Long-Term Impacts of Management Systems on Soil Carbohydrate and Glomalin-Related Soil Proteins.

The effect of long-term management (25 years) on two soil bio-product pools, hot-water extractable soil carbohydrates (HW-SC), and glomalin-related soil proteins (GRSP) in soils managed under non-tillage (NT) and conventional tillage (CT) was investigated in plots under continuous wheat (CW) or a wheat rotation (RW). Four composited soil samples (30 subsamples, 0-5 cm) with three replicates each were analyzed for each treatment. Hot-water (80 °C) extraction for 18 h followed by hydrolysis was used to determine reducing sugars equivalent to glucose. Easily extracted (EE-GRSP) and total (T-GRSP) fractions were extracted using 1.0 g of soil in 8 mL trisodium citrate (20 or 50 mM), pH (7.0 or 8.0).  The Bradford protein assay was used for quantification of protein in the extracts. Hot-water extracted soil carbohydrate and GRSP contents were significantly influenced by long-term management practices with significantly greater HW-SC and GRPS contents in soils under NT (CW or RW) than those from CT.  In the NT treatments, HW-SC content ranged from 357 to 413 µg/g of soil and in CT from 193 to 211 µg/g.  Non-tillage treatments showed 1.7 times more HW-SC content in CW and 2.1 times in RW in comparison to their respective treatments under CT. No significant effect of CW or RW rotation was observed for the amount of carbohydrates between tillage treatments. The EE-GRSP ranged from 974 to 1140 mg/g in NT treatments; while in CT it was between 721 to 755 mg/g. EE-GRSP was 43% greater in NT than in CT treatments. No significant differences between CW and RW were observed when comparing within NT or CT treatments. Correlation coefficients showed a significant relationship between EE-GRSP and T-GRSP (r=0.9172); EE-GRSP and HW-SC (r=0.9237), and T-GRSP with HW-SC (r=0.9178). The importance of these two bio-products in soil C, N and P pools will be discussed.