Nitrogen and mineral nutrition and water stress influence on vegetative growth of jojoba (Simmondsia chinensis (Link) Schneider)

Abstract

A survey of leaf mineral concentration of cultivated jojoba was conducted by selecting male and female plants of varying sizes. Mineral concentrations in jojoba were within the expected range for most cultivated plants. Nitrogen, P and Zn were higher in young leaves but K, Ca, Mg, Na and Mn were higher in old leaves. Iron and Cu were similar in old and young leaves. The order of jojoba leaf concentration was: N>K>Ca>Mg>Na>P and Fe>Mn>Zn>Cu. Soil macronutrients, Mn and Cu were adequate for jojoba growth but zinc and Fe were lower than accepted critical values for most crops. For a better understanding of jojoba mineral nutrition, a second experiment was conducted in greenhouse sand culture. Levels of 0, 4, 10, 50, and 100 ppm N in solution culture were evaluated on growth, N and P leaf concentration. Fifty ppm of solution N was adequate for optimum vegetative growth, shoot dry weight production and shoot N concentration (1.96 %) of jojoba plants. Nitrogen was higher in young (2.52%) than old leaves (1.52%) and increased with increments of N rates, as did shoot dry weight, shoot N and shoot P concentrations. Root dry weight did not change with N treatment levels but root N concentration increased with rate. Jojoba plants under field conditions are subjected to water stress and little information is available regarding the effect on leaf mineral concentration. Therefore, a greenhouse sand culture experiment was conducted to study irrigation fequencies of 3 min once every: 1) 2 hr for 10 hr/day, 2) day, 3) other day and 4) 4 days on growth of two clones and foliar, shoot and root N and P concentrations. Also, leaf water potentials were monitored. Vegetative growth increments were similar among treatments but treatment 3 resulted in statistically greater shoot and root dry weight. Leaf N concentration was similar among treatments but root N increased with greater moisture stress. Shoot P concentrations decreased with increasing water stress but root P did not show any pattern. The threshold leaf water potentials for jojoba growth cessation was in the range of -3.0 to -3.5 Mpa.