The Effects of Compost Application Rates On Soil Microbial Biomass, Enzyme Activities and the Severity of Potato Diseases.

Potato cropping systems are typically characterized by high rates of external inputs and low soil biological activity.  Supplementing organic C inputs with animal manures is one way to improve biological functions in potato cropping systems but little is known about how the rate and timing of applications influences soil biological activity.  We examined the effects of organic amendment (chicken manure compost) application rates and timing on soil biological activity and the severity of potato common scab (Streptomycetes scabies) in a sandy Michigan soil.  Our measurements included microbial biomass C and N, inorganic N, pH, soil moisture, and hydrolytic enzyme activity ( β-1,4-glucosidase; β-1,4-N-acetylglucosaminidase; acid phosphatase; and tyrosine amino peptidase). Our initial results show that the higher compost application resulted in higher potato yield but lower common scab.  Compost enhanced soil pH, microbial biomass, enzyme activities, and increased soil carbon and nitrogen contents.  Soil nitrate and ammonium concentrations were strongly correlated with microbial biomass C and N and enzyme activities. Enzyme activities were also significantly related to soil moisture content.  Potato yield was strongly related to pH and microbial biomass C and N while common scab was negatively related to microbial biomass C and N, ammonium_, and tyrosine amino peptidase (p<0.05).  Principle components analysis (PCA) was used to provide an integrated view of amendment application effects on soil biological functions and showed that amendment application rates had strong effects on overall biological activity.