| Walnut is one of the important economic forest tree species with its strong adaptability, edible,medicinal, timber and ecology functions. In recent years, with quick development of walnut industry,more and more higher quality seedlings are needed, applying nitrogen fertilizer is one of the important measures to promote seedling’s growth. But sometimes the nitrogen fertilizer harms happened when the nitrogen fertilization technology was unsuitable. In order to explore a reasonable nitrogen fertilization technique of walnut seedlings, young walnut seedlings grown in the Specimens Garden of Agricultural University of Hebei were used as the materials to study the nitrogen fertilizer harm physiology and influence factors.The results showed that:1. In the different applied urea amounts, that were 0 kg/667m2, 10 kg/667m2, 20 kg/667m2, 30kg/667m2, 40 kg/667m2, nitrogen fertilizer harm did not occur when the applied urea amount was lower than 20 kg/667m2. Nitrogen fertilizer harm began to occur when the applied urea amount reached to 30kg/667m2. When the urea amount was above the critical value, with the increasing of urea amount, the heavier fertilizer harm occured. The average fertilizer harm indexes of the four different kinds of fertilizer applying methods that were fertilizing immediately after a soaking rain with broadcasting,fertilizing immediately after a soaking rain with furrowing, broadcasting and then watering immediately after fertilizing, furrowing and then watering immediately after fertilizing were 1.37 %, 1.00 %, 0.79 %,0.63 %. The fertilizer harm disease indexes of the four kinds of fertilizer applying methods from high to low were fertilizing immediately after a soaking rain with broadcasting>fertilizing immediately after a soaking rain with furrowing>broadcasting and then watering immediately after fertilizing>furrowing and then watering immediately after fertilizing.2. When the fertilizer harm began to occur, the average air relative humidity of the seedlings growth zone whose the fertilizer amount reached to 30 kg/667m2 was 77.17 %, it was significantly higher than that of the fertilizer amounts were 0 kg/667m2 and 10 kg/667m2. The average air relative humidities of the seedling growth zone of the four kinds of fertilizer applying methods were 79.33 %,76.80 %, 72.80 %, 69.13 %, that fertilizing immediately after a soaking rain with broadcasting significantly higher than that of fertilizing immediately after a soaking rain with furrowing, and very significantly higher than those of broadcasting and then watering immediately after fertilizing and furrowing and then watering immediately after fertilizing.3. In the different applied urea amounts, that were 0 g per pot, 1.08 g per pot, 2.25 g per pot, 3.33 g per pot, 4.5 g per pot, the highest average ammonia concentration was 31.88 μl·L-1 of applied urea 4.5 g per pot, which was very significantly higher than those of 1.08 g per pot(22.91 μl·L-1) and 2.25 g per pot(24.63 μl·L-1). The average air ammonia concentrations of the seedling growth zone of the four kinds of fertilizer applying methods were 32.64, 26.45, 25.86, 23.77 μl·L-1, and the average ammoniaconcentration of fertilizing immediately after watering with broadcasting was very significantly higher than the other three kinds of fertilizer applying methods.4. The average photosynthesis rates of the different applied urea amounts of the four fertilizer applying methods were 4.99, 5.74, 6.90, 7.54, 6.80 μmol·m-2·s-1 after fertilized for the fourth days, that the applying urea amount 30 kg/667m2 was very significantly higher than the 0 kg/667m2 and 10kg/667m2. The average photosynthesis rates of the four kinds of fertilizer applying methods under different applied urea amounts were 6.86, 7.61, 5.47, 5.62 μmol·m-2·s-1, that the fertilizing immediately after a soaking rain with furrowing was significantly higher than the fertilizing immediately after a soaking rain with broadcasting, and was very significantly higher than those of broadcasting and then watering immediately after fertilizing and furrowing and then watering immediately after fertilizing. After fertilized for the 17 days and 34 days, the average photosynthesis rates of the different applying urea amounts were 4.99, 7.42, 8.78, 6.29, 5.32, 5.85, 9.34, 10.92, 5.41,4.45 μmol·m-2·s-1, the highest was applied urea 20 kg/667m2. After fertilized for the 17 days and 34 days, the average photosynthesis rates of the four fertilizer applying methods were 7.24, 7.01, 6.39, 6.35,7.25, 7.11, 6.76, 7.64 μmol·m-2·s-1, the highest was fertilizing immediately after a soaking rain with broadcasting.5. After fertilized for the fourth days, the average transpiration rates of the four kinds of fertilizer applying methods under different applied urea amounts were 2.13, 2.92, 3.11, 4.76, 4.09 μmol·m-2·s-1,that the applied urea amount 30 kg/667m2 was very significantly higher than those of applied urea amounts 0 kg/667m2, 10 kg/667m2 and 20 kg/667m2, significantly higher than that of applied urea amount 40 kg/667m2. The average transpiration rates of the different applied urea amounts of the four fertilizer applying methods were 3.09, 3.30, 3.47, 3.75 μmol·m-2·s-1, that the furrowing and then watering immediately after fertilizing was significantly higher than the fertilizing immediately after a soaking rain with broadcasting. After fertilized for the 17 days and 34 days, the average transpiration rates of the applying urea amounts were 2.96, 3.39, 3.61, 3.90, 3.53, 3.14, 3.69, 4.13, 3.48, 2.71μmol·m-2·s-1, he highest was applied urea 30 kg/667m2, 20 kg/667m2. After fertilized for the 17 days and 34 days, the average transpiration rates of the four kinds of fertilizer applying methods were 3.32,3.40, 3.42, 3.77, 3.08, 3.23, 3.70, 3.71 μmol·m-2·s-1, the highest was furrowing and then watering immediately.6. The average root activities of the four kinds of fertilizer applying methods under different applied urea amounts were 43.10, 80.59, 111.40, 158.49, 107.71 μg·g-1·h-1, the highest was applied urea30 kg/667m2, and it was very significantly higher than those of applied urea 0 kg/667m2 and 10kg/667m2, significantly higher than those of applied urea 20 kg/667m2 and 40 kg/667m2. The average root activities of different fertilizer applying methods were 69.71, 79.26, 109.26, 142.79 μg·g-1·h-1, that of furrowing and then watering immediately was very significantly higher than the fertilizing immediately after a soaking rain with broadcasting and fertilizing immediately after a soaking rain with furrowing, significantly higher than broadcasting and then watering immediately after fertilizing.7. The highest average GR activities, APX activities, CAT activities, MDA contents, As A contents,GSH contents and proline contents of the different applied urea amounts were 7.31 U·g-1FW, 22.31U·g-1FW, 9.03 mg·g-1FW 6.48 nmol·g-1FW, 18.24 μg·g-1FW, 1.69 μg·g-1FW, 15.72 μg·g-1FW which theurea amount was 30 kg/667m2. The highest average SOD activity was 8.22 U·g-1FW of the urea amount30 kg/667m2. The highest average POD activity and electrolyte leakage rate were 11.38 U·g-1FW, 68.54 %of the urea amount 40 kg/667m2.8. The highest average CAT activities, MDA contents, electrolyte leakage rates, POD activities,proline contents of the four kinds of fertilizer applying methods were fertilizing immediately after a soaking rain with broadcasting, which were 7.70 mg·g-1FW, 5.21 nmol·g-1FW, 61.28 %, 8.99 U·g-1FW,12.88 μg·g-1FW. There had no significant differences among the average SOD activities, APX activities,GR activities and GSH contents. The highest average As A content was broadcasting and then watering immediately after fertilizing, which was 11.76 μg·g-1FW. |
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