Methyl Bromide Soil Fumigation Alters Plant Element Concentrations

Soil fumigation is used to eliminate plant pathogens and weeds in commercial practice and to eliminate organisms in controlled experiments, e.g., vesicular arbuscular mycorrhizal fungi (VAMF). This study was conducted to study the effect of methyl bromide fumigation on plant accumulation of 14 elements and assess plant colonization by VAMF after fumigation. Field experiments were conducted near Mead, NE, on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll). Corn (Zea mays L.) sorghum [Sorghum tricolor (L.) Moench], and soybean [Glycine max (L.) Merr.] were used in the experiments. Fumigation increased Al, Br, Ca, Fe, Mg, Mn, and Si and decreased Cu, K, P, and Zn shoot concentrations in all three plants. Three weeks after germination, shoot Al was sevenfold greater in sorghum and soybean and 16-fold greater in corn from fumigated plots than in shoots from nonfumigated plots. Shoot bromide concentrations from fumigated plots were sixfold greater in sorghum and 17to 18-fold greater in corn and soybean than shoots from nonfumigated plots. Lower P and Zn shoot concentrations from fumigated plots were attributed to fumigation-induced suppression of VAMF root colonization or an ion balance problem resulting from the enhanced uptake of Al, Br, and other ions after soil fumigation. At harvest, Al was still threeto 10-fold and Br eightto 20-fold greater in fumigated plot stover compared with nonfumigated plots. This study shows that methyl bromide fumigation alteration of plant uptake of Al, Br, Ca, Fe, Mg, Mn, and Si should be considered when interpreting experiments using methyl bromide soil fumigation. M BROMIDE soil fumigation is used to eliminate soil pathogens and other undesirable soil organisms (Van Berkum and Hoestra, 1979), but is nonselective and kills a wide range of organisms, including desirable organisms such as VAMF (Menge, 1982). Soil fumigation can stimulate plant growth by eliminating weeds, soil insects, and soil-borne pathogens, but this process may also stunt plant growth by exacerbating existing P deficiency due to reduction of VAMF populations in low-P soils (Haas et al., 1987; Jawson et al., 1993). Plant growth reduction has been overcome by addition of P or VAMF to soil, but addition of P without VAMF reinoculation was not as effective in overcoming P deficiency in P-fixing soils (Haas et al., 1987). Methyl bromide fumigant is widely used to fumigate J.R. Ellis and G.E. Varvel, USDA-ARS, Keim Hall, East Campus, Univ. of Nebraska, Lincoln, NE 68583; D.M.H. Watson, Boyce Thompson Inst. for Plant Research, Ithaca, NY; and M.D. Jawson, Robert S. KenEnvironmental Research Lab., Ada, OK. Contribution from USDA-ARS in cooperation with the Agric. Res. Div., Univ. of Nebraska-Lincoln. Published as Paper no. 10973. Journal Series, Agric. Res. Div. Received 14 Dec. 1993. *Corresponding author ([email protected]). Published in Soil Sci. Soc. Am. J. 59:848-852 (1995). soil before horticultural crops are planted and decomposes in soil to produce inorganic Br (Hoffman and Malkomes, 1974). Accumulation of Br in vegetable crops after fumigation has been a concern for years and in recent years the U.S. Environmental Protection Agency has also recommended that methyl bromide be phased out of use (Lantz, 1993). However, many vegetable growers are careful to follow procedures to limit Br uptake by plants (Haas et al., 1987) and methyl bromide fumigant may be difficult to replace. Although altered plant uptake of some cations and anions after methyl bromide fumigation has been documented (Hoffman and Malkomes, 1974; Buttery et al., 1988; Trent et al., 1989), the effect of methyl bromide fumigation on the accumulation of Al, Fe, and Si in plants grown in nonacid soils has not been reported. Studies on plant uptake of Al are usually associated with acid soil conditions and Al toxicity (Robson, 1989), and it is generally assumed that large quantities of Al are not taken up by plants grown in neutral or alkaline soils. Because VAMF play a significant role in ion uptake from soil, three crops that differed in root structure and dependency on VAMF for P uptake (Abbott and Robson, 1984) were used in the primary fumigation experiment: corn, sorghum, and soybean. The order of dependency of the three crops on VAMF for P uptake were corn > soybean > sorghum. The objective of this research was to determine the effects of methyl bromide fumigation on (i) plant element accumulation, especially Al and Br, (ii) plant biomass production, and (iii) VAMF root colonization after fumigation. MATERIALS AND METHODS Research field plots were established on a Sharpsburg silty clay loam that had been planted to alfalfa (Medicago saliva L.) for the previous 10 yr at the University of Nebraska Agricultural Research and Development Center, Mead, NE. Treatments consisted of fumigated and nonfumigated soil planted to corn (Pioneer Hybrid 3377') fertilized with 45 kg N ha", soybean (Pella 86) inoculated with Bradyrhizobium japonicum strain (Nitragin, Lithatech, Milwaukee, WI), and sorghum (Pioneer Hybrid 8358) fertilized with 45 kg N ha~'. All plots, to check the residual effect of methyl bromide fumigation on plant performance, were planted to corn and fertilized with 45 kg N ha~' the next year. Moldboard plow and disk tillage operations were performed prior to fumigation. Tarpaulins covered both fumigated and 1 Mention of companies or commercial products does not imply recommendation or endorsement by the USD A or the University of Nebraska-Lincoln over others not mentioned.