Time To Finish This Citrus Crop
Florida oranges are now entering the maturing phase of development. The last
fertilizer applications that will impact this crop’s quality are drawing near.
Photosynthates are accumulating and being stored in the fruits. The most critical
nutrients needed to increase fruit quality are nitrogen and potassium, but they
must be balanced with other essential elements within the citrus nutritional program.
During the period from late August to December, fruit will increase in fresh and dry weight
significantly. Hamlin will gain 42% of its final fresh weight and 35% of its final dry weight. Valencia
will gain 42% of its fresh weight and 53% of its dry weight. Note that Valencia will continue to
develop into March-April and may respond favorably from the January/February application. Failure
to supply sufficient nutrients to meet fruit and tree needs will weaken both. Trees that become
stressed due to heavy crop load are more susceptible to disease pressure. Maintaining balanced
nutrient levels going into the fall and winter is critical to the next crop.
Rate of Application should be matched to crop removal
Nutrient uptake for the two varieties are slightly different during this final phase. The Hamlin will
take up 0.02 lb/bx nitrogen and 0.036 lb/bx potassium . Valencia fruit will take up 0.03 lb/bx
nitrogen and 0.035 lb/bx potassium. The removal rate by the fruit needs to be matched by the
estimated crop load that will be harvested. Therefore the grower should apply 0.02 lb/bx nitrogen
and 0.04 lb/bx K2O to his Hamlin and 0.03 lb/bx nitrogen and 0.04 lb/bx K2O to the Valencia.
A 500 box crop of Hamlin would need 10 pounds of nitrogen and 20 pounds of K2O to meet the
removal requirements. Likewise the Valencia would need 15 pounds nitrogen and 20 pounds
K2O to meet the removal requirements. The tree also needs nutrients to maintain growth, health and
to accumulate carbohydrates reserves for the next fruiting phase. Given the needs of the tree and
the efficiency uptake of fertilizers, typical rates of application per acre for nitrogen would be around
50 pounds. Spoon feeding your trees as needed should also follow the 4 R BMP practices.
Nitrogen values are stated as nitrogen on the fertilizer tag while potassium values are stated as
potassium oxide (K2O). The amount of potassium in potassium oxide is 83% (0.83). To determine
how much potassium is in your formulation you would need to multiply the formula value by 0.83 to
determine the amount of potassium. Conversely, if you know how much potassium you need, you
divide that amount by 0.83 to determine how much K2O you need to apply.
Potassium exhibits stronger demand from September to December
Hamlin N
Hamlin K
Val N
Val K
Sep
Oct
Nov
Dec
The above chart illustrates the differences in nutrient uptake patterns and relative
amounts needed by the fruit for development. [Data was collected over a six year period.]
Hamlin uses lower nutrient amounts to produce equivalent boxes. The average production
for the Hamlin was 648 boxes and 466 boxes for Valencia. Both varieties received 150
pounds of nitrogen per acre per year. It is interesting that the solids per box were about
the same. The Valencia block was only 9 years old at the end of the study and the Hamlins
were 32 years old. The lower pounds solids for Valencia could possibly be attributed to
lower levels of K2O for fruit assimilation than required. However, this study’s objective
addressed nitrogen rates and source to reduce nitrogen input levels and not potassium
fertilization. Potassium application of 1.5 times the nitrogen rate should be considered at
this growth stage.
The accumulation of solids is a critical function we can manipulate by applying the
necessary amounts of nitrogen and potassium. Nitrogen source should be in the nitrate
form to avoid uptake competition with Potassium and Magnesium. Potassium applied via
ground application with supplemental foliar application can deliver the extra potassium
needed to maximize pound solids in the fruit.
Nutrient uptake is dependent on a healthy vigorous root system . YaraLiva ® Tropicote® ,
YaraLiva ® CN-9 ® Liquid Calcium Nitrate, Yara’s Krista ® K Potassium Nitrate and
Unika Kali® Potassium Nitrate work together to insure a vigorous healthy root
system allowing your crop to obtain its full potential, this year and next. Healthy trees
have higher resistance to pest pressure and produce more profits.
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[email protected]
Sincerely,
Jerry Southwell
[email protected]
Yara North America
1-863-773-0154
www.yara.us