Compostos orgânicos adicionados a argissolo cultivado com alface: mineralização de nitrogênio e metais pesados

Abstract

The objective of this study was to evaluate the relationships between the chemical characteristics of different organic composts and the supply of nutrients readily available to plants, with emphasis on nitrogen, after short term soil incubations. Samples of fifteen organic composts prepared with industrial, urban or agricultural residues were collected and analized to detemine the contents of carbon, nutrients, lignin, poliphenols, and ashes. A laboratory soil incubation experiment was established using plastic recipients, where 50 g of an Argissolo Vermelho-Amarelo distrófico were mixed with a 0.374 g of dry mass of each compost, equivalent to a rate of 15 Mg ha-1 of compost application. The experimental design was in randomized blocks with 15 treatments (15 composts) and four incubation times (3, 7, 14 e 28 days),with three replications for each of, composing um fatorial 15x4, more um earth, ground, soil, land controls without application as of composite. In each of the four sampling dates, the soil in the recipients was analized to determine the concentration of inorganic N and, at day 28, the concentration of available P, K, Ca and Mg were also determined. Both the chemical characteristics and the effects of the composts on soil inorganic N were highly variable, causing immobilization, mineralization or no effect, depending on the type of compost.Despite this variability, there were no significant correlations between the chemical characteristics of the composts and the release of N to the soil, with the exception of the C to N ratio, which presented significant, but weak, correlations at days 7 and 14. There were also significant diferences regarding the effects of the composts on the supply of P and K to the soil, but no differences were observed for Ca and Mg. In conclusion, the contents of C, N, lignin, polyphenols and ashes, and the relationships between these parameters, did not prove to be useful as indicators of the short-term N mineralization potential of the composts under the conditions of the present study.