Chapter 18

Plant Nutrition of Greenhouse Crops

(book excerpts)

Maintaining adequate nutrition is among the most critical aspects of producing greenhouse crops. There are two aspects of crop nutrition which the grower must consider. One aspect of nutrition involves the overall level of nutrients available to the plant. The absolute quantity of nutrients a plant needs will increase as plant size and fruit load increase. An important concept to understand regarding fertilization is that plant growth is controlled by the mineral nutrient in shortest supply, even when sufficient quantities of other nutrients exist. Thus, a single nutrient element may be the only factor limiting to plant growth even if all other elements are supplied in sufficient quantities. The second aspect of nutrition involves the optimal ratio or balance of nutrients available to the plant. Nutrient balance controls the tendency for the plant to produce either vegetative or reproductive growth (i.e., leaves and stems vs. flowers and fruits). Maintaining the proper balance between vegetative growth and fruit load is the key to long-term productivity of the crop. In some cases when nutrients are out of balance severe deficiencies or toxicities may occur. The proper balance of nutrients to one another seems to be relatively consistent among plant species. In order to control nutrition, growers need to have a rapid and reliable method of monitoring the nutrient status ofthe cropping medium. The essential equipment includes a conductivity meter and a pH meter. For more detailed analysis, growers should send samples to a commercial lab. Electrical conductivity (EC) is usually a good indicator of the overall nutrient level in the growing medium. Medium pH affects individual nutrient availability. Therefore, as pH varies, the nutrient balance available to the crop will change. Knowing the nutrients required to grow plants is only one aspect of successful crop production. Optimum yield also requires knowing the rate to apply, the method and time of application, the source of nutrients to use, and how the elements are influenced by substrate and greenhouse environmental conditions.

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Topics Within This Chapter:

  • Essential Plant Nutrients
  • Common Deficiency Symptoms
  • Nutrient Mobility within the Plant
  • Nutrient Interactions
  • Electrical Conductivity and pH
  • Measuring EC
  • Substrate Extraction Methods
  • EC Meters
  • Limitations of EC Measurement
  • Closed Irrigation Systems
  • Managing Substrate EC
  • Measuring pH
  • Substrate Extraction Methods
  • pH Meters
  • Managing Substrate pH
  • Lowering Growing Media pH
  • Raising Growing Media pH
  • Diagnosing Plant Nutrient Deficiencies
  • Visual Diagnosis
  • Media Testing
  • Sampling Procedures
  • Tissue Analysis
  • Sampling Procedures
  • Plant-Sap Quick Test for Nutrient Analysis
  • Greenhouse Fertilization Programs
  • Pre-Plant Fertilization
  • Post-Plant Fertilization
  • Fertilization Frequency
  • Fertilization Rates