Limited seed and seed yield response of calendula to applied nitrogen does not justify risk of environmental damage from high urea application rates

Authors: Johnson, Jane; Gesch, Russell - Russ; BARBOUR, NANCY

Submitted to: Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2018
Publication Date: 3/13/2018
Citation: Johnson, J.M., Gesch, R.W., Barbour, N.W. 2018. Limited seed and seed yield response of calendula to applied nitrogen does not justify risk of environmental damage from high urea application rates. Agriculture. 8(40). https://doi.org/10.3390/agriculture8030040.
DOI: https://doi.org/10.3390/agriculture8030040

Interpretive Summary: Calendula is a source of industrial oils that can grow in the USA as an alternative fossil fuel or avoid imported specialty crops. Traditionally, calendula also known as pot marigold has been grown for medicinal or ornamental properties. However, little is known about nitrogen fertilizer needs when growing calendula as an oilseed crop in Minnesota. So a two-year study was done to find out how much nitrogen fertilizer should be added when growing this crop. We tested five rates of the nitrogen fertilizer called urea: 0, 30, 60, 120 and 180 pounds N as urea per acre. Grain yield, oil content, oil yield, harvest index, and the crop's nitrogen use efficiency were determined. These measures provide information on how effectively this crop used nitrogen to produce seeds and make oil. The amount of residual nitrogen in the soil was measured. Grain and oil yield increased with N rate, which as best described with a quadratic function. Maximum grain yield occurred at a nitrogen application rate of 173 pounds per acre and oil yield was greatest at 163 pounds per acre. However, indicators of how efficiently calendula used nitrogen fertilizer declined with increasing nitrogen application and the amount of nitrogen left in the soil increased. In general, we found that this crop has a low nitrogen conversion efficiency. Based on these results, it is recommended that no more than 36 pounds of nitrogen per acre is necessary for efficient grain production of calendula in the northern Corn Belt region of the USA. Nitrogen left behind in the soil can easily be lost over the winter. Nitrogen is an expensive input to producers so unused nitrogen represents reduction in potential profits. Producers who wish to grow this crop and get the most use of the nitrogen applied will benefit from this research.

Technical Abstract: Calendula (Calendula officinalis L.) is a source of industrial oil, which can serve as a domestic substitute for petroleum or imported specialty crop oils. Traditionally, calendula has been grown for medicinal or ornamental properties. However, little is known about nitrogen (N) requirement of growing calendula as an oilseed crop. The objective of this study was to determine N response of calendula; thereby, providing fertilizer recommendation for this nascent oil seed crop. A replicated plot-scale study was conducted over two consecutive growing seasons to test the effects of five N rates (0, 34, 67, 134 and 202 kg N ha-1) on grain and oil yield (0% moisture), oil content, harvest index, N use, grain N use efficiency, oil N use efficiency, agronomic efficiency, and vegetative responses. Additionally, the amount of residual N in the soil after harvest was measured. Grain and oil yield increased with N rate, which was best described with a quadratic function. Maximum grain and oil yields occurred at rates of 194 kg N ha-1 and 183 kg N ha-1, respectively. However, indices of N use efficiency declined with increasing N application and amount of residual soil N increased. The concentration of tissue N increased without a corresponding increase in biomass, indicative of a low N conversion efficiency. Based on these results, it is recommended that no more than 40 kg N ha-1 is necessary for efficient grain production of calendula in the northern Corn Belt region of the USA.