The purpose of this fact sheet is to report grain nutrient removal rates in corn, soybean, and wheat in Ohio.
Summary of Findings
- Grain nutrient concentrations were determined from over 300 on-farm fertilizer trials in 39 Ohio counties.
- Grain yields reasonably predict how much nutrient is removed in the grain at harvest.
- Since the original Tri-State Recommendations, grain nutrient concentrations of P and K have decreased, indicating lower P and K removal rates per bushel of grain.
- Decreased nutrient removal rates per bushel of grain indicate crops are becoming more efficient.
- Farmers could save fertilizer costs, if application rates are adjusted to reflect removal in grain.
- A typical corn-soybean rotation yielding 180 bushel per acre corn and 60 bushel per acre soybean removes 100–120 pounds per acre of both P2O5 and K2O. This is equivalent to 210 pounds MAP (11-52-0)/acre, 240 pounds DAP (18-46-0)/acre, 180 pounds potash (0-0-60)/acre.
Field crops take up large quantities of nutrients from the soil over the course of a growing season. These nutrients are incorporated into plant tissues such as leaves, shoots, and roots. In corn, soybean, and wheat, a large percentage of nutrients will ultimately be translocated to the grain and accumulate there as the crop reaches maturity. When grain is harvested, nutrients are removed from the field. If these nutrients are not replaced with fertilizers or manures, then plant-available soil nutrient levels will draw down over time and the fertility of a soil will be compromised.
The Tri-State Fertilizer Recommendations advocate a build-up and maintenance approach to nutrient management (Vitosh et al, 1995). Essentially, soil nutrient levels should be monitored through soil testing and built up to a recommended maintenance range. Once in the maintenance range, fertilizer application rates will roughly equal the rate of nutrients removed in the grain. In other words, once soils are in the maintenance range, if 50 pounds of P2O5 are removed at grain harvest, then 50 pounds of P2O5 should be applied to match that removal.
On-Farm Fertilizer Trials in Ohio
From 2014-2018, we conducted over 300 on-farm fertilizer trials with the ultimate goal of updating the Tri-State Fertilizer Recommendations. We conducted nitrogen, phosphorus, potassium and sulfur trials in corn, soybean and wheat across the state in 39 different counties (Figure 1). These trials represented a wide diversity of soil types, tillage practices, fertilizer sources and rates, and management histories. We collected grain and recorded yields from each trial conducted (including strips that received fertilizer and strips that did not receive fertilizer). Grain samples were analyzed to determine nutrient concentrations in the grain. Collectively, we had a total of 2338 samples for corn, 1169 samples for soybean, and 628 samples for wheat. Across all trials, corn grain yields averaged 171 bushels per acre, and ranged from 21–286 bushels per acre. Soybean grain yields averaged 49 bushels per acre, and ranged from 5–91 bushels per acre. Wheat grain yields averaged 90 bushels per acre, and ranged from 41–131 bushels per acre.
Grain nutrient removal was calculated by multiplying the grain nutrient concentration by the grain yield for each observation. The nutrient removal was then plotted against grain yield. The slope of the linear relationship is the estimate for the average grain nutrient removal rate.
Grain Nutrient Removal Rates
Grain yield is a good predictor of grain nutrient removal rate. In other words, as grain yields increase, rates of nutrient removal increase. The blue trend lines in Figure 2 represent estimated grain nutrient removal rates. Variation around this trend line shows that there can be large differences in removal rates depending on a number of factors like soil and management history of a field, genetics, growing conditions, etc. For example, at 180 bushel per acre corn, grain removal rates ranged from 17–35 pounds P2O5 per acre (Figure 2). Therefore, we consider nutrient removal rates to be a ‘best estimate,’ but need to acknowledge the inherent variability across different fields.
Figure 2. Corn, soybean, and wheat grain nutrient removal rates for nitrogen (N), phosphorus (P), and potassium (K). The blue trend lines represent average grain nutrient removal rates.
Grain nutrient removal rates are reported in Table 1. If these rates (pound of nutrient per bushel grain) are multiplied by a typical harvest, we can estimate total grain removed across a field. This is especially relevant for estimating how much P and K are removed over a rotation. For example, with a 180 bushels per acre corn harvest, we remove 62 pounds of P2O5 per acre and 36 pounds of K2O per acre. With 60 bushels per acre soybean, we remove 47 pounds of P2O5 per acre and 68 pounds of K2O per acre. Therefore, over a typical corn-soybean rotation, we would remove approximately 100–120 pounds per acre of both P2O5 and K2O. If we fertilize to maintain soil test levels, then we should apply fertilizer at the same rates as nutrients removed in grain. This is approximately equivalent to 210 pounds MAP per acre or 240 pounds DAP per acre, and 180 pounds potash per acre. This simple approach enables fertilizer recommendation rates to be adjusted based on grain yields and subsequent nutrient removal.
|Table 1. Grain Nutrient Removal Rates (lb/bushel) and Total Grain Nutrient Removed (lb/acre) For Corn, Soybean, and Wheat. Total grain nutrient removed is based on 180 bushel corn, 60 bushel soybean, and 80 bushel wheat.|
|Grain nutrient removal rates||Total grain nutrient removed at harvest|
|Corn||Soybean||Wheat||Corn (180 bu)||Soybean (60 bu)||Wheat (80 bu)|
|(lb of nutrient/bushel grain)||(lbs of nutrient/acre)|
Trends Over Time
We compared these new nutrient removal rates to previously published rates from the original Tri-State Fertilizer Recommendations to look at basic trends in grain nutrients over the past several decades. Table 2 reports previously published values compared to our new values. Our new data show that plant breeding over the past several decades have made crops more efficient. Corn, soybean, and wheat now yield more grain with less nutrient removed per bushel of grain relative to 20 or 30 years ago. In particular, potassium removal rates have dropped considerably in corn (26 percent decrease), soybean (19 percent decrease) and wheat (35 percent decrease). Reduced grain nutrient concentrations have also been reported in other states (IPNI, 2013; Mallarino et al., 2013; Nafziger, 2017). Reduced nutrient removal rates per bushel of grain ultimately translate into lower rates of fertilizer needed to replace the nutrients exported in each bushel. This provides an important opportunity for farmers to save on fertilizer input costs.
