Processors and Growers Research Organisation

Vining peas: The effect of soil phosphate levels on rhizobial population

Project summary
Phosphorous is important for vining pea root growth as well as an essential nutrient for the formation of nodules and nitrogen fixation. This project investigates the number of viable soil rhizobia in soils with different Olsen P indices and the impact of starter fertilisers on root nodulation, rhizobia and yield. The more rhizobia there are in the soil, the greater potential for root nodulation, and the greater the amount of fixed nitrogen available to the pea plant. Therefore it is essential to maintain soil conditions for rhizobial growth and survival. This project utilises vining pea plots grown in soil with different Olsen P indices and is an excellent opportunity to study rhizobia in these plots. Large scale plots will be used to identify the benefits of starter fertilisers on rhizobia and pea yield. Agronomy advice can then be given to growers to increase soil health and target nutrient applications to where it can be best utilised.
Benefits to industry
Vining peas rely on the symbiotic relationship with Rhizobia to provide nitrogen to the plant which is vital for growth and yield. A result of this relationship is a crop without the need for nitrogen applications and an increase in soil nitrogen for the subsequent crop. Rhizobia are soil dwelling and in the presence of their host form root nodules and fix atmospheric nitrogen in a form the plant can use. Therefore a healthy soil and a good root system are essential for nodulation and nitrogen fixation. Phosphorous promotes good root growth and is essential for root nodulation to occur. In addition to this, phosphorous is also required for nitrogen fixation. However phosphorous can be a pollutant and applications need to be targeted to when they can be best utilised by the crop. Soil health is vitally important to the productivity of farmland and this requires maintaining the soil microbe populations. This project will study the impact of soil phosphorous on Rhizobia and root nodulation. If phosphorous is limiting, then yields may be reduced as a result. Starter fertilisers are applied at drilling with the seed and provide an easily assessable nutrient supply, including a source of phosphorous. However, some of these contain nitrogen which can inhibit nodulation. This trial will look at root biomass and nodule formation after application of fertilisers with and without nitrogen and find out the effect of the application on yield over a two year period. The results will be disseminated to growers via PGRO open days and technical bulletins and will be directly usable by them to influence their fertiliser use. The results have the potential to impact fertiliser use not only to increase vining pea yield but also to increase and maintain soil health. By finding out if nutrients are limiting and the best timing for application, there is the potential to influence yields without increasing pollution levels.

Sector: Horticulture
Project code: FV 428
Date: 01 February 2014 - 31 January 2016
Funders: AHDB Horticulture
AHDB sector cost: £28,088
Project leader: DR KERRY MAGUIRE, PGRO









About this project
Aims and objectives
Project aim(s):
To identify difference in the relative numbers of Rhizobia in vining pea crops grown on soils with varying phosphate levels.
To assess the impact of granular fertiliser application at drilling on rhizobial numbers and nodule counts and the effect on quality and yield of the vining pea.
To provide advice to growers on ways to maximise nitrogen fixation in the pea crop
Project objective(s):
a) To quantify in relative terms the number of soil dwelling rhizobia in soils with differing levels of soil phosphate.
b) To quantify in relative terms the number of soil dwelling rhizobia before the pea crop is sown and at harvest.
c) To quantify in relative terms the effect of applying starter fertilisers (containing phosphorus with and without nitrogen) on nodule formation and yield.
d) To include this information in dissemination activities of project FV 380. This includes advice directly to growers at PGRO open days and Road shows.
All of the objectives rely on the use of the MPN method of enumerating viable free living rhizobia. This is a well-documented method. Objective a) is partly independent of the success of the 2014 field trial as the soil samples for 2012 and 2013 are available. Part of objective a) (2014 sampling) and objective b) relies on the success of the 2014 field plots established as part of project FV 380. Objective d) stands alone from the above objectives as this will be set up in a commercial vining pea field.