Nickel in Swedish soils and cereal grain in relation to soil properties, fertilization and seed quality

Abstract

This study examined nickel (Ni) concentrations in Swedish soils and cereal grains and how soil properties and different fertilization regimes affect Ni uptake by plants. Analysis of data from the Swedish environmental monitoring program on arable land showed that Ni concentrations in soils were significantly correlated with clay contents (R2 = 0.55; p < 0.001), while the correlation with organic matter content was weak, although significant (R2 = 0.02; p < 0.001). Concentrations of Ni in grains were positively correlated with the concentrations of total Ni in soil (R2 = 0.13; p < 0.001), negatively correlated with soil pH values (R2 = 0.14; p < 0.001), and multiple regression including Ni in soil and soil pH improved the correlation (R2 = 0.34). Therefore, analysis of total Ni concentrations in soils together with pH values can provide some guidance on where low Ni concentrations in crops are most likely to occur. Data from long-term field trials showed that Ni concentrations in wheat grain did not increase significantly after long-term application of cattle manure or sewage sludge compared with mineral fertilized or unfertilized treatments. Differences detected were attributed to pH changes in soil and differences in yields. It was found that Ni in organic amendments was not easily available for crop uptake. Application of inorganic fertilizer (NPK) decreased Ni concentrations in wheat grain compared with the unfertilized treatment, probably due to dilution in high-yielding crops. Concentrations in grains were low, and mean concentrations were 0.18, 0.07, and 1.20 for winter wheat, spring barley, and oats, respectively. For barley, this implies that 77% of the samples from the monitoring program had Ni concentrations below a proposed critical concentration for optimal germination (0.09 mg kg−1). Nickel shortage can be an overlooked problem in Swedish seed production that needs further attention.