Thesis (M.S.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Fabian D. Menalled. Includes bibliographical references.

Crop rotation is a key strategy of sustainable agriculture in the Canadian Prairie. Improving crop productivity and yield stability in pulses-based cropping systems with better soil biology is the ultimate goal of this research. Firstly, my studies provide information on the effect of pulses on the biodiversity of soil fungi: arbuscular mycorrhizal fungi (AM) and non-AM fungi, associated with the main pulse species grown in the Canadian Prairie (field pea, lentil, and chickpea), and their influence on wheat-based cropping systems. Secondly, the optimum 4-yr crop rotation for wheat production was determined, based on the relationship among fungal communities associated to the different crops and the yield and quality of these crops. My research included two experiments. First, in a field experiment replicated in time and site, the effect of previous pulse crops on wheat root-associated microbial communities and crop performance was assessed in four 2-yr rotation systems. Second, a 4-yr field experiment evaluated the relative influence of eight different crop rotations on root-associated microbial communities and on wheat productivity in the last year of the rotations. A greenhouse assay was conducted to evaluate, under controlled conditions, the influence of the microbial communities selected by these previous field crop rotations on wheat performance, using soil from the field as inoculant. The response of root-associated microbial communities was characterized using next generation sequencing technologies, phospholipid fatty acid markers, microscopic observation of roots and soil dehydrogenase assay. Plant response was evaluated based on crop density, biomass, yield and tissue nutrient content. My studies showed that community composition of AM and non-AM fungal communities in the roots of wheat were largely influenced by host plant identity and environmental conditions. The structure of the overall fungal community in wheat roots was not affected by the previous crops. The soil microbial legacies of previous crops were different from the fungal communities found in the roots of the following wheat, suggesting that wheat, as a host plant, selects and associates with a specific fungal community. Seasonal variations in soil moisture, temperature, pH, and nutrient cycling between sampling times have a great influence on soil microbes and could also be influencing these effects. The 2-yr crop rotation experiment revealed that wheat after a pulse crop had higher plant density and produced more seed biomass and total yield. The 4-yr crop rotation studies revealed that, in the field, diversified rotations including pea or lentil in alternate years, largely contributed to wheat performance. However, rotations including chickpea contributed little to the rotation benefits, suggesting that a careful selection of plant species is essential to improve the performance of the agroecosystem. Contrary to the field results’ findings, under greenhouse conditions, rotations that included chickpea before wheat contributed the best to wheat productivity, suggesting that in the field, factors other than the microbial community selected by chickpea were responsible for the poor performance of chickpea-wheat rotations in the field. Soil bacterial and fungal biomasses were positively correlated with wheat yield in the field experiments, which suggests that an abundant and diversified microbial community positively influences wheat productivity. Also, possible antagonistic and synergistic interactions between different AM species and root pathogens could be inferred. These results suggest that many AM fungi can potentially contribute to combat pathogens and enhance plant performance, whereas other might produce detrimental effects on the plants. Overall my studies revealed that host plant identity and environmental conditions influence the fungal community structure and dynamics. The frequency and sequence of crops in the rotations strongly influences productivity in wheat based agroecosystems. Lentil and pea alternating with wheat largely contribute to wheat performance. Thus, the productivity of wheat can be improved by selecting and including the plant species most beneficial to the rotation in order to increase soil available water and N, while promoting beneficial microbial associations and reducing disease incidence.

