Source-sink relations in fruits. VIII. The effect of nitrogen on fruit/leaf ratios and fruit development in apple

摘要

One-year-old apple cv. Aroma trees, grafted on M.9 or M.26 rootstocks, were planted in the spring of 1989 into 20-litre pots containing a proprietary peat substrate. In the spring of 1991, the trees were transplanted into 35-litre pots of the same substrate. Beginning at full bloom, the trees were irrigated daily with an excess of nutrient solution containing 1, 4, 8, 12, 18 or 24 meq N/litre. The NH4-N:NO3-N ratio increased with increasing N concentration from 0:1 at the lowest to 0.44:1 at the highest. Vegetative growth was unaffected by these treatments, whereas the number of fruits/tree decreased with increasing N application rate. In a second experiment, cv. Jonagored on M.9 was planted in 30-litre pots in spring 1991 and treated as for Aroma. In 1992, N was applied at 1, 4, 10, 16, 22 or 30 meq N/litre. As with Aroma, vegetative growth was unaffected by the treatments. However, fruit DW (kg/tree) and number of fruits/kg leaf DW were significantly increased, and fruit DM content, TSS, titratable acidity and red coloration were all significantly reduced, by increasing N application. There was a negative correlation between cropping characteristics and fruit characteristics such as fruit weight, titratable acidity and TSS.