Targeted CO2 enrichment management for modern varieties in long season tomato crop production in the UK

Summary: Changes in energy costs and the shift towards renewable fuel supplies to heat glasshouses have placed a renewed emphasis on CO2 enrichment strategies for growers.  For some heat sources such as straw and woodchip then whilst the energy and electricity generated make economic sense to the grower, the technology costs for siphoning off clean CO2 for crop enrichment are prohibitively expensive at present because the technology may not have been sufficiently developed for use in horticulture.  But CO2 enrichment is still required to achieve consistently accurate fruit specification quality targets and high and stable tomato yields and therefore CO2 emitted as a by-product from existing CHP installations or pure CO2 sources remain an integral part of the growing system; there is therefore an additional cost of supplying CO2, or the ability to accurately partition heat source technologies to supply sufficient CO2.  Because of the recent shift to renewable heat source production, without CO2 by-product, then there is a renewed emphasis on exactly how much CO2 is required and when it needs to be supplied to the crop to assist the grower to minimise costs and maximise economic return. This project will identify new practical links between commercial CO2 enrichment and plant photosynthetic demand. The overarching aim of the project is to develop a robust protocol to identify potential cultivar specific limitations to CO2 enrichment. The potential benefits to the industry are:

- Improved understanding of the link between atmospheric CO2 management and crop yield and quality. 
- The cost-effective use of CO2 enrichment to minimise energy inputs to maximise profit.
- Minimised environmental impact of long-season tomato crop production because of reduced CO2 use for long-season tomato crop production.     

Aims and Objectives: 

(i) Project aim (Phase 1): To develop a robust sampling protocol which will identify any photosynthetic limitation to CO2 enrichment for selected commercial types of glasshouse grown long season tomato. 

(ii) Project objectives:  

• 1. To establish representative leaf photosynthesis and leaf growth measurements for selected tomato cultivars at a single grower site under standard CO2 enrichment conditions.
• 2. To extrapolate single leaf measurements of gas exchange to whole plant diurnal photosynthesis.
• 3. To select cultivars with contrasting leaf area to fruit load source sink ratios to identify any end product inhibition or stomatal closure limitations to photosynthesis.
• 4. To compare current irrigation strategies to shoot photosynthetic performance and explore links with any limitations to optimum performance identified in Obj 3.
• 5.  To integrate the findings from Objs 1-4 and develop a robust sampling protocol to evaluate the daily photosynthetic response under standard CO2 enrichment of current UK glasshouse grown commercial cultivars of tomato.
• 6.  Use data from Objs 1-5 to develop preliminary key crop parameter response surfaces to CO2 enrichment using multivariate modelling approaches.