Nutrient management recommendations for field grown hardy nursery stock (HNS)

What are the recommendations?

The SNS index for each field can be determined either by the field assessment method using records of soil type, previous cropping and excess winter rainfall, or by the measurement method using measurement of soil mineral N (SMN), for more information see RB209 via the AHDB RB209 webpage.

Use this information as a basis for nitrogen application decisions and seek advice from a FACTS qualified advisor to help with interpretation of the results. Under low soil mineral N (SNS Index 0) or modest N (SNS Index 2 / 3) indices, growth of Betula pendula, Carpinus betulus and Crataegus monogyna transplants and seedlings do not respond to additional fertiliser nitrogen (N). Review whether reductions in the use of N fertiliser can be made.

Soil analysis to determine levels of P, K and Mg should be taken at least every 5 years and ideally every 3 years. Aim to keep soil at P Index 2 and K Index 2. There may be no need to apply additional fertiliser P and K above these target soil indices.  Crop offtakes of P & K were calculated for the transplants in the nutrition trials in 2023 (Table 1).

Table 1: Assessment of crop P and K offtake for transplants*

*Crop offtakes should be considered to determine if any additional P & K is required to maintain levels at the target index. Crop offtakes were not done for N as the data is of limited use as it is necessary to ascertain how much N has leached when making N application decisions.  The Soil Nitrogen Supply (SNS) index for each field can be determined either by the Field Assessment Method using records of soil type, previous cropping and excess winter rainfall, or by the measurement method using measurement of Soil Mineral Nitrogen (SMN).

Growers could benefit from both fertiliser cost savings and reductions in carbon emissions associated with reduced fertiliser use. Reducing the use of synthetic nitrogen fertilisers is a simple and effective method of reducing carbon emissions associated with the production of field grown HNS, this approach will help the horticulture sector to reach net zero by 2050.

Understand your plant nutrient needs

Research indicates that the Nitrogen requirements of some tree and hedging species are lower than previously thought. Evaluate whether other species of field grown HNS respond to your standard nitrogen applications and where possible make reductions in applied rates of N in a measured way on a proportion of your crops initially.

Monitor growth where rates of N are reduced, if crop growth is negatively impacted and the crop is responsive to N the crop should respond quite quickly to any corrective N applications (if necessary).

How do I monitor nutrient supply?

Regular soil analysis should be carried out every 3 – 5 years for P, K and Mg.

Soil mineral nitrogen testing is a useful method of determining soil nitrogen reserves; results should be taken into account before deciding to apply additional N.

An atLEAF hand held chlorophyll meter was used in our trials to help monitor plant nutrition, the device’s output can be correlated to leaf tissue N level from tissue analysis, and results can be mapped over time for individual species. In these trials, chlorophyll content was correlated to leaf tissue N.  Monitoring leaf chlorophyll content in this way, year on year, will build up a database of information that will help to build grower experience and knowledge, enabling them to identify trends relating to the plant nutritional status in their crops. A chlorophyll meter can be used to detect trends within the nutritional status of the crop which can enable growers to amend fertiliser applications in advance of visual symptoms of nitrogen deficiency, giving growers the confidence to reduce the use of N fertiliser through crop monitoring. The FieldScout GreenIndex iPhone application has also shown potential for monitoring the nutrient status of a crop in real time.  As with the atLEAF device, correlation of the device output to leaf tissue N levels can be mapped over time. Leaf sap testing can also be considered for crop nutrient monitoring and sap can be tested using a nitrate strip test and LAQUAtwin nitrate device.

EC monitoring using a hand held EC meter is also useful for identifying trends associated with fertiliser use.

Although the data from hand held devices can vary from data produced through formal laboratory analysis, it can be useful for building up a picture of trends over time which growers can respond to where unusual values are found and/or when a crop is found to develop nutrient deficiency or excess symptoms. 

Crop nutrition monitoring should also include water, soil and plant tissue analyses; all of which can build up a set of data over time to refer back to when taking decisions over crop nutrient management. 

Further information can be found from the AHDB factsheet ‘Nutrition of container-grown hardy nursery stock’ for general guidance and from ‘Sampling methodologies and analysis interpretation for growers of hardy nursery stock’ for more information on monitoring EC.

What other crop nutrition monitoring could I be doing?

Crop nutrition monitoring helps with correct management of nutrient supply suited to the crop and helps with early identification and correction of deficiency or toxicity symptoms.

Leaf tissue analysis. Tissue analysis should be undertaken to build up a data set to use in conjunction with monitoring using a chlorophyll meter such as the atLeaf device. It can also be used to help diagnose nutrient disorders, sampling from both plants with suspected nutritional problems and unaffected plants.  There are limited published standard values for specific crops and cultivars, but the AHDB Factsheet ‘Sampling methodologies and analysis interpretation for growers of hardy nursery stock’ provides a summary of nutrient values from a range of woody plant species as a general guide.