Effect of Tillage and Weed Control Alternatives on Crop Rotation

1988 Annual Report for LNC88-017

Project Type: Research and Education
Funds awarded in 1988: $40,000.00
Projected End Date: 12/31/1990
Region: North Central
State: Iowa
Project Coordinator:
Richard Cruse
Iowa State University

Effect of Tillage and Weed Control Alternatives on Crop Rotation


1) Determine the degree of weed control success obtained using different weed control strategies
for a corn-soybean-oats/alfalfa rotation managed with three different tillage systems.
2) Determine the effect of tillage systems on crop yields and legume N production in a
corn-soybean-oats/alfalfa rotation.
3) Determine the potential for small grain production with ridge tillage.
4) Evaluate the effect of nitrogen incorporation in the ridge and herbicide banding with ridge
tillage on subsurface drainage losses of nitrate and herbicides.

1) At the McNay Research Center, the experiment was a split-split plot design in four

completely randomized blocks. The plots consisted of tillage treatment (no tillage, fall plow,
spring disk). The subplots were weed management strategies (broadcast, banding, and no
herbicide in corn and soybeans). The oats/alfalfa crop received no weed control.
Corn-soybeans-oats/alfalfa was the three year rotation.
2) Nitrogen production from the 1988 legume was to be evaluated in 1989, however hot and dry
conditions in 1988 resulted in essentially no legume establishment for that year.
3) Oat yield on ridges was evaluated on two farms. Production was measured at various
positions on the ridge or in the furrow, and in 1989, oat yields for ridge tillage versus flat tillage
was evaluated. The field strip layout was that of a randomized block with 10 replications and
was part of a larger strip intercropping trial.
4) Sixteen plots were used in a field study, with half of the plots under ridge-tilled conditions
and half under chisel-plow conditions. Broadcast applications of atrazine, dye, bromide, and
nitrogen were made to half of the plots, while the other plots received band application of
atrazine and dye and point-injection of bromide and nitrogen. Each plot received 10 cm total of
simulated rainfall, and the drainage water was collected from nearly horizontal holes over a
corrugated drainage sheets. Samples were analyzed for the appropriate chemical to detect any
significant differences in water quality and chemical losses between methods.

The first two objectives of this project were based on a three year crop rotation. Year 1 (1988)
was the establishment year, 1989 was the first year in the rotation for data collection (and
unfortunately was an extremely dry year), and 1990 the project was not financially supported.
Results for the first two objectives are based primarily on data from the set-up year and the
drought year of 1989.

1) Under dry conditions, no-tillage conserved sufficient soil water to make significant
differences in yields of all crops in the three crop rotation. Tillage had a greater effect than did
the method of using herbicides for weed control. While early weed populations were reduced
with herbicide applications, those occurring after cultivation had little reflection on the herbicide
2) The results from this project indicate that oat production on ridges is feasible, however, yield
advantages were not found over those occurring with flat surface configuration. Ridge
precultivation seems a suitable management practice to help small grain establishment, although
this practice was not rigorously tested against other alternatives. Straw yield was lower on the
ridged areas, which is due, at least in part, to straw in the furrows being physical inaccessible to
the cutter bar during harvest. Producing small grains on ridges seems appropriate, particularly
for the farmer wishing to maintain the ridge configuration for the next year's row crop. Because
oat yields were very high on the ridge peaks and low in the furrows, planting schemes which
concentrate small grains on the ridges and possible legumes in the furrows seems very
3) Using annual alfalfa as a source of fixed nitrogen does not seem appropriate. Seed costs,
establishment inconsistency (particularly under dry conditions), and over winter survival are
disadvantages of using alfalfa for strictly N fixing purposes.
4) Surface configuration, i.e., ridge tillage vs. flat tillage, seems to affect movement of selected
chemicals through the soil profile. Higher infiltration rates occurring with ridge tillage seems to
increase losses of atrazine in drainage water compared to that found with chisel plowing.
Nitrate concentration in the drainage water was lower with ridge tillage, again possibly due to
greater infiltration of water. This data further suggests that banding of herbicides with ridge
tillage is environmentally beneficial. This fits with other data indicating that banding of
herbicides with ridges is more than adequate to control weeds. Broadcast applications were
particularly susceptible to drainage losses. Fortunately, this weed control management is not
normally necessary for ridge tillage systems.