1. CONSIDERING SODIUM IN NUTRIENT MANAGEMENT PLANNING
L.J. Cihacek*, North Dakota State Univ.

2. Nutrient Management
Generally, nitrogen (N) and phosphorus (P) are the nutrients we are concerned about in managing nutrients from land application of solid wastes.

3. Nutrient Management
Nutrient management planning typically involves consideration of N and P loading rates based on the N and/or P content of solid wastes, soil types, crops grown, soil management and risks for contamination of surface or ground water.

4. Nutrient Management
However, solid wastes containing up to as much as 4-5 % sodium (Na) are being generated in North Dakota and some of these are destined to be applied to agricultural (cropped) land.

5. Sodium in Soils
About 11% of all soils in North Dakota are affected by salts or Na.
Many of the prominent agricultural soils in the state have mineralogies dominated by smectitic clays.
These soils may already contain significant quantities of native Na and have a tendency to be dispersed.

6. Sodium in Soils
Na in soils is a monovalent cation (+ charged) which when it occurs in quantities of more than 5 to 10% of the total cations in the soil will cause the soil structure to deteriorate and become dispersed.

7. Sodium in Soils
Dispersed soils are “greasy” when wet, very hard when dry, have massive structure and are generally unsuitable for plant growth.
Dispersed soils also do not drain well, have water ponding on them and do not bear traffic very well.

8. Sodium in Soils
Field experience by soil scientists in North Dakota indicated that many soils began showing signs of dispersion when the exchangeable sodium percentage (ESP) reached between 5 to 7% and significant dispersion began to appear when the ESP reached about 10%.

9. Sodium in Soils
Soils that have been affected by applied sodium are difficult if not impossible to rejuvineate to their original productivity.

10. Development of ND Guidelines
NDSU Soil Science Department was approached by the ND State Health Department to assist in developing Na application guidelines for “high” Na containing wastes for the solid waste permitting process.

11. Background
Minnesota Pollution Control Agency (MPCA) Na application guidelines give values of maximum application rates of 170 lb Na/A.
Value based on choride (Cl) loading values for groundwater developed by Wisconsin.
Guidelines rarely used by MPCA because Na was not perceived as a problem.

12. Background
170 lbs Na/A appeared to be too high based on field experience of ND Soil Scientists.
Field scientists and soil testing laboratories were consulted to develop a more scientific approach in using Na guidelines.

13. Background
Cation exchange capacity (CEC) and exchangeable sodium percentage (ESP) can be estimated by relatively common standard soil testing methodologies by most soil testing laboratories.
Decision made to base Na application rates on these two tests plus on Na analysis of material to be applied.

14. Background
Since soils of differing texture and mineralogy have differing CEC then application rate would be based on soil CEC and not a fixed value.
Examples:
Coarse textured soils = low CEC
Medium textured soils = medium CEC
Fine Textured soils = High CEC

15. Background
Also, since soil ESP is based on the percentage of Na+ of the total soil cations, a simple target level of Na could be calculated.
Finally, in some soils, ESP’s of >5% may cause dispersion, so A 5% ESP was considered to be a “safe” level that would not cause soil degradation.

16. Background
Thus, Na application rates would then be calculated based on the difference of ESP levels at 5% CEC minus actual ESP as a % of CEC.
Example:
A soil with an ESP of 2% could safely handle additional sodium until an ESP of 5% was reached through waste application

17. Examples

18. Table 1. Sodium Contents of Some Agricultural Wastes
__________________________________________________________________________
Material Na Content1| Na applied /T material__
----% lb T-1 (kg Mt –1)-
Meat-packing Plant Manure (MPPM) (103)
Corn-processing Biosolids (CPB) (107)
Rendering Plant Biosolids (RPB) (11)
___________________________________________________________________________
1| On a dry-matter basis

19. Table 3. Allowable Na Application Levels for Selected North
Table Allowable Na Application Levels for Selected North Dakota Soils
Soil Series
NRCS Pedon No.
Na Content
CEC
ESP
--cmol kg –1---
--cmol kg –1--
-%-
Barnes
S79ND
1.4
1.90
7.4
Fargo2|
S93MN
0.5
1.1
Hegne2|
S93MN
0.8
46.2
1.7
Rhodes
S64ND
1.0
23.1
4.3
Williams
S54ND
0.1
23.7
0.4
S79ND
6.9
22.7
30.3
1| From USDA-NRCS National Soils Database.
2| Data for soils from Polk County, MN. These soils are widely distributed throughout MLRA 56 (Red River Valley of the North) in both Minnesota and North Dakota.

20. Table 4. Allowable Application Rates of Three Agricultural Wastes on Selected North Dakota Soils.
Allowable Rates of: 1|
Soil Series
NRCS Pedon No.
MPPM
CPB
RPB
Tons A-1 (Mg ha-1)
Barnes
S79ND
Do Not Apply
Fargo
S93MN
0.85 (1.9)
0.81 (1.8)
7.8 (17.5)
Hegne
S93MN
0.75 (1,7)
0.72 (1.6)
6.9 (15.5)
Rhoades
S64ND
0.05 (0.1)
0.5 (1.1)
Williams
S54ND
0.55 (1.2)
0.53 (1.2)
5.1 (11.4)
S79ND
Do Not Apply
1| On a dry matter basis

21. Table 2. CEC and ESP of Selected North Dakota Soils 1|
Allowable
Difference
Soil Series
NRCS Pedon No.
CEC
Maximum Na Level 1|
Na application 2|
From MN Guideline
C mol kg
lb A-1 (kg ha-1)
Barnes
S79ND 19
0.9
-23 (-26)
-193 (-216)
Fargo
S93MN 45
2.2
78 (87)
-92 (-103)
Hegne
S93MN
46.2
2.3
69 (77)
-101 (-113)
Rhoades
S64ND
23.1
1.1
5 (6)
-165 (-185)
Williams
S54ND
23.7
1.2
51 (57)
-119 (-133)
S79ND
22.7
-267 (299)
-436 (-488)

22. Summary
Science-based (rather than rate-based) guidelines have been established for application of solid wastes containing high levels of Na based on soil CEC and ESP information.
Guidelines tailor Na applications to soil properties to prevent soil degradation.

23. Summary
Guidelines have been applied to several land application permits for solid waste disposal by the ND State Health Department.
Guidelines also require post application monitoring (soil testing) to ensure Na levels have not been exceeded

24. Summary
In some cases wastes could be reapplied if 5% levels were not reached due to first application.

25. Summary
In North Dakota, on some soils, the Na application rate may limit waste application rates before N or P management considerations do.

26. ACKNOWLEDGEMENTS
The author gratefully acknowledges the valuable advice and discussions provided by Robert Deutsch, Agvise Laboratories, Northwood, ND, Larry Swenson NDSU Soil Testing Laboratory and Mike Sweeney, Professor Emeritus, NDSU, Fargo, ND.