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Agriculture in the Midwest region of the United States is based on intensive corn (Zea mays L.) production that provides food, feed, and fuel. Crop rotation is a vital management option for improved yield and environment preservation. Three rotation systems—continuous corn (CC), corn–soybean (Glycine max [L.] Merr.; CS), and corn–soybean–wheat (Triticum aestivum L.; CSW)—were selected to study their effects on grain yields and carbon (C) and nitrogen (N) accumulation and partitioning within corn grain, stover, and cob plant components. The experiment was conducted at three pre-established crop rotation experiments located at three sites in Wisconsin. Biomass sampling was performed in four consecutive years (2011 to 2014). Analysis of variance showed differences in location for most variables, an effect of crop rotation on stover biomass and stover C, and an interaction effect between location and rotation on soybean grain yield. Averaged across years and locations, final corn and soybean grain yield increased with rotation complexity where corn in the CSW rotation had 15% and 8% greater yield than CC and CS rotation, respectively. Overall, the biomass distribution among corn plant parts was 52%, 41%, and 7% for grain, stover, and cob, respectively. Stover and cobs harvested from corn grown in monoculture produced approximately 11% (0.54 Mg C ha−1) less C than corn grown in either CS or CSW rotation. Across rotations, the accumulation of N in plant tissues was not significantly different. However, these results show that crop rotation can increase grain yield and biomass C and partially offset the difference in soil C, which is expected to be greater under CC.

Prohexadione-calcium (PHD) can enhance establishment of alfalfa (Medicago sativa L.) interseeded into silage corn (Zea mays L.), but optimal application rates and timing for this growth regulator are unknown. Two experiments examined how single or split applications of 0.25 to 1.0 kg a.i. ha–¹ of PHD applied to 15 or 25 cm tall glyphosate-resistant alfalfa seedlings influenced growth, stand density, and yield of alfalfa and corn compared to untreated controls. The PHD treatments reduced seedling top growth by 13 to 32% and increased stand density of alfalfa by 19 to 81% in three out of four locations and alfalfa dry matter yield by 4 to 23% in two out of four locations the following year. Alfalfa responses were not consistently influenced by the rate and timing of PHD application, but higher rates proved advantageous under conditions that impaired alfalfa seedling survival under corn. Application of PHD on alfalfa had little or no effect on corn heights and yields. Corn population and alfalfa seeding rates influenced corn silage yield and alfalfa stand counts in at least one location, but these factors had little effect on crop responses to PHD. Combined 2-yr yields of corn followed by alfalfa were 12% greater for the interseeding system than for solo-seeded corn followed by spring seeded alfalfa. Overall, a single application of 0.5 to 1.0 kg a.i. ha–¹ of PHD on 15 to 25 cm tall alfalfa proved effective for improving stand density and occasionally first year yield of glyphosate-resistant alfalfa.

In response to climate change, there is a need to adopt more resilient cropping systems for increased productivity. In this study, three corn (Zea mays L.)-based rotations—continuous corn (CC), corn–soybean (Glycine max [L.] Merr.; CS), and corn–soybean–wheat (Triticum aestivum L.; CSW), where all residues were retained on the field after harvest—were selected to study their effects on soil properties at three managed sites in Wisconsin—Arlington, Lancaster, and Marshfield. Soil core samples were collected at four depths (0 to 10, 10 to 20, 20 to 40, and 40 to 60 cm) in 2011. In 2013 and 2015, soil core samples were collected at the two top depths. Soil water retention (WR), plant available water (PAW), bulk density (BD), soil carbon (C), soil nitrogen (N), and C/N ratio were evaluated. Water retention was determined from 0 to 10 and 10 to 20 cm depths at five different matric potentials (Ψ = 0, −5, −10, −33, and −1,500 kPa). There was a significant location × depth interaction across soil properties, which could be associated with differences in management among locations. Averaged across location, CC and CSW rotations had greater water content and PAW across WR tensions than CS rotation at 0 to 10 cm depth, while no differences existed at 10 to 20 cm depth. Crop rotations had similar BD across locations and depths (1.37 to 1.41 g cm−3). A significant three-way location × depth × rotation interaction for C and N amount was affected with generally higher C and N amount in CSW rotation at Lancaster and smaller differences among crop rotations at Arlington and Marshfield. Observed low soil C/N ratio values (

Fungal diseases can have a detrimental impact on soybean and corn yield. Foliar fungicides are used to manage fungal diseases and minimize yield loss, along with cultural practices like tillage and crop rotation. Prophylactic foliar fungicide use does not consistently increase yield for corn and soybean, especially when disease pressures are low. Also, there are concerns about the impact of fungicides on non-target organisms, including fungi living in the soil. We tested the effects of tillage, crop rotation, and foliar fungicide use on corn grain and soybean seed yield over three growing seasons. For both crops, rotation was key to achieving high yields, although there was an interaction of tillage × crop rotation for soybean and crop rotation × fungicide for corn. For soybean seed yield, both foliar fungicide treatments showed a small yield increase over untreated plots. Additionally, we assessed bulk soil fungal communities in a subset of treatments (crop rotation and fungicide treatments in no-till plots), using ITS sequencing and PLFA-FAME. We observed distinct fungal communities in the continuously cropped treatments, while annually rotated communities were very similar. There was also greater overall microbial biomass and a higher relative abundance of arbuscular mycorrhizae fungi associated with continuous corn. There were no differences in soil fungal communities or microbial biomass associated with foliar fungicide treatments. Based on our findings, we recommend that farmers use integrated pest management strategies to manage fungal diseases, which may include fungicide applications, if they are justified by economic disease thresholds or prediction tools.

Crop simulation models are used at the field scale to estimate crop yield potential, optimize current management, and benchmark input-use efficiency. At issue is the ability of crop models to predict local and regional actual yield and total production without need of site-year specific calibration of internal parameters associated with fundamental physiological processes. In this study, a well-validated maize simulation model was used to estimate yield potential for 45 locations across the U.S. Corn Belt, including both irrigated and rainfed environments, during four years (2011–2014) that encompassed diverse weather conditions. Simulations were based on measured weather data, dominant soil properties, and key management practices at each location (including sowing date, hybrid maturity, and plant density). The same set of internal model parameters were used across all site-years. Simulated yields were upscaled from locations to larger spatial domains (county, agricultural district, state, and region), following a bottom-up approach based on a climate zone scheme and distribution of maize harvested area. Simulated yields were compared against actual yields reported at each spatial level, both in absolute terms as well as deviations from long-term averages. Similar comparisons were performed for total maize production, estimated as the product of simulated yields and official statistics on maize harvested area in each year. At county-level, the relationship between simulated and actual yield was better described by a curvilinear model, with decreasing agreement at higher yields (>12 Mg ha−1). Comparison of actual and simulated yield anomalies, as estimated from the yearly yield deviations from the long-term actual and simulated average yield, indicated a linear relationship at county-level. In both cases (absolute yields and yield anomalies comparisons), the agreement increased with increasing spatial aggregation (from county to region). An approach based on long-term actual and simulated yields and year-specific simulated yield allowed estimation of actual yield with a high degree of accuracy at county level (RMSE ≤ 18%), even in years with highly favorable weather or severe drought. Estimates of total production, which are of greatest interest to buyers and sellers in the market, were also in close agreement with actual production (RMSE ≤ 22%). The approach proposed here to estimate yield and production can complement other approaches that rely on surveys, field crop cuttings, and empirical statistical methods and serve as basis for in-season yield and production forecasts.

