Acid soil amended in contaminated conditions. Effect on cultivated lettuces (Lactuca sativa var. longifolia)

Abstract

The waste amendment is a common practice to improve crop production on acid soils. This work aims to study the effectiveness of water potabilization plant sludge and lamb manure in acid soils remediation and the possible absorption of metals in cultivated lettuces, as well as the elements´distribution in roots and leaves after extra-contaminated irrigation. Al2(SO4)3-stabilized sludge, and lamb manure was added to an acid soil collected from Huasca de Ocampo, Hidalgo State, Mexico. The sludge (L), manure (M), control soil (C), unamended (S) and amended soils (SML) were characterized, and the metals´ concentrations determined. The SML was prepared by adding 2.62 % M and 5.25% L to fill up 600 L tanks. Lettuces (Lactuca sativa var. longifolia) seeds were sown in S and SML, and irrigated once by metal salts solution (Na, Mg, Ca, Fe, Ni, Cu, Zn, and Cd as sulfates, 200 mg kg-1 each). Lettuce germinated and grew satisfactorily in the SML, but they grew slowly in the unamended acid S, and the roots were affected. Leaves and roots were regularly analyzed along three months, and the metal concentrations showed higher values in S than the ones in SML. Pollutants were available from S, as they were present in roots, and desorbed after 40 days. The elements were present in higher concentrations in lettuce roots than in leaves, as expected. Conclusions. a) Acid soils can be amended with potabilization plants wastes in mining zones, but pH must be controlled to prevent the availability of metals. b) The soil texture was the principal cause of infertility due to root damage, and wastes eliminate the impairment. c) The element concentrations present in the leaves were acceptable for human nutrition.