FAQs About Using FarmLogs Nitrogen Prescriptions in the Fall

Written by Dr. Tracy Blackmer
November 19, 2016

Do you apply nitrogen in the fall? If you do, consider this: soils vary, yields vary, and weather varies. Doesn’t it make sense to match your nitrogen with where it’s needed? That’s exactly what our Variable Rate Nitrogen Prescriptions are designed to do.

Below are some of the most common questions I’ve heard about using FarmLogs nitrogen prescriptions for fall applications.

Can you account for the N in my variable rate (VR) applied MAP/DAP?  

MAP and DAP are phosphorus fertilizers that provide a secondary source of nitrogen. If you variable rate your P application, it will result in a difference in N applied across the field. If you can supply us an as-applied file (such as a shapefile), we can account for it.

If one big benefit of using a FarmLogs Prescriptions is that it adjusts for the in-season weather in my area, don’t I lose this benefit if I apply in the fall?

It is true that you wouldn’t necessarily benefit from this particular prescription feature. But one feature you would certainly benefit from is the fact that our prescriptions still adjust for the fall weather conditions up to the time of application. Plus, our prescriptions use past weather patterns to help predict future weather patterns so we can estimate the weather's impact on nitrogen loss and availability in the future.

Because weather affects how different types of soils supply more N and lose N, you also benefit from using our N prescriptions because we account for the soil variability in your fields. In addition, we also account for the differences in yield potential within each field.  

Is there a way to factor N stabilizers into my prescription?

Currently, there is not a way for us to factor in N stabilizers unless you give a blanket N credit to manually adjust your FarmLogs Variable Rate Prescription at the end of the season.

Can I adjust for my soil sample data?

No. But most areas of the country don’t use soil testing for nitrogen recommendations, and most of those areas don’t have the samples collected on a fine enough grid to accurately match the field variability. Read more about common misconceptions about using soil samples in N recommendations here.

What are the key factors in making a FarmLogs Variable Rate Prescription?  

  • How much a field’s yield has historically varied
  • Soil organic matter for N release
  • Nitrogen loss varies by type of fertilizer, soil type, and amount of rain.  More rain usually means more loss. Accounting for the soil type and fertilizer type and timing has a benefit.

I don’t think my field is variable enough to justify VR prescriptions.

As a general rule, the more your yield varies or the more your soil types vary, the more you can benefit from VR prescriptions.

If I wanted to test a VR prescription on a few fields, what types of fields would you recommend?

I’d recommend large fields that have soil variability, and where you’ve seen differences in yield.

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Dr. Tracy Blackmer


Dr. Tracy Blackmer Dr. Tracy Blackmer is an expert agronomist with over 20 years of experience incorporating precision agriculture technologies in agronomic management for growers. His work has included organizing a network of over 1,000 growers from 12 different states to conduct Nitrogen adaptive management using imagery, yield response, and other feedback assessments. Tracy also focuses on implementing large-scale, on-farm trials that are easy for growers to implement and result in improved agronomic recommendations. His work as the Vice President of Science at FarmLogs includes developing tools that improve local management for growers through better and simplified recommendations and monitoring.