Despite the use of best management practices for nitrogen (N) application rate and timing, significant losses of nitrate nitrogen (NO3(-)-N) in drainage discharge continue to occur from row crop cropping systems. Our objective was to determine whether a autumn-seeded winter rye (Secale cereale L.) cover crop following corn (Zea mays L.) would reduce NO3(-)-N losses through subsurface tile drainage in a corn-soybean [Glycine mar (L.) Merr.] cropping system in the northern Corn Belt (USA) in a moderately well-drained soil. Both phases of the corn-soybean rotation, with and without the winter rye cover crop following corn, were established in 1998 in a Normania clay loam (fine-loamy, mixed, mesic Aquic Haplustoll) soil at Lamberton, MN. Cover cropping did not affect subsequent soybean yield, but reduced drainage discharge, flow-weighted mean nitrate concentration (FWMNC), and NO3(-)-N loss relative to winter fallow, although the magnitude of the effect varied considerably with annual precipitation. Three-year average drainage discharge was lower with a winter rye cover crop than without (p = 0.06). Over three years, subsurface tile-drainage discharge was reduced 11% and NO3(-)-N loss was reduced 13% for a corn-soybean cropping system with a rye cover crop following corn than with no rye cover crop. We estimate that establishment of a winter rye cover crop after corn will be successful in one of four years in southwestern Minnesota. Cover cropping with rye has the potential to be an effective management tool for reducing NO3(-)-N loss from subsurface drainage discharge despite challenges to establishment and spring growth in the north-central USA.

There has been a trend toward narrower row width and an increase in plant population for corn (Zea mays L.) production in the northern Corn Belt. The impact of corn hybrid and plant population on grain yield may be influenced by row width. This study was designed to investigate the relationships between row width, plant population, and hybrid at three Minnesota locations from 1992 through 1994. At Lamberton and Waseca, row widths were 10, 20, and 30 in.; target populations were 25 000, 30 000, 35 000, and 40 000 plants/acre; and hybrids were Ciba ‘G4372,’ DeKalb ‘DK512,’ and Pioneer Brand ‘P3563’. At Morris, the same row widths were evaluated but the target populations were 22 000, 27 000, and 32 000 plants/acre and the hybrids were Northrup King ‘N3624,’ DeKalb ‘DK421,’ and Pioneer Brand ‘P3751’. At Lamberton and Waseca, the yield advantage for both 10‐ and 20‐in. rows compared with 30‐in. rows was 7.2% when averaged over all hybrids and all plant populations, whereas at Morris the yield advantage was 8.5%. Choice of hybrid influenced grain yield, and all hybrids responded similarly to change in row width and change in plant population at the three locations. Grain yields increased at Lamberton and Waseca with higher plant populations in 1992 and 1994, but not in 1993 when yields were limited by climatic conditions. Regression analysis of yield vs. harvest plant population showed yields were highest at populations at or above 35 000 plants/acre in 1992 at Lamberton and 1994 at Waseca and Lamberton, but were unaffected by plant populations in 1992 at Waseca and in 1993 at both locations. At Morris, regression analysis of yield vs. harvest plant population in 1993 and 1994 showed yields were highest at plant populations of 32 000 plants/acre, the highest plant population studied at that location. Choice of hybrid and the growing season climatic conditions had a greater effect on grain moisture content at harvest, test weight, and ear length than row width or plant population. These data show a yield advantage for narrowing row widths from 30 to 20 or 10 in., and that in some years maximum yields were obtained at harvest plant populations substantially higher than the current Minnesota population of 26 400 plants/acre. Research Question Most corn in the northern Corn Belt is grown in 30‐in. or wider row widths at populations ranging from 24 000 to 28 000 plantdacre. The trend has been toward narrower row widths and increasing plant populations. Some Minnesota producers want to match row width of corn and soybean with that of sugarbeet, which is typically grown in 22‐in. rows. This desire, coupled with improved genetics that have resulted in better standability and greater tolerance to higher plant populations in corn, necessitates a reevaluation of the relationship between row width, plant population, and corn hybrid. The objectives of this study were to: (i) determine whether current corn hybrids respond similarly to row width, and (ii) determine whether the response is affected by plant population. Literature Sum...

