Ecological restoration of soil respiration, microbial biomass and enzyme activities through broiler litter application in a calcareous soil cropped with silage maize

A field experiment was conducted to compare the effect of different rates of urea-nitrogen (N) and broiler litter-N on CO2 production, microbial biomass C (MBC), urease, alkaline phosphatase and invertase activities of a calcareous soil during 100 days of maize growth under field conditions. The experiment consisted of seven N treatments (i.e., control/unfertilized plots and plots received 100, 200, 300 kg N ha−1 from urea and broiler litter alone) with four replications. Results showed that urea and broiler litter applications had a significant influence (P < 0.05) on all the measured soil biological properties and maize production. However, the effect of N treatments on soil properties much depended upon the time after fertilizer application, the rate of N applied and the type of fertilizer. The averaged CO2 production (soil respiration) from the surface soil increased with broiler litter and urea additions by 6 and 11% relative to the control soil, respectively. Similarly, urea and broiler litter additions resulted in a significant increase in soil MBC (43-136%), while the soil MBC value with broiler litter treatments was 28% greater than that with urea treatments. Broiler litter and urea treatments had also greater activities of soil urease (0-76%), alkaline phosphatase (9-58%) and invertase (6-31%) than the control treatment. Nonetheless, broiler litter addition had a greater effect on soil alkaline phosphatase (12%) and invertase (17%) than urea addition, whereas urease activity in urea-treated soils was 13% higher than that in broiler litter-treated soils. Most soil biological properties were improved with increasing the level of urea-N and broiler litter-N, but broiler litter applied at 200 and 300 kg N ha−1 had the best and comparable effect on soil biological properties. Additionally, urea and broiler litter additions to this calcareous soil resulted in a significant increase in maize growth and production over the unfertilized plots. However, the application of both broiler litter and urea at 200 and 300 kg N ha−1 brought about similar maize biomass production, suggesting an adequate maize production could be obtained with urea and broiler litter when both are applied at 200 kg N ha−1. The results of this study also indicated that the soil MBC, CO2-C production and urease activity were significantly related with maize yield. In brief, broiler litter application can restore soil microbial biomass and activities in the semi-arid areas of Central Iran, where soil organic matter (SOM) level is very low due to low organic C inputs. Broiler litter has a greater effect on soil properties than urea, highlighting the importance of this organic fertilizer in ecological restoration of cropland soils for a sustainable cropping system in the studied area.