Process Water from Soybean Soapstock Refining as a Nutrient Source for Corn Production

2010 Plant Management Network. Accepted for publication 6 November 2009. Published. Process Water from Soybean Soapstock Refining as a Nutrient Source for Corn Production Douglas A. Doty, Testing Operations Manager-Trait Integration, Monsanto Company, 503 S. Maplewood Ave., Williamsburg, IA 52361, formerly Fremont County Extension, Iowa State University, 610 Clay Street, Sidney, IA 51652; and John E. Sawyer, Professor, Department of Agronomy, Iowa State University, 2104 Agronomy Hall, Ames, IA 50011 Corresponding author: John Sawyer. jsawyer@iastate.edu Doty, D. A., and Sawyer, J. E. 2010. Process water from soybean soapstock refining as a nutrient source for corn production. Online. Crop Management doi:10.1094/cm-2010-0126-02-rs. Abstract Land application is often used to agriculturally utilize by-product and industrial process wastes, which can provide essential crop nutrients and soil benefit, but often lack adequate research-based agronomic decision support information. Soybean [Glycine max (L.) Merr.] soapstock refining process water (PW) derived from soybean oil processing is a growing by-product from an important bioindustry. Objectives of this study were to determine crop availability of nutrients in PW and if Na added in the oil refining process would affect corn (Zea mays L.) production. Two years of study indicated that when fall applied the N in PW was readily plant available and essentially equivalent to fertilizer urea; PW P significantly increased soil test P (STP) as a result of the high concentration in PW relative to N and the apparent high P availability; PW S increased extractable soil S; and Na in PW increased extractable soil Na and potentially reduced yield in some instances when PW was applied at high rates and in drier soil conditions. Management of PW as part of a crop fertility program should consist of low to moderate application rates, routine PW analysis, and routine soil testing to monitor STP and Na. If STP is at High levels or Na is building in the soil, then applications should be withheld until levels are reduced. Introduction Land application is often used to agriculturally utilize by-product and industrial process wastes, which can provide essential crop nutrients and soil benefits while reducing costly disposal. Some of these products come from the expanding bio-industry and are land applied as crop nutrients with little research-based agronomic support information. Process water (PW), derived from soybean oil processing by acidulating soapstock, is one such product produced in large quantities for example, an oil refiner in Western Iowa annually produces five million gallons of PW. Similar PW and by-products have been studied in the lab and greenhouse (6,10,11). However, there are no field research-based recommendations for PW use in crop production or precautions about environmental limitations. Process water contains several crop nutrients, as well as Na, and is currently being used on significant corn acreage as an N, P, and S source. Sodium application is not needed for crops, and at high levels in soils can have detrimental effects on soil properties and plant growth. Knowledge of the soybean oil refining process helps understand the source of nutrients and other constituents in PW. The major steps in oil refining are degumming, neutralizing, bleaching, and deodorizing. Degumming with concentrated phosphoric acid removes phosphatides. Oil neutralization (alkali refining), typically with sodium hydroxide, eliminates free fatty acids. The fatty acids settle out as alkali soaps, with this soapstock the end by-product of soybean oil refining (5). Secondary processors create further value by refining the soapstock to produce salable products, such as oil, livestock feeds, crop

