Wheat Grain Cadmium as Affected by Long-Term Fertilization and Soil Acidity
Several studies have reported increases in grain Cd from long-term continuous wheat (Triticum aestivum L.) systems. Increases in grain Cd have been associated with commercial fertilizer use, but information on long-term use of N and P fertilizers on wheat grain Cd is limited. The objective of this study was to evaluate the impact of fertilization on wheat grain Cd from eight long-term experiments that received 15 to 63 yr of N, P, and K fertilizer. Total Cd and Zn in soil and grain and soil properties including pH were determined. In general, long-term N or P fertilization did not increase grain Cd, grain Zn, or soil Cd. In part, N and P fertilizer did not increase grain Cd because fertilizer did not increase soil Cd or Zn. Nitrogen fertilizer decreased soil pH in two experiments but these decreases were small (≤0.5) and did not affect grain Cd or Zn. Grain Cd and Zn were inversely related to soil pH, but not related to N or P fertilization. The relationship between soil pH (3.8 to 6.8) and grain Cd (9.7 to 45.2 µg kg−1) was described by a plateau-linear-plateau model with a negative slope from soil pH 5.0 to 6.4. The largest soil Cd and Zn contents were associated with high pH values, but grain Cd and Zn were inversely related to soil Cd and Zn. The maximum grain Cd content (45 µg kg−1) determined in this study was less than maximum limits of 50 to 100 µg Cd kg−1 in wheat grain established in other countries.
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