Nitrous oxide (N2O) is a potent greenhouse gas with implication for climate change. Agriculture accounts for 10% of all greenhouse gas emissions in the United States, but 75% of the country's N2O emissions. In the absence of PRE herbicides, weeds compete with soybean for available soil moisture and inorganic N, and may reduce N2O emissions relative to a weed-free environment. However, after weeds are killed with a POST herbicide, the dead weed residues may stimulate N2O emissions by increasing soil moisture and supplying carbon and nitrogen to microbial denitrifiers. Wider soybean rows often have more weed biomass, and as a result, row width may further impact how weeds influence N2O emissions. To determine this relationship, field studies were conducted in 2013 and 2014 in Arlington, WI. A two-by-two factorial treatment structure of weed management (PRE + POST vs. POST-only) and row width (38 or 76 cm) was arranged in a randomized complete block design with four replications. N2O fluxes were measured from static gas sampling chambers at least weekly starting 2 wk after planting until mid-September, and were compared for the periods before and after weed termination using a repeated measures analysis. N2O fluxes were not influenced by theweedbywidthinteraction orwidthbefore termination, after termination, or for the full duration of the study at P ≤ 0.05. Interestingly, we observed that POST-only treatments had lower fluxes on the sampling day immediately prior to POST application (P = 0.0002), but this was the only incidence whereweedinfluenced N2O fluxes, and overall, average fluxes from PRE + POST and POST-only treatments were not different for any period of the study. Soybean yield was not influenced bywidth(P = 0.6018) orweedbywidth(P = 0.5825), but yield was 650 kg ha−1higher in the PRE + POST than POST-only treatments (P = 0.0007). These results indicate that herbicide management strategy does not influence N2O emissions from soybean, and the use of a PRE herbicide prevents soybean yield loss.

Atrazine has been used for control of many weeds, primarily broadleaf weeds, in U.S. corn fields since 1957. Recently, the adoption of glyphosate-resistant corn hybrids have led to glyphosate eclipsing atrazine as the most commonly used herbicide in corn production. However, the evolution and spread of glyphosate-resistant weeds is a major concern. Atrazine use in Wisconsin is prohibited in 102 areas encompassing 0.49 million ha where total chlorinated residues were found in drinking water wells at concentrations > 3 μg L−1. Atrazine has been prohibited in many of those areas for > 10 yr, providing an opportunity to evaluate weed community composition differences due to herbicide regulation. In question, has the abundance of broadleaf weeds increased, coupled with an increased reliance on glyphosate, where atrazine use has been discontinued? To answer this, an online questionnaire was distributed to Wisconsin growers in June and then weeds present in 343 fields in late July through mid-September in 2012 and 2013 were counted. Data were summarized for frequency, uniformity, density, and relative abundance to compare weed community composition in fields with discontinued vs. recent atrazine use. Growers used glyphosate in 70 vs. 54% of fields with discontinued vs. recent atrazine use, respectively (P = 0.021). Moreover, broadleaf weeds were found more frequently, (73 vs. 61%; P = 0.03), they had 50% greater in-field uniformity (P = 0.002), and density was 0.4 vs. 0.19 plants m−2(i.e., twofold greater; P < 0.0001) in discontinued vs. recent atrazine-use fields. Changes were most evident with troublesome glyphosate-resistant broadleaf weeds such asAmaranthusspecies and giant ragweed. In conclusion, weed community composition consisted of more broadleaf weeds in fields where atrazine has not been used in the recent decade coupled with greater glyphosate use. These results provide evidence of negative long-term implications for glyphosate resistance where growers increased reliance on glyphosate in place of atrazine.

Atrazine is an important herbicide for broadleaf weed control in corn. Use rates have declined in many corn production systems due to environmental concerns and the availability of other effective herbicides, especially glyphosate in glyphosate-resistant hybrids. However, using multiple effective herbicide modes of action is ever more important because occurrence of herbicide-resistant weeds is increasing. An experiment to compare application timings of reduced rates of atrazine to benefit resistance management in broadleaf weeds while protecting corn yield was conducted in Wisconsin across four site-years in 2012 and 2013. Herbicide treatments consisted of five atrazine rate and timing combinations and three POST base herbicides: glyphosate, glufosinate, and tembotrione. Metolachlor was applied PRE at 2.1 kg ai ha−1 for grass control in all treatments. A linear regression model estimated that atrazine rates ≥ 1.0 kg ai ha−1 applied PRE would prevent exposure of common lambsquarters plants to POST herbicides, but giant ragweed and velvetleaf exposure was not influenced by timing. Corn yield was also not influenced by atrazine rate and timing combinations at the α = 0.05 level; however, at P = 0.06, corn yield was greater for atrazine applied PRE at 1.1 kg ha−1 than for atrazine applied PRE at 0.5 kg ha−1, POST at 1.1 kg ha−1, or not at all. In summary, higher rates of atrazine applied PRE may improve yield, as reported by others, but this study concludes reduced rates of atrazine (i.e., ≤ 1.1 kg ha−1) applied to corn in a POST tank mixture combination provided more consistent control of giant ragweed, velvetleaf, and common lambsquarters compared with atrazine applied PRE. This information should help direct atrazine application timing applied POST when applied at low rates to improve proactive herbicide resistance management.

We analyzed grain yield data from annual field experiments during 1990-2010 in Wisconsin to test hypotheses that maize expressing these transgenic traits alone or in combination (stacked) has greater productivity (as measured by the mean harvested yield) and lower production risk (as measured by the variance, skewness and kurtosis of harvested yield). Compared with conventional hybrids, the impact of transgenic traits (both single and stacked traits) on mean yield ranges from -12.2 to +6.5 bushels per acre. This shows that reducing yield risk is an important source of benefits of transgenic technology, especially for stacked traits.Correspondence

Genotype x environment interaction influences the market value of soybean [Glycine max (L.) Merr.] protein, oil, and fatty acid traits. The objectives of this research were (i) to evaluate agronomic trait performance and stability of soybean genotypes in individual environments and across environments; and (ii) to evaluate the relationship of test environments for selecting superior genotypes within the mega-environment for soybean production in the southern region of Wisconsin. A total of 68 soybean genotypes were selected from University of Wisconsin soybean evaluation trials and grown at four locations in 2003 and 2004. Soybean genotypes, grown in trials with conventional and Roundup Ready herbicide treatments were analyzed for yield, protein, oil, and the fatty acid components palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid. Repeatability estimates among genotypes ranged from 0.27 to 0.98 with yield and the fatty acid component linolenic acid being the most sensitive to environment effects. Superior genotypes could be consistently selected for yield, protein, oil, and fatty acid components using biplot analysis and stability estimates. Among locations in the southern region in Wisconsin, Arlington provides unique information for soybean fatty acid evaluations, but similar information about soybean yield, protein, and oil with Janesville or Lancaster. So, if soybean fatty acid is not important then Arlington could be dropped as a test site.

