Research On The Characteristics Of Nitrogen Cycling In Korla Fragrant Pear Tree-Soil System

Taking the 6-year-old Korla fragrant Pear as experimental material, knowledge on fruit tree nutrition, physiology, nutrition diagnosis was comprehensively applied. To carry out the field experiment of fertilizer, and study the characteristics of nitrogen cycling in Korla fragrant pear tree-soil system, master the ammonia volatilization, denitrification, N2 O emission, and inorganic nitrogen dynamics under applying nitrogen fertilizer in the Korla fragrant pear tree-soil system, might provide a theoretical and practical basis for optimizing Korla fragrant pear tree fertilization, enhancing nitrogen use efficiency as well as improving the orchard eco-environment.The results show that:1. The single Korla fragrant pear tree can absorb nitrogen 96.11 g from the soil in the annual growth, which the nitrogen absorption of flower stage accounts for 20.86 %, the nitrogen absorption of fruit setting stage accounts for 27.93 %, and the nitrogen absorption of fruit expanding stage accounts for 41.26 %, flower stage, fruit setting stage and fruit expanding stage are the three key period of nitrogen nutrition of Korla fragrant pear tree. Korla fragrant pear leaves carry away of nitrogen 38.74 g in the annual growth, which accounts for 40.31 % of total nitrogen absorption. Korla fragrant pear fruits carry away of nitrogen 24.45 g in the annual growth, which accounts for 25.44 % of total nitrogen absorption. The new organs leaves and fruits are the main sites of nitrogen absorption, accumulation and distribution in the various organs of Korla fragrant pear tree. Take the yield 5.77 t·hm-2(12.82 kg·plant-1) of the 6 years Korla fragrant pear as the production target, the recommended quantity of N is 135.25 kg·hm-2.2. The soil ammonia volatilizations of Korla fragrant Pear orchard are impacted significantly by three factors fertilization, irrigation and temperature. Because of the temperature changed, the changes of soil ammonia volatilization rate take on the afternoon(16: 00-20: 00) > noon(12: 00-16: 00) > morning(8: 00-12: 00) > night(20: 00-08: 00) in a day, and the soil ammonia volatilization rate reaches the maximum value 0.032 kg ? hm-2 ? h-1 in the afternoon(16: 00-20: 00)of the fourth day after fertilization; The diurnal cumulative amount of ammonia volatilization is reduced gradually with the growth progress of Korla fragrant Pear under no fertilization, it is stabilized finally. On April 1 and June 1, after fertilization of the test plots, the diurnal cumulative amounts of ammonia volatilization are increased significantly, they reach 0.411 kg ? hm-2 ? d-1 and 0.318 kg ? hm-2 ? d-1 on April 5 and June 5.After the irrigation of the test plots on the 10 th of each month, the diurnal cumulative amounts of ammonia volatilization are increased significantly, it reaches the maximum value 0.24 kg?hm-2?d-1 on May 15. The monthly cumulative amounts of ammonia volatilization are much higher on April and June than other months, because of based fertilizer and chased fertilizer, they reach 9.086 kg?hm-2?m-1 and 7.619 kg?hm-2?m-1 separately. In the entire growth period of Korla fragrant Pear, the cumulative amount of ammonia volatilization reaches 36.52 kg ? hm-2, it takes up 12.17 % for the total amount of fertilizer, it is large loss.3. The emissions of the nitrous oxide increase obviously after fertilization, the peak value of flux in the afternoon of the fifth day after applying basal fertilizer is 0.2498 g?hm-2?h-1, the diurnal cumulative amount is 4.216 g?hm-2?d-1; the temperature will have an significantly effect on the nitrous oxide emissions, the variation of nitrous oxide in one day mainly embodies the phenomenon as follows: afternoon(16:00-20:00) >noon(12:00-16:00) > morning(8:00-12:00) > night(20:00-08:00); after irrigating the test sample in the middle of each month, nitrous oxide emissions increases obviously due to alternating wet and dry seasons too frequently; in the month without fertilizer, nitrous oxide emissions present the following characteristic: the middle of the month >in the beginning of the month >the end of the month; the accumulative amount of nitrous oxide is higher in April and June after fertilization, respectively is 106.564 g·hm-2·m-1 and 97.276 g?hm-2?m-1. In the growth period of fragrant pear, the amount of nitrous oxide accumulation is 455.54 g?hm-2.4. The distribution of inorganic nitrogen in the soil has aggregation effect, on April 5 and June 5, the inorganic nitrogen contents of soil in the 0-20 cm layer reach the maximum; for fertilizer on April and June, the inorganic nitrogen contents of soil with different layers are extremely significant difference, but the inorganic nitrogen contents of soil under 20 cm layer are no significant difference with growth period carrying forward; the nitrate accumulation amount is 15.1 kg?hm-2 in the growth period of Korla fragrant pear, the accumulation amount of ammonium nitrogen is 13.43 kg?hm-2, the total accumulation amount of inorganic nitrogen in the soil is 28.53 kg?hm-2.