The overall purpose of this research project is to provide demonstrations of and more information about practical alternative and sustainable cropping systems for farmers in Iowa. These cropping systems include oilseed, cereal, and perennial legume species uncommon to current Iowa crop rotation, which is primarily dependent on two species, corn and soybean. Improving farmer economic stability and reducing the negative ecological impacts of current Iowa farming practices are additional goals of this project. Three different crop rotations are being evaluated on an Iowa State University research farm. The first rotation (Rotation A) represents a corn-soybean system common to Iowa. The two other rotations represent alternatives to the common and include ‘third’ crops, double-cropping, and legume interseeding. In one alternative rotation (Rotation B), a corn crop will be succeeded by a double- crop of spring wheat and winter canola. In the other alternative rotation (Rotation C), corn will be succeeded by a double-crop of spring canola and winter wheat. The winter annual is planted shortly after the spring annual is harvested, thus providing ample time for the winter annual to establish and the best opportunity for winter survival. Red clover is then frost-seeded into the winter annual (canola or wheat) the following late winter/early spring. The red clover remains after harvest of the winter annual and over-winter into the following spring before being terminated for another corn crop completing the rotation. These latter two rotations ensure winter cover (in the form of a winter annual or perennial legume) in two of the three winters in each rotation. Moreover, these alternative rotations include three cash crops (corn, canola, and wheat) as well as a green manure legume crop (red clover) that may also increase farmer profitability by reducing farm input costs incurred by pest control and fertility requirements. The reduced reliance on these inputs may play a role in reducing the ecological footprint of farming practices. Furthermore, the increased winter cover can serve to reduce system leakages contributing to farm ecological footprint in the form of soil erosion and nutrient leaching.
The typical Iowa corn-soybean rotation is detrimental to the ecological sustainability of
Iowa’s soils and agriculture. In this rotation 1) ?elds remain open during the winter, increasing
the potential for wind and water erosion of soil 2) soybeans host a number of pest management
problems reducing pro?tability and 3) the crop rotation lacks plant diversity that could enhance
pest management. The purpose of this research project is to increase crop species diversity on
the Iowa farming landscape. This will be achieved by developing longer crop rotations that
include summer and winter annual species as well as perennial species. Oilseed crops such as
canola and cereal grains such as wheat exhibiting summer and winter annual life cycles as well
as perennial legumes such as red clover could possibly ?t into an Iowa crop rotation providing
growers with alternative options. Additionally, the inclusion of summer and winter annual crop
species in rotations increases the potential of economically viable double-cropping scenarios.
The inclusion of species with different life cycles such as these can also serve to improve
cropping systems by increasing the amount of ground cover throughout the year and help
disturb life cycles of problematic weed species. Incorporating multiple species into a crop
rotation may also improve yields of other crops such as corn and improve a farmer’s economic
stability, while at the same time reduce the ecological footprint as a result historical land
cultivation. The potential to reduce the amount of off-farm, synthetic inputs also exists when
longer, more diverse crop rotations that include legumes are employed. Before growers can
reap the bene?ts of alternative crop rotations, the ecological and economical viability of ‘third’
crops and double-cropping systems must be evaluated with a strong emphasis on making any
information as a result of this research readily available to growers.
The main objectives of this project are to:
1. increase the amount of information available to growers regarding canola as an alternative
oilseed or ‘third’ crop in Iowa;
2. increase the amount of information regarding winter canola, winter wheat, and red clover as
cover crops in Iowa;
3. assess the ecological and economical impact of the alternative cropping systems to be studied.
Ecological implications, such as entire-system fertility and mechanical input requirements among the rotations are being assessed. These implications will surely impact the financial competitiveness of the rotations. The diverse rotations generally require more passes through the field, yet costs of seed and fertility may in fact be greater in the conventional rotation making them more expensive. We continue to hypothesize that the reduction of synthetic fertilizer and weed control methods due to the inclusion of the alternative crops, compared to conventional cropping systems, will result in the economical competitiveness of rotations incorporating alternative crops.
