Ontario Field Crop Report – August 3, 2022

Nitrogen deficiency symptoms can appear due to lack of mineralized N in the soil.

Improved nitrogen testing may be around the corner

Ontario’s corn crop is past the halfway point at this time and is left to Mother Nature’s will to help mature the corn and give us a decent harvest. For the most part, that means we can look back at what 2022 brought us and how we can adjust and improve our field and nutrient fertility plan moving forward.

One of the biggest challenges that corn fertility planning faces is with nitrogen (N) (see Figure 1.). The right rate of N is dependent on so many other factors that it remains one of the hardest to predict in any given year. Too much N leads to higher chance of losses to the environment, and too little N prevents a crop from maximizing yield, economic return, or both. One of the most difficult aspects of N rate planning is accounting for the plant available nitrogen that is mineralized in the soil and is accessible to the crop through the growing season.

Figure 1. Nitrogen deficiency symptoms can appear due to lack of mineralized N in the soil.
Figure 1. Nitrogen deficiency symptoms can appear due to lack of mineralized N in the soil.

Water-extractable mineral nitrogen (WEMN) testing has shown to be a strong indicator of the soil’s ability to provide plant available nitrogen to a corn crop in Ontario, according to a recently published study.

Research completed by Stoeckli et al., and funded by the Grain Farmers of Ontario, indicates that Ontario corn producers may soon have a more reliable tool for N fertilizer rate recommendations ahead of planting.

Currently, corn growers have a few tools at their disposal for N fertilizer recommendations, including the Pre-Plant Nitrate Test (PPNT), Pre-Sidedress Nitrate Test (PSNT), and the Ontario Corn N Calculator, among others. The PPNT and PSNT involve nitrate testing of the soil, and can improve accuracy of N recommendations, but can be limited by variables like early season rainfall or timing and method of testing in-field. PPNT and PSNT recommendations are also calibrated to a fertilization system that has not yet received broadcast N fertilizer and doesn’t have organic sources of N such as manure or legumes in the previous year. When used in situations that don’t meet these criteria, it’s very difficult to identify where the soil test nitrate value is coming from, making it difficult to adjust N fertilization rates. 

The study evaluated different methods of measuring nitrogen and carbon portions of the soil in lab-based testing. Soil cores were taken to a 30cm (12”) depth consistent with standard N sampling procedures (see Figure 2.). Researchers compared the soil test results from the lab to yield and Maximum Economic Rate of Nitrogen (MERN) to identify correlation. The study was conducted on 13 different sites over 2 years within Ontario corn fields with a history of synthetic N fertilizer use, with most sites being part of OMAFRA’s corn response trials.

Figure 2. Proper sampling techniques are crucial to obtaining an accurate nitrogen analysis and useable recommendation.
Figure 2. Proper sampling techniques are crucial to obtaining an accurate nitrogen analysis and useable recommendation.

Water-extractable mineral nitrogen is the readily available form of N in the soil solution. WEMN testing is performed in the laboratory using room-temperature water, as the name suggests, instead of a Potassium Chloride (KCl) solution that is used in PPNT and PSNT tests. Among the lab-based testing done on these sites, WEMN showed the strongest correlation with yield and MERN, outperforming tests looking at the organic-N portion of the soil. 

Soil texture has a great impact in the availability of nitrogen in the soil. Heavier clay soils were found to have lower N availability to the corn crop in season, when compared to coarser textured soils. Soil texture leads to differences in N loss pathways as well, where fine-textured clay soils are less prone to leach nitrogen, but more likely to have denitrification occur in wet conditions.

However, WEMN tests showed consistent results across soil types, leading researchers to conclude that this testing should be suitable for use throughout the highly variable soils across Ontario. Since the research focused on fields receiving synthetic N fertilizer, fields receiving a high amount of their plant nutrition from organic sources like manure may not follow the same trend with WEMN testing. Nevertheless, for farmers without livestock, this testing could be a game-changer in the future.

