What is the role of nitrogen in apples?
Nitrogen has a major effect on yield and quality. It is a component of the chlorophyll molecule and involved in nucleic acid synthesis and hence important for cell division and the growth of young tissues (e.g. buds, flowers, leaves). Nitrogen is involved in amino acid synthesis and protein production.
Nitrogen and yield
Yet, some trials show that spring and fall applications have the most influence on performance. Fall inlets help bud development after leaf fall and in winter. In spring, the tree taps into the soil reserves to develop new leaves.
Nitrogen and fruit quality
The nitrogen form introduced impacts the absorption of calcium in the fruit. The use of calcium nitrate, in solid or soluble form, allows a better absorption of calcium than ammonium nitrate. On the other hand, an excessive supply of nitrogen induces an over-abundant foliar development at the expense of fruit development. This vigorous and excessive leaf growth can also cause too much shade. Trees receiving too much nitrogen are more susceptible to disease (eg fire blight). The quality of fruits can deteriorate with weakened tissues and more exposed to the risk of physiological disorders. These effects will often be closely correlated with a decrease in the calcium content in fruits,
Nitrogen and firmness
Excessive or late application of nitrogen results in lower fruit firmness, which can result in more losses during transport and storage and limited shelf life.
Nitrogen and soluble sugar contents
The effects of a nitrogen supply are generally positive on the synthesis of sugars and this effect is found on the content of Total Soluble Sugar (SST). Beyond certain doses, the effect disappears or even reverses, and excessive use of nitrogen also causes significant qualitative problems on the fruit. This effect of nitrogen remains highly correlated with the varieties and doses. For example, in the trial presented, an intake greater than 50 kg / ha on the Golden Delicious variety has a negative effect on the SST content.
Nitrogen and colouring of apples
Excessive or late application of nitrogen causes a reduction in the red color in red apples. This nitrogen supplementation induces an excessive development of the foliage causing an excessive shading for the fruits. Less competitive than leaves, fruits will produce a lower rate of carbohydrates responsible for the red pigmentation of the skin.
Nitrogen and colouring of green apples
On green apples, excessive nitrogen application can be beneficial by improving green colour by reducing yellow and red pigments.
