Calcium: The Soul of Soil and Plant Health Don TrotterHello fellow Earthlings, and welcome to a series of articles on the minerals and nutrients that make our precious plants grow. Our first article will be on my personal favorite mineral for soil and plant vigor. So lets take a stroll out to the garden.

Calcium has always taken a back seat to the "big boys" of soil fertility. The industry buzz is usually nitrogen and new forms are frequently being released to the market. Referred to as a secondary nutrient behind nitrogen, phosphorous and potassium, calcium is finally starting to take its place in the ranks of important plant nutrients. It is true that NPK is used in greater percentages than calcium, but calcium is used more by weight and volume than any other nutrient. Practically speaking, calcium is rarely considered as a nutrient at all! Instead the focus on calcium has been more as a soil buffer to help adjust pH. Calcium is of huge importance to both the plant and the soil in many more ways than simply moving the pH scale. It plays a major role in the physiology of the plant, strengthening its physical structure and helping in protection from disease attack. In the soil, the importance of calcium is many fold, including the reduction of soil compaction and helping to provide a better environment for the proliferation of beneficial bacteria. Some research even suggests that calcium play a role in decreasing weed populations. The list goes on and yes, it can have a role in the pH of the soil! THE PLANT
Imagine the room that you're sitting in is a plant cell of your favorite plant. The walls that surround you are made of calcium pectase (if you were inside a plant calcium pectase would be the least of your problems). The more calcium that is available to that cell, the stronger those walls become.

If calcium is limited the walls are as weak as jelly. As more calcium becomes available, those walls take on the strength of cinder blocks. The stronger the cell, the stronger the plant, and the quicker its recovery from the enormous pressures that it's faced with in the garden. This works for both leaves and roots. The stronger the root cells are the more aggressively the roots will be moving through the soil. Proper levels of calcium within the plant strengthens the whole plant and allows for efficient use of sunlight, carbon dioxide, water, nitrogen and mineral nutrients. Calcium also plays a major role in the construction of numerous hormones, and enzyme systems that can help protect the plant from insect and disease attack. It has been reported that as a pathogen probes its way into a cell it injects an enzyme to help break that cell down. There is research that suggests that, as this occurs, proper levels of calcium within the cell can actually slow this attack down, or stop it all together. The levels of calcium within the cell are going to be dictated, to a large extent, by the management of calcium within the soil. THE SOIL
Calcium plays many roles in the soil, but it is the relationship with other nutrients such as magnesium, potassium and sodium that are most significant. To associate calcium only as a buffer of pH in the soil is an injustice. In fact, pH can be driven by numerous minerals, like magnesium, potassium, sodium, or even aluminum. Often time calcium is applied to the soil to lower pH. It is important to understand that an imbalance of calcium will lead to tight, hardpan soils, which will restrict the flow of air and water through the soil profile. This will not only affect the plant roots, but perhaps even more important, will slow down the growth of beneficial microorganisms.

The soil is an extremely dynamic environment consisting of numerous chemical, biological and physical reactions. It is on all three levels that we must manage the soil. We can change the physical structure of a soil by properly managing the chemistry, thus providing a stronger biological environment. It is this biology that is so important to the success of managing any crop. For the first time in recent memory soil biology has risen to the forefront of our industry. Pathologists are introducing soil inoculants as biological controls for pests, advocates of IPM are starting to look closer at soil management as an integral part of their success and we are all beginning to understand the need for soil carbohydrates. If we are going to make any improvement in the health of the plant, proper soil management is imperative and this all starts by managing calcium levels in the soil. MANAGING CALCIUM IN THE SOIL
Dr. William Albrecht, the former head of the soils department

At the University of Missouri, established the protocol for balancing the basic cations on the soil colloid over 50 years ago. Today that research is the backbone behind a growing interest in sustainable soil management. Many of the pre-eminent soil testing laboratories use this methodology today. His research focuses on the soil tests' base saturation readings, where calcium plays the largest role.

Base saturation measures the relationship between the cations on the soil colloid. These nutrients are expressed in percentages and will always add up to 100%. The beauty of base saturation methodology is the fact that it deals with the relationship among the cations, not the actual pounds per acre of any one nutrient. On a soil with a high holding capacity, or CEC, the pounds per acre of a nutrient is naturally going to be much higher than on a similar soil with a lower CEC. If we manage soils to specific levels of a nutrient, the relationship between the cations will vary significantly depending on this holding capacity.