|Table 2: Phosphorus and Potassium Grain Nutrient Removal Rates from Previous Tri-States Recommendations (1995) as Compared to New Data Reported Here.|
|Crop||Nutrient||Tri-State (1995) (lbs/bushel)||New Data (lbs/bushel)||Percent Decrease|
The data presented here represent a robust estimate of grain nutrient removal rates across Ohio. If farmers multiply their grain yields by the values in Table 1, they can estimate nutrient removal rates for any given nutrient in a field. Overall, grain nutrient removal rates per bushel of grain have decreased over the past several decades. If soils are in the maintenance range, then fertilizer rates should be revised to better reflect nutrient removal rates from grain exported from a field. Ultimately, adjusting fertilization based on reduced grain nutrient removal rates could translate into considerable savings in fertilizer costs.
It is important to understand that grain nutrient removal rate is only a fraction of the total crop nutrient uptake. A crop takes up nutrients in the leaves, stems, and roots, and only some of these nutrients are translocated to the grain during grain fill. Grain nutrient removal rates do not provide information of the total nutrient required by a crop, but rather estimate how much nutrient should be applied to replace nutrients exported to maintain soil test levels.
The authors wish to acknowledge the contribution of many farmer cooperators, crop consultants and Ohio State University Extension educators for making this work possible. The authors thank the Ohio Soybean Council, Ohio Corn Checkoff and Ohio Small Grains Checkoff, as well as U.S. Department of Agriculture for funding this work.
IPNI, 2013. International Plant Nutrition Institute Online Nutrient Removal Calculator: ipni.info/calculator; ipni.net/article/IPNI-3296
Mallarino, A.P., J.E. Sawyer, and S.K. Barnhart. 2013. PM 1688 (A General Guide for Crop Nutrient and Limestone Recommendations in Iowa), Iowa State University, Ames. store.extension.iastate.edu/product/5232
Nafziger, E. 2017. New Grain Phosphorus and Potassium Numbers. The Bulletin, Pest Management and Crop Development Information for Illinois: bulletin.ipm.illinois.edu/?p=3967
Vitosh, M.L., J.W. Johnson, and D.B. Mengel. 1995. Tri-State fertilizer recommendations for corn, soybeans, wheat and alfalfa. Ext. Bull. E-2567. Michigan State Univ., East Lansing.
Grain Nutrient Concentrations
Grain nutrient concentrations varied in corn, soybean, and wheat across the trials. Table A1 reports the average nutrient concentrations across all studies. Macronutrients (N, P, K, Ca, Mg, S) are in percentages, while micronutrients (B, Cu, Fe, Mn, Zn, Na) are in parts per million (ppm).
|Table A1. Average Grain Nutrient Concentrations in Corn, Soybean and Wheat.|
Grain nutrient concentrations were weakly related to yield for any crop (Figures A1-A3). For most nutrients, as yields increased, grain nutrient concentrations decreased slightly, suggesting higher yielding grain contains more starch (or lipids) relative to nutrient. Regression parameters can be found in Table A2.
Figure A1. Corn grain nutrient concentration relationship with grain yield. Macronutrients (N, P, K, Ca, Mg, S) are in percentages, while micronutrients (B, Cu, Fe, Mn, Zn, Na) are in parts per million (ppm).
Figure A2. Soybean grain nutrient concentration relationship with grain yield. Macronutrients (N, P, K, Ca, Mg, S) are in percentages, while micronutrients (B, Cu, Fe, Mn, Zn, Na) are in parts per million (ppm).
Figure A3. Wheat grain nutrient concentration relationship with grain yield. Macronutrients (N, P, K, Ca, Mg, S) are in percentages, while micronutrients (B, Cu, Fe, Mn, Zn, Na) are in parts per million (ppm).
Most slopes of nutrient concentrations are negative (Table A2), reflecting that—as grain yields increase—nutrient concentrations generally decrease. However, the decrease is very subtle, as the slopes reported are all very small numbers. Likewise, the R2 values in Table A2 are very low, underscoring the poor relationship between grain yield and nutrient concentrations overall.
|Table A2. Slopes and R2 of Regressions Between Grain Nutrient Concentration and Grain Yield (Figures A1-A3). Negative slopes reflect nutrient dilution as yields increase and R2 values indicate the strength of the relationship between nutrient concentration and grain yield.|
Grain Nutrient Removal Rates
Overall, grain yields are a good predictor of grain nutrient removal rate. In all nutrients and crops, as grain yield increased, nutrient removal rates increased (Figures A4-A6). The strength of this relationship varied by crop, with soybean generally having a stronger relationship (higher R2 values), followed by corn and then wheat as having more variability around average removal rates (Table A3).
Figure A4. Corn grain nutrient removal rates as related to grain yield.
Figure A5. Soybean grain nutrient removal rates as related to grain yield.
Figure A6. Wheat grain nutrient removal rates as related to grain yield.
|Table A3. Slopes and R2 of Regressions Between Grain Nutrient Removal Rates and Grain Yield (Figures A4-A6).|