These are nutrients needed in large quantities by plants; nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), sodium (Na). They generally do not become toxic due to their dynamic soil bio-chemical cycles *. They will get taken up by the plant, leached out of the system, or volatilized into the atmosphere. Both high OM and microbial activity increase macronutrient and other trace mineral availability. *Na can be toxic if it is out of balance or excessively high.
NO3– – Nitrate (Plant available nitrogen (N)) nitrate-nitrogen (NO3– – N) is the form of N that is most available to the plant. Both high OM and microbial activity increases N availability. Nitrogen fixing bacteria increase the N in your soil by “fixing” N from the air (N₂) and converting it to ammonium (NH₄+) in the soil. Nitrate (NO3–) is a very mobile form of nitrogen and leaches easily from the soil; If you don’t use it, you lose it. Over use of nitrate will harm the watersheds, ecosystems and pocketbooks – a soil test will help you regulate this.
NH₄+ – Ammonium (Plant available nitrogen) Ammonium – nitrogen (NH₄+-N) is another type of plant available nitrogen (N). In natural soil systems plants receive the bulk of their nitrogen through nitrate (NO3–), but can also take up ammonium (NH₄+). Ammonium can be taken up by plant roots or turned in to ammonia (NH3) and volatilized into the atmosphere, especially in dry environments. The bulk of the ammonium is converted to nitrate (NO3–) by nitrifying bacteria (another type of bacteria in the N cycle). This occurs because ammonium (NH₄+) is unstable in the soil and is quickly converted to nitrate (NO3–).
SO42- – Sulfate (Plant available sulfur) Sulfate (SO42-) is the plant available form of sulfur, another essential plant macronutrient. It is highly mobile and readily leaches from the soil. Optimal levels depend on the amount of available exchange sites on the organic matter (OM). The need for sulfate (SO42-) increases in soils with low OM, Cation Exchange Capacity (CEC) and pH, as well as soils with heavy nitrogen fertilizer.
PO43- – Phosphate (Plant Available phosphorus) Phosphate is the plant available form of phosphorus (P). It is very finicky and is only available in a narrow pH range (6.0-7.0). At high pH it “complexes” with calcium (Ca2+) and magnesium (Mg2+) ions, which binds P up in the soil and is not available to your plants. At low pH it complexes with aluminum (Al3+) and iron (Fe3+) ions. We recommend a pH of 6.5 for optimal P availability.
This is another case where if your plant does not use it, you lose it. If phosphate (PO43-) is available to the plant, it is also available to be leached. The plant will take up what it can and the rest will be leached or complexed. Mycorrhizae (beneficial fungi) will increase a plant’s ability to take up P. These biological helpers free up some if this much needed nutrient for the plant. Excessive P applications increase input costs, does nothing for yield, damages our watersheds and wastes money.
“Exchangeables” – Exchangeable Cations (Ca2+, Mg2+, Na+, K+) These are positively charged plant nutrients. Soil particles as well as plant roots are negatively charged (-) whereas “exchangeables” are plant nutrients that are positively charged (+). This creates an attraction to each other. The plant root takes a nutrient from the soil solution which gets replaced or “exchanged” by a nutrient from the soil particle, and from there conveyor belt continues. This process of exchanging regulates the availability of nutrient flow in your soil-plant system. These ions need to be in balance relative to one another in order to be used effectively by the plant. This balance is called the “exchangeable ratio.”
% Ratios: Potassium (K) – 38% Magnesium (Mg) – 9% Calcium (Ca) – 45% Sodium (Na) – <5%
Ca2+ – The ionic form of calcium dissolved in the soil solution (plant available) Lime – calcium carbonate (CaCO3) adds just calcium (Ca) while dolomite – CaMg(CO3)2 – adds both calcium (Ca) and magnesium (Mg). Gypsum – CaSO4*2H2O – adds calcium (Ca) and sulfur (S) but does not affect soil pH like lime and dolomite will. “CalPhos” and rock phosphate both add calcium (Ca) and phosphorus (P).
Mg2+ – Ionic form of magnesium in soil solution (plant available) Magnesium Sources: Dolomite – CaMg(CO3)2 – adds both calcium (Ca) and magnesium (Mg). Epsom Salts –MgSO4*7H2O add both magnesium (Mg) and sulphur (S).
Ca:Mg Ratio In order for plants to effectively use calcium (Ca) and magnesium (Mg) it needs to be in the correct ratio – generally accepted ratio is 5:1 calcium to magnesium.
Na: Ionic form of Sodium (Na) in soil solution (i.e. plant available form). We measure Na+ for potential imbalance or toxicity. It is not an essential macronutrient, but is needed in trace amounts. If Na is too high it will cause plant cells to dry out which will cause the plant to wilt and/or die. High Na levels can occur naturally (desert/arid regions), or through the use of marine-based materials or salt-based fertilizers.
K+: Ionic form of potassium in soil solution (i.e. plant available form) K is a mobile plant nutrient that moves relatively easily throughout the plant and is important for water balance and pressure inside the plant. Deficiency reduces plant metabolism, photosynthesis, plant growth, and crop quality.
Potassium Sources: Sulfate of potash – K2SO4 – 50% K2O; 17% SO42- Kelp Meal – Adds K as well as trace elements Green Sands – Time released K from sand particles containing high amounts of Potassium