Roots to resilience: climate-proofing crop yields within future salad production

Climate change has and will result in more extreme climatic conditions (e.g. 2018 had 63% of the long-term average rainfall and evapotranspiration increased by 13%) that threatens the resilience of UK outdoor salad production. Lettuce is shallow-rooted, with outdoor crops initially raised in peat blocks in the nursery, then transplanted into intensively prepared seedbeds that are vulnerable to soil drying should heatwave conditions occur after transplanting. Rapid root establishment is critical to ensure adequate water uptake from the seedbed (decreasing reliance on water stored in the peat block) and allow less frequent irrigation (to minimise evaporative losses) as roots extract water from depth. How nursery conditions affect root establishment of lettuce transplants has attracted limited interest.

The environmental impacts of peat harvesting place pressure on the industry to decrease its reliance on peat as a growing substrate. Several peat-free and peat-reduced substrates are now becoming available (Barrett et al. 2016; Sci. Hort. 212, 220-234), and transplant block size may be reduced, but their effects on root development in transplants (both in and out of the nursery) has seen little research.

Changes in transplant production methods may require altered irrigation scheduling to increase the efficiency of water use. High frequency irrigation can maximise shoot growth at the expense of root development and possibly quality, while lowering water use efficiency. A tradeoff between economic yield (determined by crop size versus taste) and sustainability is needed in any amended production system.

This project aims to evaluate how:
1. lettuce root development under existing production systems affects water extraction patterns in the field
2. nursery environmental conditions affect root growth in lettuce transplants in situ, and in the field after transplanting, and determine the underlying physiological mechanisms
3. irrigation frequency affects crop yield, quality and water use efficiency in the field.