Efficiency of MGDA and GLDA ligands in extracting plant-available Zn from calcareous soils: kinetics and optimization of extraction conditions

Abstract

The selection of an appropriate soil nutrient-availability index, exhibiting high correlations with crop responses, is the first step in a soil-testing program. This study aimed to test if the quantity and rate of zinc (Zn) release from calcareous soils by two new extracting ligands provide suitable Zn availability indices for maize (Zea mays L.) or not. To this end, Zn extraction from diverse calcareous soils by three concentrations (0.005, 0.05, and 0.1 mol L−1) of glutamic acid N,N-diacetic acid (GLDA) and methylglycinediacetic acid (MGDA) ligands with different shaking times were studied. A greenhouse pot experiment was also conducted to determine how Zn absorption by maize plants is correlated to the quantity and rate of Zn release from the soils. The result showed that the initial Zn release rates from the soils were significantly (r = 0.77 to 0.94, P < 0.05) correlated to plant Zn uptake. The results of the greenhouse correlation study also revealed that Zn uptake by maize represented the highest correlations with the amount of Zn extracted from soils by 0.05 M GLDA for 2 h (r = 0.87, P < 0.05), 0.05 M MGDA for 1 h (r = 0.86, P < 0.05), and 0.005 M MGDA for 0.5 h (r = 0.84, P < 0.05). These correlations were stronger than those obtained between the DTPA-extractable soil Zn and plant Zn uptake (r = 0.77, P < 0.05). Based on the finding of this study, both quantity and rate of Zn release from the soil by MGDA and GLDA ligands could be satisfactorily considered as Zn availability indices for maize in calcareous soils.