Interested in what Discovery Farms has been up to this summer? Check out the fact sheet to learn more about how Discovery Farms is communicating science, as well as progress on the Nitrogen Use Efficiency Project and Watersheds. The full document and the September Discovery Farms newsletter can be found at the Discovery Farms website (www.uwdiscoveryfarms.org).
Two of Dr. Ruark’s presentations on nutrient cycling and cover crops are now available online. The first was as part of Minnesota’s Crop Nutrient Management Conference (February 9, 2015 in Mankato, MN). Power points are available on the Minnesota Agricultural Water Resource Center’s website: http://www.mawrc.org/events.html
The second event was the Iowa Cover Crops Conference (February 17-18, 2015 in Des Moines, IA). Power points are available on the Soil and Water Conservation Society’s slideshare site: http://www.slideshare.net/swcsevents. This event also includes presentations from farmers on how they are using cover crops on their farm.
Two field days are being hosted by the UW Discovery Farms program. The first is on August 11, 2014 in New Richmond, WI. Dr. Ruark will be presenting on nitrogen fertilizer efficiency, with a specific emphasis on nitrogen uptake in corn grain and corn silage. Additional presentations include an update on a Discovery Farms watershed project in Dry Run Watershed and residue and cover crop management to reduce runoff. Check out the flyer here. A dinner is included.
The second field day on August 28th is in Westby, WI, where Dr. Ruark will also be presenting on nitrogen use efficiency.
The most common problem for farmers and crop consultants when determining an optimal nitrogen (N) rate for corn is that they never truly know if and by how much they “over” applied their N fertilizer. Under-application of N is readily seen in corn plants through classic N deficiency symptoms of yellowing of the midrib on lower leaves, likely resulting in reduced yields (http://www.agronext.iastate.edu/soilfertility/photos/photossdef.html). There are a few metrics used to determine if N was over-applied, such as the corn stalk nitrate test (https://store.extension.iastate.edu/Product/pm1584-pdf) and end-of-season soil nitrate test. These tests require extensive sampling, only pertain to corn, and the relationship between stalk or soil nitrate values and crop yield are not well documented in Wisconsin. What I suggest here is the use of nitrogen use efficiency (NUE) calculations as simple metrics that can be used to understand how efficient you are (and can be) with N fertilizer.
The partial nutrient balance. One way that farmers and crop consultants can “see” the unused nitrogen is through nitrogen use efficiency calculations. There is no one specific calculation that is the true NUE, but instead the term NUE represents a suite of calculations that each have a specific meaning. The simplest calculation is the partial nutrient balance (PNB), which is the amount of N removed in the grain divided by the N applied (http://go.wisc.edu/1467hc). A PNB of 1 (or slightly less) is considered ideal (i.e. system sustainability). If the value is much less than one, then this indicates there are opportunities for improvement. The PNB is a calculation that can be done by all growers on a field-by-field basis as long as they know their yield and the amount of N applied. Based on average N concentrations from corn samples analyzed at the University of Wisconsin Soil and Plant Analysis Laboratory, 0.70 lb-N is removed with 1 bu of corn grain (at 15.5% moisture). Therefore, multiplying 0.70 by the yield (bu/ac) gives an estimate of the amount of N removed. This calculation can also be used to “see” a simple N budget for the field (N input vs. N output) by subtracting the N removal from the N applied; if it is negative, more N was removed than what was applied. If it is positive, this is the amount of N remaining in the soil system. However, a lot of this N can still be tied up in the crop residue and for many systems there is a limit on how close we can get this value to 1. More accurate PNB values can be determined if the actual N concentration of the grain is known.
The value of the zero-N check strip. To get a sense of how much N is available from the soil, we can use the amount of N taken up by the corn plant (ears, stalks, and leaves – the entire above ground biomass) when no fertilizer is applied. This will involve cutting a whole plant at ground level, drying, and analyzing for total N; this is obviously not a standard sample practice. This value (total N uptake in unfertilized corn) can then be subtracted from the N in the above ground biomass from fertilized corn and then divided by the amount of N applied to give us the apparent crop recovery efficiency (RE). It is called the “apparent” crop recovery efficiency because we aren’t using the N taken up in root biomass and we are making assumptions about the fate of the applied N. In this case a value of 1 would indicate that the increase in N uptake from unfertilized to fertilized was the same as the amount of N applied (this is an unrealistic system). Snyder and Bruulsema (2007) provide some context, stating that values of 0.5 to 0.8 represent corn systems under best management practices. So, the value of the zero-N check strip allows you to know how much of your N was “needed” by the crop. This is in contrast to the partial nutrient balance calculation, which doesn’t indicate anything about crop need of the fertilizer, only the N balance of your soil and cropping system.
Recovery efficiency verifies the need of the fertilizer. Different soils will supply different amounts of N. For example, in an N rate trial conducted in 2011, corn fertilzied with 150 lb/ac of N at the Lancaster Agricultural Experiment Station had a RE of 63% while corn grown at the Arlington Agricultural Experiment Station had a RE of 28%. This indicates that would want to thing about altering our N rates at Arlington because less than 30% of the N that was applied was taken up. At Lancaster, we may not be able to improve much as nearly 70% of the N applied as take up by the plant.
