Can indigenous microbes release phosphorus to crops?

An innovative new project aims to select and use indigenous, phosphorus-solubilising fungi and bacteria to increase the yield of crops by reducing phosphorus deficiency in the tropical soils of Cameroon. Isolation and testing of the microbes in the laboratory at SCRI will be followed by trials in Cameroonian fields.

The background - phosphorus in short supply

Photograph of croplands in the dry season (Geoff Squire)Agriculture is the dominant sector in most sub-Saharan countries of Africa. It provides employment for most of the rural population and makes an important contribution to GDP, GNP and foreign exchange. Agricultural productivity is low and the people depending on agriculture are generally poor. Many of the soils are mostly low in fertility (for example, photograph right), particularly in phosphorus (P) and nitrogen, and need to be fertilised for adequate yield.

Fertilisers are expensive, however, and phosphorus, which is essential for plant growth, is becoming in short supply globally. Phosphorus can be tightly bound in soils and not be available to plants, while P added as fertililser can be washed out of soil in heavy rain.There are also increasing problems to health and environment associated with the use of fertilisers and other synthetic chemicals. The need to reduce the amount of P applied while maintaining or increasing crop yield has stimulated the search for biological solutions to the phosphorus shortage.

The possibilities - microbes as biofertilisers

Photograph of maize crop (Geoff Squire)Among possible options is the use of native beneficial microorganisms to regulate the flow of P from soils to crops. The objective of this study, which is targeted at soils in the sub-Saharan country of Cameroon, is to identify and characterise efficient phosphate-solubilising microorganisms that improve the mineral nutrition of plants. We are examining whether the wide range of natural microbes in Cameroonian soils could be used to improve the amount of P that is available to crops. Microbes get P from soils for their own purposes, so could these natural abilities be harnessed? For example, some soils have a natural high P content and the capacity to absorb P fertiliser, but the P is locked up and much of it is unavailable to plants. Such problem soils are readily identified since they tend to be high in aluminium and iron and low in pH (acid). However, there are indications that the soil microbes could regulate the release of P in soils so that it becomes available to growing crops when they need it. If the microbes could be identified and isolated, they offer possibilites as biofertilisers, to be applied to the fields along with seed or fertiliser.

The study - isolating, characterising and testing the microbes

Photograph of a fungal colony (centre) spreading into a growth medium (blue)The search is now on for microbes that could act to regulate the release of P from soils at a rate and time most useful to crops. Soil is being sampled from the highly diverse regions of Cameroon, from the coast of the Atlantic ocean over hundreds of kilometres inland to the edge of the Saharan drylands. The microbial communities in these soils are being characterised by their DNA profiles which can then be referenced against the physical and chemical properties of the soils. The microbes are tested in a variety of ways for their ablity to release P. The first test is in petri dishes (photograph right). The microbes are placed in the centre of a medium, here a turquoise colour, that contains P in different chemical forms: the growing colony forms  a halo-zone, the size of which indicates how successful the micobes are at releasing the phosphorus from the medium for their own growth.

Photograph of the experiment in the SCRI glasshousesThe next stage in the investigation is to grow plants in soils innoculated with promising microbial communities to see if the microbes actually make the P available to the plants. As testing material, the study is using barley plants grown in containers in one of SCRI's research glasshouses (photograph right). The plants are grown in an experimental design that includes different levels of added phosphorus and different microbial innoculents mixed with the soil. The plants need daily attention and careful watering to ensure uniform soil conditions.

If suitable microbial communities can be identified, they can be isolated and reproduced, in preparation for field testing in Cameroon.

Contacts and funding

This research is conducted by Henri Fankem from the University of Douala, Cameroon, who is on a ten-month visit to SCRI supervised by Tim George and Tim Daniell from the EPI Programme.

African Fellows Programme logoHenri Fankem is funded by the Rothamsted International African Fellows Programme, a 'scheme that aims to facilitate capacity building and training in agricultural science by providing sub-Saharan African scientists with Fellowships to work with a research group at a European laboratory.'