Soil fertility - changes during the conversion process.

This paper describes changes in key parameters measuring aspects of soil fertility that have occurred throughout the conversion period and beyond (1996 to 2003) on ten commercial farms. The farms all produced field vegetables but otherwise they reflected a range of farming systems on varied soil types throughout England. There were very few changes in organic matter levels. The importance of the fertility building crops for providing nitrogen has been increasingly recognized by the farmers but there have been notable examples of deficiencies. Available phosphorus (P) and potassium (K) remained relatively stable overall, suggesting that the inputs of soil amendments (usually FYM) were broadly satisfactory. Problems with soil structure, particularly compaction, were apparent on several farms. Sometimes this was due to pre-existing problems which had been masked by the use of conventional fertilizers.