Farmers can use three basic strategies to meet the phosphorous requirements of their crops; find other local sources, reduce the need, and improve the availability of the phosphorous that does exist. Two major alternative sources are animal manure and local rock phosphate. Cattle manure usually ranges between 0.2% and 0.4% P2O5.
Rock phosphate deposits exist in several developing counries including Tanzania Malawi, Senegal, Mali, Canary Islands and Peru. Materials are of various compositions and have very different solubilities. Historically, these materials have been treated with acids to concentrate and make the phosphorus more available. However, research in Senegal, Mali, Tanzania, Peru and Australia has demonstrated that ground rock phosphate applied to tropical soils can often have a dramatic impact on their phosphorus status.
Other researchers have investigated low cost, biological methods to make the rock phosphate more soluble. Researchers in India have had good results when they added the rock phosphate while starting compost piles. Other researchers have found exciting and dramatic associations between phosphorus absorption and a group of fungi called vesicular arbuscular mycorrhizas (VAM) that infect plant roots.
Finally, plant breeders have had success breeding plants that have increased ability to absorb phosphorus, particularly in low phosphorus soils. Phosphorus is a relatively immobile nutrient in the soil. Hence roots generally are only able to absorb directly phosphorus which is within 10 mm of the root surface. By increasing the root mass in low phosphorus environments, selected plants are better able to extract the low levels of existing nutrient.
While all of these alternatives offer hope for the farmer in the developing world, we would researchers to increase their effort in this important area.