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Re: Erosion vs. herbicides



Rick:  corn is probably the most "unecological" field crop one could 
grow, in that:

a)  it is a warm season crop being grown in a cool season 
environment; this means slow seedling growth and delayed ground 
cover, which provides a niche in both space and time for weeds

b)  it is a wide row crop, which further delays attainment of full 
cover and a competitive canopy; this has very clear implications not 
simply for weed control but also for soil degradation/compaction and 
erosion because the soil surface is itself unprotected by the 
buffering effect of a crop canopy for weeks to months.

c)  it is very responsive/demanding of N and other nutrients, but is 
not a particularly good scavenger for N; this means that large 
amounts are needed to attain high yields, but N use efficiency is 
poor; I seem to recall a figure of 45-50% "capture" of applied N in 
grain - the rest is available for immobilization in the soil OM 
(unlikely, given the soil OM is being lost rather than gained in many 
places) or loss - through either gaseous or leaching routes

d)  because it is a full season crop, it tends to require timely 
spring seeding and harvest late in fall, when the soil may well be 
wet; some Ontario beef producers of my acquaintance no longer grow 
corn, specifically because they were obliged to do serious damage to 
their soil when harvesting in a wet fall; it is more common than one 
might think to see producers harvesting corn in February here, 
specifically because they couldn't get onto the land to harvest 
earlier, or because a late spring delayed planting and maturation.

e)  because it is a full season crop, manure application must be made 
before seeding or after harvest, which is to say, prior to meaningful 
nutrient sink capacity has developed and after crop nutrient demand 
is completed.  Thus, apart from the soil damage done from trying to 
apply and work in the manure under wet conditions, manure nutrients 
are not well utilized by the crop.

For these reasons, corn is not a common sight on organic farms in 
Ontario.  They prefer to get their carbohydrates from more 
ecologically "sound" crops, like small grains.  Ann
ACLARK@crop.uoguelph.ca
Dr. E. Ann Clark
Associate Professor
Crop Science
University of Guelph
Guelph, ON  N1G 2W1
Phone:  519-824-4120 Ext. 2508
FAX:  519 763-8933