In last month’s issue I introduced the concept of the whole-farm nutrient mass balance (NMB) for dairy farms as a nutrient management tool that can help farms better understand the sources and sinks of phosphorus (P), nitrogen (N), and potassium (K) throughout the farm to increase profitability (reduce costly grain and fertilizer purchases) and reduce pollution potential (fewer instances of nutrient applications exceeding crop needs). Tracking your farm’s K balance is not to be overlooked, but the combined pollution potential and economic cost of P and N make them somewhat more interesting targets and thus, the two factors I’ll focus on for this discussion. Admittedly, while diving into this process the first year may seem a bit daunting, we’ll walk through some of the basics this month and hopefully convince some of you that it’s not actually too heavy of a lift relative to the benefits gained from a clearer vision of your production system as a whole. Then next month we’ll start getting into the good stuff and look at an example report and what kind of recommendations you can expect to receive after submitting your farm data. As mentioned last month, visit the Cornell University Nutrient Management Spear Program (NMSP) website for background information, including farmer testimonials and all necessary datasheets/software (http://nmsp.cals.cornell.edu/NYOnFarmResearchPartnership/MassBalances.html).
After familiarizing yourself with some of the resources, the first step is to download the “Input Data Sheets”. These are well-organized, fillable PDFs that walk you through each source of data you’ll need to track down and record. While it might be a bit tough to retroactively go back and collect some of the data in the first year, depending on your level of organization and detail, looking at the required information can help you organize your files to more easily summarize things at the next year’s end. The following are the three general categories of data requested: basic farm characteristics (animal numbers, tillable acres, etc.), nutrient imports and nutrient exports. If interested in estimating greenhouse gas emissions, there is also a fourth section of data that can be submitted to examine the N balance in more detail. However, that’s outside the scope of the NMB discussion we’ll focus on here.
Screenshots of the main portions of the data input sheets illustrate that while there’s a handful of major factors we need to keep track of across the farm, it all boils down to having a reasonably reliable estimate of the tonnage of the major N and P sources (fertilizers, grown/purchased feeds, milk, animals) that enter and exit the farm. By multiplying the N and P content (percentage) of each of those sources by the total tonnage brought on or off the farm, we get the tons of N and P from each source. Weights of the sources should be estimated by the best reliable methods (yield monitors, truck scales, invoices, etc.) and the N and P contents are estimated through a combination of measured (lab) values (whenever possible) and accepted book values (if/when samples aren’t available for lab analysis).
The more detailed the inputs, the more useful the outputs will be, but work with whatever you have and try to improve your data management a little bit each year if major changes aren’t possible or desirable. But regardless of whether you have truck scales for every forage load with matching lab data or you only know the total tonnage of all the corn silage harvested and are relying on book values for the nutrient content, you’re still very likely going to find benefit in beginning to track these additional data streams across your farm. In many cases you may already have a farm consultant tracking much of this data who can assist with some of the collection and collation. Don’t be afraid to reach out to the feed mill or your fertilizer rep to get a summary of your purchases for the current year, as they’ll also be able to help you identify the total tonnage of P and N across your purchases. As the tool is only intended to help inform the farm’s decision-making processes, you can include estimates for the data as much as you feel comfortable with, as you ultimately will be the only one deciding how useful the recommendations that you’ll receive in the report are and whether or not to implement them. Tune back in here next month when we’ll finally dive into some example outputs and we’ll see what you’d actually get in return for all your diligent data collection!
— Laura Klaiber