Does green cane harvesting and residue retention improve silicon uptake in ratoon crops of sugarcane?

Phytogenic silicon (PhSi) accumulated in soils during plant decomposition is an important silicon (Si) source for plants in natural and agricultural ecosystems. In sugarcane, accumulation of PhSi from crop residues may provide a sustainable source of Si for crop uptake. To test this, the effects of a leaf residue mulch (‘green harvested cane’) versus burning treatment on leaf and soil Si content were examined in three ratoon (regrowth) crops of sugarcane planted under rainfed, irrigated, and temperate conditions. Leaf Si content increased significantly (by 20.3–28.9%) under mulch in one crop at each site and decreased by 19.2% in the burn treatment of one crop at the rainfed site, but did not differ significantly between treatments in five of the other crops. Leaf Si also differed by 25.8–189.7% between crops. There was no consistent effect of the mulch treatment on plant-available soil Si (range: 4.7–57.9 mg L −1 across sites). Mulching is therefore unlikely to provide a reliable short-term source of Si for sugarcane, as availability and uptake appear to be strongly influenced by environmental conditions. However, a principle component (PC) analysis, wherein leaf and soil Si, soil organic matter, soil calcium and total cation concentration loaded positively on the first PC (accounting for 43.4–63.8% of the total variance), indicated that these soil characteristics may be important drivers of Si availability, which may interact with imposed practices such as mulching and silicate slag amendments in determining available soil Si and plant Si uptake.