Correlations between kernel vitreousness and ruminal in situ (RDMD) and total tract dry matter (TDMD; sum of ruminal in situ and post-ruminal in vitro measurements) degradabilities were determined for 33 diverse corn germplasm sources. These included a wide range of endosperm characteristics from opaque 2 (o2) types to densely packed flint types, and a number of intermediates. Harvests were done at two growth stages; 1/2 milk-line (ML) and black-layer (BL). Kernels from middle portion of ears were oven dried at 40 °C for 72 h and ground through a Wiley mill (6 mm screen) for measurement of in situ RDMD after 0 and 14 h of incubation using two steers (1.5 g/bag × 8 replicates per time point per steer in 5 cm × 5 cm bags of 50 μm pore size). Residue from the 14 h bags proceeded to an 8 h in vitro enzymatic post-ruminal digestion after which the residue was oven dried at 62 °C for 48 h and dry matter content determined. Inbred by harvest-stage interactions were observed for 0-h disappearance and TDMD. Vitreousness had strong negative correlations with degradability measurements, particularly for more mature (BL) samples (−0.728, −0.770 and −0.603) versus ML (−0.569, −0.541 and −0.338) for 0 h disappearance, RDMD and TDMD, respectively. Vitreousness was highly correlated with corn degradability, especially at a black-layer stage of harvest, in this diverse corn germplasm.

Crop rotation and N are management methods that can increase corn (Zea mays L.) grain yields. Our objective was to determine the corn grain yield response to six crop rotation sequences and four N rates in a long-term (35-yr) study. The rotations were continuous corn (CC), corn-alfalfa (Medicago sativa L.) (CA), corn-soybean [Glycine max (L.) Merr.] (CS), corn-corn-corn-alfalfaalfalfa (CCCAA), corn-corn-oat (Avena sativa L.) with alfalfa seeding-alfalfa-alfalfa (CCOaAA), and corn-soybean-corn-oat with alfalfa seeding-alfalfa (CSCOaA). From 1970 to 2004, first-yr corn grain yields (CCCAA, CCOaAA, and CSCOaA) increased from 79 to 100 kg ha -1 yr -1 . Increasing N rates did not influence grain yield trends, indicating that an alfalfa crop produced the N required by first-yr corn. However, 224 kg N ha -1 was needed to improve second and third-yr grain yield trends 69 and 58 kg ha -1 yr -1 , respectively. Grain yield trends for CC did not improve despite increasing N treatments, although grain yield tended to increase over time at 224 kg N ha -1 (P < 0.10). From 1989 to 2004, corn grain yield trends ofCA and CS decreased by 161 kg ha -1 yr -1 if no N was added. The 2-yr rotation was not sufficient to improve grain yield trends, whereas the 5-yr rotation was able to enhance corn grain yield and decrease the need for fertilizer N. Effects on pathogens and insects were not evaluated but warrant further investigations. Overall, this data shows that extended rotations involving forage crops reduce N inputs, increase corn grain yields, and are more agronomically sustainable than current short-term rotations.

Hail damage can be a serious problem on corn (Zea mays L.) grown for silage. The value of corn grown for silage is a function of both the yield and quality of the forage produced. An improved understanding of the effects of defoliation on forage quality would improve the ability of agronomists, farmers, and crop insurance adjusters to assess the economic impact of hail damage to corn harvested for forage. The objective of this study was to evaluate the effects of defoliation on the forage quality corn grown for silage production. Experiments were conducted during 2000, 2001, and 2002 at Arlington and Marshfield, WI, and State College, PA. Corn quality measures responded similarly to defoliation treatments across most environments. Increasing defoliation either did not affect quality, especially at V7 and V10 stages, or lowered quality, especially at the R1 and R4 stages of development. The largest differences in neutral detergent fiber (NDF), acid detergent fiber (ADF), and in vitro true digestibility occurred at R1 and R4. Starch content was most affected when defoliation occurred at Rl. The response of NDF digestibility was inconsistent across environments. These changes in forage quality resulted in decreases in Milk Mg -1 and Milk ha -1 with increasing defoliation in most environments. Predictive models for estimating forage quality and yield losses can be used to improve estimates of the impact of defoliation caused by hail on corn grown for silage.

Yield comparisons do not provide the appropriate basis for decision-making regarding cropping systems. The dominant factor influencing the adoption of cropping systems is economics. The objective of this 15-yr study was to evaluate the long-term effect of four N fertilization treatments on the economic returns of seven crop rotations in Wisconsin, based on annual market prices and production costs. The seven crop rotations were continuous corn (Zea mays L.) (CC), continuous alfalfa (Medicago sativa L.) (AA), corn-soybean [Glycine max (L.) Merr.] (CS), corn-alfalfa (CA), corn-corn-corn-alfalfa-alfalfa (CCCAA), corn-corn-oat (Avena sativa L.) with alfalfa seeding-alfalfa-alfalfa (CCOaAA), and corn-soybean-corn-oat with alfalfa seeding-alfalfa (CSCOaA). The four N treatments were 0, 56, 112, and 224 kg N ha -1 for the corn phase. Across all crop rotations, the average return was greatest for the 112 and 224 kg N ha -1 treatments, which returned on average $32 and $85 ha -1 more than the 56 and 0 kg N ha -1 treatments, respectively. Across all N rates, average returns were highest for the CS rotation. The CS rotation returned $58 ha -1 more than the CSCOaA and CCOaAA rotations, $129 ha -1 more than the CCCAA rotation and AA, $224 ha more than the CA rotation, and $269 ha -1 more than CC. Under second degree stochastic dominance, the stochastically efficient treatments were CS at all N rates and CC at 224 kg N ha -1 . All other cropping systems were inefficient relative to these five treatments (i.e., they would not be chosen by a risk-averse decision maker). This research shows that the most profitable systems (CS) remain the most efficient when risk is taken into consideration. However, these results also show that when 224 kg N ha -1 is added, risk can be reduced for continuous corn. Individual circumstances will dictate the optimal choice among the efficient rotations.

