Paul M. Porter

Organic and other management strategies with two- and four-year crop rotations in minnesota

are many reasons for this, among them the development of effective fertilizers and pesticides, government poliIn the USA, the corn (Zea mays L.)–soybean [Glycine max (L.) cies, and favorable economics. Interest in developing Merr.] rotation depends on high levels of external inputs. Few research data exist comparing conventional production practices with practices alternatives to the present agricultural system has arisen involving reduced external inputs and expanded rotations. Two trials from a number of environmental, economic, and social initiated in 1989 near Lamberton, MN, evaluated a 2-yr corn–soybean issues, including heightened concern over water quality, rotation and a 4-yr corn–soybean–oat (Avena sativa L.)/alfalfa (Medincreased reliance on government subsidies, and a conicago sativa L.)–alfalfa rotation under four management strategies. tinued decline in rural populations. The four management strategies were zero (ZI), low (LI), high (HI), Agricultural productivity gains since the 1950s reand organic (OI) inputs. One trial (V1) was on land with a history sulted from the development of farming systems that of no fertilizer and pesticide usage. The other trial (V2) was on land rely heavily on external inputs of energy and chemicals with a history of conventional fertilizer and pesticide usage. From to replace management and on-farm resources (Oberle, 1993 through 1999, average corn yield in the 2-yr HI strategy was 1994). Continuous rotation of corn and soybean cannot 8.96 Mg ha 1 in V1 and 8.72 Mg ha 1 in V2. Corn yield in the 4-yr HI strategy was 4% less than in the 2-yr HI strategy in V1, whereas be sustained without substantial additions of fertilizer in V2, the yields were not different. Soybean yield in the 2-yr HI and pesticides (Heichel, 1978; Pimentel et al., 1978). A strategy was 2.90 Mg ha 1 in V1 and 2.74 Mg ha 1 in V2. Soybean number of research studies have been conducted comyield in the 4-yr compared with the 2-yr HI strategy was 3% greater paring conventional corn–soybean production systems in V1 and 6% greater in V2. These results suggest soybean was more with low-input and organic production systems, includresponsive than corn to the expanded rotation length in the HI strating those by Chase and Duffy (1991) and Karlen et al. egy. Corn yield in the 4-yr OI strategy compared with the 2-yr HI (1995) in Iowa, Munn et al. (1998) in Ohio, Liebhardt strategy was 9% less in V1 and 7% less in V2 while soybean yield in et al. (1989) in Pennsylvania, Smolik and Dobbs (1991) the 4-yr OI strategy compared with the 2-yr HI strategy was 19% less and Smolik et al. (1995) in South Dakota, and Posner in V1 and 16% less in V2. These results suggest that yield of organically et al. (1995) and Mallory et al. (1998) in Wisconsin. produced soybean was reduced to a greater extent than that of organically produced corn relative to conventional production practices. By The economics of organic grain and soybean production comparing yields of the 2and 4-yr rotations for each management from several studies conducted by researchers at numerstrategy, this research documents the beneficial yield effects of the ous midwestern U.S. land-grant universities was reexpanded crop rotation, which can be masked by external inputs in ported by Welsh (1999). In summary, these studies rethe LI and HI treatments. ported a range of responses to low-input and organic production systems, from lower yields and economic returns to comparable yields and greater returns. C sequence in the midwestern USA has inIn 1989, two trials, titled the Variable Input Crop creasingly evolved to a greater reliance on the Management Systems (VICMS) trials, were initiated in corn–soybean rotation over the last half century. There Minnesota (Perillo et al., 1996). Each trial evaluated two rotation lengths and four management strategies. Rotation lengths included a 2-yr corn–soybean rotation P.M. Porter, Dep. of Agron. and Plant Genet., 1991 Buford Circle, Univ. of Minnesota, St. Paul, MN 55108-6026; D.R. Huggins, USDAand a 4-yr corn–soybean–oat/alfalfa–alfalfa rotation. ARS, 233 Johnson Hall, Pullman, WA 99164-6421; C.A. Perillo, Dep. The four management strategies compared were conof Crop and Soil Sci., Washington State Univ., Pullman, WA 99164ventional production, low purchased inputs, organic 6420; S.R. Quiring, Southwest Res. and Outreach Cent., Lamberton, production, and a system where fertility levels were not MN 56152; and R.K. Crookston, College of Biol. and Agric., Brigham Young Univ., 301 WIDB, PO Box 25250, Provo, UT 84602-5250. Abbreviations: HI, high purchased input(s); LI, low purchased inReceived 2 Oct. 2001. *Corresponding author (pporter@umn.edu). put(s); OI, organic input(s); SCN, soybean cyst nematode; ZI, zero input(s). Published in Agron. J. 95:233–244 (2003).