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Master of Science / Department of Agronomy / Nathan O. Nelson / Phosphorus (P) loss from non-point agricultural sources has been identified as a main contributor to degraded surface water quality throughout the United States. Excessive P inputs to surface waters can lead to eutrophication, increased water treatment costs, and negative health impacts. Therefore, agricultural best management practices (BMP) that promote water quality, through minimizing P loss, must be identified. Studies outlined in this thesis aim to determine the impacts of cover crops and P fertilizer placement on P loss in surface runoff and nutrient cycling in a no-till corn (Zea mays)-soybean (Glycine max) rotation and provide insight into how cover crop species selection and termination method affects potential P loss from crop tissue. The first study examined combined effects of cover crop and P fertilizer placement on total P, dissolved reactive P (DRP) and sediment losses in surface runoff from natural precipitation events. This large-scale field study was conducted near Manhattan, Kansas, at the Kansas Agricultural Watershed (KAW) Field Laboratory during the 2016 and 2017 cropping years. Two levels of cover crop [no cover crop (NC) and cover crop (CC)] and three levels of P fertilizer management [no P (CN), fall broadcast P (FB), and spring injected P (SI)] were used. Flow-weighted composite water samples were collected from precipitation events generating greater than 2.0 mm of surface runoff. Results from this study found the CC treatment increased DRP losses compared to NC in both cropping years; however, CC reduced sediment loss by over 50% compared to NC. Application of P fertilizer increased DRP losses compared CN in both cropping years, although SI resulted in lower quantities of DRP loss compared to FB. In addition, this study found that CC reduced biomass and yield of corn compared to NC and therefore decreased nutrient uptake, removal, and deposition during the 2017 cropping year. However, no negative impacts of CC on biomass or yield were observed during the 2015 (corn) and 2016 (soybean) cropping years. Application of P fertilizer increased the concentration of Melich-3 P and total P in the top 0-5 cm of soil compared to CN; however, no differences between P fertilizer management practice were observed for concentrations of Melich-3 P at 5-15 cm. A greenhouse-based study determined the impacts of cover crop species (brassica, grass, and legume), termination method (clipping, freezing, and herbicide), and time after termination (1, 7, and 14 days after termination) on total P and water-extractable P (WEP) release from cover crop biomass. Freezing increased WEP concentration of crop tissue by more than 140% compared to clipping and herbicide. Additionally, at 7 and 14 days after termination, both concentration of WEP and fraction of WEP compared total P increased compared to 1 DAT. Findings from these studies suggest the use of cover crops may unintentionally result in greater DRP losses in surface runoff. However, addition of a cover crop can dramatically reduce erosion losses. In addition, cover crop species selection can directly impact the quantity of P being taken up and released by crop tissue. Understanding the impact of crop species selection may help create new BMPs which aim to reduce P loss.

