Coriander: Potential management options for yield decline


CP 117a - Coriander: Potential management options for yield decline

Start Date: 
Completion Date: 
Project Leader: 
Ian Singleton, Edinburgh Napier University
CP 117a
Industry representative: Robert Gibbs
AHDB Horticulture Cost: £22,644 
SummaryCoriander yield decline is a major problem facing the UK herb industry. Information from growers suggests that coriander yield declines by over 50% when the crop is planted in successive years in the same field. Yield decline persists up to 8 years and has been observed throughout the UK. Compounding the problem, growers are often limited by the amount of available land for crop rotation making commercial coriander production extremely challenging. At present the cause of coriander yield is unknown and growers urgently require further information both on the cause of the problem and on potential remedies. Based on a survey of growers (carried out in 2015 as part of the AHDB funded project CP117) the phenomenon occurs throughout the UK in a range of different soil types used to grow coriander. Interestingly coriander growers in Southern Spain do not observe any signs of yield decline in their crops (despite repeated cropping on the same soil) and it is suspected this is due to the soils being ‘solarised’ over the summer period : a method that raises soil temperature and dries soil probably resulting in partial soil sterilisation of the soil and a change to the microbial community present.

Causes of yield decline: Yield decline (or ‘soil sickness’) is an increasing global problem and has been observed in a wide range of crops including oil seed rape, potatoes and wheat (Bennet et al., 2011). Yield decline is a complex issue and several factors have been suggested as a cause including soil microbial populations (e.g. build up of specific pathogens or deleterious rhizosphere populations), plant autotoxicity and soil compaction (Bennet et al., 2011). In the case of coriander, there is no published information on the cause of yield decline and growers have not specifically observed any potential pathogens. Plant growth is stunted and yields are reduced, but this does not seem to be related to root infection. In the specific case of early season cold, wet soils Pythium root infection has been observed but this is not considered to be related to the ‘normal’ yield decline phenomenon (Gibbs, pers comm). A detailed literature search on coriander has demonstrated that this particular crop is understudied, Given this background we envisage that any information derived from this project would be of benefit to the growers.

Previous unpublished findings : Our previously AHDB funded research on coriander yield decline (CP 117, 2014-2016) has shown that the phenomenon can be reproduced under controlled greenhouse conditions using different coriander varieties and soil types. We also believe that root autotoxicity is not the main cause of yield decline based on the results of an experiment where coriander roots were buried in fresh soil and a coriander crop grown in this soil : no yield decline was observed. Detailed analysis of soil microbial communities using next generation DNA sequencing methods appears to show that no single microbe (bacterial and/or fungal) appears to cause yield decline and that different soil communities (from different soils) can produce the same plant response i.e. decrease in above ground biomass. One hypothesis from these observations would be that coriander growth under current horticultural production conditions (minimum tillage) results in the formation and persistence of a soil community that has the ability (overall function) to reduce coriander yield. Therefore it is possible that a perturbation of this community e.g. by deeper soil tilling after coriander growth, soil amendment, desiccation or biofumigation may prevent or reduce yield decline.Given this background, the aim of this project will be to examine potential soil management strategies that change the soil microbial community present in the hope of reducing the yield decline effect. This will be a ‘proof of concept’ approach to demonstrate that methods capable of changing the soil microbial community are able to prevent or reduce coriander yield decline. 

Aims: The overall aim of this project is to investigate potential soil management methods to prevent coriander yield decline that are aimed at altering the soil microbial community. The work will concurrently examine several methods for growers to consider applying when growing coriander commercially. 
1. Assess the effect of ‘deep’ ploughing on coriander yield decline
2. Assess the effect of adding a soil amendment on coriander yield decline
3. Determine if soil drying/desiccation after coriander growth reduces yield decline
4. Determine if a commercially available biofumigant reduces yield decline.