A winter rye (Secale cereale L.) cover crop can be seeded after corn (Zea mays L.) silage to mitigate some of the environmental concerns associated with corn silage production. Rye can be managed as a cover crop by chemical termination or harvested for forage. A field study was conducted in Morris, MN in 2008 and 2009 to determine the impact of killed vs. harvested rye cover crops on soil moisture and NO3–N, and to monitor the impact of the rye on subsequent corn yield. Corn for silage was seeded either after winter fallow (control), after a rye cover crop terminated 3 to 4 wk before corn planting (killed rye), or after a rye forage crop harvested no more than 2 d before corn planting (harvested rye). Soil moisture after killed rye was similar to the control, but after harvested rye was 16% lower. Available soil NO3–N was decreased after both killed rye (35%) and harvested rye (59%) compared to the control. Corn biomass yield after killed rye was similar to the control, but yield following harvested rye was reduced by 4.5 Mg ha−1 Total forage biomass yield (silage + rye) was similar for all treatments. This work demonstrates that the environmental benefits of a winter rye cover crop can be achieved without impacting corn yield, but the later termination required for rye forage production resulted in soil resource depletion and negatively impacted corn silage yield.

Farmers, industry, governments and environmental groups agree that it would be useful to manage transgenic crops producing insecticidal proteins to delay the evolution of resistance in target pests. The main strategy proposed for delaying resistance to Bacillus thuringiensis ( Bt) toxins in transgenic crops is the high-dose/refuge strategy. This strategy is based on the unverified assumption that resistance alleles are initially rare (<10(-3)). We used an F(2) screen on >1,200 isofemale lines of Ostrinia nubilalis Hübner (Lepidoptera: Crambidae) collected in France and the US corn belt during 1999-2001. In none of the isofemale lines did we detect alleles conferring resistance to Bt maize producing the Cry1Ab toxin. A Bayesian analysis of the data indicates that the frequency of resistance alleles in France was <9.20 x 10(-4) with 95% probability, and a detection probability of >80%. In the northern US corn belt, the frequency of resistance to Bt maize was <4.23 x 10(-4) with 95% probability, and a detection probability of >90%. Only 95 lines have been screened from the southern US corn belt, so these data are still inconclusive. These results suggest that resistance is probably rare enough in France and the northern US corn belt for the high-dose plus refuge strategy to delay resistance to Bt maize.

Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.], the backbone of Midwestern crop production, respond to rotation, but how growing conditions affect this is not well documented. Our objectives were to determine the effect of various corn and soybean cropping patterns on yields and to evaluate environmental effects on the rotation effect. The study began in 1981 at Lamberton, MN, on a Webster clay loam (fine-loamy, mixed, mesic Typic Endoaquoll), in 1982 at Waseca, MN, on a Nicollet clay loam (fine-loamy, mixed, mesic Aquic Hapludoll), and in 1983 at Arlington, WI, on a Plano silt loam (fine-silty, mixed, mesic Typic Argiudoll). Cropping sequences were (i) continuous monoculture of each crop; (it) annual rotation of the two crops; and (iii) I, 2, 3, 4, and 5 yr of each crop following 5 yr of the other crop. Results are based on II yr of data at Lamberton, 8 yr (soybean) or 9 yr (corn) at Waseca, 9 yr at Arlington. Corn rotated annually with soybean yielded 13% more, and Ist-yr corn following multiple years of soybean yielded 15 % more than continuous corn. Soybean annually rotated with corn yielded 10% more, and Ist-yr soybean following multiple years of corn yielded 18% more than continuoos soybean. The crops differed in response to increasing years of consecutive planting: 2nd-yr to 5th-yr corn yields were no different from continuous corn yields; 2nd-yr soybean yielded 8% more than continuous soybean, 3rd-yr soybean yielded 3% more, and 4th-and 5th-yr soybe.'in yielded the same as continuous soybean. Relative increase in yields of both crops in annual rotation compared with monoculture was approximately twofold greater in low-yielding than in high-yielding environments. In low-yielding environments, the yield advantage of an annual rotation of corn and soybean compared with monoculture was frequently greater than 25%. The commonly practiced annual rotation of corn and soybean maximized corn yields, but not soybean yields, relative to the other sequences studied.

