Chun- derova and Zubeta [54] showed that after 4 years of cropping, high phosphate concentrations at field testing sites inhibited microbial phosphatase activity. However, no such effects were observed in N300 or PS45 plots even after 8 years of continuous applications, and others have published similar results [55]. Indeed the treated plots showed a higher phosphatase activity than control plots, probably due to the presence of phosphatase in maize roots. High levels of soluble inorganic phosphate are probably required to inhibit phosphatase activity in the soil [54,56].
Microbial biomass carbon is an indicator of microbial abundance in the soil and responds rapidly to disturbances caused by tillage or fertilizers [57]. Short-term measurements of MBC can therefore reflect the long-term measurements of the organic material in the soil [58]. It was observed a slight (but not statistically significant) increase of the MBC in N300 and PS45 plots compared to control plots, but surprisingly a statistically significant increase in MBC was observed from 2010 to 2011 corresponding to a significant reduction in gravimetric soil moisture (