Is Declining Soil Quality Affecting Our Food? | by Shannon Peterson

Consumers don't think much about soil when they are buying food. Farmers, on the other hand, know that soil plays an essential role in crops and yields. 

But does the quality of the soil actually affect the food we eat?

Author Daniel A. Marano examined this possibility in his article "Nature's Bounty: Rich Dirt, Poor Dirt," which was actually published in Psychology Today earlier this year. He notes that "the calcium content of broccoli averaged 12.9 milligrams per gram of plant tissue in 1950 ... but only 4.4 mg per gram by 2003."

Is it possible that "just when we want more from our food, we are getting less, and the declining quality of soil may be the root of the problem?"

It's an article worth checking out because the issue may continue to crop up. You can read the entire article here: Nature's Bounty: Rich Dirt, Poor Dirt

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Shannon Peterson Marketing Content Editor Shannon joined Valley Irrigation in 2013. She writes and edits materials about irrigation equipment. Shannon enjoys traveling with her family, particularly to national parks, and she occasionally writes about her travels for tourism magazines. She also likes trying new restaurants, seeing movies, and watching Husker football and Creighton basketball.

Happy World Soil Day!

Originally published on Soils Matter, Get the Scoop.

In honor of World Soil Day, we are sharing a blog on the importance of soil and how it cleans our water.

Q: How can soils filter or purify water, such as for drinking water purposes? There are just so many chemicals and bacteria in the soil that you would expect the opposite.

A: If we put some soil in a glass column and pour "dirty" water through it, the water will come out cleaner than when it went in. The soil, in other words, is a reactor. It has the potential to clean up dirty water by a variety of methods. So how does soil do this?

There are three basic ways. The soil is a physical filter that removes particles suspended in water; it is a chemical reactor that removes dissolved chemicals from water; and it is a bioreactor that transforms and degrades chemicals by the action of soil microbes.

The soil is the largest filter on the planet. The size of the pores in soil (which is based on the amount of sand, silt, clay, and organic matter that make up the soil) determine how effective the soil is at filtering out particles. A finer textured soil (more clay) with many small pores is a better filter. Yet, a soil can be too fine with too many small pores, so that water does not efficiently flow through the soil. A perfect soil has a distribution of pores of different sizes that can both filter water and allow adequate movement of water through soil.

The soil is the largest chemical reactor on the planet. The soil has a net negative (-) charge that triggers the removal of positively (+) charged ions in the water which moves through the soil. These (+) ions are removed from the soil solution much like a magnet with a (-) charge attracts another magnet with a (+) charge. The figure to the right shows how ions like calcium, magnesium, and potassium are attracted and held on soil surfaces. Still other chemicals are removed by the soil by becoming part of the soil structure through a process called covalent bonding.

The soil is the largest bioreactor on the planet. Within the soil, bacteria and fungi transform and decompose chemicals. The nitrogen cycle is especially dependent on the soil reactor. Microbes change organic forms of nitrogen into the ion, ammonium. More microbes change ammonium to nitrate, and even more microbes change nitrate into nitrogen gas, which then enters the atmosphere. Similarly, if the soil "sees" an organic pollutant, microbes go to work transforming and decomposing it, so eventually it becomes carbon dioxide and water.

The net effect is that the soil provides a service to society. It cleans the water that makes its way to rivers and streams. It helps keep the water clean for us to use and for wildlife to survive. If we don’t take care of the "largest reactor on the planet" we may destroy the service it provides and hurt our environment in the process.

By Nick Comerford, a University of Florida soil scientist and Soil Science Society of America member.

Irrigation Soil Types: Part I | by Travis Yeik

Soils are a leaky bucket of water. Even though rain and precipitation continually fill up the bucket, leaks are a result of evaporation, transpiration, runoff, and deep percolation (Figure 1). As more water is added to a soil, more water will be readily available to the plant; however, the downside to adding more water is that our bucket becomes leakier as well. For example, a saturated soil will have greater potential for runoff and deep percolation than a soil at field capacity. Maximum water loss from transpiration occurs between field capacity and the permanent wilting point. Soil water management aims to reduce leaks in our bucket, while, at the same time, providing adequate water to our crops.

The amount of water in our bucket, or available water holding capacity (AWC), depends on soil type and depth of the root zone. The AWC depends on two soil properties: the colloidal content (or amount of clay and humus) and the pore size/structure of a soil. A sandy soil, which typically has less colloidal content and larger pore sizes, won’t have an AWC as large as silts or clays per unit volume of soil (Figure 2). Because sandy soils cannot hold as much water as silt or clay soils, these areas will be the first to show signs of crop water stress.

A common misconception is that we can just add more water to the sandy soils to prevent crops from showing signs of water stress as quickly. However, as noted earlier, too much water added to a soil results in excess runoff and deep percolation. In fact, healthy plants if we consider equal crop types, growth stages, and other growth factors use water at the same rate regardless of what soil type they are grown in. Thus, a sandy soil which has a smaller bucket doesn’t need more water, but simply needs to be watered more frequently than other soil types.

Consider the example shown in Figure 3. At field capacity, clay soils can hold 1.9 inches of water/1 foot of soil, whereas sandy soils can hold 0.8 inches of water/1 foot of soil. Therefore, if we have a corn (maize) crop with a root zone of 3 feet, the available water at field capacity in clay soils will be 5.7 inches, but 2.4 inches in sandy soils. Corn may consume water (also known as evapotranspiration [ET], or the combination of evaporation and transpiration) at a rate of 0.32 inches per day in a moderately hot climate. This will result in an ET of 0.96 inches over a three-day time period. At that rate, clay soils lose 17 percent of its available water compared to sands, which will lose 40 percent of its available water!

In order to effectively manage irrigation in a field with various soil types, the amount and timing of water applied should be targeted to the soils with the lowest AWC.

Figure 1. Illustration of a soil profile as a leaky bucket. Soil water inputs are a direct result of irrigation and precipitation, whereas soil water losses occur from evaporation, transpiration, runoff, and deep percolation. Field capacity is represented as the lid of the bucket, where each addition of water will result in increased runoff or deep percolation. The permanent wilting point is represented as the bottom of the bucket.

Figure 2. Representative “clay” bucket (at top) and “sand” bucket (at bottom). The clay bucket has a larger volume than the sand bucket, meaning it has a larger AWC and can store larger amounts of water per unit volume.

Figure 3. A clay soil, which can hold 5.7 inches of water per 3 feet of soil, and a sandy soil, which can hold 2.4 inches of water per 3 feet of soil, will lose water through crop use (ET) at the same rate. However, because sand has a smaller bucket, it will reach its depletion point much sooner than the clay bucket.

Stay tuned for Part II of the irrigation soil types blog series, coming later this week!

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Travis Yeik Variable Rate Irrigation Agronomist Travis joined Valley Irrigation in February 2013 after completing his graduate degree at the University of Nebraska - Lincoln. His work focuses on writing prescriptions for the Valley VRI products. As a native of Wyoming, Travis enjoys outdoor activities, including fly fishing and hiking. He also enjoys sports and is looking forward to baseball season.