Balancing Soil Using Organic Minerals
Soil Fertility
Fertile soil is a mixture of well-balanced minerals, high organic matter, humus, humic, fulvic and carbonic acids, good aeration and bountiful soil life. The biology or life in the soil is at its healthiest when the nutrients are plentiful and balanced, and there is sufficient oxygen and water. The top few inches of soil is the most vital, holding about 70% of the life and 70% of the organic matter. Below 6 inches the roots are feeding on mostly soluble nutrients since the micro-organisms are not able to thrive without sufficient oxygen. It is possible to create biological activity deeper with deep double dug or mechanical disturbance like spading. It is crucial to leave the soil as undisturbed as possible, although nontillage is very difficult in organic annual crops.
Increasing the quantity of earthworms and planting deep-rooted plants will let air into lower levels of the soil. Micro-organisms like bacteria, fungi, actinomycetes, algae, nematodes and protozoa, need oxygen to contribute directly to the release of nutrients to the plant. Some species of mycorrhizae tolerate very low oxygen levels, and infest roots much deeper than other species of beneficial microbes, providing nutrients and root protection. There are many symbiotic relationships going on between roots, organic matter, clay and micro-organisms to support the plant. Soil that is worked too wet annihilates air and water space, destroying the environment that microbes need. Soil that is worked too dry creates similar problems. Tending soil for optimum production means adding minerals and compost every year. Balanced, fertile soil makes for higher yields, better flavor, less disease and insect pressure and more nutritious food.
Compost
The best and cheapest organic fertilizer is compost. It contains organic matter, humus, calcium, phosphorus, potassium, nitrogen and many micro-nutrients, billions of microbes in each ounce and is a great food source for the biology in the soil. Compost made from plant residues and animal manures that have been fully decomposed can be applied every year at 1 to 8 tons per acre. In poor soils initial compost applications should be much higher, if the compost is fully digested and mature with proper C:N ratio. Vegetable crops often benefit from higher application rates, if the compost is aerobically digested and mature. Compost made from branches, leaves and plant residues without manures are best for orchards since this best supports fungal growth. Forests have soils that are inhabited predominantly by fungal growth. Orchard (non tilled) soil biology closely resembles forest soil biology. Compost containing woody residues mixed into the soil robs plants of soil nutrients. If the compost contains woody residues, it is not finished, or was made incorrectly. It should be used as mulch or added to the top of the soil. Too much compost in the soil is hard for the soil to break down quickly and will temporarily tie up nutrients. If the compost has a proper C:N ratio of approx. 10-12:1, it does not tie up nutrients. High carbon composts always tie up nitrogen and sulfur, and sometimes other nutrients when worked in to the soil.
Taking a Soil Sample
The aerobic zone is usually only 6-7” deep and should be all you need to sample for annual crops. Perennial crops may need to be sampled at greater depth to determine toxicity issues such as sodium, boron and carbonates. If the soil is double dug or mechanically deep tilled or spaded, soils sampling could go to 8” plus. Using a tube type soil probe or a shovel, take a minimum of five probes in different zones of the area being tested. Do not combine probes from areas that are not uniform to the sample desired, ie rocky, clayey, silty, flooded, or where noted difference in crop or weed growth occurs. Sample these areas separately but don’t combine them with the “normal” sample. Mix the soils together for each sample. It should be about 1½ cups. Don’t touch the soil with your hand. Don’t use a rusty shovel. Don’t place sample in plastic bag.
The highest rates of soil fertility are seen in the testing done in May and June, the lowest in the winter. To get consistent results test soil at the same time of the year from test to test. Scrape away the surface organic material or get an abnormally high reading.
Reading the Soil Test
There are many labs around the country that give soil results. The following recommendations are based on lab results from A&L Ag Labs in Modesto, California. Every lab uses different testing methods so the numbers may not be the same. It is best to use one lab consistently to track annual results.
(Note: To covert pounds per acre to pounds per 100 square feet divide by 440.)
Organic Matter (O.M.)
Increasing organic matter levels will help with the soils texture, structure, drainage, aeration, water holding capacity and availability, nutrient availability, root development and dramatically improve soil biology. Working soil wet destroys organic matter. Organic matter (humus) holds three times more nutrients than clay and up to 5 times as much water.
2% Organic matter is poor. Over 4% O.M. to 10% is ideal. Above 10% organic matter often inhibits micro-nutrient uptake, and if composed primarily of woody materials will greatly reduce nitrogen availability. Most soils need additional organic matter every year, especially if tilled, or in arid climates. Compost, cover crops, mulches and leaving the soil undisturbed are the best choices for increasing organic matter.
Phosphorus
Phosphorus is most important in the storage and transfer of energy in the plant. It is essential in every metabolic process, protein synthesis, sugar development and legume nitrogen fixation. It is crucial for root development. Optimum phosphorus levels are needed for rapid seedling growth, winter hardiness, disease resistance, efficient water use, early maturity, and maximum yield. Phosphorus needs to be placed where it will be used, as it is less mobile in the soil than any other nutrient. Legumes can move phosphorus to deeper areas of the soil, where it will become available for other crops after the legume roots decay.
Phosphorus becomes immobilized at low pH by large concentrations of aluminum, zinc and iron, and at high pH by too much calcium.
