Agronomic value of alkaline-stabilized sewage biosolids for spring barley

Land application of sewage biosolids is a cheap disposal method that permits recycling of plant nutrients, but there are concerns about its long-term agronomic value and environmental effects. This study investigated the fertilizer value of alkaline-stabilized biosolids applied annually to spring barley (Hordeum vulgare L.). Dewatered biosolids [320-350 g kg(-1) dry matter (DM)] were alkaline stabilized by mixing them with cement kiln dust and composting aerobically, The product had some liming value (300 g kg(-1) DM CaCO, equivalent on average) and contained an average of 7.2, 2.3, and 19.5 g kg(-1) DM of N, P, and K. Two field experiments compared the P or K value of the biosolids with inorganic fertilizer P or K for seven consecutive annual spring barley crops on two contrasting soils. All biosolid and fertilizer treatments gave higher yields than the controls. Biosolids gave higher grain and straw yields than fertilizer P, similar grain and straw yields to fertilizer K, and higher grain weights and more grains per ear than fertilizer P or K. These effects may have been due to, inter alia, higher soil pH and S inputs. An increasing soil pH from biosolid application was associated with lower shoot Mn concentrations, but no Mn deficiency symptoms were observed. Alkaline biosolids acted as a slow-release P fertilizer, and biosolid P was at least as available to the crops as inorganic fertilizer P. Biosolid K was also as available as fertilizer K, A calculation of nutrient balances indicated that current fertilizer P recommendations could he lowered.