How Much Nitrogen Does a Satsuma Orange Tree Need?

Calculating Actual Nitrogen

• Actual nitrogen is different than the amount of nitrogen fertilizer. Fertilizer numbers show the ratio by weight of nitrogen, phosphorus and potassium. Ammonium sulfate is 21-0-0, ammonium nitrate is 34-0-0 and Urea is 46-0-0. To calculate the amount of actual nitrogen in these fertilizers, multiply the total weight of the fertilizer by the first number. For example, 20 pounds of ammonium nitrate contains 20 x 0.21 or 4 1/5 pounds of actual nitrogen. Using the same method of calculation, 20 pounds of urea contains 9 1/5 pounds of actual nitrogen.

Young Trees

• If your satsuma is 2 to 3 years old, spread 2 tablespoons of actual nitrogen over its roots then water well. The nitrogen can be in the form of ammonium nitrate, ammonium sulfate or urea. Do this three to four times the first two years and double the rate in the third year. Make the first application in early spring and the second before the beginning of summer. Make an additional application in fall only if you live in a frost-free climate. If you apply nitrogen late in the season, it can delay ripening of the fruit. Do not apply more nitrogen on the theory that more is better. Applying too much nitrogen can lower your satsuma tree's ability to withstand cold. In place of these chemical fertilizers, mix in 1 gallon of composted manure into the soil under the tree, making sure you water it well.

Mature Trees

• If your tree is more than 3 years old, give it 1 to 3 pounds of actual nitrogen annually, divided into three or more applications. As with young trees, you can use ammonium nitrate, ammonium sulfate or urea. Scatter the fertilizer over the roots and 1 to 2 feet beyond the drip line of the canopy and water the ground thoroughly. Alternatively, mix 1/2 inch of composted manure under the drip line once a year, preferably in fall.

Using Manure

• Manure can be high in salts that can damage satsuma roots, causing yellow leaves or leaves that are dead on the tips and around the edges. When you apply manure, water the soil well to wash the salts out of the root zones. While you can use manure in place of chemical fertilizers in spring, it is not a good idea. It is best to use only well-composed manure and apply it in October or November so winter rains can leach the salts from the roots while they are less active.