Hello to all...
Dr. Weil's recent reference to the energy efficiency of no-till systems
prompted me to
get out my copy of "Crop Ecology" by Loomis and Connor. On pages 404 and
405, Loomis and Connor present a table of the energy costs of a wide array
of field operations as well as embodied energy costs of agricultural inputs.
The embodied energy costs of paraquat and glyphosate (roundup) are listed
as 460 MJ/kg (Megajoules/kilogram) and 450 MJ/kg.
My understanding is that both paraquat and roundup are typically applied at
rates > 1 kg of active ingredient/ha (~ 1 lb/acre) when used to burn down
weeds/cover crops prior to no-till planting.
Thus the energy cost of the burn down spray in no-till systems is often
greater than 450 MJ/kg.
To put this in perspective, the embodied cost of a single burndown spray
appears to be similiar to the energy costs of a primary tillage operation,
a secondary tillage operation and several cultivations all added together
(e.g. Loomis and Connor report that moldboard plowing medium textured soil
18 cm (7") deep has an energy cost of 210-370 MJ/ha).
When it all boils down however, the energy costs of tillage and herbicides
pale compared to the energy cost of N fertilizer. Loomis and Connor report
that N (NH3) fertilizer has an embodied energy cost of ~ 60 MJ/kg. A
typical application of 100 kg N/ha would have a total energy cost of 6000
MJ/ha !
Joel
BTW Why is the energy cost of producing a kg of paraquat/glyphosate so much
higher than the cost of producing a kg of N fertilizer ?
Joel Gruver
Visiting Faculty
Principia College
Elsah, Illinois 62028
(618) 374 - 5289
jgruver@principia.edu
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