Table 8. Amount of fertilizer nitrogen required for a
sufficiency level of 2.70% N in corn ear leaves.
 (Kg N/ha) FERTILIZER
COVER CROP MANAGEMENT NECESSARY FOR SUFFICIENCY
Crimson CT-Forage 144
clover CT-Green manure 91
 NT-Mulch 57
 NT-Forage 179
 Fallow (control) 119

Rye CT-Forage 143
 CT-Green manure 151
 NT-Mulch 170
 NT-Forage 230
 Fallow (control) 191


 Economically, the less N fertilizer required for the corn crop
to reach the 2.70% N sufficiency level6, the less cost for the
farmer to produce the crop. If we assume that the farmer must buy
the N fertilizer at $0.66 per kg, then, under the clover cover
crop, it costs this farmer $40.92/ha more to achieve the
sufficiency level required for a healthy crop under the control
(fallow) rather than no-tillage mulching of the clover. It would
cost that farmer $80.52 more to achieve the sufficiency level under
no-tillage forage rather than no-tillage mulch. Thus, no-tillage
mulch is the best management practice (BMP), assuming that the
farmer has no livestock to feed.

 If the farmer could not afford any N fertilizer when using a
clover cover crop then the BMP would be conventional-tillage green
manure. In this no added N situation, conventional-tillage green
manure provided 2.53% N concentration in the ear leaves, only 0.17%
less than the sufficiency level of 2.70% N6. Under conventional
tillage the cover crop (in the form of green manure) is immediately
exposed to the soil, releasing the organic N in the green manure to
the soil where micro-organisms can convert it into absorbable NO3.
Thus the N in the cover crop is maximized at the 0 kg N/ha level of
applied N fertilizer. However, only after 57 kg inorganic N/ha, at
a $37.62 cost to the farmer ($0.66 per kg N) the farmer would reach
the sufficiency level with less labor, conservation of land and
fuel (for plow, etc.), reduction of erosion, and increased
efficiency under no-tillage mulch. He would most likely earn that
$37.62 back with less wear on his plows and land, as well as less
labor for himself and field workers.

 Under the influence of the rye cover crop, the farmer must pay
$31.68 more to achieve the sufficiency level required for healthy
corn under the control (fallow) then under conventional-tillage
foraging of the rye. He would also receive the benefits of the
forage which he could sell off or use for his own livestock.
However, under a conventional-tillage system, he works harder than