This experiment was designed to determine if intercropping corn (Zea mays L.) with climbing beans is a viable option to increase crude protein (CP) concentration in forage rather than purchasing costly protein supplements for livestock rations. In these experiments, corn was intercropped with three beans—lablab bean [Lablab purpureus (L.) Sweet], velvet bean [Mucuna pruriens (L.) D.C.], and scarlet runner bean (Phaseolus coccineus L.)—or grown in monoculture near Arlington and Lancaster, WI. Corn was sown in early May and late April in 2004 and 2005, respectively, and later thinned to 55,000 (low density) or 82,500 (normal density) plants ha –1 . Beans were sown in rows 8 cm on one side of the corn rows at 82,500 plants ha –1 2 or 4 wk after corn planting. Averaged over four environments, mixture forage dry matter (DM) yields were similar. However the velvet bean and scarlet runner bean mixtures produced signifi cantly higher forage DM yield, 1.2 Mg ha –1 and 0.89 Mg ha –1 more, respectively, in the late bean planting treatment. Beans, except scarlet runner bean, which was damaged by mold and insects, increased the CP concentration of all mixtures, with the greatest increases from the lablab bean (13%) and velvet bean (16%). The experiments show that lablab bean grown with corn has the greatest potential of the three beans to increase CP concentration above monoculture corn, without compromising forage yield or calculated milk ha –1 and increasing forage nutrient value.

Current research indicates that plant populations should increase above the current Wisconsin recommendation of 74100 plants ha 21 for higher corn (Zea mays L.) grain yields. However, stalk lodging is a major constraint to increasing plant populations. One option growers have is using Bt (Bacillus thuringiensis) hybrids, which are known to lodge less. A new method for assessing stalk lodging risk is needed. The objectives of this study were to (i) assess rind strength of corn hybrids with or without the Bt trait to increasing plant populations at natural levels of European Corn Borer (ECB, Ostrinia nubilalis (Hubner)), and (ii) determine the potential of rind strength measure- ments for predicting stalk lodging. In 2003 and 2004, rind penetrom- eter resistance (RPR) was used to measure rind strength for four Bt and five non-Bt hybrids with plant populations ranging from 64220 to 123500 plants ha 21 at 10 locations in Wisconsin. Stalk lodging increased from 6 to 18% as plant population increased, and only at one location, Arlington, did Bt hybrids lodge significantly less (20 vs. 42%) than non-Bt hybrids. The RPR of both Bt and non-Bt hybrids decreased from 3.9 to 3.7 load-kg plant 21 with increasing plant population. Plants with rind strength measurements , 3.9 load-kg plant 21 taken at physiological maturity showed more lodging. Thus, such measurements appear to be a good indicator of stalk lodging potential in a high plant population situation. This new method has potential to help growers prepare for grain harvest by identifying fields with plants having average RPR below a 3.9 load-kg plant 21 thresh- old, and adjusting harvest schedules of suspect fields earlier to avoid yield losses caused by stalk lodging. Further research using more hybrids across a range of environmental conditions and plant popu- lations will be necessary to fully understand the importance of this tool and its potential importance in understanding and identifying high lodging potential environments.

Fusarium spp. are common fungal pathogens that infect a number of field and vegetable crops. Crop rotation, genetic resistance, and fungicides are the primary methods used for managing these pathogens; however, there is a lack of information regarding the interactions between these management strategies and how they impact Fusarium spp. population dynamics. Therefore, the objective of this research was to quantify the effect of crop rotation and management (i.e., variety selection and fungicide use) on F. graminearum, F. oxysporum, and F. virguliforme populations in the soil using real-time quantitative polymerase chain reaction (qPCR). Soil samples were collected in 2011 and 2012 from a long-term corn (Zea mays L.)–soybean [Glycine max (L.) Merr.]–wheat (Triticum aestivum L.) rotation study near Arlington, WI, and populations for each species (spores g−1 of soil) were quantified from extracted soil DNA. Fusarium oxysporum was the most prevalent Fusarium sp. found. Crop rotation and management did not impact F. oxysporum populations nor F. virguliforme presence. A crop rotation by fungicide interaction was found for F. graminearum (P < 0.001), but this interaction was primarily affected by crop rotation. As expected, F. graminearum was found more often in plots with wheat as part of the rotation. This study found few interactions among crop rotation, variety selection, and fungicide use for controlling populations of three Fusarium spp. in the soil, and significant interactions or individual control methods were dependent on the species being examined. US Wheat and Barley Scab Initiative/[]/USWBSI/Estados Unidos National Institute of Food and Agriculture/[]/NIFA/Estados Unidos Wisconsin Institute for Sustainable Agriculture/[]//Estados Unidos UCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Agronomía

Bt (Bacillus thuringiensis) corn (Zea mays L.) hybrids resist Euro- pean corn borer (Ostrinia nubilalis (Hubner)) damage and lodge less, creating interest among growers, agronomists, and seed companies in their yield response to increasing plant population. Corn hybrids with Bt and non-Bt traits were evaluated from 2002 to 2004 across 10 loca- tions in Wisconsin in 76-cm rows at target populations from 61750 to 123 500 plants ha 21 to (i) determine the agronomic and economic op- timum plant population for corn and (ii) identify agronomic and economic optimum plant populations for Bt and non-Bt hybrids. The quadratic model for both grain yield and grower return response to plant population was significant. The maximum yield plant popula- tion (MYPP) for Bt and non-Bt corn was 104500 and 98800 plants ha 21 , respectively. The overall MYPP for corn was 102 400 plants ha 21 , which is 28 300 plants ha 21 more than the current Wisconsin recommendation of 74100 plants ha 21 . Planting corn to the MYPP increased grain yield by 4.2% over the current population recom- mendation. However, the economically optimum plant population (EOPP) for both Bt and non-Bt corn was 83 800 plants ha 21 . It was concluded that Bt corn hybrids require higher plant populations for maximizing yield potential; however the higher harvest costs related to those greater yields and the higher seed costs associated with attaining those populations resulted in no difference in the EOPP between Bt and non-Bt corn. Plant population recommendations for corn should be near 83 800 plants ha 21 , the point where the EOPP was achieved. Since this recommendation is affected by rising seed and management costs and variable market prices, a periodic evaluation of plant popu- lation response for newly released hybrids should be done.

Recent interest in establishing uniform spacing of corn (Zea mays L.) plants in the field has prompted many seed companies to offer planter-tuning services. Experiments were conducted in Wisconsin environments between 1999 and 2001 to investigate the response of corn to plant spacing variation (PSV). During 1999, adapted hybrids were grown in the field by overseeding and thinning to 37 000 and 74 000 plants ha -1 in a two-plant pattern with target PSV treatments of 0, 10.2, 20.3, and 30.5 cm and 0, 2.5, 5.1, 7.6, 10.2, and 12.7 cm, respectively. During 2000 and 2001, two-, four-, and eight-plant hill patterns were established with target PSV treatments of 5.1 and 10.2 cm; 5.1, 10.2, and 20.3 cm; 5.1 10.2, 20.3, and 30.5 cm standard deviation. The control treatment was a target PSV of 0 cm. In this study, PSV never affected plant lodging or grain test weight. In one of 24 environments grain moisture was significantly affected, but no relationship was observed with PSV. Grain yield was rarely affected by PSV in two-plant patterns. Relative grain yield was reduced up to 18% as plant spacing became more hill-like in two-, four-, and eight-plant patterns. Relative grain yield was reduced 1.06% cm -1 standard deviation as PSV increased above 12.0 cm. However, for most farmer field situations at current plant density recommendations, corn grain yield would not be affected by PSV, except when obvious hills are planted.

