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\n\t\t\t\t\t<\/div>\n<\/figure>\nA Season to Recharge\u00a0<\/b><\/h1>\nDon\u2019t let solar energy go to waste this fall<\/b><\/h2>\n
By Brian Dougherty<\/span><\/i><\/p>\n Everyone has probably dealt with a dead car battery at some point. It doesn’t matter how big the battery is; eventually it will go dead if the alternator doesn\u2019t recharge it.<\/span><\/p>\n Soil works the same way. It is the battery of life, and it is recharged by plants capturing solar energy via photosynthesis. A plant is a solar panel. It\u2019s the only thing we have that can take energy from sunlight and put it into a form the soil can use. There is no substitute for this miracle of life. Think of it like the battery in your tractor. You can have a large battery (like having a large amount of organic matter in your soil) but if the battery does not stay charged up your tractor will not start. On the flip side, you can have a fairly small battery, but if it stays fully charged (like having lots of readily available carbon to feed soil microbes) your tractor will still start. Most of us are running our fields on a low battery and wondering why nothing works the way it should.<\/span><\/p>\n I want to walk through what actually charges your soil battery, why it matters more than anything we measure, and why the months your ground sits bare are the most expensive months on your farm.<\/span><\/p>\n Start with the equations everybody saw in junior high science class and promptly forgot:<\/span><\/p>\n Photosynthesis:\u00a0 6 CO\u2082 + 6 H\u2082O \u2192 C\u2086H\u2081\u2082O\u2086 + 6 O\u2082<\/b><\/p>\n Respiration:\u00a0 6 CO\u2082 + 6 H\u2082O \u2190 C\u2086H\u2081\u2082O\u2086 + 6 O\u2082<\/b><\/p>\n It\u2019s the same equation going in two different directions. Photosynthesis takes sunlight and packs that energy into the bonds of a sugar molecule. Respiration takes it back out to do work. The carbon atom is charged (takes on electrons) or discharged (gives up electrons) in the process.<\/span><\/p>\n Here\u2019s where it gets interesting and <\/span>extremely<\/span><\/i> important to you as a farmer or rancher.<\/span><\/p>\n When chemists talk about a molecule being \u201coxidized\u201d or \u201creduced\u201d they\u2019re talking about electrons. An electron is just a tiny particle that carries a negative electrical charge. Electrons flowing through the wire are what makes the light bulb turn on when you flip the switch. Reduction means gaining electrons. Oxidation means losing them. Together we call these \u201credox\u201d reactions. Photosynthesis is the primary reduction reaction on Earth. It is literally the process of stuffing electrons and protons (hydrogen or H<\/span>+<\/span> from water) into carbon molecules that started as CO<\/span>2<\/span>. That is the charging step, and it\u2019s the only free one we\u2019ve got.\u00a0<\/span><\/p>\n Soil scientists measure this as redox potential, or Eh, in millivolts. It can be measured with a probe, just like pH. Low Eh means the soil is electron-rich and reduced. High Eh means it\u2019s electron-poor and oxidized. Corrected to pH 7, the electrical neutral point is around 400 mV. Above that you have an oxidized environment in the soil. Below it you have a reduced environment<\/span>2<\/span>.<\/span><\/p>\n We have spent more than a century treating pH as the master variable of soil chemistry and essentially ignoring Eh. pH describes proton activity, Eh describes electron activity. Agronomists have been depriving themselves of half the picture. Dr. Olivier Husson\u2019s conclusion, after pulling together literature from soil science, plant physiology, and microbial ecology, was that <\/span>Eh and pH don\u2019t just influence soil; they jointly drive the whole soil-plant-microorganism system<\/b>1<\/b>.<\/b><\/p>\n So how does the charge get from the leaf into the ground?<\/span> Through the roots, as root exudates. A plant doesn\u2019t just make biomass with the sugar it produces. It pumps a portion of it through the roots into the soil. This can vary from as little as 5% to as much as 95% of what it produces depending on species, growth stage, and how well the plant is photosynthesizing.<\/span><\/p>\n Those exudates are carbon compounds loaded with electrons. When a plant does this, it is literally pumping charge into the root zone. Some of that shifts soil Eh directly. Most of it works through the microbes, which eat the exudates and shuttle electrons around as they respire, ferment, cycle nutrients, and get eaten. Husson\u2019s model describes the loop plainly: plants release exudates \u2192 exudates alter rhizosphere Eh and pH \u2192 altered Eh and pH conditions determine which microbes thrive there \u2192 those microbes alter conditions further.<\/span><\/p>\n Plants actively \u201cengineer\u201d the root zone to make the conditions more favorable for their growth, just as we modify our habitat by building a house to live in. Researchers have put microelectrodes in soil and observed plants push Eh up to oxidize overly reduced soil or down or reduce overly oxidized soil near the root zone. <\/span>The plant is managing the electrical condition of its root zone like you\u2019d manage a thermostat.