Nutrient Dynamics in a Highly Weathered Soil Under No-Till and Heavy Metal Phytoavailability as Affected by Biochar Amendment

Abstract

The nutrient dynamics in soils are affected by cropping systems, soil properties and environmental conditions. A field experiment under NT has been conducted in an Oxisol, which assesses rates of inorganic P and K fertilizers for soybean production in conjunction with liming since 1995. The objectives were to evaluate the effect of rates of P and K fertilizers on soybean yields, and to access the P species in solid state by X-ray fluorescence (P-XANES). The optimum amounts of P and K fertilizers were revealed, which will help farmers improve their crop yields while minimize the impact of fertilization on soil and water quality. The long-term mineral phosphate fertilizer application led to P stabilization in soils under more thermodynamically stable forms, such as P-Fe and P-Al, in spite of the effects that soil organic matter (SOM) might have on P reactivity. A second project studied the heavy metal (HM: Zn, Pb and Cd) dynamics in a contaminated soil of NE Oklahoma. High concentrations of HM in soils have negative impacts on plants, human health and the environmental quality. The purpose was to evaluate the effects of biochars on the Zn, Pb and Cd phytoavailability in Tar Creek contaminated soils, as well as on the growth and uptake of these elements by perennial ryegrass (Lolium perenne). Biochars produced from switchgrass (SGB) and poultry litter (PLB) feedstocks at 350 and 700 °C (pyrolysis temperatures) were characterized as their potential use as soil amendment. Those pyrolyzed at 700 oC were used to investigate their effect on ryegrass dry matter yield and the accumulation of HM in shoots and roots. Biochars were applied to the soil at 0, 0.5, 1, 2 and 4% (w/w) and the soils were extracted by DTPA to estimate the available HM contents. Soils amended with low amounts of biochars reduced HM phytoavailability thus reduced plant metal uptake. Biochar also increased plant biomass but reduced metal transfer from roots to shoots. It is effective using readily available bioproducts to remediate HM contaminated soils and to enhance ryegrass forage yield with acceptable amount of HM in the shoots.