How to Store 5,000 Gallons of Water in 1/4 Acre
This ancient gardening technique will let you store about 5,000 gallons of water in ¼ acre of soil. This is water that your plants can access, reducing your water usage.
According to U.S. Department of Agriculture, “a 1 percent increase in soil organic matter content can hold an additional 19,000 gallons of water per acre.” Article here. Increasing the level of organic matter in your soil involves a combination of things to do and not to do. This is not a quick fix and will takes years to achieve, so we’d better get started right away. Here is the equation:
Increase the level of organic matter in your soil by 1% and your soil’s water holding capacity will increase by about 5,000 gallons per quarter acre. This is not a small pond, it’s a small lake living in your soil. This water often deposited by winter rains, or during irrigation, will be there for your plants to use.
You can store a lot of water in dense clay soil, but your plants will have a hard time using that water. Clay soil particles hold onto the water tightly and your plants, especially annuals, do not have the energy to extract that water. In contrast, organic matter in your soil acts like a sponge. It holds water and nutrients and when plants need them, it releases the water and nutrients to the plants. Organic matter is one of the most powerful tools you can deploy for water conservation. It works without your intervention.
(Note: Organic matter and organic material are two different things. If you don’t know the difference, read this straight forward article, What Does Organic Matter Do In Soil? by Eddie Funderburg.)
To garden effectively, you must “grow” soil that can capture the rainwater (and nutrients) and store it for future plant use. There are several factors that effect the water holding capacity of your soil. This includes, depth, texture, physical structure of your soil, levels of organic matter and levels of biological activities in your soil. You can manage all these factors.
In order for you to store water in your soil, the following three conditions must be satisfied:
1- Rainwater (or irrigation water) must be able to penetrate the soil. If your soil is compacted with a crusty surface, much of the water will runoff and the soil below will be dry.
2- Once the water is in your soil, water evaporation must be minimized
3- How much water you can store in your soil depends on how much water holding capacity you have developed in your soil.
Organic matter effects two of the above three factors. It loosens the texture of the soil so water can be absorbed and it holds onto the water for future release. Reducing water evaporation is mostly controlled by your gardening practices. More about this at a later post.
How to Increase Levels of Organic Matter
There are many practices that effects the level of organic matter in the soil. Here my top 5 recommendations for a backyard gardener:
Compost – Compost includes a lot organic material that has been decomposed into stable organic matter form. Add compost to your soil and your soil’s water holding capacity goes up. If you are thinking to add a lot of compost all at once, don’t. Add two or three inches of compost to the top of you soil and mix it in the top six inches of the soil. You can also add a one inch layer of compost as top dressing around your plants. Any more compost and you may change the soil chemistry with undesirable side effects.
Cover Crop – Cover crops are a cheap and highly effective way of increasing organic matter in the soil. Cereal Rye as a cover crop grows 3 miles of roots (mostly root hair) per day. That’s over 600 miles of root per growing season. If you harvest the plant and leave the root structure in the soil, the root system decomposes and eventually turns into organic mater. This is my preferred way of improving the soil at a deeper level.
Avoid Tillage – When soil is tilled, the stable organic matter is exposed to oxygen and begins to decompose. If you are starting with undeveloped land, it may be necessary to till the area (and import organic matter such as compost) to get started.
Once you establish a growing area, try not till the soil. Instead use cover crops as a tool for improving the soil. In early years use cover crops with extensive root systems such as cereals and grasses. This will improve your soil quickly and let you switch to other cover crops that can improve fertility or microorganism activities in your soil.
Fertilizers and (Pesticides,Herbicides, Fungicides) – Fertilizers (and most other chemical agents) stimulate plant grow. However high nitrogen fertilizers (most of the commercial fertilizers are N rich) also stimulate the levels of microorganism activities in the soil. This speeds up decomposition of the organic matter. Pesticides do the same thing. They increase the levels of microorganism activities.
More importantly excess nitrogen from fertilizers can leach into underground water reducing the availability of yet another source of fresh water. Read Gulf of Mexico Dead Zone and See Nitrate Contamination of Domestic Groundwater and Agricultural Irrigation for California.
These are some of the actions you can take this growing season that will have long lasting impact on your water use. From now on, part of your job as a gardener growing plants in drought condition is to grow organic matter.