Browsing by Subject "Soil fertility"

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    Nitrogen Management for Corn Following Alfalfa: Field, Literature, and Geographic Analyses
    (2013-12) Yost, Matt Alan
    First- and second-year corn (Zea mays L.) following alfalfa (Medicago sativa L.) often require less supplemental N than corn grown continuously or following soybean [Glycine max (L.) Merr.]. The results of seven on-farm trials indicated that alfalfa can provide the entire N requirement of first-year corn no-till planted following alfalfa terminated in the fall. Eight other on-farm trials also indicated that first-year corn following alfalfa often does not require supplemental N (fertilizer or manure). The conclusion that first-year corn following alfalfa often requires no fertilizer N has been supported for decades, yet no research has identified site-specific conditions that cause first-year corn to respond to supplemental fertilizer N. The most widely used predictive test, the presidedress soil nitrate test (PSNT), had limited success in identifying response to N when trials from this study were combined with literature research; the test was 55% accurate across 94 site-years. An end-of-season test used to assess N supply to corn, the corn stalk nitrate test (CSNT), also was not successful in 11 trials at identifying when first-year corn would have required fertilizer N. An analysis of the literature was conducted to identify site-specific conditions that cause first-year corn following alfalfa to respond to N. Soil texture and alfalfa termination timing on medium-textured soils were significant covariates for identifying responsiveness to fertilizer N in first-year corn. First-year corn following alfalfa rarely required fertilizer N when alfalfa harvested for ¡Ý2 yr was fall-terminated on medium-textured soils; corn following alfalfa harvested 1 yr responded more frequently. The frequency of response to fertilizer N increased greatly when alfalfa was grown on coarse- or fine-textured soils and when alfalfa was terminated in the spring on medium-textured soils. For these conditions, combinations of alfalfa stand age and weather conditions explained much of the variation in whether a site would respond to N and the economically optimum N rate (EONR) at various price ratios (PRs) of fertilizer N/corn grain. The regression models developed to predict fertilizer N response appear robust, but require independent validation. Alfalfa also provides N to the second consecutive corn crop following alfalfa termination. Results from 28 on-farm trials in Minnesota and Iowa revealed that second-year corn required fertilizer N only 50% of the time. The same trend occurred when these trials were combined with 39 trials in the literature. The PSNT had higher accuracy for second-year corn (65%) than for first-year corn, but improvements in accuracy are still necessary in order for this test to be a reliable tool for growers. A geographic analysis revealed that growers in the U.S. Corn Belt region of the upper midwestern United States (North Dakota, South Dakota, Nebraska, Minnesota, Iowa, and Wisconsin) rotate alfalfa more frequently than in other parts of this region and that alfalfa phase length, soil texture, and year affect the type of crops grown for 2 yr following alfalfa termination. Supplemental files include data and references used for the literature analysis (Supplemental Table S4.1; Supplement S4.2), data used for analysis of second-year corn response to N (Supplemental Table S5.1), and alfalfa hectare estimates by state and year for the geographic analysis (Supplemental Table S6.1).
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    Understanding Cyanobacteria-based Biofertilizers in Soil-Water and Soil-Plant Systems
    (2021-10) Alvarez De La Hoz, Adriana
    Growing pressures to increase agricultural productivity amid rising environmental impacts and global climate threats call for critical strategies that preserve the soil resource and improve sustainability. Microalgae, including cyanobacteria, are emerging as promising platforms to enhance soil structure and fertility and reduce our reliance on chemical fertilizers. To advance applications, further understanding is needed with different strains, plants, agroecological regions and types of soil including Mollisols, which are among the most productive soils in the world. This dissertation reviewed aspects of microalgae that might be applied in agriculture and evaluated effects of soil inoculations with the dinitrogen (N2)-fixing cyanobacterium Anabaena cylindrica UTEX 1611 on a Mollisol from the U.S. Upper Midwest. First, a comprehensive literature review supported microalgae as renewable resources for the potential development of biofertilizers, organic fertilizers, biostimulants, biocontrol agents, and soil conditioners. Furthermore, experiments with cyanobacterial soil inoculations described effects on soil structure and nutrient dynamics, soil loss and water nutrient levels after high-intensity rain simulations, and soil mineralization of cyanobacterial biomass. The results revealed changes in soil structural components that might be resistant to wind and water erosion, potential for reducing rainfall-induced soil loss, and a gradual nutrient release from the cyanobacterial biomass. High-intensity rain simulations also indicated depth-related positive changes in soil microbial dynamics that persisted after consecutive rains. Finally, experiments with a local variety of spring wheat consistently evidenced improvements in soil nutrients, microbial biomass, and microbial activity, and demonstrated that cyanobacteria, and a mixture with a local green microalga, supplied nitrogen (N) to support plant growth and partially replace urea. These findings provide insights on the positive role cyanobacteria might have as resources to enhance the sustainability and resiliency of agricultural systems.