How to fertilize citrus trees
How to design a fertilization program for orange trees
One of the main ways to keep your crop vigorous, healthy, and productive for many years is to apply a suitable fertilization program. The type of nutrients and the amount of fertilizers are highly affected, among other factors, by the:
- soil type and nutrient availability
- variety and age of the tree
- end use of the fruit (for fresh consumption or juice)
- yield potential
Before planting your orange trees and every couple of years, you are strongly advised to perform a soil analysis test and a leaf tissue analysis (do not forget to check for the micronutrients, too) and adjust the nutrients added to avoid any nutrient deficiencies and yield reduction. Every field is different and has different needs. Nobody can advise you on a fertilization program without studying carefully your soil and tissue analysis.
In general, orange trees are the most nutrient-demanding among the most commercially cultivated citrus trees, benefiting from fertilization methods like fertigation (using soluble fertilizers) and foliar sprays.
Common fertilization recommendations for orange trees
When to fertilize orange trees
Orange trees require specific levels of nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca), along with trace amounts of iron, boron, magnesium, manganese, zinc, and copper. A nitrogen deficiency can lead to slow vegetative growth, leaf yellowing, premature leaf drop, and reduced yields. On the contrary, sufficient amounts of nitrogen in the tree have been positively correlated with both increased canopy size and flowering rate (Menino et al., 2003). Annual soil and tissue analysis can help you balance nutrient application and avoid over-fertilization or deficiencies.
Source: CDFA
Fertilizing Young (Non-Bearing) Orange Trees
In newly planted orange orchards, fertilization is, in most cases, essential since the young plants do not still have a well-developed root system. The first fertilization application of newly planted orange trees takes place 6 weeks after planting or when the new vegetation starts to grow. In 1-year-old orange trees, the nitrogen should be applied in 2-5 doses. Each tree should receive around 1 tablespoon or 0.7 kg (1.5 pounds) of nitrogen. As a general rule, the amount of nitrogen can be increased by 0.45-0.7 kg (1-1.5 pounds) every year until the age of 6, when the trees can receive 2.7-4 kg (6-9 lb).
Fertilizers should not be applied during dormancy. For optimal results, most of the total nitrogen (2/3) needed is usually applied during spring (or late winter) from the start of vegetation growth to the fruit set. The rest can be applied in early fall. Late applications should be avoided. Nitrogen is usually applied as urea, ammonium nitrate, or a mix of both.
Many farmers apply farm yard manure as an alternative or in combination with synthetic fertilizers. Keep in mind that 45 kg (100 lb) of well-rotted/composted cow manure contains around 0.45 kg (1 lb) of nitrogen.
While phosphorus is necessary to help your young orange trees grow their root system, farmers are advised to check the soil analysis results and define whether it is needed to add phosphorus and potassium fertilizers. As a result, in soils with low phosphorus or potassium, it is suggested to add 45-136 grams (0.10-0.30 lb) of P2O5 and/or K2O per tree during the first year of establishment, while the amount can be increased to 154-408 grams (0.34-0.90 lb) for 3-year-old trees.
Fertilizing Mature (Bearing) Orange Trees
In fruit-bearing trees, the farmer should prioritize compensating the trees for the nutrients removed from the harvest. So, for example, a yield of 33,626 kg per hectare (30,000 lbs per acre) removes per hectare around:
- 40-63 kg of nitrogen per hectare (35-56 lb N/ac),
- 13.5 kg of P2O5 per hectare (12 lb P2O5/ac)
- 60-80 kg of K2O per hectare (53-71 lb K2O/ac)
The amount of fertilizers added continues to increase as the tree grows and reaches the maximum level when the trees are 12 years old. The farmer may add up to 5.4-8 kg (12-18 lb) per tree at that time. However, depending on the region, references have mentioned that even 0.9 kg (2 lbs) per year per tree for 8-year-old sweet orange trees can give good yields and great quality.
We can say that the annual fertilizer requirements of the average orange tree are:
- 120 to 200 kg per hectare for N (107-178 lb/acre)
- 30 to 45 kg per hectare for P (27-40 lb/acre)
- 60 to 150 kg per hectare for K (54-134 lb/acre)
The amounts of nitrogen applied can be decreased in fields with an organic matter content above 2% or if there is a cover crop of nitrogen-fixing plants (e.g., legumes).
Orange farmers often provide 5.5 – 7.7 lb (2.5-3.5 kg) P2O5 in every adult tree for 4-5 consecutive years. In many cases, they may also add 3.3-6.6 lb (1.5-3 kg) K2O in every adult tree for two consecutive years. Another pattern for adult trees intended for table oranges includes three main fertilization applications per year.
Farmers start the applications at the end of winter (February) when they apply for each tree 4.4 to 6.6 lb (2-3 kg) of a top dressing similar to N-P-K 12-12-17. The second application occurs during the fruit setting stage (late spring, May-June). At this point, they apply 2.2 to 4.4 lb (1-2 kg) of fertilizer for each tree, providing only N and K to the plants.
Heavy nitrogen fertilization should be avoided at this stage because it will probably cause blastomania and will inhibit the fruit setting of the trees. The final application is performed during the fast-growing stage of the fruits (usually late summer, July-August). At this point, producers apply 2.2 to 4.4 lb (1-2 kg) fertilizer for each tree. Fertilization during the fruit growing stage aims at increasing the fruit's size and weight. Finally, farmers often add the micronutrients needed in a sulfate form (e.g., zinc or iron sulfate).
Fertilization Methods
Application is generally performed by soil or foliar fertilization.
Soil vs. Foliar Fertilization
- Soil Application: Fertilizers should be spread within the tree canopy's projection (not directly against the trunk) to prevent root toxicity. A mechanical incorporation or an irrigation (or rainfall) is usually needed.
- Foliar Fertilization: Quickly addresses deficiencies in iron, magnesium, boron, copper, or phosphorus, especially when timed during critical growth stages. Potassium phosphite, ammonium phosphite, and phosphorous acid are mostly preferred. Prebloom application and spraying during the fruit set have the best results.
The soil pH must also be checked at least once a year. If soil pH is greater than 7, you may have to take action to correct it by applying an acidifying fertilizer after consulting a licensed agronomist.
However, these are just some common practices and should not be followed without doing your own research. Every field is different and has different needs. You can discuss a balanced fertilization plan based on the latest soil and tissue analysis with a local licensed agronomist.
References
Menino, M. R., Carranca, C., de Varennes, A., d'Almeida, V. V., & Baeta, J. (2003). Tree size and flowering intensity as affected by nitrogen fertilization in non-bearing orange trees grown under Mediterranean conditions. Journal of plant physiology, 160(12), 1435-1440.
https://hort.purdue.edu/newcrop/morton/orange.html#Yield
https://www.cdfa.ca.gov/is/ffldrs/frep/FertilizationGuidelines/Citrus.html
https://ipm.ucanr.edu/PMG/GARDEN/FRUIT/CULTURAL/citfertilization.html
https://txmg.org/jcmg/garden-blog/fertilizing-citrus-2/
1.) Orange Tree Information & Uses
3.) How to grow Orange Trees from seed
4.) How to grow an Orange Tree from cuttings
5.) Growing Orange Trees for Profit
6.) Orange Tree Climate & Soil Requirements
7.) Choosing Orange Tree variety
8.) Orange Tree Propagation & Pollination
10.) Orange Tree Fertilizer Requirements
11.) Orange Tree Water Requirements
13.) Orange Tree Harvest & Yields
