Assembly of N and K Uptake Capacity during the Alternate Bearing Cycle

摘要

Knowledge of the effect of alternate bearing on tree capacity for nitrogen (N) and potassium (K) uptake should allow us to increase the efficiency of fertilizer N and K recovery in pistachio orchards by matching N and K availability in the soil with the tree's capacity for fertilizer N and K uptake. Major differences in N and K concentrations and contents occurred between on- and off-year trees over the alternate bearing cycle. Leaf N and K concentrations of on-year trees, for example, were 18 percent and 35 percent lower than from off-year trees, respectively, at nut harvest in September. Fruits were the primary organ for N and K accumulation at this time. At maturity, the fruit contained almost half of the total N and K present in 20 year old pistachio trees. Nitrogen and potassium uptake were determined during a) winter/spring (mid-December to late May); b) nut fill (late May to early September); and c) the postharvest (late September to early December) periods. Nitrogen uptake occurred duringthe spring flush and nut fill periods, while potassium uptake was restricted to the nut fill period. On-year trees took up 35 percent more N and 112 percent more K than off-year trees during the nut fill period, and the fruit accounted for more than 50 percent of tree N and K accumulated during this period in on-year trees. Over the whole season, on-year trees took up 10 percent more N and 128 percent more K than off-year trees. The N and K stored over winter in woody tree parts contributed between 65 percent and 99 percent of the total N and K content of on-year shoots (fruits, leaves and current year wood) in mid-May and between 38 percent and 42 percent of the total amount of N and K accumulated in on-year shoots at nut maturity. Thus, the storage pools of N and K are important in the spring to support new fruit, leaf and wood growth, but are insufficient to provide for the total N and K demands of the fruit during nut fill. Our data support the hypothesis that N and K demand regulates uptake and distribution in pistachio.