Ontario Field Crop Report – August 3, 2022

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.

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.

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

Location	Year	Highest Temp (°C)	Lowest Temp (°C)	Rain (mm)	Rain (mm) April 1st	GDD 0C April 1st	GDD 5C April 1st	CHU May 1st
Harrow	2022	28.2	13.6	0.3	302	2015	1437	2173
	2021	31.5	11.6	1.5	375	2021	1429	2086
	10 YR Avg. (2011-20)	28.1	16.0	28.1	379	2006	1398	2169
Ridgetown	2022	28.7	12.8	1.5	211	1896	1326	2000
	2021	30.5	8.7	7.4	361	1900	1317	1961
	10 YR Avg. (2011-20)	27.4	13.8	36.7	337	1885	1283	2020
London	2022	27.8	11.8	2.8	231	1843	1277	1937
	2021	30.0	8.6	18.0	300	1888	1309	1929
	10 YR Avg. (2011-20)	27.5	14.5	16.7	341	1863	1265	2002
Brantford	2022	28.9	11.2	0.3	231	1843	1272	1890
	2021	29.4	7.3	16.4	281	1857	1277	1892
Welland	2022	26.8	12.0	14.6	264	1891	1311	2002
	2021	28.2	8.9	14.9	289	1854	1270	1904
	10 YR Avg. (2011-20)	27.4	15.0	14.0	322	1871	1272	2014
Elora	2022	27.7	9.0	0.0	196	1684	1126	1729
	2021	28.2	6.4	15.0	256	1713	1143	1746
	10 YR Avg. (2011-20)	26.2	12.0	21.5	338	1677	1091	1786
Mount Forest	2022	26.9	11.6	21.5	260	1686	1134	1766
	2021	28.6	7.6	22.3	307	1714	1147	1748
	10 YR Avg. (2011-20)	26.1	12.3	24.9	347	1656	1078	1783
Peterborough	2022	27.8	9.9	0.2	263	1697	1125	1767
	2021	29.4	7.2	18.8	290	1707	1126	1728
	10 YR Avg. (2011-20)	28.4	12.1	20.7	300	1702	1116	1791
Kemptville	2022	27.6	13.0	1.1	387	1822	1230	1920
	2021	29.4	9.2	9.0	238	1837	1249	1835
	10 YR Avg. (2011-20)	28.9	13.5	14.7	329	1785	1200	1906
Earlton	2022	28.5	11.6	25.7	277	1536	1012	1659
	2021	25.5	8.3	25.5	418	1589	1027	1577
	10 YR Avg. (2011-20)	26.4	11.8	12.4	282	1429	927	1576
Sudbury	2022	25.5	13.0	9.2	257	1538	1006	1667
	2021	25.9	9.9	10.2	301	1613	1053	1629
	10 YR Avg. (2011-20)	26.7	13.4	13.8	312	1532	1008	1687
Thunder Bay	2022	28.7	8.9	21.9	410	1311	816	1370
	2021	31.1	4.5	9.8	219	1485	938	1498
	10 YR Avg. (2011-20)	27.1	11.1	14.9	310	1344	830	1436
Fort Frances	2022	28.6	8.3	17.2	523	1388	894	1515
	2021	29.4	6.0	16.1	183	1578	1024	1623
	10 YR Avg. (2011-20)	27.1	10.5	22.7	310	1470	938	1593