ROOT VOLUME EFFECTS ON NITROGEN UPTAKE AND PARTITIONING IN PEACH-TREES

Although soil root volume can be modified under field conditions by adjusting irrigation frequency and emitter geometry, little is known about the effect of root volume on tree growth, uptake, and yield. The objective of this work was to investigate effects of physical restriction of root systems on N absorption by peach trees [Prunus persica (L.) Batsch.] and N partitioning among tree organs, and to compare experimental data with simulated results. Cumulative NO3 uptake by 3- and 3.5-yr-old trees grown in containers increased linearly with increasing root volumes from 5 to 10, 20, 44 and 80 L tree(-1). This effect was simulated better when assuming a constant ratio of N to dry matter weight in the tree than when assuming a Michaelis-Menten uptake mechanism. Nitrogen partitioning among leaves, branches, fruits, trunk, and roots differed at fruit harvest and at the end of the season. Despite considerable differences in tree organ weights, N concentration in the tree parts was quite similar in the various root volumes and along the growing season. Simulation of N concentration in annual tree parts was less satisfactory than in perennial organs, where initial conditions could be defined accurately. It is suggested that the physical restriction of root growth reduced N uptake, root hormone synthesis rate, and N accumulation in the canopy. The trees have a N-concentration-stat mechanism, which maintains a constant N percentage in the tops by adjusting photosynthesis and grow,vth in direct proportion to the N and cytokinin accumulations in the canopy.