Effect of Si-rich substances on phosphorous adsorption by sandy soils.

The poor adsorption capacity of sandy soils is one of the primary reasons of a high level of phosphorus (P) leaching. Silicon (Si)-rich soil amendments have the potential to improve the low absorption capacity of sandy soils for P. The objective of this study was to evaluate the ability of different Si-rich materials to regulate P adsorption and retention by sandy soils. Amorphous fine silica (FSS), calcium silicate (CaSiO3), chemically pure CaCO3, and two types of Ca-silicate slags from metal industry (Pro-Sil) and chemical industry (TS) were used in laboratory experiments being conducted with pure quartz sand and cultivated and virgin Entisols and Spodosols collected in the South Florida. The binding energy-related constants were evaluated for soils treated by Si-rich materials and then incubated during 2 months. The following row of tested materials on the increasing level of "affinity parameter" was determined: for virgin Spodosol, Pro-Sil < CaCO3 < FSS< CaSiO3 < TS; for cultivated Spodosol, FSS < Pro-Sil < CaCO3< CaSiO3 < TS; for virgin Entisol, Pro-Sil < CaSiO3 < CaCO3 < FSS < TS; and for cultivated Entisol, FSS < Pro-Sil < CaSiO3 < CaCO3 < TS. Chemical, physical, and physical-chemical mechanisms of increasing soil adsorption capacity are hypothesized and discussed to explain the results obtained. The conducted experiments have demonstrated high prospective of Si-rich materials for reduction of P leaching from cultivated sandy soils.

Effect of silicon fertilizers on cadmium in rice (Oryza sativa) tissue at tillering stage.

Silicon has been found to enhance the plants' tolerance to heavy metal stress. In a field study, the effect of different types of Si-rich soil amendments (slag, ground slag, and diatomaceous earth) and fertilizers (activated slag, ground activated slag, and commercial Si fertilizer) on the distribution of soluble and insoluble forms of Cd in the rice plant organs grown on long-term cultivated paddy soil contaminated with Cd (central part of Hunan Province, China) was investigated. The soluble Si and Cd were tested in the apoplast and symplast of the roots, stems, and leaves of rice at a tillering stage. The Si-rich materials increased rice biomass by up to 15.5% and reduced the total leaf Cd by 8.5 to 21.9%. Commercial Si fertilizer was the most effective. Three main locations of the most active Si-Cd interactions were distinguished in the soil-plant system: soil, where monosilicic acid affords adsorption and fixation of the bioavailable Cd and root apoplast and apoplast above roots, where monosilicic acid can precipitate Cd. The transport of Cd to stems and leaves and the mobility of Cd in the soil depend on the content of monosilicic acid in the system.