Economics & Agronomics – Crop Management Decisions Need Both!

It’s an obvious statement to say successful farm management decisions need both agronomic and economic considerations. Farmers weigh out input cost versus the benefit to yield and quality of grain before making the decisions to buy and use new or additional products.

 Agronomy and economic crop management goes much beyond inputs. Consideration of crop rotation, Cost of Production, seeding date and weather indicators for disease all need to be considered. Within agronomic decisions there can be tools to estimate the economic impacts of different decisions. The ‘My Farm’, ‘Cost of Production’, ‘Canola Reseed Calculator’ and ‘Sclerotinia Treatment Decision Tool’ are all based on yield trends and agronomy to help make economic decisions easier.

See slideshow at

Submitted by Roy Arnott – Farm Business Management, Killarney and Anastasia Kubinec – Crops Branch, Carman.

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Why is My Corn Purple?

Several farmers will be noticing the incidence of purple corn in their fields.

Phosphorous Deficient Corn

P-deficient Corn. Note the purpling of the leaves.

Purple corn syndrome results from a number of stress factors.  The purple colour results from anthocyanin production in the leaves due to the accumulation of simple sugars.  The simple sugars build up in the plant because some other factor is limiting their further transformation or translocation in the plant.  Sometimes you will see the purpling at leaf tips of corn that are kinked by damage and the leaf can no longer transport or process the accumulating sugars resulting from the photosynthesis that is still occurring there. Many associate the purpling to reduced phosphorus nutrition of the plant.

Factors that can lead to reduced uptake of phosphorus – either due to lack of phosphorus (low testing soils, inadequate sidebanded application) or reduced rooting efficiency in taking up soil P (lack of mycorrhizae following canola,  root injury by toxic fertilizer bands, cold soils temperatures, dry soils, saturated soil, compaction, herbicide injury, insect feeding, etc).  And usually this is associated with adverse growing conditions – usually cold or saturated soils.

The crop usually “grows out” of this funk once weather and soils warm up and it is rarely seen beyond the V6 stage.  Some hybrids exhibit the purpling more than others.  This does not mean the other hybrids are any better at tolerating low P or cold conditions- they just hide their hurt better.  It would be negligent to shrug and chock it up to cold stress alone – consider whether you P fertilization practices, crop rotation or soil management are contributing to the syndrome,  then plan changes for 2015.

Submitted by: John Heard, MAFRD Crop Nutrition Specialist

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Should you plant corn after canola?

Planting corn after canola can result in corn being impacted by phosphorus deficiency, or what is commonly called “corn after canola syndrome”.  Phosphorus enters the corn plant through root hairs, root tips, and the outermost layers of root cells.  Beneficial fungi, called mycorrhizae, enhance P uptake in corn early in the season because the mycorrhizae strands increase the effective rooting volume of plants.  This is extremely important for uptake of immobile nutrients, such as P.

In corn, up to 80% of early season P uptake is by mycorrhizae since the strand network may extend 8-12 inches from root.  Crucifer plants, such as canola, sugarbeets, and mustard, are not hosts for mycorrhizae so the mycorrhizae must regrow from spores.  This is why early in the growing season you might see corn suffering from P deficiency.

Although the mycorrhizae eventually regrow and colonize the roots, the damage done by lack of P early in the growing season may have already occurred.  Yield may be impacted by the early season P deficiency, maturity of the crop may be delayed and grain moisture content at harvest may be higher (leading to higher drying costs).

How Common is Grain Corn Planted After Canola in Manitoba?

In Yield Manitoba 2014, Anastasia Kubinec (Provincial Oilseed Crops Specialist) updated her crop rotation tables based on information MASC contract holders provide to MASC.  These tables provide trends that can be used to help with crop rotation choices.  If we dig into the data from the 2008 to 2012 time period, 22% of the grain corn acres were planted into canola stubble.  In fact, it was the most popular choice for producers, followed by planting corn into soybeans (16%) and into spring wheat (10%).  So the data illustrates there are other factors producers look at when planning their grain corn crop rotations, and not necessarily the influence of beneficial fungi.

What is the potential impact to yield?

The same data source provides details on the yield response of those rotations (see Table 1 below).  Grain corn  yields are lower following canola than soybeans or spring wheat.

Table 1: Relative Yield Response (per cent of 2008-2012 average) of Manitoba crops sown on previous crops (stubble >120 acres)

Previous   Crop  Crop   Planted – Grain Corn 
Hard Red Spring Wheat 100
Winter Wheat 87
Barley 99
Oat 93
Canola 95
Soybean 103
Sunflower 99
Grain Corn 87
Yield (bu/ac)  95

The initial phosphorus uptake can be an issue but is this practice manageable?

To avoid ‘corn after canola syndrome’, producers should grow a crop less dependent on mycorrhizae for P uptake after canola (corn & flax are two of the most dependent crops).

If rotation requires corn after canola, a “Plan B” is to supply high starter P levels to try and overcome any P deficiency problems that might occur.

Variable results are seen with in-crop treatments to remedy phosphorous deficiency.   If products are tried, it is recommended to leave a check strip to determine effectiveness on crop recovery and yield.

For more information, please see the complete article by Anastasia in Yield Manitoba 2014 at:

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist

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Why Do Sunflowers Do Poorly After Canola?

We don’t know all the reasons that sunflowers seem to do so poorly after canola, but the most likely culprit  is sclerotinia.  Sclerotinia kills or greatly reduces sunflower yields in three ways, throughout the season – basal rot (early), mid-stalk (mid-summer) and head rot (late summer).  Canola is also a host for the disease and sclerots from a previous year infection would be present and germinating  in very close proximity to the sunflower plants.  This would provide prime opportunities to cause multiple plants to be infected at different times in a growing season.  Yields  reported to MASC (MB Agricultural Services Corp.) in the Harvest Acreage Reports from 1998 to 2007, show sunflowers after canola yielding 87% as compared to the overall average sunflowers yield.

Other issues contributing to the yield reduction may also include common insects between crop species grown in succession, herbicide carryover, soil moisture availability and nutrient availability. 

For more information on growing sunflowers see:

Specifically on Sclerotinia in sunflowers: 

Information on Re-cropping Restrictions for Residual Herbicides see the Guide to Field Crop Protection at:


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