Effect of manure N input ratios on the utilization of different soil microbial carbon sources

Objectives The investigation on the utilization of different soil microbial carbon sources, and the diversity and activity of soil microbial could provide theoretical basis support to refine fertilization management in winter wheat-summer corn rotation systems.

Methods Soil samples were collected from a field experiment with winter wheat-summer maize cropping system, which was conducted continuously in Xushui Experimental Station, Hebei Province. Except for CK (no N applied), the nitrogen input in both winter wheat and summer maize were N 200 kg/hm² in all the other four treatments with 0%, 20%, 50% and 100% of N were replaced by dry cow manure in winter wheat, recorded as M0, M20, M50 and M100, respectively. Biolog ECO plate method was selected to determinate the surface soil (0–20 cm) microbial diversity and activity.

Results 1) The replacement of partial N input by manure in the winter wheat basal fertilization significantly increased the utilization efficiency of different fractions of soil carbon. The highest capacity of the total carbon utilization was found in M50 treatment, and the M100 treatment had the highest microbial growth rate. 2) The soil microorganism had the higher utilization capacity of D-cellobiose, α-D-lactose, D- mannitol, Twain 40 and phenylethylamine than that of D, L-α-glycerol phosphate and γ-hydroxybutyric acid in all treatments. The average utilization rate of soil microorganisms to the carbon sources was in order of carbohydrates > amines > amino acids > multi cluster > carboxylic acids and phenolic acids. 3) The diversity index of carbon source utilization was enhanced by different fertilization treatments. Shannon index, richness index and dominance index of M20, M50 and M100 were significantly higher than those in the treatments CK and M0, but evenness index was significantly lower. The difference was more obvious with the increasing of organic nitrogen substitution.4) Soil microbial carbon metabolism was closely related to soil organic matter content. The greater the content of soil organic matter, the higher Shannon index, richness index, dominance index and AWCD value was, but the lower the evenness index was.

Conclusions Manure nitrogen substitution in autumn base fertilizer significantly increases the carbon source utilization of soil microorganisms and further improves soil microbial diversity and activity. The optimum of the base fertilizer in autumn is 100% manure nitrogen substitutions (M100).