adding Phosphorus to new orchard

Asked June 15, 2018, 10:09 PM EDT

We have a new apple orchard consisting of about 100 trees. The trees went into the ground this spring. The soil Phosphorus is low (8.2 ppm). The pH is 6.

What is the best way to add Phosphorus at this stage? It seems rather urgent. We are certified organic, so that may limit our options.

Thank you!



Lane County Oregon orchard

2 Responses

While 8.2 ppm is low, the best indicator will be leaf analysis in August. See https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/fs118.pdf for more information on leaf analysis and https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em8712.pdf for information on interpreting the results for apples. If the trees aren't suffering from P deficiency, then the soil test result is not critical. Apples typically aren't responsive to P in the southern Willamette Valley area.

P is very immobile in the soil, so pre-plant incorporation is the easiest way to increase soil P to the depth of incorporation. Since the orchard was planted this spring, incorporation obviously isn't an option, but manure can help. If you use manure for your nitrogen source, that will result in excess P being applied, and it tends to be more mobile in organic form, so that will aid in P moving from the surface down into the root zone. It will be important to continue monitoring soil P, as long-term manure applications can drive P to excessive levels. The nutrient management guide for apples (linked above) gives guidelines for N rates based upon tree age. You'll need to know the N content of whatever manure source you may use. Note that tree growth is the best gauge of N needs. If trees are putting on more than about 30 inches of growth annually, cut back on N a bit.

Thank you! We will plan to get leaf tissue analyzed in August.