Response of Nitrogen Fertilizer Rates on Agronomic and Environmental Performance of Ethiopian Mustard (Brassica carinata) in South Dakota.

The introduction of non-food oilseed crops can aid in diversifying biofuel sources and lessen the demand of producing biofuels from food-based crops such as corn and soybean. Ethiopian mustard (Brassica carinata) has been identified as a potential non-food biofuel crop suitable for production in South Dakota (SD). However, the best fit for the crop in current cropping systems, best management practices, and environmental impacts remain to be determined. This study was conducted in SD with the specific objectives of the study are to (i) evaluate the response of carinata to various nitrogen fertilizer rates in South Dakota, and (ii) evaluate soil and environmental impacts associated with carinata production managed with nitrogen fertilizer in South Dakota. Separate nitrogen fertility trials were conducted in 2013 and 2014.  In 2013, trials evaluated the response of one carinata variety to five nitrogen rates (0, 34, 67, 101, and 134 kg/ha) at four locations (Brookings, Pierre, Wall, and Bison) in South Dakota. Plot size was 1.5 m x 7.6 m, with no border rows between plots. The variety 080814EM was used at Brookings and AAC A110 was used at the other three locations. In 2014, trials evaluated the response of two carinata varieties to four N rates (0, 28, 56, and 84 kg/ha) at two locations (Brookings and Pierre). Plot size was 1.5 m x 7.6 m, with border plots between treatment plots. The nitrogen treatments were broadcast over the top of the plots immediately after planting. Soil samples were collected at the start of the experiment and at harvest from 0-10, 10-20 cm depths for analyzing soil organic carbon (SOC), soil inorganic carbon (SIC), pH, EC, and total nitrogen (TN). Soil surface greenhouse gas (GHG) fluxes were also monitored. Data show that seed yields in 2013 were highest at Brookings, likely owing to better stands and more precipitation during the seed-filling period. In 2013 there was no yield response to applied nitrogen at any of the locations, despite early visual differences between low and high levels of applied N.  Lack of border rows between treatment plots may have confounded the response to N.  In 2014, both carinata varieties showed a positive, statistically significant response to applied N at the Brookings location. The best yields were observed at the N rate of 84 kg/ha. The trial at Pierre was abandoned due to herbicide drift injury. Soil parameters such as SOC, SIC, TN, pH and EC were not impacted by N rate treatment. Whereas soil surface CO₂, N₂O and CH₄ fluxes were highly variable in all the treatments and did not provide any clear trend, research work is ongoing to address these further. It can be concluded that the trials showed that good yields of carinata are possible with adequate plant stands and precipitation. In 2014, the greatest carinata yields were observed at the highest nitrogen fertilizer rate used in these studies