Stability of Ion Exchange Resin Under Freeze–Thaw or Dry–Wet Environment

reduced adsorption of NO3–N and NH4–N by anionic and cationic resins, respectively. Kjonaas (1999) also Ion exchange resins have widely been used in mineralization studies observed no detectable effect of freezing on resin staof organic materials. However, the stability of resin (anionic and cationic) under changing physical environmental conditions is not bility. Lehmann et al. (2001) have observed that the well known. Our objective was to evaluate N and P adsorption or amount of NO3–N and NH4–N removal from solution desorption characteristics of resins exposed to freeze–thaw or dry–wet was specific to resin type. cycles. Mixed bed resins (1:1 oven-dry mass strong base anion A464-D Studies have also shown minimal effect of storage and strong acid cation C-249) were subjected to 0, 1, and 30 freeze– conditions on recovery of ions adsorbed on resin (Skogthaw or dry–wet cycles. To accomplish the dry–wet cycles, fresh resin ley et al., 1997; Kjonaas, 1999). However, knowledge of was kept in a forced-air oven at 25 ( 2) C for 28 h and rewetted to the stability of resins under changing physical environinitial moisture condition for 20 h. To accomplish the freeze–thaw ments for in situ measurements of nutrient mineralizacycle, fresh resin was frozen for 16 h and thawed to room temperature tion year-round in regions with soil freezing and fluctuatfor 8 h daily. At the end of the freeze–thaw or dry–wet cycles, resin was equilibrated with 3.2 mM L 1 NH4–N, 3.2 mM L 1 NO3–N, or ing soil moisture is not well documented. The hypothesis 0.97 mM L 1 PO4–P for a period of 1 h. Dry–wet cycles induced of this experiment was that cycles of alternating freeze– desorption of N and P associated with shrinkage of resins and expulthaw or dry–wet may not shift resin ion-adsorption/ sion of interstitial liquid. At the highest dry–wet cycle, 3.3, 0.35, and desorption characteristics or alter its effectiveness as a 0.15% of the total adsorbed PO4–P, NH4–N, and NO3–N was desorbed, nutrient trap. For example, as the resin experiences respectively. Scanning electron microscopy (SEM) revealed that the dry–wet cycles in the summer, its efficacy as a nutrient dry–wet or freeze–thaw cycles did not alter the physical integrity of sink should not be reduced or nutrients that had been these resins. Freeze–thaw cycles had no effects on N and P adsorption previously trapped should not be released during the or desorption characteristics of resins of the specific resins used in dry–wet cycles. The objective of this experiment was to this study. Ion exchange resins used for in situ nutrient monitoring should be screened using similar techniques to assess its adsorption measure changes in N and P adsorption and desorption and desorption stability and physical integrity to fluctuating environof mixed bed resins that have undergone several freeze– mental conditions. Resin types and stability should be mentioned thaw or dry–wet cycles. when comparisons are made to other studies. MATERIALS AND METHODS S phase ion exchange resins are used to extract Resin Characteristics and Preparation plant-available nutrients in situ and/or in the laboraAnionic and cationic resins, strong base anion A464-D and tory as a possible substitute for liquid extraction (Skogstrong acid cation C-249 (US Filter, Warrendale, PA) were ley and Dobermann, 1996; Giblin et al., 1994; Yang et used in the experiment. These resins were selected because al., 1991). Ion exchange resins are also widely used to they are currently being used to detect seasonal N mineralizameasure nutrient movement or fluxes in agricultural tion in plots treated with manure (Eghball, 2000). Both anion fields (Zou et al., 1992; Sakadevan et al., 1994; Lehmann and cation resins had a styrene-divinyl benzene matrix with et al., 2001). In most soil studies, resins are used as a an exchange capacity of 1.2 and 1.9 molc kg , respectively nutrient sink rather than a source to monitor seasonal (Table 1). fluctuations in nutrient status over the growing season. Water holding characteristic, size distributions, and ionic Resin offers the advantage of representing the actual impurities of fresh (as received from manufacturer) and fresh mixed resins are listed in Table 1. The fresh mixed bed resin soil environmental conditions (i.e., temperature and was prepared using a 1:1 oven-dry mass ratio of each resin moisture) and minimizes the need and cost of periodic type to facilitate anionic and cationic exchange. Subsamples soil sampling throughout the growing season. Under of each resin type were placed in a forced air oven at 105 field conditions, resins have been used in the soil for ( 3) C overnight to obtain moisture content. For consistency, periods ranging from 4 (Eghball, 2000) to 48 wk (Giblin drying at 105 ( 3) C is called oven-drying and the moisture et al., 1994). In the field, resins are exposed to a variety status is described as oven-dry. Resin mix was presaturated of changing physical conditions including freeze–thaw with water and placed on a tempe cell (Soil Moisture Corp., or dry–wet cycles. Kjonaas (1999) found that drying Santa Barbara, CA) and subjected to 0.033 MPa to determine its moisture content (equilibration time of 3 to 4 d). EquilibM. Mamo, D. Ginting, and R. Renken, Dep. of Agronomy and Hortirium was assumed when the daily outflow volume reached culture, Univ. of Nebraska, Lincoln, NE 68583; B. Eghball, USDAabout 10% of the total outflow volume since initiating the ARS, Lincoln, NE 68583. A contribution of the University of Nebraska pressure. Moisture content was determined by oven-drying Agricultural Research Division, Lincoln, NE 68583. Journal Series overnight. Fresh mixed resin impurities for NH4, NO3, and No. 14151. Received 14 Feb. 2003. *Corresponding Author (mmamo3@ PO4 ions were determined after extraction with 2 M HCL unl.edu). (Dobermann et al., 1997). Published in Soil Sci. Soc. Am. J. 68:677–681 (2004).  Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: SEM, scanning electron microscope.