Articles
EFFECT OF NITROGEN FERTILIZATION ON YIELD AND QUALITY OF MOLTKE PEAR
During senescence most of the leaf nitrogen migrates to the perennial parts of the tree.
Application of 6 per cent urea in mid-October led to an 18 per cent increase in the nitrogen content of the flower buds within two days of spraying; this difference in the nitrogen content of the flower buds of sprayed and unsprayed pear trees was maintained throughout autumn and winter.
In 1967 a field experiment was started to compare annual soil applications of calcium nitrate at nil, 93, 186 or 279 kg N ha-1 in the spring with a single 6 per cent urea spray in mid-October.
In addition a split application of 6 per cent urea as a spray in mid-October and 93 kg N ha-1 as a soil application of calcium nitrate applied in the spring was included.
The experiment has been continued for 12 years (1967–1978).
Despite heavy dressings the pear trees, which were 15 years old and in full production when the experiment started, showed only small responses to differential nitrogen fertilization as measured by the nitrogen content of shoot leaves at the end of August.
The control trees maintained an average leaf nitrogen content of 2.02 per cent (dry matter) as compared to 2.20 per cent on trees receiving 279 kg N ha-1 annually.
The results indicate that the roots of pear trees exhibit a highly buffered reaction to nitrogen uptake.
Within the range of 1.9–2.4 per cent leaf nitrogen, a very satisfactory fruit set was obtained.
Consequently high yields (30 t ha-1) were obtained throughout the experimental period and no effects of the differential nitrogen fertilization on yield were demonstrated.
Fruit size was normal and showed no response to the differential amounts of nitrogen applied.
Fruit quality was evaluated in terms of soluble solids, firmness and ground colour.
No differences in fruit quality due to nitrogen supply were found and it is concluded that the pear fruit is insensitive to differential nitrogen fertilization.