Phosphorus for Tomato Plants
- Tomatoes are in the nightshade family of plants.Jupiterimages/Comstock/Getty Images
Tomato plants respond especially well to phosphorus, as Ohio State University notes. Phosphorus is one of the three main nutrients that manufacturers include in commercial fertilizers -- the other two being nitrogen and potassium. Adding phosphorus to the soil can help stimulate tomato plant growth, as the nutrient allows plant cells to transfer energy for biochemical reactions, like photosynthesis. - Like all plants, tomato plants can only utilize phosphorus that is in phosphate form. Phosphates are chemicals that occur naturally in soils and in bodies of water. In a phosphate molecule, each phosphorus atom has four oxygen atoms surrounding it.
More specifically, tomato plants can only absorb inorganic phosphates; or phosphates that are not bound to carbon molecules. The plants are able to obtain these phosphates naturally through the phosphorous cycle. During the phosphorus cycle, minerals and solidified animal dung breakdown -- due to erosion or other factors -- and release inorganic phosphates into the soil. Plants absorb these phosphates through their roots and convert them into organic phosphates. Animals, in turn, can eat the plants and "steal" their organic phosphates. When animals excrete these phosphates as dung, microorganisms feed on the dung and convert organic phosphates back into inorganic phosphates. This process is known as mineralization. - According to the University of Minnesota, phosphates in the active P pool are the primary sources of phosphorous for plants. The pool contains three types of phosphates: inorganic phosphates that are connected to small soil particles; organic phosphates that can easily undergo mineralization and will soon become inorganic; and semi-soluble, solid phosphates that have reacted with aluminum, calcium or other elements. All of the phosphates from the active P pool slowly but consistently provide tomato plants with soluble, usable molecules of phosphorus. As the University of Minnesota notes, an acre of land can contain up to a few hundred pounds of active P pool phosphates.
- Tomato plants absorb phosphates in the solution P pool much more rapidly than in the active P pool. For this reason, the solution P pool is much smaller, and will typically account for less than a lb. of phosphates per acre of land. According to the University of Minnesota, the majority of phosphates in the solution P pool are water-soluble, inorganic phosphates known as orthophosphates. Orthophosphates occur as salts or esters, and are the most basic types of phosphates. They occur most commonly in the compound HPO42-, in alkaline soil conditions, and in the compound H2PO4-, in acidic soil conditions. Tomato plants deplete solution P pool phosphates quickly, but fortunately, the active P pool is able to replenish it continuously.