Farmers, agronomists, and crop insurance adjusters question whether leaf defoliation damage caused by hail or other factors affects corn (Zea mays L.) forage yield the same as grain yield. Our objective was to evaluate the effects of defoliation on corn grown for forage production. In studies conducted during 3 yr at two sites in Wisconsin and one site in Pennsylvania, forage yield decreased as leaf removal increased in severity, and as time of defoliation neared silking. Forage yield response to increasing levels of defoliation was quadratic. Averaged across all environments, forage yield decreased 16% when 100% defoliation occurred at V7. Likewise 100% defoliation decreased forage yield 43, 70, and 40% at V10, R1, and R4 growth stages, respectively. Greater forage yield decreases are measured with early defoliation (V7-V10) than predicted grain yield decreases currently used by hail adjusters. This likely occurred because both increased leaf removal and decreased grain yield combine to reduce forage yield. The response to defoliation from simulated hail damage is different between corn forage and corn grain. Alternative predictive models for estimating forage yield losses should be used by insurance adjusters.

Maize (Zea mays L.) silage is a high-quality forage for ruminants, but there have been few significant breeding efforts specifically dedicated to improving maize forage yield or quality by breeders in the USA. The objective of this study was to evaluate the forage yield and quality of the Wisconsin Quality Synthetic (WQS) and related populations developed by the University of Wisconsin Maize Breeding Program for agronomic and nutritional attributes. Three cycles of divergent S, recurrent selection have been completed for stover fiber, silica, and lignin concentration for populations WFISIHI (Wisconsin-fiber-silica-high) and WFISILO (Wisconsin-fiber-silica-low). The third cycle (C3) of WFISILO was crossed to two high-quality inbred lines, Mo17 and H99, to create WQS C0, which then underwent two cycles of S 2 -topcross selection for improved forage yield and quality. All cycles of selection for WFISIHI, WFISILO, and WQS were evaluated for forage yield and quality at two field locations in Wisconsin in 2000 and 2001. Results for WFISIHI and WFISILO demonstrated that S, selection for stover composition altered both stover and whole-plant composition in the anticipated directions. Selection for whole-plant yield and composition of S 2 -topcrosses was also effective for WQS, especially when using selection indices incorporating whole-plant yield, neutral detergent fiber (NDF), neutral detergent fiber digestibility (NDFD), crude protein (CP), and starch. WQS C2 whole-plant and stover in vitro true digestibility (IVTD), whole-plant and stover add detergent lignin, and milk yield per megagram dry matter (DM) were similar to the brown-midrib check hybrid, F657. WQS C2 whole-plant and stover NDFD were lower than F657 but higher than other commercial check hybrids. In addition, WQS population testcrosses improved over cycles of selection for whole-plant yield and most quality attributes. Our results indicate that it is feasible to develop silage maize germplasm with both high whole-plant yield and excellent nutritional quality.

Soybean [Glycine max (L.) Merr.] benefits in yield when rotated with corn (Zea mays L.), but the mechanism of the rotation effect is not fully understood. The objective of this study was to determine effects of cropping sequence and tillage on soybean growth and plant development. A 2-yr field study was conducted using conventional tillage and no-tillage systems in seven different corn and soybean rotation sequences. At physiological maturity, plots of first-year soybean after 5 yr of consecutive corn and the annually rotated soybean averaged 8% higher soil moisture content and 17% more dry matter per plant than the remaining five rotation sequences. Conventional tillage averaged 6% higher soil moisture content and 5% greater leaf area index than the no-tillage system. In 2000, leaf area index was 29% higher for the first-year soybean after 5-yr corn and the annually rotated soybean than the remaining five rotation sequences. No differences in leaf area index were observed among the different rotation sequences in 2001. Soybean plants were 6% taller in first-year soybean after 5-yr corn, second-year soyssean, and annually rotated soybean than the remaining four rotation sequences. The no-tillage system averaged 6% more dry matter plant per plant and 7% taller plants than the conventional tillage system. These findings support the hypothesis that growth and alterations in plant development occur when soybean is grown in different rotation sequences and tillage systems. These alterations may reflect the plant response to the corn-soybean rotation effect on soybean growth and development, but the underlying mechanism of the effect remains unknown.

Soybean [Glycine max (L.) Merr.] has the ability to produce similar yields across a broad range of management systems and planting dates. Our objective was to better understand growth factors affecting yield component compensation in the upper Midwest under different management systems. An older cultivar, Hardin, and two newer cultivars, DeKalb CX232 and Spansoy 250, were grown in five management systems during four growing seasons from 1997 to 2000. Four of the five management systems were located near Arlington, WI, on a silt loam soil consisting of conventional and no-tillage systems with and without irrigation. The fifth management system was located near Hancock, WI, on a conventionally tilled, irrigated sandy loam soil. Yield component compensations gave similar grain yield among cultivars, planting dates, and management systems. At R6, CX232 and Spansoy 250 averaged greater dry matter (DM) accumulation, leaf area index (LAI), and crop growth rate (CGR) than Hardin. Early planted soybean had more total DM than the late-planted soybean. No-tillage systems produced more total DM, LAI, and CGR after R3 than the two conventional tillage systems at Arlington. Irrigated systems had higher LAI than the nonirrigated systems. These results indicate that the compensatory growth and alterations in plant development among cultivars, management systems, and planting dates had no impact on soybean yield.

The CROPGRO-Soybean model has not been extensively evaluated in the upper Midwest. The objective of this project was to determine if modifications of the CROPGRO-Soybean model would improve predictions in the upper Midwest using three cultivars in five management systems and two planting dates from 1997 to 2000. Version 3.5 of the model was compared with 1998 data and found to underestimate total biomass and grain yield at harvest. Changes in temperature function on leaf expansion rate and base temperature for pod addition improved model performance and decreased root mean square error (RMSE) for biomass at harvest and grain yield from 734 to 707 kg ha -1 and from 410 to 362 kg ha -1 , respectively. The modified model was then tested with independent data from 1997, 1999, and 2000. Overall, the model parameters calibrated from 1998 data improved the fit slightly but with higher RMSE values for the three independent years than the 1998 data set. Averaged across the 3 yr, the modified model underpredicted biomass at harvest and grain yield by 14 and 6%, respectively, with RMSE for biomass at harvest and grain yield averaging 1181 and 814 kg ha -1 , respectively. The inaccuracy was related to underprediction of early vegetative growth because of the effect of site-specific and planting date-specific differences in temperature on biomass accumulation and leaf area index. It was concluded that the modified parameters improved the accuracy of the CROPGRO-Soybean model for the calibration year but did not significantly improve prediction for the three independent years.