<\/b> It has a range it needs to operate in, and it will spend photosynthetic energy to move into that range.<\/span><\/p>\n Once you see soil as an electrical system, a lot of things that seemed unrelated start to connect.<\/span><\/p>\n Why should you care about this science stuff? A plant growing in favorable conditions spends more of its photosynthetic energy on growing leaves, roots, and grain or fruit. A plant growing in unfavorable conditions has to put more energy into correcting Eh and pH around its roots just to keep functioning. That energy comes out of the total budget. <\/span>Every \u201cdollar\u201d of photosynthate spent fixing a soil problem is a dollar not spent making a crop.<\/b> You are paying for degraded soil in lost productivity.\u00a0<\/span><\/p>\n Tillage floods the soil with oxygen. Oxygen is the strongest oxidizing agent there is. This causes microbial activity to spike, organic compounds in the soil are consumed, and carbon leaves as CO\u2082, just like the respiration equation above shows. In electrical terms, we are discharging the soil battery. Sometimes this is necessary, but tillage should never be done without a very good purpose for doing it, and without a plan for how you will recharge the battery afterwards.<\/span><\/p>\n Husson and colleagues measured this across four contrasting soil types<\/span>3<\/span>. Conventionally managed fields showed oxidation and acidification of the surface horizon. Conservation agriculture fields showed the opposite. They had lower Eh at the surface than in the horizons below it, a completely reversed profile compared to conventional. The conservation systems moved back toward favorable Eh-pH conditions for plant growth.<\/span> Think about what that means. In a healthy soil, the most biologically active, charged-up zone is at the top where the roots are. In a heavily tilled soil, it\u2019s upside down.<\/span><\/p>\n Overapplying nitrogen does the same thing. Add a lot of readily available nitrogen with no carbon to go with it and microbes multiply rapidly, then seek out carbon (their food source) to balance it out. They eat root exudates first. If they run out of those, they eat the biotic glues that hold aggregates together and they break down organic matter that is foundational for soil function. The result is the same as with tillage; a discharge of the soil battery.<\/span><\/p>\n Energy flow is one of the four ecosystem processes, and it is different from the others. Water cycles. Minerals cycle. Solar energy does not cycle. It flows in one direction, from the sun to the earth, and it either gets captured by something green or it hits bare soil. A corn or soybean crop captures sunlight for around 120 days. In moderate climates, that leaves roughly 150 days of opportunity. On bare ground, that energy is lost as heat. Nothing is captured and nothing is stored.\u00a0<\/span><\/p>\n<\/div>\n Meanwhile the soil is still respiring CO<\/span>2<\/span> and discharging its battery because it\u2019s not plugged in.<\/span> The soil battery is off the charger for eight months, and then we are disappointed in May when it won\u2019t crank the engine and produce vigorous early growth.<\/span><\/p>\n An overwintering cover crop fixes this for the price of seed and an equipment pass. Living roots means exudates. Exudates mean electrons moving into the soil and food going to the microbes that<\/span> build aggregates<\/span><\/a>. It means the surface horizon staying reduced and biologically active instead of oxidized and burnt out. It means nitrate getting taken up and held in living tissue instead of moving to the tile line or groundwater. It means armor on the surface to prevent erosion in the spring.<\/span><\/p>\n If you\u2019ve got time and a good window, plant a diverse mix with different root architectures working at different depths. If it\u2019s late in the season, a simple single species cover crop will still charge the battery. <\/span>When in doubt, get it out.<\/span><\/a> And remember the <\/span>compounding<\/span><\/a> rule: nothing on a farm or ranch is neutral. Every time you leave ground bare over the winter it compounds <\/span>against<\/span><\/i> you. Every fall you get something growing after harvest it compounds <\/span>for<\/span><\/i> you.<\/span><\/p>\n The sun is going to shine on your fields whether you catch it or not. That energy is free. You don\u2019t have to buy it, haul it, or apply it. You just have to have a green plant to use it.<\/span> Leaving the ground bare guarantees you get none of it.<\/span><\/p>\nPlants are solar panels<\/b><\/h2>\n
What “charge” actually means in the soil<\/b><\/h2>\n
Roots are the battery charger<\/b><\/h2>\n
Why redox is important<\/b><\/h2>\n
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Draining your soil battery<\/b><\/h2>\n
A window of lost opportunity<\/b><\/h2>\n
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