protection products, dust control products, fuels, and fuel additives (5). When refining for oil, the soapstock is acidulated with sulfuric acid, resulting in separation of the oil and PW. Resulting PW contains nutrients inherent to the soybean seed and from additives in the oil refining processes. Major constituents in PW from the oil refining process are P from phosphoric acid and Na from sodium hydroxide, and from secondary refining are S from sulfuric acid and N from anhydrous ammonia (ph adjustment). The PW used in this research originated in the manner described above. Uncertainty about crop nutrient availability and Na effects on soil and crop growth have led farm input suppliers to limit PW land application rates. Sodium at high levels can result in soil colloid dispersion, which decreases several desired soil physical and related properties including soil structure and water permeability, with resultant negative effects on plant growth and production (2). Experience with Na application to Iowa soils is limited and thus the potential effect of PW is not clear. The lack of field research-based recommendations, claims of greener plant tissue and increased yields with use of PW in corn production, coupled with the concern about Na application, prompted this on-farm research. Objectives of the study were to determine crop availability of nutrients in PW, specifically N, P and S, and determine if Na added in the oil refining process would affect soil test levels and corn production. Field Trials Sites and Applications The study was conducted with two producers in Fremont County, Iowa, during 2006 and 2007 (designated as Birkby and Lorimor). The study utilized two new sites each year. The soils were McPaul silt loam (Birkby 1 site in 2006), Marshall silty clay loam (Lorimor 1 and Lorimor 2 sites in 2006 and 2007), and Kennebec silt loam (Birkby 2 site in 2007). Corn followed soybean each year. There was no recent history of manure application. Corn production practices were chosen and implemented by the producer. Treatments were applied in the fall preceding corn, with a randomized complete block design replicated four times. Plots were 50 ft long by 15 ft wide (six 30-inch rows). Treatments consisted of three nutrient sources, urea fertilizer (U), urea plus gypsum fertilizer at 55 lb S/acre (US), and by-product process water (PW), each applied at six rates of N (0, 40, 80, 120, 160, and 200 lb total N/acre). Each year before application, a tank wagon containing PW was obtained from the local supplier. A sample of the PW was collected from the tank wagon and analyzed for specific gravity, ph, and nutrient composition by a commercial laboratory. Analysis of the PW is given in Table 1. The PW application rates in Table 2 were based on the total-n analysis. Process water was dribbled by hand onto the soil using buckets with holes drilled in the bottom. Urea and US fertilizers were broadcast by hand. All treatments were applied in late November when soil temperatures were less than 50 F and trending downward, and were disk incorporated to a 4-inch depth the day of application. Soil samples were collected prior to treatment application from the 0 to 6 inch depth to determine initial soil test levels (all U and PW rates). Soil samples were analyzed for ph, Ca, Mg, P, K, and extractable Na and S by a commercial certified laboratory using the Mehlich-3 extract. After corn harvest, the same plots were sampled. Data was analyzed by site and across site-years using PROC MIXED (SAS Institute Inc., Cary, NC), and PROC GLM and NLIN was used to investigate yield and soil test response to PW application. A 95% probability level was used to determine statistical significance.

Table 1. Analysis of process water (PW), as-is basis. 2006 2007 Unit Specific gravity 1.12 1.11 ph 6.0 6.3 Total-N 1.32 1.69 % Nitrate-N n.d.* n.d. Urea-N n.d. n.d. NH4-N 0.95 1.21 Total-P (as P2O 5) 2.86 2.27 Orthophosphate-P (as P2O 5) 1.18 n.d. K (as K2O) 0.50 0.45 S 1.77 1.88 Na 1.44 1.45 Mg 0.12 0.03 Ca 0.19 0.03 Fe 141 n.d. ppm Mn n.d. n.d. Zn 72 n.d. Cu n.d. n.d. B n.d. n.d. * Not detected. Table 2. Nutrient application rates from process water (PW), with rates based on PW total N. 2006 2007 * As P2O 5 and K2O. PW P* K* S Na PW P* K* S Na (gal/acre) (lb/acre) (gal/acre) (lb/acre) 0 0 0 0 0 0 0 0 0 0 0 40 324 87 15 54 44 255 54 11 44 34 80 648 173 30 107 87 510 107 21 89 69 120 972 260 45 161 131 765 161 32 133 103 160 1296 347 61 215 175 1020 215 43 178 137 200 1620 433 76 268 218 1275 269 53 222 172 Weather Conditions The 10-year average annual rainfall in Fremont County, IA is 30 inches with a growing season (April-September) rainfall average of 21.5 inches (4). Climatic conditions varied between years that affected productivity. The 2006 growing season had a rainfall deficit (4 inches from the previous September-November and 3.8 inches in the growing season) and above average July heat stress causing accelerated plant maturity and reduced yield. The 2007 growing season was cooler than normal with little heat stress and nearly 8 inches above normal rainfall.

