Blog > December 2019 > Episode 3 | S, N, Zn, and other Micronutrients

Episode 3 | S, N, Zn, and other Micronutrients

December 19, 2019

12.19.19 | Soil Testing Part 3 from Central Valley Ag on Vimeo.

Episode 3 | S, N, Zn, and other Micronutrients

Sulfur (S):  Sulfur is a mobile nutrient and can be difficult to fully assess with just an 8 inch deep soil sample. Organic matter levels, soil texture, and plant tissue tests taken in-season can also help the grower with his decision on S applications. If the sulfur soil test is under 20 ppm and the soil is of medium texture, sulfur is unlikely to leach through the profile quickly, a small application of sulfur (10-15 lbs/acre) would be appropriate. This will ensure that S is available to the crop in a cool, wet season, which limits the mineralization of the sulfur contained in organic matter. If the soil is sandy or OM is very low, sulfur application becomes much more important and should be applied multiple times in the season.  

We used to get free sulfur from burning diesel with high sulfur content and from the emissions of coal-fired powerplants. That has changed with tightening restrictions on sulfur emissions. This has caused increased instances of sulfur deficiency and sulfur being applied on more acres as a fertilizer product.     

Zinc (Zn): Zinc levels of 1-2 ppm or above are usually adequate for corn and soybean production. Small amounts of zinc applied near the seed in a starter fertilizer may be beneficial for early-season corn growth. Very high Zn levels are often an indication of a history of manure application. 

Other Micronutrients:

The ranges that CVA likes to see for other micronutrients are as follows (assuming DTPA extraction):

Manganese (Mn):  12-22 ppm

Iron (Fe):  12-40 ppm

Copper (Cu):  1.0-1.5 ppm

Boron (B): 0.8 to 1.5 ppm

The recommended amounts of fertilizer to apply will be very small (often only one lb/acre for each nutrient). Consideration should also be given to the grower/advisor’s experience with response to these nutrients in their area. Some plant tissue samples for the crops commonly grown in a field would also help make these decisions.  Multiple tissue samples taken through the growing season are a better indicator than a single sample.

Nitrate N:  Expected yield of the corn crop and N credit from previous legume crops are usually more important factors in an N recommendation for corn than the carryover nitrate in the top 8 inches. A separate sample taken at a depth of 2-3 feet is more appropriate for measuring carryover nitrate. Often, a shallow sample may only have around 5 ppm in the top 6 inches, which converts to approximately 10 lbs of N per acre. This amount will have very little impact on the overall N recommendation. If you see an unusually high carryover nitrate amount, you need to ask yourself why. And also if this amount is really appropriate for the whole field or just a small area? Be careful with carryover nitrate seen in the fall. Will it still be there next summer when the crop needs it? Another question to ask yourself is: What can you do to keep from having large amounts of nitrate sitting in the soil at the end of the crop year? 

Prioritizing Nutrients:  We want growers to fix issues related to soil fertility in an order that is most likely to limit yields. We generally talk about things like soil pH and phosphorus before we discuss micronutrients like boron or manganese. The reason we do this is soil pH and phosphorus are proven to have yield-limiting effects much more often than boron or manganese. This does not mean boron or manganese are not important; they are just less likely to be a problem than what soil pH or phosphorus levels are. If soil pH is in a good range (6.3 – 7.2) and soil test phosphorus is in a good range (P1 Bray at 30 ppm or higher), then it is appropriate to move on to nutrients like boron, manganese, copper, or other micronutrients. 

We hope this three-part series has been helpful. If you didn't see parts one and two, click the links below:

If you have additional questions, please see your Field Sales Agronomist or feel free to contact Mick or Tim directly.
Posted: 12/19/2019 4:33:11 PM by Kelli Reznicek | with 0 comments

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