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Decomposition of Biotechnology By-Products in Soils

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011-1010.

^* Corresponding author (malit{at}iastate.edu).

ABSTRACT

Recent processes in the biotechnology industry result in many byproducts that have potential values as soil amendment. Laboratory experiments were conducted to evaluate organic C mineralization of various biotechnology by-products and their effects on glycosidases in soils. A soil sample was mixed with biotechnology by-product material to approximate a field application of 9 g organic C kg^–1 soil (0.9% or 50 Mg C ha^–1), and incubated under aerobic conditions at room temperature (20 ± 2°C) for 30 d. The CO₂ evolved was trapped in standard KOH solution by continuously passing CO₂-free air over the soil. Results showed that, in general, the amount of CO₂-C initially released increased rapidly, but differed among the biotechnology by-product materials. Expressed as percentages of total organic C added, the amounts of CO₂-C evolved ranged from 0.5% with DEE in Weller soil (fine, montmorillonitic, mesic Aquic Hapludalfs) to 73.6% with FSL in Grundy soil (fine, montmorillonitic, mesic Aquic Argiudolls). Most of the CO₂ evolution data conformed to a first-order kinetic equation. The potentially mineralizable organic C values (C_o) of the biotechnology by-product-treated soils ranged from 1.2 to 33.4 g C kg^–1 soil. The half-lives of the C remaining in soils ranged from 14 to 239 d. The rate constants of the first and second phases of decomposition (k₁, and k₂) were significantly correlated (r > 0.90***) with the percentages of CO₂-C evolved in 30 d. The k₁ values fitted an equation similar to the Michaelis-Menten kinetic equation with respect to total sugars, and the k₂ values were significantly correlated with the high molecular-weight organic C fractions (organic C - total sugars, r = 0.42**) in the biotechnology by-products. The biotechnology by-products contained considerable amounts of cellulase, - and β-glucosidase, and - and β-galactosidase activities, contributing to decomposition of organic C in the biotechnology by-products in soils. Several biotechnology by-products are useful as soil amendments.

Journal Paper no. J-16783 of the Iowa Agric. and Home Econ. Exp. Stn., Ames. Projects 2710, 3022, and 3047. This work was partly supported by the Biotechnology By-Products Consortium of Iowa.

Received for publication March 18, 1996.