Innovative Education in Agroecology: Experiential Learning for a Sustainable Agriculture

The transdisciplinary field of agroecology provides a platform for experiential learning based on an expanded vision of research on sustainable farming and food systems and the application of results in creating effective learning landscapes for students. With increased recognition of limitations of fossil fuels, fresh water, and available farmland, educators are changing focus from strategies to reach maximum yields to those that feature resource use efficiency and resilience of production systems in a less benign climate. To help students deal with complexity and uncertainty and a wide range of biological and social dimensions of the food challenge, a whole-systems approach that involves life-cycle analysis and consideration of long-term impacts of systems is essential. Seven educational case studies in the Nordic Region and the U.S. Midwest demonstrate how educators can incorporate theory of the ecology of food systems with the action learning component needed to develop student potentials to create responsible change in society. New roles of agroecology instructors and students are described as they pursue a co-learning strategy to develop and apply technology to assure the productivity and security of future food systems.

Response of canola cultivars to Sclerotinia sclerotiorum in controlled and field environments

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, can be a devastating disease of canola (Brassica napus) in the northern United States. No canola cultivars are marketed as having resistance to SSR. Field trials were established in Red Lake Falls, MN (2001, 2003, and 2004) and Carrington, ND (2001, 2002, 2003, and 2004) to evaluate canola cultivars for resistance to SSR. These cultivars also were evaluated for resistance to SSR under controlled conditions using the following methods: petiole inoculation technique (PIT), detached leaf assay (DLA), and oxalic acid assay (OAA). Significant (P ≤ 0.05) differences were detected among cultivars for SSR and yield in the field trials, with SSR levels varying from low to high among years and locations. Cultivars with consistent high levels and low levels of SSR in the field trials were identified. Significant (P ≤ 0.05) differences were detected among cultivars for SSR using the PIT and OAA methods, but not the DLA method. No significant (P ≤ 0.05) correlations between SSR levels in the controlled studies with SSR levels in the field trials were detected; however, significant negative correlations were detected between SSR area under the disease process curve values from the PIT method and yield from Carrington, ND in 2001 and 2002. Although the PIT and OAA methods differentiated cultivars, neither method was able to predict the reaction of cultivars to SSR in the field, indicating that field screening for SSR resistance is still critical for the development of resistant cultivars.

Soybean Cyst Nematode Population Development and Associated Soybean Yields of Resistant and Susceptible Cultivars in Minnesota

