Soil health and nutrient management

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Is magnesium deficiency a causal agent of sugarcane Yellow Canopy Syndrome? : ASSCT peer-reviewed paper
(ASSCT, 2019) Tippett, O; Olsen, DJ; Ostatek-Boczynski, Z
Yellow Canopy Syndrome (YCS) is a disorder affecting sugarcane in the Australian industry, the cause of which is unknown. This paper reviews YCS research focusing on magnesium imbalance as a possible cause of the condition. Four studies were undertaken to evaluate the role of Mg in YCS incidence and severity. In Trial 1 sugarcane leaves were collected at multiple locations in the Burdekin and Herbert with samples taken from sugarcane blocks with both YCS symptomatic and asymptomatic plants. Despite adequate soil-Mg, leaf-Mg concentrations were significantly lower (p?0.05) in leaves 2, 3, 4, 5 and 6 of YCS symptomatic plants in both regions suggesting an imbalance of this critical nutrient. Trial 2 measured Mg concentrations in sugarcane leaves before, during, and after YCS symptom expression. Symptomatic cane showed decreased leaf-Mg concentrations, but this returned to normal levels once the cane recovered. Trial 3 treated YCS symptomatic cane with foliar and soil applications of Mg in an attempt to mitigate the condition. Neither treatment resulted in alleviation of the YCS symptoms. Trial 4 treated sugarcane with foliar-Mg and soil-Mg prior to onset of symptoms. Despite elevating the Mg concentration in leaves, these pre-symptomatic treatments did not prevent YCS expression and plants exhibited YCS symptoms similar to that of the untreated control. We conclude that YCS affected cane is associated with reduced leaf Mg concentrations, but it is unlikely that this is the cause of YCS per se, as concentrations were well above critical thresholds for plant health. YCS occurs independently of Mg and low Mg is an indirect effect rather than a cause. Given that disruption to plant nutrient balance has been described as a symptom of some plant diseases, we speculate that these findings suggest a biotic causal agent.
The physiological and growth response of sugarcane to the sodium absorption ratio in flowing solution sand culture
(1994) Crema, AT
The growth of sugarcane variety Q117 in sand culture using nutrient solutions with sodium absorption ratios of 0, 5, 10, 15, 20 and 30, each with a constant electrical conductivity of 1.5 dS/m was determined under glasshouse conditions. Increasing the SAR of nutrient solutions from 0 to 30 while holding EC and ionic strength constant, was found to have no significant effect on sugarcane grown in coarse sand for 12 weeks. Thus, sugarcane growth was not inhibited by Na+ concentrations up to 12 mM when Ca2+ and mg2+ were each present at 76uM. It can be tentatively concluded from these results that increasing levels of sodium, in the absence of high levels of soluble salts are not toxic to the variety Q117, as long as other major cations are present at concentrations uninhibitative to plant growth. The major growth effect on sugarcane of sodic soils occurs as a result of the physical limitations associated with soil structure deterioration.

Soil health and nutrient management

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