COMPARISON OF EFFECTS BETWEEN FOLIAR AND SOIL N APPLICATIONS ON SOIL N AND GROWTH OF YOUNG GALA/M9 APPLE TREES

The increasing concern about environmental contamination by nitrate leaching from agricultural land has stimulated a search for more efficient ways to apply N fertilizers. An experiment was carried out to compare the effectiveness of foliar and soil N applications on apple tree growth and soil nitrogen status in order to evaluate N use efficiency. One-year-old, uniform Gala/M9 apple trees were selected and transplanted into 4-litre pots with a typical loamy sand soil. The plants grew in the greenhouse and were randomly divided into five groups of 17 trees. The experiment included a control (no N) and 4 N treatments where the same amount of N as urea was applied once every two weeks started when shoot growth exceeded 5cm. N was applied by 1) foliar only, 2) soil only, 3) soil early and late, foliar midsummer (combination I), or 4) foliar early and late, soil midsummer (combination II). New shoot number was recorded, and shoot length, plant and soil N nutrients were measured throughout the growing season. Plants were moved from the greenhouse in late October to over-winter outside. Five trees were sampled for total N analysis at the dormant stage. The remainder was put in the screen house for re-growth evaluation in the following season. Shoot number was unaffected by treatments in the first season, but soil N application alone and combination I significantly increased shoot length. All N treatments significantly increased leaf N status and leaf color (as indicated by SPAD-chlorophyll readings) compared to the unfertilized control, but there were no significant differences among different N treatments. Foliar application increased reserve N content at the dormant stage and promoted re-growth, but all N treatments resulted in similar root/shoot ratios, which were lower than that of the control treatment. Both soil NO₃^- and NH₄⁺ were significantly increased by soil N application compared with either control or foliar application, an indication that soil N application created a higher potential for leaching loss.