The findings of this project have been presented at The Empire State Fruit and Vegetable Expo, In-depth Fruit School on Apple mineral Nutrition, New York Fruit Quarterly, Hudson Valley Winter Fruit School, Mid-Atlantic Fruit and Vegetable Conference, and Great Lakes Expo, and Great Lakes Fruit Workers In-Service Training Meetings to apple growers in New York, Great Lakes region and Mid-Atlantic region. As a result, more apple growers have adopted optimal nutrient management practices in their orchards for high yield, good fruit size and quality, which have helped to increase the profitability of the apple industry.
impact statement issue
‘Gala’ apple being too small has been a major concern for apple growers in New York. This has been related to several factors. First, Gala is a small-fruited cultivar. Second, Gala trees differentiate flowers readily, have heavy fruit set, and are difficult to thin when tree vigor is low, and as a result trees often carry heavy cropload. Finally, heavy cropping reduces vegetative growth, which further decreases leaf area to fruit ratio.
But the market prefers large size fruit at a significant premium, which has prompted growers to strive for large size fruit. We have conducted field trials for three years to determine the optimal rate of nutrient supply to improve Gala fruit size, but the results were inconsistent. We found that when cropload was maintained at a medium level, increasing the rate of nitrogen fertilization led to an increase in fruit size.
However, under heavy cropload, we didn’t find any significant effect. These inconsistent results have brought up the following two questions:
1) How does nitrogen supply affect the source-sink relationship, leading to differences in final fruit size?
2) How much nitrogen and other nutrients are required by high density ‘Gala’ trees for high yield and good quality?
impact statement response
To address the two questions above, we first provided five-year-old ‘Gala’/M.26 trees with a wide range of nitrogen (3.0g to 40g actual nitrogen) supply via fertigation using a complete nutrient solution, with cropload adjusted to the same level (6.5 fruit per cm2 trunk cross-sectional area).
We found that 1) within the range of N supply used, increasing N supply improved leaf N status and leaf area to fruit ratio, leading to larger fruit and higher soluble solids; and 2) good size ‘Gala’ (180g/fruit) corresponded to a leaf N of 2.0 to 2.2% and a leaf area to fruit ratio of 550 cm2/fruit.
In the second experiment, six-year-old Gala/M.26 trees received the optimal nutrient supply regime obtained from the first experiment, with cropload adjusted to 8.2 fruit per TCA at 10 mm king fruit. At each of the key developmental stages throughout the annual growth cycle, we destructively excavated a set of four trees for complete nutrient analysis. These trees produced high yield (about 1110 bushels/acre) with an average fruit size of 181 g, soluble solids of 14.5% and fruit firmness of 16.8 lbs. Therefore, the accumulation of nutrients can be interpreted as the nutrient requirements by these trees. The nutrient requirements for N, P, K, Ca, Mg, S, B, Zn, Cu, Mn and Fe from budbreak to fruit harvest are 50 lbs, 8.2 lbs, 90 lbs, 35.5 lbs, 11 lbs, 4.0 lbs, 0.23 lb, 0.15 lb, 0.12 lb, 0.46 lb and 0.37 lb per acre.
Fruit and shoots and leaves have differential nutrient requirements. In general, active shoot growth and leaf area development from bloom to the end of shoot growth have high requirements for all the nutrients whereas the bulk nutrient requirements by fruit occur from the end of shoot growth to fruit harvest. At fruit harvest, shoots and leaves have more N, Ca, Mg, S, Zn, and Mn whereas fruit has more P, K, and B.
In conclusion, to grow good quality ‘Gala’, sufficient nutrient supply must be provided to achieve a leaf N status (2.0 to 2.2%) that translates into a good leaf area to fruit ratio (550 cm2/fruit) and sustained high canopy photosynthesis; 2) nutrient requirements of high density ‘Gala’ trees from budbreak to fruit harvest are N: 50, P: 8.2, K: 90, Ca: 35.5, Mg: 11, S: 4.0, B: 0.23, Zn: 0.15, Cu: 0.12, Mn: 0.46 and Fe: 0.37 lbs/acre; 3) fruit and leaves have differential requirements for nutrients: the high demand period for leaves and shoots is from bloom to end of shoot growth whereas that for fruit is from the end of shoot growth to fruit harvest; in addition, fruit needs more P, K, and B than shoots and leaves. 4) Nutrient management has to be integrated with other cultural practices (irrigation, thinning, pruning, etc) in order to achieve high yield and good quality.
impact statement summary
Gala apple being too small has been a concern for apple growers in New York and elsewhere. To improve Gala apple fruit size while achieving high yield and fruit quality, we conducted two experiments using Gala/M.26 trees grown in sand culture.
We found that:
1) sufficient nutrient supply must be provided to achieve a leaf N status (2.0 to 2.2%) that translates into a good leaf area to fruit ratio (550 cm2/fruit) and sustained high canopy photosynthesis.
2) nutrient requirements of high density Gala trees from budbreak to fruit harvest are N: 50, P: 8.2, K: 90, Ca: 35.5, Mg: 11, S: 4.0, B: 0.23, Zn: 0.15, Cu: 0.12, Mn: 0.46 and Fe: 0.37 lbs/acre.
3) fruit and leaves have differential requirements for nutrients: the high demand period for leaves and shoots is from bloom to end of shoot growth whereas that for fruit is from the end of shoot growth to fruit harvest. In addition, fruit needs more P, K, and B than shoots and leaves.
Also, nutrient management has to be integrated with other cultural practices (irrigation, thinning, pruning, etc) in order to achieve high yield and good quality.
These findings have been presented at various winter fruit growers meetings, an in-depth fruit school on apple mineral nutrition, and in New York Fruit Quarterly. As a result, more apple growers have adopted optimal nutrient management practices in their orchards for high yield, good fruit size and quality, which have helped to improve the profitability of the apple industry.
