DIVISION S-8—NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS Spatial Variability of Grain Cadmium and Soil Characteristics in a Durum Wheat Field

of North America. A total of about 1.5 million ha of durum is planted annually in the USA, with about 80% The accumulation of Cd in edible crops is undesirable because of concentrated in northern North Dakota. In some locapotential risks to human health. Agronomic efforts to lower Cd in foods will be more effective if we understand the extent and causes of spatial tions, durum wheat grain may easily accumulate enough variability of Cd in crops in the field. The primary objective of this Cd to approach or exceed the concentration limits being study was to characterize the spatial variability of grain Cd and eight considered by international regulatory agencies (Chasoil characteristics in a field of durum wheat [Triticum turgidum L. ney et al., 1996; Norvell et al., 2000). Our understanding subsp. durum (Desf.) Husn.] in northeastern North Dakota. A rectanof the factors that regulate Cd uptake by durum wheat gular area of about 0.5 ha was selected to provide a range in several is still quite limited, but it is clear that the concentration soil characteristics that are reported to influence Cd uptake by plants. of Cd in durum wheat grain is influenced by differences These included chelate-extractable Cd, total soil Cd (Cdt ), pH, cationin geographic location, soil conditions, cropping season, exchange capacity (CEC), organic C (OC), and soluble Cl, S, and and cultivar (Li et al., 1994; Clarke et al., 1997; Norvell Na. Location data and paired samples of soil and durum grain were et al., 2000). Among the soil characteristics that are collected at 124 sites. Semivariograms showed that the variations of grain Cd and most soil properties were strongly spatially dependent, known or suspected to influence uptake of Cd by plants with range distances that varied from about 30 to 55 m. A spherical are pH, CEC, clay content, organic matter content, carmodel was fitted successfully to variograms for all characteristics. bonate content, salinity (especially Cl), and the amount Maps of grain Cd and soil characteristics were generated by interpolatand form of soil Cd (Li et al., 1994; McLaughlin et al., ing among measured values by block kriging. Visual and statistical 1994; Clarke et al., 1997; Norvell et al., 2000). comparisons of maps showed that grain Cd was distributed similarly Relatively little is known about the spatial variability to measures of soil salinity, especially to the logarithm of soil Cl. of Cd in grain or available Cd in soil. However, this Locations with somewhat poorly drained soils, which contained eleinformation will be needed to develop and apply agrovated Cl, produced grain with much higher Cd. Our results suggest that nomic practices to lower the accumulation of Cd by knowledge of the spatial distribution of soil characteristics, especially durum wheat or other crops. Site-specific management, salinity, should be helpful in developing or applying agronomic practices to reduce Cd in durum grain. in particular, requires knowledge of the spatial distribution of relevant soil factors within the scale of field operations (van Es, 1993; Cahn et al., 1994; Camberdella et al., 1994; Borges and Mallarino, 1997). Substantial C is a heavy metal that is present in all soils, field scale variability in crop and soil Cd seems probable usually as a trace constituent. Soils are the main for several reasons. First, field-scale variability is comsource of Cd in plants, and plant-derived foods are the mon for many soil and crop characteristics (Trangmar main source of Cd in human diets (Wagner, 1993). Accuet al., 1985; Webster, 1985; Warrick et al., 1986). Second, mulation of Cd in edible crops is undesirable because our previous results (Norvell et al., 2000) showed that of potentially harmful effects on health. The concentraconcentrations of Cd in durum grain from a single field tions of Cd in food crops are subject to regulation by can vary about as widely as the range reported for the national and international agencies. If adopted, the limentire durum-producing region of the northern Great its now being considered (0.1 mg kg 1 as a guideline Plains (Chaney et al., 1996; Grant et al., 1999). Third, level and 0.2 mg kg 1 as the maximum level) for Cd in a low density geochemical survey of soils of the northern small grains (Council of Europe, 1994; Codex AlimenGreat Plains indicated that 95% of the variability in tarius Commission, 1999) are likely to restrict the marCdt was found at distances 20 km (Garrett, 1994). ketability of durum wheat, because this crop tends to Geostatistical methods have been widely used to docaccumulate more Cd than most other small grains (Wolument the spatial variability of soil properties (Trangnik et al., 1983; Chaney et al., 1996; Clarke et al., 1997). mar et al., 1985; Webster, 1985; Warrick et al., 1986; Durum wheat is an important and valuable crop in West et al., 1989; Cahn et al., 1994; Camberdella et al., many parts of the world, including the upper Great Plains Abbreviations: Cdg, concentration of Cd in grain; Cddtpa, DTPA-extractJ. Wu, Dep. Crop and Soil Sci. Cornell Univ., Ithaca, NY 14853; able Cd; Cdt, total Cd; CEC, cation-exchange capacity; CV%, coefW.A. Norvell* and R.M. Welch, U.S. Plant, Soil & Nutrition Lab., ficient of variation (%); DTPA, diethylenetriaminepentaacetic acid; USDA-ARS, Tower Rd., Ithaca, NY 14853; D.G. Hopkins, Dep. Soil ICPES, inductively-coupled argon plasma emission spectrometry; LnCl, Sci., North Dakota State Univ., Fargo, ND 58105. Received 13 Oct. natural logarithm of water-extractable Cl; LnS, natural logarithm of 2000. *Corresponding author ([email protected]). water-extractable SO4-S; LnNa, natural logarithm of soluble Na extracted by DTPA; OC, organic C; SD, standard deviation. Published in Soil Sci. Soc. Am. J. 66:268–275 (2002).