Photosynthesis - 101a

Photo credit: Marc Suderman

Photosynthesis – Everyone, everywhere benefits from plants; specifically from Photosynthesis. It’s the plant process that takes water (6H₂O), carbon dioxide (6CO₂) and sunlight (energy) and transforms them, into glucose (C₆H₁₂O₆) and oxygen (6O₂) during daylight hours. This supplies food for plants and oxygen (and food) for the rest of us. It is the most vitally important activity on earth.

Approximately 95% of all plant structures are made up of carbon, hydrogen, oxygen…95%! These are taken from the air via the photosynthetic process. While this is a plant activity, it is dependent upon a living, nutrient-rich soil for supplying water and the necessary mineral nutrition, which cannot be gotten from the air. The mineral nutrition is the part where we have a direct effect; the 5%. To make this dynamic system work well requires “give-and-take” action. There’s a symbiotic relationship between plants and soil (biology). Plants need what only the microbes can provide and are unable to get for themselves and vice versa. Plants make sugars and soil microbes eat sugars. Soil microbes liberate soil-bound minerals that plants cannot release, but need for survival; interdependence. Of the sugars produced, plants use ⅓ of these photosynthates within the canopy and the remaining ⅔ are sent down into the root system. This is a win-win arrangement. The more diverse and active the rhizosphere (the area surrounding plant roots where microbes live), the more the food demand will be, but this also means there is more reproduction too. This will improve nutrient translocation for better plant health and therefore higher glucose production for better rootzone health. This creates, in effect, a perpetuating action between soil and plant.

Plants are made to be in the sun. They are designed to absorb sunlight and the heat that comes with it. Summer brings plenty of sunlight and higher temperatures. A healthy canopy should provide food and protection to the developing crop, but sometimes there are limitations to the canopy’s effectiveness. These can be a challenge at critical stages of development and can cause problems for growers. A good understanding of the key growth stages for your crop is important. This can help you better plan for potential stressors, like weather, drought, bloom, fruit set, fruit fill, etc. Designing a fertility plan for the nutrient demands of growing crops (before they need them) and emphasizing key nutrients, like phosphate, magnesium, iron, boron, manganese, etc. to lessen plant stressors and promote better plant/soil health via the photosynthetic process, is in your best interest. Dan Skow wrote, in Mainline Farming for Century 21, “In photosynthesis there is one limiting factor, in putting sugars into plants, namely phosphate...” For instance, excessive light and heat can cause plant stress. The Stress is not the problem, but a symptom of the Problem, namely nutrient deficiency. Considering every nutrient, with the exception of nitrogen, enters the plant in phosphate form, shows how key a nutrient this is to overall plant health and function. In calcareous soils, this is a challenge. Adding specialized soil microbiology will provide an ample soil phosphate supply and plants respond by building larger, thicker, hardier leaves that are better suited to care for themselves. These are plants’ solar panels and the better they are equipped for “catching” sunlight, the better the sugar production. “The number of layers [in the mesophyll] varies, principally due to nutrition. More layers mean a thicker leaf, more photosynthesis, and more crop.” wrote Dr. Arden B. Andersen in Science in Agriculture. Thicker leaves have a larger storage volume and higher solute (sugars) content. As a result, this gives a plant more resistance to rising ambient temperatures and helps to regulate its internal temperature better. This also allows the guard cells of the stomata to remain open longer into the day before shutting down to conserve water. More photosynthetic production yields more energy and more energy equates to more plant health. It takes healthy plants to grow nutrient-rich food. The crop produced can be nothing more than the “nutrient-template” provided it from the diet of the parent-plant; “Garbage in, garbage out” or “You are what you eat”. Making assumptions about the soundness of your fertility plan without verifying with timely tissue testing can prove to be costly. Growing high quality fruits or vegetables doesn’t just happen. It’s a lot like trying to hit a moving target. It requires a good plan and execution to get good canopy efficiency. The opposite is also true, if anything occurs to limit a plant’s ability to absorb sunlight and build photosynthates. I mention this because; summer is a critical time for fruit bud development which happens concurrently with all other plant operations and can place added energy/nutrient demands, onto a plant. Deficiencies, at this stage, can ill-affect production for the coming year. Remember, the higher the photosynthetic efficiency, the better equipped a plant is to address all plant issues. This includes generating high quality crops and higher quality equals better ship-ability and shelf-life. But, to do this takes energy (sugars). Plants “bundle” sugars to form primary and secondary metabolites. It takes ten times more energy to produce secondary plant metabolites than glucose. Without secondary metabolites, strong, high quality, nutrient dense fruits or vegetables are not possible. This is directly dependent upon how well plants photosynthesize. Bottom line: When plant glucose production fails to meet plant demands, crop quality suffers. Don’t let this happen to you!

