Aggregate stability and monosaccharides after three years of fall conservation deep tillage

WINGEYER, ANA B.; OLK, DAN; DRIJBER, RHAE; GRIMARD, TERRY

Mar del Plata

Congreso; XIX Congreso Latinoamericano y XXIII Congreso Argentino de la Ciencia del Suelo; 2012

Asociación Argentina de la Ciencia del Suelo

Soil monosaccharide abundance can be used as an indicator of carbon (C) inputs, incorporation and extent of decomposition. Aggregate stability (mean weight diameter, MWD) is often attributed to the abundance of microbial derived monosaccharides and is sensitive to soil management. We evaluated the abundance and composition of monosaccharides in slake-resistant aggregates (>250, 250-53 and <53 µm) from 0-5, 5-15 and 15-30 cm soil depths for an irrigated continuous maize field under no-till (2005) and after three (2008) years of fall conservation deep tillage (FCDT) with addition of N fertilizer to residues. At all times and depths, monosaccharides were more abundant in large aggregates than in mid- and small-size aggregates. Preferential accumulation of plant monosaccharides occurred in largest aggregates while microbial monosaccharides were preferentially stabilized in small-size aggregates. By 2008, MWD decreased in 0-5 and 5-15 cm depths while monosaccharide concentrations of aggregates increased in the 5-15 and 15-30 cm depths, leading to a less stratified distribution of monosaccharides compared to no-till. By 2008, monosaccharide stocks in the profile had increased in the >250 µm aggregates (xylose) and <53 µm aggregates (all monosaccharides). Our results indicate that a change from no-till to FCDT can promote the incorporation of plant residues deeper into the soil profile and promote the transfer and stabilization of new C into finer soil fractions. A significant positive linear relationship between MWD and monosaccharide abundance was found in 2005, but no in 2008 indicating monosaccharides have an indirect effect on the stability of aggregates in thus system.