As we strive to take better care of our water resources, all growers would do well to be mindful of the effects of nutrient leaching and the benefits of good fertilizer practice, writes Andrew Wilson, ICL technical manager for fertilizers. Controlled release fertilizer (CRF) and slow release technology has now been applied to base fertilisers in a bid to optimise plant quality and nutrient efficiency by minimising nutrient losses.
Historical base fertilizers
When it comes to base fertilizers, calcium nitrate [Ca(NO3)2] – also known as Norwegian Saltpeter – has historically been widely used in both agriculture and horticulture. Routinely added by growing media manufacturers to substrate mixes, it is there to provide a nitrogen (N) source to help stimulate good early plant growth.
Relatively inexpensive, calcium nitrate is a commodity ingredient which can provide a supply of N for up to 3-4 weeks. However, the nitrate ions are negatively charged and highly soluble. As most soils and growing media substrates – including peat – are negatively charged, Ca(NO3)2 can be quickly leached; a particular problem with substrates that are difficult to wet-up, ie requiring lots of water.
These issues are further exacerbated in peat-reduced and peat-free growing media containing wood-fibre. N reserves tend to be depleted by the biologically active microbes, that take the ions up themselves; meanwhile these substrates tend to be more water repellent, ie have a lower water holding capacity, which increases leaching potential. Of course, the inclusion of a quality wetting agent in the growing media mix, such as H2Gro, can help mitigate this.
Two other commonly used sources of N in horticulture and agriculture are urea [Co(NH2)2] and ammonium nitrate. Compared to calcium nitrate, urea is formed of a longer chain; slower to break down, the leaching risk is reduced. However, this process requires biological activity and in cold temperatures can proceed too slowly to be effective.
Ammonium nitrate containing positively charged NH4 ions, and negatively charged NO3 ions. High levels of NH4 can cause damage to young plants. The use of ammonium nitrate has been restricted due to its oxidising effect and potential use in explosives.
Precision Nutrition
In a bid to stay one step ahead of likely future legislation in regard to N leaching, ICL has taken the necessary steps to replace Ca (NO3)2 in all its growing media mixes.
CRFs and quality slow release fertilizers can be used to help regulate nutrient levels through the entire plant’s growth cycle. A world leader in the development of CRFs and slow release fertilizer technology, ICL has recently replaced Ca(NO3)2 with two new products – Osmoform High N and Osmocote N.
Our two new base fertilizers promote higher nutrient efficiency in the early stages of plant growth, while being better for the environment due to reduced leaching.
For short term crops, Osmoform High is a slow release fertilizer with a long chain that breaks down slowly and is not water soluble. While the N release is influenced by temperature, microbial activity and humidity, Osmoform High N breaks down steadily over an 8-10 weeks period making it ideal for bedding crops and some perennial and container grown nursery stock.
The fine granules are easily incorporated into growing media mixes and the 7.5% urea is readily available, generating a quick response in the plant. Meanwhile, the 30.5% Urea formaldehyde becomes available more slowly as it has a longer chain.
For longer term perennials and container nursery stock, ICL has developed Osmocote N (+K) which is releases over 5-6 months. Containing 36% fully coated Nitrogen enriched with 5% potassium (K), it is suitable for peat-reduced substrate to buffer N immobilisation and reduce leaching.
Another useful product is Osmocote CalMag. This not only supplies supplementary N over 3-4 months, but has the added benefit of containing calcium and magnesium – elements often lacking in peat reduced media and soft water systems.
For a complete precision nutrition programme, these new base fertilizers can be combined in growing media mixes with other products from the extensive Osmocote range to deliver exactly what the plant needs throughout its growth cycle on the nursery, in the retail outlet and beyond.
Fertigation practices
As the need to protect the UK’s precious water resources becomes ever-more pressing, ornamental growers are being encouraged to be mindful of their fertigation practices.
With less than 16% of England’s waters given the EU’s Water Framework Directive’s ‘good’ water quality status or higher, growers need to be mindful of the impact their growing practices can have on their nurseries’ surrounding environment.
Currently the Nitrates Directive limits the volume of nitrates that can be applied to certain crops. It protects nitrate vulnerable zones (NVZs) – areas designated as being at risk from agricultural and horticultural nitrate pollution.
At present, plants grown under protection, such as in glasshouses, are exempt from NVZs. However, the remit could be extended – particularly now there is increasing emphasis on environmental issues. This could be further compounded by the fact many UK ornamental nurseries are situated in South East England – an area the Environment Agency has classified as being ‘water stressed’.
In a bid to get ahead of the curve, AHDB Horticulture is undertaking a couple of projects relating to nutrient application and water use. They aim to develop best practice and optimum fertiliser application regimes for all protected and outdoor-grown nursery stock categories.
Part of the research is determining the best practice for managing groups of plants – including holding plugs, nutrient management in different growing media and the nitrogen application applied to field-grown narcissi. The other project is developing nutrient management guidance for hardy nursery stock (HNS).
The results of these two projects – which are trialling both controlled released and liquid fertilisers as well as combinations of the two – will be used to establish helpful guidelines for inclusion in the The Nutrient Management Guide – the fertilizer ‘bible’ otherwise known as (RB209).
This balances the benefits of fertiliser use against the costs – both economic and environmental.