Objectives
Determine the effects of fertilizer, soil type and location on cadmium accumulation in flax seed. Correlate the uptake of cadmium (Cd) with weather variables and soil background levels of cadmium.
Project Description
Field studies were conducted at a range of sites in Saskatchewan and Manitoba over a three-year period to determine the effect of year-to-year variability, location and applications of N, P, K, S and Zn on Cd concentration in flaxseed.
Location had the greatest impact on Cd concentration, with concentrations ranging by more than 5-fold from site to site. Year to year variability was also substantial. Fertilizer applications influenced Cd concentration in flax at some locations, although effects were relatively small compared to that of location. Where fertilizer effects occurred, application of N generally led to lower Cd concentration, although increases sometimes occurred. Nitrogen may reduce Cd concentration through dilution when Cd concentration in the medium is low and crop production increases with N application. In contrast, N may sometimes mobilize Cd through osmotic effects or microsite acidification, leading to increases in Cd concentration. This appeared to happen more frequently when N was applied in combination with other nutrients. Placement of N had little effect on Cd concentration. Use of ammonium sulphate sometimes led to higher concentrations of Cd than did other N sources. The greater acidifying effect of ammonium sulphate could have enhanced Cd availability.
Phosphate fertilizer contains Cd at varying levels, depending on its source. Therefore, in the long term, application of Cd could increase Cd content of the soil and encourage higher Cd concentration in crops. However, the short-term effect of P was small in these trials. Where P had an influence on Cd concentration, it generally led to higher levels. However, the effect was inconsistent.
In other studies, Zn has been shown to reduce Cd concentration of crops. However, in this study, only “sausage” application of ZnSO4 decreased Cd concentration, while application of EDTA-chelated Zn increased Cd concentration of flaxseed. Sulphur did not generally influence Cd concentration. Potassium chloride tended to increase Cd concentration in flaxseed at the effect was somewhat more consistent than the effects of the other fertilizer materials tested. Chloride can form complexes with Cd in the soil, increasing its mobility and enhancing its availability for crop uptake.
Based on the results of these studies, it appears that site selection is the most important management factor that can be used to reduce Cd concentration in flax. Flax that is intended for entry to the food market, where low Cd level is desired, should be produced on soils that have been shown to produce low-Cd crops. Application of N to optimize crop yield should not lead to higher Cd levels. Application of P or KCl could lead to higher Cd levels, but the effect is small relative to the impact of location. In an area marginal for production of low-Cd flax, over-fertilization or use of “just-in-case” applications of these nutrients should be avoided. In some studies, Zn has been shown to decrease Cd in flax, but only a “sausage” application of ZnSO4 was effective at the single location in this study. However, there was no yield response to Zn application at this location so it is possible that Zn application may reduce Cd concentration on locations where Zn level in the soil is marginal or deficient.