Part of the reason for uncertainty with pre-plant N recommendations is because of nitrogen’s relationship with water. Nitrogen moves into the plants as nitrate or ammonium in a solution with water in the soil. In very dry conditions, if the plant can’t access water, it won’t be able to utilize the N, no matter how much is in the soil.

The next step for this research should involve a multi-year study looking at the relationship between WEMN and N fertilizer recommendations, with more field sites to achieve proper calibration throughout Ontario soils. Still, this gives hope that Ontario agriculture may soon have a more reliable way of generating corn N recommendations on an individual field level.

With an ever-increasing focus on reducing nutrient losses from the field, as well as reducing greenhouse gas emissions from our fertilizers, fine-tuning N recommendations for corn using WEMN tests could optimize N rates for the growing crop and reduce the risk of adverse environmental effects. This includes limiting the amount of residual Nitrate-N left in the soil after corn harvest, which would improve Nitrogen Use Efficiency.

At the same time, an improved N fertilizer calculation could increase yield and profitability, especially in times of volatile input costs and grain markets. Better determination of N fertilization rates helps improve the sustainability of Ontario’s corn production. As the research continues, Ontario’s farmers can hope to put together one more piece of the nitrogen fertility puzzle in the coming years.

References:

Brown, C (editor). 2017. Agronomy Guide for Field Crops Publication 811. Queen’s Printer for Ontario.

Stoeckli, J.L., Sharifi, M., Hooker, D.C., Thomas, B.W., Khaefi, F., Stewart, G., McDonald, I., Deen, B., Drury, C.F., Ma, B.-L. and Motaghian, H.R. 2021. Predicting soil nitrogen availability to grain corn in Ontario, Canada. Canadian Journal of Soil Science. 101(3): 389-401. https://doi-org.subzero.lib.uoguelph.ca/10.1139/cjss-2020-0104

Weather Data – July 25 – 31, 2022

LocationYearHighest Temp (°C)Lowest Temp (°C)Rain (mm)Rain (mm) April 1stGDD 0C April 1stGDD 5C April 1stCHU May 1st
Harrow202228.213.60.3302201514372173
202131.511.61.5375202114292086
10 YR Avg. (2011-20)28.116.028.1379200613982169
Ridgetown202228.712.81.5211189613262000
202130.58.77.4361190013171961
10 YR Avg. (2011-20)27.413.836.7337188512832020
London202227.811.82.8231184312771937
202130.08.618.0300188813091929
10 YR Avg. (2011-20)27.514.516.7341186312652002
Brantford202228.911.20.3231184312721890
202129.47.316.4281185712771892
Welland202226.812.014.6264189113112002
202128.28.914.9289185412701904
10 YR Avg. (2011-20)27.415.014.0322187112722014
Elora202227.79.00.0196168411261729
202128.26.415.0256171311431746
10 YR Avg. (2011-20)26.212.021.5338167710911786
Mount Forest202226.911.621.5260168611341766
202128.67.622.3307171411471748
10 YR Avg. (2011-20)26.112.324.9347165610781783
Peterborough202227.89.90.2263169711251767
202129.47.218.8290170711261728
10 YR Avg. (2011-20)28.412.120.7300170211161791
Kemptville202227.613.01.1387182212301920
202129.49.29.0238183712491835
10 YR Avg. (2011-20)28.913.514.7329178512001906
Earlton202228.511.625.7277153610121659
202125.58.325.5418158910271577
10 YR Avg. (2011-20)26.411.812.428214299271576
Sudbury202225.513.09.2257153810061667
202125.99.910.2301161310531629
10 YR Avg. (2011-20)26.713.413.8312153210081687
Thunder Bay202228.78.921.941013118161370
202131.14.59.821914859381498
10 YR Avg. (2011-20)27.111.114.931013448301436
Fort Frances202228.68.317.252313888941515
202129.46.016.1183157810241623
10 YR Avg. (2011-20)27.110.522.731014709381593
Report compiled by OMAFRA using Environment Canada data. Data quality is verified but accuracy is not guaranteed. Report supplied for general information purposes only. An expanded report is available at www.fieldcropnews.com.