Using a soil quality index to assess the effects of applying swine manure compost on soil quality under a crop rotation system in Taiwan

Soil quality indices (SQI) have been proposed in recent years as tools for assessing soil management practice effects on soil quality. In this paper, we report the result of our 4-year study on the use of a SQI to assess the effects of applying swine manure compost on soil quality. Cabbage (Brassica camperstris L.) and maize (Zea mays L.) were grown in rotation in plots applied with low, medium, and high rates of swine manure compost while the control received only chemical fertilizers. Selected soil physical, chemical, and biological properties (bulk density, aggregate stability, organic carbon content, soil pH, available N, P, and K, extractable Cu and Zn, and microbial biomass), all of which were identified as possible soil quality indicators, were monitored at regular intervals. Tissues of harvested crops were analyzed for Cu and Zn concentrations because they were anticipated to increase due to the high amounts of the metals in the manure compost. A SQI model was derived based on Mausbach and Seybold's research and on our soil database and research experience in Taiwan. Data from our manure application experiment were used to calculate the SQI values for the different treatments. Results revealed that application of swine manure compost improved the soil quality of surface soil as indicated by increased values of soil quality indicators, SQI, and yields of the crops. In addition, Cu and Zn levels in the soil and in the crop tissues did not increase to harmful levels. Thus, it seems that the SQI was an effective tool to assess the effects of swine manure compost application on soil quality. The soil indicators we found effective included the monitored properties except for bulk density. All of these soil properties were significantly increased by manure compost application. Long-term application of 40-60 tons ha year of manure compost may improve the soil quality and increase the yield of the crops without polluting the soil and crops with Cu and Zn.