are many reasons for this, among them the development of effective fertilizers and pesticides, government poli-In the USA, the corn (Zea mays L.)-soybean [Glycine max (L.) cies, and favorable economics. Interest in developingMerr.] 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 Ϫ1 in V1 and 8.72 Mg ha Ϫ1 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 Ϫ1 in V1 and 2.74 Mg ha Ϫ1 in V2. Soybean number of research studies have been conducted comyield in the 4-yr compared with the 2-yr HI strategy was 3% greaterparing 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. (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 egy. Corn yield in the 4-yr OI strategy compared with the 2-yr HIThe economics of organic grain and soybean production comparing yields of the 2-and 4-yr rotations for each management from several stud...

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 ABSTRACT 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.

lock, 1994), the ability to scavenge excess soil nitrate N and reduce nitrate leaching following corn (Staver and There is a need for improved soil and water conservation in the corn Brinsfield, 1998; Strock et al., 2004), weed suppression (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation common to for up to 5 wk from rye mulch (Liebl et al., 1992; Wilthe upper Midwest, and an appropriate cover crop may fulfill this need. A corn-soybean rotation that included a rye (Secale cereale L.) liams et al., 1998), and the production of allelopathic cover crop was studied at two Minnesota locations in 2002 and 2003compounds that increase weed suppression (Barnes and to evaluate rye management method and timing for no-till soybean Putnam, 1987). production. Fall-planted rye following corn harvest at Waseca andDespite the potential benefits of rye, its adoption as Rosemount was managed the next spring by: (i) mowing once, (ii) a cover crop in the corn-soybean rotation has been mowing twice, (iii) applying glyphosate herbicide once, (iv) applying minimal. The limited use of rye can be attributed to cost herbicide twice, and (v) mowing once followed by applying herbicide, of establishment and termination as well as possible interwith four mow dates beginning 1 May separated by approximately ference with the subsequent crop growth. When rye was 1 wk. Rye regrowth after mowing but before stem elongation in early used as a cover before corn, yield was reduced in part to mid-May was similar to that of uncut rye but decreased dramatically due to N immobilization (Tollenaar et al., 1993; Vaughan when mowed at anthesis in early June. At Rosemount, low weed populations and the presence of the rye cover crop, when properly man-and Evanylo, 1998; Wagger, 1989). Soybean grown folaged, had only a minimal affect on soybean yield, resulting in the onelowing rye has not shown the same yield reductions as pass mowing system being equally profitable as the no-rye two-pass corn. In Ontario, Wagner-Riddle et al. (1994) found that herbicide system. At Waseca, where weed pressure was high, the rye while soybean growth was reduced early in the season, cover crop treatments without subsequent herbicide application asthere was no yield difference at harvest. Bauer (1989) well as the early one-pass herbicide applications did not provide adereported that soybean yield was not reduced when rye quate control, making these systems less profitable. Our research was managed with a herbicide but was reduced when indicated soybean yields following a rye cover crop were often comparye was mowed without subsequent application of a rable to yields where no rye cover crop was grown, but economic herbicide due to rye regrowth. Studies by Bauer (1989) returns were usually reduced. and Eckert (1988) indicated that soybean stand establishment was reduced when planted into rye residue. Bauer (1989) also reported delayed physiological devel-1991 Buford Circle, St Paul, MN 55108.