Effects of different Mg fertilizer sources on the magnesium availability in soils

Abstract

Pot experiments with different soils were conducted to determine the effect of different Mg fertilizer sources on magnesium availability. The sources studied included Kieserite ͑MgSO 4 H 2 O͒, a synthetic magnesium sulphate ͑SMS͒ with variable content of crystal water and a calcined magnesite ͑Mg-oxide͒. The three magnesium fertilizers vary greatly in their solubility in water, affecting the availability to plants once applied to the soil. Whereas Kieserite dissolved gradually and SMS immediately, Mg-oxide released only insignificant amounts of Mg in cool water ͑20°C͒ after intensive stirring. Due to the fact that these dissolution properties may distinctly affect Mg availability in soils, Kieserite as a standard magnesium source was tested against a slow release Mg-oxide in the fine and the coarse form. Soil extraction of samples taken from 0-10 and 10-20 cm depths at 4, 8 and 12 weeks after applying the fertilizers to the soil surface revealed that the rate at which Mg appeared in the available pool ͑CaCl 2 extracts͒ varied significantly between Mg sources. Mg availability from Kieserite was much greater than from Mg-oxide. Nutrient availability from Mg-oxide depended on the fineness of the material, i.e. the coarser the less available. Maize grown as test plant in the pots revealed a 10.6% larger yield and 19.6% larger Mg uptake in Kieserite than in Mg-oxide treated pots. High solubility of a fertilizer under high rainfall conditions, however, may also affect the Mg availability through large losses occurring by Mg leaching. Therefore, in a second experiment, the behaviour of surface applied magnesium fertilizers, Kieserite versus a quickly dissolving synthetic magnesium sulphate ͑SMS͒ was studied, using an Ultisol ͑Serdang Series soil from Malaysia͒. A simulation of high rainfall by excessive irrigation of 20 mm per day over a period of 16 days to a water saturated soil revealed that the amount of Mg lost by leaching differed between the two Mg sources tested. The lowest amount with 8.7% of the applied Mg was lost in the Kieserite treatment at the low application rate and the highest with 22.3% in the SMS treatment at the high application rate. It is concluded that a gradual but strong release to match plants requirements is the most desired characteristic to maximize crop uptake and minimize losses.

Magnesium mobility in soils as a challenge for soil and plant analysis, magnesium fertilization and root uptake under adverse growth conditions

“…Here leaf and/or soil application of readily available Mg sources can be advantageous (Römheld and Kirkby 2007). This view was underlined by Härdter et al (2004), who investigated the effect of different Mg fertilizer sources on Mg availability in soils. The authors recommended that for maximization of crop uptake while minimizing Mg losses Mg sources exhibiting a gradual but strong release matching the plants requirements should be applied.…”

Role of magnesium fertilisers in agriculture: plant–soil continuum

“…On the other hand, several naturally occurring soil minerals (such as kieserite) mined from the ground contain Mg in hydrated form (MgSO 4 ) and are used as soluble Mg fertilisers; these include magnesium sulfate monohydrate and/or magnesium sulfate heptahydrate (Kawamura and Rao 2007). The release rates of available Mg to soil solution from various mineral fertilisers are determined by their physical and chemical compositions, which are based on particle size and water solubility (Mayland and Wilkinson 1989;Härdter et al 2004;Loganathan et al 2005).…”

“…Leaching of Mg should be less severe in soils under a crop than under bare fallow but may increase when fertilisers are added. The potential for applied Mg to be taken up by crop plants and not lost via leaching greatly depends on the solubility of Mg fertilisers (Loganathan et al 1999;Mitchell et al 2000;Härdter et al 2004). Applications of Mg fertilisers known as slow-release fertilisers (e.g.…”

“…kieserite and SMS) may lead to Mg losses by leaching when applied to sandy soils with high water conductivity (e.g. sandy soils), specifically in wet seasons (Härdter et al 2004;Loganathan et al 2005).…”

Effect of serpentine rock and its acidulated products as magnesium fertilisers for pasture, compared with magnesium oxide and Epsom salts, on a Pumice Soil. 2. Dissolution and estimated leaching loss of fertiliser magnesium

“…The rates of dissolution of these fertilisers in soil are expected to vary widely (Loganathan et al 1999;Mitchell et al 2000;Hardter et al 2004) because their water solubilities vary widely (Edmeades 2004;Hanly et al 2005 this issue). Magnesium fertilisers with very low rates of dissolution may lead to an under-supply of Mg to plants, whereas those with rapid rates of dissolution may lead to large leaching losses of Mg below the plant root zone under high rainfall conditions (Hardter et al 2004). The ideal Mg fertilisers are those which release Mg at rates which match the Mg demands of both plants and animals for an extended period, in the case of pasture for one or more years, with minimal leaching losses.…”