 

 

Photosynthesis, on the surface, can be assumed to be nothing more than the plant activity of absorbing sunshine and growing. But, it is a very complex process; one that works for you, but can be limited or benefitted by your fertility plan, both in the soil and the plant. Nutrition has a major influence on crop yield, plant health and soil response. Fertilizing a crop, with good intentions doesn’t guarantee good results. Regular and timely tissue and soil testing are useful tools for tracking your growing progress. Fertilizers and lab testing cost you money, but so does delivering a crop that has sub-par quality, size, color, brix, firmness, etc. on your bottom line. Utilizing test results to make timely nutrient decisions is good stewardship. Good stewardship is also making sure your plant’s canopy is functioning at a high level of efficiency to support your efforts to produce the best crop possible each and every year.

Here’s to your harvest success!

Chill Hours - The Importance of Rest and Nutrition

           

            Chill hours are important to tree and vine crops during dormancy. This is the timeframe when the plant rejuvenates. This time is critical. Trees and vines, just like you and me, have to take a “vacation” from the busyness of the growing and producing stages. These hours are the time or opportunity for the plant to rest up for the next crop. It’s a vacation period for trees and vines to get rested. In California’s San Joaquin valley, this usually occurs when kids get excited because its foggy day schedule weather and shortened school days. It’s wet and cold and there is not a lot of sunshine. But this is perfect weather for permanent crops like pistachio, almond, peach or grapevines.

            Without adequate rest or “chill”, the plant works from an “energy deficit” position. This is a problem. It is the monetary equivalent of drawing money from your savings account because the interest earned isn’t enough to live on. You can’t do this for very long without dire consequences and the same is true with your crops.

            When you get enough rest, you wake up ready to go better. The same goes for trees. When they get enough rest, they wake up ready to grow better. When trees do not get enough rest, they will have delayed canopy development. This is an important detail because without leaves the plant cannot feed itself effectively. The more efficiently a tree can start growing leaves and a healthy canopy the sooner it can begin taking in sunlight, water, and carbon dioxide so that through photosynthesis glucose production kicks into gear and provides food for the plant and developing crop to feed on.

            On a year with short chill hours, the problem becomes an issue of how to make the most of a bad situation. For instance, in January you find that you have 400 hours or less of chill accrued to date. Historically by this time, we have between 700-800 hours. This is a harbinger and we need to pay attention because it’s telling us to be prepared for “what” the outcome of this can potentially be. This is important because some crops use an awakening agent to help crops rouse themselves, in order to harvest earlier. The problem with this is, when you apply a product to awaken a plant that has not gotten enough chill hours you induce an extreme stress condition or worse actually damage the plant’s fruit buds. That can have a long-term adverse effect. Think of how trees grow fruit buds. It usually develops on 2^nd year wood. So, if you hurt your tree badly, it could take two to three years to recover, assuming there are no other major stressors that occur to limit recovery. Growers should consider the tradeoffs carefully before proceeding with a “dormancy-breaker” spray for their trees especially those that have not gotten the proper amount of chill hours. We cannot merely wish good seasonal weather on our crops. If our crops don’t get enough chill, the plants themselves will be underdeveloped and this ultimately affects profitability.

Keeping energy in mind as you go through dormancy is important. Dormant plant energy comes from carbohydrate reserves. This becomes a high demand on heavy crop load years. As fall passes, the plant behaves much like a bear before going into hibernation. It eats and stores up food to carry it through winter until awakening in the spring. The difference with a plant is that, while it does its best to make and store up food reserves with both photosynthesis and the fall root-flush, it often falls short due to outside influences such as drought, large crop load stress, heightened insect pressure, imbalanced nutrition, etc. The bottom line: If you go to bed hungry, you will awaken very hungry and nutrient deficient.

As a grower, you decide what nutrition your crops receive. Therefore, if you want to ensure your crops are well fed for dormancy, feed them well BEFORE dormancy with next bloom in mind, as the goal. Remember good intentions don’t equal good actions. More to the point don’t apply materials because your neighbor is or it was a “good deal”. You should be testing your soil and tissues in the fall or before harvest, in order to determine what “got in” and what “ran short”. These are an annual progress report of your field’s health. If your adviser doesn’t offer these services, look around for one that does. After all, it’s your asset and investment. This information will help guide you to make more accurate decisions on what should be applied and at what rates. If you aren’t sure what should be applied, ask your crop adviser for counsel. If they aren’t experienced with your crop or soil type, get a second opinion. But, don’t fall prey to “analysis-paralysis” or information overload. If you trust your adviser (and you need to), because of their experience, success or approach, go forth with confidence.

Photo by Marc Suderman from Traver, CA