Phosphorus (P), potassium (K), zinc (Zn) and lime recommendations based on soil testing are provided in this publication for the major agronomic crops grown in Iowa. Interpretation of soil test values and nutrient recommendations are based on soil samples taken to a 6 to 7-inch depth. Research results from long-term and short-term field experiments have been used to determine the interpretation of soil test values and the nutrient recommendations.

Nutrients applied to meet the recommended amounts may be from inorganic sources, from manure, or both. Nutrient contents of manures are most accurately determined by laboratory analyses, but if not analyzed, use average tabled values.

SOIL TEST PROCEDURES

The soil tests for which interpretations are given in this publication are the Bray P1 and the Olsen tests for P, the ammonium acetate test for K, the DTPA test for Zn, and the SMP buffer method for lime requirements. The Olsen test is the preferred test for P for soils with soil pH greater than 7.4. These tests, and that for soil pH, are among the tests prescribed for the North Central Region by the NCR-13 Regional Committee on Soil Testing and Plant Analysis. These and other tests are described in the North Central Regional Publication No. 221 (Revised), Recommended Chemical Soil Test Procedures for the North Central Region.

SOIL TEST CATEGORIES

Soil test numerical values are reported as parts per million (ppm). Soil test values for phosphorus and potassium have been put into categories designated very low (VL), low (L), optimum (Opt), high (H), and very high (VH). These categories represent a decreasing probability of an economic yield response ranging from very high to very low.

The optimum category is the most profitable category to maintain over time.

The very high category indicates that the nutrient concentration exceeds crop needs, and further additions of that nutrient very seldom produce a profitable yield response.

Soil test categories for the numerical soil test values of P and K are given in Table 1. The interpretation of P and K soil test values into categories depends on the nutrient demand of the crop to be grown, the subsoil concentrations of P and K, and the soil test value. The interpretation of P soil test values for wheat and alfalfa is different than for the other agronomic crops indicating that these two crops require a higher soil P level in the tillage zone for profitable production. The interpretation of P soil test values for all crops other than wheat and alfalfa and K soil test values for all agronomic crops differs according to subsoil P and K levels of the soil.

Subsoil P and K levels are determined at the depth which provides the greatest range of soil test values for each nutrient. Subsoil P is determined by the Bray P1 soil test for samples taken from the 30- to 42-inch depth. Subsoil K is determined by the ammonium acetate soil test for samples taken from the 12- to 24-inch depth. Subsoil P is designated low for subsoil test values of 8 ppm or less and high for values of 9 ppm or more. Subsoil K is designated low for subsoil test values of 50 ppm or less and high for values of 51 ppm or more. The effect of a high subsoil level of P or K is to require a lower concentration of that nutrient in the surface soil for optimum crop production.

Subsoil P and K levels for soil series with more than 5,000 acres and a corn suitability rating (CSR) greater than 30 are given in Table 18 for each of the major soil areas in Iowa that contain the principal soil associations shown in Figure 1. Subsoil levels do vary by soil series but not by soil mapping units within a soil series.

RECOMMENDATIONS

The recommended amounts of P2O5 and K2O for very low (VL) and low (L) soil test categories are based on long-term research. These recommended amounts are not based on a yield goal. Annual application of the recommended amounts for these soil test categories should increase soil test values over time.

The recommended amounts of P2O5 and K2O for the optimum (Opt) soil test category will be based on nutrient removal for the reported yield of the harvested crop. The intent of this recommendation is to maintain soil test levels in the optimum category that are more profitable to maintain than a high or very high category. The nutrient contents per unit of yield of Iowa's primary agronomic crops, which will be used, are given in Table 2.

The recommended amounts of P2O5 and K2O for all soil test P and K categories are given in the following tables:

Table 3 corn grain

Table 4 corn silage

Table 6 soybean

` Table 7 alfalfa and alfalfa-grass hay

Table 8 oat with forage seeding

Table 9 oat with no forage seeding

Table 10 wheat

Table 11 sunflower

Table 12 legume-grass pasture

Table 13 tall cool-season grasses for pastures

Table 14 warm season grasses for pasture and hay

Table 15 bluegrass pasture

Table 16 sorghum-sudan pasture

These recommended amounts are based on yield responses to broadcast applications in current conventional tillage systems. Research is currently underway to determine if these recommendations should be modified for different methods of placement in no-till, ridge-till and conventional tillage systems. Until the current research indicates otherwise, the recommended amounts are for all tillage systems and methods of placement.