The three-year ?eld experiments conducted on Iowa State University research farms will
be used to evaluate three different crop rotations. This research will be conducted as part of the
?eldwork required of Mr. Gailans’ PhD dissertation in the Graduate Program in Sustainable
Agriculture/Department of Agronomy at Iowa State University. Two of the rotations will utilize
alternative crops, double-cropping, and legume interseeding. The different rotations (Fig. 1) are
• 2yr rotation (Rotation A): a corn-soybean-corn rotation, a system common to Iowa farming operations.
• 3yr rotation (Rotation B): a corn-spring canola/winter wheat-red clover(frost-seeded in late winter)
• 3yr rotation (Rotation C): a corn-spring wheat/winter canola-red clover(frost-seeded in late winter)
All phases of each rotation will be present in each of the ?eld experiment years.
Data collection through all three years will include crop yields, oilseed oil content, nitrogen content of red clover biomass, weed density and biomass, and soil cover by living (green) plant material throughout the year. For the economic analysis, the information above will be used; additionally, the amount of time and cost for different field operations and inputs will be determined.
Crop and soil sampling
Spring regrowth aboveground biomass of red clover frost-seeded the previous year was determined by clipping shoot material at the ground level from three randomly located 0.25-m2 quadrats in plots just prior to chemical termination, and subsequent corn planting, on 2 May 2011, 23 April 2012, and 6 May 2013. Upon clipping of red clover, replicate samples were combined, dried at 60ºC for at least 4 d, and weighed. Carbon and nitrogen concentration of red clover biomass was determined by the Iowa State University Soil and Plant Analysis Laboratory. Yields of corn were determined from the central four rows (121 m2) of each plot using a combine and an on-board yield monitor. Yields of soybean were determined the same way from the central six rows (180 m2) of each plot. Yields of winter wheat and spring wheat were determined the same way from the central 24 rows (180 m2) of each plot. Yields of winter canola and spring canola were determined by hand-harvesting plants from three randomly located 0.25-m2 quadrats in each plot just prior to machine harvest. Upon hand-harvest of canola, replicate samples were combined, placed in paper bags, and air-dried for at least 5 d. After drying, canola seed was machine-threshed using a stationary research thresher and then hand-sieved and finally weighed. Yields of winter and spring wheat straw were determined by weighing bales harvested from entire plots. Yields were adjusted for moisture levels of 155 g kg-1 for corn, 130 g kg-1 for soybean, 130 g kg-1 for winter and spring wheat, 100 g kg-1 for winter and spring canola, and 110 g kg-1 for straw. End-of-season red clover aboveground biomass was determined in the same manner as spring regrowth on 26 Oct. 2010, 11 Nov. 2011, 9 Nov. 2012, and 10 Nov. 2013. Seed oil concentration of soybean was determined by calibrated near infrared spectroscopy at the Iowa State University Grain Quality Lab and seed oil concentration of winter and spring canola grain was determined in the same manner at the University of Minnesota in St. Paul, MN.
The concentration of soil NO3-N was determined at depths of 0 to 30 cm. Soil samples were collected from corn plots 20 to 30 d after planting when corn was 15 to 30 cm high (late-spring sample). A minimum of four cores was taken from each plot. These samples were used to determine if any supplemental N fertilizer should be applied to the corn as a side-dressing application.
Ambient weed density was determined in each plot by counting the number of emerged weeds from 10 randomly located 0.25-m2 quadrats in each plot. This occurred on 8 and 13 June 2011, 5 and 6 June 2012, and 11 and 20 June 2013. Weeds in spring canola, spring wheat, winter canola, and winter wheat plots were characterized as grasses and broadleaves, while weeds in corn and soybean plots were identified to the species level when possible.
