Raised bed planting and green manuring increased tomato yields through improved soil microbial activity in an organic production system

ABSTRACT This study investigated the effect of two planting systems (raised bed and flat) in combination with incorporation of faba bean green manure at two plant growth stages (FS, incorporation at flowering; SAH, incorporation after harvest of fresh pods) on soil microbial activity, yield and quality of tomatoes grown in an organic cultivation system. Treatments without the faba bean green manure in raised beds and flat planting system were used as controls. Soil microbial biomass-C and CO2 production were significantly affected by the interaction between the planting system and green manure treatments; they were generally higher in the raised beds than in the flat planting system and in treatments with incorporation of green manure compared with the controls. The highest leaf chlorophyll concentration (45.6 CCI), stomatal conductance (74.8 mmol m−2 s−1) and yield (2.24 kg plant−1) were recorded in the raised bed planting system with FS green manure. Although the green manure had important effects on the soil microbial activity and the yield, the differences between incorporating the faba beans at the different growth stages (FS and SAH) were less clear. Significant positive correlations (p < 0.01) were found between yield and leaf chlorophyll concentration, stomatal conductance, soil microbial biomass-C and soil CO2 production, while soil compaction was negatively correlated with yield, stomatal conductance, soil microbial biomass-C, soil CO2 production and leaf chlorophyll concentration.