Lesquerella seed and oil yield response to split-applied N fertilizer

Agronomic management information is critical for successful commercial production of new crops such as lesquerella [Physaria fendleri (A. Gray) O'Kane & Al-Shehbaz]. Response of lesquerella to six nitrogen (N) fertilizer rates under well-watered and water-stressed treatments were studied in irrigated desert conditions in the southwestern United States to establish guidelines for lesquerella N management. Seed and oil yield, seed and straw N concentrations, N harvest index, and total N uptake were recorded at harvest and destructive biomass samples were also collected during growing season for plant N status. Although soil NO₃-N was low due to a cover crop to remove excessive N in the soil, pre-plant N fertilizer did not affect lesquerella growth at the early growth stage. For the treatments with high N fertilizer rates (224 and 336kgha^-1), lesquerella plant N concentrations were relatively stable before the first bloom, decreased drastically until mid-bloom (one month after the first bloom), and then continued to decrease at a lower rate until harvest. As N fertilizer rates increased, seed and straw N concentration increased linearly under both well-watered and water-stressed conditions. Lesquerella seed and oil yield had a quadratic relationship with N fertilizer rate. Because seed oil concentration decreased as N fertilizer increased, N fertilizer rate for the optimum oil yield was lower than the N fertilizer rate for the optimum seed yield. According to seed and oil yield as well as plant N status under different N fertilizer rates, we provided a guideline for N fertilizer management for lesquerella.