Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/19/2007
Publication Date: 5/1/2008
Publication URL: hdl.handle.net/10113/18484
Citation: Berti, M.T., Johnson, B.L., Gesch, R.W., Forcella, F. 2008. Cuphea Nitrogen Uptake and Seed Yield Response to Nitrogen Fertilization. Agronomy Journal. 100(3):628-634. Interpretive Summary: Cuphea is a new oilseed crop that is starting to be grown commercially by farmers. However, the amount of nitrogen fertilizer needed to optimize cuphea yields in the upper Midwest is not known. Therefore, a study was done at three different field sites to test different levels of nitrogen fertilizer on the growth, seed yield, and nitrogen uptake of cuphea plants. Results of the study showed that as nitrogen fertilizer increased in the soil, the plants definitely took up more nitrogen. As plants got old and reached maturity, the amount of nitrate nitrogen (the form of nitrogen used by the plant to make proteins) in the plant itself deceased. Nitrogen uptake by plants was greatest at a soil nitrogen fertilizer concentration of 124 pounds per acre (this includes nitrogen fertilizer and nitrogen already present in the soil). However, seed yield only significantly increased with added nitrogen fertilizer at a field site in Morris, MN. The increase in seed yield was not great enough to offset the cost of the added fertilizer. Therefore, from results of the study, it is suggested that nitrogen fertilizer application for cuphea production may not be economical. These results will be valuable to farmers growing cuphea as well as state extension personnel and crop consultants serving to help farmers manage cuphea production.
Technical Abstract: Cuphea (Cuphea viscosissima Jacq. x C. lanceolata W.T. Aiton, PSR23), is an oilseed crop that is a rich source of medium-chain fatty acids. Progress has been made on improving cuphea agronomically, but little is known about nitrogen fertility requirements for optimum cuphea production. The objective of this study was to determine the nitrogen necessary for maximizing seed yield and oil content. Experiment 1 (Exp. 1) was conducted at Casselton, ND, in 2005 and at Glyndon, MN, in 2005 and 2006 in which fertility treatments (soil + fertilizer N) were 44, 60, 80, 100, 150, and 200 kg N ha-1. Experiment 2 (Exp. 2) was conducted at Morris, MN, in 2005 and 2006, in which fertility treatments (soil + fertilizer N) were 51, 93, 140, and 185 kg N ha-1. As nitrogen fertility increased, plant tissue NO3-N increased, but as developmental stage advanced, plant NO3-N was diluted and decreased. According to the regression model, maximum total nitrogen uptake at harvest occurred at 139 kg N ha-1 nitrogen fertility, which includes nitrogen from the fertilizer and from the soil. This could classify cuphea as a medium-nitrogen requirement crop. Seed yield was enhanced with nitrogen fertility only at Morris, where maximum seed yield occurred at 185 kg N ha-1. However, seed yield increase obtained with added nitrogen fertilizer (134 kg N ha-1) was only 71 kg ha-1. Nitrogen fertilizer cost would be greater than the profit obtained with the incremental seed yield, thus nitrogen fertilizer application may not be economical.