https://hdl.handle.net/10217/100514 2017-07-09T21:22:52Z 2017-07-09T21:22:52Z Wenz, Joshua https://hdl.handle.net/10217/181472 2017-07-06T18:04:44Z

The influence of outdoor light on biomass, nitrogen, and phytohormone concentrations of a nitrogen-fixing Anabaena sp. Cyanobacterium Wenz, Joshua To view the abstract, please see the full text of the document. 2017 Spring; Includes bibliographical references.

de Lara, Alfonso https://hdl.handle.net/10217/178935 2017-01-09T20:43:18Z

Remote sensing and apparent electrical conductivity to characterize soil water content de Lara, Alfonso Improvement in water use efficiency of crops is a key component in addressing the increasing global water demand. The time and depth of the soil water monitoring are essential when defining the amount of water to be applied to irrigated crops. Precision irrigation (PI) is a relatively new concept in agriculture, and it provides a vast potential for enhancing water use efficiency while maintaining or increasing grain yield. As part of site-specific farming, PI needs to be explored, tested, and evaluated which continues to be a research issue. Neutron probes (NPs) have consistently been used for studies as a robust and accurate method to estimate soil water content (SWC). Remote sensing derived vegetation indices have been successfully used to estimate variability of Leaf Area Index and biomass, which are related with root water uptake. Crop yield has not been evaluated on a basis of SWC as explained by NPs in time and at different depths. One among many challenges in implementing PI is the reliable characterization of the soil water content (SWC) across spatially variable fields. For this purpose, commercial retailers are employing apparent soil electrical conductivity (ECa) to create irrigation prescription maps. However, the accuracy of this method has not been properly studied at the field scale. The objectives of this study were (1) to determine the optimal time and depth of SWC and its relationship to maize grain yield (2) to determine if satellite-derived vegetation indices coupled with SWC could further improve the relationship between maize grain yield and SWC (3) to assess the potential of ECa measurement to characterize spatial distribution of SWC at field scale, and (4) to determine whether soil properties coupled with ECa could further improve the characterization of the SWC. For objectives 1 and 2, the study was conducted on maize (Zea Mays L.) irrigated in two fields in northern Colorado. Soil water data was collected at five soil depths (30, 60, 90, 120 and 150 cm), 21 and 12 times at Site I and II, respectively. Three vegetation indices were calculated on seven dates (Emergence to R3). Maize grain yield was harvested at the physiological maturity at each NPs location. Automated model selection of SWC readings to assess maize yield consistently selected three dates spread around reproductive growth stages for most depths (p value < 0.05). For objectives 3 and 4, the study was conducted on two fields located in northeastern Colorado. In-field SWC was measured using neutron probes at 41 and 31 locations for Site I and II respectively. Soil ECa measurements were acquired using Geonics EM38-MK2 unit. In addition, cation exchange capacity, clay, organic matter and salt content were coupled with soil ECa to estimate SWC. Data analysis was performed using the statistical software R. Statistical correlations and multiple linear regressions were obtained from the properties that were statistically significant (p value < 0.05). Results of the study showed that the SWC readings at the 90 cm depth had the highest correlations with maize yield, followed closely by the 120 cm. When coupled with remote sensing data, models improved by adding vegetation indices representing the crop health status right before the reproductive growth stage (V9). Thus, SWC monitoring at reproductive stages combined with vegetation indices could be a tool for improving maize irrigation management. Likewise, the SWC was found to be statistically different across ECa derived zones, indicating that ECa was able to accurately characterize average differences in SWC across management zones. Organic matter and salt content significantly improved the SWC assessment when combined with the ECa. The development of prescription maps for variable rate irrigation should be tailor made depending on the specific field characteristics influencing SWC. Includes bibliographical references.; 2016 Fall

