WICST On-Farm Cover Crop Research

Tom Mulder and Norm Harris [1]

Introduction

The term "cover crop" describes an important use of crops grown to provide ground cover and protect the soil from erosion. Additional benefits of cover crops include providing nitrogen to a following crop, adding humus and organic matter to the soil, improving soil structure, collecting and temporarily storing potentially leachable nitrogen, and providing forage for cattle.

Previous small plot and on-farm cover crop research at the University of Wisconsin has compared various species of cover crops and cover crop establishment strategies. Areas of comparison reported in the Second through Fifth WICST Annual Reports have been 1) time to establish complete ground cover, 2) biomass and nitrogen production , and 3) effect on subsequent corn yields. This research has aided in the design of the WICST Cropping System 3 (corn-soybean-wheat\cover crop) rotation where a red clover cover crop is spring frost seeded into a winter wheat crop. A fall back in this system if the clover frost seeding is not successful, is to plant hairy vetch after wheat harvest.

Some farmer collaborators in past on-farm cover crop research noted their preference for summer establishment of a cover crop following the small grain rather than spring establishment of the cover crop where it grows under the small grain canopy. The reason for their preference was their desire to be able to sell clean straw uncontaminated by the green cover crops. Hairy vetch has been the cover crop species best suited to summer establishment. Two additional plant species recently introduced as summer seeded cover crops are berseem clover and annual medics. These species are both completely winterkilled at this latitude while the survival of the hairy vetch is determined by the severity of the winter. This difference may give an advantage to the berseem clover and annual medic in a minimum or no-till situation since there will be no potential for these crops to become weeds competing with the corn crop.

Field Activities

An on-farm trial was initiated the summer of 1995 on the Norm Harris Farm in Dane County to test the potential of these two new cover crops and compare them to hairy vetch. The cover crops were seeded August 14, 1995 after winter wheat grain and straw harvest. Seeding was later than desired because wet weather delayed straw harvest. Three one half acre areas seeded with 2 bu/a oats and the three cover crop species at the following rates: hairy vetch - 25 lb/a, berseem clover - 12 lb/a, and annual medics - 12 lb/a. Seeding with a double disk drill was preceded by one pass with a field cultivator and followed with a light harrowing. The 1995 field layout is shown in figure 1. An identical trial was initiated in 1996. In 1996 a field cultivator was used on August 5 but rain delayed seeding until August 8. The field was not harrowed. Looking back, we should have cultivated this field again, since later the weather turned very dry.

Three above ground oat and cover crop biomass samples (.5m x 1m each) were collected from each of the cover crop areas. These samples were weighed, dried, and brought to the UW soils laboratory for crude protein analysis. Following this harvest the entire field was chisel plowed. Cover crop seeding rates and yields for 1995 and 1996 seeding are shown in Table 1.

The cover crop areas were relocated the following spring and preplant anhydrous ammonia (82-0-0) was applied to all the field except the 30 foot wide strips shown in figure 1. Corn with 200 lb/a of a 5-26-30 starter was planted on May 7,1996. After corn planting, these 30 foot strips were again relocated and split into three ten foot wide repetitions. Each repetition contained five treatments of nitrogen additions (0, 40, 80, 120,160 lb/a) in the cover crop and one treatment in the no cover crop area with no added nitrogen. Plot size was 10 ft x 30 ft. Nitrogen in the ammonium nitrate form (33-0-0) was applied June 18 at 10 inch corn height. Weed control practices were post emergence applications of Harness on May 15 and Permit on June 13 followed by one between-row cultivation.

Corn was harvested October 24 and 25 by hand snapping the ears from 25 feet of the center two rows of each plot. Corn was shelled and moisture content was determined. Samples were also collected from nearby no cover crop areaswhich had received the preplant anhydrous. The yield from these samples as well as the no cover crop no nitrogen area would be used as benchmarks to measure possible differences caused by field variation rather than the cover crop species.

Results

Hairy vetch had highest fall above ground nitrogen production both years (Table 1). Both aboveground biomass and crude protein were highest for the hairy vetch. Germination and growth of cover crops were slowed by very dry late summer weather in 1996.

Table 1. Seeding rates and above ground biomass and nitrogen production of three cover crops on the Norm Harris farm

* each cover crop was seeded with 2 bu/a of oats
** seed costs were: hairy vetch - $.75/lb, annual medic - $2.00/lb, berseem clover - $1.05/lb.

Cover crops had similar impacts on corn yield. Although yield was lower for the corn following annual medics, non cover crop corn yields from this area were also lower. When comparing the average yields of corn following cover crops to corn without cover crops, ratios for each of the three cover crop areas of hairy vetch, annual medics and berseem clover were 1.00, 1.10, and 1.09, respectively. When averaging yield responses following the three cover crop species, an addition of 100 lb/a of sidedress nitrogen was required to equal corn yields without cover crops and 160 lb/a nitrogen.

Conclusion

Corn yield response to the cover crop nitrogen was less than expected given the amounts of above ground nitrogen in the fall harvested cover crops. Spring 1996 weather was wetter and cooler than normal and a possible explanation may be delayed nitrogen availability with slower than normal plant residue breakdown. Cover crop nitrogen production is dependent on planting date and weather, therefore it is important to develop a method to estimate the nitrogen replacement value of the cover crop. A mixture of compatible cover crops may both give quick ground cover and reduce the variation in growth caused by varied weather conditions. It is unlikely that any cover crop planted after July 31 in southern Wisconsin will alone be able to provide the entire nitrogen requirement of a corn crop.

1 WICST Project Manager, Agronomy Dept, UW- Madison; Farmer, Poynette, WI.

Home | Who we are | Research | Publications | Links | Site map | Contact us

University of Wisconsin-Madison
College of Agricultural and Life Sciences
If you have any difficulty accessing this page, please contact our web master.

Site hosted by UW-Madison Center for Integrated Agricultural Systems