Michigan State University Extension
Soils & Soil Management - Fertilizer - 06039716
07/10/97
Tri-state Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa Extension Bulletin E-2567 (New), July 1995
M.L. Vitosh, Michigan State University; J.W. Johnson, The Ohio State University; D.B. Mengel, Purdue University; Co-editors
Tri-state phosphorus (P) and potassium (K) fertilizer recommendations are based on the nutrient needs of the crop to be grown and the quantity of those nutrients available in the soil as measured by a soil test. In the tri-state region, the Bray P1 test is used to estimate P availability and the 1 normal ammonium acetate test is used to estimate K availability. Tri-state recommendations are designed to provide adequate nutrition for the crop, and to create or maintain a soil capable of providing sufficient nutrients without fertilizer addition for one or more years. Thus, the tri-state recommendations utilize a buildup and maintenance approach to fertilizer management.
The key to these recommendations is field calibration and correlation studies that have been conducted over the past 40 years. The conceptual model for these recommendations is illustrated in (Vis.11). The fundamental component of the model is the establishment of a "critical level"- the soil test level above which the soil can supply adequate quantities of a nutrient to support optimum economic growth. The critical level is determined in the field and represents the results of hundreds of field experiments. There are two important concepts to keep in mind. First, some crops are more responsive to a nutrient than others, so the critical level can vary between crops. In the tri-state region, research has shown that wheat and alfalfa are more responsive to P than corn or soybeans. Thus, the critical P level for wheat and alfalfa is higher than the critical level for corn and soybeans. Second, the critical level can vary between soils. Recent research has shown that some soils, especially high clay soils in Ohio, require higher K levels to support optimum crop growth than other lower clay content soils. This information has been incorporated into the recommendations and is seen as an increase in critical level for K as the cation exchange capacity (CEC) increases.
When soil tests are below the critical level, the soil is not able to supply the P and K requirements of the crop. The tri-state recommendations are designed to supply additional nutrients and to raise the soil test to the critical level over a four-year period. **Soil tests below the critical level should be considered as indicating a soil that is nutrient deficient for crop growth.** For deficient soils, recommended rates of fertilizer should be applied annually. Placement techniques to enhance nutrient availability, such as banding or stripping, may also be beneficial on nutrient-deficient soils. Applying 25 to 50 percent of the recommended fertilizer in a band to enhance early growth should be considered.
Above the critical soil test level, the soil is capable of supplying the nutrients required by the crop and no response to fertilizer would be expected. The tri-state recommendations use a maintenance plateau concept to make recommendations at or slightly above the critical level. The maintenance plateau is designed to safeguard against sampling or analytical variation. Recommendations for soil test values on the maintenance plateau are designed to replace the nutrients lost each year through crop removal. Because the purpose of fertilizer applications in the maintenance plateau range is to maintain fertility, no response to fertilizer in the year of application would be expected. Therefore, farmers may choose to make multiple year applications. No response to placement techniques such as banding or stripping or the use of P and K starter fertilizers would be expected in the maintenance plateau region.
When soil test levels exceed the maintenance plateau level, the objective of the fertilizer recommendation is to utilize residual soil nutrients. Fertilizer recommendations are rapidly reduced from maintenance levels to zero. There is no agronomic reason to apply fertilizer when soil tests are above the maintenance plateau level.
Actual fertilizer recommendations are calculated using one of three relationships--one applicable to buildup, another for maintenance and a third for drawdown:
BUILDUP EQUATION
for P: lb. P2O5/A to apply = ((CL - STL) x 5) + (YP x CR)
for K: lb. K2O/A to apply = ((CL -STL ) x ((1 +(0.05 x CEC))) + (YP x CR) + 20
MAINTENANCE EQUATION
for P: lb. P205/A to apply = YP x CR for K: lb. K2O/A to apply = (YP x CR) + 20 (for non-forage crops)
DRAWDOWN EQUATION
for P: lb. P2O5/A to apply = (YP x CR) - ((YP x CR) x (STL - (CL + 15))/10)
for K: lb. K2O/A to apply = (YP x CR) + 20 - (((YP x CR) + 20) x (STL - (CL + 30))/20) (for non-forage crops)
Note: The K maintenance and drawdown equation for forages, including corn silage, is:
lb. K2O/A to apply = ((YP x CR) + 20) - (((YP x CR) +20) x (STL - CL)/50) where:
CL = critical soil test level (ppm) STL = existing soil test level (ppm) YP = crop yield potential (bu per acre for grains, tons per acre for forages) CR = nutrient removed per unit yield (lb./unit) CEC = soil cation exchange capacity (meq/100g)
(Vis. 12, Vis. 13) provide the critical soil test values and crop removal values used for calculating tri-state fertilizer recommendations at various soil test levels.
| Visual title - Visual size | Visual title - Visual size |
|---|---|
| Fertilizer recommendation scheme used in the tri-state region - 11K | Critical soil test levels for various agronomic crops - 24K |
| Nutrients removed in harvested portions of agronomic crops - 14K |
