Nitrogen Input and Liming Affect Soil Microbial and Nematode Communities.

Soil microbial and nematode communities in a long-term crop rotation system were examined. The field experiment, Cullars Rotation (circa 1911), consists of a three-year rotation of cotton, crimson clover, corn, wheat, and soybean on a Marvyn sandy loam. Soil samples were collected from four treatments (no input, NPK+legume without lime, NPK+legume+lime, and PK+legume+lime) at 0-5 cm depth. Soil pH values for treatments without any input or lime were much lower than other treatments. Soil bacterial growth was determined using the thymidine incorporation technique. Generation times for bacteria in low pH soils were more than 10 times longer than those in limed soils. Soil samples were incubated with ¹³C-acetate for 24 hours and lipids were extracted and fractionated. Phospholipids contained much higher ¹³C contents than neutral or glycolipids. ¹³C incorporated into phospholipids was much higher in limed soil. Generation times and ¹³C incorporation were not affected significantly by different nitrogen treatments. Soil nematode populations at Cullars Rotation were dominated by bacterivores (58-75%), followed by plant feeders (20-37%). Fungivores consisted of <2% of the total population. Liming appeared to have a positive impact on soil nematode populations. Overall, soil pH appeared to have a greater impact on soil bacterial growth, soil microbial community structure and activity, and nematode populations than nitrogen treatments.