Phosphorus and Almonds

Fertilizer prices are increasing. I recently received an email inquiry from a farmer in California who was asking about phosphorus requirements for almond. I thought the question was well timed and relevant to the 2021 season - so I thought I would share: 

Question: I’m relatively new to almond farming. An issue that came up today is that my crop advisor told me the cost of my N-P-K (8-8-8) application has increased by $40/acre due to increased costs of phosphates. That translates into a $5,600 increase from prices just two months ago. Are you hearing of this? If our Spring 2020 leaf analysis showed phosphorus at 0.13% which was at borderline. Do you suggest getting the application or would we be okay putting it off?

My response: All fertilizers have dramatically increased over the past few months due to increased commodity prices - from corn to oil. These expenses are making their way through the supply chain, with fertilizers seeing double digit increases from just a few months ago.

In regards to phosphorus, typically, soils within California are not phosphorus (P) deficient As such, P only needs to be added to meet the tree's demand. Trees will extract around 10-12 lbs/acre of P2O5 for every 1000 kernel pounds. This is a relatively small amount of the nutrient, which can be easily replaced with fertilizers or composts.

To determine the need for P, i would recommend soil sampling. Sample down to 18" within the wetted area and send to an analytical lab. They will either use the the Bray test if the pH is less than 6.5, or the Olsen if pH greater than 6.5. For the Bray, sufficient soil P will be between 5-10 PPM, for Olsen it is 10-20 ppm. If the soil test shows that P levels are above 8 ppm for the Bray test or  15 ppm for the Olsen test, the trees probably have enough soil reserves of phosphorous to get them through the year (and maybe more) with no additional P applications. If under 5/10 for the Bray/Olsen test, respectively, additional P applications are needed. This can take the form as liquid blends, solid fertilizers, or composted materials. Generally, liquid P materials are expensive per unit of P applied, but they do provide the ease of application.

 P leaf levels can be distracting.  I wouldn't worry too much about leaf sample values unless they are below 0.1% - especially if soil levels are adequate.  If P leaf levels are low, make sure that the soils aren't too wet which can inhibit root P uptake. Lastly, foliar applications can be used to provide a short term boost of P if needed on the rare occasion.

 There are many farmers who have never applied P and still have maintained very high yields. In these cases the trees are sourcing the P required from the soil. This is especially true in deep, alluvial finer textured soils. Also, the use of mycorrhizae and other symbionts can help the tree increase P levels. 

In general, the use of 8-8-8 for the entire season's fertility program most likely isn't needed.  If using this material to meet nitrogen and potassium needs, nearly 200 lbs/acre of phosphorous will be applied - which is way too much (enough for 8-10 years!). In total, I would not apply more than 30 lbs/acre of P2O5 for a crop of 2,500 lbs/acre. Applying too much P can create micronutrient deficiencies. If the material is used in the past, there may be enough stored P to meet this year's demand. 

If wanting to fertilize with a blend, a 9-1-9 (or 8-1-8) would be a perfect blend to match tree demand for the crop produced.