There has been a rapid increase of soybean [Glycine max (L.) Merr.] production in cropping systems in Wisconsin. The objective of this research was to determine the influence of five management systems on agronomic traits for three soybean cultivars grown at two different planting dates. An older cultivar (Hardin) and two newer cultivars (DeKalb CX232 and Spansoy 250) were grown in five management systems between 1997 and 2000. Four management systems were located on a silt loam soil and consisted of conventional and no-tillage systems with and without irrigation. The fifth management system was located on a sandy loam soil that was irrigated. A planting date x cultivar interaction was observed on the silt loam soil where CX232 yielded 7% greater for the early planting date (4.37 Mg ha -1 ) than for the late planting date, but no planting date effect was observed for Hardin and Spansoy 250. Over all cultivars, yield was 4% greater for early planting on the silt loam soil. Grain yield and other agronomic traits were not influenced by cultivar and planting date on the sandy loam soil. Tillage and irrigation did not affect grain yield or most of the other agronomic traits. Regression of cultivar means on management system indicated an equal stability for yield among the cultivars tested with Hardin tending to be the most stable. It was concluded that soybean cultivar decisions in the Upper Midwest should be based on selecting the highest yielding cultivars adapted to a particular geographic region and location regardless of management system.

The selection of corn (Zea mays L.) hybrids and the timing of harvest are important management considerations for dairy and livestock operations. Objectives of this study were to determine the effect of harvest date on yield and quality of corn hybrids and to describe the relationship between harvest date and the yield and quality of corn forage, silage, and stover. During 1998 and 1999, four hybrids were harvested at eight different harvest times between 521 and 1224 growing degree units (GDUs) after planting. Few hybrid or hybrid × harvest date effects were observed. As GDUs accumulated, dry matter yield increased from 8 to 25 Mg ha -1 . Lowest concentrations of neutral detergent fiber (NDF) and acid detergent fiber (ADF) and highest concentrations of in vitro true digestibility (IVTD) occurred when forage was harvested between 700 and 650 g kg -1 moisture (1025 and 1186 GDUs after planting). Potential milk yield indices of milk Mg -1 corn forage (794 kg) and milk ha -1 corn forage (19 049 Mg) were reached when corn was harvested between 670 and 630 g kg -1 moisture. In general, silage had 15% lower concentrations of NDF, 8% lower IVTD, 48% lower cell wall digestibility, 7% lower crude protein, and 15% higher concentrations of ADF than unfermented fresh forage. Harvesting can be accomplished until 580 g kg -1 moisture while maintaining 95% of the maximum yield and milk ha -1 .

Producers believe that corn (Zea mays L.) forage can be planted at later dates than corn grain because forage harvest does not have to wait until the grain matures fully. The objectives of this study were to determine relationships between planting date and corn forage yield and quality and to determine optimum planting dates of corn forage for the state of Wisconsin. Full- and shorter-season hybrids were planted on six dates at six locations in Wisconsin during 1998 and 1999. Few significant hybrid × planting date interactions or hybrid differences were observed. The optimum planting dates for dry matter yield and quality for southern, central, and northern Wisconsin were 10 May, 27 April, and 8 May, respectively. Corn forage yields remained at 95% of maximum yields when corn was planted in late May for all zones. In all zones, early June plantings exhibited an accelerated rate of yield decline of 0.2 Mg ha -1 d -1 delay in planting. Corn forage quality decreased progressively as planting dates progressed into June. The optimum planting date for milk yield ha -1 was 2 May in southern and central zones and late April in the northern zone. As planting was delayed past mid-May, rates of quality decline were more severe in central and northern zones compared with the southern zone. Therefore, planting of corn forage should occur between late April and mid-May for all production zones in Wisconsin, but planting could occur into late May in the southern production zone because milk yield ha -1 declined by only 8%.

Gains in corn (Zea mays L.) grain yield over time are well documented, but corresponding changes in forage and stover yield and quality have received less attention. Our objective was to describe yield and quality changes of representative cultivars used by farmers in the northern Corn Belt. Six open-pollinated cultivars used prior to 1930, 24 cultivars representing four 15-yr eras between 1931 and 1990, and six modern cultivars, for a total of 36 cultivars, were divided into early- and late-maturity trials. Each trial was grown at three locations in Wisconsin during 1997 and 1998. Since 1930, corn forage dry matter yield has increased at the rate of 0.128 to 0.164 Mg ha -1 yr -1 with stover dry matter yields increasing at the rate of 0.043 to 0.054 Mg ha -1 yr '. Forage crude protein has not changed significantly with time. Forage neutral detergent fiber concentration has decreased 0.825 to 0.948 g kg -1 yr ', while forage in vitro digestibility increased 0.538 to 0.612 g kg 1 yr 1 . Stover neutral detergent fiber concentration and in vitro digestibility have not changed over time. Since 1930 forage, stover, and ear yield have increased 1.4, 0.7, and 2.4% yr 1 , respectively. This trend will no doubt continue, but greater progress might be made if corn forage breeding improvement concentrates on yield and quality changes in stover.

Cropping systems that improve soil conservation are needed for mixed grain and forage enterprises in the upper Midwest. Our objective was to determine whether established kura clover (Trifolium ambiguum M. Bieb.) stands could serve as a living mulch for no-till corn (Zea mays L.) production, followed by a return to dover without replanting. Treatments included corn sown into established kura clover that was: (1) killed and sidedressed with N, (2) killed, (3) band-killed, leaving 15 cm of untreated kura dover between rows, (4) suppressed and sidedressed with N, and (5) suppressed and (6) untreated kura clover without corn. Corn whole-plant yield in 1996 ranged from 14.0 to 15.7 Mg ha -1 and was greatest in Treatments 2 and 4 and least in Treatment 5. Corn whole-plant yield in 1997 ranged from 9.5 to16.9 Mg ha -1 and was greatest in Treatments 1 and 2 and least in Treatment 5. Grain yields in 1996 were not different among treatments, while in 1997 yields ranged from 7.2 to 11.1 Mg ha -1 and were greatest in Treatments 1 and 2 and least in Treatment 5. Clover yield in 1997 following 1996 corn production was greatest in the untreated control, but there was no clover yield difference in 1998 following either 1996 or 1997 corn production. Kura clover can be managed as a living mulch in corn with little or no corn whole-plant or grain yield reduction and clover will recover to full production within 12 mo without replanting.