Ambient weed biomass was determined in each plot around the time of final plot disturbance in the form of grain harvest or a killing frost in plots finishing the growing season in red clover. In corn plots, this occurred before grain harvest and on 30 Sept. 2011, 15 Oct. 2012, and 12 Oct. 2013. In soybean plots, this occurred before grain harvest and on 30 Sept. 2011, 19 Sept. 2012, and 29 Sept. 2013. In winter wheat and winter canola plots, this occurred before grain harvest on 5 July 2011, 19 June 2012, and 10 July 2013; and from stubble with established red clover on 11 Nov. 2011, 9 Nov. 2012, and 10 Nov. 2013. In spring canola and spring wheat plots this occurred before grain harvest on 20 July 2011, 12 July 2012, and 25 July 2013. This was determined by clipping all non-crop shoot material at the ground level from three randomly located 0.25-m2 quadrats in each plot. Upon clipping, replicate samples were combined, dried at 60ºC for at least 4 d, and weighed. In winter wheat, winter canola, spring wheat, and spring canola plots, weed shoot material collected before grain harvest was separated by species when possible prior to drying and weighing.
Ground cover sampling
To determine temporal patterns of living crop cover among the three crop rotation systems, the proportion of photosynthetically active radiation (PAR) intercepted by the crop canopies was measured approximately every two weeks throughout the growing season in each plot. Measurements were initiated in April at the time of winter crop green-up and continued until a killing frost in late October or early November. A 1 m quantum sensor bar (LI-COR Biosciences, Lincoln, NE) was used to measure below-canopy PAR transmission, and a LI-COR point quantum sensor was used to measure above-canopy PAR. Measurements were taken as 5 sec averages on sunny days between 10:00 and 14:00 h, with three measurements per plot at each sampling date. Proportion of living crop cover (LC) was calculated as the difference between the above-canopy PAR and below-canopy PAR divided by the above-canopy PAR. Values for LC were then averaged among crop rotation for analysis.
Crop yields, 2011-2013
Corn yields differed by year and rotation. In 2011, corn in in the 2yr rotation, Rotation A, (12.9 Mg/ha) out-yielded corn in both 3yr rotations, Rotations B and C (11.3 and 10.8 Mg/ha, respectively). In 2012, corn in Rotation A (8.4 Mg/ha) once again out-yieled corn from both Rotations B and C (6.2 and 6.4 Mg/ha, respectively). Central Iowa experienced extreme drought conditions in 2012 that substantially reduced corn yields. The average corn yield in 2012 in Boone County, where the experiment took place, was 9.4 Mg/ha, far below the 10-year average of 11.1 Mg/ha. In 2013, there was no difference in corn yield among the three rotations. Mean corn yield in 2013 was 7.6 Mg/ha. Corn yields in 2013 were once again below long-term average yields due to an excessively moist spring that delayed planting followed by yet another extreme drought period during the growing season. In 2013, corn in Rotations B and C required less applied nitrogen as dictated by soil tests conducted prior to side dressing fertilizer in June. Red clover in those rotations was adequately terminated prior to planting corn that year. The clover’s decomposition and consequent mineralization of nitrogen was likely concomitant with the corn’s needs.
Soybeans were only grown in the 2yr rotation, Rotation A. Yields differed by year. Soybean yields in Rotation A were 3.9, 3.1, and 2.8 Mg/ha in 2011, 2012, and 2013, respectively. As with corn, soybean yields were lower in 2012 and 2013 due to the adverse growing conditions noted above. The 10-year average soybean yield in Boone County is 3.3 Mg/ha.
Canola was only grown in the 3yr rotations, Rotations B and C. Spring canola was grown in Rotation B and winter canola was grown in Rotation C. Canola yields differed by year and rotation. Canola yields in Rotation B were 1.0, 0.1, and 0.2 Mg/ha in 2011, 2012, and 2013, respectively. Canola yields in Rotation C were 2.5, 1.6, and 1.6 Mg/ha in 2011, 2012, and 2013, respectively. In each year, winter canola (Rotation C) out-yielded spring canola (Rotation B). This is not all that surprising as fall-seeded, winter varieties have greater yield potential than spring-seeded varieties. Additionally, we did have difficulties establishing spring canola following corn in Rotation B. The heavy amount of corn residue left in the field following grain harvest provided a less than ideal seedbed for the spring canola thus negatively affecting germination and stand.
