Horseweed (Erigeron canadensis) is a competitive winter or summer annual broadleaf weed. When uncontrolled, horseweed can reduce soybean (Glycine max) yields by 93%. Research was conducted to advance our knowledge on horseweed growth stage response to foliar-active and residual herbicides, fall applications, and the utility of differing herbicide technologies. Greenhouse results determined that herbicide efficacy was greatest when applied to early rosette horseweed providing an average control of 70% across herbicide treatments. Field trials determined that preventing new emergence with flumioxazin, added with dicamba or paraquat to kill existing plants in the fall, increased control to 99% the following spring. Field trials also determined that dicamba, applied PRE or POST, provided excellent horseweed control and was an effective soybean technology system for horseweed-infested fields. Saflufenacil controlled existing plants, but residual benefits were unclear. Further research must be done to investigate residual activity of PRE herbicides applied before horseweed emergence.

Determining optimum N fertilization rate and timing is critical to improve yields and economic sustainability for no-till winter wheat (Triticum aestivum L.) in the Virginia Coastal Plain. Little data are available evaluating N management strategies, optimum N rate prediction methods, or potential NO3 leaching under no-till wheat in soils and climate similar to the mid-Atlantic region. The objectives of our research were: (1) to determine economic optimum N fertilization rates and timings; (2) evaluate selected methods for predicting optimum N rates at GS 25 and GS 30; and (3) measure NO3 leaching loss under selected N management strategies. Eleven experiments over three years evaluated N rates at GS 25 and GS 30. Six experiments over two years evaluated pre-plant and December or GS 25 N rates under no-till winter wheat in farm fields of the Coastal Plain region of Virginia. Nitrate leaching was measured under selected pre-plant and December or GS 25 N application rates. All sites represented common Coastal Plain soil types and cultural practices for no-till wheat production. Yield data were used to calculate economic optimum N rates for a range of combinations of N management strategies. Optimum N rates were regressed against tiller density at GS 25, and wheat tissue N content and SPAD chlorophyll meter readings at GS 30, to determine their effectiveness as predictors of the optimum N rate at GS 25 or GS 30. Tiller density was an effective predictor of optimum GS 25 N rate in these split application management strategies. However, wheat tissue N contents and SPAD chlorophyll meter readings were not effective predictors of optimum N application at GS 30. Yields across all experimental designs were affected by planting date. Timely planted no-till wheat consistently produced higher yields compared to late planted. Sites under continuous no-till production for 8 years or more also produced higher yields than sites under continuous no-till production for less than 8 years. Including an additional December N application with the more traditional N management strategy of pre-plant, GS 25 and GS 30 N applications improved yields. Nitrate leaching loss at selected pre-plant and December or GS 25 N rates was not higher than background check plot levels under timely planted no-till wheat. Additionally, economic optimum N application rates and timings at these sites did not produce NO3 leaching losses above background levels under timely or late planted wheat, except at one late planted site. These data indicate N application rates and timings in no-till wheat can be managed for improved economic sustainability and reduced environmental impact. / Ph. D.

Master of Science / Department of Agronomy / Scott A. Staggenborg / Abstract Hard red winter wheat (Triticum aestivum L.) is the predominate crop grown in North Central Kansas; and no-till wheat production practices have gained popularity in this region. No-till advantages may include: increased stored soil moisture, decreased labor costs, and increased soil conservation compared with conventional cropping systems. Seeding rates and fertility rates are two important no-till management decisions for producers. Therefore, a two-year study was conducted to determine the optimum wheat seeding and fertility rates in north central Kansas comparing the winter wheat cultivars 'Overley' and '2145'. Treatments also included seeding rates (100 kg ha-1 vs. 134 kg ha-1) and fertility rates (0, 78, 112, 146 kg ha-1). A fungicide application study was also conducted with this two-year study but proved to be statistically insignificant during the two years. Overall, the variety selection and fertility rates affected grain yields. The higher fertilizer treatments increased wheat grain yields. However, the seeding rate yield differences were not significant either year of this study. In the fungicide study, 2145 responded more to fungicide applications than Overley in 2006; but in 2005 there was no statistical advantage for a fungicide treatment with either variety. For this study, wheat varieties were planted during the recommended optimum "fly-free" seeding date period (4 October through 10 October). Although this study did not record yield differences between wheat drilled at higher or lower seeding rate during the recommended seeding period, other research does indicate that seeding rates should be increased if planting dates are extended well beyond the optimum period. Further outcomes from this study indicate that nitrogen rates should be adjusted based on field yield expectations. Although timely rainfall and/or stored soil moisture are the most limiting yield factors in dryland wheat production in north central Kansas, research results indicate that wheat yields increase with higher fertility rates when moisture is not a limiting factor. This research may be applied to north central Kansas wheat fields particularly where no-till farming practices are being used in wheat following wheat fields.

