Economic and Biological Benefits of Intercropping Berseem Clover with Oat in Corn-Soybean-Oat Rotations

Sustainability of Iowa agriculture may require change from predominantly a corn (Zea muys L.)-soybean [Glycine max (L.) Merr.] rotation to more diverse cropping systems. Alternative crops are vital for providing temporal diversity. Reincorporating small grains into a three-crop rotation with corn and soybean can provide greater temporal diversity, especially if a forage legume is included as a companion crop. A field study was established in 1991 on a Kenyon (fine-loamy, mixed, mesic Typic Mapludoll) soil to evaluate the economic and biological benefits of an oat (Avena sativa L.) crop under-seeded with berseem clover (Trifolium alexandrinum L.) in a three croprotation. Two rotation treatments were compared: (i) corn-soybean-oat and (ii) corn-soybean-oat intercropped with berseem clover. In 1992, 1993, 1994, and 1995, oat grain yield was not significantly changed when berseem clover was underseeded with the oat crop. However, in 5 yr, oat under-seeded with berseem clover produced up to 70% more biomass (harvested material without the grain) than sole-crop oat straw. The biomass (40% oat straw and 60% berseem clover forage) also had adequate digestible material (51%) to be considered as low quality forage. Berseem clover regrowth after oat grain harvest produced an average 1.2 tons/acre of forage, which could have been harvested for hay or left in the field as green manure. During this trial, berseem clover regrowth was left as groundcover and green manure, which contributed an average of 39 lb N/acre to the succeeding corn crop. Corn grain yields following berseem clover were 10% higher over the trial period. Soybean grain yields were the same for both treatments. Intercropping berseem clover with oat returned an average of %39/acre more than sole-crop oat. This study demonstrated both economic and biological advantages for more diverse cropping practices. Research QuestionAlternative crops are vital for providing diversity and enhancing sustainability. In Iowa, approximately 78% of the 27 million harvested acres are managed with an annual corn and soybean production. Inclusion of oat as third crop in rotations has been unpopular, largely because of low grain market value and the high year-to-year variability in grain yield. However, oat allows inclusion of a forage legume as a companion crop, which may improve profitability. The objectives of this study were to evaluate the economic and biological benefits of an oat crop underseeded with berseem clover in two crop-rotation systems. Literature SummaryIncreased corn and soybean production throughout the Midwest has decreased crop diversity, contributed to significant environmental problems, and limited opportunities to integrate livestock into the cropping system. Inclusion of an alternative small grain as a third crop can significantly improve soil productivity. Research in Minnesota indicated that total production increased when a small graidegume is added to a corn-soybean rotation. Legume cover crops may also contribute N to the subsequent crop, reducing the fertilizer requirement by 39 lb N/acre or more. Selecting an appropriate legume cover crop requires consideration of the characteristics and associations of the legume with a primary crop, management practices, and environmental factors. Berseem clover seeded as a companion crop, in contrast to traditional legumes, grows rapidly after seeding and responds very well to multiple cutting schedules and winter kills in Iowa. Study DescriptionA field experiment was conducted for 5 yr (1991 to 1995) at the Northeast Iowa Research Farm on a Kenyon soil. The experimental design was a split-plot with two whole plots (three-crop rotation) randomized within four blocks. Whole plots (Treatments I and II) included corn-soybean-oat. Each crop within Treatments I and II was grown in a 15 by 200 ft plot and rotated annually. The corn plot was then split into four 50-A subplots and four N rates (0, 50, 100, and 150 lb N/acre) were applied before the first cultivation. Grain yields, straw, and biomass were determined. In Treatment II, berseem clover was seeded with oat in the spring. At oat grain harvest, berseem clover biomass was separated fiom straw to determine quality and quantity of biomass. Berseem clover regrowth dry matter production was measured before the killing frost each year. Nitrogen concentration of the aboveground berseem cover crop was determined before snowfall. Response to N fertilizer rates was determined fiom corn both after sole-seeded oat and after oat underseeded with berseem clover. Regression equations were calculated and used to determine fertilizer replacement values for berseem clover cover crop. Applied QuestionsCan oat production in Iowa be improved by intercropping? Oat grain yields in 1992, 1993, 1994, and 1995 were not significantly different for sole-crop plots and those interseeded with berseem clover. In contrast, biomass (minus grain) production was 67, 150, 68, and 19% greater with berseem clover than without it from 1992 to 1995, respectively, at oat grain harvest. Feed quality of berseem clover forage and straw mix (oat straw 40% and berseem clover hay 60%) were higher than straw. Berseem clover also had approximately 1.2 ton/acre dry matter regrowth after oat grain harvest. Does intercropping berseem clover improve profitability? Intercropping berseem clover with oat returned an average of $39/acre more than sole-crop oat. Additionally, berseem clover regrowth after oat grain harvest may have duectly or indirectly enhanced the profitability of subsequent corn crop. Berseem clover's 1.2 ton/acre regrowth hay can add $75/acre to profit; however, haying results in less ground cover and limited N contribution. Keeping all of the berseem clover regrowth as ground cover and green manure will save at least $9/acre because of the N contribution (considering inexpensive anhydrous ammonia fertilizer and no application cost) to the succeeding crop. How does berseem clover perform as a cover crop? Most winter legume cover crops used in Iowa either delay planting or compete with the succeeding crop. However, berseem clover winter killed and presented no management obstacle the following spring. In the last 4 yr, berseem clover has shown favorable companionship with the oat crop and seems well adapted to the climatic conditions in Iowa. Berseem clover regrowth provided ground-cover until corn was no-till planted the following spring, reducing winter soil erosion. What effect did berseem clover have on yield of crops in the rotation? The three-crop rotation treatments, including berseem clover with oat, had no effect on soybean yield. However, grain yield was significantly higher for the corn following berseem clover cover crops than for corn following sole-crop oat. Weed control problems in the corn plots after berseem clover in 1994 resulted in relatively lower yield than in previous years. Did the cover crop contribute nitrogen to the succeeding corn crop? Higher corn yields following oat underseeded with berseem clover may be due to the N contribution of the legume cover. Determining N contribution of the cover crop is complex because of several confounding practices, such as potential nitrate leaching, tillage, and rate of decomposition of residues. Calculated potential N contributed by N content of the cover crop in the fall and estimated N fertilizer replacement value from response of the succeeding corn yield, indicate that a significant contribution of N by berseem clover occurred. In this study, the contribution averaged at least 39 lb N/acre.