Essential Plant Nutrition: Macronutrients, Micronutrients, and Fertilizer Forms

Mineral NutritionA discussion in Chapter 5 Are Plants What They Eat? or What is Plant Food?

Sixteen essential elements • Carbon, Hydrogen, Oxygen • Nitrogen, Phosphorus, Potassium • Ca Calcium, Mg Magnesium, Sulfur • Fe Iron, Mn Manganese, Mo Molybdenum • Cu Copper, Boron, ZnZinc • ClChlorine • C Hopkins CaFe, Mg B MnCuZn, Cl Mo

Essential Elements: • CHO come from air and water • All the rest come into plants as dissolved solutes in soil water • Not only must they be in the soil, they must also exist in a form usable to plants • Nutrient usage in plants is categorized by the relative amounts used in plants • Macronutrients • Micronutrients

Primary Macronutrients • Nutrients used in largest amounts • Nitrogen • Phosphorus • Potassium

Secondary Macronutrients • Used in lesser amounts than primary, but still a lot more than micronutrients • Calcium • Magnesium • Sulfur

Micronutrients • Minerals used in much smaller amounts • Iron, Manganese, Molybdenum • Copper, Boron, Zinc • Chlorine

Availability by pH levels All nutrient forms are affected by soil pH, but especially the micronutrients. This is why we often have iron-deficient plants in the West.

Nitrogen • Can cause rapid vegetative growth • Fixed by bacteria on legume plants • Absorbed as NO3-, NH4+, NH2+ • Is easily leached from soils • Especially sandy soil

N Fertilizer composition and effect on soil pH

Phosphorus • Not very soluble in soil water • Does not leach • Deficiencies show up as exceptionally dark green or purple leaves • Flowering, fruiting, root development, disease resistance

Potassium • Easily leached • Important in stomata opening and closing, water retention, starch formation, chlorophyll formation • Deficiency results in stunted plants, older leaves may wilt, intervenal chlorosis begins at base

Iron • Often deficient in plants grown on alkaline soils • Not due to lack of Fe in soil, but unavailable form • Intravenous yellowing progressing to white foliage • Many micro fertilizers are formulated as ‘chelates’

Chelate • Greek, meaning claw • Large organic molecules that hold specific cations allowing them to be absorbed and used by plants • Chelates hold Fe, Mn, Zn, and S and prevent them from reacting with inorganic anions • Sequestering agents

Fertilizers • Divided into 2 common types • Organic • Inorganic

Organic Fertilizers • Derived from decomposition of animal wastes or plant products • Also act as soil amendments or conditioners • Nutrients are released slowly through decomposition • Slow and unreliable in cold soil • Expensive for the amount of nutrients they actually contain

Inorganic Fertilizers • Come from mined and manufactured raw materials • Much more concentrated than Organics • Can be formulated as fast-release or slow-release • As far as N goes, most plants use the same form (NO3-), regardless of how it gets there • Can cause rapid depletion of soil OM

Fertilizer Forms • Liquids • Salty so they dissolve in water • Sprayed on root zone or as a foliar application • Have high tendency to ‘burn’ plants • Are usually short-lived • Granules • Most common form • Heavy pellets don’t drift too far • Can be slow-release

Fertilizer Forms • Tablets and Spikes • Large compressed items that are pushed into the soil or placed in a hole • Expensive for the amount of nutrient they contain • Release nutrients very slowly over time • Several months to more than a year

Purchase • Many factors exist when choosing a fertilizer to purchase • Slow or fast release • Organic or inorganic • Liquid or solid • Analysis • Price

Analysis • Is a statement of the type and quantity of nutrients, and must be included on every package • The standard statement form is 3 numbers separated by hyphens on the bag • 15-5-15 for example • The numbers give %N, %P as P2O5, and %K as K2O

Analysis • Fertilizers are also grouped based on relative amounts of N, P, and K • Balanced = 10-10-10 • Complete = 20-8-16 • Single Element – 21-0-0

Application Methods • Topdressing • Pre-plant incorporation • Sidedressing • Needle Feeding • Drilled-hole • Foliar

Mineral Nutrition @ Home • Macronutrients • Nitrogen will be needed by turf, flowers, shrubs, trees, and the garden, add yearly in early spring as roots start to grow • For turf two applications - early spring and early fall • Use residual acid form - ammonium sulfate

Mineral Nutrition @ Home • Macronutrients • Phosphorus may be needed every 3 - 5 years for turf, flowerbeds, shrubs, trees and gardens • Potassium will generally not be needed. There is a sufficient supply in Utah soils and Utah waters are high in potassium

Mineral Nutrition @ Home • Secondary mineral nutrients are usually not needed • Calcium Magnesium Sulfur

Mineral Nutrition @ Home • Micronutrients • Iron • Manganese • Zinc • Look for early signs of deficiencies • Test with chelated materials applied to the foliage to determine needs

Essential Plant Nutrition: Macronutrients, Micronutrients, and Fertilizer Forms