No description available.

Doctor of Philosophy / Department of Agronomy / Kraig L. Roozeboom / Previous research has revealed that winter wheat (Triticum aestivum L.) yields are often reduced following grain sorghum [Sorghum bicolor (L.) Moench] compared to wheat after other summer crops. The objectives of the study were to: (a) evaluate grain sorghum residue management strategies to improve the performance of a following winter wheat crop in no-till systems; (b) determine grain sorghum hybrid characteristics that facilitate planting wheat following grain sorghum, and identify winter wheat cultivars that are suitable for planting after grain sorghum; (c) evaluate effect of environment, sampling time, and grain sorghum hybrid plant pigmentation on phenolic acid concentration in sorghum residues. Experiments were conducted in environments suitable for planting winter wheat following a summer crop. Treatments for objective one were: glyphosate (pre-harvest application, post-harvest, none), residue (removed, chopped, left standing), and nitrogen (34 kg ha⁻¹ applied to residue, none). Treatments for objective two and three were grain sorghum hybrids representing three maturities (early, medium, medium-late) and two plant pigmentations (red, tan), wheat cultivars occupying significant planted acreage and having favorable performance within the region. Wheat yields increased in two environments by 217 and 630 kg ha⁻¹ when glyphosate was applied to the sorghum pre-harvest. Residue chopping or removal either had no effect or a negative effect on wheat yields compared to residue left standing. Nitrogen applied to the sorghum residue increased wheat yields in only one environment. Grain sorghum hybrid characteristics did not influence winter wheat yields in any environment, but winter wheat cultivar did influence grain yields of the winter wheat in three of the four environments. Breakdown of phenolic acids depended on environment. Results for these studies indicate that wheat yield after a grain sorghum crop can be maximized by planting a red-pigmented sorghum hybrid of an early or medium maturity, desiccating the sorghum crop with pre-harvest glyphosate if it can be applied to the sorghum roughly 45 to 50 days before a frost, and with a wheat cultivar that is well suited to no-till planting.

Weed control is the primary challenge in organic dry edible bean (Phaseolus vulgaris L.) production, however no previous Canadian studies have considered cereal cover crops for organic pulse production. The objectives of this study were to characterize the effects of fall rye (Secale cereal L.), barley (Hordeum vulgare L.) and oat (Avena sativa L.) cover crops and tillage management on weeds and the soil microclimate in organic dry beans. Above ground weed biomass was significantly lower in fall rye (3778 kg ha -1) and NT treatments (4867 kg ha -1). Fall rye significantly lowered spring soil nitrate-N by 72% and 74% in 2011 and 2012, respectively. Cover crops did not affect soil moisture or soil growing degree day (GDDsoil ) accumulation in early spring. Further research is needed on fall-seeded fall rye termination in organic conditions to reduce its competitiveness with the main crop. / October 2015

The objective of this study was to investigate the effects of using the blade roller for no-till/reduced tillage in organic green manure management. The study was conducted in Carman, Manitoba and Oxbow, Saskatchewan. In the spring, a pea/oat intercrop was seeded as a green manure. The green manure was terminated by rolling, tilling, or a combination of the two. The following spring, spring wheat was seeded. In the year of the green manure, measurements taken included: biomass, soil nitrogen, and ammonia emissions. In the year of the wheat, measurements taken included: soil cover, soil moisture, weed competition, soil nitrate-N, and wheat biomass. Results showed increased soil cover, minimal effect on soil moisture, delayed wheat development, an effect on weed communities, reduced rate of nitrogen release, and reduced wheat yield. No-till green manure management can therefore provide benefits of soil conservation and nitrogen conservation but may result in decreased wheat yield.

The objective of this study was to investigate the effects of using the blade roller for no-till/reduced tillage in organic green manure management. The study was conducted in Carman, Manitoba and Oxbow, Saskatchewan. In the spring, a pea/oat intercrop was seeded as a green manure. The green manure was terminated by rolling, tilling, or a combination of the two. The following spring, spring wheat was seeded. In the year of the green manure, measurements taken included: biomass, soil nitrogen, and ammonia emissions. In the year of the wheat, measurements taken included: soil cover, soil moisture, weed competition, soil nitrate-N, and wheat biomass. Results showed increased soil cover, minimal effect on soil moisture, delayed wheat development, an effect on weed communities, reduced rate of nitrogen release, and reduced wheat yield. No-till green manure management can therefore provide benefits of soil conservation and nitrogen conservation but may result in decreased wheat yield.

