Splitting for citrus is usually over watering. Are you in Cal or AZ either way, we have a lot of rain + watering Hum

I'm in az nw glendale. I'll have to watch the water more carefully ... Darn !! What a waste!

From September through November splitting in navel oranges often occurs in green fruit. It's attributed to the rind not being able to expand when the fruit is filling with moisture and the rinds burst open due to the pressure. Rinds that are sunburned or have lost their elasticity are more apt to split. The number of fruit affected seems to vary from year to year. Fruit on the south or west sides of the tree may be more vulnerable due to sun exposure. Splitting seems to be related to extreme fluctuations in temperature, humidity, soil moisture, and even fertilizer levels. Regular, deep irrigations are a good practice as is using a 3 inch layer of mulch over the root zone. Here's a link to irrigating citrus, fertilizing, etc. http://cals.arizona.edu/maricopa/garden/pubs.htm