A few more thoughts on soil fertility…

By Greg LaBarge, Ohio State University Extension Agronomy Field Specialist

Our last article covered some things to think about with higher 2021-2022 fertilizer prices. Unfortunately, there was an error with the soybean removal rates in that article. So let’s correct that and give you the current phosphorus and potassium removal rates for our major grain (Table 1) and forage crops or crop residues (Table 2).

Including nutrient removal numbers for crop residue is not something we often do. The most common residue harvested is wheat straw, but the removal of corn stover and occasionally soybean residue are becoming more common. If a field has frequent residue removal, for instance, fields close to livestock facilities, the nutrients removed with residue should be considered in nutrient plans. The nutrient removal values here can help evaluate that need on your farm.

Table 1. Nutrients removed in harvested grain
 Nutrient Removal Rate (pounds/bushel)
CropP2O5K2O
Corn0.350.20
Soybean0.801.15
Wheat0.500.25
Source: Bulletin 974, Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa
Table 2. Nutrients removed in harvested forage or crop residues
 Nutrient Removal Rate (pounds/ton of dry matter)
CropP2O5K2O
Corn Silage*3.17.3
Alfalfa*1249
Grass/legume mix**1249
Grass**1249
Wheat Straw*3.729
Corn Stover***4.818
Soybean Residue***4.723
Sources:* Bulletin 974, Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa** ANR-96, Nutrient Removal for Field Crops in Ohio ***PM 1688, A General Guide for Crop Nutrient and Limestone Recommendations in Iowa

There is another fertility topic to discuss while we have these tables in front of us. We continue to identify plant potassium deficiencies symptoms more frequently. There are a variety of explanations given for those symptoms. For example, compaction, soil moisture affecting root growth, and the Tri-state Fertilizer Recommendation are inadequate. As we evaluate the symptom patterns across a field, we might add a couple of other considerations to the list. The two items are residue distribution and fertilizer spreader patterns.

How does residue distribution potentially relate to potassium deficiency? To know if this is an important consideration in your case, answer two questions. One, are you using a wider grain table than you did 10 years ago? And the second question, do you vary your harvest pattern? 

For question one, a consequence of wider headers is that residue may not be distributed back across that entire width of the header. For question two, GPS guidance is a beautiful tool, yet we often set up A-B lines following that pattern for various machinery passes. If we follow the same pattern at harvest for several years, that pattern of residue placement could affect the spatial distribution of nutrients. Now take a look at the removal table. The spatial distribution of what nutrient might be impacted first? Answer: potassium. 

From Table 2, you see potassium is in the highest amount per ton of dry matter. This is because the primary plant form of potassium is a soluble ion in plant tissue. Potassium serves to regulate plant functions and compound transfers across cell membranes. In contrast, phosphorus is primarily in organic compounds.

Fertilizer spreader patterns also may play into spatial nutrient patterns across a field. Spinner spreader equipment is the primary delivery method for bulk fertilizer applications. Proper maintenance, operation, and calibration are necessary to deliver fertilizer evenly across the field. We do not want to go into spreader calibration in this article. However, if it is a topic of interest for you, there is an excellent three-part factsheet series from OSU Extension. Start at https://ohioline.osu.edu/factsheet/fabe-561, and you can walk through all three. 

There is one spreader topic related to potassium that we do want to talk about here. Unfortunately, this topic is one we cannot change by proper calibration. It is that the edge of spread patterns has a lower product delivery. The outside 20 to 30 feet get a lower application rate. The caution here is, do not evaluate potassium or any nutrient deficiency symptom from the edge of the field.  Always move out into the field.

We always want to look for patterns when evaluating crop problems. So, as you go through this harvest season, make a mental note of residue deposition patterns and spinner spreader operation, especially in problem fields. It might be part of the answer to nutrient issues you see in the 2022 crop.

Greg LaBarge and Harold Watters, OSU Extension Agronomy Field Specialists, are rarely in their offices, so they can best be reached: Greg LaBarge at labarge.1@osu.edu; or watters.35@osu.edu or by phone at 937 565-6064.

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