A series of experiments was carried out in the Department of Agriculture, University College of North Wales, Bangor, during October 1987 to September 1989. The purpose of these was to study the effects of water stress and salinity stress at different stages on long (Norman), medium (Fenman) and short duration (Wembley) wheat varieties in different environments. Effects of water stress were tested in large pots in different types of soil. Effects of salinity were tested by growing plants in solution culture. In both experiments water stress and salinity stress were imposed at three major stages, tillering to stem extension (TL-SE), stem extension to booting (SE-BG) and booting to maturity (BG-MT). These were tested in each variety in comparison with a control of each variety. Growth measurements, leaf number and area, stem area, shoot number, plant height, nitrogen %, nitrogen uptake, dry weight per plant were determined at the end of each stage. Soluble carbohydrates were determined at anthesis. This was done to find out how much these growth measurements were decreased during each stress period. Yield and yield components were determined at harvest. In these experiments the long duration variety took a long time in growth during TL-SE, in comparison to mid winter and spring wheat varieties. The long duration variety gave a higher plant, more straw dry weight production and more leaf number than the short duration variety. The long duration variety also gave a higher yield than the medium and short duration varieties, due to larger ears, more spikelets vi per ear, more grain number per ear and more grain number per spikelet. All varieties experienced higher temperatures and longer days during SE-BG and BG-MT in both experiments. The lengths of these stages therefore showed smaller variation between varieties. In water stress experiments the mixed peat-soil used in Experiment 2 dried out quicker than the normal field soil used in Experiment 1. The upper portion of the soil was dried before the lower portion of the soil during the stress period. With water stress at SE-BG and BG-MT the soil dried out quicker in both years. Gypsum blocks were used to give readings of water stress. with water stress at BG-MT the soil was completely dried out after the third week, in all varieties, due to higher plant height, higher temperature and more evaporation. Because of this water stress at BG-MT resulted in a short duration for ripening. In both water stress Experiments 1 and 2, in all varieties all water stress treatments decreased the growth measurements, decreased yield and yield components. In Norman water stress at TL-SE had a long stress period due to slow growth processes during cold winter. However, this stage had a similar effect on yield in Norman, Fenman and Wembley. In both water stress experiments in all varieties, water stress at SE-BG caused the largest reductions in growth measurements, because at this stage the plant had the greatest leaf area and temperature was higher, although the period of stress was only a few weeks. However, water stress at BG-MT caused the greatest decreases in yield. This stage showed the greatest vii decreases in yield and yield components, due to small grain size, fewer fertile spikelets, small size of ear, earlier leaf senescence, short duration for ripening, higher temperature, lack of soluble carbohydrate for grain f~lling from stem and pollination problems at anthesis time. In both salinity Experiments 1 and 2, all varieties had a larger green leaf area, more tillers and all varieties were much stronger after stem extension than in the water stress experiments due to the solution culture teChnique. Norman was more strong than the other varieties because of its long period grown in solution culture. Salinity at TL-SE was more damaging than other stages in all varieties. Salinity at TL-SE decreased the growth measurements, such as leaf area, stem area, plant height, dry weight per plant. Because of the growth measurement reduction, grain weight per plant, grain number per plant, grain number per ear, grain number per fertile spikelet and fertile spikelet per ear were decreased by salinity at this stage. Salinity at SE-BG and BG-MT also decreased growth measurements, decreased grain yield and yield components. Salinity at BG-MT decreased grain yield and yield components more than salinity at SE-BG. In Experiment 2 in all varieties with salinity at BG-MT plants were harvested a few days before other stages and the control. Norman was more sensitive with salinity at TL-SE than the other varieties because of its long period grown under salt stress. Norman was much stronger with salinity at SE-BG. Norman gave lower yield, yield components at BG-MT than other varieties at this stage.

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Average soybean [Glycine max (L.) Merrill] yields in North Dakota remain below north central USA averages, and crop yield potentials. The effect of planting date (PD), cultivar relative maturity (RM), and seeding rate (SR), on yield, were evaluated in 821 producer fields in 2014-2016 seasons. Crop management varied by location. State average PD was 19 May, and planting after 1 May reduced yield average 0.4% d-1. Planting a cultivar with 0.1 RM earlier than recommended reduced yield by 1.3%. Producers estimated seedling mortality at 10%; when observed, it was 12.3%. An additional 7.9% reduction of established population occurred in-season. In-season plant reductions of 4.5% were also observed in research trials. North Dakota producers should plant closer to 1 May if conditions are favorable, select latest-maturing cultivars adapted for area, maximize established plant population relative to seeding rate, and determine causes of in-season plant reductions to adapt management practices if necessary.

Field experiments were conducted to evaluate cover crop interseeding time and species effect on sugarbeet production during 2018 and 2019 growing seasons. Cover crops were first interseeded in June and second interseeding was done in late June or early July. Four cover crops species, Austrian pea (Pisum sativum L.), winter rye (Secale cereale L.), winter camelina [Camelina sativa (L.) Crantz], and brown mustard (Brassica juncea L.), were examined. First interseeding resulted in significantly higher cover crop biomass than second interseeding. In 2018, the highest recoverable sugar yield was observed with pea (13.9 Mg ha-1) and camelina (6.6 Mg ha-1) first-interseeded, at Ada and Downer, MN, respectively. In 2019, camelina (11.2 Mg ha-1) at Ada, MN, and pea (12.4 Mg ha-1) at Prosper, ND both second-interseeded, had the highest recoverable sugar yield. Cover crops had no negative impacts on sugarbeet, but the selection of species and planting time are critical.