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

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

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.

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.

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.

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.

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.

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%.

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

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.

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.

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.

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.

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

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.

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

Examples

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) 4.6 92 (103) Corn-processing Biosolids (CPB) 4.8 96 (107) Rendering Plant Biosolids (RPB) 0.5 10 (11) ___________________________________________________________________________ 1| On a dry-matter basis

Table 3. Allowable Na Application Levels for Selected North Table 3. 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-021-005 1.4 1.90 7.4 Fargo2| S93MN-089-026 0.5 1.1 Hegne2| S93MN-119-021 0.8 46.2 1.7 Rhodes S64ND-011-002 1.0 23.1 4.3 Williams S54ND-101-002 0.1 23.7 0.4 S79ND-015-007 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.

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-021-005 ------------------------Do Not Apply--------------------- Fargo S93MN-089-026 0.85 (1.9) 0.81 (1.8) 7.8 (17.5) Hegne S93MN-119-021 0.75 (1,7) 0.72 (1.6) 6.9 (15.5) Rhoades S64ND-011-002 0.05 (0.1) 0.5 (1.1) Williams S54ND-101-002 0.55 (1.2) 0.53 (1.2) 5.1 (11.4) S79ND-015-007 -------------------------Do Not Apply----------------------   1| On a dry matter basis

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-1----- lb A-1 (kg ha-1) Barnes S79ND-021-005 19 0.9 -23 (-26) -193 (-216) Fargo S93MN-089-026 45 2.2 78 (87) -92 (-103) Hegne S93MN-119-021 46.2 2.3 69 (77) -101 (-113) Rhoades S64ND-011-002 23.1 1.1 5 (6) -165 (-185) Williams S54ND-101-002 23.7 1.2 51 (57) -119 (-133) S79ND-015-007 22.7 -267 (299) -436 (-488)

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.

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

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

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

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.