Browsing by Author "Dobbratz, Michelle"

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    Early Season Corn Development in a Kura Clover (Trifolium ambiguum Bieb.) Living Mulch
    (2017-04) Dobbratz, Michelle
    Kura clover (Trifolium ambiguum Bieb.) perennial living mulch has many agronomic and ecological benefits, but corn produced in this system is often lower yielding than monocrop corn, and this yield loss is often preceded by delayed emergence and development. To prepare rows for corn production, kura clover is selectively killed in strips using mechanical or chemical means. We monitored kura clover health, soil moisture & temperature, corn emergence, corn development, and corn yield in four row preparation strategies: herbicide band kill (BK), shank tillage (ST), novel rotary zone tillage (RZT), and dual tillage (DT) which consisted of shank tillage followed by rotary zone tillage. Our primary objective was to compare novel RZT with the traditional strip tillage unit (ST). In 2015, corn grown in RZT plots emerged and developed faster than corn grown in ST plots, but this did not lead to a difference in grain or stover yield. In 2016, corn grown in RZT and DT plots emerged and developed faster than corn grown in ST and BK plots, and grain yield in 2016 was higher (P=0.05) in the RZT and DT (10.9 Mg ha-1 and 11.6 Mg ha-1) than in the ST and BK treatments (6.9 Mg ha-1 for both treatments). Kura clover biomass was not affected by treatment in either year. Based on these results, rotary zone tillage is a promising row preparation strategy in kura clover living mulch for corn production with minimal herbicide use.
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    PERENNIAL FUEL, FEED, AND CEREAL: HIGH DIVERSITY PERENNIALS FOR BIOFUEL AND INTERMEDIATE WHEATGRASS FOR GRAIN AND FORAGE
    (2019-12) Dobbratz, Michelle
    Perennial crops may counteract negative effects of annual agriculture, such as carbon emissions, water pollution, and erosion, and systems are being developed that supply fuel, feed, and cereal. One source of fuel is cellulosic ethanol from perennial sources, and one source of feed and cereal is intermediate wheatgrass. Regarding cellulosic ethanol, markets are not currently supported by policy, making adoption of these systems largely a matter of carbon storage benefit. Regarding intermediate wheatgrass, little is known about its nitrogen balance and reproductive morphology, complicating long-term management. In the perennial cellulosic ethanol system, I measured aboveground biomass, change in total soil C, soil microbial biomass, and extracellular enzyme activity with and without nitrogen in four species mixture treatments ranging from 1-24 native species at four sites across Minnesota. I found no overall trends, possibly due to variation across sites or due to minimal management over the 12 years since establishment. Over time, soil carbon increased in the shallower depths at one site and decreased in the deeper depths at two sites. I measured plant, tiller, and rhizome densities in plants from sown seed, vegetative propagation, or seed shatter at four sampling times in 1 year old and 2 year old intermediate wheatgrass stands. Tiller density was similar in both stands, but rhizome and propagule densities were greater in the 2 year old stand. Likely, tiller replacement and death rates are equal, but vegetative propagation increases between years, increasing plant population, possibly leading to competition and affecting long-term yield. Also in intermediate wheatgrass, I measured nitrogen in shoot, root, and grain tissue along with soil mineral and mineralized nitrogen in three nitrogen treatments (80 kg N ha-1 in spring, 40-40 kg N ha-1 in spring and summer, and unfertilized control) at four sampling times in 1 year old and 2 year old stands. The spring treatment had greater root nitrogen, but it also had greater lodging. The late fall sampling had the greatest soil nitrogen, and since soil mineral N was low at that time there was likely an influx of organic nitrogen, likely due to root turnover.