Published on 04/03/03

Scientists focus on phosphorus fertility problem

By Brad Haire
University of Georgia

Farm crops worldwide have a tough time getting enough phosphorus for healthy growth. An international guest scientist at the University of Georgia is looking to solve this problem with a common food item.

To grow, plants pull elements from the soil through their roots. Phosphorus is one of the hardest elements for their roots to soak up, especially in acidic tropical and subtropical clay soils, like those of Georgia and Kenya.

This is due to chemistry and how phosphorus interacts with other elements in the soil, said Charles Gerroh, a soil scientist from Kenya conducting research at the UGA College of Agricultural and Environmental Science campus in Tifton, Ga.

Common concern

"Phosphorus availability to plants is considered a major soil fertility problem around the world," he said.

Gerroh is head of the horticulture department at Maseno University in Kenya and a Fulbright scholar working with Gary Gascho, a UGA CAES crop and soil scientist.

The Fulbright grant program was established in 1946. Sponsored by the U.S. State Department, its mission is to increase understanding between the United States and other countries through the exchange of people, knowledge and skills.

Phosphorus, Gerroh said, is essential for healthy plant growth, especially when the plant is young. Phosphorus helps roots develop and gives a plant a good head start.

It's one of the three major fertility elements, along with nitrogen and potassium. Depending on conditions, it's the most expensive fertilizer element farmers apply.


The study of soil fertility can be complicated. But to put the phosphorus problem simply, it doesn't move through the soil as other elements do.

Phosphorus can become fixed in a form that's not easily accessible to plants. If it's not applied directly around a plant's root area, the plant has little chance of getting it into its system.

"Only about 5 to 10 percent of the phosphorus in low-pH soil is able to be used by plants," Gerroh said. Plants can access and use 50 percent to 60 percent of the nitrogen applied in the soil.

But another element, silicon, holds the answer, Gerroh said. Silicon can interact in the soil to make phosphorus more available to a plant.


Using silicon this way is nothing new, he said. Several Asian countries are doing it. The difference is Gerroh's silicon comes from rice.

Rice hulls, generally considered trash after rice processing, have a large concentration of silicon. Gerroh is working to find the best way to get and apply this form of silicon as a soil amendment to fix, or unfix, the phosphorus fertility problem.

Gascho has worked in the Southeast using silicon as a potential solution to the fertility problems here. This is one reason the two soil scientists have joined forces through the Fulbright program.

Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.