Nutrient Deficiencies and Soil Fertility

Problem type: Environmental

Name of problem: Nutrient Deficiencies and Soil Fertility

Plant name(s): All plants

Symptoms / Characteristics:
Nutrient deficiencies in plants have various visual symptoms depending on which nutrients are lacking. Symptoms are generally similar from one plant species to another. Stunted growth is common but not easily detected. Leaves may change shape and/or color in a certain pattern to indicate a deficiency. Discoloration starting from leaf tips or margins and moving downward, or between the veins of the leaf, are common indicators of nutrient deficiencies. However, similar symptoms may also indicate environmental stress or other problems.

Nitrogen, phosphorus and potassium are the three nutrients required in the largest amounts for healthy plant growth. Deficiency symptoms for some major nutrients are as follows:

Nitrogen (N) - Reduced growth, yield and quality due to poor protein and chlorophyll production. Leaves turn pale yellow or tan before dying. Symptoms are more prominent on older leaves, as nitrogen is drained from older tissue to supplement new leaves, as well as developing flowers and fruit.

Phosphorus (P) - Stunted growth occurs, since phosphorus is essential for cell division and growth. Plant leaves turn darker green or purplish in colour, and older leaves may brown as they die.

Potassium (K) - Leaf margins appear scorched and leaf surfaces may have chlorotic (yellowing) spots. Potassium is important for proper functioning of the plant as a whole, including food production, respiration and structural strength. Plants may develop weak stems, collapsing easily.

Iron (Fe) - When iron chlorosis occurs, leaves become chlorotic (yellow) between the veins of leaves. The mid-rib and main veins remain green and interveinal tissue may become white or bleached looking. Severe deficiency will result in necrotic (dead) spots that will eventually kill the leaf.

Deficiencies can occur for a number of reasons, including insufficient water, which prevents the uptake of nutrients, poorly developed or damaged root systems or simply infertile soil. In addition, if one mineral element is lacking, or is too concentrated in the soil, it may inhibit the uptake of other elements.

Control / Preventions:
Soil tests are recommended to determine nutrient levels as well as pH levels in the soil. The pH level (acidity of soil) plays an important role in nutrient uptake. Soil structure is also a very critical factor, and determines how plants will grow and develop. Heavy soils, such as clay have a much greater capacity to hold water and nutrients than sandy soils. However, heavy soils lack proper drainage and air space, which can damage roots from lack of oxygen and reduce fertilizer uptake and plant growth. Amending soils with organic matter will increase water and nutrient holding capacity for sandy soils while providing more air space in heavier soils. As organic matter breaks down, nutrients become more available for plants to use.

The pH level in most soils should be around 6.0 to7.0 for optimal plant growth, although certain plants grow better in slightly acidic or alkaline soils. Soil pH values between 6.0 to 7.0 result in the greatest number of mineral elements being available for uptake by plants. The addition of lime will increase the pH, making it more alkaline. Adding sulfur will lower pH, making in more acidic.

A 20-20-20 bag of fertilizer represents the amount of N, P and K, respectively in the bag. These numbers change as nutrient levels needed throughout the growing season change. Organic fertilizers provide nutrients at a slower rate than chemical fertilizers, but can be more beneficial to the environment and plant growth in the long run. Wherever possible, when chemical fertilizers are purchased, it may be best to use a slow release type so nutrients are not lost due to leaching (moved down through the soil by water).

Fertilizer application rates and timing of application will vary, depending on the site, type of plants, health of plants as well as other factors. Woody plants generally need to be fertilized less often than herbaceous plants as they can adjust their growth according to the nutrients available. Keep an eye on the visual appearance of plants, and feed them nutrients when required. Soil fertility is necessary to maintain optimal plant growth.