Impacts of Steel-Slag-Based Silicate Fertilizer on Soil Acidity and Silicon Availability and Metals-Immobilization in a Paddy Soil

<div><p>Slag-based silicate fertilizer has been widely used to improve soil silicon- availability and crop productivity. A consecutive early rice-late rice rotation experiment was conducted to test the impacts of steel slag on soil pH, silicon availability, rice growth and metals-immobilization in paddy soil. Our results show that application of slag at a rate above higher or equal to 1 600 mg plant-available SiO₂ per kg soil increased soil pH, dry weight of rice straw and grain, plant-available Si concentration and Si concentration in rice shoots compared with the control treatment. No significant accumulation of total cadmium (Cd) and lead (Pb) was noted in soil; rather, the exchangeable fraction of Cd significantly decreased. The cadmium concentrations in rice grains decreased significantly compared with the control treatment. In conclusion, application of steel slag reduced soil acidity, increased plant–availability of silicon, promoted rice growth and inhibited Cd transport to rice grain in the soil-plant system.</p></div

Effects of different silicon (Si) treatments on rice brown spot development at the anthesis stage (%).

<p>Si₀: no Si fertilizer; Si₁: slag fertilizer applied at a rate of 187 mg plant-available Si per kg soil; Si₂: slag fertilizer applied at a rate of 560 mg plant-available Si per kg soil; Si₃: slag fertilizer applied at a rate of 935 mg plant-available Si per kg soil; H: slag fertilizer H, Q: slag fertilizer Q; Data are means ± SD of three replicates; mean values followed by different letters (a, b, c) are significantly different (<i>P</i>≤0.05).</p

BCR extraction concentration of Cr, Cd and Pb in steel slag used in the field experiment.

<p>BCR extraction concentration of Cr, Cd and Pb in steel slag used in the field experiment.</p

Effect of steel slag fertilizer application on silicon concentration in rice straw.

<p>Data are means of three replicates. Mean values followed by different letters (a, b, c) in the same season are significantly different (<i>P</i>< 0.05).</p

BCR sequential extraction method of heavy metal in steel slag.

<p>BCR sequential extraction method of heavy metal in steel slag.</p

Effect of steel slag fertilizer application on relative content of Cd and Pb in each fraction of soil.

<p>Effect of steel slag fertilizer application on relative content of Cd and Pb in each fraction of soil.</p

Scanning electron micrographs with 150 K magnification of rice leaves.

<p>Scale bars  = 20 µm. SC, silica cell; WP, wart-like protuberance; SG, stomatal guard cell. <b>A</b>: <b>t</b>he top second leaf epidermis of a control plant without silicon fertilizer at the anthesis stage; <b>B</b>: The top second leaf epidermis of a silicon-treated rice plant grown with slag (H) applied at a rate of 935 mg plant-available Si per kg soil at the anthesis stage.</p

The main chemical characteristics of two slag-based silicon fertilizers tested in the present study (%).

<p>The main chemical characteristics of two slag-based silicon fertilizers tested in the present study (%).</p

Effect of steel slag fertilizer application on on dry weight of rice organs.

<p>Data are means of three replicates. Mean values followed by different letters (a, b, c) in the same season are significantly different (<i>P</i>< 0.05).</p

Transmission electron micrographs of chloroplasts from leaves of rice.

<p>Scale bars  = 1 µm. CW, cell wall; SG, starch grain. <b>A</b>: Chloroplast of a control plant grown without silicon fertilizer at the anthesis stage; <b>B</b>: Chloroplast of a silicon treated plant grown with slag (H) applied at a rate of 935 mg plant-available Si per kg soil at the anthesis stage.</p