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Methods to quantify plant available silicon (Si) from Si-based slags for use as fertilizers are not well defined. Although it is possible to estimate total Si from a potential Si fertilizer source; this approach does not represent how much Si is available for uptake by the plant. In this study, Si was extracted from ten sources [Wollastonite W10; calcium silicate slag from the US; calcium silicate from Canada; magnesium silicate; Excellerator; silican gel; 00-00-12 + Si (liquid source) and three types of potassium silicate with different concentrations in the liquid form, K53; K120 and AgSilTM25] using each of the following seven methods: hydrochloric acid (HCl) plus hydrofluoric acid (HF) extraction, leaching column; sodium carbonate (Na2CO3-10 g L-1) + ammonium nitrate (NH4NO3-16 g L-1); citric acid (50 g dm-3 or 5%); hydrochloric acid (0.5 N); neutral ammonium citrate (NAC); and resin (Amberlite IRC-50, pK 6.1). All the Si-containing products were added to pots at rates equal to 600 kg ha-1 of Si based on the total Si extracted. Poa trivialis cv. 'Darkhorse' was grown for 24 days with these sources to determine Si plant uptake. Based on the correlation coefficients, the best extractor for available Si in solid fertilizer was determined to be Na2CO3 + NH4NO3, while for liquid fertilizers, the total Si (HCl + HF) was found to be the best. Consequently, regulatory agencies now have two extractors for estimating the plant available Si from fertilizers depending on the physical property of the material (solid or liquid). [ABSTRACT FROM AUTHOR]

This study aimed to determine if potassium silicate (KSi) sprays could reduce the intensity of angular leaf spot. In field experiment 1, bean plants were sprayed with KSi (pH 10.5) at rates of 8, 20, 40, and 60 g L-1. In field experiment 2, with the same treatments, the pH of the KSi solutions was 5.5. In experiment 3, the treatments were KSi (40 g L-1, pH 5.5), potassium hydroxide (KOH) (6.5 g L-1, pH 5.5), tebuconazole (0.5 L ha-1), and control. In experiment 4, the treatments were the same as in experiment 3, but the pH of the KSi and KOH solutions was 10.5. Plants sprayed with water served as a control treatment for all field experiments. Plants were artificially inoculated with Pseudocercopora griseola before products application. For experiments 3 and 4, the treatment with KOH was included to equalize the amount of potassium (K) with the treatment corresponding to the application of KSi. Disease severity was evaluated using a scale with values ranging from 0.2 to 30.4% at 85 days after seedling emergence. Plant defoliation, Si, and K concentration in the plant tissues, and yield were also determined. There was no relationship between KSi rates and Si concentration in leaf tissues, but Si concentration increased by 58 and 57%, respectively, as the KSi rates increased from 0 to 60 g L-1 regardless of the pH. The K concentration in leaf tissues did not change among the treatments. Disease severity decreased by 42 and 30%, respectively, at the highest KSi rate with pH 5.5 and pH 10.5 over the control. Disease severity levels were similar between the KSi and KOH treatments, but they were significantly higher compared to the tebuconazole. Plant defoliation at the highest KSi rate with pH 5.5 and 10.5 was 17 and 33%, respectively, less than the control. Plant defoliation decreased with the application of KSi with pH 5.5 and 10.5 in 29 and 34%, respectively, compared to the control. Yield increased by 30 and 43%, respectively, as the KSi rates increased from 0 to 60 g L-1with pH 5.5 and 10.5. No statistical difference in yield was detected between the KSi and KOH treatments regardless of the pH used, but both were different from tebuconazole. Significant differences in yield were found only between tebuconazole and the control. Results from this study suggest that foliar application of KSi and KOH has the potential to reduce angular leaf spot severity. The KSi did not offer any advantage over the KOH spray, suggesting a lack of a direct effect of Si accumulated in the leaf tissue on disease control. [ABSTRACT FROM AUTHOR]

Calibration of field crop response to nutrient availability is the bases for making a fertilizer recommendation from soil and tissue analyses. The purpose of this study was to evaluate and summarize results from a series of experiments on silicon (Si) fertilization of rice in the Everglades Agriculture Area. Twenty-eight rice field experiments were conducted from 1992 through 1996. The experiments consisted of 2 to 5 rates of calcium silicate applied to soils (Histosols) of varying Si soil-test values. Soil samples were taken before planting and analyzed for acetic acid (0.5 mol L-1) extractable Si. Straw samples were collected at harvest and analyzed for total Si. Grain yield was determined. The “critical” levels for Si in the soil (point below which response to Si fertilizer is expected) calculated by the Cate & Nelson procedure was 19 mg Si L-1 soil. The amount of silicon to correct Si deficiency in the soil and to obtain optimum rice yield was 1500, 1120 and 0 kg ha-1 for low (<6 mg L-1), medium (6 to 24 mg L-1), and high (>24 mg L-1) level of soil Si, respectively. Silicon in the straw was classified as high when Si concentration was >34 g kg-1, medium when in between 17 and 34, and low when <17 g kg-1 (3.4 and 1.7%, respectively). *Florida Agricultural Experiment Station Journal Series No. R-06752. [ABSTRACT FROM AUTHOR]