Monday, November 29, 2010

The couve crop: Day 70

By day 70 all the couve had been harvested. We picked 27.7 tons per ha from the wetter side and 33.3 tons per ha from the drier side. When we add in the thinning harvest around day 40, the totals were 35.2 t/ha on the wetter side and 33.3 t/ha on the drier side. The crop looked good and tasted good, but we do not have any benchmark to compare it to. We could not find any other data from Mozambique.

It took a total of 159 mm to grow 35.2 t/ha of couve and 134 mm to grow 33.3 t/ha on the dry side. Moreover the last few large irrigations probably were not needed – I just wanted to get samples from the 30 and 50 cm deep detectors. For those familiar with crop water use, this is an incredibly small amount of water to grow a 70 day crop. There is no weather station or evaporation pan data available in Maputo, but we know that irrigation averaged just 2.3 mm/day (wet side) and 1.9 mm/day (dry side) during the warm to hot weather marking the end of the dry season. Of this irrigation water, some must have been lost to direct evaporation from the soil. And maybe some to drainage? (more later on this topic!)

The big irrigation at the end of the season wet the soil profile up again and allowed us to get some more nitrate samples from the detectors. The nitrate at 30 cm was 24 mg/L and at 50 cm was 37 mg/L – just a bit lower than the readings back around day 40.

The big irrigation also refilled the profile on the dry side. The nitrate reading at 30 cm was 51 mg/L and at 50 cm still a high value – 139 mg/L. Both the wet and the dry side started with high levels of nitrate. How much of this did the plant actually get, and how much leached below the roots? Amazingly, we pretty much know the answer to this question.
Coming soon!

1 comment:

Stephanie said...

Hi...I'm rather new to your blog and have sort of breezed through past ones. But, if you are seeing "how little water you can get away with" why aren't you mulching? I'm in Senegal, by the way, and people here water their market gardens by hand at least once a day, and very often twice a day. We're in the dry season now, and people also have to deal wiht drying winds. Just a bit of background if it makes a difference.