Corn Plant Response Corn plant height. Corn plant height, as measured from the soil to the tip of the most extended leaf at the V4-V6 (8) corn growth stage, was increased with N application rate for all nutrient sources, with taller plants from PW but no response to fertilizer S (Table 3). Corn plant height was not reduced with any rate of PW, indicating no early season detrimental effect from applied Na in the PW. The increase in early season corn growth with PW is similar to responses found with starter P fertilization. Table 3. Effect of nutrient source and on corn plant height at the V4-V6 growth stage, relative leaf chlorophyll meter value (RCM) at the V10-V15 and R1 growth stages, and stalk NO3-N concentration at harvest across site-years. Plant height (inch) RCM at V10-V15 U w US x PW y Mean U US PW Mean 0 22 22 22 22 0.87 0.87 0.88 0.87 40 23 22 24 23 0.95 0.95 0.93 0.94 80 23 23 26 24 0.98 0.98 0.97 0.98 120 24 24 27 25 1.00 1.00 1.00 1.00 160 24 24 27 25 1.00 1.00 1.01 1.00 200 24 24 28 25 1.00 1.00 1.02 1.01 Mean 23 23 26 0.97 0.97 0.97 Nutrient source (S) <0.001 0.685 (R) <0.001 <0.001 S X R 0.001 0.176 RCM at R1 Stalk NO3-N (ppm) U w US x PW y Mean U US PW Mean 0 0.87 0.86 0.87 0.86 119 z 181 150 40 0.94 0.95 0.92 0.94 884 335 610 80 0.98 0.98 0.97 0.97 2925 1164 2045 120 0.99 0.99 1.00 0.99 4881 1875 3378 160 1.00 1.01 1.00 1.00 6322 3485 4904 200 1.00 1.00 1.01 1.01 6869 4726 5797 Mean 0.96 0.96 0.96 3667 1961 w U = urea fertilizer. x US = urea plus S fertilizer. y PW = process water. z Not determined. Nutrient source (S) 0.716 0.101 (R) <0.001 0.001 S X R 0.087 0.019 Corn leaf greenness. Corn plant N status, as measured with a Minolta SPAD 502 chlorophyll meter (Konica Minolta, Ramsey, NJ) (CM) (as outlined in reference 7) at V10-V15 and R1 growth stages, showed an response for all nutrient sources with no difference between fertilizer N, N plus S, and PW (Table 3). The CM reading for each plot was normalized to the 200 lb N/acre U

rate to produce a relative chlorophyll meter value (RCM), which reduces variability attributed to factors other than N stress (3). The PW appeared to provide equivalent crop available N as urea fertilizer (same RCM values at each ) with no additional response to S. The RCM critical value is 0.97 for corn following soybean (3). In this study, that was obtained at the 80 lb N/acre rate at both growth stages. Corn stalk NO3-N. Corn stalk samples were collected the same day as grain harvest from all U and PW rates (8-inch segment 6 to 14 inches above the soil surface) (1), and analyzed for NO3-N by a commercial laboratory. Concentrations increased with increasing N application rate (Table 3). Despite similarity in plant N status measurements (RCM values) between U and PW, there was apparently less crop available N in the soil for plant uptake late in the season with PW, as indicated by greater stalk NO3-N concentrations at each N rate with the U rates. Concentrations greater than approximately 2000 ppm indicates luxury N accumulation (1). This concentration was generally reached with U at the same where maximum corn greenness response was measured, but at a higher rate with PW. Nitrogen application in excess of plant need resulted in high concentrations with both U and PW. Corn grain yield. Corn grain was machine harvested from the center three rows of each plot, with yields calculated at 15.5% moisture. Corn yield and N response was detrimentally affected by moisture stress due to mid-to-late season dry and hot conditions in 2006 (Table 4), especially at the Lorimor 1 site. Also, in 2006 at the Birkby 1 site there appeared to be yield suppression with increasing PW rate (nutrient source by interaction). This could be due to applied Na, but cannot be known for certain. However, corn plant N status measures with leaf RCM and stalk NO3-N did not indicate lower PW N availability at that site (data not shown). With adequate rainfall and no moisture stress in 2007, there was no interaction between fertilizer source and (Table 4). However, grain yield at Birkby 2 had a mean lower yield with PW compared to U or US, perhaps due to lower N availability or other constituents like Na. The leaf RCM values were not different for nutrient sources in that site year (data not shown), yield did increase with increasing PW, but the stalk NO3-N concentrations were lower for PW than U at all s. A high fraction of the total N in PW is in the NH4-N form (72%), and hence should provide early and high crop available N. However, there was some indication of lower PW N availability at the Birkby 2 site. For the 2007 sites, yield response to was fit to a quadratic-plateau model. Using a grain price of $4.00/bu and an N price of $0.40/lb N, the economic optimum was 87 lb N/acre for the Birkby 2 site and 116 lb N/acre for the Lorimor 2 site. These rates are approximately where the RCM values and stalk NO3-N concentrations indicated optimal N response. Sulfur response. The US treatment contained 55 lb fertilizer S per acre, and was applied to provide comparison to U and PW for potential S response. No RCM or yield differences were measured between the U and US fertilizer sources, therefore, it is assumed that S contained in PW did not contribute to yield response with that application and that S fertilization was not needed at any site. Therefore, no direct evaluation of the potential crop availability of S in PW could be made.

