This is the first year that the UC Early Season Protocol (UC ESP) model for predicting July almond leaf nitrogen (N) levels from April leaf samples, has been available for public use. This model was developed by UC Davis researchers led by Dr. Patrick Brown. Based on calls to several reputable ag labs and questions from PCAs, there seems to be some uncertainty about availability and use of the new model. Where is the model? How does is it used? Who should use it to develop the July leaf N prediction and what should be done with the results? Does an analytical lab run it for growers and PCA/CCAs? If the lab doesn’t do it, should/can the grower or their PCA/CCA to do it, and, if so, where is the model? This blog post is intended to answer these questions and help interested almond industry members use the UC ESP model.
Why: July leaf N nutrient levels are too late to inform THIS season fertility management. Since adequate N THIS season is critical to good to excellent almond yields and excessive soil N is a potential environmental pollutant, careful N management is critical to sustainable almond production.
What: UC ESP model has been developed and carefully tested by UC Davis researchers led by Dr. Patrick Brown. This model, in the form of a Microsoft Excel spreadsheet, generates a prediction of the July leaf Non-pareil variety N level from 10 different leaf nutrient levels sampled in April following a specific protocol, described in a previous post on this blog. All these nutrient inputs are needed to deliver an accurate prediction. The model is simple to use for anyone with some experience with MS Excel. It is available, free, from the internet by clicking this link and downloading the Excel file from the box on the right of the web site page. Two versions of the same model are available, a larger sized file with 1000 sample entry – probably best for commercial labs and PCA/CCAs – and a smaller sized version that takes input from a single sample. Both models deliver the same output for each sample input.
Some analytical ag labs have developed and use their own, proprietary, early season models to determine orchard fertility levels. I don’t have experience with those models. This is the first publicly available model for early season prediction of July leaf N levels.
When: Leaf samples must be taken 42 days (plus or minus 6 days) after full bloom. Leaf N levels this time of year are a moving target, and sampling timing is critical to accurate prediction using the model. Leaves must also be sampled in a certain way for the model output to be useful. This protocol is not the same from the standard practices developed years ago. Don’t use the old sampling practices to get information (leaf nutrient levels) to use in the new model. Click here to see a previous post on this blog that describes the new protocol.
If you miss the sampling window, let it go for this year and use cropload estimates and previous experience to determine how much N fertilizer to use. Reminder: almond orchards use 80% of annual N requirement between bloom and mid-June.
Who: Anyone with MS Excel experience, a PC with the Excel program loaded and a copy of the model plus leaf analysis results from the 42 (±6) days from full bloom window can “crunch” the numbers and deliver a predicted July leaf N level. This information is key to planning efficient and effective N application rates to deliver optimum N nutrition for the remainder of the year. See the table in a previous blog post to help with this planning.
Where: Leaves sampled at the right time in the right way from separately managed blocks to a reputable lab for a total nutrient analysis package (less expensive than individual nutrient sampling). Download the model from the internet to your PC (or the cloud) and run the model with lab results as the input. Use output and cropload estimate to decide on N fertility program and rates for the rest of the season.
The Nickels Soil Lab just got our leaf analysis results back from the lab this week. Next step, decide on our next N fertigation rates for each sampled block and apply N fertilizer at appropriate rates to each. The goal is flexible, accurate, block by block N fertilization to deliver high yield and minimize N loss to air and water outside the rootzone.