Managing nitrogen (N) and phosphorus (P) in agricultural systems in the Mid-Atlantic is an important practice due to environmental and economic concerns. The objectives of the experiments reported in this dissertation were: (1) evaluate irrigation via evapotranspiration (ET) calculations for fresh market tomatoes grown using polyethylene mulch; (2) determine optimum N application method and rate for fresh market tomatoes; and (3) evaluate changes of soil P pools from applications of poultry litter (PL), PL amended with alum (PLA), triple super phosphate (TSP), and no P fertilizer in a long-term no-till corn-wheat-soybean rotation. A calculated irrigation rate, based on 30-year average historical weather data, of 0.5ET provided sufficient irrigation for optimum tomato yields in near average climactic seasons. Utilizing a tensiometer in a warmer and drier season than average protected against under-irrigation rates for fresh market tomatoes. Nitrogen applications ranging from 200 to 242 kg N ha-1 using a combination of a banded method, incorporation, and fertigation produced optimum tomato yields while significantly reducing residual post-harvest inorganic soil N compared to higher N fertilizer rates. The incorporated only method resulted in crop loss and reduced yields with N fertilizer rates greater than 224 kg N ha-1 in the unseasonably hot and dry season. Applications of PL and PLA to no-till land on a N basis significantly increased Mehlich-1 extractable P and 1 M NH4Cl extractable P (loosely bound P) in shallow (0-5 cm) soil samples compared to 0-P control and TSP treatments. However, alum additions in PLA significantly reduced loosely bound P compared to soils fertilized with non-amended PL in shallow soil samples. Overall, results from these studies offer insight into production practices that increase profitability and environmental stewardship in fresh market tomatoes by optimizing fertilizer and irrigation use while maintaining marketable tomato yields. Additionally, PLA reduced the amount of loosely bound P in 0-5 cm soil samples that could potentially move to surface water in these coarse textured soils. / Ph. D.

Master of Science / Department of Agronomy / Johanna A. Dille / Palmer amaranth and horseweed are problematic weeds in no-till soybeans in Kansas. Integrating cover crops and herbicide programs could suppress weed populations. To determine the emergence pattern and survival of horseweed, a study was conducted across six locations in eastern KS in 2014-2015 and 2015-2016. Horseweed seedlings and leaf number per seedling were recorded at two-week intervals. Cumulative GDDs required to reach 50% horseweed emergence increased from north to south. Horseweed survival ranged from 4 to 90%, and majority of horseweed emerged in the fall. Field studies were conducted to determine effects of cover crops and herbicide programs on Palmer amaranth near Manhattan, KS in 2014-2015 and 2015-2016. Five cover crop treatments included no cover, fall-sown winter wheat, spring-sown oat, pea, and mixture of oat and pea. Cover crops were terminated in May with glyphosate and 2,4-D alone or with residual herbicides of flumioxazin and pyroxasulfone. By 10 weeks after termination in 2014-2015, Palmer amaranth biomass and density, averaged across cover crops. was 95 and 69% less with residual herbicides than without, respectively, and Palmer amaranth biomass was 98% less in winter wheat and 91% less in spring oat, averaged across termination methods, compared to no cover. Time to 50% Palmer amaranth emergence was delayed with winter wheat, spring oat, and spring oat/pea mix without residual herbicide. Soybean yields were greater with residual herbicide and greater with winter wheat or spring oat cover crop in 2014-2015. A field study was conducted to determine suppression effects of cover crop and herbicide programs on horseweed and Palmer amaranth near Manhattan, KS in 2015-2016. Three fall treatments included fall-sown rye, a residual herbicide tank mix of glyphosate, dicamba, chlorimuron-ethyl, tribenuron-methyl, and AMS, and no fall application. Four spring treatments included no spring application or three herbicide tank mixes: glyphosate, dicamba, and AMS alone or with flumioxazin and pyroxasulfone as early preplant, or as split applied with 2/3 preplant and 1/3 at soybean planting. Similar levels of horseweed suppression were observed when some control measure was used in fall or spring. Fall rye completely suppressed horseweed while the fall herbicide suppressed biomass by 93% and density by 86% compared to no fall application. Palmer amaranth suppression was observed when a spring herbicide application was used. In rye, total weed biomass was reduced by 97% or more across all spring treatments. Total weed biomass was reduced with a spring herbicide was used. Soybean yields were least when no herbicide treatment was used in the spring. An integrated program of fall cover crops or herbicide applications together with spring herbicide applications maintained soybean yields.