The soil nitrogen supply (SNS) index is an integral part of decision-making for fertiliser applications.
The aim of the joint HGCA and HDC project FV 345b was to develop best-practice guidelines for SNS assessment. It addressed when growers should take samples, the correct sampling depth, transport to the laboratory, analysis of samples, consistency of lab results and how results should be interpreted.
The greatest benefits can be achieved where samples are taken from fields with high residues, such as intensively cropped brassica rotations or where regular inputs of organic manure have been made. Samples should be taken as close to the planting date as possible after nitrogen has mineralised from previously incorporated residues.
Soil samples should be taken in 30cm depth increments to 90cm and care exercised to avoid contamination between depths. A minimum of 15 sampling points are needed. Samples should be chilled to 2-4 degsC and analysed within 48 hours. A decision-support tool can be used to interpret results when mineral nitrogen is not evenly distributed between the soil layers.
An HDC fact sheet (09/12) was published this summer providing advice on how to measure and interpret soil nitrogen for vegetable crops using the fertiliser manual.
Date for your diary
6 December: Field vegetables panel meeting, Stoneleigh Park.
Horticultural Development Company
For details on all HDC activity, visit www.hdc.org.uk