Plant, Soil, Fertilizer Relations

Plants must have chemical nutrients to live, grow, and reproduce. The soil is the storehouse for plant nutrients. If the soil's natural content is low in any required nutrient, the nutrient can be added through chemical fertilizers or soil amendments.

Plants get nutrients through their roots. The plants contain complex uptake and distribution systems that move essential materials to every living cell. Growth and nutrition of all plants depend on an adequate supply of nutrients distributed where needed.

Plant nutrients can also be absorbed through openings in leaves and stems, and sometimes it is practical to apply them in this manner.

Nutrients dissolved in water enter plant roots and circulate throughout the plant. A moist but unsaturated soil is desirable. For plants to get nutrients, the nutrients must be in the root zone and must be in a soluble form.

Nitrogen deficiency is usually the most limiting to plant growth. It is an essential part of proteins and amino acids in protoplasm and nuclei of all living plant cells.

Nitrogen is usually concentrated in fast-growing areas such as tips of shoots, buds, and new leaves. It is often called the growth element. Adequate nitrogen encourages a dark green color, rapid growth, and profuse fruiting. Excess nitrogen causes excessive vegetation and reduces fruiting.

Pale greenish yellow leaves and stunted plants indicate a nitrogen deficiency. Older leaves are affected first, and tissue along the leaf midribs will eventually die.

Phosphorus provides the "energy currency" of all living cells. Adequate phosphorus encourages root development, growth, and fruiting. It is essential in activation and regulation of certain enzyme systems. Phosphorus deficiency causes slow growth and stunting, and the leaves turn dark green or blue green.

Phosphorus moves slowly in the soil. Highly water-soluble or weak acid soluble sources are needed for quick plant response.

Potassium increases plant vigor and strength, reduces lodging, encourages early root formation, and increases resistance to certain diseases. Inadequate potash results in spindly, poorly developed plants that lodge easily and are more susceptible to leaf and stem diseases. Severe deficiency causes leaf burn along the margins from the tip, beginning with the lower leaves and moving up the plant.

The pH of a soil indicates the degree of acidity or alkalinity, not the amount. For example, two sandy soils with the same pH require about the same amount of lime to raise the pH one unit. A clay soil, however, with the same pH may require several times as much lime as the sandy soil to raise the pH one unit. In addition, soil testing laboratories run special tests to measure reserve acidity in order to make accurate recommendations for lime or other soil amendments.

The pH of the soil solution greatly influences nutrient availability to plant roots. Although extremely acid soil solutions may injure living plant tissue, soil acidity in nature is seldom toxic to plants.

Top, filling in address on soil sample bag, which is sent to Pennsylvania State University lab for analysis, and results returned to gardener in printout form, above.

Certain elements such as aluminum and manganese found in large quantities in some soils may, however, become soluble to levels toxic to plant growth at a pH below 5.5. In the Southeast, the subsoils may be leached to the point that subsoil acidity actually reduces the rooting depth of certain plants. Soils having these properties are identified in soil surveys.

Plant species differ in the pH range at which they grow best. Most plants are at their best in a pH range of 6.0 to 6.5 if most nutrients are available in sufficient but not toxic quantities. Examples of plants that do well in acid soils are blueberries and Irish potatoes.

Soil pH can be changed by adding lime or sulfur to meet the pH requirements of the plant to be grown. Adding a liming material increases pH by reducing soil acidity. Adding sulfur increases soil acidity by reacting with water in the soil to form sulfuric acid, thus reducing soil pH.

Test for Fertilizer Needs One way to determine lime and fertilizer needs is to have the soil tested. Reliable soil testing services are available from both private and public laboratories throughout the Nation. Many land grant universities provide this service through the cooperative Extension service. Extension offices are located in each county and some cities.

Soil samples should be representative of the area they are taken from. Use the soil map as a guide for locating sample sites. Sample different soil types separately. Small garden areas should be taken as one sample and the crops to be planted listed. Soil testing helps take the guesswork out of lime and fertilizer programs.

Kind, rate, frequency, and method of fertilizer application are everyday questions of gardeners. The kind of fertilizer, type of plant, and soil and moisture conditions all affect these decisions.

The nature of the major plant nutrients and their movement within the soil is important. If placed on the soil surface, nitrogen moves rapidly into the soil with water, phosphorus moves in very little, and potassium moves fairly well into porous soils. Movement is mostly downward, but there is some upward and lateral movement in some soils as wetting and drying occurs. These features are discussed by kinds of soil in many soil survey reports.

Nitrogen is easily lost from most soils, so frequent small applications to the surface or shallow incorporation is advised. Watering will help speed response.

Phosphorus should always be placed in the soil before or at planting if practical. Potassium applied as a topdress or sidedress should be incorporated in the upper few inches. One application of phosphorus or potassium per crop or year usually is enough for most vegetable or orchard plants.

Many long-season vegetables and most orchard plants will need several applications of nitrogen.

Special liquid, mixed fertilizers for spraying the leaves of orchard and vegetable crops are available. They must be used in dilute solution, which requires several applications to provide enough plant nutrients for one crop. This is a good way to apply several of the minor nutrients such as boron, zinc, copper, iron, and manganese.

A soil survey and a soil test are a good introduction to your garden. They help you select the most suitable site. Through knowledge of soil properties you can learn to manipulate your soil for a wide selection of plants.