Corn (Zea mays L.) hybrid selection and plant density are important management considerations for successful forage production in dairy and livestock operations. The objectives of this study were (i) to determine the effect of plant density on high- and low-quality corn hybrids and (ii) to describe the economic trade-off between plant density and forage yield and quality. Two adapted hybrids selected for high and low quality characteristics were grown in the field at five plant densities ranging from 44 500 to 104 500 plants ha -1 at six locations in Wisconsin during 1994, 1995, and 1996. Forage quality response among hybrids was similar across the range of plant densities evaluated. As plant density increased, dry matter yield increased 1.7 to 4.1 Mg ha -1 , depending on location. Maximum dry matter yields were observed at 97 300 to 102 200 harvested plants ha -1 . In vitro true digestibility decreased 16 to 23 g kg -1 as plant density increased. Crude protein decreased 6 to 8 g kg as plant density increased. Neutral-detergent fiber increased 20 to 35 g kg -1 , and acid-detergent fiber increased 19 to 29 g kg with increasing plant density. A trade-off exists between yield and quality for corn forage. Milk Mg -1 decreased 98 to 143 kg milk Mg -1 with increasing plant densities, but milk ha -1 increased 926 to 2176 kg milk ha -1 until about 75 000 to 85 000 harvested plants ha - 1 , and did not change with higher plant densities.

Growers frequently are concerned about the response of corn (Zea mays L.) to planting date. Early planting of corn is recommended because full-season hybrids utilize the entire growing season, achieve physiological maturity before a killing frost, and start to dry, thereby increasing profit through reduced drying costs. The objective was to evaluate the influence of planting date and hybrid maturity on corn grain yield and harvest moisture in Wisconsin. Two or three corn hybrids ranging in relative maturity from 80 to 115 d were planted between 19 April and 22 June at six locations in Wisconsin from 1991 to 1994. In southern Wisconsin locations, the optimum planting date for grain yield of full- and shorter-season hybrids ranged between 1 and 7 May, and was still at 95% of optimum between 9 and 18 May. In northern Wisconsin, the optimum planting date for grain yield of hybrids ranged between 8 and 14 May, and was still at 95% of optimum between 15 and 23 May. Grain yield did not change much when corn was planted between 24 April and 8 May. Grain yield of corn planted after 8 May in southern Wisconsin declined at the rate of 0.5 to 1.1% d -1 over the next 2 wk, accelerating to 1.3 to 1.9% d -1 and 2.0 to 2.8% d -1 over the next two 2-wk periods. Grain yield of corn planted after 8 May in northern Wisconsin declined at the rate of 0.2 to 1.7% d -1 over the next 2 wk, accelerating to 1.7 to 2.2% d -1 and 3.2 to 3.8% d -1 over the next two 2-wk periods. The decision to begin planting corn early should be based on soil temperature and field conditions. After 20 April, planting of full-season hybrids should proceed as rapidly as field conditions allow. The date to switch from full-season to shorter-season hybrids depends on numerous factors, including corn price and drying costs, but generally occurs by mid-May in southern and by late May in northern Wisconsin.

European corn borer (ECB; Ostrinia nubilalis Hubner), is a major pest of corn (Zea mays L.) in North America. Recently, seed companies have begun to offer control of this pest by introducing synthetic genes derived from Bacillus thuringiensis spp. kurstaki (Bt) into the corn genome. Our objectives were to compare the yield of Bt hybrids with adapted high yielding non-Bt hybrids, and to evaluate Bt hybrid yield under economically significant ECB infestation. Experiments were established in the field at three locations in 1995 and one location during 1996. Three groups of corn hybrids were evaluated : transformed hybrids with the Bt gene, closely related isoline hybrids without the Bt gene, and standard high yielding hybrids adapted to these locations. ECB infestation treatments consisted of natural infestation, inoculation four times during the growing season, and insecticide application resulting in an ECB free treatment. Grain yield of Bt corn hybrids was not affected by ECB. Yield of isoline hybrids was 10% lower than both standard and Bt hybrids regardless of ECB treatment. Yield of Bt hybrids was 4 to 8% greater than standard hybrids when inoculated with ECB. However, yield of Bt hybrids was 8% less than standard hybrids when an insecticide was applied. Meld of initial Bt hybrid introductions was equivalent to or better than standard hybrids, except in environments with low ECB.

With the increased presence in the Corn Belt of combine-mounted yield monitors generating yield maps, more producers are asking questions like when do spatial yield differences become important? and should I change my production practices because of observed yield differences ? This study examined variations in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields over time. Yields were monitored from four continuous corn plots, four continuous soybean plots, and eight corn-soybean rotation plots over a 10-yr period from 1986 through 1995 at two Minnesota locations and one Wisconsin location. At each location, all plots were on a similar soil type in a uniform 2-acre field. Plot size was at least 450 sq ft. At each location, each of the four continuous corn plots and each of the four continuous soybean plots produced the highest yield compared with the other three plots at least once during the 10 yr. In any single year for both continuous corn and continuous soybean, a yield range among the four plots at each location of more than 25% occurred in one-fourth of the growing seasons studied. When averaged over 10 yr, however, the yield range among the four continuous corn plots and among the four continuous soybean plots at each location was less than 10%, and in five of six cases yield differences among the four plots were not significantly different. At each location, the yield range averaged at least 20 bu/acre for corn and 6 bu/acre for soybean. Yield variability among years was approximately three times greater for soybean and four times greater for corn than was variability among plots. Similar results were observed for the plots in the corn-soybean rotation. These results demonstrate a relatively high amount of inherent yield variability, and suggest producers should not change management practices to influence yields when small yield differences occur (areas yielding up to 20 to 25% less than the field average), unless the differences are shown to be consistent over years.

Producers and processors have lengthened the sugar beet (Beta vulgaris L.) factory campaign by beginning harvest about 1 mo earlier. Agronomic practices may need to be adjusted to maximize yield and quality of sugar beet harvested earlier. The objective was to describe yield and quality relationships between dates of planting and harvest among 18 sugar beet genotypes. The experiment was conducted at the University of Wyoming Research and Extension Center near Powell, WY, during 1992 and 1993 on a Garland clay loam (fine-loamy over sandy or sandy-skeletal, mixed, mesic Typic Haplargids). Treatments consisted of five planting dates between 30 March and 8 June, and four harvest dates every 2 wk beginning 10 September. When averaged across all years, genotypes, and harvest dates, a delay in emergence of 46 d decreased root yield 38% (from 52.5 to 32.3 Mg ha -1 ), sugar content 4% (183 to 175 g kg -1 ), and recoverable sucrose 42% (9.25 to 5.34 Mg ha -1 ). Delaying planting 46 d increased loss to molasses by 21% (7.75 to 9.41 g kg -1 ). Root yield varied 18% among sugar beet genotypes (40.9-50.1 Mg ha -1 ), sugar content varied 6% (173-185 g kg -1 ), loss to molasses varied 13% (7.90-9.10 g kg -1 ), and recoverable sucrose varied 14% (7.14-8.33 Mg ha -1 ). Over the 43-d harvest period, root yield increased 22% (from 41.1 to 50.2 Mg ha -1 ), sugar content 15% (165 to 190 g kg -1 ), and recoverable sucrose 45% (6.41 to 9.28 Mg ha -1 ). Over the harvest period, loss to molasses decreased 21% (from 9.10 to 7.12 g kg -1 ). The relationships for both yield and quality between planting and harvest dates was linear and nearly parallel. Genotypic differences for yield and quality were greatest on early planting dates as compared with later planting dates. Recoverable sucrose ranking of genotypes at the beginning of harvest was similar at the end of harvest. Producers should consider planting high root yield genotypes in early planted fields that are harvested late, thereby taking advantage of the entire growing season, and genotypes with average root yield and above-average sugar content should be used for late planted or early harvested fields.

