NITROGEN STIMULATED INCREASES IN PEACH YIELDS ARE ASSOCIATED WITH EXTENDED FRUIT-DEVELOPMENT PERIOD AND INCREASED FRUIT SINK CAPACITY

This study was designed to characterize the mechanisms of N-stimulated peach Prunus persica (L.) Batsch productivity. The effects of N ferti lization on potential assimilate availability (source capacity) and on the growth capacity of individual fruit (sink capacity) were assessed . On heavily thinned trees, fertilization did not stimulate fruit grow th rates relative to those on nonfertilized trees, suggesting that fru it growth rates were not assimilate-limited throughout the period of f ruit development. However, N fertilization resulted in a longer fruit development period and increased the growth potential of individual fr uit by 20% (fresh mass) and 15% (dry mass) vs. controls. In unthinned trees, N fertilization increased total fruit yield by 49% (fresh mass) and 40% (dry mass) compared to the unthinned, nonfertilized controls. N fertilization increased total fruit yield per tree in unthinned pea ch trees by extending the fruit development period and thus increasing the amount of assimilate accumulated for fruit growth. The fruit deve lopment period was prolonged both by assimilate deprivation associated with increasingly higher crop loads and by N fertilization. Thus, the prolongation of the peach fruit development period by N-fertilization appears inconsistent with the role of N in increasing assimilate avai lability for fruit growth. We conclude that N fertilization stimulates peach yields by increasing the period for fruits to use assimilates ( sink capacity). The effect of N on assimilate availability was not dir ectly evaluated. The timing of fertilizer N availability did not influ ence fruit growth potential.