Working with water and nutrients

Sounds of water

If you want some seriously relaxing audio to listen to, why not download our audio file of the ambient sounds about the cress farms here

How The Watercress Company works with 50 million litres of water per day and achieves the targets set by the EA

Watercress is a truly unique crop and the vital ingredient for growing watercress is, of course, water – pure, mineral-rich spring water, from which this peppery leaf derives its powerhouse of nutrients.  

This water originates from deep aquifers below ground and flows through our beds before being returned to the river system. It is our aim to grow watercress with as little effect on water quality as possible.

Each farm has its own abstraction licence and discharge permit, issued and

we are regulated by the Environment Agency which stipulate the limits that are set on our discharges.

The two main considerations in our discharge waters are suspended solids (from bed cleaning) and phosphate (from fertiliser applications).

Our farms in Hampshire discharge through settlement ponds into the River Itchen, a chalk river which has been designated as a Special Area of Conservation (SAC) under the EU Habitats Directive. This designation means that the targets for water quality are much more stringent than the Water Framework Directive targets which need to be met by watercress farms in other areas. 

Because of this legislation, the Environment Agency (EA) has set limits for phosphate levels in watercress discharge water for any watercress growers discharging into an SAC. These limits were determined  in 2014 and came into force in September 2016 and are very low, set typically at around 40 µg/l above base levels (base levels being the natural levels found in our spring water).  As well as limits on phosphate, a limit was also set for ammoniacal nitrogen at 0.5mg/l which came into force immediately when the permits were first issued in 2014.

How do we reduce fertiliser use, manage effluent and reduce suspended solids ....…

Suspended solids are created when we clean out a watercress bed.  This clean out process is necessary before the beds can be re-drilled with a new crop.  In order to reduce the level of suspended solids generated from this operation the water is sent through settlement ponds.  These ponds are designed to slow the water flow down so that the solids are able to settle out before reaching the discharge point. The ponds are cleaned out on average once per year to allow their efficient operation.  Since 2017 we have reduced the number of times each bed is cleaned out and replanted thereby vastly reducing the amount of suspended solids produced.  Our aim for 2018 was to drill only twice in each bed and this has reduced the loading on the ponds and helped to protect the downstream environment.

The by-product of the cleaning out process is a mix of watercress waste and gravel. We have recently redeveloped our composting area for this material.  Once it has been removed from the bed the material is initially stored on a concrete pad. The liquid effluent from the watercress is collected into a tank and the aim is for this liquid to be used as an additional nutrient source.

all water that passes through a watercress farm flows through a series of settlement ponds before entering the river system

We have been able to reduce our fertiliser requirement by reducing our plant densities at the time of sowing. This lower density enables the growing plants to take up a greater percentage of the available nutrition.  It is worth noting that, for the majority of the year, we use no fertiliser at all and, during the summer growing period, fertiliser is only needed for less than 4% of the plant’s growing life. As the permit limits set by the EA for both phosphate and ammoniacal nitrogen are so low, we have had to trial innovative methods to reduce the quantity and type of fertiliser in order to successfully meet the new limits.   

We have completely cut out all nitrogen application as the crop is able to get all the nitrogen it needs from the spring water

Whilst we were able to remove nitrogen applications completely, phosphate has proved more challenging and complicated.  Phosphate deficiency can lead to an unmarketable crop, particularly during the flowering period. Between 2007 and 2018 we have managed to reduce the quantity of phosphate being used on our farms by 88.4%, however this has not been achieved easily and has come at considerable cost in terms of productivity. Additionally we are seeing elevated levels of flowers and purple stems which devalue the finished product however this huge reduction in applications has seen us achieve the standard set by the EA in the first year.  Our compliance results are based on samples taken by the EA and these results are below.

All the liquid effluent is collected in a tank. The aim is to use this liquid as an additional nutrient source. This should enable further reductions in fertiliser use in the years to come.
The Environment Agency said “that we have undertaken our annual mean total reactive phosphorus assessment on your permits:
All were compliant with their Annual Mean limit as detailed within each permit for 2017. Great news!”

How we monitor ourselves with testing of water and calculating annualised averages

In addition to the EA monitoring of our discharges, we also deploy our own autosamplers (ISCO 3700s) on each farm and monitor phosphate discharges for the 24 hour period after a fertiliser application has taken place. We combine the information from this testing with information from the periods when we do not apply fertiliser to calculate an annualised average.  This testing is significantly more frequent than the tests carried out by the EA and corroborates their findings.  We know that there are still peaks in the levels of phosphate after a fertiliser application, but these peaks are short lived and when averaged out, the discharge levels are below permit levels.  In fact there is evidence that, in winter, watercress actually removes a certain amount of phosphate from the incoming water (although this reduction is not used in the calculations)

In 2018, we carried out some intensive monitoring on the discharge from one of our farms and at two further sites; one 1km downstream and another 3.3km downstream. We timed this testing to ensure that we were testing after multiple fertiliser applications. Although there were some peaks at our precise discharge point, no effect was measured at either the 1km or 3.3km testing points downstream. Based on the levels taken from our discharge (without even adding in the period of the year when we don’t apply any additional nutrients) the average level detected was well below the level required by our permit.