Swathing and Windrowing as Harvest Aids for Cuphea

Cuphea (Cuphea viscosissima Jacq.3 C. lanceolataW.T. Aiton) is a potential new oilseed crop for temperate regions. Harvesting problems occur because current varieties are nondeterminate and shatter seeds. Because swathing may help overcome some of these problems, cuphea was swathed and allowed to dry in windrows for 0, 1, 2, 3, and 4 wk before combining. Measured variables at the time of combining were windrow weight, seed water content, seed yield, seed oil content, and post-swathing evaporation (Eps). Windrow weights decreased from about 40 to 14Mg ha as combining was delayed until 3 wk after swathing. Weights decreased over time due to dehydration and leaf abscission, and they were associated hyperbolically with Eps. Similarly, seed water content decreased from about 670 g kg at swathing to about 250 g kg at 30 mm Eps. Seed shattering apparently was low as high yields were maintained each year until after at least 30 mm Eps. Seed oil content was affected only slightly by delayed combining dates. Thus, swathing and windrowing cuphea and delaying combining until 30 mm Eps substantially decreased the weight of material processed by the combine, reduced seed water content, but maintained high seed yields and seed oil contents. FOR many recently domesticated seed crops, nondeterminate growth habit and propensity for seed shattering reduce harvesting efficiency and harvestable seed yields. At time of harvest, nondeterminate crops may support green leaves and stems, and their seeds can be at a wide range of maturities and moisture levels, all of which decrease efficient processing in modern harvesting equipment. Long-term solutions to these problems involve breeding varieties whose growth habits are determinate, mature plants dry rapidly, and ripened fruits retain seeds. With these traits crops can be left in the field to mature and dry naturally. Unfortunately, breeding newvarieties is costly and time consuming and, therefore, near-term solutions also are needed during the domestication of new crops. One nearterm solution involves application of desiccants. When followed by direct combining, desiccants can reduce high plantmoisture content at harvest and arrest the shattering process in ripening fruits. Another near-term solution involves swathing and windrowing followed by drying of windrows and then combining. Such harvesting alternatives are common for many partially or recently domesticated crops (e.g., Simpson, 1993; Thomas et al., 1991). Cuphea (Cuphea viscosissima Jacq. 3 C. lanceolata W.T. Aiton) is a newly domesticated crop suffering from the aforementioned harvesting problems. Cuphea is of interest because its seeds contain about 300 g kg oil, the preponderance of which is comprised of medium chain fatty acids (Graham et al., 1981; Thompson and Kleiman, 1988). Nearly all commercial medium chain fatty acids currently are derived from oils of coconut (Cocos nucifera L.) and palm kernel (Elaeis guineensis Jacq.), of which 600 000Mg were imported into the USA and Canada in 2003 (FAOSTAT, 2005). Domestic supplies of such oils would be beneficial to North American agriculture, as well as industries that manufacture detergents, cosmetics, lubricants, hydraulic fluids, and confectionary products. Although cuphea grows well in states such as Minnesota, up to half of seed production of Minnesotagrown cuphea is lost through shattering before and during direct combining operations (Gesch et al., 2005). Furthermore, directly combined seeds have water contents .400 g kg if harvested at times (late September to early October) when yield is maximized (Berti et al., 2005). Because stored seed must have water contents #100 g kg to preserve seed quality during long-term storage (personal observations), directly combined seeds must be dried. Seed drying incurs a separate timeconsuming operation for producers, and it can be expensive, especially as energy costs continue to rise. Lastly, unless cuphea harvest is preceded by the application of a desiccant or a leaf-killing frost, harvested plants are turgid and support a dense green canopy of leaves. All of this wet material must be processed by the combine, andsomeof it inevitably contaminates thecombine’s seed hopper. Our objectives were to increase harvesting efficiency and decrease seed drying costs. Accordingly, we swathed and windrowed cuphea, and examined the effects of differing lengths of windrow drying time before combining on total windrow weight, seed water content, seed oil content, and seed yield. MATERIALS AND METHODS Experiments were performed at the USDA-ARS Swan Lake Research Farm, Morris, MN, in 2004 and 2005. Seeds of PSR23 cuphea (Knapp and Crane, 2000) were sown in mid-May each year at a rate of 8 kg ha, at a soil depth of 1 cm, and at a row spacing of 61 cm. The total area sown each year was eight rows wide and 200m long, but only small and homogenous sections of these areas were used for the swathing experiments. Soils were Barnes loams (Calcic Hapludoll, fine-loamy, mixed, superactive, frigid; with organic matter at 60 g kg, a bulk density of about 1.0 g cm, and a pH of 6.8). Fields had been plowed, fieldcultivated (chiseled), and harrowed before sowing. Fertilizer was broadcast after sowing at rates of 70, 30, and 30 kg ha of N, P, andK, respectively.Weedswere controlled by herbicides: trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] applied preplant incorporated at 1 kg ai ha; and mesotrione USDA-ARS North Central Soil Conservation Research Laboratory, 803 Iowa Ave., Morris, MN 56267, and USDA-ARS National Center for Agricultural Utilization Research, Peoria, IL 61604. Received 9 Feb. 2006. *Corresponding author ([email protected]). Published in Agron. J. 99:415–418 (2007).