I hope that last week’s blog post on soil was helpful. Whether the information was a review or new, it gives you something to process and possibly plan a new strategy for improving your own soil. I know that I am! This week I would like to continue to explore soil and specifically four important aspects of it.
First, soil is full of life! There are live plant roots, earthworms, insects and a whole host of microorganisms that cannot be seen. In ¼ teaspoon of soil, there can be as many as 1 billion microorganisms, and they are the most abundant in the root zone. Their main function is to break down plant remains, and this break down process releases nutrients and creates soil organic matter. It is a diverse population, and many of the organisms are beneficial such as mycorrhizae fungi and rhizobia bacteria. Others are not beneficial and can cause disease and damage. Microbial populations are the highest in soils that are warm, moist, and have organic matter. Good practices to keep the microorganism populations high and performing well are adding organic matter annually and growing a winter cover crop each year.
Second, soil pH measures the acidity or alkalinity of a soil. Why is the pH important? It affects the availability of plant nutrients and it affects the activity of soil microorganisms. In arid climates, soils tend to be alkaline, and in rainy areas, soils tend to be acidic. The middle of the pH range, 5.5 to 7.5, is where most plants perform the best (with a few exceptions) and where microbial activity is the highest. Here’s a chart that shows the effect of soil pH on the availability of plant nutrients.
Soil pH is important, and getting the pH tested can be done easily and inexpensively. Once your soil is tested, and you’ve determined if the pH needs to be increased or decreased, you can purchase the recommended amendment and apply it to the soil. To increase the soil pH, lime is most commonly used. To decrease the soil pH, elemental sulfur, ammonium sulfate fertilizer or urea can be used.
Third, soil salinity is another factor that can especially be a problem in arid climates. Salts can accumulate from fertilizers, composts, and manure applications. If the amount of salt reaches a certain level, there can be potentially harmful effects on plants. In areas of more rainfall, salts are leached from the soil each winter and are not accumulated in the root zone. Soil salinity can be tested for, and if the level is considered to be too high, the salt can be leached from the soil by irrigating more than the holding capacity of the soil. The excess water, draining downward will carry the salts out of the root zones.
Lastly, the fourth area is soil nutrients. On the chart above, there is a list of essential plant nutrients. To know what your soil has and what it needs, a soil test is highly recommended as well as repeating the test every 3 – 5 years.
Where do the nutrients go? Nutrients are lost when there is soil erosion, when a crop is harvested, and when there is too much rainfall or irrigation and the nutrients leach from the soils. Fertilizers are then added to increase the amount of nutrients which will improve plant growth and yield of produce.
The primary nutrients needed by plants are nitrogen, phosphorous, and potassium, and the most common deficiencies are for these primary nutrients. As a general rule, these nutrients support:
- Nitrogen: leafy top growth
- Phosphorous: root and fruit production
- Potassium: cold hardiness, disease resistance, and general durability
What is fertilizer? It’s simply a substance that contains one or more essential nutrients for plants. Fertilizers that are commercially sold must be accurately labeled with grade, weight, and manufacturer. The grade is what gives the breakdown of minimum guaranteed percentages of nitrogen, phosphorous and potassium. Fertilizers can also be broadly classified as inorganic or organic.
What’s the difference between the two? Here is a chart to help explain the differences:
|Organic Fertilizer||Inorganic (Processed) Fertilizer|
|Source||Natural materials; little or no processing||Manufactured or extracted from natural materials|
|Examples||Manure, cottonseed meal, rock phosphate, fish by-products||Ammonium sulfate, processed urea, potassium chloride|
|Nutrient availability||Usually slow-release; nutrients are released by biological and chemical processes in soil||Nutrients usually are immediately available to plants|
|Nutrient content||Usually low||Usually high|
Here are some fertilizing basics:
- Always read the label!
- Apply fertilizer before anticipated plant growth
- Nitrogen applications have its greatest effect for 3 – 4 weeks after application
- Use a liquid fertilizer when starting plants to provide phosphorous to new roots
- Do not apply fast-release fertilizers prior to heavy rainfall or over irrigate after application
- Do not apply fertilizers around wells or where run-off could carry into waterways
- Calculate how much you need (based on soil test and plant needs) and do not use more than needed
Some natural practices to maintain nutrient rich soil:
- Add organic matter, 1 – 2 inches to soil each year. Organic matter is a long-term, slow-release storehouse of nutrients which continuously becomes available as the soil microorganisms break it down.
- Make your own compost or purchase commercial compost for your source of organic matter. Composting deserves its own blog post at a later time!
- Make use of green manure or a cover crop each fall. Plant them as early in the fall as possible to achieve enough growth to cover the soil. Use legumes to supply nitrogen to the soil. In the spring, if it’s too wet to till under before the crop flowers, cut if off and compost the foliage for later use. The benefit of organic matter from the crowns and roots will be available when you can turn the soil under.
We have covered a lot of information in this post, and it is all fairly elementary with much more that could be written. Extension agencies are a great source of help for improving soil, and they often have free publications to address each of these four areas and more. Check out your local extension office!
Question for the week: Do you have a favorite fertilizer that you cannot garden without?
Diagram of availability of soil nutrients from: http://www.eatcology.com/index/
Chart comparing organic and inorganic fertilizer from: OSU Master Gardener text book, Sustainable Gardening
By Kimberly Bell