Placement of fertilizer with corn seed is not generally recommended, but if it is done, limit the amount of N + K2O to 10 pounds or less per acre. If soils are sandy or dry, reduce the amount of N + K2O by one-half. It is recommended that no fertilizer be placed in contact with soybean seed.

MICRONUTRIENTS

Iowa State University recommends only zinc for corn based on soil testing. The zinc soil test has been calibrated on Iowa soils. Zinc recommendations for corn are given in Table 5. Soil test procedures for the other micronutrients have not been calibrated because of either lack of or inconsistency of occurrence of deficiencies with the exception of iron deficiency on soybean. Iron deficiency on soybean occurs on high pH (calcareous) soils in central and north central Iowa and can be predicted by soil occurrence as shown in soil survey reports. Development of soybean varieties tolerant to low iron availability in calcareous soils has been an acceptable solution to the problem.

Limestone

Limestone recommendations are given in pounds of pure fine calcium carbonate (CaCO3) as given in Table 17. This recommendation is equal to pounds of effective calcium carbonate equivalent (ECCE) that is determined for all agricultural limestone sources in Iowa. Soil pH is to be used to determine whether or not to lime the soil. The SMP Buffer (also termed the Ohio Buffer) solution has been calibrated to determine the amount of lime to be applied to increase soil pH to a certain pH.

Recommendations are given to increase soil pH to 6.5 or to 6.9. Soil pH 6.0 is considered to be sufficient for grass pastures and grass haylands. Soil pH 6.9 is recommended for alfalfa. Soil pH 6.5 is considered to be sufficient for corn and soybean. Because of high pH subsoils in the Clarion-Nicollet-Webster, Galva-Primghar-Sac, Moody, Ida-Monona, Marshall, and Luton-Onawa-Salix soil associations, soil pH 6.0 is considered sufficient for corn and soybean grown in these soil associations, but when liming is required, lime is recommended to raise soil pH to 6.5.

The amount of limestone recommended is adjusted for the depth of tillage which determines the volume of soil to be neutralized. The depth for no-till is considered to be 2 to 3-inch depth unless specified otherwise.

Table 1. Interpretation of soil test values for phosphorus (P) determined by Bray P1 extractant or Olsen extractant and potassium (K) determined by ammonium acetate extractant for surface soil samples (6 to 7-inch deep cores).
 

	Bray P1: Phosphorus (P)			Potassium (K)
	Wheat, alfalfa	All crops except wheat, alfalfa		All crops
		Subsoil P		Subsoil K
Relative level*		Low	High	Low	High
ppm
Very low (VL)	0-15	0-8	0-5	0-60	0-40
Low (L)	16-20	9-15	6-10	61-90	41-80
Optimum (Opt)	21-25	16-20	11-15	91-130	81-120
High (H)	26-30	21-30	16-20	131-170	121-160
Very High (VH)	31+	31+	21+	171+	161+
	Olsen: Phosphorus (P)
Very low (VL)	0-10	0-5	0-3
Low (L)	11-14	6-10	4-7
Optimum (Opt)	15-17	11-14	8-11
High (H)	18-20	15-20	12-15
Very High (VH)	21+	21+	16+

*The optimum soil test category is the most profitable to maintain.

The very high soil test category indicates that the nutrient concentration exceeds crop needs, and further additions of that nutrient very seldom produce a profitable yield response.

Table 2. The nutrient content of harvested crops used to calculate nutrient removal and recommended amounts of P2O5 and K2O for optimum soil test category.
 

		Pounds per unit of yield
Crop	Unit of Yield	P2O5	K2O
Corn	bu	0.375	0.30
Corn silage	bu grain equivalent	0.55	1.25
Corn silage	ton, 65% H2O	3.50	6.50
Soybean	bu	0.80	1.50
Oat and straw	bu	0.40	1.00
Oat straw	ton	5.0	33.0
Wheat	bu	0.60	0.30
Wheat straw	ton	4.0	25.0
Sunflower	100 lb	0.80	0.70
Alfalfa	ton	12.50	40.0
Red clover	ton	10.0	33.0
Vetch	ton	12.0	47.0
Smooth bromegrass	ton	9.0	47.0
Orchardgrass	ton	14.0	68.0
Tall fescue	ton	12.0	66.0
Timothy	ton	9.0	32.0
Perennial ryegrass	ton	12.0	34.0
Sorghum-sudan	ton	12.0	38.0
Switch grass	ton	12.0	66.0

 

Table 3. Phosphorus and potassium recommendations for corn grain production.
 

