Phytotoxicity of glyphosate soil residues re-mobilised by phosphate fertilisation

Abstract

It has been repeatedly demonstrated that phosphate (P) and the herbicide glyphosate compete for adsorption sites in soils. Surprisingly, the potential consequences of these interactions for plants e.g. resolubilisation of phytotoxic glyphosate residues in soils by application of P fertilisers or by root-induced mechanisms for P mobilization have not been investigated so far. In model experiments under greenhouse conditions, the potential for glyphosate re-mobilisation by P-fertiliser application was evaluated by bio-indication with soybean (Glycine max L.) cultivated on five contrasting soils with or without glyphosate application at 10-35 days before sowing. Different levels of P-fertilisation (0, 20, 40, 80, 240 mg P kg −1 soil) were supplied at the date of sowing. Visual symptoms of glyphosate toxicity, plant biomass, intracellular shikimate accumulation as physiological indicator for glyphosate toxicity and the plant nutritional status were determined. On glyphosatetreated soils, P application induced significant plant damage. Expression of damage symptoms declined in the order Arenosol > Acrisol ≈ Ferralsol > Luvisol subsoil > Regosol. On the Arenosol, Ferralsol and Luvisol subsoil plant damage was associated with increased shikimate accumulation in the root tissue. On the Acrisol decline of germination and plant damage in absence of shikimate accumulation indicate toxicity of AMPA (aminomethylphosphonic acid) as the main metabolite of glyphosate in soils. On the Regosol, a growth-stimulating effect of glyphosate soil application (hormesis) was detected. The results suggest that remobilisation of glyphosate may represent an additional transfer pathway for glyphosate to non-target plants which is strongly influenced by soil characteristics such as P fixation potential, content of plant-available iron, pH, cation exchange capacity, sand content and soil organic matter.

Impact of phosphate on glyphosate uptake and toxicity in willow

“…Inorganic phosphate (PO 4 3-) and glyphosate's methylphosphonic group compete for similar adsorbing sites [9,10], and, as a result, glyphosate sorption and its availability in soil solution are determined by the soil's capacity to adsorb PO 4 3-. Phosphorous is an essential nutrient, participating in crucial metabolic events, such as energy transfer and protein metabolism in plants [11], and PO 4 3-fertilization of soil is a common agricultural practice to assure plant growth and development [12]. PO 4 3-fertilization of agricultural fields submitted to glyphosate application may invariably influence the herbicide's bioavailability in soil solution, since the two compete for soil adsorbing sites [13].…”

Resposta Diferencial Das Culturas De Milho Rr E Soja Rr À Exposição a Glyphosate E Adubação Fosfatada

“…Savin et al (2009) observaram alteração significativa na infecção por fungos micorrízicos arbusculares em soja, milho e algodão, resistentes ao glyphosate, submetidos à adubação fosfatada ou não, em solos pobres em fósforo; no entanto, essa alteração pode ser dependente de outras na microbiota do solo, por influência de outros fatores. Bott et al (2011) relatam a possibilidade de remobilização do glyphosate do solo influenciada pelo seu potencial de fixação no solo. Pasaribu et al (2013) observaram efeitos similares aos supracitados em plantas de amendoim, evidenciando que a dose do herbicida aplicado influencia significativamente na resposta da planta.…”

Untitled

“…Although glyphosate is currently the most important active ingredient for controlling weeds, low-dose applications offer the commercial use of glyphosate as a growth regulator [9]. A hormesis effect of glyphosate has been observed in various plants [10][11][12][13][14]. Studies on the increase of shikimic acid production in plants by treatment with low doses of glyphosate can be cited [15][16][17][18].…”