Where to Start with On-Farm Assessments of Nitrogen Optimization?

Optimizing N has the dual benefit of improved economic return and the reduction of nitrate leaching

By Matt Ruark, Department of Soil Science, University of Wisconsin (UW)-Madison & UW-Madison Division of Extension

There is renewed interest in conducting on-farm research to optimize nitrogen (N) fertilizer use for potato production. Optimizing N has the dual benefit of improved economic return and the reduction of nitrate leaching to groundwater.

The Wisconsin Department of Agriculture, Trade, and Consumer Protection (DATCP) has funding available through its nitrogen optimization pilot program (NOPP) that may be used to facilitate on-farm research. On-farm nitrogen research on potato will be a priority over the coming decade, whether funded by NOPP or other sources.

At the 2022 Grower Education Conference & Industry Show, I proposed a framework for how nitrogen studies can be categorized and how information from different studies can complement each other (Figure 1).

The foundational work in N research is to develop baseline N fertilizer recommendations (Figure 1, in blue). This work involves assessing crop yield and quality across multiple (six or more) N rates.

This type of research is the basis for

N recommendations found in the A2809 UW-Division of Extension publication.

Fundamentally, this research identifies the range of N rates that optimize production. However, more data is always needed to feed the development and updating of these recommendations.

This is particularly important for potato production, as most of the data comes from a single location, the Hancock Agricultural Research Station (HARS).

The second type of research focuses on adjustments to in-season N management and the technology used to help guide those decisions (green in Figure 1).

This is a topic of considerable research at the moment, as remote sensing and direct plant sensing technologies are showing promise in assessing the N status of the crop.

What remains to be evaluated is if there is value in adjusting N application rates based on the remote sensing results.

Current diagnostic tests, such as the petiole nitrate test, remain popular, as there are optimal ranges for most varieties. However, these tests are primarily used for justification of additional N applications rather than guiding N inputs earlier in the season. This category could also involve modeling programs to guide N application based on seasonal weather variability. These tools are available for corn production, although it is not clear if they are still being used after an initial rise in popularity.

After assessing the range of N needed to grow a potato crop and understanding the benefits and limitations of in-season assessment tools, the last area of research can focus on how to reduce N leaching losses.

The second type of research focuses on adjustments to in-season N management and the technology used to help guide those decisions (green in Figure 1).

This is a topic of considerable research at the moment, as remote sensing and direct plant sensing technologies are showing promise in assessing the N status of the crop.

What remains to be evaluated is if there is value in adjusting N application rates based on the remote sensing results.

Reduction in losses can occur through changes in the baseline N management approach. Utilization of polymer coated urea has been widely researched and has demonstrated reductions in

N leaching on sandy soils. More innovative work is needed to capture N that has escaped the shallow rooting system of the potato. An example of this type of research is the work of Dr. Jed Colquhoun, who is

Current diagnostic tests, such as the petiole nitrate test, remain popular , as there are optimal ranges for most varieties. However, these tests are primarily used for justification of additional N applications rather than guiding N inputs earlier in the season.

This category could also involve modeling programs to guide N appl ication based on seasonal weather variability. These tools are available for corn production, although it is not clear if they are still being used after an initial rise in popularity.

After assessing the range of N needed to grow a potato crop and understanding the benefits and limitations of in-season assessment tools, the last area of research can focus on how to reduce N leaching losses.

Reduction in losses can occur through changes in the baseline N management approach. Utilization of polymer coate urea has been widely researched and has demonstrated reductions in N leaching on sandy soils.

More innovative work is needed to capture N that has escaped the shallow rooting system of the potato. An example this type of research is the work of Dr. Jed Colquhoun, who is attempting to inter-seed deep rooting cover crops in the furrow to trap N deeper in the soil profile.

The fundamental idea is that there will be limitations to nitrogen use efficiency on sandy soils, and alternative methods of nitrate capture are necessary.

Another continued from pg. 61 attempting to inter-seed deep rooting cover crops in the furrow to trap N deeper in the soil profile.

Badger Beat. . .

The fundamental idea is that there will be limitations to nitrogen use efficiency on sandy soils, and alternative methods of nitrate capture are necessary.

CHALLENGES TO ON-FARM RESEARCH WITH POTATO

The Wisconsin Potato & Vegetable Growers Association has funded on-farm N rate trials for the last three years. The trials have worked well with the collaborating farmers, who provide us a sliver of a pivot where they can skip N fertilization applications.

This allows us to produce data presented in Figure 2, where regression analysis can be used to identify an optimum N rate (in this case, for total yield).

Potato is a challenging crop to grow and to study, but there are exciting opportunities for collaboration and

This work is laborious and time consuming as it involves establishing 54 plots (five to six rows wide by 25 feet long) and requires hand digging (although we have been lucky enough to have equipment from HARS transported to the site to do the digging, but all potatoes must be picked up by hand).

In my 14 years conducting nitrogen rate, timing, and source research on potato, I have come to the following We must figure out a way to increase collaboration in on-farm research. It is the key to advancing our ability profitably grow potatoes while reducing our impact to the environment.

This highlights the largest limitation to on-farm N research in potato— the lack of a yield monitor. Good agricultural research requires randomization, replication and many research plots. Is hand digging a viable option for on-farm potato research?

Another struggle with conducting onfarm N research is the method of N application. If most of the N is applied via pivot, are there opportunities to vary the N rate applied, or skip the application altogether?

Potato is a challenging crop to grow and to study, but there are exciting opportunities for collaboration and innovation.

In my 14 years conducting nitrogen rate, timing, and source research on potato, I have come to the following conclusion: We must figure out a way to increase collaboration in on-farm research. It is the key to advancing our ability to profitably grow potatoes while reducing our impact to the environment.