Candidate in Philosophy
Soil, Plant, and Environmental Science
The integration of winter annual cover crops into a cropping system can potentially improve soil health and crop production, however, the impact of variables such as seeding rates, across two very different soil types, has not been well documented. A two-year study was conducted at the Dean Lee Research Station and Extension Center in Alexandria, Louisiana to evaluate the effects of cover crop seeding rate and soil type on cover crop biomass, weed suppression, soil fertility, and soybean (Glycine max L) growth and yield. Analysis of potential economic impacts was also performed to estimate financial net returns for three broadcast seeding rates of tillage radish (Raphanus sativus var. L), cereal rye (Secale cereale), and crimson clover (Trifolium incarnatum). Low seeding rates of tillage radish produced greater biomass than high rates (1,812 and 807 kg ha-1, respectively) but did not significantly affect cereal rye or crimson clover. Weed biomass for all seeding rates of cereal rye and low and medium rates of tillage radish was lower (ranging from 18-323 kg ha-1) compared with all seeding rates of crimson clover. Nutrient levels for macro and specific micro-nutrients fluctuated with sample date and soil type, but overall, levels were lowered by 7-88% over the course of this study. Soil organic matter levels were significantly different by sample date across years and soil types, but overall levels decreased from 2.5% to 1.9%. Soybean yield was different by soil type and year, with Coushatta silt loam plots yielding 41% higher than Moreland clay (3,504 and 2,079 kg ha-1, respectively). Although production year 2017 (3,434 kg ha-1) yielded 39% greater than 2018 (2,147 kg ha-1), cover crop seeding rate had no impact on soybean yield in this study. Economic estimations were calculated based on cover crop inputs and soybean grain yield with high rates of tillage radish and cereal rye being less profitable compared with a fallow treatment (all other species and seeding rates were equal to fallow) for Coushatta silt loam soil. In contrast, all rates and species were equal to fallow in Moreland clay except for low rate of cereal rye. Under specific conditions and soil type, low and medium cover crop seeding rates may provide adequate biomass and weed suppression without sacrificing biomass or net monetary returns.
Morgan, Donna S., "Evaluation of Soil Type and Seeding Rate on Winter Cover Crop Species in a Soybean Production System" (2019). LSU Doctoral Dissertations. 5097.