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Title: Seed moisture at physiological maturity in oilseed and confectionary sunflower hybrids in the Northern U.S.

item Gesch, Russell - Russ
item JOHNSON, BURTON - North Dakota State University

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2012
Publication Date: 4/29/2012
Citation: Gesch, R.W., Johnson, B. 2012. Seed moisture at physiological maturity in oilseed and confectionary sunflower hybrids in the Northern U.S. Field Crops Research. 133:1-9.

Interpretive Summary: Even after seed on a sunflower head have matured enough to harvest, often the leaves and stems of plants are wet, making harvest difficult. This means that a farmer has to wait longer to harvest, which can also mean that the crop is potentially exposed longer to conditions such as bad weather and bird predation that can reduce yields. Therefore, farmers often spray chemical herbicides on sunflower plants when they are nearing harvest to kill and dry them out (i.e., desiccation), allowing them to be harvested sooner. However, it is important that they do this after the seed have obtained their maximum weight, which is called physiological maturity, so that there is no yield loss. Currently, it is recommended that if herbicide is used to kill and dry plants that it be applied at 35% or less seed moisture because seed are fully mature at this point. There is considerable evidence, however, that seed maturity in sunflower, especially for different varieties, might occur at higher seed moisture content. If so, then farmers could desiccate their crop earlier than currently recommended and potentially harvest earlier as well, avoiding conditions that could cause yield loss. We conducted a two-year field study in Prosper, ND, and Morris, MN, to determine the moisture content in seed at physiological maturity in two commonly-grown oilseed varieties and one confectionary variety of sunflower. We found that the moisture content for the two oil varieties at seed maturity averaged about 40%, and that of the confectionary variety was 50%. This means farmers could desiccate these sunflower varieties when their seed reaches moisture contents of 5 to 15% higher than that recommended without losing any yield because seeds were not fully mature at the time the herbicide was applied. Moreover, this means that the crop could be harvested earlier, which can potentially reduce the loss of seed yield caused by severe weather or predation by migrating birds. This information will help the ag chemical industry to update recommendations for desiccant application, and will be useful to crop consultants and farmers in determining the best time to desiccate sunflower, and this could translate into improved crop yields.

Technical Abstract: Desiccating sunflower (Helianthus annuus L.) to hasten harvest has become a common practice in the northern U.S. and can aid in reducing yield loss associated with severe weather and bird predation. Currently, it is recommended to apply desiccants to sunflower at 35% or less seed moisture corresponding to physiological maturity (PM). However, evidence from the literature suggests PM may occur at higher moisture. A 2-yr field study was conducted in Prosper, ND, and Morris, MN, to determine seed moisture at PM across different seed positions on sunflower capitulum for two high-oleic oilseed hybrids and one confectionary hybrid. Between R6 stage and seed maturity, capitulum were sampled at 4 to 7 d intervals. Seeds were separated from the inner, middle, and outer concentric thirds of the capitulum for analysis. Dynamics of seed dry matter accumulation and moisture were modeled to estimate moisture content at PM. Moisture content at PM for both oil hybrids across middle and outer seed was about 40% regardless of environment, but it was 50% for the confectionary hybrid. Inner seed responded differently, but only made up a small fraction of total seed. Approximately 600 to 666°C d were required for seed to progress from R6 to PM for the oil hybrids and 486 to 612°C d for the confectionary hybrid. For both types of hybrids, PM occurred about 3 d later in the middle seed as compared to the outer seed. Indeed, our results indicate modern sunflower hybrids can be desiccated at higher seed moisture than currently recommended without sacrificing yield loss due to not reaching PM.