Development of standard methodologies: Bio-indicators and methodologies to quantify soil quality
The objectives of this research were to: 1) Develop methodologies for assessing soil health using indicators of soil organic matter (SOM) quality, and to inform the public on the impacts of farming practices on soils. 2) Characterize the variabilities of soil health indicators, and to determine the influence of management practices on their random variability. 3) Establish quantitative relationships between soil indicators with soil attributes of soil qality in soil agro-ecosystems. The tested indicators were soil enzymes, lipids and light fraction of SOM. This report emphasizes information on soil enzymes and lipids as indicators of soil health relative to that of the light fraction of soil organic matter (SOM). Soil mineralizing enzymes transform soil organic matter and provide essential nutrients for the growth of crops and soil organisms. Soil lipids help form stable aggregates and influence the structural support for rooth growth. Establishing quantitative methodologies to use in assessment of soil health requires knowledge on how soil enzymes and lipids are influenced by farming practices in soil landscapes. Methodologies presented in this report will assist farmers in defining the state of soil nutrient mineralization power and the structural stability of soils
and will indicate when to implement changes in farming practices once changes in nutrient mineralization power are detected. Assessment of soil health also informs policy makers and the public on the current state of soils and the sustainability of crop production systems. The 3 yr research was conducted on four farms with differing soils, climate and crop production systems. At two of these sites (Rockwood and Clinton) there has been significant amount of other information collected. Soil lipids and six nutrient mineralizing enzymes (?-glucosidase, dehydrogenase, L-glutaminase, urease, alkaline phosphatase and arylsulfatase) were sensitive to the effects of land use, tillage system, manure and fertilizer application. Some soil enzymes (i.e. dehydrogenase) behaved as early indicators of SOM accumulation by expressing changes before soil organic carbon (OC) content showed any similar change. Other soil enzymes (i.e. urease, alkaline phosphatase and arylsulfatase) correlated with OC content and behaved as surrogate measurements of SOM. Crop growth and slope position influenced soil enzyme activities and lipid content. These factors need to be considered when assessing the functions of soil nutrient mineralization and structural stability. In earlier studies conducted in vitro, pure cultures of organisms showed that the six tested soil enzymes control key processes of mineralization in the C, N, P and S cycles. This project tested specifically for the ecological function of enzymes and N mineralization. Soil L-glutaminase, dehydrogenase, and to a lesser extent urease, were associated with the power of soils to mineralize N. Simple linear models predicted the N mineralization power of soils based on enzyme activity level. Seven enzyme activity levels defined for each of the six enzymes were the same in all soils and ranged from very low to very high. Overall, very high levels of enzyme activity, lipid content and soil structural stability were found in undisturbed soils under forest, sod and zero-tillage. Soils cropped with conventional tillage always presented medium to low enzyme activity levels and low soil structural stability. This report presents two methods for monitoring and evaluating the fuctions of soil nutrient mineralization and structural stability. Quality control charts (QCC) were used succesfully for monitoring large and small shifts in the activities of enzymes asociated with N mineralization power. A method using principal component analysis (PCA) integrated soil chemical and physical properties into a vectorial scale defining the relative status of soil structure stability. Both methods consistently represented the effects of different management systems on nutrient mineralization and structural stability in landscapes of soils with different pedogenesis. We predicate that high enzyme activity level and soil structural stability represent a high state of soil health. Conversely, low soil health is associated with soils having both low soil enzyme activity level and structural stability.