northeastern Ohio | barsfarm - 6/24/2015 20:10
As a fellow Minnesotan I believe U of M article is good but leave that to us because I do think bean yields over 70 bushels nitrogen starts to become a late season limiting nutrient. Research Missouri high yielding soybeans like Kip Cullers (just read over all the snake oils). HIGH HIGH YIELDS do need some extra N but <60 dont worry about it.
My $.025 cents
Tim,
You are right that high yield beans require a lot of nitrogen. As JimmyP mentioned above, it is about 5# per bushel. So, 70 bushel beans need about 350# of N. Rhizobia can produce between 250 and 350 pounds of N, depending on the strain of rhizobia as well as the environmental conditions. If there are no other limiting factors, you could add 50# of N and get them to yield 80 bushel. Unfortunately, there is usually another limiting factor beside N that is keeping the yield at 70 bu.
But lets look at the economics of adding 50# of N to gain 10 bushel. 114# of urea would contain 50# of N and should cost around $23. If that simple addition of N would boost the yield by 10 bushel, the plant would also remove 8# of phosphate and 14# of potash (and many micro's) to produce that 10 bushel. So total cost of NPK would be about $43 plus the cost of application. I'm not going to break down the cost of all the nutrients removed, but 10 bushel would also remove about 2 pounds of calcium, 2 pounds of sulfur, and 2 pounds of Mg. So there is some additional cost there, but not significant.
Lets say the total cost is around $50 total with application. Current price of soybeans is around $10, so you could double your money IF the gain is 10 bushel. But unfortunately, the research that I've seen would show a 2 to 3 bushel gain (on average) with the added nutrients. The P, K, CA, and Mg would stick around for next years crop, so you don't really lose those. But the N and S would be lost and there would be no net gain in profit.
I've had beans average 90 bushel with no addition of N fertilizer. Of course the N had to come from somewhere. It was either from the rhizobia or from mineralization of residual N that was already in the soil. And all other nutrients had to be there as not to be the limiting factor.
Conclusion: If someone can consistently get a bushel of beans for each 5 pound of added N, then adding N would be profitable. 1/2 bushel per 5 pound of N is breakeven. 1/4 bushel is losing money.
Edited by Jay NE Ohio 6/26/2015 06:45
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Soybean nodulation
