Managing Apple Expectations with Nitrogen Regulation

For many cash crops, the more inputs and higher management practices lead to higher yields. A certain amount of nutrition is needed to produce the yield goal and still get a positive return on investment. With nitrogen, the higher the rate usually equates to higher yield. The same can be applied to apple production. There needs to be a calculation that leads to how much nitrogen can be applied to obtain a certain yield and receive a positive return on investment. To figure out what the best application rate will be, an end goal must be established.

Some growers prefer dessert apples, others culinary and sauce or cider. There are many different products produced using apples and this will be the leading variable to nitrogen rates. The cultivar can have a great influence on nutrient requirements. Seasonal changes and environmental factors, as well as soil test levels, play a key role in nutrient applications.

Nitrogen is one of the major drivers for vegetative growth in plants. Too much nitrogen uptake can lead to rapid vegetative growth and shoot elongation. This will lead to shading of fruiting areas, increased humidity in the canopy and a competitive fight for nutrients from the fruit. This is where apples can experience diseases, such as Bitter Pit, because the calcium is being used in cell construction of vegetative growth rather than fruit production. From a management perspective, it creates much more pruning to contain efficient harvest heights and open canopies.

For dessert apples, higher nitrogen rates can be used. The producer wants a large apple that is juicy. Using the term “juicy” does not necessarily mean better juice, perhaps just more of it. The higher the nitrogen, the higher the water content of the fruit juice. By pruning correctly, fruit size will increase but it is important to regulate nitrogen applications for higher sugar content. For cider and sauce uses, the amount of tannin, pectin and fruit size is mostly dictated by the cultivar. However, to have the highest sugar content, low nitrogen rates create smaller fruit. This leads to more fruit skin surface area resulting in much higher tannins and less water concentration creating a higher sugar content.

Precipitation amounts will play a large role in water content of an apple. A wet, rainy season during fruit growth stages will increase water uptake, carrying nitrogen with it, which will increase the fruit size and decrease sugar content. The type of soil, slope and location of trees can have a large impact as well. Soil with good drainage, will hold less water. Heavier soils with higher organic matter will mineralize more nitrogen and typically yield larger fruit with less sugar content.