The warm winter has many thinking about getting out in the garden, but hold your horses. Winter weather could be just around the corner. I thought I would talk about the major plant nutrients and their role in the growth of plants in the garden and landscape. I recommend taking a soil test, as this is a way to see what nutrients you have in your soil’s bank account.
Remember one primary rule about plants and soils: Changes are generally gradual and slow. If excessive fertilizer is applied, the plant will die from fertilizer burn to the root system.
After a fertilizer application, time is needed for the material to be converted into a usable form by the plant. The solubility of the product used will also govern just how fast it moves into the soil and becomes available to the root system. In some cases, chemical changes are necessary before the fertilizer elements are in a form that the roots can absorb.
Fastest growth response probably comes from the various forms of nitrogen. Most sources are water-soluble. They move quickly in the soil water and undergo little change before being absorbed by the root system.
Nitrogen enters the plant as a nitrate or ammonium. Plants benefit immediately if nitrogen is applied as ammonium nitrate, ammonium sulfate or potassium nitrate. Organic forms of nitrogen generally rely on either chemical or bacterial action to convert the nitrogen into a useable form. Organic forms react slower but often last longer in the soil.
Phosphorous in fertilizer is present in a soluble form. As soon as it is applied to the soil, calcium reacts with it to form a low soluble phosphate material. The phosphate is then released into the soil solution where it is absorbed by the root. Because phosphorous has low solubility and limited mobility in soil, it is essential to spread phosphorous fertilizer before planting.
It is possible to add phosphorous fertilizer to a soil a number of years before you actually begin to see results. After absorbing the phosphorous, the soil holds it from plant roots or releases it back very slowly.
Regular soil tests of a garden area may call for the same amount of phosphorous fertilizer for a few years in a row until the soil’s needs have been satisfied. After that point, applications should decline.
Potassium differs from phosphorus in that it is soluble and mobile in the soil solution. Like nitrogen, it is subject to leaching from the soil. Soil tends to bind potassium on its clay particles with an electric charge. The potassium has a positive charge while clay carries a negative charge, and the opposite charges weakly attract each other.
Potassium is needed in lower amounts than other elements. Therefore, it is often easy to overapply potassium. A soil test will definitely help prevent overfertilization.
You can go to the following site to get information on Penn State Soil Test Kits: www.aasl.psu.edu/ssft.htm, which are available at the County Extension Offices for $9. Bill Lamont is a professor and extension vegetable specialist in the department of horticulture at Penn State and can be reached by email at wlamont@psu.edu.
