July 2003

Manure Management, PSNT, and GPS: Hoowie for thought!

Phil Walker, Stephen Hawkins and Greg Blumhoff

 

            Making efficient use of nitrogen (N) resources for corn production requires understanding the potential nitrogen sources and how to incorporate these into a crop production system. In the eastern corn-belt, there is generally no carryover of fertilizer N from one season to the next from commercial fertilizers. However, residual N from soybeans can reduce fertilizer N requirements by 30 to 40 lb/A and by as much as 140 lb/A when corn follows a good stand of alfalfa. Routine soil tests do not tell the whole story when dealing with manure as a nitrogen source.

 

            In order to target desired manure application rates to meet crop nutrient needs, cropping information such as yield trends, cropping sequence, and soil test values for nutrients other than N are evaluated along with manure application timing, rates and analyses (Worksheets 1-3). The plant available nitrogen value of manure can be estimated on a case by case basis, but to zero in on whether sufficient N is present early in the growth of a corn crop, the Presidedress Nitrate Test (PSNT) can be used. The PSNT is based on soil sampling prior to sidedressing nitrogen in corn and comparing the result to expected yield ranges and a calibrated scale in NO5-ppm and determining a recommended sidedress nitrogen rate.

 

            Since manure supplied nitrogen application rates can vary due to the heterogeneous nature of manure varying application dates that result in different N mineralization rates and variations in N mineralization rates due to location in the field. Sampling for the PSNT with these differences in mind can lead to varying nitrogen recommendations

 

            A combination of GPS-based scouting / recording of manure application rates and dates within a field and the use of variable rate application equipment can take advantage of the varying PSNT results within a field.  Information gained from mapping manure application rates may also influence future soil sampling strategies within a field. This would be considered a knowledge-based adaptive sampling plan. Additional references relating to manure and nutrient management are listed below.

 

            Two scenarios in northeast Indiana are provided as examples. The first is a cornfield where 20 tons/A solid beef manure was surface applied over six months from the fall of 2002 to the spring of 2003, Fig. 1. The previous crop was wheat. In the second example, 6,000 gal/A of swine manure plus some of solid swine manure with straw bedding was applied over four months, Fig 2. The previous and current crop is corn for grain. WAAS-enabled GPS was used to map management areas based on application dates and soil types of similar drainage classes.  Neither producers had used the PSNT or GPS-based mapping techniques in the past and were interested in improving the system and maximizing their manure resources. Both producers conduct routine soil samples and apply manure on these fields every three to four years. The manure was analyzed as recommended in the list of references and the plant available N was estimated for both locations.

 

            The nutrient value of the manure and the estimated plant available nutrients are listed in Table 1.  In both cases, the estimated plant available N is adequate for the production of corn for grain, Table 2.  Utilizing the PSNT can confirm the presence of adequate N or help zero in on the recommended rate that can be sidedressed to insure achievement of the desired yield goal.

 

            In the first example, six soil sample were taken for the PSNT. At 25 ppm of NO5, no additional N is recommended regardless of the yield goal. The results in Table 3 indicate no additional N is needed. The producer was able to save $900+ on an N application that he would have otherwise made.

 

            In the second example, nine soil samples were taken for the PSNT. In this case, the results vary across the field reflecting the varying N mineralization rates encountered with different manure application dates and field location. Utilizing GPS-based mapping of the application dates and recognizing the different soil drainage patterns will allow the producer to vary the sidedress N rate.

 

            Variable rate N application does not always require equipment capable of changing rates on-the-go.  In the first example, the long axis of the PSNT sampling areas parallels the row direction.  Using a handheld GPS receiver when applying sidedress N, a producer could stop when moving from one sampling area to another, change N application rates and continue.  A full featured variable rate N application system would eliminate this step and also allow rate changes within a pass across the field.  This method would require a GPS-based rate controller and the variable values on the application tool.  Whether a producer has all of the GPS tools or a handheld computer with WAAS and changes N rates manually, there is the potential to enhance the PSNT management tool to apply the recommended N rate to the desired area.

 

 

Worksheet A.1.  General field Data  (from ID-205)

 

Field

Number

 

 

Acres

Miles from

Manure

Storage

 

 

Soil Type

 

 

% Slope

  

Soil Test

P

K

1

15

0.1

silty clay loam

6-12

low

low

2

30

0.75

silt loam

0-6

med

med

 

 

Worksheet A.2.  Crop Rotation and expected yield  (from ID-205)

 

Year-1

Year-2

Year-3

 

 

Expected

 

Expected

 

Expected

Field

Crop

Yield

Crop

Yield

Crop

Yield

1

corn

175

soybean

55

corn

175

2

corn

155

soybean

55

corn

155

 

 

Worksheet A.3.  Annual crop nutrient recommendations for 3-yr rotation  (from ID-205)

 

Avail. N, lb/a

P2O5, lb/a

K2O, lb/a

Field

Yr-1

Yr-2

Yr-3

Yr-1

Yr-2

Yr-3

Yr-1

Yr-2

Yr-3

1

181

0(175)

181

113

95

113

145

170

145

2

154

0(175)

154

55

45

55

65

105

65

 

 

Table 1.  Nutrient value of the manure used.

 

 

Lb / 1000 gal (liquid))

Sample

Moisture %

Solids %

Total N

P

K

Water

Solids

Total N

1st

 yr

N

P2

O5

K2

O

Swine

96.07

3.93

0.369

0.097

0.144

8646

354

33

26

20

16

 

 

Lb/ton (dry)

Beef

66.26

33.74

1.042

0.281

0.768

1325

675

21

12

13

18

 

 

Table 2.  Nutrient Application Rates Using Manure.

 

Rate per acre (Avail. 1st year, lb)

Sample

N

P2O5

K2O

Swine (6000 gal/a)

156

120

94

Beef (20 T/a)

244

258

370

 

Table 3.  PSNT Results, Spring 2003, corn at growth stage V6. 

Field

Sample

Month/Year

Manure Appl.

NO3-N (ppm)

1

1-1

Nov-02

39

1

2-1

Nov-02

33

1

3-1

Feb-02

36

1

3-2

Feb-02

26

1

5-1

Mar-03

31

1

5-2

Mar-03

40

2

1-1

April-03

30

2

1-2

April-03

19

2

2-1

Feb-03

16

2

2-2

Feb-03

20

2

2-3

Feb-03

28

2

3-1

April-03

11

2

4-1

Feb-03

27

2

8-1

April-03

50

2

8-2

Jan-03

59

 


 





 


AY-317-W, Determining nitrogen fertilizer sidedress application needs in corn using a chlorophyll meter, http://www.agry.purdue.edu/ext/pubs/AY-317-W.pdf.

 

AGRY-01-01.pdf, Nitrogen fertilizer management in good economic times and bad, http://www.agry.purdue.edu/ext/pubs/AGRY-01-01.pdf.

 

AY-314-W, The presidedress soil nitrate test for improving N management in corn, http://www.agry.purdue.edu/ext/pubs/AY-314-W.pdf.

 

ID-205, SWINE MANURE MANAGEMENT PLANNING, http://www.extension.purdue.edu/extmedia/ID/ID-205.html

 

ID-206, POULTRY MANURE MANAGEMENT PLANNING, http://www.extension.purdue.edu/extmedia/ID/ID-206.html

 

ID-208, DAIRY MANURE MANAGEMENT PLANNING, http://www.extension.purdue.edu/extmedia/ID/ID-208.html

 

Manure Management Planner, MMP software, http://www.agry.purdue.edu/mmp/