Nitrogen cycling in a semi-arid Mediterranean region: changes in soil N and organic matter under several crop/livestock production systems

Abstract

There is a need to quantify the effects on soil N of introducing different legumes into the farming systems of West Asia and North Africa. This paper presents 6 years results from an on-going experiment aimed at examining the productivity of several crop/livestock farming systems in north west Syria. Changes in total soil N and organic matter when either medic pasture (3 stocking rates), vetch, lentil, fallow or watermelon were rotated yearly with wheat were examined. In addition, in the sixth year of the experiment, mineral N levels in the soil and the N content of the wheat and legumes shoots were determined in order to formulate a simple N balance for each rotation. Medic pasture and vetch rotations increased total soil N and the organic matter content of the soil. Lentil had no effect on total soil N or the organic matter content. Total soil N also remained constant in the fallow rotation, but organic matter content of the soil tended to decrease. The changes in soil properties had implications for the long term production from the different rotations, and highlighted the importance of retaining legume residues for maintaining fertility.