Table 4. Effect of nutrient source and on corn grain yield, by site in 2006 and 2007. 2006 Birkby 1 Lorimor 1 U w US x PW y Mean U US PW Mean Corn grain yield (bu/acre) 0 174 171 176 174 108 117 112 113 40 176 180 192 182 116 129 106 117 80 174 181 182 179 97 105 107 103 120 188 175 159 174 94 107 135 112 160 194 181 167 181 119 108 94 107 200 174 199 163 179 86 80 106 91 Mean 180 181 173 103 108 110 Nutrient source (S) 0.126 0.634 (R) 0.649 0.141 S X R 0.011 0.325 2007 Birkby 2 Lorimor 2 U w US x PW y Mean U US PW Mean Corn grain yield (bu/acre) 0 150 145 140 145 164 167 171 167 40 160 166 152 159 178 185 179 181 80 162 173 158 164 191 182 182 185 120 165 169 163 166 194 195 188 192 160 174 168 160 167 202 193 192 195 200 175 170 168 171 194 198 189 194 Mean 164a z 165a 157b 187 187 183 Nutrient source (S) 0.002 0.272 (R) <0.001 <0.001 S X R 0.510 0.480 w U = urea fertilizer. x US = urea plus S fertilizer. y PW = process water. z Letters within a row and site indicate significant difference between means, P 0.05. Soil Test Levels Soil NH4-N and NO3-N. Soil samples were collected from all six U and PW rates in early June from the 0 to 6 inch-depth and extractable NH4-N and NO3- N determined by a commercial laboratory. There were low and no differences in NH4-N concentrations (Table 5), indicating conversion to nitrate from the fall application. Nitrate-N concentrations increased with increasing, and no difference between nutrient sources (Table 5). This indicates similar equivalency of N supply from U and PW.