Wheat was only grown in the 3yr rotations, Rotations B and C. Winter canola was grown in Rotation B and spring wheat was grown in Rotation C. Wheat yields differed by rotation, but were consistent across years. Mean wheat yields were 3.2 Mg/ha for Rotation B and 2.1 Mg/ha for Rotation C. Winter wheat (Rotation B) consistently out-yielded spring wheat (Rotation C). As with canola, winter varieties have greater yield potential than spring varieties of wheat.
Oil concentration of soybean (Rotation A), spring canola (Rotation B), and winter canola (Rotation C) was assessed to calculate the oil content contribution of the oilseed crops in each of the rotations. Oil content is calculated as the product of grain yield and oil concentration. Oil content differed by year and rotation. Oil content in Rotations A and C (soybean and winter canola, respectively) were consistently greater than oil content in Rotation B (spring canola). On average oil content of soybean and winter canola was 0.8 kg/ha while oil content of spring canola was 0.2 kg/ha. The equivalent oil contents from Rotations A and C are resultant of the relatively greater soybean yield and the relatively greater seed oil concentration of winter canola. The low oil content of spring canola (Rotation B) is owing to the relatively low spring canola yields throughout the experimental period.
Red clover was only grown in Rotations B and C. In Rotation B, red clover was underseeded into winter wheat while in Rotation C, red clover was underseeded into winter canola. End of season aboveground biomass was assessed late in the year well after wheat and canola grain harvest but just before a hard freeze event. Aboveground biomass did not differ between the rotations but did differ by year. Mean end of season aboveground biomass was 2.4, 1.4, and 2.1 Mg/ha in 2011, 2012, and 2013, respectively. Nitrogen content provided to the rotations by the aboveground biomass was likewise similar between the rotations but differed by year. Mean end of season N content was 60, 30, and 43 kg N/ha in 2011, 2012, and 2013, respectively.
Aboveground spring regrowth of red clover seeded into winter wheat and winter canola the previous year was assessed prior to chemical termination and subsequent corn planting. As with fall biomass, spring biomass did not differ between rotations but did differ across years. Mean spring aboveground biomass was 1.4, 2.4, and 1.1 Mg/ha in 2011, 2012, and 2013, respectively. Nitrogen content provided to the rotations by the spring aboveground biomass was likewise similar between the rotations but differed by year. Mean end of season N content was 45, 82, and 33 kg N/ha in 2011, 2012, and 2013, respectively. The relatively lower biomass and N content of red clover in the fall of 2012 and spring of 2013 is likely due to the extreme drought conditions experienced during 2012 that affected the growth and productivity of all crops studied.
The number of weeds/m2 were assessed in each plot following corn and soybean emergence. At this point of the season, wheat and canola canopies were nearly fully established and corn and soybeans had received at least one herbicide pass at the time of planting. Weed density was affected by rotation but did not tend to differ by year. Weed density was always greater in Rotations B and C. On average, the weed density of the 2yr rotation, Rotation A, was 52 weeds/m2. Meanwhile, the average weed density of the 3y rotations, Rotations B and C, was 157 weeds/m2. Though not directly compared statistically, wheat and canola (both spring and winter varieties) consistently contained greater weed densities than any of the corn and soybean. This obviously resulted from the management decision to not treat any of the wheat or canola with herbicides. Winter canola contained less weeds than spring canola in 2011 (92 vs. 186 weeds/m2), but weed densities were similar in 2012 and 2013 (163 and 209 weeds/m2, respectively).
