A Step-by-Step Guide to Nutrient Management
A Step-by-Step Guide to Nutrient Management
Richard P. Wolkowski
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This publication is designed to help farmers, consultants, governmentalagencies, fertilizer dealers, and others determine the cropnutrient requirements of individual fields. The assessment willfocus on the primary nutrients . nitrogen (N), phosphorus (P),and potassium (K) . because they represent the largest cost tothe farmer and present the greatest risk to the environmentwhenimproperly managed. A logical, step-wise process is used to calculatethe amount of nutrients needed to grow a crop byaccounting for nutrients that are available from several sources.
The assessment begins with the fertilizer recommendations foundon the soil test report. The soil test recommendations are basedon the level of available nutrients in the soil and the nutrientdemand of the crop(s) to be grown. Nutrient credits for soilorganicmatter,manure, legumes, and/or residual soil nitrate needto be subtracted from the fertilizer recommendation to determinethe adjusted nutrient need.Worksheets for conducting field-specificnutrient assessments can be found near the end of thispublication. Oncecompleted, thisworksheet can be filed with thesoil test report to furnish a record of fertilization and croppinginformation. Recommendations and credits used in this publicationare identical to those used by the University of WisconsinSoil Testing Program and can also be developed by using theWisconsin Interactive Soil Program for Economic Fertilizer Recommendations(WISPer) computer program.
Where the University of Wisconsin soil test recommendationprogram is used, and accurate manure and legume creditinginformation is provided with the soil samples, nutrient credits aresubtracted from the total nutrient requirement. In this case, theadjusted nutrient need has been calculated and the farmer candetermine a fertilization program. Where other soil testing programsare used or when a change inmanagement plans occur, theadjusted nutrient need may have to be calculated by the individualgrower, farm manager, or crop consultant.
Ideally, nutrients should be applied to fields at rates matching theadjusted nutrient need. However, for reasons of practicality it isexpected that fields with similar nutrient recommendations willbe grouped together. Then awhole-farm fertilization program canbe developed using the adjusted field nutrient needs from theworksheet to determine a reasonable number of rates and blendsof fertilizer materials. An additional worksheet, found at the endof this publication, tallies the adjusted nutrient requirements fromindividual fields. This can serve as a nutrient management planfor the entire farm.
Completing theWorksheet
Step 1. Field Information
Fill in the appropriate information for field identification, year,size, crop, soil name(s), and previous crop. This will provide acondensed record containing the treatment of each field and canserve as a future reference. Enter this information on the worksheetin the space provided in box 1.
Step 2. Nutrient Need
Determine field-specific nutrient needs by completing the worksheetaccording to the following directions.
Recommended N-P2O5-K2O. From the soil test report form fillin the recommendations for N, phosphate (P2O5), and potash(K2O) in the spaces at line 2a. These are the nutrients which thesoil test levels, crop to be grown, and yield goal indicate areneeded for each acre in the selected field. University of Wisconsinsoil test reports provide nutrient recommendations for twodifferent crop rotation options. It is important to note that nutrientrecommendations from soil test reports may not account fornutrient creditswhen services other thanUniversity ofWisconsinor ASCS- approved soil testing laboratories are used.
Special N-P2O5-K2O. Certain cropping conditions can affectcrop nutrient needs. Special nutrient recommendations areprinted as a comment on University of Wisconsin soil testreports. These recommendations are not considered in the cal-culation of the report.s fertilizer recommendation. It is the responsibilityof the user to include the special nutrientrecommendations in the final calculation of nutrient applicationrates.Asummaryof the mostcommonof these recommendationsis listed inTable 1. Enter any specialN, P2O5,K2Orecommendedat line 2b.
The nutrient need for the primary nutrients can be determinedby adding lines 2a and 2b. Fill in the sum for each nutrient atline 2c.
Starter fertilizer. It is commonly recommended that a minimalamount of starter fertilizer be applied for corn planted in soils slowto warm in the spring. For corn grown on medium and finetextured soils, apply at least 10 lb N, 20 lb P2O5, and 20 lbK2Oper acre at planting as a starter fertilizer. In most row crop fields,all the recommended P2O5 and K2O can be applied as starterfertilizer. On soils with test levels in the excessively high range,starter fertilizer applications in excess of 10 lb/a N, 20 lb/a P2O5,and 20 lb/aK2O should be avoided. The amount ofN applied asstarter fertilizer that exceeds 20 lb/a should be credited against theoverall N recommendation.