Phosphorus (P) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	100	75	50	0	0

 
 

Potassium (K) Soil Test (ppm)*
Soil Test Category	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
Fine Textured	120	90	40	0	0
Sandy Textured	100	70	40	0	0

*The recommended amounts of P2O5 and K2O for the optimum soil test category are based on nutrient removal for the reported yield. The amounts shown in the Table for the optimum soil test category are for 140 bu corn grain per acre, which will be used if no yields are given on information sheet.

Recommendation for soils with a corn suitability rating (CSR) of 30 or less will be based on expected crop yield and nutrient removal for soil test categories of optimum or lower.

Although P2O5 and K2O are not recommended at high soil test category, a small amount equivalent to that contained in 100 pounds of a common complete NPK grade, applied as a starter fertilizer banded to the side and below the seed row, may be advantageous under conditions of limited soil drainage, cool soil conditions, or crop residues on the soil surface. None is recommended for the very high soil test category.

Table 4. Phosphorus and potassium recommendations for corn silage or sorghum silage production.
 

Phosphorus (P) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	105	90	75	0	0

 
 

Potassium (K) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
Fine Textured	220	200	175	0	0
Sandy Textured	200	180	175	0	0

*The recommended amounts of P2O5 and K2O for the optimum soil test category are based on nutrient removal for the reported yield. The amounts shown in the Table for the optimum soil test category are for 140 bu corn grain equivalent per acre, which will be used if no yields are given on information sheet, or approximately 20 tons corn silage per acre.

Recommendation for soils with a corn suitability rating (CSR) of 30 or less will be based on expected crop yield and nutrient removal for soil test categories of optimum or lower.

Although P2O5 and K2O are not recommended for the high soil test category, a small amount equivalent to that contained in 100 pounds of a common complete NPK grade, applied as a starter fertilizer banded to the side and below the seed row, may be advantageous under conditions of limited soil drainage, cool soil conditions, or crop residues on the soil surface. None is recommended for the very high soil test category.

Table 5. Zinc recommendations for corn and sorghum production.
 

Zinc (Zn) Soil Test (ppm)
Soil Test Category:	Low	Marginal	Adequate
DTPA Extractable Zn:
	0-0.4	0.5-0.8	0.9+
	Zn to apply broadcast (lb/acre)
	10	5	0
	Zn to apply in band (lb/acre)*
	2	1	0

*Recommendation for amount to apply in band is based on other states' information.

Table 6. Phosphorus and potassium recommendations for soybean production.
 

Phosphorus (P) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	80	60	40	0	0

 
 

Potassium (K) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
Fine Textured	90	75	65	0	0
Sandy Textured	80	65	65	0	0

*The recommended amounts of P2O5 and K2O for the optimum soil test category are based on nutrient removal for the reported yield. The amounts shown in the Table for the optimum soil test category are for 45 bu soybean per acre, which will be used if no yields are given on information sheet.

Recommendation for soils with a corn suitability rating (CSR) of 30 or less will be based on crop yield and nutrient removal for soil test categories of optimum or lower.

Table 7. Phosphorus and potassium recommendations for alfalfa and alfalfa-grass hay production.
 

Phosphorus (P) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
All Subsoil P Levels	0-15	16-20	21-25	26-30	31+
Olsen P:
All Subsoil P Levels	0-10	11-14	15-17	18-20	21+
P2O5 to apply (lb/acre)
	110	80	60	0	0

 
 

Potassium (K) Soil Test (ppm)*
Soil Test Category	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
All Soil Textures	300	240	200	0	0

* 30 lb. P2O5 is recommended at seeding time regardless of soil test category. The recommended amounts of P2O5 and K2O for the optimum soil test category are based on nutrient removal for the reported yield. The amounts shown in the Table for the optimum soil test category are for 5 ton per acre harvested yield, which will be used if no yields are given on information sheet.

Recommendations for soils with a corn suitability rating (CSR) of 30 or less will be based on nutrient removal of the expected crop yield for soil test categories of optimum or lower.

Table 8. Phosphorus and potassium recommendations for oat grain and straw production with a forage seeding.
 

Phosphorus (P) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	90	70	35	0	0

 
 

Potassium (K) Soil Test (ppm)*
Soil Test Category	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
Fine Textured	150	120	90	0	0
Sandy Textured	130	100	80	0	0

*If alfalfa is being established for forage production in following years, 30 lb. P2O5 is recommended at seeding time regardless of soil test category.

The recommended amounts of P2O5 and K2O for the optimum soil test category are based on nutrient removal for the reported yield. The amounts shown in the Table for the optimum soil test category are for 80 bu oat grain per acre and straw with a forage seeding, which will be used if no yields are given on information sheet.

