Continuous corn cautions

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included. 

Lots of economic and agronomic factors are affecting Monroe County and area farmers’ decision regarding crop rotation and sequence for 2007 and perhaps into 2008 and even 2009. The corn marketplace has been telling farmers that it needs 10 million more acres, at trend yields, to provide enough supply for projected demand. Higher corn prices, relative to soybeans and wheat, means that farmers are generally going to plant more acres to corn this year.

Issues of corn on corn are not necessarily the same as continuous corn, which implies several years of monocropping. Briefly, here are some issues that farmers who are considering corn on corn and increased corn acreage need to be cognizant of as we enter the all-important spring planting season.

Crop residue issues

The good 2006 corn crop not only meant good yields, but lots of corn residue. One estimate is that 180 bushels of corn has left 10,000 pounds of corn residue. Long term studies at Purdue University have shown a yield “drag” for continuous corn of 3, 5 and 18 percent for moldboard plow, chisel plow and no-till systems respectively.

  • Crop residue harbors greater levels of disease inoculum.
  • Crop residue keeps soils cooler and wetter during or after planting.
  • Crop residue can interfere with planter row units.
  • Crop residue can decrease the efficacy of soil-applied herbicides.
  • Crop residue can keep soils wetter during or after harvest.

Nitrogen fertility issues

  • Most agronomists agree that optimum nitrogen fertilizer rates for corn following corn are higher than for corn following legumes (including soybeans) and range from 30 to 50 pounds of additional N required per acre.
  • Farmers who routinely sidedress most or all of their N fertilizer will require more days to complete this operation. Corn plant height limitations will limit traditional ground sidedress applicator tools.

Phosphorus and potassium fertility issues

  • Corn removes more soil phosphorus and less soil potassium than soybeans.
  • A one-time move to second year corn will have negligible effects on P and K soil fertility levels.

Stand establishment issues

  • High levels of corn residue in continuous corn cropping systems may translate into difficult corn establishment conditions, partly due to slow soil warming and drying of poorly drained soils.
  • High levels of trash can also interfere with furrow opening and closing functions of the corn planter.
  • Not only can germination and emergence be delayed or uneven, but so can initial seedling development. Delayed stand establishment lengthens the potential period of seedling exposure to insects and diseases.

Insect, weed and disease issues

  • Western corn rootworm was prevalent in isolated fields in 2006.
  • European corn borers overwinter in corn residue anyway.
  • Seedling insects such as wireworms, seedcorn maggots, white grubs and slugs may all be problems, particularly in heavy crop residue fields.
  • Gibberella stalk rot is the same host pathogen as head scab in wheat.
  • Gray leaf spot and Northern corn leaf blight are more common in corn following corn.
  • Higher crop residues will “capture” some herbicides. Furthermore, some weed species such as giant ragweed, burcucumber, waterhemp and crabgrass have relatively longer emergence periods, possibly requiring a two pass herbicide program.

Harvest season issues

  • Planting more acres to corn effectively lengthens the corn harvest season because of time and capacity demands on harvest machinery, drying facilities, transportation and storage.
  • Corn on corn means that some fields will be in the field longer and therefore under more standability pressure from insects and stalk diseases.

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