Cranberry Response to Soil Aeration and Soil Matric Potential.

Cranberry yields have increased about 10% over the last decade in Quebec. New irrigation methods contributed to this increase and some of this increase has been attributed to poor aeration conditions.

The objective of this study was to to determine the threshold at which soil aeration becomes insufficient and affects cranberry yield and photosynthesis.

To highlight the impact of groundwater and subsequent level on the plants, six treatments were imposed randomly and replicated four times to 24 soil blocks (26 cm width x 26 long x 42 cm high) column sampled in cranberry fields with limited disturbance. They were later brought to a growth cabinet and imposed a controlled environment. Water levels associated to matric potential of -0.25, -0.5, -1, -2, -3 and -5 kPa were imposed for the duration of the experiment. Matric potential, water contents and oxygen concentrations were measured every 30 minutes at the 5 to 15 cm depths using respectively pressure sensors, T.D.R. and Apogee probes connected to dataloggers while transpiration, stomatal conductance, and photosynthesis were measured as plant physiological indicators. Correlations are established between air porosity and diffusive flux of oxygen with indicators of the plant activity.

Measurements indicated that at a matric potential threshold of about -3 kPa, a decrease in photosynthesis rate was observed and was associated to insufficient oxygen diffusion to the roots. Plant activity decreased significantly by 30% after one week in the wettest treatments (-0.25, -0.5, -1 kPa). This indicates a high sensitivity of cranberry to excess water, contrarily to the common belief for this crop.