Making Every Pound Count: Nutrient Management in Corn

Fertility starts with the soil and the variables that make nutrients available to a growing crop.

Know Your Soil Texture

• Clay – very fine, soils with >50% clay
• Silt – rock & mineral particles that are larger than clay and smaller than sand. Soils with >87% silt
• Sand – very coarse, soils with >70% sand
• Loam – a balanced mixture of clay, silt and sand (approximately 20-40-40)

Soil texture determines a soil’s water holding capacity. Sand has low capacity to hold water and low water content at permanent wilting point (~10-15% v/v). Clay loam has a higher capacity to hold water, therefore has a higher water content at permanent wilting point (~15-20% v/v).

Nutrient Balance

Nutrient balance is vital to soil fertility and crop production. Nitrogen is most commonly the first and most limiting nutrient for non-legume crops, but without an adequate fertility blend with other nutrients, nitrogen use efficiency is not “maxed out” and suffers.

A poorly fertilized corn crop uses just a little less soil water over the season than an adequately fertilized crop, and yet fewer bushels of corn are produced per inch of water used. The properly fertilized crop is able to be much more efficient in water usage to produce more grain per inch of water used.

Nutrient Uptake

 Nutrient movement in the soil and uptake by plant roots is important to understand because it dictates where fertilizer placement best facilitates root uptake. Nitrogen and sulfur are very mobile in the soil and move via mass flow. This essentially means that they move with the soil water. As a plant transpires water, the roots are required to draw in more nutrient-rich soil water and they do this by creating tension that draws the soil water to the roots. The rate of transpiration is related to environmental conditions, so poor soil moisture or cold temperatures,  for example, will decrease the rate of transpiration, therefore decrease uptake of soil water (and nutrients) via mass flow. Phosphorus and potassium move in the soil via diffusion, meaning that with the help of soil moisture, the nutrients move from areas of high P or K concentration to areas of lower P or K concentration. As the nutrients are absorbed by plant roots and moved up into the plant, the roots become an area of low concentration, thereby drawing nutrients towards the roots from a higher concentration zone.