In-row placement of fertilizer is an efficient means for supplyingcrop nutrients. The fertilizer is placed near the germinating seedand is immediately available to the crop. Starter fertilizer applicationis an ideal method of applying a relatively small amount ofnutrients to row crops. Starter applications usually supply all therecommended P2O5 and K2O for soils testing in the optimum orhigher ranges.
Secondary and micronutrients. If soil tests for other nutrients(eg.,Ca,Mg, S,Zn,B,Mn)were performed, refer to the commentssection of the soil test report form to determine if any of the testsindicate a need for secondary or micronutrients. Applications ofthese nutrients may also be considered without a soil test whenthere is evidence of a need through plant analysis, visual deficiencysymptoms, or previous experience. Enter therecommended application of the appropriate nutrient at line 5a.
Table 2. Availability estimates for N, P2O5, and K2O for un-analyzedsolid manure.
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| Animal Type |
Available |
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N |
P2O5 |
K2O |
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————- lb per ton ————— |
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| First Year | |||
| Dairy |
3(4)1 |
3 |
8 |
| Beef |
4(4) |
5 |
8 |
| Poultry |
13(15) |
14 |
9 |
| Swine |
4(5) |
3 |
7 |
| Second Year |
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| Dairy |
4(5) |
3 |
9 |
| Beef |
5(6) |
6 |
9 |
| Poultry |
15(18) |
16 |
10 |
| Swine |
5(6) |
4 |
8 |
| Third or more |
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| Dairy |
5(5) |
4 |
9 |
| Beef |
6(6) |
6 |
10 |
| Poultry |
16(19) |
18 |
11 |
| Swine |
6(7) |
4 |
8 |
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1 Nutrient values in parenthesis are for incorporated manure
Lime needs. The need for lime must not be overlooked, becausea low soilpHwill reduce the response to applied nutrients. Wherea lime recommendation is given on the soil test report, enter therecommended rate of 60-69 or 80-89 neutralizing index (NI) limeat line 5b. If the lime to be used has a different NI calculate theamount needed using the equation provided below.
Lime to apply = (t/a 60-69 required ) ?65Midpoint NI of your lime
Step 3. Nutrient Replacement Credit
A goal of nutrient management planning is to allow farmers theopportunity to maximize the value of their on-farm nutrients. Formost Wisconsin farms this means utilizing fertilizer replacementcredits for legumes, manure, or carry-over soil nitrogen.
Manure. Manures contain significant amounts of the primaryplant nutrients (N, P, and K), as well as other essential plantnutrients.Anaccuratemanure nutrient credit can be determinedonly if the available nutrient content of the manure and themanure application rate are known.
Table 3. Availability estimates for N, P2O5, and K2O for the application of
un-analyzed liquid manure.
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| Animal Type |
Available |
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N |
P2O5 |
K2O |
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————- lb per 1000 gal————— |
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| First Year | |||
| Dairy |
8(10)1 |
8 |
21 |
| Beef |
10(12) |
14 |
23 |
| Poultry |
35(41) |
38 |
25 |
| Swine(f.u.) |
22(28) |
15 |
26 |
| Swine(f.n.) |
12(15) |
6 |
8 |
| Second Year |
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| Dairy |
11(13) |
9 |
24 |
| Beef |
14(16) |
16 |
26 |
| Poultry |
42(48) |
45 |
28 |
| Swine(f.u.)2 |
28(33) |
18 |
29 |
| Swine(f.u.)2 |
15(18) |
7 |
9 |
| Third or more |
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| Dairy |
13(14) |
10 |
25 |
| Beef |
16(18) |
17 |
28 |
| Poultry |
45(52) |
48 |
30 |
| Swine(f.u.) |
30(36) |
19 |
31 |
| Swine(f.n.) |
17(20) |
8 |
9 |
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1.Nutrient values in parenthesis are for incorporated manure.
2.f.u. = finishing unit; f.n. = farrow nursery
Author: Richard Wolkowski