Building Healthy Soils to Safeguard Nutrition in the Face of Heavy Rain

While rain is generally a blessing for growers, too much can strip the soil of key nutrients, leaving crops with insufficient nutrition and washing away costly fertilizers. But by focusing on building soil health, growers can prepare their fields for wet weather and safeguard their investment through the season. 

With expertise provided by Landon Williams, Agronomist, and Research Scientists Alex Greenlon and Erin Baggs.

When it comes to rainfall, the biggest factor leading to nutrient loss is leaching. Nitrogen and phosphorus fertilizer in the soil can dissolve in rainwater and, instead of going into the plant to support growth and yield, are instead carried away from the field. 

“Leaching is a major concern, especially in sandy and coarse-textured soils,” says Landon Williams, an agronomist at Sound Agriculture. ​“It’s an economic loss for growers and those nutrients can contaminate groundwater.”

Because nitrogen isn’t held by soil minerals as well as phosphorus, it is more likely to end up in groundwater when it leaches out of a grower’s field. Drinking water contaminated by excess nitrogen can harm both humans and livestock by interfering with the blood’s ability to carry oxygen. 

Nutrient runoff is also tied to large, harmful algae blooms in the Gulf of Mexico and the Chesapeake Bay; algae thrive in nutrient-rich water, choking out other aquatic plant life and depleting the oxygen levels in the water as they decompose. To address this, states like Maryland have instituted nutrient management programs to protect water quality and reduce nutrient runoff.

For growers, nutrient loss represents dollars directly down the drain — costly fertilizers that won’t make it to the plant to support better yields. What a grower’s risk factors are for leaching depends on a variety of factors. 

“Managing leaching comes down to the amount of fertilizer used, the timing of application, whether it’s split applied, when you’re likely to get rain, and especially what kind of soils you have,” explains Landon. ​“Sandier soils won’t hold nutrients as well and are more prone to leaching, so soil health plays a big role in reducing nutrient loss.” 

Landon recalls a trip to Iowa the summer of 2018. Between May and July, the state had seen record amounts of rain, with unfortunate consequences for many farmers. 

“There were fields that were just flooded out. There was nutrient loss, but there was also just too much water — the soils couldn’t handle it,” he says. ​“It all goes back to the soil and how growers manage it.” 

Key soil factors that play particularly important roles in reducing nutrient loss during precipitation are organic matter content, soil texture and cation exchange capacity (CEC). Soil texture and organic matter content are particularly important for improving water-holding capacity, and both positively impact CEC, which is an indication of the amount of nutrients the soil can hold and supply to a crop. Coarse, sandy soils tend to have lower CEC, meaning any fertilizer or nutrition applied to the soil is harder for the soil to store. Water also moves more easily through coarse soils, so the loosely-held nutrients are easily washed away. 

“The higher your CEC, the more fertilizer you can use and the higher the soil’s water holding capacity, the more water can infiltrate at one time,” explains Landon.

Soil microbes are tiny but powerful weapons in the fight against nutrient leaching. Plants have developed relationships with soil organisms to trade carbohydrates made through photosynthesis for plant-available forms of key nutrients. For growers, the nutrition provided by phosphorus-solubilizing and nitrogen-fixing microbes is free, in-season and easily taken up by the crop. 

“Most soil microbes have ways of surviving when it’s very dry, but all of them need some soil moisture to grow and perform the soil processes they contribute, like nitrogen fixation and phosphorus solubilization,” says Alex Greenlon, Research Scientist at Sound.

During times when water is limited, more water will increase microbial activity in the soil, which is good news for growers. But just as too little water can hamper microbial processes, too much water can also pose a problem.

“Many plant pathogens need moisture, including oomycetes like the potato late blight fungus and powdery mildews,” explains Erin Baggs, Research Scientist. 

“And, if there’s too much moisture, that creates anoxic conditions in the soil — a lack of oxygen,” adds Alex. ​“That can cause problems for farmers, resulting in nutrient loss and denitrification.” Higher levels of organic matter in the soil also support drainage and reduce the risk of anoxic conditions. 