The soybean cyst nematode (SCN), Heterodera glycines, is a major soybean yield-limiting factor, and the use of resistant cultivars is one of the most effective means to manage the nematode. During the past decade, a number of resistant cultivars in maturity groups I and II have been developed and made available to growers. A total of 47 resistant cultivars and nine susceptible cultivars were evaluated at 15 SCN-infested field sites and two noninfested sites during 1996 to 1998 in Minnesota. As expected, more nematodes developed on susceptible cultivars than on resistant cultivars. Egg density on susceptible cultivars increased by 1.9- to 10.6-fold during the growing season at 12 sites and did not change at the other three sites. Average egg density decreased over time for resistant cultivars at all sites, except where the initial egg density was low (≤455 eggs per 100 cm3 soil). Nematode reproduction factors (Rf = egg density at harvest/egg density at planting) for individual resistant and susceptible cultivars were highly consistent across the eight sites where initial SCN density was more than 1,000 eggs per 100 cm3 soil. Resistance, however, varied among the cultivars, with the average Rf of individual resistant cultivars across the sites ranging from 0.3 to 1.7. Resistant cultivars produced an average yield of 3,082 kg/ha compared with 2,497 kg/ha by susceptible cultivars at eight of 10 sites where egg density at planting was greater than 700 eggs per 100 cm3 soil. In contrast, no difference in yield was observed between resistant and susceptible cultivars at sites where egg density at planting was lower than 500 eggs per 100 cm3 soil. Yield differences between resistant and susceptible cultivars increased with increasing initial SCN egg density. In six fields infested with initial densities of more than 5,000 eggs per 100 cm3 soil, resistant cultivars produced 28.4% (676 kg/ha) more yield on average than susceptible cultivars. Soybean yield increased when cultivars with increasing resistance to the SCN (lower Rf or females formed on roots) were grown in fields infested with SCN. Average relative yield (yield of a cultivar/average yield of all resistant cultivars at a site) of individual resistant cultivars across all SCN-infested sites ranged from 0.76 to 1.10. Yield consistency of soybean cultivars was low among the different sites, indicating that many other factors affected yield. Our results suggest growing resistant cultivars is an effective method to manage SCN in Minnesota while minimizing yield loss due to SCN.

Impact of sclerotinia stem rot on yield of canola

Sclerotinia sclerotiorum is the causal agent of Sclerotinia stem rot (SSR) of canola (Brassica napus). In North Dakota, the leading canola producer in the United States, SSR is an endemic disease. In order to estimate the impact of this disease on canola yield, field experiments were conducted from 2000 to 2004 at several locations in North Dakota and Minnesota. Experimental plots were either inoculated with laboratory-produced ascospores or infected by naturally occurring inoculum in commercial fields. Applying fungicides at different concentrations and timings during the flowering period created epiphytotics of diverse intensities. Disease incidence was measured once prior to harvesting the crop on 50 to 100 plants per plot. Results of the study indicated that 0.5% of the potential yield (equivalent to 12.75 kg/ha) was lost for every unit percentage of SSR incidence (range of 0.18 to 0.96%). Considering the current cost of fungicide applications and the market value of this commodity, a 17% SSR incidence could cause losses similar to the cost of a fungicide application. Additional efforts are required to improve current levels of tolerance of canola plants to this pathogen.

Efficacy of Fungicides for Control of Sclerotinia Stem Rot of Canola

Sclerotinia stem rot (SSR), incited by Sclerotinia sclerotiorum, causes yield reductions to canola (Brassica napus) grown in North Dakota and Minnesota. Field trials were conducted in North Dakota and Minnesota from 2000 to 2004 to evaluate the effect of foliar fungicides on SSR and canola yield. Levels of SSR varied among years and location. In general, fungicides that consistently reduced SSR incidence compared with an untreated control were azoxystrobin, benomyl, boscalid, iprodione, prothioconazole, tebuconazole, thiophanate-methyl, trifloxystrobin, and vinclozolin. Significant reductions in SSR incidence with fungicides did not always translate into differences in canola yield, however. Inconsistent results were observed with different timings of applications based on percent bloom. This indicates that application timing should be based on factors in addition to percent bloom.

Comment on "Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass"

Tilman et al. (Reports, 8 December 2006, p. 1598) argued that low-input high-diversity grasslands can provide a substantial proportion of global energy needs. We contend that their conclusions are not substantiated by their experimental protocol. The authors understated the management inputs required to establish prairies, extrapolated globally from site-specific results, and presented potentially misleading energy accounting.

