Nutrient Management Research Database

http://ucanr.edu/sites/nm/files/76732.pdf

• Not all fertilization timings are equal. Particular growth stages indicate elevated crop nutrient demands.
• For perennial tree crops, these stages of heightened nutrient requirements are flowering, fruit set, and fruit drop.
• Foliar application of some nutrients is an effective way to remedy mid-season deficiencies.
• This paper provides examples of cost effective utilization of foliar applied fertilizers.

• The particular levels and timings recommended for the following observations are included within this paper.
• The importance of foliar applied fertilizer timing:

1) For sweet oranges, winter prebloom foliar application of low-biuert urea or potassium phosphite (a P source) can increase yield, yield of large fruits, and total soluble solids.

2) Applying potassium sulfate at the post-shooting stage of bananas increased yield, fruit quality, and shelf life.

3) Potassium applied during cantaloupe fruit development and maturation improved fruit market quality by raising levels of beta-carotene, ascorbic acid, and K.

4) Canopy applications of boron or urea prior to avocado inflorescence expansion increased the number of viable ovules and the number of pollen tubes that reached the ovules. This resulted in a yield increase of about 5 tons/ac.

5) Foliar applied potassium phosphite increased ‘Hass’ avocado total yield, yield of fruit packing sizes 60 and 48, and the combined yield of fruit packing carton sizes 60, 48 and 40 in off-crop years.

• The importance of properly timing soil applied fertilizer:

1) Applying a double dose of N fertilizer for a single fertilization event (one of the six separate events used to limit nitrate pollution) was effective in increasing ‘Hass’ avocado yields by around 35%. The two key plant timings this held true for were 1) when shoot tip buds had four or more secondary axis inflorescence meristems (around mid-November) and 2) from anthesis to early fruit set and the initiation of vegetative shoot flux (around mid-April).