Soil Management (2024)

There are 15 essential elements that plants must have in order to grow properly.

18 Essential Nutrients

• Nutrient elements obtained from atmosphere through photosynthesis
  • Hydrogen
  • Carbon
  • Oxygen
• Nutrient elements obtained from the soil
  • Nitrogen
  • Phosphorus
  • Potassium
  • Sulfur
  • Magnesium
  • Calcium
  • Iron
  • Boron
  • Manganese
  • Zinc
  • Molybdenum
  • Copper

Out of the 15 essential elements that come from the soil, we deal with only the 12 that are generally managed by the growers. These 12 elements are ‘mineral nutrients’ and are obtained from the soil. We further divide mineral nutrients into 3 groups: primary, intermediate, and micronutrients. Our presentation will exclude cobalt, chlorine, and nickel from our discussion on the management of essential mineral nutrients, though are included by many as essential nutrients.

• The primary nutrients are nitrogen, phosphorus and potassium. You may be most familiar with these three nutrients because they are required in larger quantities than other nutrients. These three elements form the basis of the N-P-K label on commercial fertilizer bags. As a result, the management of these nutrients is very important. However, the primary nutrients are no more important than the other essential elements since all essential elements are required for plant growth. Remember that the ‘Law of the Minimum’ tells us that if deficient, any essential nutrient can become the controlling force in crop yield.
• The intermediate nutrients are sulfur, magnesium, and calcium. Together, primary and intermediate nutrients are referred to as macronutrients. Macronutrients are expressed as a certain percentage (%) of the total plant uptake. Although sulfur, magnesium, and calcium are called intermediate, these elements are not necessarily needed by plants in smaller quantities. In fact, phosphorus is required in the same amount as the intermediate nutrients, despite being a primary nutrient. Phosphorus is referred to as a primary nutrient because of the high frequency of soils that are deficient of this nutrient, rather than the amount of phosphorus that plants actually use for growth.
• The remaining essential elements are the micronutrients and are required in very small quantities. In comparison with macronutrients, the uptake of micronutrients is expressed in parts per million (ppm, where 10,000 ppm = 1.0%), rather than on a percentage basis. Again, this does not infer that micronutrients are of lesser importance. If any micronutrient is deficient, the growth of the entire plant will not reach maximum yield (Law of the Minimum).

Since the soil provides most essential nutrients, it is crucial that we understand the soil processes that determine the availability of each essential nutrient for plant uptake.

Table 4. Forms of Essential Elements Taken up by Plants

In this website, we will discuss major factors that affect the availability of the essential nutrients.

• In the tropics, the management of nitrogen and phosphorus can be problematic. Thus, it is appropriate that we discuss management issues of each nutrient separately.
• In a second section, we will collectively discuss the availability of potassium, calcium, and magnesium in Hawaii soils.
• Lastly, we will address issues of micronutrient management in the tropics.
• We will omit a discussion on sulfur, since it is seldom deficient in Hawaii soils.