Weed biomass from each plot was assessed just prior to grain harvest of each crop. Weed biomass differed by year and was affected by rotation only in 2011. In that year, average weed biomass at harvest was 7.7 g/m2 in the 2yr rotation, Rotation A, and 56.0 g/m2 in the 3yr rotations, Rotations B and C. In 2012 and 2013, weed biomass did not differ among the rotations. Mean weed biomass at harvest across the rotations was 33.3 and 158.7 g/m2 in 2012 and 2013, respectively. Weed biomass tended to be greater in corn in Rotation A than corn in Rotations B and C. This may be a function of the spring-terminated red clover biomass in the corn in Rotations B and C acting as a mulch and helping to control weed pressure. Weed biomass at harvest in winter canola was less than at harvest in spring canola in 2011 (25 vs. 207 g/m2), but was similar in 2012 and 2013 (52 and 223 g/m2, respectively).
Ground cover, 2011-2013
We assessed the difference in duration of living crop cover among the three crop rotations by finding the time-integrated proportion of living crop cover data over the growing season. Time-integrated proportion of living ground cover was calculated by finding the area under the curve beginning 1 March and ending 30 November each growing season, which was before and after any crop growth was observed, respectively. The duration of living crop cover was always greatest in the 3yr rotations, Rotations B and C. This observation is owing to the greater diversity of crop life cycles in Rotations B and C compared to the 2yr rotation, Rotation A.
Educational & Outreach Activities
Results from this research are currently being prepared for Mr. Gailans’ PhD dissertation and eventual publication. Portions of the research results have been features of numerous radio, TV, and popular press interviews:
- Iowa Public Radio, 2011
- Radio Iowa, 2011
- WHO-TV, 2011
- Associated Press, 2011
- THonline.com, 2012
- Ames Tribune, 2012
- Iowa Farmer Today, 2013
- The Furrow, 2013
- Leopold Center for Sustainable Agriculture news briefs, 2011-2013
Results of the project have also been discussed at two farmer field days:
- Dave Keninger, Iowa Falls, IA, August 2010
- Paul Mugge, Cherokee, IA, September 2010
The alternative, 3yr rotations, Rotations B and C, posses the ability to produce equivalent corn yields and oil contents (from canola) to the conventional, 2y rotation, Rotation A. These results also stem from an overall reduction in synthetic, chemical inputs in terms of pesticides across the duration of a rotation. Indeed, mean rotation weed pressure in terms of density and biomass was less in Rotation A only in 2011 despite greater reliance on chemical control of weeds.
Rotations B and C, in addition to containing corn, contain spring-seeded and fall-seeded varieties of wheat and canola that mature and are harvested by mid-July in central Iowa. Their life cycles are such that the crop primarily grows in the fall (fall-seeded varieties) and spring (both varieties), thus creating a full canopy by mid-May in central Iowa. Furthermore, Rotations B and C contain red clover, a perennial legume species, that grows in the fall following harvest of winter wheat (Rotation B) and winter canola (Rotation C) and re-grows the following spring prior to chemical termination and subsequent corn planting. As such, red clover creates a full canopy by late-September in the fall and mid-April in the spring. Rotation A, on the other hand, contains only corn and soybean. These crops have similar life cycles–planted in the spring, creating full canopies by mid-July, and harvested in September (soybeans) and October (corn). As such, the ground in the spring and fall is either not covered or only partially covered in Rotation A. Therefore, no matter what time of year, Rotations B and C contain a crop or crops that are growing and/or covering the ground. This is important as a substantial amount of annual precipitation, approximately 52%, occurs in central Iowa between October and May. Growing, living crops capture water and nutrients that would otherwise be vulnerable to drainage and runoff. Thus, Rotations B and C, because of their greater duration of living crop cover, pose a greater potential relative to Rotation A to prevent any contamination of ground and surface waters by agricultural practices.
