, give you an example from our farm.
Normally on a Midwest Labs Mehlich 3 test, I want all my P levels to be above 100 ppm, as I am shooting for over 250-bushel corn and 80-bushel soybeans. While we certainly don’t get that all the time, I at least want 100 ppm so P is not my yield-limiting factor. However, if I’m only going for 200-bushel corn and if I’m concerned about how much I’m spending, 50 ppm is my drop-dead level for P on Mehlich 3 test. If we are below that, I feel like we’re in trouble. Therefore, let’s say it’s a year like this year when commodity prices are low and phosphorus prices are high. When I see zones that are above 100 ppm, there is no way I’m applying phosphorus there. On the other hand, even though P is expensive right now, if my level is below 50 I will still put phosphorus there because my odds for a good return on investment in those zones are high.

2. SINCE PHOSPHORUS IS IMMOBILE IN SOIL, BANDING IS A FAR MORE EFFICIENT WAY TO APPLY IT THAN BROADCASTING.

Don’t get me wrong. On ground we own, we love broadcasting. The problem is it could be a decade or more before you recover most of what you applied. I know that may sound crazy, but we once ran an 11-year study on our farm comparing roughly 500 acres of banded P to 500 acres of broadcast P. In all 11 years, we applied 50% more phosphorus in the broadcast than the band — 50%!!! You know how much yield that gained us? Zero! While we quit the study after 11 years, by about year 13 I could see that all that extra fertilizer in the broadcast fields was finally starting to pay off. Since we plan to farm our owned land for the next 40 years, I don’t mind investing for the long term, but there is no chance I want to do that for ground I may not farm in the near future. The reason why banding pays is two-fold. If you place immobile nutrients like P where crop roots will grow, the plants are more likely to find the phosphorus in the short term. Plus, having a concentrated band means it takes longer for the soil to tie up the phosphorus. Again, banding pays, but when I say banding you may just think about in-furrow. The challenge with applying excessive rates in-furrow is salt. Too much salt will hurt your crop, and the last thing you want is to spend money and have it cost you yield. If you want to go in-furrow keep your rate low, use a low-salt product and add water to better spread the fertilizer/salt through the seed trench. If you want to band higher rates, we suggest using deep-applied fertilizer with strip-till, but 2 X 2 is an option, as well.

3. WHILE THERE ARE MANY RATIOS TO CONSIDER IF YOU WANT TO KEEP SOIL FERTILITY IN BALANCE, HERE ARE TWO THAT HAVE MADE A HUGE DIFFERENCE FOR US AND THE FARMERS WE WORK WITH WHO STUDY THESE THINGS CLOSELY — P:ZN AND P:CU.

Again, each lab and each test you run could lead you to a different conclusion, but with a Midwest Labs Mehlich 3 test, we’ve found the best ratios for phosphorus to zinc are around 8 to 1 or 10 to 1, and with copper it is somewhere in the ballpark of 30 to 1. You don’t have to be exact, but we’ve found you also can’t be dramatically off these ranges. For example, when the phosphorus parts per million to zinc parts per million is 100 to 1 or 2 to 1, neither is great.

Think about it this way. If you are still applying the same rate of phosphorus across every acre without looking at your soil test levels for P, Zn, or Cu, the phosphorus you spread could actually be HURTING your yield instead of helping, since you may already have more P than you need for yield AND you may make an already bad P:Zn or P:Cu ratio even worse.

Our suggestion for you is NOT to cut phosphorus across the board. Instead, do it scientifically. Cut where you have an excess. Cut where yields are low. Cut where your P:Zn or P:Cu is already way too high. Never (or at least almost never) cut where yields are fantastic and P levels are critically low.