2019 ASHS Annual Conference

In the past several decades, southwest pecan (Carya illinoinensis) production has been steadily rising in its contribution to total U.S. yield. Soils in the southwest pecan growing areas are typically alkaline and calcareous (>7.5 pH); thus phosphorus and most micronutrients, including Nickel (Ni), are poorly available for root uptake. Nickel deficiency disrupts the normal nitrogen metabolism in plants. Symptoms of Ni deficiency (“mouse-ear”) are commonly seen in Arizona pecan orchards. One of the many known functions of Ni within the plant is to activate the enzyme urease that converts nitrogen into a usable form for leaf and shoot expansion in the spring. There is currently no recommended level of Ni in pecan leaf tissue in Arizona. Researchers in Oklahoma and New Mexico have recommended >2-3 ppm in leaf tissue of pecan. Southeast Arizona pecan orchards are frequently below that level. Currently in research there is no information on the effect of Ni deficiency to photosynthesis. Our approach is to characterize the relationship between leaf Ni concentration, photosynthesis, and mouse-ear severity. In 2016 and 2017, an experiment was conducted on 6.5 hectares of 8^th leaf ‘Western Schley’ and ‘Wichita’ pecan trees in San Simon, AZ. There were two treatments with three replications in which 1) NiSO₄ (10% nickel sulfate) was foliar applied (946 ml per 0.4 hectare) with two applications during the growing season, and 2) no application of Ni (Control). Gas exchange was measured using a portable photosynthesis system and correlated to leaf Ni tissue concentrations. Mean leaf Ni concentration in 2016 was 0.7 and 3.6 ppm in the Control and Ni-treated, respectively. Concentrations in 2017 were 4.9 and 15.9 ppm in the Control and Ni-treated, respectively. All other nutrients were within normal ranges. Analyzed by year, in 2016 Ni-treated pecan trees had significantly higher photosynthesis and stomatal conductance (α = 0.05) than the Control. In 2017, the difference of treatments in relation to photosynthesis was not significant. Due to possible drift, a third year of treatments (2018) was issued with the same treatments except expanding the treated area for added buffer. The results of 2018 measurements will be presented for discussion.