Effect of Zn binding to phytate and humic substances on its uptake by wheat(Triticum durum L.)as affected by carbonates and Fe oxides

Although complexation with soil organic matter may improve zinc(Zn)bioavailability to plants,the effect of Zn sorbent surface on the use of complexed Zn by plants remains unknown.The objective of this research was to elucidate how Zn complexation with humic substances(HS)and phytate affects the uptake of Zn by wheat plants depending on the main sorbent surface in growth media,i.e.,carbonates and Fe oxides.To this end,two pot experiments were performed,one using Fe oxide-coated siliceous as the siliceous growth medium sand and the other using a mixture of calcareous sand and siliceous sand as the calcareous growth medium.Each experiment involved three Zn sources,Zn-HS complex,Zn phytate,and ZnSO_(4).All sources were applied with surface irrigation at two Zn rates(0.25 and 2 mg kg^(-1) growth medium).The Zn-HS complex significantly increased Zn uptake by plants in both media,relative to the other two Zn sources,but no significant difference was observed between Zn phytate and ZnSO_(4).In the calcareous medium,Zn-HS complex and Zn phytate resulted in significantly higher dry biomass yields of wheat than ZnSO_(4).In the siliceous medium,spike and shoot dry biomass yields with Zn-HS complex at the low rate and Zn phytate at both rates were not significantly different from those with ZnSO_(4) at the high rate.After harvest,approximately 50%of the Zn applied as Zn-HS complex remained extractable by diethylenetriaminepentaacetic acid(DTPA),while this proportion was less than 20%for the other Zn sources.Thus,Zn-HS complex and Zn phytate are sources of available Zn for plants,and they are more effective than ZnSO_(4) in increasing plant growth,particularly when carbonates are the main Zn sorbent surface.

Influence of Soil Properties on Zinc Solubility Dynamics Under Different Redox Conditions in Non-Calcareous Soils

Zinc(Zn) deficiency in paddy soils is often a problem for rice production.Flooding can decrease metal availability in some noncalcareous soils through different mechanisms associated with soil redox status.Laboratory experiments were performed in order to better understand the processes that governed the dynamics of Zn in non-calcareous paddy soils at varying redox potentials(Eh).Airdried non-calcareous soil samples collected from four different paddy field sites in the Philippines were submerged and incubated in a reaction cell with continuous stirring and nitrogen purging for 4 weeks,and then purged with compressed air for another week to reoxidize the system.The Eh of the four soils started at 120 to 300 mV,decreased to —220 to —300 mV after 100 to 250 h of reduction,and was maintained at this low plateau for about 2 weeks before increasing again upon reoxidation.Zinc solubility showed contrasting patterns in the four soils,with two of the soils showing a decrease in soluble Zn as the Eh became low,probably due to zinc sulfide(ZnS) precipitation.In contrast,the other two soils showed that Zn solubility was maintained during the reduced phase which could be due to the competition with iron(Fe) for precipitation with sulfide.Differences in the relative amounts of S,Fe,and manganese(Mn) oxides in the four soils apparently influenced the pattern of Zn solubility after flooding.