New standard leaf nutrient concentrations for passionfruit based on seasonal phenology and leaf composition

The seasonal patterns of vegetative and reproductive growth and leaf nutrient composition were investigated in four passionfruit orchards over two years in subtropical Queensland. Vegetative growth occurred all year round with major activity in September and October and least in November. Flowering occurred throughout the year but was very low in May-August or May-June and November. Fruit set also occurred throughout the year, but was lowest in January and February and July-September or in May- September. Yield was highest between November-April and lowest in September. The concentration of N, P and K in the recently matured leaf decreased between October- December. Leaf N and K also declined in April. These declines in nutrient concentrations were associated with periods of heavy vegetative flushing and/or fruit set. Concentrations of Ca, Mn, Zn, Cu and B were generally highest between March-September. In contrast, leaf Mg and Na declined during the year while leaf Cl and Fe fluctuated with peaks in March or May and October. The concentrations of N, P, K, Ca, Mg, Mn, Zn, Cu and B were most stable in June and July when the amount of vegetative flushing was stable and flowering and fruit set were low. In contrast, there was no preferred time for estimation of leaf Mg, Fe, Na or Cl. The choice of sampling time would influence the diagnosis for N, K and Zn at these orchards. It is recommended that for purple x golden passionfruit in subtropical Australia, leaves be sampled for diagnostic purposes from dormant branches in late winter before active vegetative growth resumes in spring. Passionfruit in other areas may have different patterns of growth which need to be taken into account when sampling for leaf analysis. Standard values were determined from the range in concentrations from May-August. Leaf N, P and K were generally lower and leaf Ca and Mg higher than French or Brazilian standards. Leaf N, P, K and Ca were higher and leaf Mg lower than Indian standards. Tentative standards for the most recently matured leaves in Australian passionfruit orchards during May to August before the commencement of active vegetative growth are 4.25-5.25% for N, 0.15-0.25% for P, 2.0-3.0% for K, 1.75-2.75% for Ca, 0.30-0.40% for Mg, <2.0% for Cl, 100-200 |xg g"' for Fe, 100-500 jag g“1 for Mn, 50- 80 ng g“1 for Zn, 5-20 ng g~' for Cu, 40-60 |ig g_l for B, and <800 )u.g g_l for Na. These nutrient standards will also be a reliable guide for purple or golden passionfruit provided sampling during major periods of leaf growth and fruiting are avoided.