When evaluating the base saturation percentages of a soil the ideal targets are:

With an ideal range of calcium in the high 60 percentile it becomes very clear to see why calcium is so important. Using these percentages as a standard, the manipulation of these nutrients becomes manageable. If one nutrient is high it can be exchanged off the soil colloid by applying one of the other nutrients. For example, if magnesium is excessive in a soil, 20% or higher, another nutrient becomes weaker. The relationship is always 100% so it becomes a game of "give and take (sounds like soil politics)." Very often the nutrient given up will be calcium. The addition of calcium will drive out the excessive magnesium allowing calcium to saturate the colloid. This manipulation will work with any nutrient that is out of balance.

When imbalances among these minerals occurs, the soil becomes very tight and air and water can not penetrate. When this occurs roots are not the only things that suffer, but beneficial bacteria suffer as well. Since the relationship between calcium to magnesium makes up 80% of the soil colloid it is this relationship that is most important. As calcium drops below 60% and magnesium creeps above 20%, the soil becomes very tight. These are looked at as heavy, unmanageable soils, and excessive mechanical aeration appears to be the only help. Unfortunately, this aeration does not address the real problem, and until the Ca:Mg ratio is addressed that soil will remain tight. We have seen soils all over the country "open up" through the use of appropriate calcium sources, and the balance of base saturation. Because air and water movement improves so does biological activity. This helps to suppress disease problems, reduces isolated dry spots (hot spots) and allows for the reduction of nitrogen usage. Earthworms that were once not present are now actually becoming a management problem, one that is agronomically the best "problem" to have. TYPES OF CALCIUM
There are a number of good ways to supply calcium to a soil, but when calcium levels are below 60% base saturation, limestone is the most appropriate. Not all limestone is created equally! There are two basic forms of lime, high calcium lime, or calcitic lime, and high magnesium lime/ dolomitic lime. Depending on the source, calcium levels can vary from around 30% to 45%, but the real difference is that percentage of magnesium. High calcium lime will have a magnesium oxide reading of about 5% while dolomitic lime will read closer to 20%. This difference in magnesium is significant since it will drive pH up faster than calcium and will quickly create a tight soil. In soils with excessive magnesium levels dolomitic lime would not be appropriate, and in fact can create even worse imbalances in the soil. In this situation high calcium lime will actually allow for the exchange of magnesium for calcium and can often actually lower soil pH by better balancing the base saturation, and allowing for better hydrogen saturation. In many situations both high calcium and dolomitic lime would be called for to best balance this critical Ca: Mg ratio. The specifics of these recommendations are often best left to a qualified consultant, but in general terms, if the soil shows a high percentage of magnesium and calcium levels are below 60%, high calcium lime is the lime of choice.

Gypsum is calcium sulfate and is typically around 23% calcium and 18% sulfur. It has this magical reputation of reducing soil compaction, which it will do in many situations, but is often misused. Gypsum is not very effective in a soil that shows less than 60% base saturation calcium. A soil with a significant calcium deficiency often needs large quantities of calcium to saturate the soil colloid. If this is applied as gypsum, too much sulfur is being applied and problems can occur. It is important to use the appropriate type of lime on calcium poor soils. Once the calcium base saturation is above 60% gypsum becomes the calcium of choice for many. Here it will help to knock excessive magnesium (or any other excess) off the soil colloid through a reaction with sulfur and the exchange with calcium. Since it is sulfur rich it will typically not raise the pH.

Calcium is an extremely immobile nutrient. If it is appropriate to use gypsum, mobility can be improved slightly. But watch out for that sulfur. It is imperative we balance the calcium in the soil so we can provide the environment that microbial populations need to proliferate, but it is also very important we provide the plant cell with calcium. This is how it can lower the soil pH, which is getting a lot of attention for disease suppression. Is it possible that this available calcium may play a role in this disease suppression? Dr. Curly says You betcha!THE CONCLUSION
Calcium perhaps plays more roles in the overall health of both the plant and the soil than another nutrient. If well balanced on the soil colloid it will help to physically open up the soil for better air and water movement. This in turn provides the needed environment for beneficial bacteria creating checks and balances for pathogens. Within the cell it provides turgidity and is needed for numerous physiological reactions. It helps in root and leaf development and makes phosphorous and micronutrients more available. If well balanced the proper levels of calcium are going to help reduce the need for nitrogen by making organic matter decomposition more efficient. As Dr. Albrecht explains it in his volumes of research, if we get the calcium right in the soil most of our work is done. Next time well be talking about early holiday wishes for gardeners. See you in the Garden.