In addition to water, soil microbes need oxygen to survive. In extremely wet conditions, microbes can get the oxygen they need from nitrate and nitrite in the soil, which is then converted into nitrogen and nitrous oxide that leave the soil as nitrous oxide (N2O), a potent greenhouse gas. This process of denitrification is another way growers can lose applied nutrients to excessive precipitation, and reducing soil N2O emissions could be a way for growers to access carbon credits.

When applied fertilizers leach out of the soil, not only is that nutrition not available to the crop, but the money growers spent on that input is washed away without benefiting the field. To reduce the impact of heavy rain, growers can work to increase the soil’s nutrient holding capacity while focusing on precise nutrient application. 

“Sandier soils and soils with lower CEC just can’t hold a lot of water or fertilizer, so we see higher levels of nutrient leaching,” says Landon. ​“The way to increase that holding capacity and improve CEC is through soil health.” 

Practices that can help growers support soil health include:

• Cover cropping
• Reducing or eliminating tillage
• Limiting chemical and synthetic inputs
• Other regenerative agriculture practices

Meanwhile, growers should also consider their fertility plan and if there are ways they can be more precise. Landon says his two biggest recommendations for growers are split applying fertilizer and conducting periodic soil and tissue sampling. 

“As an agronomist, I generally recommend farmers split apply fertilizers because first, the plant needs nutrition throughout the whole season. But second, if you put all your fertility out at one time, the soil can’t handle it all and if you get a big rainfall, you’re going to lose a lot of that fertility,” he explains. 

Soil sampling will help growers determine what nutrients they actually need to ensure they’re not over-applying and tissue sampling will tell growers what nutrients their crops are taking up. If the nutrients growers apply aren’t making it into the plant, that’s important information to know. Both tissue and soil sampling are key to improving a grower’s nutrient use efficiency (NUE) score, which can help growers lower operating costs, maintain yield and reduce nutrient loss.

Growers may also want to examine their tillage practices to see if there are any improvements that can be made. In addition to disrupting the soil microbiome, tillage can increase wind and water erosion and even cause soil compaction. 

“Tillage can make the pore space between the soil particles tighter, which makes it harder for water and nutrients to get down through the soil like they should,” says Landon. ​“Often, when you get a hard rainfall, that’s why water sits on top of the soil — it can’t infiltrate properly, and the water-holding capacity of the soil is lowered.” 

Because each operation is unique, growers should also look at what the limiting factors are on their own farm, whether the challenge is water, getting oxygen into the soil or erosion. Once growers understand the conditions on their own farm, solutions can be tailored to their specific needs.

Today, a variety of products exist to help growers keep costly fertilizer inputs in the soil. For growers who need it, there are nitrogen stabilizers that can be applied to help prevent leaching and loss. On the other hand, SOURCEⓇ, Sound’s microbiome activator, boosts the power of the soil. SOURCE attracts the beneficial microbes already in a grower’s fields to the crop’s root zone where they unlock free access to plant-available forms of nitrogen and phosphorus. 

“It helps bring microbes to the root zone and lets the crop make use of the nutrients already there,” explains Landon. ​“Many growers have phosphorus in their soil already, but it’s tied up with other elements and SOURCE attracts the microbes that unlock phosphorus and turn atmospheric nitrogen into a plant-available form.” 

Unlike nitrogen stabilizers, SOURCE doesn’t address the leaching of applied fertilizer directly. Instead, it boosts the microbe environment that converts and stores nutrition and can be used to replace up to 25 pounds of nitrogen and 25 pounds of phosphorus. SOURCE can be applied with either a fungicide or herbicide for a free trip across the field and it doesn’t need to be watered into the crop, giving growers peace of mind whatever the weather. 

Once SOURCE has attracted the microbes already in a grower’s field to the crop’s root zone, those microbes begin bringing nutrients like nitrogen and phosphorus to the plants in forms they can use. When that big storm hits, unlike fertilizers and other traditional forms of nutrition, the nutrients unlocked by the soil won’t be washed away; they’ve already been used by the plant. 

“SOURCE unlocks the nitrogen and phosphorus that’s already in the soil to make it work for the grower,” says Landon. ​“And by improving that microbe environment in the soil, growers can reduce leaching and fertility loss.”