Submitted to: American Oil Chemists' Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/12/2004
Publication Date: 5/12/2004
Citation: Gesch, R.W., Sharratt, B.S., Forcella, F., Olness, A.E. 2004. Physiological response and seed yield of irrigated cuphea [abstract]. American Oil Chemists' Society. p. 71. Interpretive Summary:
Technical Abstract: Cuphea is a potential new oilseed crop being developed as a domestic replacement source for medium-chain oils that are important feed stocks for chemical manufacturing. Previous studies have shown that cuphea lacks a deep root system and inefficiently utilizes water in producing seed, making it potentially prone to drought-stress. The present study was conducted to determine maximum seed yield under non-limiting soil moisture conditions. Cuphea was grown in 2002 and 2003 on a Barnes loam soil in west central Minnesota. Plots 6 x 6 m were drip-irrigated to maintain soil moisture at 100% field capacity (fully irrigated) and 50% field capacity (partially irrigated); soil matric potential was measured twice weekly using tensiometers buried at 10, 30, 80 and 100 cm. Non-irrigated check plots were included and all treatments were replicated three times in an RCBD. Additionally, soil water content was assessed weekly by neutron attenuation at 15, 45, 75 and 105 cm. Midday leaf water potential and photosynthesis were measured periodically between early July and mid August in 2003. Seed yield did not differ between irrigated and non-irrigated cuphea in 2002, and averaged 795 kg ha**-1 across treatments. Lack of yield variation in 2002 was mainly due to receipt of ample precipitation throughout mid to late summer (i.e. July through early September). As a consequence, the soil in the upper 45 cm of the soil profile stayed relatively moist throughout the growing season, even on non-irrigated plots. In 2003, precipitation was below normal throughout July and August. By mid August, when peak seed development occurs in this region, midday leaf water potentials of non-irrigated plants were about two-fold lower than those fully or partially irrigated. Drought-stress symptoms (e.g. leaf rolling and wilting) were apparent for non-irrigated cuphea later in the growing season and leaf photosynthesis declined as much as 82% as compared to irrigated plants. This severe decline in assimilation rate translated into substantially lower seed yield. Non-irrigated cuphea yielded 530 kg seed ha**-1, while that of fully irrigated plants produced 1400 kg seed ha**-1. Evidence clearly indicates that soil moisture is a critical factor for cuphea production. Landscapes with coarse textured soils or regions that are prone to dry growing season conditions will likely require supplemental irrigation to maximize cuphea seed yield.