Recommendation for soils with a corn suitability rating (CSR) of 30 or less will be based on nutrient removal of the expected crop yield for soil test categories of optimum or lower.

Table 9. Phosphorus and potassium recommendations for oat grain and straw production with no forage seeding.
 

Phosphorus (P) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	50	40	30	0	0

 
 

Potassium (K) Soil Test (ppm)*
Soil Test Category	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
All Soil Textures	90	85	80	0	0

*The recommended amounts of P2O5 and K2O for the optimum soil test category are based on nutrient removal for the reported yield. The amounts shown in the Table for the optimum soil test category are for 80 bu oat grain per acre and straw, which will be used if no yields are given on information sheet.

Table 10. Phosphorus and potassium recommendations for wheat production.
 

Phosphorus (P) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
All Subsoil P Levels	0-15	16-20	21-25	26-30	31+
Olsen P:
All Subsoil P Levels	0-10	11-14	15-17	18-20	21+
P2O5 to apply (lb/acre)
	60	50	30	0	0

 
 

Potassium (K) Soil Test (ppm)*
Soil Test Category	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
All Soil Textures	60	40	15	0	0

*The recommended amounts of P2O5 and K2O for the optimum soil test category are based on nutrient removal for the reported yield. The amounts shown in the Table for the optimum soil test category are for 50 bu wheat per acre, which will be used if no yields are given on information sheet.

Table 11. Phosphorus and potassium recommendations for sunflower.
 

Phosphorus (P) Soil Test (ppm)*
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	70	50	15	0	0

 
 

Potassium (K) Soil Test (ppm)*
Soil Test Category	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
All Soil Textures	80	50	15	0	0

*The recommended amounts of P2O5 and K2O for the optimum soil test category are based on nutrient removal for the reported yield. The amounts shown in the Table for the optimum soil test category are for 2,000 lb per acre seed yield, which will be used if no yields are given on information sheet.

Table 12. Phosphorus and potassium recommendations for legume-grass pasture.
 

Phosphorus (P) Soil Test (ppm)
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	70	50	40	0	0

 
 

Potassium (K) Soil Test (ppm)
Soil Test Category	Very Low	Low	Optimum	High	Very High
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
All Soil Textures	90	70	50	0	0

 

Table 13. Phosphorus and potassium recommendations for tall cool-season grasses for pasture; bromegrass, orchardgrass, tall fescue, and reed canarygrass.
 

Phosphorus (P) Soil Test (ppm)
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	60	40	0	0	0

 
 

Potassium (K) Soil Test (ppm)
Soil Test Category	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
All Soil Textures	80	60	0	0	0

 

Table 14. Phosphorus and potassium recommendations for warm season grasses for pasture and hay.
 

Phosphorus (P) Soil Test (ppm)
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	60	45	30	0	0

 
 

Potassium (K) Soil Test (ppm)
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
All Soil Textures	80	60	30	0	0

 

Table 15. Phosphorus and potassium recommendations for bluegrass pasture.
 

Phosphorus (P) Soil Test (ppm)
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
All Subsoil P Levels	0-8	9-15	16-20	21-30	31+
Olsen P:
All Subsoil P Levels	0-5	6-10	11-14	15-20	21+
P2O5 to apply (lb/acre)
	40	30	0	0	0

 
 

Potassium (K) Soil Test (ppm)
Soil Test Category	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
All Subsoil K	0-60	61-90	91-130	131-170	171+
K2O to apply (lb/acre)
All Soil Textures	40	30	0	0	0

 

Table 16. Phosphorus and potassium recommendations for sorghum-sudan pasture.
 

Phosphorus (P) Soil Test (ppm)
Soil Test Category:	Very Low	Low	Optimum	High	Very High
Bray P1:
Low Subsoil P	0-8	9-15	16-20	21-30	31+
High Subsoil P	0-5	6-10	11-15	16-20	21+
Olsen P:
Low Subsoil P	0-5	6-10	11-14	15-20	21+
High Subsoil P	0-3	4-7	8-11	12-15	16+
P2O5 to apply (lb/acre)
	60	40	0	0	0

 
 

Potassium (K) Soil Test (ppm)
Soil Test Category	Very Low	Low	Optimum	High	Very High
Ammonium Acetate Extractable K:
Low Subsoil K	0-60	61-90	91-130	131-170	171+
High Subsoil K	0-40	41-80	81-120	121-160	161+
K2O to apply (lb/acre)
All Soil Textures	80	60	0	0	0

 

Table 17. Nitrogen recommendations for forage grasses.
 

