Container Nursery Stock (CNS) growers face many production challenges and with the recent introduction of the Water Framework Directive, Nitrogen leaching can be added to the list. Technical Area Sales Manager Sam Rivers provides a technical overview of nutrient leaching in CNS production and explains how controlled release fertilizers (CRF), such as Osmocote, can help reduce the potential risk.
Nitrogen (N) is a key element of many fertilizers. The frequency of fertilization and irrigation can contribute to high levels of N leaching and runoff, especially in CNS production. Over a period of time this can affect local surface and ground water quality, potentially contributing to water eutrophication causing low oxygen levels in rivers from excessive algal growth, impacting on fish life and human health. Uncoated N fertilizers also have the potential to be volatilised as ammonia gas, or to be lost to the atmosphere as nitrous oxide, - posing serious risks to the environment.
Nitrogen in fertilizers
Plants’ requirement for N is greater than any other element, due to its importance in growth and development. Fertilizer formulations commonly include N in the forms of ammonium, nitrate and urea. Ammonium and nitrate are directly utilised by the plant, while urea has to be hydrolysed by soil microorganisms into ammonium before being directly absorbed. Furthermore, ammonium can also be nitrified by soil bacteria into nitrate.
Nitrate is highly mobile in soil due to its inability to bind to most substrate particles. In water soluble fertilizers it is the main nutrient ion lost from the soil through leaching.
Leaching reduction strategies
Growers already employ numerous practical strategies to help reduce leaching during CNS production such as utilising different fertilizer regimes, improving the water holding capacity of the growing media and implementing different irrigation practices.
Understanding the N requirements of different plant species is crucial in developing appropriate fertilization and irrigation regimes. ICL’s Angela Web 2.0 specifically maps the optimal nutrition required for different plant species to ensure the correct amount of fertilizer is applied. This minimises the risk of over feeding, which could lead to unnecessary leaching. Improving substrate properties such as increasing water holding capacity by adding products such as H2Gro can also reduce the incidence of leaching.
Why CRFs help reduce leaching
Encapsulating nitrate in CRFs helps to reduce mobility and thus leaching. Other highly water soluble compounds such as urea can also be used in CRF`s to help reduce the risk of leaching and plant scorch. The speed and efficacy of nutrient release is determined by the quality, thickness, coating type and ultimately the quality of the coating process.
Nutrient release in the highest quality CRFs, such as Osmocote, is activated when water penetrates the granule’s exterior coating. As osmotic pressure builds within the CRF, the granule swells and the nutrients are gradually released at different rates depending on the product longevity. The amount of release rate is only affected by temperature.
In poorer quality CRF`s the osmotic pressure can surpass the membrane resistance causing the coating to crack, releasing the nutrients days, rather than months. This can lead to high soil electrical conductivity (EC), which is detrimental to plant health and can result in increased leaching. ICL’s superior production and coating technology, which has been developed over five decades, ensures this cannot happen with Osmocote. The release pattern has been developed to match plant requirements, ensuring less release at the start and more later when plants need it.
So, quality CRFs help reduce the risk of leaching as they gradually release nutrients at different rates to match different plants’ needs and reduce the mobility of nutrients within the soil. This ultimately helps to reduce the environmental impact of CNS production and improve plant quality.