Agriculture Reference
In-Depth Information
and Sadeghi, 1995; Lyons et al., 1996; Shipitalo and Edwards, 1998). Herbicide resistance
could cause farmers to revert to using tillage as weed control, thereby potentially undoing
soil and water quality improvements made with no-till systems. In a study by Krutz et
al. (2009), the authors evaluated the impact of cover crops and tillage on water, sediment,
and herbicide loss in glyphosate-resistant cropping systems. Their results indicated that a
rye cover crop (see Section 7.3) established in fields requiring tillage for weed control can
potentially limit water, sediment, and preemergence herbicide losses to levels equivalent
to or less than those of no-till.
“Standard no-till” with herbicides is not an option in organic production systems. To
reduce frequency or intensity of tillage in organic systems, many farmers are exploring
the option of terminating a cover crop mechanically by mowing, undercutting, or rolling
instead of plowing. While plowing incorporates the cover crop into the soil, leaving it bare
as a result, mowing, undercutting, and rolling all keep the cover crop on the surface to
act as a weed-suppressing and moisture-conserving mulch. Flail mowing is usually the
preferred method of cover crop mowing. It cuts low, right above ground level, and leaves
an even layer of residue. Undercutting terminates a cover crop with sweeps or blades that
travel just below the soil surface, cutting the plants below the crowns. Rolling is performed
using a rolling drum with blunted blades that terminate the cover crop by rolling it into
a mat without cutting the stems. Both undercutting and rolling keep the plants more or
less intact and in place, thereby reducing decomposition rates and increasing the time the
mulch stays on the soil surface and works to suppress weeds. Mowing chops the plant
biomass into small pieces, increasing the surface area and the rate at which the cover crop
breaks down. Cover crops are already a common feature of organic systems and fulfill
numerous functions (see Section 7.3).
Recent field trials examining the effectiveness of the roller as a mechanical termina-
tion technique showed promising results. Cover crop rollers can successfully terminate
annual crops, including cereal grains (rye, wheat, oats, and barley) and annual legumes
(hairy vetch, winter pea, and crimson clover) without the use of any herbicides (Ashford
and Reeves, 2003; Mirsky et al., 2009; Mischler et al., 2010). Although much of the inter-
est for the roller comes from organic producers, it can also be used in conventional sys-
tems: Some studies have shown that the roller-crimper in combination with a burndown
herbicide, such as glyphosate, can both increase the effectiveness of cover crop control
and reduce the rate of herbicides needed to kill the cover crop (Ashford and Reeves, 2003;
Curran et al., 2007).
Another advantage of the roller is the fairly small amount of energy required to oper-
ate it. Fuel need for the roller is similar to a cultipacker (a corrugated roller that is usu-
ally used as the last step in seedbed preparation to break up clods and firm the soil) and
10 times less than the energy required for mowing (Hunt, 1977, as cited in Ashford and
Reeves, 2003). In an organic system, rolling a cover crop before soybeans can save farm-
ers up to 5 gallons of fuel per acre by reducing tillage operations (Mutch, 2004), and when
averaged over a 3-year corn-soybean-wheat rotation, no-till planting with a roller uses 25%
less energy than traditional field operations for organic crops (Ryan et al., 2009).
Yield results and weed suppression for the roller-crimper system are also promis-
ing. In a field trial in Illinois, no-till soybeans grown after rye termination with a roller
achieved similar yields to those in a chemically terminated cover crop while reducing
residual weed biomass (Davis, 2010). Smith et al. (2011) conducted a field trial in North
Carolina in which soybeans were no-till planted into a rolled or flail-mowed rye cover
crop. Both treatments controlled weeds in the soybeans sufficiently (no herbicides were
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