Table 5. Effect of nutrient source and on late spring soil NH4-N and NO3-N concentration across site-years, 0 to 6-inch depth. NH4-N NO3-N x U = urea fertilizer. y PW = process water. U x PW y Mean U PW Mean Concentration (ppm) 0 4 4 4 8 9 9 40 4 5 5 9 9 9 80 5 5 5 13 9 11 120 4 4 4 14 13 14 160 5 5 5 17 16 17 200 5 5 5 21 18 20 Mean 5 5 14 12 Nutrient source (S) 0.908 0.409 (R) 0.206 <0.001 S X R 0.887 0.562 Soil test P. Initial STP levels (and soil test K) (Table 6) at the study sites were at levels where added P or K would result in low probability of yield increase and small if any yield response (9). Since the PW contained considerable total P and 40% in the orthophosphate form, increasing PW application rate significantly increased STP. Fig. 1 shows the change in STP with increasing PW P application rate after one crop year. Based on the slope of the linear regression fit, STP increased 1 ppm for each application of 10 to 14 lb of PW P (as P2O 5). That indicates highly available P in the PW. For an unknown reason the increase in STP per amount of P applied was greater in 2006 than 2007. This could be due to a difference in chemical composition of the PW P between years, or difference in soils although this is not likely since soil textures were the same at sites each year (silt loam at Birkby sites and silty clay loam at Lorimor sites). Table 6. Average initial soil tests for each site, 0 to 6-inch depth. Test Unit 2006 2007 Birkby 1 Lorimor 1 Birkby 2 Lorimor 2 OM % 1.6 1.9 1.6 2.2 ph 6.6 5.8 6.5 6.1 CEC meq/100 g 11 11 11 11 P ppm 37 18 19 20 K ppm 221 246 140 297 Ca ppm 1901 1700 1996 1781 Mg ppm 258 206 285 233 S ppm 7 9 7 10 Na ppm 6 7 17 16 Mehlich-3 extractant for CEC, P, K, Ca, Mg, S, and Na determination.

Fig. 1. Effect of PW P application rate on change in soil test P (STP) across sites one year after application, 0 to 6-inch depth. Extractable sulfur. Despite the large total S application with the highest rate of PW (Table 2), the extractable SO4-S concentration was only increased by 4 to 5 ppm in the top 6 inches of soil after one corn production year (data not shown). It is not known why the increase was small, but could be related to actual amount of S applied, form of S in the PW, or movement of SO4-S below the 6-inch sample depth. The PW application significantly increased extractable S compared to urea without S, which indicates that PW should supply crop available S. However, there was no yield response to applied S with either the PW or S fertilizer at any site so plant response to S applied with PW could not be determined. Extractable sodium. Since the PW contained considerable Na, increasing PW application rate significantly increased extractable Na. Fig. 2 shows the change in extractable Na concentration with increasing PW Na application rate after one crop year. For an unknown reason the increase per amount of Na applied was greater in 2006 than 2007. It is possible that the wetter 2007 environment resulted in more Na movement below the 0 to 6 inch sample depth. The extractable Na concentrations measured are not high considering the application rate, and not high enough for any potential negative effect on soil properties or crop growth, and concentration relative to the soil cation exchange capacity.

Fig. 2. Effect of PW Na application rate on change in extractable soil Na across sites one year after application, 0 to 6-inch depth. Soil test levels Two-year post application. The PW 0, 40, 120, and 200 lb N/acre rates were soil sampled at each site two years after application (after two crop years, following the corn-soybean sequence) to determine change in STP and extractable Na. Table 7 gives the STP and extractable Na for incremental depths to 42 inches. Application rate increased STP (see Table 2 for PW P application). After two years with the 200 lb N/acre PW rate, the STP was still 19 ppm higher than with no PW application. Since the STP after two crop years with high PW application was higher than the initial STP, it is clear that PW is a viable source of P for multiple crops and that PW application should account for P application as well as N. Table 7. Effect of process water (PW) on soil test P (STP) and extractable Na in the fall after two crop years (corn and soybean) across site-years. STP Extractable Na * Soil sample depth, inches. 0-6* 0-6 6-18 18-30 30-42 ppm 0 25 22 25 32 37 40 27 28 29 38 33 120 33 39 39 30 31 200 44 38 39 29 36 N Rate (R) <0.001 0.023 0.070 0.596 0.291 Extractable Na was increased at the 0 to 6 and 6 to 18-inch depths two years after PW application (Table 7). This indicates some movement of Na in the soil profile. For the commonly practiced PW rate being applied for corn production in the geographic study area (PW at 40 lb N/acre), extractable Na was increased

