Do foliar applications of nickel increase urease activity and nutrient levels in pecan leaflets?

Nickel (Ni) deficiency limits the production of pecan. Concentrations of mineral nutrients and urease activity in leaflets of young pecan plants cv. Pawnee were evaluated in response to foliar applications of Ni as Ni sulfate or Ni citrate, or as chelates with EDDHA, EDTA, or DTPA. Significant variations were found in N-total concentration with Ni-EDDHA (27.17 ± 0.98 g/kg) and Ni-sulphate (28 ± 0.89 g/kg), where the latter together with Ni-citrate were high in phosphorus concentrations. Levels of Ni2+ (3.70 mg/kg), Mn2+ (222.73 mg/kg) and Zn2+ (38.69 mg/kg) were all increased in leaflets sprayed with Ni-EDDHA but the Mn2+ concentrations were similar for leaflets sprayed with Ni-sulphate. The Ni-DTPA spray significantly reduced foliar Fe2+ concentration (73.66 ± 3.44 mg/kg). No significant effects of the sprays were observed on the concentrations of total chlorophyll or carotenoids. The plants sprayed with Ni-EDDHA showed significant increases in leaflet area and leaflet dry weight and also in root dry weight. The urease showed maximum activity in leaflets sprayed with Ni-EDDHA, Ni-citrate and Ni-sulphate. This study suggests growers of the pecan should consider foliar sprays of Ni-EDDHA or Ni-sulphate to increase the levels of Ni in their trees if Ni is a growth-limiting factor.