Authors: Rolf Härdter¹; Martin Rex²; Kristian Orlovius³

Source: Nutrient Cycling in Agroecosystems, Volume 70, Number 3, January 2005 , pp. 249-259(11)

Publisher: Springer

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 (MgSO₄ H₂O), a synthetic magnesium sulphate (SMS) with variable content of crystal water and a calcined magnesite (Mg-oxide). 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 °C) 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 (CaCl₂ extracts) 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 (SMS) was studied, using an Ultisol (Serdang Series soil from Malaysia). 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.

Keywords: Availability; Kieserite; Leaching losses; Magnesium forms; Magnesium oxide; Magnesium sulphate; Magnesite; Maize; Solubility

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s10705-005-0408-2

Affiliations: 1: K+S KALI GmbH, P.O. Box 10 20 29, D-34111, Kassel, Germany, Email: rolf.haerdter@kali-gmbh.com 2: Kamperhof Experimental Station, Mintarder Str. 264, D-45481, Mülheim/Ruhr, Germany, 3: K+S KALI GmbH, P.O. Box 10 20 29, D-34111, Kassel, Germany,

Publication date: 2005-01-01

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