Soil Oxygenation Effects on Growth, Yield and Nutrition of Organic Greenhouse Tomato Crops

Soil oxygen deficiency (hypoxia) reduces respiration, mineral uptake and water movement in roots, and may thus have a negative impact on plant growth and productivity. The supply of air or oxygen to the rhizosphere usually improves crop performance under anoxic/hypoxic soil conditions. However, little is known about the effect of O-2 enrichment of the irrigation water or soil on organic greenhouse crops. The objective of this study was to determine the effect of soil oxygenation on soil biological activity, plant growth and development, yield and fruit quality. Seedlings of Lycopersicon esculentum ('Macarena' grafted on 'Beaufort') were transplanted into a loamy soil and grown in a greenhouse from February to October (oxygenated vs. control plots; four complete blocks). In 2008, O-2 enrichment was provided by the irrigation water using pure O-2 gas and venturi injectors (mean water O-2 similar to 16 ppm), whereas in 2009 pure O-2 was released from a network of small perforated (0.5 mm diameter holes) tubes installed at 25-cm depth into the soil (mean soil O-2 similar to 25%). Soil surface CO2 flux was measured three times/year to determine biological activity. Growth parameters, yield and fruit quality were measured weekly. Soil and leaf mineral content were determined monthly. There was no difference in marketable yield between O-2-enriched and control plots in 2008 but increased production (similar to 2 kg m(-2), P=0.108) under soil O-2 enrichment in 2009. Soil CO2 fluxes were also higher in O-2-enriched plots but on three sampling dates only. In general, no significant differences were observed in plant growth parameters or fruit quality. Leaf Mg and Fe levels and several soil nutrients (NO3, NH4, P and K) were significantly higher in O-2-enriched plots. Long-term effects of soil O-2 enrichment should be examined in different types of organically cultivated soils to conclude on any significant beneficial effect on soil biological activity and crop productivity.