Water height and irrigation time effect on substrate water content in subirrigation

ABSTRACT

Subirrigation is a closed system which recirculates nutrient solution and reduces water and nutrient improper disposal in soils and groundwater. The system is used commercially by the ornamental industry. However, technical information regarding substrate moisture retention in subirrigation still scarce. Our study evaluated the effect of different water heights and irrigation time on volumetric water content (VWC) of commercial substrates in subirrigation. We tested five water heights (1, 2, 4, 6 and 8 cm), five irrigation times (2.5, 5, 10, 15 and 20 min), and three commercial substrates (coconut coir, pine bark with vermiculite, and peat moss with carbonized rice hulls without ashes and vermiculite), arranged in a complete randomized design (factorial 5×5×3), with three replications. We used 55-cm³ cone-shaped containers divided into three 4.16-cm equal layers (top, middle, and bottom) to study the water capillary action dynamics. All substrates presented a large range of VWC across the container layers (p<0.0001). The substrate moisture varied according to the water height (r ²>0.9), with little or no influence of the irrigation time. The middle layer provided the best moisture indication among treatments, with moisture ranging from 0.29 to 0.61 m³/m³ in coconut coir, 0.29 to 0.63 m³/m³ in pine bark, and 0.24 to 0.56 m³/m³ in peat moss with carbonized rice hulls. The water height of 4 cm with any irrigation time for coconut coir and peat moss, and the water height of 2 cm and irrigation time of 10 or 20 min for pine bark resulted in the moisture range recommended for most crops (0.4 m³/m³). The understanding of capillary action dynamics in subirrigation allows the optimization of water heights and irrigation time to apply water efficiently to meet the crop evapotranspiration.

Keywords:
capillary action; irrigation management; volumetric water content.