Water Quality Impacts of Cover Crop/Manure Management Systems
Kern, James Donald
- Publisher: Virginia Tech
water quality | manure | cover crop | injection
Crop production, soil system, water quality, and economic
impacts of four corn silage production systems were compared
through a field study including 16 plots (4 replications of
each treatment). Systems included a rye cover crop and
application of liquid dairy manure in the spring and fall.
The four management systems were: 1) traditional, 2) double-
crop, 3) roll-down, and 4) undercut. In the fourth system,
manure was applied below the soil surface during the
undercutting process. In all other systems, manure was
surface-applied. In the third system, the rye crop was
flattened with a heavy roller after manure application.
Simulated rainfall was applied within 48 h of manure
application. Measured constituent concentrations in runoff
were compared with water quality criteria. Costs and returns
of all systems were compared. The undercut system reduced
loadings of all nutrients, but increased total suspended
solids (TSS) concentration as compared with all other
systems. The mean volume of runoff from the undercut system
was less than half that from any other system, which
influenced all constituent loadings. Mean TSS concentration
in runoff from the undercut system was over three times the
mean of any other system. The roll-down system had no
significant effect on water quality as compared to the
traditional system. The undercut system was reasonably
effective in keeping phosphate phosphorus levels below the
criterion set for bathing water. None of the systems
generally exceeded nitrate nitrogen concentration criteria.
However, total phosphorus, orthophosphate, fecal coliform and
e. coli criteria for drinking, bathing, shellfish harvest,
and aesthetics were regularly exceeded by all of the systems.
There were no differences among the treatments in effects on
bacterial concentrations. The double-crop system produced
significantly higher net returns than all other systems only
if the value of the rye crop was $92.31/Mg or more. There
were no significant differences in net returns of the
traditional, roll-down, or undercut systems.