Nitrogen rate and timing effects on meadowfoam oil yield and oil-yield components

Abstract

Unlike earlier meadowfoam ( Limnanthes alba Hartw. ex Benth.) accessions and genetic lines, seed yield of the more recently released cultivar ‘Mermaid’ is increased with low to moderate rates of N-fertilizer. Understanding N-fertilizer effects on oil yield and yield components is useful for improving fertilizer management which is important economically and environmentally. The objective of this experiment was to evaluate effects of 12 combinations of N rate and timing treatments (50, 100 and 200 kg N ha −1 × fall, winter, spring and split fall/spring applications) plus a control (0 kg N ha −1) on Mermaid oil yield and oil-yield components. Experiments were conducted in 1982–1983 and 1984–1985 on a Woodburn silt loam (fine-silty, mixed, mesic Aquultic Argixerolls) near Corvallis, OR, USA. Except for the 50 and 100 kg N ha −1 applied in the fall of 1984, all N rates significantly increased oil yield over the control. Combined over years, there was a quadratic relation between N rates and oil yield. Application timings did not interact with rates for their effects on oil yield, or on any of the oil-yield components. Fall N application resulted in smaller oil-yield increase than the other timing treatments. Total flower number was the only oil-yield component significantly affected by treatments in both years. Averaged over years, flower number increased by 38, 72 and 92% when 50, 100 and 200 kg N ha −1 were applied, respectively. However, the relationship between N rates and flower production was also quadratic. Slight reductions in seeds per flower and weight per seed caused by N applications were more than offset by increased flower number. Effects of N application on seed oil content contributed little to oil-yield differences. Regardless of timing or rate, the primary effect of N fertilizer on oil yield was through increased flower number, and consequently, increased seed number.