Winter Wheat Studies

1.  Winter Wheat Establishment Following Soybeans

J. Hall [1] , J.L. Posner [2] , T.A. Mulder[2]

Introduction

At the Lakeland Agriculture Complex, a WICST satellite experiment was designed to determine the best method for winter wheat establishment following soybeans.  In the WICST corn-soybean-wheat/red clover rotation (R3), the winter wheat is fall established during the same growing season the soybeans are in production.  The winter wheat can be planted either before or after soybean harvest.  If planted before soybean harvest, wheat seed must be broadcast on the soil surface.  Since ground driven broadcast equipment will damage the soybean plants, most farmers apply seed by airplane if using this seeding method.

Materials and Methods

Two varieties and four methods of wheat seeding were tested. The varieties chosen were Merrimac (lower yield potential but very winter hardy) and Cardinal (higher yield potential but less winter hardy).  Seeding times/methods were 1)broadcast at soybean leaf yellowing, 2)broadcast at soybean leaf drop, 3)broadcast after soybean harvest, and 4)no-till drilled after soybean harvest.  A four repetition, split-plot design was used with main plots (wheat varieties) 20 ft (8 30" soybean rows) by 210 ft.  Subplots (times/methods) were 10 x 210 ft for the drilled and 10 x 70 ft for the broadcast wheat.  Broadcasting was by hand, scattering wheat seed at the rate of 3 bu/a.  Drilling was with no-till drill at 3 bu/a.  Harvest was with a small plot harvester.  Harvest area was 5 x 70 ft.  Yield from the three harvested plots in each drilled wheat plot (10 x 210 ft) were averaged for comparison with the broadcast wheat treatments.

 Wheat planting dates are summarized in Table 17.  No measurements were taken in 1992 due to severe winterkill of all treatments.  Wheat agronomists estimate that 80% of the winter wheat stands in southern Wisconsin were lost that year (pers. comm. E. Oplinger).  Harvest of the 1992 and 1993 plantings took place on July 19, 1993 and July 28, 1994.

Results

1993.  Winter kill and a cold wet spring reduced 1993 winter wheat yields.  For both wheat varieties, wheat yield decreased as broadcast seeding was delayed and drilled wheat produced better than that broadcast after harvest.  Over all times/methods, Cardinal yielded higher than the Merrimac variety.  Combining varieties, yield was reduced significantly from 34 to 30 bu/A by delaying planting from soybean leaf yellowing to leaf drop and to 12 bu/A by waiting until after harvest.  Drilled wheat yielded 29 bu/A, which was not significantly different from broadcasting at leaf drop.

1994.  Wheat planting was slightly earlier in 1993 than 1992 and more importantly, winter weather was favorable.  Again in 1994, wheat yield decreased for both varieties as seeding was delayed.  Combining varieties, yield was lowest for the after harvest broadcast seeding while yields for the after harvest drilling and two before harvest broadcast seedings were not significantly different.  Over all times/methods Cardinal again yielded higher than the Merrimac variety.

Table 17.  Wheat planting dates and soybean planting dates and yield for the wheat establishment study at the Lakeland Agricultural Complex.

¹ Soybean variety Pioneer 9272
² Soybean variety Kaltenberg 241

Conclusions

Our strategy for wheat establishment on the WICST R3 rotation was changed from aerial seeding at leaf yellowing (T1) in 1990 and 1991 to drilling after harvest (T4) since 1992.  Prior to drilling a light tillage is done to level off the ridges and valleys formed by wide row soybean cultivation.  These ridges and valleys appeared to reduce wheat winter survival of the aerially seeded wheat.  Results from this satellite study show slight to no yield loss from the strategy change from aerial seeding to drilling and we feel that risk of winterkill is greatly reduced. On the main trials we have also changed varieties from Cardinal wheat to the winter hardy Glacier variety which has a higher yield potential than Merrimac. 

2.  Wheat Row Spacing

J. Posner and T. Mulder[2]

Introduction

Wise use of crop rotations can reduce purchased inputs and decrease soil erosion.  Legumes in a rotation can reduce requirements for purchased nitrogen and improve soil tilth.  Each crop has a role in the system and therefore the failure of one crop will negatively affect the entire system.  The challenge is to develop systems with low risk of a crop failure or a practical emergency strategy.

One of the Wisconsin Integrated Cropping System rotations is a three-year rotation of corn - soybeans/winter wheat - winter wheat/red clover.  One of the challenges of this rotation is frost seed establishment of a red clover crop with enough biomass to provide sufficient nitrogen for the following corn crop.  An emergency strategy is to plant hairy vetch following wheat harvest.  However, the hairy vetch seed is more expense than red clover and requires soil tillage and planting in July when rainfall often arrives by thundershowers with high erosion potential.  Are there ways to improve red clover production in this rotation without reducing the wheat yield?

Methods

A WICST satellite experiment was designed to determine if red clover establishment and production could be increased by increasing winter wheat row width.  Two varieties of winter wheat,  Glacier (bearded, very winter hardy) and Caldwell (beardless, less winter hardy) were planted in row widths of 7 and 10.5 inches, both at 30 seeds/ft² (1.6 bu/a) Sept 24,1992 and Oct 6,1993.  Arlington clover with added inoculum was frost seeded with a hand operated cyclone seeder at 12 lb/a April 2,1993 and 20 lb/a March 11,1994.  A check treatment was tilled and seeded with clover after wheat harvest.  All treatments received 50 lb/a N as ammonium nitrate at wheat green up.  Wheat was harvested Aug. 5,1993 and July 25,1994.  Wheat stand counts of grain producing stalks were taken after wheat heading, wheat grain and straw weights were collected at harvest, and red clover weights after a killing frost. 

Results

In 1993 both variety and row spacing had no significant effect on wheat plant stands .  Wheat stand appears to be lower for the wider row spacing in 1994, but the difference is not significant.  Grain yields were higher for the Caldwell variety in 1993 (71 vs. 59 bu/a) and higher for the more winter hardy Glacier variety in 1994 (61 vs. 45 bu/a) following the late fall 1993 planting.  In both years row width did not affect grain yield.  Straw yield was similar to grain yield with the Caldwell straw yield higher in 1993 and the Glacier higher in 1994.  Row width did not affect straw yield either year.  Clover yield was slightly higher in the 7-inch wheat row spacing in 1993 but in 1994 row spacing had no significant effect on clover growth.  Wheat variety did not affect clover growth either year.  Clover production was severely reduced by delaying planting until after wheat harvest.

Conclusion

We conclude that neither variety selection nor widening winter wheat row spacing are recommended practices for increasing Red Clover (and thus nitrogen) production for a following crop requiring high levels of nitrogen.  From our past experience it is clear that weather and soil conditions at and following frost seeding have the greatest effect on Red Clover growth.  Since we cannot control the weather, a grower's strategy should be to have an alternative plan if the clover stand is unacceptable.  One strategy is to plant a fast growing legume species after wheat harvest.  Wisconsin research by Stute and Posner (1993) has shown that Hairy Vetch is one legume species that if planted following an oat crop can provide nitrogen amounts comparable to an underseeded crop of Red Clover.

Reference

Stute, J.K. and J.L. Posner. 1993. Legume cover crop options for grain rotations in Wisconsin. Agron. J. 85:1128-1132

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