Year-round accumulation of dry matter and NPK of ‘Nanguo’ pear trees

【Objectives】 Understanding the year-round dry matter and nutrient accumulation will provide a base for the optimized fertilization of Nanguo pear tree.【Methods】 Pear tree (Nanguo pear) of 12-years old was chosen in the experiment. Samples were collected in 10 d (budbreaking), 30 d (blooming), 65 d (initial fruit expanding),100 d (fruit expanded or new branch growth stop),130 d(before fruit coloring),155 d(harvesting),185 d(after harvest),210 d(before defoliation). Three trees with uniform heights and trunk diameters were dug out from soil every each sampling time, and divided into fruit, leaves, shoots, trunk, axial roots, lateral roots and fibrous roots. All the parts were weighed individually and 200 g of samples were taken and washed in turn with water, detergent, water and 1% HCl, three times of de-ionized water, then dried and grounded into 0.15 mm. The contents of N, P and K were determined. 【Results】 1) The net accumulation ofdry matter of the whole tree was 19.7 kg per tree in anniversary growth period of Nanguo pear. The accumulation rate of dry matter attained peaks at the fruit expanding stage (0.15 kg/d) and fruit harvesting stage (0.11 kg/d), respectively. 2) The N accumulation is 154.0-301.0 g in the whole tree, 131 g in annual organs with the peak at the fruit expanding stage and 154.0-194.8 g in perennial organs with the peak before the leaf fall. 3) The P accumulation is 17.1-37.2 g in the whole tree, 12.2 g in annual organs with the peak at the fruit harvesting stage and 12.6-24.9 g in perennial organs with the peak before the fruit coloring. 4) The K accumulation is 27.9-174 g in the whole tree, 89.3 g in annual organs with the peak at the fruit harvesting stage and 27.6-76.6 g in perennial organs with the peak before the defoliation. 5) The net accumulation of N, P and K from the bud breaking to defoliation was respective 146.2, 20.1 and 146.1 g/tree with a yield about 17 t/hm2, and the accumulations of N, P and K were respective 5.4, 0.7 and 5.4 kg per ton of pear fruits.【Conclusions】 The accumulation of dry matter in the whole tree is 41.4 kg with the net increase of 19.7 kg in the growth season. The dry matter is accumulated mainly from the bloom to fruit expansion and from the fruit coloring to one month after the fruit harvesting, accounting for 47.3% and 47.5% of the total accumulation, respectively. The net increase of N, P and K accumulation is 146.2, 20.1 and 146.1 g/tree from the bud breaking to defoliation with the total accumulations of N, P and K of 5.4, 0.7 and 5.4 kg per ton pear fruits, respectively. The peaks of net N accumulation are at the fruit expansion and after harvest which account for 39.0% and 49.0%, respectively, but those of P and K are from the bud breaking to blooming period, and net P and K gain at the peak account for 67.4% and 65.1%.