However, too much nitrogen at a late growth stage can restrict fruit size and quality, therefore a balanced nutrient application is crucial. Phosphorus as well as calcium have been shown to improve fruit growth too.
Iron supply also positively influences fruit size/weight, increasing crop yields.
Trials on plums confirm that the improved yield from nitrogen is due, in part, to an increase in fruit size.
On soils where phosphorus levels are low, moderate phosphorus application has a direct effect on fruit size and yield of peaches.
Common practice is to use soil phosphorus applications prior to the spring. However, a particularly heavy fruit load can significantly reduce leaf phosphorus-content over the season. In this situation, foliar phosphate applications can maintain a good fruit growth.
Trials with sour cherries and peaches confirm that some of the yield increase comes from an increase in fruit weight after application of potassium.
Calcium is essential for cell division and cell elongation, thereby ensuring good fruit growth. The calcium content of fruits can be rather low, because it moves mainly with the water to the transpiring organs, i.e. the leaves. In this situation, calcium sprays can help to increase the fruit calcium content and maintain a good fruit growth.
Iron is primarily required for a strong photosynthetic activity of the leaves to fuel growth and maximize fruit number, size and yield. Peaches are the most sensitive stone fruit crop to iron deficiency and on alkaline soils the use of iron chelates is necessary for peach production.