Understanding Crop Nutrient Access

Matt Fryer, a technical agronomist with Koch Agronomic Services (KAS), walks through the top four factors that can impact your crop’s ability to uptake nutrients.

"Soils are complicated," Fryer said. "You’d think soil would be simple, but it's not. So many different factors play a role in how nutrients interact with soils. That’s why it’s so important for growers to know about the key factors that go into nutrient conversion."

The physical properties of soil vary from field to field. Crop success can be impacted throughout the growing season by several soil-based factors, including soil pH, nutrient supply, soil moisture and soil temperature.  Soil pH – the acidity or alkalinity of soil – can also have a great effect on plant nutrients. 

"Soil pH is the master variable when it comes to plant nutrient availability," Fryer said. "Submitting soil samples every 2 to 3 years for routine soil analysis to a local lab will give invaluable information on soil pH and many other indices which are crucial for your nutrient management program."  

Nutrient availability and plant root growth can be negatively affected by a higher pH value. For example, phosphate ions form less soluble compounds for plant growth at pH levels higher than 7.5.

The solid particles that comprise soil are sand, silt, clay and organic matter. The surface of clay and organic matter are negatively charged. Just like a magnet, the positively-charged nutrients are attracted to the negatively-charged soil matrix. Nutrients are absorbed in both positively and negatively charged forms, but some are stronger than others.

MOBILE & IMMOBILE NUTRIENTS

Not all nutrients behave the same way in the soil. Negatively charged nutrients, or anions, are typically mobile in the soil, which can increase the risk of leaching away from the root zone. Positively charged nutrients are typically immobile due to their attraction to negatively charged soil particles. Insoluble precipitate formation with some nutrients can also cause nutrient immobility. Immobile nutrients are mainly taken up by the plant via direct root interception or through diffusion over very short distances, so they need to be in very close proximity to the root to be taken up by the plant. 

However, not everything is set in stone. Some nutrients that are generally classified as immobile, can become moderately mobile given the right conditions.

"Potassium is an example of an immobile nutrient," Fryer said. "Because it's positively charged, it should adhere to soil cation exchange (CEC) sites. But potassium has a fairly weak bond to the CEC, so it will tend to fall off the CEC relatively quick to replenish the soluble soil potassium in solution, and when very high soil potassium concentrations are present, it is possible the potassium will leach down the soil profile or run off the field via surface water runoff."

THE NEED FOR WATER

Many different factors can limit crop yields, but among them, water and nutrient availability are key. However, it is important to know what rate is needed as having too much or too little can become a detrimental situation for crops.

Whether from rain or by irrigation, crops need the right amount of water to reach their maximum yield potential. 

"Most nutrients are taken up by the plant via water, so if water is not being taken up by the plant, then neither are those nutrients," Fryer said. "But when there's excess water and you have saturated soil conditions, those roots are not getting the oxygen they need. And if they're not getting oxygen, the systems in the plant aren't functioning to be able to even take up those nutrients. During those times, nutrients are no longer the limiting factor in those situations."

Nutrients can also move toward the plant roots through diffusion, from higher concentration in the soil to a lower concentration. Directly around the root hair could be a lower concentration because the roots are taking those nutrients up, so nutrients can diffuse from the area of higher concentration toward the roots. When soils are cold, diffusion rates and microbiology activity is much lower as well. Microbes are responsible for mineralizing nutrients that are trapped in organic matter into a plant-available form. If that activity is slowed, fewer nutrients become available to the crop.

COVER CROPS AND NO-TILL RESIDUE

Cover crops and conservative tillage practices can be beneficial for many growers. They can prevent erosion and improve soil health. But growers need to be mindful about nutrient management when it comes to cover crop termination and preparing fields for spring planting.

"In the early season, cover crop residue on top of the soil is going to keep the soil colder longer," Fryer said. "In general, it’s going to slow the warm up of soils in the spring unless it’s terminated at the right time. Slowing biological activity doesn’t help facilitate nutrient interactions and plant functions."

Cover crops are intended to scavenge residual nutrients, preventing them from running off the field. Even after termination or tillage, nutrients are still tied up in the residue until the organic matter breaks down and decomposes in the soil. Microbes require nitrogen to break down organic material, so if the organic material from the cover crop residue has a low nitrogen to carbon ratio, the microbes can temporarily immobilize surface-applied nitrogen, making the nutrients unavailable to the crop for uptake over several weeks. 

There is also a risk for increased nitrogen loss via volatilization from cover crop residue due to greater urease enzyme activity, additional moisture and reduced soil contact. Volatilization losses can be as high as 40% when urea nitrogen is not adequately incorporated into the soil and may be an additional 10% greater in high residue systems.¹ 

SOLUTIONS TO OVERCOME NUTRIENT ACCESS LIMITATIONS

To help growers overcome the limiting factors of nutrient access, KAS has three solutions you should consider using in your fields.

Early in the growing season, root systems are still young and not as able to access nutrients. PROTIVATE^™ nutritional seed enhancer is designed to help optimize crop establishment by providing nutrients directly on the seed, enabling plants to thrive in those critical early stages of growth. A highly concentrated nutrient source for young crops, PROTIVATE also provides operational efficiencies to growers as a talc replacement.

Boosting crop performance, WOLF TRAX™ DDP micronutrients are formulated to simplify nutrient management for growers. With its patented EvenCoat™ Technology, WOLF TRAX is uniquely designed to coat onto dry fertilizer blends and deliver highly available nutrition through better distribution across the field than traditional granules. By making nutrients more accessible to the plants, WOLF TRAX products promote crop performance. Each WOLF TRAX formulation is engineered to deliver nutrients throughout the growing season. 

Since urea and UAN are at risk for volatilization in high-residue cropping systems, a urease inhibitor, like ANVOL™ nitrogen stabilizer, will help you keep nitrogen available for uptake. CENTURO™ nitrogen stabilizer is an easy-to-handle nitrification inhibitor offering below-ground protection for anhydrous ammonia or UAN. CENTURO is proven to keep applied nitrogen in the ammonium form up to three times longer than without an inhibitor², helping growers improve their nitrogen use efficiency and keeping more nitrogen available for plant uptake.

To learn more about the KAS solutions that can help you improve nutrient access, contact your KAS representative today.

¹The underlying data was provided by Instituto Nacional de Tecnologia Agropecuaria under a Research Trial Financial Support Agreement with Koch Agronomic Services, LLC and neither Instituto Nacional de Tecnologia Agropecuaria, nor the individual researchers referenced, endorse or recommend any product or service. ²The underlying data is based on third-party laboratory studies funded by Koch Agronomic Services; results may vary based on a number of factors, including environmental conditions. Improvements in nutrient use efficiency, yield and nitrate leaching may not be observed in all cases.