Comparing the RE and the PNB. A stark contrast between these two calculations can be seen with irrigated sweet corn in the central sands in 2011. Yields without N were incredibly low, leading to RE of 88%, while the PNB was only 43% (150 lb/ac of N was used in this example). The 43% PNB is quite low, indicating a lot more N is applied to the system than is removed. However, a large percentage of the N applied ended up being taken up by the crop. Thus, for sweet corn on sandy soil, the PNB alone doesn’t tell the whole story regarding efficiency and fate of the N applied.
Overall, you’ll notice that I’ve used a lot of terms like “estimate” and “apparent” throughout the past few paragraphs. These calculations are not meant to be the last word on how efficient you are with your N fertilizer, but simply provide a tool for farmers and crop consultants to assess the current state of their N management. These measures need to be conducted across many growing seasons to get a range of efficiency values across different rainfall patterns. But, if we can make the “unseen” nitrogen “seen”, this will give both farmers and consultants more confidence with continuing their current N management plan or identify fields on which improvement strategies are warranted.
For more information on nitrogen use efficiency calculations see http://go.wisc.edu/1467hc. For more general information on nitrogen in soil check out Soil and Applied Nitrogen (http://www.soils.wisc.edu/extension/pubs/A2519.pdf).
A recent article in Agri-View highlights key research findings on nitrogen crediting from cover crops, use of polymer-coated and nitrification inhibitors, and managing nitrogen on tile drained land. Research was presented at the 2013 Soil, Water, and Nutrient Management Meetings and presentations will be made available shortly.
Full article can be found here.
Nitrogen efficiency: Products, cover crops can improve system
Efficient use of nitrogen in corn production makes sense.
That was evident from the big audience UW-Madison soil scientist Matt Ruark had at Corn-Soy Expo in Wisconsin Dells when he addressed the topic, including use of controlled release fertilizers and nitrogen stabilizers and cover crops that supply nitrogen to the next crop.
Noting that nitrogen use efficiency has been on a steady climb upward since the mid-1970s, Ruark still thinks growers should be tracking their nitrogen use efficiency by simply dividing grain produced by nitrogen applied, field-to-field and year-to-year.
The number goes up if yield increases with the same nitrogen rate, yield is maintained with less nitrogen, or best yet, yield goes up with less nitrogen.
Full article can be found here.
Joe Lauer, Carrie Laboski, Francisco Arriaga, and I will be presenting at an Extension event on August 5th. This “Corn University” will cover topics of nitrogen, soil, and agronomic management of modern corn production. I will be presenting on nitrogen management of corn (including controlled-release fertilizers and crop rotations) and cover crop management. Click here for more details.
To check out this presentation and other presentations at the 2013 Central Wisconsin Processing Crops Meeting
Take home messaged from nitrogen and snap bean research:
1) Different snap bean varieties respond differently to nitrogen fertilizer applications.
2) Variations in rainfall timing cause huge differences in response to nitrogen
3) There is a huge nitrogen use efficiency decrease when nitrogen is applied in excess of 60 lb/ac, but any slight yield gains achieved with extra nitrogen can be justified from an economic perspective (i.e. the high economic value of the crop far exceeds the cost of additional nitrogen fertilizer)
It may have been the promise of coffee and bagels, but the RuarkLab meeting was well attended. The 2010 field season is upon us!
The 2009 Area Soil, Water & Nutrient Management Meetings are underway! This year’s topics include:
- Update of water quality research findings from Discovery Farms
- Soil mapping in Karst topography
- Wisconsin nutrient management update (DATCP)
- What you need to know about gypsum
- Nitrogen and soybean: application to and credit from
- The “Big Laboski” Hour – research updates from Dr. Laboski’s research program
For more info on the Area Meetings click here
Soil testing is the only tool we have to evaluate the pH, phosphorus (P), and potassium (K) status of the soil. Knowing this information allows growers to make economically optimum applications of lime and phosphorus and potash fertilizer. In these times of economic uncertainty, managing input costs is an important component of farm sustainability. Many growers have opted to cut costs by eliminating soil testing as part of their management program. This is not a recommended strategy. There are two main misconceptions about soil testing:
MISCONCEPTION #1: Soil testing is expensive.
FACT: Routine soil testing costs less than 40 cents per acre. University of Wisconsin soil testing recommendations are to analyze one composite sample per 5 acres and to soil test at least once every four years. Using a standard rate of $7.00 per analysis, this averages out to $0.35 per acre per year. Most, if not all, certified laboratories will also provide fertilizer recommendations based on University of Wisconsin recommendations along with the soil test values. Some laboratories may have slightly higher prices or may charge shipping costs.
MISCONCEPTION #2: Maintenance applications of P and K are good enough.
FACT: Soils testing in the very low to low range for P and K require additional inputs beyond removal rates to optimize yield.
FACT: Soils testing in the high to excessive range require less than removal rates to optimize yield.
In either case, money is lost from either reduced yields or over application of P and K. When soils tests indicate the soil is in the very low to low category, this suggests that there is a very high likelihood that yields will increase due to application of fertilizer. However, it also indicates that the crop would benefit from building the “fertility” of the soil through additional P and K inputs over time.
For more information on soil testing, please visit our website www.soils.wisc.edu/extension/soilsampling.php.