Agro-industrial residues and their biological activity on maize (Zea mays L.) metabolism

One way to counteract the increasing amount of organic residues which derive from agroindustrial processes is their use, after functional transformation, as soil additives. The present study focuses on the effects of four different agro-industrial by-products from rape (Brassica napus L.), castor-oil plant (Ricinus communis L.), linen (Linum usitatissimum), and digestate, on maize (Zea mays L.) growth and metabolism. The products were first analyzed for their content in carbon, nitrogen, sulfur, and total flavonoids and phenols. The presence of indoleacetic acid and isopentenyladenosine was also determined both via immunoassay and bioassay methods. Maize plantlets were grown in the absence (control) or presence of 0.1 and 1 mL L-1 by-product doses. From our results, both the concentration and treatment, as well as their interaction, were statistically significant in influencing the maize growth. The products increased root and leaf biomass and had a positive effect on nitrogen metabolism, as resulted from the increasing activity of nitrate reductase, glutamine synthetase, and glutamate aminotransferase enzymes. From these results it can be assumed that the agro-industry byproducts tested in this study may be successfully used as bioactive plant growth enhancers.