Optimizing Nitrogen Application for Jojoba under Intensive Cultivation.

Although jojoba ( Simmondsia chinensis ) has been cultivated for years, information on its N requirements is limited. A 6-year study of mature jojoba plants grown under field conditions with an intensive management regime evaluated the effect of N application rate on plant nutrient status, growth, and productivity, and nitrate accumulation in the soil. Five levels of N application were tested: 50, 150, 250, 370, and 500 kg N ha-1 . Fertilizers were provided throughout the growing season via a subsurface drip irrigation system. Leaf N concentration, in both spring and summer, reflected the level of N applied. A diagnostic leaf (youngest leaf that has reached full size) concentration of 1.3% N was identified as the threshold for N deficiency. Increasing rates of N application resulted in higher P levels in young leaves. Plant K status, as reflected in the leaf analysis, was not affected by N treatment but was strongly affected by fruit load. Vegetative growth was inhibited when only 50 kg N ha-1 was applied. Soil analysis at the end of the fertilization season showed substantial accumulation of nitrate for the two highest application rates. Considering productivity, N costs, and environmental risk, 150 kg N ha-1 is the recommended dosage for intensively grown jojoba. N deficiencies can be identified using leaf analysis, and excess N can be detected via soil sampling toward the end of the growing season. These results and tools will facilitate precise N fertilization in intensive jojoba plantations.