only 6 ppm (25 versus 19 ppm) after one year, with essentially no change in concentration after two years compared to after one year (data not shown). At the 200 lb N/acre PW rate, the extractable Na was 16 ppm higher in the 0 to 6- inch depth. The differences in results over time could be due to the small concentration of Na, shallow soil sampling and missing Na leached in the profile, laboratory error with determination of extractable Na, and crop uptake which was not measured. Comments and Recommendations This research showed that PW by-product from soybean soapstock oil refining can be considered a viable source of plant nutrients, with PW N and P crop availability essentially equivalent to fertilizer. Unfortunately, the crop availability of S could not be directly determined due to lack of plant response to applied S. However, based on soil testing, PW S should supply crop available S. Of concern is the Na content of PW. Despite a low influence on extractable soil Na in this study, even with high PW rates, care should be taken to not apply excess Na. In some situations the PW when applied at high rates had a negative effect on corn yield, potentially due to high Na application and with moisture stress conditions. Also, with the high PW P concentration relative to total N, PW application should be limited to part of a corn crop N requirement to avoid excess application of P, and Na. Nitrogen rates, close to that currently being provided from PW in production fields, approximately 40 lb N/acre, can supply one to two years of crop P removal and limit Na application amount. At the same time, multiple-year S requirement can be met. Other nutrient constituents of PW can contribute to crop nutrient supply, and at reasonable PW application rates should not pose a problem for crop growth and may enhance yield if soil supply is short. Use of PW on well drained soils with good internal drainage should help reduce the chance of Na accumulation. Due to the nature of soybean oil production and soapstock refining, no standard concentration of crop nutrients or Na is possible for PW. Therefore, routine PW sampling and analysis will be needed. In addition, management of PW as part of a crop fertility program should consist of routine soil testing to monitor STP and extractable Na levels in order to avoid concentrations beyond recommendations or to levels that could cause negative plant, soil, or environmental effects. If STP is at High levels or Na is building in the soil, then applications should be withheld until levels are reduced. Acknowledgments Partial funding for this project was provided by Farm Service Company, Council Bluffs, IA, and Feed Energy Company, Des Moines, IA. Literature Cited 1. Blackmer, A. M., and Mallarino, A. P. 2000. Cornstalk testing to evaluate nitrogen management. PM 1584. Iowa State Univ. Univ. Ext., Ames. 2. Brady, N. C., and Weil, R. R. 1999. The Nature and Properties of Soils. 12th Edn. Prentice Hall, Upper Saddle River, NJ. 3. Hawkins, J. A., Sawyer, J. E., Barker, D. W., and Lundvall, J. P. 2007. Using relative chlorophyll meter values to determine nitrogen application rates for corn. Agron. J. 99:1034-1040. 4. IEM. 2008. Climodat report. Iowa Environmental Mesonet. Online. Dept. of Agron., Iowa State Univ., Ames, IA. 5. Johnson, L. A. 1998. Recovery, refining, converting, and stabilizing edible fats and oils. Pages 181-226 in: Food Lipids: Chemistry, Nutrition, and Biotechnology. C. C. Akoh and D. B. Min, ed. Marcel Dekker Inc., New York, NY. 6. Martinez, C. E., and Tabatabai, M. A. 1997. Decomposition of biotechnology byproducts in soils. J. Environ. Qual. 26:625-632. 7. Peterson, T. A., Blackmer, T. M., Francis, D. D., and Schepers, J. S. 1993. Using a chlorophyll meter to improve N management. Coop. Ext. Serv. NebGuide G93-1171-1, Univ. of Nebraska, Lincoln, NE. 8. Ritchie, S. W., Hanway, J. J., and Benson, G. O. 2005. How a corn plant develops. Coop. Ext. Serv. Spec. Rep. No. 48, Iowa State Univ., Ames, IA.

9. Sawyer, J. E., Mallarino, A. P., Killorn, R. J., and Barnhart, S. K. 2008. A General Guide for Crop Nutrient and Limestone Recommendations in Iowa. Univ. Ext. PM 1688, Iowa State Univ. Ames, IA. 10. Sutarta, E. S. 1998. Biotechnology by-products and animal manures as sources of phosphorus for plants. Ph.D. diss. Iowa State Univ., Ames, IA. 11. Ul Haq, M. 1994. Cation interactions in plant nutritional studies in bromegrass. M.S. thesis. Iowa State Univ., Ames, IA.