Effects of organic compost, gypsum, and topdress sulfur rates on bioactive compounds and physicochemical characteristics of collard greens

Abstract

This study evaluates the use of sulfur, gypsum, and organic compost as to their effects on bioactive compounds and physicochemical characteristics of collard greens. Twelve treatments were assessed in randomized blocks in a split-plot scheme, where the main plots received three types of soil amendments (preplanting incorporation of organic compost; gypsum; and organic compost + gypsum), and the subplots received four rates of topdress-applied sulfur (0; 80; 160; and 240 kg ha-1 of S). Flavonoid bioactive compounds, total antioxidant activity, and total phenolic compounds were evaluated. The physicochemical characteristics assessed were: reducing sugars, total sugars, sucrose, soluble solids, pH, titratable acidity, fiber, protein, pigments (chlorophyll a, b, anthocyanins, and total carotenoids), and the relative chlorophyll index (SPAD index). The treatment whose soil was prepared with organic compost and a topdressing of sulfur from ammonium sulfate increased the flavonoid content in the collard plants. Gypsum application to soil increased the antioxidant activity in the collard leaves but, when combined with organic compost, it decreased the levels of phenolic compounds thereof. The rates of topdress-applied sulfur and the use of organic compost or gypsum in the soil, or the combination of both methods, did not affect the physicochemical characteristics and the pigments of commercial collard leaves. The use of organic compost combined with gypsum during soil preparation decreased the SPAD index in commercial collard leaves. The rates of topdress-applied sulfur showed no influence on the SPAD index in commercial collard leaves.