Over the course of the study, the 2yr rotation, Rotation A, appeared to out-perform the 3yr rotations, Rotations B and C, in an economic sense. In terms of financial return to land and management, Rotation A averaged $1,042/ha/yr while Rotations B and C averaged $288.92 and $369.73/ha/yr. Much of this disparity owed to the fact that corn, the most lucrative crop in the study, tended to perform best in Rotation A, thus gross revenues were greater. Also, as spring canola and spring wheat did not perform in the field as expected in terms of grain yield, returns to these enterprises were disappointing and on two occasions, a financial loss. Costs of production were slightly higher in Rotations B and C, generally due to more passes through the field with tillage and harvest equipment, and thus diesel fuel and labor required, than in Rotation A.
It should be noted, however, that Rotations B and C required far less herbicides than Rotation A. Over the course of the study, the mean amount of herbicides used in Rotation A was 3.1 kg a.i./ha/yr while in Rotations B and C was 1.2 kg a.i./ha/yr. This is owing to the necessity to treat soybeans two to three times annually with herbicides for weed control before soybeans can adequately canopy and out-compete weeds for sunlight, moisture, and nutrients. As mentioned above, we did not treat any of the wheat or canola with herbicides but instead relying on narrow rows and early-season crop growth to adequately compete with ambient weed pressure.
Both Dave Keninger and Paul Mugge began growing spring canola–Mr. Keninger in 2010 and Mr. Mugge in 2009. Mr. Keninger has since stopped growing canola while Mr. Mugge continues to do so. The primary reason for this is that Mr. Mugge’s farm is located within 10 miles of a canola oil processing facility while Mr. Keninger’s farm is roughly 140 miles from the facility.
Since the project began, and because of the various media coverage, Mr. Gailans and Dr. Wiedenhoeft have consistently received phone calls and emails from farmers inquiring about growing canola in Iowa, underseeding legumes (red clover) into small grains (wheat/oats), and growing corn after a small grain + legume green manure crop.
Continued farmer adoption of canola (and wheat) will be dependent on both adequate crop management information and viable markets.
Areas needing additional study
Producing higher-yielding canola (spring and winter) is necessary. Realizing where spring (and winter) canola best fits into a rotation is essential if wider-spread adoption is to be accomplished. Difficulties establishing spring canola following corn illustrate that this may not be the best phase of a crop rotation for spring canola. Perhaps following soybean would bring better spring canola yields as less residue is left in the field following soybean harvest to interfere with planting spring canola. Likewise, if winter canola could be preceded in rotation by a more productive and financially lucrative crop than spring wheat in Rotation C of this study, adoption would be all the more likely. A soybean variety that matures by early September in central Iowa could be the answer.
Ensuring winter survival of winter canola in central Iowa is another concern. During the course of our study, winter survival was poor-to-average in only one winter (2012-2013) due to a lack of moisture in the fall of 2012 and less than adequate snow cover during that winter. Snow cover protects the crowns of canola plants from ice and subzero air temperatures that can result in plant death. Seeding winter canola in the fall with a companion grass cover crop (e.g. oats) that would winterkill but also provide additional crop residue to help catch snow in the field may present a solution.
Adequately terminating red clover prior to planting corn in Rotations B and C presented a challenge in this project. We chose to use an herbicide cocktail to terminate the red clover, however, we did encounter less-than-ideal cool and wet periods when spraying the red clover that likely affected the herbicide activity and efficacy. We submit that inadequate termination of red clover resulted in competition with young corn seedlings and also may have failed to decompose and mineralize enough nitrogen for the corn. This may have been the reason for lower or equivalent yields in Rotaitons B and C to the corn in the 2yr rotation, Rotation A, rather than increased yields. Tilling or plowing spring red clover may be a solution to this challenge; however, terminating red clover via herbicide rather than tillage did provide the corn with a reside mulch that helped to manage weed pressure that corn in Rotation A was not a beneficiary of.
Finally, the exploration or markets for canola in Iowa is necessary. Either facilities that already specialize in processing of soybean (an oilseed crop) or the potential for on-farm energy production from canola (to power machinery and generators) could be pursued.