Seasonal pattern of nitrate-N losses through leaching in orchards

Project aim: To monitor nitrate leaching during the growing season in intensive pear, apple and cherry orchards under different nutrient management systems.

The adoption of high density orchard planting in UK will increase reliance on irrigation to maintain or improve yields against a backdrop of higher summer temperatures and decreasing water supplies. Broadcast or foliar fertilizer applications have been traditionally used to improve or sustain the nutrition of deciduous orchards in UK, although these approaches are often replaced by fertigation in high density irrigated orchards. The major fruit tree growing regions are in areas designated as Nitrate Vulnerable Zones (NVZ’s) and growers must reduce their inputs to comply with legislation (The Nitrates Directive Action Programme). Growers farming in NVZs are audited by the Rural Payments Agency and must be able to justify nitrogen applications, the relationship between yield and N applications, and prove that industry ‘good practices’ are being followed. Fruit trees recover only about 20% of the applied nitrogen fertiliser. The effective rate of nitrogen fertigation in orchards is also influenced by irrigation scheduling, as excess water can leach nitrogen below the root zone.
Amounts of nitrogen leaching and runoff have not been extensively quantified for orchards in the UK. Quantifying nutrient inputs and outputs from orchards will help to identify potential nutrient excess or shortage, will improve nitrogen use efficiency and decrease fertiliser costs.