Use of Organic Compost and Residues as an Alternative to Commercial Substrate for Lettuce Cultivation (Lactuca sativa L.)

Aims: The objective of this work was to evaluate the physical and biological characteristics of the substrates formulated from organic compost (OC), carbonized rice husk (CRH), sewage sludge (SS) and commercial substrate, as well as the vegetative development of lettuce seedlings cultivated in the compositions.

Study Design: Eight treatments were studied in a completely randomized design: TO- commercial substrate (CS), T1- 50% OC & 50% CRH, T2 – 75% OC & 25% CRH, T3- 50% SS & 50% CRH, T4- 75% SS 25% CRH, T5- 100% SS, T6- 100% OC and T7- 30% SS, 30% OC & 40% CRH, being carried in box of expanded polystyrene (PEE) with four replicates.

Place and Duration of Study: The experiment was conducted in an experimental area of Campus Pelotas, Federal Institute Sul-rio-grandense, Pelotas, Brazil, period from November until December 2015.

Methodology: The physical characteristics evaluated were: total porosity, macroporosity, microporosity, water retention capacity and density. The microbiological analysis as carbon in the microbial biomass (Cmic), basal respiration (BR) and metabolic quotient (qCO2). Also, organic matter, electrical conductivity and dry matter and plant growth.

Conclusion: The addition of organic compost, treated sewage sludge and carbonized rice husk are suitable for the formation of alternative substrate for the cultivation of lettuce seedlings. The T2 (75% OC & 25% CRH) and T7 (30% SS, 30% OC & 40% CRH) treatments were the most promising in relation to physical characteristics resulting in good microporosity, total porosity, water retention capacity and density, but low macroporosity. Regarding the microbiological characteristics the T2 treatment presented greater microbial activity and ideal electrical conductivity. For vegetative growth and dry matter T2 and T7 presented similar results to the commercial substrate.