Multi-analytical techniques to study changes in carbon and nitrogen forms in a tomato-cultivated soil treated with biochar and biostimulants

Agro-environmental applications of biochar and biochar in combination with biostimulants require a full understanding of the mobility and fate of the carbon and nitrogen fractions in soils. The effects of biochar and biostimulants on forms of nitrogen and carbon in soil during a field-scale incubation were investigated by a multi-analytical approach. This study was conducted on a tomato-cultivated agricultural land treated with low doses of biochar (about 0.1%) and different biostimulants: Micosat F®, arbuscular mycorrhiza fungi (AMF), or a consortium of Pseudomonas fluorescens, Bacillus sp., and a nitrogen-fixing bacteria (Consortium B). Forms of carbon and nitrogen and their mobility before, during, and after tomato growth, were studied with different techniques including elemental analysis, adsorption and molecular fluorescence spectroscopy, ion chromatography, and a column leaching test. Due to the low load of biochar and the short study time, elemental analyses might not be sensitive enough to determine C and N variation in the soil. Based on the dissolved organic carbon (DOC) and dissolved nitrogen forms, the treatments with biochar and biostimulants affected the mobility of these elements with an overall decrease at the end of tomato growth. The organic carbon is mainly ascribable to humic and fulvic acids, as indicated by spectroscopic analysis. The leaching column test demonstrated that cumulative leached C is about one order of magnitude lower than the DOC. In addition, simulated rain cycles profoundly affected their leaching, so it is important to design leaching tests based on local and seasonal weather conditions. In short, positive effects were observed in the marketable production of tomato when soil was treated with biochar combined with a mixture of biostimulants.