Quantification of Nutrients Lost during Annual Pruning, Leaf Abscission, and Fruit Harvest in Pear Trees

To investigate the amount of mineral nutrients lost from mature pear trees, we determined the nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) content in the pruned branches of various ages, fallen leaves, and mature fruit of four varieties (Huangguan, Lvbaoshi, Yuanhuang, and Yali) of 15-year-old pear trees growing in the same orchard. Furthermore, we calculated the weight of the pruned branches and fallen leaves, and the total fruit weight per tree. The nutrient abundance ranged from Ca>N>K>Mg>P in the pruned branches and fallen leaves of all four varieties, whereas it ranged from K>N>P>Ca>Mg in the fruit. The N, K, and P contents decreased with increasing age of the pruned branches. The Ca and Mg contents in the fallen leaves were about 58% and 100% higher than in the pruned branches, but 44-fold and 6-fold that of the fruit. The annual loss of N, P, K, Ca, and Mg from pear trees by pruning, leaf abscission, and fruit harvest was 241.4, 26.3, 117.6, 435.1, and 36.4 kg/hm², respectively, of which 37~78% was due to pruning. The percentage of N, Ca, and Mg lost through fallen leaves was higher than that lost through fruit, being around 15~46% in fallen leaves and 6~16%, 0.9~1.2%, and 5.7~8.7% in fruit, respectively. However, the loss of P and K through fallen leaves was less than through fruit, which was around 6~24% and 22~38%, respectively. Amongst the varieties tested, Lvbaoshi trees exhibited the greatest loss in nutrients through pruning, leaf abscission, and fruit harvest, with the exception of Yali, which lost more N, K, Ca, and Mg through falling leaves than did Lvbaoshi. Therefore, there is great variation in the amount of mineral nutrients lost from different varieties of pear tree during the growth season, and fertilizers should be flexibly applied in accordance with this variation.

Key words: Pear; pruning; fruit; fallen leaves; mineral nutrient