It has been two months since I arrived at ICRISAT. In less than one day I realised that this is a calm and green paradise inside India, nothing to do with the world outside! The campus is surrounded by fields, isolated from the chaos of the city, definitely the right place to open the mind and run experiments!
As a PhD student of the RAINDROPS project I am working on the development of a methodology for the identification of past crops water availability in drylands. In ICRISAT I am pursuing an internship on physiology of water transport in plants supervised by Dr Jana Kholova, Senior Scientist of Crops Physiology, Innovation system for Drylands Program. The thing is: we are trying to figure out if phytoliths and isotopes could be used as proxies for ancient water management practices. So what do we need first? Modern crops, grown in experimental field with a precise water treatment, to extract phytoliths and isotopes. Hopefully with these samples we will also work on phenotyping, in order to connect isotope values and phytolith production to genotypic variation.
Now my task is to produce seeds, stems and leaves of Eleusine coracana (finger millet), Pennisetum glaucum (pearl millet) and Sorghum bicolor (sorghum). If you are wondering why these plants, well, many reasons! First they have a C₄ photosynthetic path, extremely interesting in terms of drought adaptation. In addition they belong to two different C₄ pathways so their physiology appears much more attracting, at least isotopically speaking! Then they are traditional crops of East Africa and Pakistan so they are comparable with the archaeobotanical remains we find in the archaeological contexts under study.
The crops are growing under constantly controlled conditions of water inside lysimeters: large tubes in PVC, placed inside a concrete pit 2 m deep and covered by a rainout shelter. The cylinders are spread inside the pit to simulate the normal distribution in open field. They could be filled with any soil, for example I chose a mixture of Vertisols and Alfisols. The cylinders can be lifted and weighed with a block-chained pulley and an S-type load cell. Why? To asses transpiration rate! I decided to focus on transpiration because it’s a physiological process linked to phytolith production but not only: through transpiration, we can measure the response of crops in water stress condition. For this reason before weighing we stopped soil evaporation by applying specific plastic sheets and polyethylene beads. To obtain equal starting value, before weighing for the first time we saturated all the cylinders. The transpiration rate of crops is measured weekly to obtain a complete picture of crops water stress response.
The water stress treatments can be conducted at vegetative and reproductive stages depending on the purpose of the study while the well water condition depends on the soil type and corresponds to the 80% of the field capacity. In my case late water stress treatments have been chosen following two principles: to stress plants as much as possible in order to simulate the real field condition and to ensure, at the same time, grains production. In this way I can try to simulate irrigation (well water), rain-fed and décrue cultivation (late water stress), as we trust these could be the past water management practices! Giving this I set two different experiments. One involves two water treatments and 10 different traditional genotypes for each specie: well-water plants have been irrigated weekly to maintain 80% of the soil field capacity and drought-stress replicas received water only until flowering. In this way I will be able to compare the water-stress response of different varieties evaluating also possible differences in drought stress adaptation. In the second experiment we were meaner! We set 4 different baselines of water-stress treatment: each species is receiving water respectively until the second week from the sowing, the fourth, the sixth and finally, the seventh! In this way we can furthering our knowledge about environmental phytolith production and isotope discrimination in water stress conditions!
At the end things are less complicated then they may appear: what I really do in my daily routine it’s the farmer’s job! After sowing I took care of the cylinders, giving water to plants weekly, mulching and tilling when necessary. After the saturation I have been weighing and watering the cylinders once a week. I am also facing insects infection and rats infestation but there’s not much to do: nature goes on its way and the only thing I can do it’s to be patient. If all goes well in two more months I will show you the first results! Keep your fingers crossed for me! And if you want to see more detail on my work you can follow me on twitter @Fra_DAgostini