We live in a beautiful environment here in the Pacific Northwest. The lush green forests, snow-capped mountains, crystal lakes and fertile rivers we enjoy are here thanks to the amount of precipitation we receive west of the Cascade Mountain Range. This rainfall and our native soils are ideal for the temperate rainforests that used to dominate the landscape. The rock our soils were created from, and the leaching of soil nutrients due to rain, contributed to acidic soil conditions that allow native plants such as red cedar, huckleberry and sword fern to thrive.
Changing the land from temperate rainforest to the plethora of today’s uses meant adapting the landscape. Most gardening and agricultural endeavors require us to change the soil to create better growing conditions for a wide variety of crops. From pasture to potatoes, and pumpkins to hay, lime is more often than not a key component in creating the ideal soil for our current agricultural activities. Without the addition of lime, native soils are usually too acidic for many of the crops we want to grow.
Soil pH refers to how acidic or alkaline soils are on a numeric scale of 0 to 14, with 7 being neutral (see chart below). The pH scale is logarithmic, meaning each whole number represents an increase or decrease of tenfold. Therefore, a pH of 5 is ten times more acidic than a pH of 6, and 100 times more acidic than a pH of 7. Most crops prefer soil pH to be between 6.0 and 7.0.
Importance of Soil pH
Soil pH functions as a control mechanism within the soil ecosystem. The rate of chemical reactions within soil is dependent on its pH level, as is the activity of the microorganisms that live in that soil. Different nutrients become more or less available to plants based on the pH. In the chart below we can see, for example, that nitrogen is readily available to plants when the soil pH is around 6.5. As the pH decreases to 5.5, nitrogen becomes much less available. As soil pH decreases, the activity of beneficial nitrogen-fixing bacteria slows down significantly, making nitrogen less available to plants. Disease-causing fungi and other harmful organisms can function rather well under low pH conditions, further compounding problems for desired crops.
When considering soil health and nutrients for whatever crop you’re growing, pH is a very important factor. Lime is one way to control soil pH. Lime brings our naturally acidic soils (pH between 5.0 and 6.5) up into a more appropriate pH range for growing many crops. After applying lime to a pasture or lawn, many people notice the area will visibly “green-up” because nutrients in the soil become more readily available to lawn and pasture grasses.
Different plants grow best at differing pH levels. Blueberries love our native acidic soils, thriving between 4.0 to 5.3, while many other crops require a pH much higher. Therefore, it’s important to know the optimal pH range for the crops you’re growing and how to manage pH to obtain the highest crop vigor and disease resistance.
How to Apply Lime
Depending on your starting pH, adjusting your overall soil pH can be a long process. There are two main things to consider when determining how much lime you will need to apply:
1. You need to take soil tests. This is a very important step and ensures you apply an accurate amount of lime to your soils.
2. You need to take into account what you want to grow. As previously mentioned, different plants require different pH levels for optimal health. Pasture is going to require a different pH than a vegetable or berry crop. The crop you desire to grow can be factored into your soil test, so the recommendations you receive will be for your specified crop or crops.
In general, you don’t want to apply more than two tons per acre of lime at any given time. More than this can cause damage to the micro-organisms in your soils. If your soil test results call for more than a two-ton application, split your application in half – apply half the first season, and the second half later in the year.
When to Apply Lime
Lime can be applied any time of the year, however in the Pacific Northwest, applying lime in the fall has specific advantages. It takes approximately four months for lime to fully react with the soil. With a fall application, pH should be ideal by the spring growing season. Applying in the fall also draws the lime farther down into the soil during the rainy months, creating benefits deeper in the soil.
Make Sure There’s Contact
When applying lime, you want it to have as much contact with the soil as possible. Lime sitting on grass or other vegetation is going to blow or wash away and have limited contact with and effect on the soil. Depending on your operation, you might be able to lightly till lime into your soil. This will help reduce wind drift and rain run-off. Broadcast spreading is another option, using a pelleted form to get it down to the soil.
Choosing Your Source of Lime
There are many different sources of lime on the market. When choosing lime, consider neutralizing value, particle size and cost. Neutralizing value is expressed by the percentage of calcium carbonate equivalent (CCE), the purest is 100 percent. The higher the CCE, the greater effect the lime will have on soil pH. Some agricultural limes like dolomitic limestone are at 100 percent, while others contain impurities such as sand or clay. The table below shows various lime materials and their percent purity.
Particle size indicates how fast lime will react with your soil. The finer the particles, the faster acting it will be. However, finer particles are more difficult to apply. For example, a powdered lime can blow away with wind, clog machinery if moisture is present, coat everything in a fine dust, and be harder to get good soil contact. Pelletized forms of lime can be much easier to handle, make better contact with soil, and will change pH more slowly, which some plants prefer.
Animals and Lime
After an ag lime application, animals can safely continue grazing. If you use other sources of lime, however, keep animls off the area until a good rain has washed lime off vegetation and into soils. Sources of lime, other than ag lime, can cause irritation to hooves and paws of livestock and pets.
For further information on lime or soil testing, contact Carrie Brausieck, Resource Planner, at email@example.com or 425-377-7014. The Conservation District also has a pull-type spreader available to borrow (donation suggested) for broadcasting lime by calling 425-377-7019.