Farmers need information on herbicide technology and crop performance to assess the profitability of new herbicide-resistant crop technologies. First-generation imazethapyr-resistant corn hybrids evaluated at the University of Wisconsin yielded less than other commercial hybrids. To determine if this resistance trait affected yield or agronomic traits, 10 near-isogenic pairs of imazethapyr-resistant and -susceptible corn hybrids were compared. Whether treated with imazethapyr or not, imazethapyr-resistant hybrids yielded the same when averaged across hybrids, although yield varied among a few individual hybrids within single experiments. Seven of the imazethaypr-resistant hybrids yielded the same, two yield more, and one yielded less than their susceptible near-isogenic counterpart during eight site-years. Grain moisture was not affected, but imazethapyr-resistant hybrids had fewer broken stalks than did susceptible hybrids. The imazethapyr resistance trait does not appear to affect yield potential, but the backcrossing procedure may have caused early resistant hybrids to lag behind in yield compared to other new hybrids.

The sugar beet (Beta vulgaris L.) industry has adopted an early harvest option that lengthens the processing campaign by 15 to 30 d. Field experiments were conducted near Powell, WY, from 1989 to 1991, to determine whether plant density and N rate should be adjusted for earlier harvests. Main plots were N application rates of 0, 112, 168, 224, 280, and 336 kg N ha -1 ; split plots were target plant densities of 37 100, 61 800, 86 500, and 111 200 plants ha -1 . Harvests were at regular intervals beginning 13 September and ending 25 October. During the harvest season, root yield increased 8.0 Mg ha -1 , sucrose content increased 29 g kg -1 , and recoverable sucrose increased 2A4 Mg ha -1 . The first 112 kg N ha -1 increased root yield 11.8 Mg ha -1 , while the next 56 kg N ha -1 increased root yield 5.2 Mg ha -1 . Sucrose content decreased from 164 to 157 g kg -1 as N rate increased from 0 to 336 kg ha -1 The first 168 kg N ha -1 increased recoverable sucrose 2.48 Mg ha -1 . Plant density had no effect on root yield. Sucrose content increased 5 g kg -1 as plant density increased from 42 000 to 112 000 plants ha -1 . Recoverable sucrose increased from 7.40 Mg ha -1 at 42 700 plants ha -1 to a maximum of 7.79 Mg ha -1 at 88 600 plants ha -1 . No consistent harvest date x plant density interactions were observed for yield and quality measurements, suggesting that no adjustments in plant density were needed for earlier harvest dates. A harvest date x N rate interaction for recoverable sucrose implies that N rate should be decreased for earlier harvest dates.

A recent significant change in the sugar beet (Beta vulgaris L.) industry has been the adoption of an early harvest option in the grower-processor contract which allows harvest and delivery of sugar beets 30 days earlier than normal. This lengthens the harvesting period from 30 to 60 days or more. Management adjustments may be necessary for early harvested fields. The objectives of this study were: 1) to describe sugar beet yield and quality response to harvest date, and 2) to determine optimum management strategies for early versus normal harvest, with emphasis on irrigation, cultivar selection, and N rate. From 1986 to 1988, a total of three cultivars were established in experiments conducted at Powell, WY. Irrigation was either normally applied or discontinued four to six weeks prior to harvest. Ammonium nitrate was applied at rates ranging from 0 to 336 kg N ha -I. Harvests were at 4 to 15 d intervals beginning 4 September and ending 19 October. Discontinuing irrigation increased sucrose content from 174 to 183 g kg-I, but did not significantly affect root yield or recoverable sucrose. Significant irrigation treatment X harvest date interactions were observed for some sugar be-et yield and quality traits during early harvest, but when all treatments were irrigated immediately prior to the last harvest date, no differences were observed between irrigation treatments for any trait. Depending upon location and year, cultivar differences were observed for yield and quality traits. Root yield increased with later harvest date 0.363 Mg ha -I d -), sucrose content increased 8.94 g kg-I d-\ and brei impurities and sucrose loss to molasses decreased thereby improving quality. Under the management conditions of this study, few interactions with harvest date were observed. Management adjustments involving irrigation, cultivar, and nitrogen may not be necessary for early versus late harvested fields. Additional Key Words: Beta vulgaris L., harvest management, sugar beet production, extended factory campaign, harvest premium.

Ethephon ([2-chloroethyl] phosphonic acid), typically increases barley (Hordeum vulgare L.) spikes per square meter by increasing the frequency of late emerging green tillers, resulting in uneven crop maturity. This study was conducted to evaluate barley tiller grain yield and malting quality response to plant density and ethephon, with special reference to late-emerging green tillers. Field studies were conducted at Povvell. WY between 1987 and 1989 on a Garland clay loam (fine, mixed, mesic Typic Haplargid). Target plant densities of 150 and 300 plants nr2 were established. Ethephon was applied at the Zadoks growth stages (ZGS) of 13, 32, or 39, and one treatment was split-applied at ZGS 32 and 39. Early emerging primary tillers (Tl, T2, and T3) and the main shoot contributed 86% of the total grain yield at high plant density vs. 73% at lo * plant density. In general., increasing plant density resulted in progressively greater differences for kernel plumpness and kernels per spike on the MS, Tl, T2, and T3. Ethephon applied at ZGS 39 reduced plant height 6 to 15 cm depending on year. Lodging was reduced by ethephon application, although the lodging level was low in every year of the study. Ethephon did not affect grain yield or protein content, but it often reduced volume mass and kernel plumpness compared to the untreated control. Regardless of ethephon treatment, kernels on late emerging tillers were of lower mass, volume mass, and plumpness than kernels on early emerging tillers;. Ethephon applied at ZGS 39 increased the number of late emerging green tillers by 225 spikes nr2 compared with the control. These late emerging green tillers contributed 8% to the total grain yielc, but produced grain of substandard malting quality. Dep. of Plant, Soil and Insect Sciences, Univ. of Wyoming, UWREC, 747 Road 9, Powell, WY 82435. Contribution of the Wyoming Agric. Exp. Stn. Journal paper no. 1616. Received 9 July 1990.

(...) This study was conducted to determine planting date and N rate effects on grain yield, grain protein, kernel plumpness and yield components of spring malting barley grown under a production system that minimized crop water stress. Between 1984 and 1988, Klages' barley was planted at 2-wk intervals between 15 April and 19 May (expressed as days from 1 January) at Powell, WY on a Garland clay loam. Ammonium nitrate was applied at rates of 0, 67, 134, and 202 kg N ha -1 (...)