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Crop rotation matters

There aren’t too many things that deliver 100% of the time. But one agronomic attribute that comes mighty close is that corn following soybeans will out-yield corn after corn, according to Dan Walters, soil scientist at the University of Nebraska-Lincoln.

The yield boost from rotation is substantial — especially in a drought.

In upper Midwest rotation trials, first-year corn outyielded continuous corn by 15%, and corn rotated annually enjoyed a 13% boost. Another study — a four-decade series of crop rotations at the University of Wisconsin’s Lancaster Agricultural Research Station — recorded a 10% drop in yield in second-year corn and an additional 5% to 7% reduction in third-year corn; then it leveled off, according to UW agronomist Joe Lauer.

You can’t buy yield back with high rates of nitrogen. The long-term trials showed a yield gain in continuous corn of just 0.9 bushel per acre per year after 200 pounds of applied nitrogen. In the extended rotations, applying 100 to 200 pounds of N increased corn yields
as much as 80% more — 1.4 to 1.6 bushels per acre per year.

Repeating challenges

Rotating crops impacts a wide array of factors, including:

  • disease pressure
  • populations of insects, including corn rootworm
  • weed management, as rotating crops may open up opportunities to rotate herbicide modes of action as well to control resistant weeds
  • residue buildup, which can interfere with consistent, uniform emergence
  • soil compaction, which can be aggravated by tillage and heavy equipment in corn or alleviated by deep-rooted crops like alfalfa or wheat
  • nitrogen tie-up, as microbes monopolize soil N supplies to fuel the breakdown of crop residue
  • balance in the soil microbial community

“What’s good for the soil will ultimately be good for the pocketbook,” notes Lauer.

Decreased long-run economics

A 2007-2011 study by economists at the Illinois Farm Business Farm Management Association, or FBFM, demonstrated that intensifying corn production when corn prices are high didn’t add much to profits. Higher seed and fertilizer costs, greater fuel and machinery needs, and yield drag in continuous corn sucked the extra return out of the extra corn acres and pulled it down much closer to the profitability of corn-soybean rotations.

University of Illinois agricultural economist Gary Schnitkey drew the same conclusions from his comparison of returns from continuous corn vs. various rotations.

“Adding more corn to a one-half corn/one-half soybean rotation often increases short-run returns and decreases long-run returns,” he explains.

Corn returns have higher variability than soybean returns do, Schnitkey explains, so adding corn acres increases risk. When he evaluated rotations through the University of Illinois’ Planting Decision Model in 2011, Schnitkey found that corn after soybeans had a return of $559 per acre, while corn after corn returned $491 per acre.

That corn-after-corn profit is still more than the return on soybeans, but planting extra corn today means more acres will suffer the corn-after-corn yield lag in the future, dragging down profits in the long term.

“There’s no magic bullet out there that will solve all the problems in trying to boost yields,” says Lauer. “However, utilizing good crop rotations can play a key role in reducing some of the risk and in sustaining good yields over time.”


The high yield factor

Shifting to more acres of continuous corn may be advantageous for operations with particularly high corn yields, according to Gary Schnitkey, agricultural economist at the University of Illinois. To see if you fit in that category, divide corn yield by soybean yield. If the result equals more than 3.4, more intensive corn production could work for you. But any corn after corn adds uncertainty, as well as costs from yield drag, higher seed and fertilizer costs, and the need for additional machinery.


Yield map is road map to profit

That harvest map is still the basis for a lot of decision-making on your farm. Can it help you find yield-limiting factors? It all starts with making sure the data you collect is accurate across the field. Then, quality time with your agronomist can help you identify what’s keeping you from a top-yielding return.

Instead of a tutorial about cleaning up the yield map before review, check with your software provider for the steps you need to take to make sure the information you look at is correct. Then you can start looking at patterns. One tip to maximizing these maps is analyzing them as quickly as possible after harvest so any factors that caused yield troubles may be fresh in your mind.

The key to that colorful map is the patterns. Where do you see higher yields? Where do yields drop off?

Those patterns can be natural or man-made. The natural pattern will most likely appear as an irregular area and may be caused by soil-type changes, wet spots, pests or localized weather issues.

If you identify those bad spots and they’re not well-defined, a trip to the field is in order for some “ground-truthing,” where you can see just what might be happening. A review of soil and drainage maps will help, too.

Man-made problems will usually show up in straight lines or geometric shapes that have abrupt boundaries. If you use manure as a nutrient source and you see a sudden change in yield at the boundary of an application, you know the impact of that practice — good or bad. This is also a great way to spot hybrid or variety changes and how they fared, especially if the underlying soil type didn’t change.

Quick figuring

Here’s an interesting tip. Every yield map for a field has summary information — average yield, average moisture and total acres covered. Tracking those summaries across all your fields can give you a quick tally of total yield and yield per acre, and if you have an average price, you can get gross profit per acre pretty fast.

That yield map is a starting point, and sometimes some detective work is needed. You and your agronomist will find useful information in the changes across a field so you can keep improving.

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