Partitioning of Phosphorous and Potassium In Pecan Trees In Relation to Annual Crop Intensity

Potassium (K) and phosphorus (P) partitioning were characterized in bearing pecan [Carya illinoinensis (Wangenh.) K. Koch] trees at selected times of the year during successive three years.  The first year trees had little to no crop, followed by a small crop and a near optimal to excess crop during the third year.  Trees bearing a commercial crop accumulated more K and P in July than trees with little or no crop.  Potassium and P content in trees increased from budbreak until July then decreased until budbreak the following year.  Allocation patterns of K and P among tree components changed during the growing season with the greatest changes occurring in the annual plant parts.  Results indicate that leaves were the principal source of labile K and P for developing fruit.  A rapid accumulation of K in the fruit with a concurrent loss from leaves started in July when fruit began a rapid volume increase that continued during carbohydrate deposition in the cotyledon.  At first detectable shuck split K transported to the fruit ceased, but leaf K was partially replenished between shuck split and defoliation, presumably from K in perennial tissue since total tree K was static or decreased slightly.  In contrast, rapid P transport to fruit began after fruit expansion while cotyledons were developing, presumably associated with oil synthesis and after initial shuck split for storage.  Leaf P content continued to decline until leaves were killed by freezing temperatures in the fall.