EVALUATING NITROGEN-FERTILIZER RATE AND TIMING FOR MEADOWFOAM SEED AND DRY-MATTER PRODUCTION

Previous reports on N fertilization effects on meadowfoam (Limnanthes alba Hartw. ex Benth.) seed yield are inconsistent. This study was conducted to determine whether N fertilizer application rate and timing could be manipulated to increase seed yield in 'Mermaid.' Field experiments were conducted during the 1982-1983 and 1984-1985 seasons on a Woodburn silt loam (fine-silty, mixed, mesic Aquultic Argixeroll) to evaluate the influence of twelve combinations of N rate and timing on Mermaid dry matter production and seed yield. Treatments included 50, 100, and 200 kg N ha-1 applied in fall, winter, spring, and split fall/spring timings. Except for the 50 and 100 kg N ha-1 applied in the fall of 1984, seed yields for all N treatments were greater than the control. Application rate and timing interactions on dry matter production, seed yield, and harvest index were not significant in either growing season. Averaged over rates, fall application resulted in significantly lower seed yield and total dry matter than the other timing treatments, presumably because of N loss through leaching. The effects of application rates above 50 kg N ha-1 on dry matter production and seed yield varied between years. The data suggest that 50 kg N ha-1 applied in late winter or early spring increases meadowfoam seed yield. Under climatic conditions such as during the 1984-1985 season when lodging was low, higher rates of N might be beneficial. However, application of more than 50 kg N ha-1 in spring could reduce seed yield if the climatic conditions are conducive to lodging.