Ecology in Sustainable Agriculture Practices and Systems

Sustainable and productive agroecosystems must be developed that will meet todays needs for food and other products, as well as preserving the vital natural resource base that will allow future generations to meet their needs. To increase production efficiency, to improve farming strategies based on local resources, and to design systems that are resilient in the face of changing climate require thorough understanding of the ecology of agricultural systems. Organic and sustainable farmers have developed many production practices and integrated crop/animal systems that are finding application in more conventional farming enterprises. While they do seek greater resource use efficiency and substitution of more environmentally benign inputs to replace chemicals used in conventional farming, sustainable farmers increasingly depend on thoughtful redesign of production systems to provide internal management of soil fertility and pests, careful use of contemporary energy and rainfall, and reliance on internal resources rather than imported inputs. Evaluation of systems based on productivity, sustained economic return, viable environmental indicators, and equitable social consequences of agricultural production are central to future sustainable farming and food systems.

Open-Ended Cases in Agroecology: Farming and Food Systems in the Nordic Region and the US Midwest.

Abstract Our aim is to describe open-ended case studies for learning real-life problem solving skills, and relate this approach to conventional, closed-ended decision case studies. Teaching methods are open-ended cases in agroecology, an alternative to traditional strategies that lead students through prepared materials and structured discussions to determine an outcome already known to the instructor. Our method promotes a culture of curiosity. Multiple evaluation criteria show how this learning strategy provides students with practice in researching, envisioning and designing potential scenarios for clients in the field. In agroecology case studies, students and instructors are co-learners in a discovery process that includes gathering information from key clients, interviewing major stakeholders, and building an understanding of the current context of the local farming and food systems. Two agroecology courses in Norway, a field course in the US Midwest, and an experimental course in Sweden and Vietnam illustrate this learning strategy. Student evaluations of learning have been highly positive, and skills and methods from courses have been applied in their thesis projects and professional careers. Practical results reveal that students are well prepared for an uncertain, complex, multi-dimensional and dynamic future, have the capacity to develop alternative future scenarios, and have practiced methods to evaluate options based on production, economic, environmental and social criteria and impacts. This innovative strategy is offered as a complement or alternative to conventional decision case studies and evaluated as an approach to experiential learning, an important and effective method for adult learners.

Response of Soybean Insects to an Autumn-Seeded Rye Cover Crop

ABSTRACT We evaluated the hypothesis that the use of an autumn-seeded winter rye, Secale cereale L., cover crop in soybean, Glycine max (L.) Men., could lead to decreased insect pest pressure. We compared insect pest and natural enemy populations in an organic soybean production system with soybeans planted into an autumn-seeded rye cover crop (i.e., soybeans planted in spring into a rye cover crop that had been planted the previous autumn). Small-plot experiments were conducted at two locations in southwestern Minnesota to compare insect populations on soybean planted into fallow ground versus soybean planted into rye that was managed by mowing using three different techniques. Densities of potato leafhopper, Empoasca fabae (Harris), were significantly lower on soybean in all of the rye treatments compared with soybean without rye at both locations. Densities of soybean aphid, Aphis glycines Matsumura, were significantly lower on all of the treatments incorporating rye than the soybean-only treatment at one site, but the suppressive effect of rye depended on the specifics of rye planting at the other site. Densities of bean leaf beetle, Cerotoma trifurcata (Förster), were significantly lower in the rye plots than soybean-only plots at one of the two sites. Foliar-foraging insect predator densities did not differ significantly among treatments at either site. Soybean yields did not differ significantly among treatments at either location although there was a trend for lower yield in two of the rye treatments. A statewide survey also was conducted to compare A. glycines infestations in Minnesota soybean fields with and without a rye cover crop. The proportion of plants infested and infestation ratings were both significantly lower in soybean fields with rye than in those without.