Magnesic soils: first principle soil management strategies for increased productivity

Yingcan Zhu, Alla Marchuk, John McLean Bennett
2019
Irrigation waters containing considerable amounts of magnesium (Mg) are increasingly used in farming, due to the scarcity of good quality irrigation water. This increases the concern for Mg accumulating in soil systems. Together with naturally formed magnesic soils, irrigation induced Mg affected soils have been reported in many countries. In magnesic soils – for which there is limited information – the combination of poor soil structural properties, calcium deficiency and magnesium toxicity
more » ... gnesium toxicity have been suggested as stress factors for plants. Unfortunately, there is a paucity of conclusive information detailing Mg effects on soil structure, with existing literature suggesting Mg has a specific effect. This thesis is focused on the effect of Mg, either Mg in irrigation water or soils, on the soil structural stability. This is one of the prerequisites in decision making for soil management that maintains and/or increases soil productivity. To investigate the effect of Mg on soil structural stability, fundamental studies based in the laboratory were conducted in both soil clay suspensions and aggregated systems. Other factors influencing structural stability were also considered, including soil pH, electrolyte concentration, clay mineralogy, organic matter, texture and mechanical stress. To quantify clay dispersion, a rapid and inexpensive method was developed via use of a turbidimeter. The measured turbidity (NTU) of dispersed clay in suspension, can be easily and quantitatively converted to the dispersed clay quantity (mg/L, % of soil). This method was used in all experimentations throughout the whole thesis for the investigation of the effect of Mg on soil structural stability. The dispersive behaviour of Mg-saturated soil clay with contrasting mineralogy was studied at pH 3–8. The results demonstrated that, at low pH, Mg clays flocculate, although different clay types had different flocculation ranges; at neutral pH, Mg clays had higher dispersed clay (%) than Ca clays under similar conditions. This study furthe [...]
doi:10.26192/fp4j-sj70 fatcat:yubrkbfs7re3dedqzm4inejtse