Chemical characteristics of soil after 40 years of continuous maize cultivation

The objective of this study was to determine the changes in chemical characteristics following 40 years of a conventionally tilled continuous maize cropping (CM) compared with those of an adjacent untilled native grass-land (NG) soil. Results indicate that there was a significant decrease of organic C and N, of the exchange capacity and exchangeable bases as well as of the enzyme activities. In spite of a general decline in the content, but not of the concentrations of the inorganic N forms, the NO3-N/NH4-N ratio increased in the tilled system CM. As a consequence of yearly fertilization in excess of crop removal, cultivation enhanced the available P and soluble S contents as well as the heavy metal level, without, however, causing toxic concentrations in soil. Long-term maize cultivation did not seem to cause any adverse effect on soil pH, texture and electrical conductivity