The Couve crop: Day 42

By day 42 the couve had grown substantially. Every second plant was harvested around this time, to give the remaining plants the space to grow to full size. We harvested the equivalent of 8 t/ha from the wet side and 7.1 t/ha from the ‘dry’ side of the block from this 'thinning'.

Between day 15 and 35, irrigation was applied every second day for about 30 minutes. During the last week of this period three larger irrigations in the range of 2-4 hours were applied to try and push water down to the detectors buried at 30 and 50 cm. Over the 15-42 day period the ‘wet side’ received an average of 2.5 mm per day and the dry side 2.1 mm per day.

Irrigation on the wet side every second day for about 30 minutes up to day 35 resulted in the soil drying slightly at both depths (to around 20 kPa). Each of the three longer irrigation events after day 35 activated the detector at 30 cm depth, giving nitrate values of 79 (day 36), 33 (Day 38) and 46 mg/L (day 41). The third event activated the detector at 50 cm giving 42 mg nitrate/L. At the same time the watermark sensors recorded the soil suction returning to close to zero art both depths.

The soil suction also rose on the ‘dry side’ as the water use by the couve exceeded the 2.1 mm/day provided. Each of the three longer irrigation events between days 38 and 42 activated the detector at 30 cm depth giving values of 400, 235 and 192 mg nitrate/L. The third event activated the detector at 50 cm giving 164 mg nitrate/L.

These nitrate values were much higher than the ‘wet side’, showing how small differences in irrigation management can have a huge impact on nutrition.