Forage grass	N to apply (lb/acre)*	Comment
Tall cool-season grasses	120	Early spring; under high levels of management may reapply 50 to 60 lbs N in 2 or 5 months
Bromegrass
Orchardgrass
Reed canarygrass
Tall fescue
Bluegrass	80	Early spring; under high levels of management may reapply 30 to 40 lbs N in 2 or 5 months
Warm-season grasses	90	Early to mid-May
Switchgrass
Big bluestem
Indiangrass
Legume-grass pasture	40	Only if legume is less than 1/3 of stand
Sorghum-sudan	80	May reapply after grazing or harvest period; 1/2 rate for fall regrowth period.

*These recommended N rates are economic optimum rates for high level of management in utilization of the forage produced.

Table 18. Lime recommendations, based on SMP Buffer Test, are given in pounds of pure fine calcium carbonate (CaCO3) to increase soil pH from its present level to pH 6.5 or 6.9 for the depth of soil to be neutralized.
 

Buffer pH	Depth of soil to be neutralized*
	2 inch		3 inch		6 inch		8 inch
	pH 6.5	pH 6.9	pH 6.5	pH 6.9	pH 6.5	pH 6.9	pH 6.5	pH 6.9
CaCO3 to apply (lb/acre)
7.0	0	400	0	600	0	1,100	0	1,500
6.9	0	600	0	1,000	0	1,900	0	2,500
6.8	200	900	300	1,400	600	2,700	800	3,600
6.7	400	1,200	700	1,800	1,300	3,500	1,700	4,700
6.6	700	1,500	1,100	2,200	2,100	4,400	2,800	5,900
6.5	900	1,700	1,400	2,600	2,800	5,200	3,700	6,900
6.4	1,200	2,000	1,800	3,000	3,500	6,000	4,700	8,000
6.3	1,400	2,300	2,100	3,400	4,200	6,800	5,600	9,100
6.2	1,700	2,600	2,500	3,900	5,000	7,700	6,700	10,300
6.1	1,900	2,800	2,900	4,300	5,700	8,500	7,600	11,400
6.0	2,200	3,100	3,200	4,700	6,400	9,300	8,600	12,400
5.9	2,400	3,400	3,600	5,100	7,100	10,100	9,500	13,500
5.8	2,600	3,700	4,000	5,500	7,900	11,000	10,600	14,700
5.7	2,900	3,900	4,300	5,900	8,600	11,800	11,500	15,900

* Soil pH 6.9 is recommended for alfalfa.

Soil pH 6.5 is considered to be sufficient for corn and soybean. Because of high pH subsoils in the Clarion-Nicollet-Webster, Galva-Primghar-Sac, Moody, Ida-Monona, Marshall, and Luton-Onawa-Salix soil associations, soil pH 6.0 is considered sufficient for corn and soybean grown in these soil associations, but when liming is required, lime to soil pH 6.5.

Soil pH 6.0 is sufficient for grass pastures and grass haylands.

Lime recommendations are derived from the following equations:

If soil pH is less than 6.4, to increase soil pH to 6.5 use:

[49,886 - 7,245 (buffer pH)] [Soil depth x 0.167]= pounds calcium carbonate

If soil pH is less than 6.8, to increase soil pH to 6.9 use:

[58,776 - 8,244 (buffer pH)] [Soil depth x 0.167]= pounds calcium carbonate

The amount of ag lime to apply is determined by dividing the effective calcium carbonate equivalent (ECCE) of the ag lime into the calcium carbonate recommendation.

Table 19. Suggested average N, P2O5 and K2O contents for solid manure.
 

Type of Manure	Nutrients, lbs per ton
	N	P2O5	K2O
Manure scraped from outside lots
Beef-earth lots	22	16	14
Swine-concrete lots	15	14	9
Dairy-concrete lots	11	6	11
Bedded manure from confinement systems
Beef	12	6	12
Swine	14	9	11
Dairy	12	6	12

 

Table 20. Suggested average N, P2O5 and K2O contents for liquid manure.
 

Type of Manure	Nutrients, lbs per 1000 gal.
	N	P2O5	K2O
Pit manure from confinement systems
Swine
Growers, finishers	50	35	25
Farrowing	25	20	15
Nursery	35	20	20
Gestation	25	25	25
Dairy	30	15	25
Beef	40	25	35
Anaerobic lagoons for confinement systems
---Liquid portion only; no sludge, no agitation
Swine	4	3	4
Dairy	4	3	4
Beef	4	3	4