On 26 September 2002, Corine de Groot, a researcher at Plant Research International in Wageningen, obtained her doctorate from the Faculty of Biology at Utrecht University. Her thesis demonstrated that the use of phosphorus and nitrogen as fertilizers in greenhouses can be reduced. As well as offering obvious environmental benefits, this would also provide financial savings for growers.
The study showed that tomato plants that receive a small amount of phosphorus or nitrogen each day grow just as well as those which are given a high concentration in the nutrient solution. This means growers can reduce the amount of fertilisers given. A proviso herein is the need to ensure the tomato plants receive sufficient fertiliser. It is vital to have a system in place that signals even the slightest shortfall in fertiliser levels, so that growers can take action before the plants growth is stunted.
The research also showed that the amount of "leaf surface per plant weight" changes as a result of even a small reduction in fertiliser. This is not easy to measure in a crop situation. The surface per weight of individual leaves is probably a better method for the early detection of a lack of nutrients. The maximum speed at which a plant can convert carbon dioxide into sugars is another possible measurement technique.
In addition, De Groot's research demonstrated that it is more likely that the dry matter division between the roots and shoots in tomato plants is regulated by cytokinin rather than nitrate.
The control of photosynthesis when there is a limited amount of phosphorus or nitrogen was also extensively studied. It appeared that the reduction in photosynthesis rate that occurs when phosphorus is lacking is regulated by a different mechanism than when there is a shortfall in nitrogen. The thesis also showed that depending on the seriousness of the phosphorus or nitrogen shortage, the growth of the tomato plants was ultimately decided by their physiology or morphology.
This research has provided important information on the functioning of young tomato plants without fruits when levels of phosphorus and nitrogen are restricted. The data will be used in further research studies looking at practical applications.
List of press releases for 2002