Defining the terms used.
Soil Fertility: The capacity/ability of a soil to supply essential plant nutrients in readily available and balanced forms.
pH: Tells you how acidic or basic a soil is. Nutrients need a certain pH in order to be able to feed your plants. A pH of 6.5 is the “sweet spot” for plant available nutrients. Nutrients need to be dissolved (or dissolvable) in the soil solution for plants to use them. Nutrients get bound up in the soil (unavailable to your plants) when pH is too high or low.
EC – Electrical Conductivity: The ability of your soil/water nutrient solution to conduct an electrical charge. The elemental ions that feed your plants, like Ca2+ and NO3–, carry an electrical charge (+ and -). The more ions, or nutrients, there are in the soil solution, the higher the EC.
Humus: These fine organic particles make up the bulk of organic matter. These particles have thoroughly decomposed reaching a point of stability and will not break down any further. These organic particles greatly affect texture, as well as water and nutrient holding properties of the soil.
CEC – Cation Exchange Capacity: The ability of a soil to hold positively charged nutrients. Calcium (Ca2+), Magnesium (Mg2+), Sodium (Na+), and Potassium (K+), and other trace minerals that are positively charged, are attracted to the negative (-) charge of soil and OM particles. Soils with a lot of clay and or OM have a higher CEC than sandy and/or low OM soils which have a relatively have a low CEC. Low CEC soils often need to be “spoon fed” as the soil has a hard time retaining nutrients. High CEC soils hold more nutrients but are harder to correct when they are out of balance. Microbes, like bacteria and fungi, help turn unavailable elements into a form that can attach to a soil or OM particle, becoming readily available to the plant.
BS – Base Saturation: A measure of nutrients currently IN your soil compared to the amount of nutrients you COULD HAVE in your soil (nutrient holding capacity – how many nutrients COULD be held by your soil IF they were added). (i.e. How “full” is the CEC. Only a % of total exchange sites actually has a nutrient on it.)
Lime Requirement: The optimal pH for plant available nutrients is 6.5. Most plants cannot access nutrients at an extremely low pH. It is imperative to maintain an optimal pH or plants will not be able to obtain proper nutrition. The Lime Requirement is the amount of lime needed to raise the pH of a soil to 6.5…..the optimal level. Liming is generally unnecessary if your pH is above 6.5. It is important not to lime too much because high pH will decrease nutrient availability. Another important role that lime plays is to help lower Sodium (Na) levels in soil. When Calcium (Ca) enters the soils system, it displaces Sodium (Na) from the soil exchange sites and allows water to leach Sodium (Na) from the soil matrix. Note: ALWAYS lime at a different time than you apply organic or potentially acidic nutrients (Manure/Compost/Humic’s). They will interact with each other rather than acing upon your soil chemistry.
Soluble Salts: In the world of chemistry, salt is more than what seasons our food! Many of these soluble salts are essential plant nutrients. When an acid and a base are combined, they react until they become neutralized. After this reaction, the neutral solution contains equal parts of positively and negatively charged ions. When you feed your soil fertilizer/amendments you are catalyzing many of theses acid/base reactions that create usable food for your plants.
Common soluble salts used by plants:
Iron Fe2+ and Fe3+
**These soluble salts are the forms we test for. The fertilizers you buy consist of a percentage (%) of these salts. (ex. Sulfate of Potash is 50% potash and 17% Sulfate.)
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. What ever the plant can not take up what is currently available it will wash away. 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. The bulk of it 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–) in the soil environment.
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”
Potassium (K) – 2-5%
Magnesium (Mg) – 10-12%
Calcium (Ca) – 68-75%
Sodium (Na) – <1.5% or less.
Ca2+ – The ionic form of Calcium dissolved in the soil solution (plant available)
Lime – Calcium Carbonate (CaCO3) adds just Calcium (Ca)
Dolomite – CaMg(CO3)2 – adds both Calcium (Ca) and Magnesium (Mg)
Gypsum – CaSO4*2H2O – adds Calcium (Ca) and Sulfur (S)
Triple Super Phosphate (TSP) a.k.a. “CalPhos” – Adds Calcium (Ca) and Phosphorus (P)
Mg2+ – Ionic form of Magnesium in soil solution (plant available)
Dolomite – CaMg(CO3)2 – adds both Calcium (Ca) and Magnesium (Mg)
Epsom Salts –MgSO4*7H2O
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
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.
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
Nutrients needed in small quantities but still very much needed. These can become toxic ordeficient more easily than the macronutrients. Availability of micronutrients is dependent on soil pH. Chelated forms are the best.