Daniels, Judith Marie https://hdl.handle.net/10217/178876 2017-01-09T20:43:15Z

The impacts of long-term cultivation on soil degradation in the San Luis Valley, Colorado Daniels, Judith Marie Essentially all agricultural lands globally are under pressure to meet the food demands of an additional 2 billion people over the next 20 years. All of the agroecosystems possess limitations that constrain their ability to optimize production, however, these limitations are magnified in semi-arid regions where permanent, seasonal or periodic moisture deficiency results in evaporation and transpiration rates that exceed precipitation. Traditional cultivation practices that utilize modern technology have resulted in substantial amounts of soil loss through wind and water erosion, decreased soil organic matter, reduction in soil water-holding capacity, and alterations to the microbial community composition. Cultivation also affects soil chemical processes and conditions (e.g., pH, cation exchange complexes, electric conductivity, and sodium adsorption ratio) that can lead to further soil degradation. Changes in one or more of these properties often have direct or indirect effects on the fertility of soils, which influence resiliency and soil health. While research has clearly established the most common modifications to soil systems from cultivation, further investigation is needed in semi-arid regions to identify the critical links between physical, chemical, and biological properties that regulate resiliency and soil degradation. In establishing these critical links, I evaluated the importance of parent material (basalt versus granite) in assessing the impacts on the physical, chemical, and biogeochemical soil properties as a function of cultivation, specifically sprinkler and flood irrigation. I also distinguished microbial community composition by parent material and land use and identified key soil properties that regulate changes in microbial community structure by sampling native and cultivated soils in the San Luis Valley (SLV), located in the South Central part of Colorado. The SLV is a high elevation semi-arid agroecosystem with basalt and granite substrates, that receives 177 mm of precipitation annually and the potential evapotranspiration that exceeds 1016 mm. The SLV has also has a 150-year history of irrigated agriculture practices, which add an additional 153 to 1226 mm of water during the growing season. This alters the natural climate and possibly results in some degree of land degradation. Overall, the results indicate the importance of parent material (basalt vs. granite), as a soil forming factor in assessing the impact of cultivation on soil degradation processes. The initial clay percent in the native soils was 20% for basalt and 18% for granite. The additional accumulation of clay from irrigation was slightly higher for basalt soil, (22%) and 20% for granite soils. Soils derived from basalt have greater quantities of the major cations while soils derived from granite have lower quantities and a poor nutrient status. Soils derived from basalt have greater percentage of soil organic carbon in the soil surface horizons than soils derived from granite. The uncultivated soils derived from basalt classify as saline-sodic while those derived from granite were consistently non-saline, non-sodic. As a function of irrigation, the nutrient concentrations of calcium, magnesium, sodium, potassium, chloride and sulfate were reduced in basalt soils while concentrations increased in granite. In addition, the greatest accumulation of clay and soil organic carbon occurred in granite soils with flood irrigation which resulted in similar concentrations as the basalt soils. Also, basalt soils re-classified as non-saline and non-sodic while those derived from granite remain consistently non-saline non-sodic. These results demonstrate a convergence among the basalt and granite soil properties as a function of land use. Using the ester-linked fatty acid methyl ester (EL-FAMEs), which evaluates differences among soil microbial community composition based on the condition variables of parent material (granite and basalt) and treatments (control, sprinkler, and flood). The results indicated that total microbial biomass and the stress ratios differed between basalt and granite with flood irrigation and the most variation was observed in the basalt-flooded soils. The fungi-to-bacteria ratios were the same in basalt and granite soils and both irrigation types (sprinkler and flood). Arbuscular Mycorrhizal (AM) Fungi did not differ between basalt and granite, however, the concentrations of AM fungi increased in irrigated soils, suggesting alfalfa and pasture hay grasses nurture root biomass. The correlations analysis identified pH, magnesium, sodium, potassium, chloride, and organic carbon as being the primary soil properties associated with the microbial communities in both soils and treatment types. The results from the sensitivity model for microbial communities in granite soils indicated changes in these soil properties were more pronounced pH, magnesium, sodium, potassium, chloride, and soil organic carbon in both sprinkler and flood irrigation. While the microbial communities in basalt soils were sensitive to pH and soil organic carbon in both irrigation practices; the responses were negligible compared to granite soils. Physical soil properties were not significant in determining correlations or sensitivities among the microbial communities. Overall, my data revealed the importance of communally evaluating the physical, chemical, and biological properties in determining the key properties that collectively regulate resiliency and indicate soil degradation. The key indicators in this study are soil texture, bulk density, clay, soil organic matter, sodium, chloride, sulfate, and AM Fungi microbial communities, which provide a benchmark for quantifying the magnitude and directional change of soils in cultivated systems with respect to their native counterparts. The findings revealed that long-term cultivation in the SLV has not degraded the soils according to the indices used. The parameters used this study improve the understanding of long-term irrigation impacts on agroecosystems in arid and semi-arid regions by linking the substrate properties with the soil-forming factors and irrigated water quality. This study provides the key information that can be used as a matrix by which to evaluate the impacts of climate change and a growing global population in other water-limited regions. Includes bibliographical references.; 2016 Fall

