Agronomic Evaluation of Various Sources of Phosphate Rocks and Modified Products

A systematic program has been developed by IFDC to determine whether a phosphate rock is suitable for direct application as influenced by factors such as solubility of phosphate rock, soil properties, management practices, and crop species. When the conditions are not favorable for direct application, phosphate rocks can be modified by calcination, partial acidulation or compaction with water-soluble phosphate fertilizers to form cost-effective products, which can be agronomically effective. Examples of recent reimbursable projects on the agronomic evaluation of phosphate rocks and modified products include the countries of Tunisia, Jordan, Algeria, India, China, Australia, and Senegal.

Appropriate management practices to increase nutrient efficiency, e.g., liming, incorporation of crop residues, and use of biological nitrogen fixation, can improve soils with poor fertility (e.g., acidity, aluminum toxicity, low nutrients, and low organic matter). The basic and applied research conducted at the Headquarters provides the support to the agronomic field trials in developing countries.

IFDC has conducted research on the agronomic effectiveness of various sources of secondary and micronutrient fertilizers of calcium, sulfur, iron, and zinc. Factors affecting their fertilizer efficiency have been identified such as solubility of fertilizers, soil properties, and crop types.

Various nitrogen fertilizers can increase soil acidity after long-term application because of nitrification of ammonium in nitrogen fertilizers. IFDC compared and quantified the relative effectiveness in acidification of various ammonium-containing fertilizers such as ammonium sulfate, ammonium nitrate, and urea after a 3-year agronomic study.

It has been found that conventional soil tests developed for recommendation of water-soluble phosphate fertilizers are not suitable for phosphate rock and modified phosphate rock fertilizers. IFDC has developed a new soil test using iron oxide-impregnated filter paper strip (Pi test), which works well for both water-insoluble and water-soluble phosphate fertilizers in different types of soil. The Pi test can also be used to monitor potential eutrophication in aquatic environments due to surface run-off of sediments carrying phosphorus. (For more information on this work, contact Dr. Norman Chien--nchien@ifdc.org)

Use of Phosphate Rock for Canola Production on Neutral and Alkaline Soils

Many agricultural soils in Africa, the Middle East, and Central and Southern Asia are neutral and alkaline soils that are usually low in P, an essential nutrient for crop production. Application of expensive conventional water-soluble P fertilizers has not been widely practiced by resource-poor farmers. Many countries in these regions possess significant phosphate rock (PR) deposits. However, direct application of low-cost PR is not feasible for crop production in these regions because of high soil pH.

Recent IFDC greenhouse studies have found that direct application of PR alone or a mixture of PR and water-soluble P fertilizer can be agronomically effective for canola (rapeseed), which is a high-value oilseed crop, grown on neutral and alkaline soils because the canola's root can exudate two organic acids (malic and citric acid) to dissolve PR. These results have tremendous agronomic and economic implications for the use of indigenous PRs on the production of canola and similar crops grown on neutral and alkaline soils if they are verified under field conditions. (Contact: nchien@ifdc.org)

Inadequate intake of iron (Fe) is one of the main nutritional problems that affect human health, especially women, infants, and children in developing countries. Plant breeders have devised two strategies toward the solution. One is to breed genotypes that are more efficient to absorb Fe from soils and also to increase Fe translocation to grains.  The other is to develop genotypes that produce grains with low phytic acid that is known to reduce Fe bioavailability to humans. However, a successful plant-breeding program will require an effective fertilizer strategy to achieve the goal of sustaining or increasing crop yields with nutritional value.

IFDC has conducted several greenhouse studies on the use of low-cost calcined Fe-rich PRs as P and Fe fertilizers for different grain crops (wheat, barley, upland rice, flooded rice, and soybean) grown on alkaline soils in which P and Fe nutrients are limiting crop growth. It was found from previous studies that these types of fertilizers are effective P sources for upland and flooded rice in alkaline soils. The studies have also included the use of rice and barley seeds with low phytic acid developed by the U.S. Department of Agriculture (USDA) breeders and rice seeds with an Fe-efficient trait developed by IRRI breeders. A preliminary result showed that Fe density of barley grain was increased by 32%-38% whereas phytic acid was decreased by 40%-50% when a calcined Fe-rich PR was applied to an alkaline soil. More results will be obtained later. (Contact: nchien@ifdc.org)