Soft rock phosphate is the fastest working phosphate. 300#/acre is the minimum application. 2000#/acre of soft rock phosphate should supply enough phosphorus for years. When planting perennial crops in low P soils, add soft rock phosphate to the planting hole, 1-10 pounds per hole depending on perennial size.
P1 tests immediately availability. 25 ppm is the minimum and above 40 ppm is ideal.
P2 tests for future availability. 40 ppm is the minimum and 60 ppm is ideal. Above 60 PPM often ties up trace minerals such as zinc and copper. The greater the OM, the greater the availability of phosphorus.
Potassium
Potassium is a regulator of metabolic activities. It is essential for photosynthesis and protein synthesis as well as carbohydrate transport and storage. It promotes root reserves, winter hardiness, cell development, strong walls, and reduces stalk lodging. Potassium improves water use efficiency, increases yield, improves crop quality, and reduces incidence of disease.
Most soils have less than 1% of the potassium available due to insufficient microbial activity and organic matter content. There are about 30,000 to 50,000 lbs. per acre of potassium in an average soil, but most of this is not plant available until microbial activity releases it. It is possible to release small amounts of potassium over time by increasing microbial activity with compost, compost tea and cover crops.
Apply mined granular sulfate of potash (50% K2SO4) in April for orchard crops, or solution grade sulfate of potash may be added to irrigation during the growing season, or foliar fed if severely deficient. Avoid winter and autumn applications as the potassium will be tied up in the soil before it can be used.
Too much potassium ties up boron, calcium and manganese.
2% cation saturation potassium is the minimum and 5% to 7% is much better.
Magnesium
Magnesium is an essential component in the chlorophyll of green plants. It is also necessary for metabolic processes and in every operation involving phosphorus. Magnesium levels have important interactions with calcium, sulfur, and nitrogen. The ratio of magnesium to calcium should be around one to six. Excess magnesium will reduce potassium availability. Having a soil with too much magnesium will take more nitrogen because the excess magnesium makes the soil too tight. Excess magnesium is what makes clay soils “tight”, restricting air and water availability, water drainage, root development and restricting microbial activity and organic matter decay.
The higher levels of magnesium in a sandy soil will help to tighten the sand. For sandy soil the optimum would be 16% to 20% and for clay soils closer to 12%. It will always be necessary to add more nutrients to a clay soil than to a sandy soil.
Note: Two pounds of sulfur will leach out one pound of magnesium when there is at least 60% calcium saturation.
Calcium
Calcium is part of cell walls and membranes; it controls movement in and out of cells, reacts with waste products and neutralizes toxic materials. Calcium activates many enzyme systems, it improves microbial activity and it enhances uptake of other nutrients. Essential for cell division. Increases cell density, and improves texture (crunch) of crops. Critical for balancing excess nitrogen. Critical for disease suppression.Having the correct amount of calcium in the soil will require less nitrogen. The calcium will loosen the soil and make more nitrogen available. Too much calcium can tie up all other nutrients especially magnesium, potassium, boron, zinc and copper.
Calcium cation saturation needs to be over 60% before you add gypsum (calcium sulfate) to lower excess magnesium otherwise the sulfur in the gypsum will take out the calcium first. Add limestone first to raise calcium to 60%, and then add enough gypsum to raise calcium levels to 68%. One third of applied calcium will become available the first year and it takes 3 years to be completely utilized. Solution grade limestone will become 100% available within 1-3 months.
Limestone applied to the surface of the soil will work its way into the soil at the rate of 1” per year.
Calcium leaches with excess rain or irrigation. Don’t add over 4 tons per acre of limestone in any one year.
Sodium
Widespread in nature, sodium is found in all plant material. Although it does not seem to be necessary to the growth and development of plants, it is used advantageously, particularly when potassium is low. Sodium seems to be able to partly substitute for potassium.
Excess sodium is a problem in many dry areas particularly if the irrigation water is alkaline. Sodium toxicity to plants is often observed in saline and alkali lands and unfavorable soil structures can be present due to high sodium as well. Excess sodium suppresses soil biology, root development and nutrient availability. Any time your sodium and potassium together are over 10% then the manganese won’t be able to get into the plant.
Apples get their best color with sodium levels over .5%. .5 – 3% is ideal.
pH
The acidity and alkalinity of soil is measured as pH . For the most fertile soil,
the cation saturation is balanced and the pH will fall into a range of 6.3 – 6.8. Outside this pH range nutrients become unavailable and soil biology is suppressed. Decay of organic matter into humus is also reduced.
C. E. C.
C. E.C. is the Cation Exchange Capacity and is a number that represents the soils ability to hold onto and provide nutrients. A sandy soil has a C.E.C. of between 4 and 9 and cannot hold onto very many nutrients. A heavier clay soil would have a C.E.C. of over 16 and hold more nutrients than a sandy soil. The strongest soils have CECS in the 20’s to 30’s. CEC measures the quantity of clay and humus in a soil. By increasing the humus the CEC will increase, providing improved nutrient retention and availability. CEC goes up 2 points for every 1% organic matter goes up.
Cation Saturation
Cation saturation is the percentage of calcium, magnesium, potassium, sodium and hydrogen held on the clay and humus sites on a soil test. The ideal calcium would be 68% to 72%. The ideal magnesium depends on how much sand or clay the soil contains. For sandy soil the optimum would be 16% to 20% and for clay soils closer to 12%. The ideal potassium would be at least 2% and 4% to 6% is better. The ideal sodium is at least .5% and not over 3%.