Wickham, Allison https://hdl.handle.net/10217/176725 2016-08-30T20:34:18Z

Effects of cyanobacterial fertilizer, commonly-used organic fertilizers, and plant growth regulators on yield and growth characteristics of carrots (Daucus carota var. sativus), cucumbers (Cucumis sativus), and bell peppers (Capsicum annuum) Wickham, Allison Nitrogen (N) is arguably the most important agricultural nutrient. More money and resources are spent on N management in agricultural systems than any other nutrient. Producing N fertilizer for agricultural use accounts for more than half of the carbon footprint of crop production. Nitrogen plays a crucial role in plant growth, and adding N fertilizers to agricultural systems can lead to noticeable increases in productivity. Nitrogen fertilizers commonly used in organic production are often energy intensive to produce and expensive to transport. Cyanobacteria fertilizer (cyano-fertilizer) produced on-farm could decrease fertilizer impacts on the environment as well as reduce production costs for organic farmers. In addition, cyanofertilizer may perform similarly to products marketed to increase production via plant growth hormones such as seaweed extract, which is shipped all over the world from coastal regions. The effects of common organic fertilizers as well as organic liquid cyano-fertilizer on carrot (Daucus carota var. sativus) and cucumber (Cucumis sativus) growth and yield characteristics were tested during field experiments at the Horticulture Field Research Center in Fort Collins, CO in 2014 and 2015. Bell peppers (Capsicum annuum) were grown in a greenhouse experiment in 2015 at the Colorado State University Plant Growth Facility. Cyano-fertilizer was produced and evaluated in this study to compare effects of farm-grown cyano-fertilizer and commonly-used organic fertilizers. The purpose of this study was to identify fertilizer and foliar seaweed application effects on yield, stress, and growth characteristics of all three plant species. In all experiments, hydrolyzed and non-hydrolyzed fish fertilizers, and cyano-fertilizer treatments were applied at prescribed N rates throughout the growth period approximately every 10 days. Control treatments received no supplemental N. Each treatment, including the control, was repeated with the addition of two forms of concentrated organic seaweed extract applied foliarly. Neptune’s Harvest and Seacom PGR brand seaweeds were used for their lack of N content. Seaweeds were applied at the manufacturers’ recommended rates. Phytohormones were detected in all N fertilizers and in the PGR seaweed. No phytohormones were detected in the Neptune’s Harvest seaweed. In 2014, carrot length and yield were increased by the addition of cyano-fertilizer compared to the unfertilized control. All fertilizers increased post-season soil N compared to the control. Nitrogen fertilizers increased carrot leaf tissue Mg concentrations compared to the control. Nitrogen fertilizers and foliar seaweed influenced the number of carrots with deformities, and a significant interaction between N fertilizers and seaweed with regard to stress indicated a stress response to the addition of both fish fertilizer and a foliar seaweed application. In 2015, cyano-fertilizer produced a higher carrot yield than hydrolyzed fish fertilizer. Nitrogen fertilizers impacted the total number of cucumbers harvested as well as total cucumber yield, but the results were not consistent across years. The majority of significant differences occurred in the pepper study. Nitrogen fertilizer had an effect on leaf tissue nutrient concentrations as well as phytohormone content. Nitrogen fertilizer also impacted flower death and leaf abscission as well as plant stress. Foliarly applied seaweed treatments had very little significant influence in the carrot or cucumber field studies, but did have an effect on pepper shape and color (crop quality). Pepper yield was impacted by the addition of N fertilizers. Foliar seaweed impacted pepper branching behavior as well as fruit color and shape. Based on these experiments, it can be concluded that cyano-fertilizer can be used as a N source in place of commonly-used organic fertilizers. With regards to plant growth characteristics, it is unclear that any of the products applied consistently impacted plant growth characteristics in a way that improved yield or quality. Includes bibliographical references.; 2016 Summer