The Agro-Shrub Alliance
‘Bio-irrigation’ - How it works
The shrubs have deep tap roots that suck up water from the wet deep sub-soil and deposit this small amount of water in the dry upper soil layers at night when photosynthesis stops. Surrounding crops take advantage of some of this water that is drawn up. This is called hydraulic lift or hydraulic redistribution. We call it bio-irrigation.
To test they hypothesis of water transfer, we set up a simulated drought experiment in Senegal during the dry season using irrigation to manipulate the amount and timing of water delivery.
Once we observed the daily drying and nightly re-wetting of the soil that is characteristic of hydraulic lift, we began our study.
We attached bottles with labelled water (deuterium) tracer to the deep roots of the shrub. Then, we collected aboveground leaf samples of the shrub, and adjacent millet plants growing over a period of five days which were analyzed for the tracer.
We found evidence of the tracer in a shrub on the first day after injecting the labelled water, and then a day later we found it in the millet growing nearby.
This finding confirms for the first time that hydraulically lifted water by shrubs can be transferred to the adjacent millet crop.