Trials shaping tolerant seed mixtures worth their salt
As Turf Managers, we are well aware of the wide range of environmental conditions that impact us on a daily basis - and how we can best equip our surfaces and our maintenance programmes to best manage those challenges.
Heat, drought and disease are all examples of frequently encountered and well-researched areas, but perhaps lesser so is the implications of salt. Technical Manager for DLF, David Rhodes, explains why salinity is a growing consideration for an increasing range of facilities and what research is currently underway to provide more tolerant seed varieties.
Salt happens - it's just that in some environments it is more prevalent than others. Some venues may have areas of salt affected soils naturally or, for example in coastal locations, turf may be subject to sea mist and/or spray. Naturally, when one thinks of salt-affected turf, our thoughts go straight to links golf courses. However, it extends to roadsides and verges exposed to salt de-icing, community surfaces constructed on areas of reclaimed sea bed and any venue that use impaired or recycled water for irrigation.
Research conducted by UNESCO and the World Economic Forum widely reports that the gap between global water supply and demand is expected to reach 40% by 2030 if current practices continue. This is therefore a major driver for both fine and sports turf clubs to be looking at more effective usage of rainwater to reduce the reliance on freshwater irrigation, and be well placed to cope with the prolonged periods of hot and dry weather we are seeing as a result of the shifting climate.
Brackish (or brack) water is found naturally in the environment, often in areas where freshwater meets marine waters, the best-known example being an estuary. Brackish water provides a more sustainable source than freshwater for irrigation use, however, it has a higher salt content than freshwater, though not as saline as seawater. We also know that salt content is higher in recycled water too, so when we cannot change these environmental factors, we must adapt our products and practices to suit the known conditions.
Grass plants may suffer from salt stress when exposed to saline conditions. Salt stress can reduce a plant's absorptive capacity - leading to nutrient deficiencies, ion imbalances and damage to the chloroplast structure, ultimately reducing a plant's ability to germinate and grow. This is known as ionic toxicity and osmotic stress. If a plant is suffering from salt stress, the above ground symptoms will show in the form of wilting (similar to drought) and noticeable plant growth stunting and management problems.
A plant tolerant to salt is sometimes called a halophyte, a word derived from Ancient Greek (halas) 'salt' and (phyton) 'plant'. A plant's tolerance to salt is characterised in two main ways:
- Its ability to handle ion toxicity - controlling the distribution and concentration in the tissue
- Its management of salt stress in the root zone - limiting the entry of salt at the root
Left: Chewings fescue (left), strong creeping red fescue (middle) and top-performing slender creeping red fescue (right). Right: Hunter irrigation at Bromley FC.
While some wild grass plants express some natural salt tolerance, DLF have recently conducted a large trials and screening programme of more than 300 turf varieties to establish those with the highest tolerance. In the trials conducted over the last seven years, each variety was sown at 100mg seed per 'block', with three to five replications and grown under optimal germination conditions. Salt was applied at regular intervals and at increasing levels from moderately saline up to brine.
Blocks were monitored daily and regularly evaluated for the percentage of green leaves and dry matter yield.
The results demonstrated a huge variation in salt tolerance between species.
Fescues tended to perform well, with tall fescue, slender creeping red fescue and strong creeping red fescue making up three of the top four ranked varieties. Creeping bent and tetraploid perennial ryegrass (4Turf) complete the top five.
Before salt stress (left) and after (right).
What is interesting is the apparent difference in tolerance levels of varieties of the same species. For example, a poor performing slender creeping red fescue will still be a preferable choice for salt tolerance than the best performing chewings fescue.
Using this information, breeders can then choose the highest-ranking varieties in terms of salinity tolerance to incorporate into mixtures for less risk of failed establishment, better growth and maintenance of the normal variety characteristics such as visual merit and wear and disease tolerance.
As increasing pressure falls on everybody to find more sustainable sources of water, it is critical that we as breeders and suppliers are providing the right range of products to perform under these changing conditions. While research has already shaped a number of proven salt tolerant mixtures, there is
David Rhodes - DLF Technical Manager