Eb. Roberson et al., NUTRITIONAL MANAGEMENT OF MICROBIAL POLYSACCHARIDE PRODUCTION AND AGGREGATION IN AN AGRICULTURAL SOIL, Soil Science Society of America journal, 59(6), 1995, pp. 1587-1594
Microbial extracellular polysaccharides (EPS) contribute to the stabil
ity of soil aggregates. Nitrogen supply affects microbial growth and m
etabolism. The effects of fertilizer and cover crop N supply on EPS pr
oduction and soil aggregation were examined in an irrigated annual cro
pping system. Two winter cover crops, wooly pod vetch (Vicia dasycarpa
L.), a N-2 fixer, and oat (Arena sativa L.), and three N fertilizer r
egimes [0, 168, or 280 kg ha(-1) (NH4)(2)SO4-N] were used to vary soil
N supply in a California tomato (Lycopersicon esculentum Mill.) field
. Carbohydrate in the soil heavy fraction (HF, density >1.74 g mL(-1))
was found to have a monosaccharide composition consistent with microb
ial EPS and was used as an indicator of EPS. The HF carbohydrate conte
nt, aggregate slaking resistance, and saturated hydraulic conductivity
(K-sat) were greatest in the vetch and 168 kg N ha(-1) treatments and
lower in the 0 and 280 kg N ha(-1) treatments. The HF carbohydrate co
ntent was significantly correlated with K-sat and aggregate stability.
Organic C and N, microbial biomass, and light-fraction carbohydrate (
density <1.74 g ml(-1)) were not correlated with either aggregate stab
ility or K-sat. These results demonstrate that EPS can be important fa
ctors affecting soil structure in cultivated soils and that EPS produc
tion can be managed by N supply. The HF carbohydrate content may be a
useful indication of the effects of soil nutrient and organic matter m
anagement on microbial EPS production.