Wetting agents - hold on to water for healthy root uptake

We have received frequent comments of a 'green-up effect' seen during greenkeepers' user trials with Qualibra; where treated areas have responded with a rapid visual improvement in colour. A key factor in this is believed to be the enhanced uptake of nutrients, through a combination of greater immediate availability from better contact of soil moisture along the root and, over the longer term, increased retention of nutrients in the rootzone.

Initially, new research is looking to assess the effect of soil moisture being distributed more evenly through the soil, and thereby increasing the area of contact with the roots that will enhance uptake of water and nutrients. Where roots are growing in hydrophobic soils - or even small pockets of hydrophobicity within the soil profile - there will be lengths of the root that have little or no contact with soil moisture.

Where the use of a combination wetting agent creates a more even distribution of soil moisture in hydrophobic areas, and thereby along a greater length of the root mass, it should lead to a greater nutrient uptake. Even in a wet season, the issue of hydrophobicity can still lead to dry patches within the soil profile.

To achieve the desired even spread, you need to have the right sort of wetting agent. It needs a combination of sufficient penetrant to move the water and achieve the spread along the roots and through hydrophobic soils, along with effective polymer retention of moisture right through the rootzone. A conventional polymer wetting agent is unlikely to provide sufficient even distribution of moisture to achieve such a benefit.

In fact, the reason turf typically starts to yellow off in the summer is not lack of water, but most likely lack of nitrogen. Since N in soluble form is only available in water, where the wetting agent makes moisture more accessible in the soil, it should lead to greater uptake and greater availability in the plant, thus delaying the onset of summer senescence or, where plants have started to suffer, alleviating the symptoms quicker.

This will be most noticeable during periods of hot, dry weather - when the turf plants are transpiring rapidly and there is a higher risk of limitations in water availability. But, even on free-draining sand construction greens and tees, water availability can fall rapidly over the duration of the day, affecting the turgor of turf leaves; better soil moisture retention through the rootzone will see potential benefits of reduced plant stress and improved playing surface consistency.

Secondly, with soil moisture being held more effectively deeper in the soil profile, there would be a reduced leaching of nutrients, which results in more available for root uptake and increasing the efficiency of fertiliser applications. This would also have an implication for the environmental impact of nutrient loss through groundwater.

Furthermore, with greater availability, soil moisture in the existing root structure can be supported, which could further improve water and nutrient utilisation.

The use of Qualibra has no effect on root development per se but, if there is more soil moisture in the rootzone, a greater root mass can be actively supported. Contrary to popular belief, turf roots do not 'grow down to seek out moisture' but, if moisture is available deeper, the roots will grow more vigorously at depth.

For most golf course turf plant species, such as Fescue and Bentgrass, however, the root mass can decline significantly over the summer in hot, dry conditions - typically by up to 50%, but with research showing losses of over 75% on Bentgrass greens between May and the end of August. The problems could be exacerbated on greens that are predominantly Poa annua, which is typically more shallow rooted; where a 50% loss of a 75mm root depth, for example, would have a greater impact than 50% loss of a 150mm root.

If we can better retain the root structure over the summer - through any combination of actions, including combination wetting agent programmes, raising the height of cut, aeration, irrigation and Primo Maxx - it should also enhance overall plant health, minimise the energy requirement for root mass recovery in the autumn and give the turf plant greater carbohydrate reserves ready for the winter.

Visit www.greencast.co.uk for further information