Abstract
This work assessed the seasonal dynamics of the substrate oxygen content and the response to oxygen enrichment of nutrient solution (oxyfertigation) of autumn-winter sweet pepper and spring melon crops grown on rockwool slabs (2003/04 season) and perlite grow-bags (2004/05), compared to non-enriched crops. Dissolved Oxygen (DO) values in the nutrient solution were higher for all the oxygen enriched treatments (>20 mg L-1) than for the non-enriched ones (~4 mg L-1), but no significant differences were found in the substrate solution. For pepper crops, DO values were highest at the onset and, especially, at the end of the cycle in winter, while the lowest DO values (3 to 4 mg L-1) occurred during September and October. For melon, DO values decreased progressively from the onset of the cycles to values ≤3 mg L-1 during the second half of the cycles. For pepper crops, there were no significant differences between oxygen treatments for fruit production, which could be attributed to the fact that DO values were >3 mg L-1 throughout each crop cycle. However, a significant 7% increase in total and marketable yield, associated with a higher fruit number, was observed for the oxygen enriched melon grown on rockwool slabs, whereas no significant differences were found for the melon grown on perlite grow-bags. In conclusion, the use of inexpensive systems of substrate oxygen enrichment should be restricted to rockwool substrates and to crop periods when a high oxygen demand coincides with low oxygen availability, such as the period from melon flowering phase.
Highlights
Soilless-grown vegetable crops represent around 20% of the total area of greenhouse crops in the southeast of the Spanish Mediterranean coast, a mild winter climate area (Montero et al, 1985) with one of the largest concentrations of greenhouses in the world (Castilla and Hernández, 2005)
Substrates under long cultivation periods: i) usually increase organic matter content and micro-organism activity, which could increase the competition for oxygen in the root environment; and ii) roots are densely matted within the substrate, which could alter oxygen diffusion and supply
Air-filled porosity (AFP) values of the new and reused substrates, measured by Acuña (2007), were around or higher than 30% and 45% (v/v) for rockwool slabs and perlite grow-bags, respectively
Summary
Soilless-grown vegetable crops represent around 20% of the total area of greenhouse crops in the southeast of the Spanish Mediterranean coast, a mild winter climate area (Montero et al, 1985) with one of the largest concentrations of greenhouses in the world (Castilla and Hernández, 2005). Soilless vegetable crops from this area are most often grown on limited volumes of two inert growing media: perlite and rockwool (Castilla and Hernández, 2005) These substrates usually have high air-filled porosity values, vegetable roots can experience suboptimal oxygen conditions as a result of various factors (Schröder and Lieth, 2002; Raviv et al, 2004), especially in the non-controlled climatic conditions of Mediterranean greenhouses (Guri, 2002; Bonachela et al, 2005; Urrestarazu and Mazuela, 2005). Substrates under long cultivation periods: i) usually increase organic matter content and micro-organism activity, which could increase the competition for oxygen in the root environment; and ii) roots are densely matted within the substrate, which could alter oxygen diffusion and supply
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