Chelation: The word chelate (pronounced “key-late”) comes from the Greek word “Chele” which literally means “claw”. Many necessary trace metal nutrients get bound up in the soil and are unavailable to the plants. Bacteria and fungi are natural chelators, breaking bonds and releasing nutrients to the plant. There are other non-biological chelators that can be added to manures and fertilizers.
Zn2+ – Zinc ion Zinc is necessary for plant function, especially in plant reproduction. Residual effects of Zn can last for several years so broadcast applications are recommended for heavy application. Increase in soil temperature raises Zn availability.
Mn2+ – Manganese ion Manganese quickly reverts to unavailable forms shortly after application so soil banding or foliar applications are recommended.
Fe2+ and Fe3+ – Iron ion Iron (Fe) quickly reacts with other elements and can become unavailable for the plant. Again, OM and biological activity keep iron in a plant available form.
Cu2+ Copper ion High OM, Soil pH, as well as excessive Nitrogen (N) and Phosphorus (P) applications can cause Cu deficiency. Soil applications of Cu can be effective for several years.
Cl– Chloride ion The Chloride ion (Cl–) is highly soluble and mobile in the soil solution. Coastal areas can see naturally high depositions (100 lbs/acre) of Chloride due to wind-sea interactions. Because of its mobility,
Cl– readily leaches and moves with groundwater flow. Accumulation of Cl– can occur in areas with restricted drainage, a shallow groundwater table, or as part of seasonal fluctuations.
Raising Soil pH:
Use a product containing Calcium Carbonate (CaCO3) ALWAYS lime at a different time than you apply organic amendments. They will interact with each other when you want them to act upon the soil.
Pay attention to the % CaCO3 in the product you buy.
Lime – ~100% CaCO3 – Just adds Calcium (Ca) and raises pH
Dolomite – CaMg(CO3)2 – Adds Calcium (Ca), Magnesium (Mg) and raises pH, add only when you need both magnesium and calcium.
Gypsum – CaSO4*2H2O – Adds Calcium (Ca) and Sulfur (S) without affecting soil pH.
Lowering Soil pH:
Put a “pH down” Like Citric Acid in your irrigation water. Organic matter like peat and humus are naturally low in pH and will help neutralize some of the carbonates that are causing high pH.
Aluminum Sulfate is a fast NON-organic way of lowering pH. We do not recommend this method.
Ag Sulfur can be used to lower the ph.
Organic vs. Mineral soil:There is a BIG difference
Organic Soil: Organic soils are made of Organic materials like peat, coco, and compost. Naturally occurring organic soils can be found in peat bogs and marsh soils. GrGreenhouseedia/potting soil are another type of organic soil.
Native/Mineral Soil: These are soils created from the weathering of rock and/or deposition of mineral material by wind or water. Over time soils form into unique mixtures of weathered and layered geologic material. Landscape shapes as well as climate, impact the local soil formation, hence the variability of soil across the landscape. Soil mapping is a technique used by soil scientists to map the variability of soils over a given area. These maps are very useful for any land-based planning or management.
Soil Texture: Soil texture is defined by the particle size make-up of the mineral soil fraction.
There are three main soil particle sizes: Sand, Silt, and Clay. Sand is the largest, most coarse particle and clay is the finest, smallest particle. The particle make-up of your soil drastically affects its nutrient holding capacity, moisture holding capacity, and drainage. In turn, this impacts the chemical and biological environment in your soil.
Soil Texture Types:
Sand, Loamy sand, Sandy loam
These are well drained, aerated, and workable for most of the year. They are very light to handle and quick to warm up in the spring. These rapidly draining soils have a tendency to dry out too quickly, so extra watering and addition of Organic Matter (OM) is often necessary to improve moisture retention. Excessive watering leaches essential plant nutrients from the soil. These soils tend to be acidic and do not have a large nutrient holding capacity and are often referred to as “hungry soils” because they need lots of extra feeding. With careful management, however, they can be amongst the most productive soil types.
Loam, Sandy clay loam, Silt loam
A loam has a relatively equal parts sand, silt, and clay. These soils have excellent water and nutrient holding capacity, while also having good drainage, the best of both worlds! These soils achieve a good balance between the ability to be very productive with minimal attention.
Clay, Sandy clay, Sandy clay loam, Silty clay, Silt Although theses soils are difficult to work with, they are usually nutrient rich with little plant access to nutrients that are locked up in the dense matrix. The main drawbacks are slow drainage, difficult for plant root to penetrate soil and access nutrients, and the effort required to work them. You will need to catch just the right weather conditions to avoid hard work and damage to the soil structure. Using heavy machinery or grazing animals should be avoided, especially when soil is wet.