The fate and biostimulant potential of metal lactates in silt loam soil

Conventional farming practices have negatively impacted micronutrient fertility and overall soil health. Metal lactates are an organic micronutrient amendment that provide both a labile carbon substrate as well as mineral nutrition for plant and microbial growth. To determine the ability of metal lactates to provide readily available micronutrients, Zn, Cu, Mn, Ni, and Co in lactate and chloride salt form were amended to soils and incubated for 28 days. Operationally defined speciation was determined using sequential extraction on samples incubated for 1, 5, or 28 days. The results show a comparable distribution of metals in chloride and lactate form; however, differences were detected in water-soluble and exchangeable Ni and Zn at each timepoint. For example, in the water exchangeable fraction, there was 2.6%–2.9% less Ni and 0.2%–0.3% less Zn in the metal lactate-treated soil compared to soil treated with metal chlorides. Furthermore, carbonate-bound Ni averaged 4.1% and 4% less in metal lactate-treated soils as compared to metal chloride-treated soils on days 1 and 5, and Cu decreased 2.9%–3.3% during the treatment period for the lactate-bound form. Additionally, microbial phospholipid fatty acid (PLFA) was performed and found a stimulatory effect of metal lactates on bacterial biomass with an increase of 12%–18% relative to the metal chloride treatment. Results from this study support the use of metal lactates as a sustainable alternative to conventional fertilizers by providing bioavailable micronutrients for plant nutrition in addition to a labile carbon source to support the growth of microbial populations.