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Fertilizers, crops, and soils
Dr. Victor Martin

The weather overall cooperated this past week. Soils are warming and perhaps most importantly, we avoided rain that would delay fieldwork. Corn should be going in the ground now. This is being written on Friday and there is a chance of rain today. Today is the twenty-first and especially for dryland corn, and the seed should be in the ground no later than the end of this week. Next week is May and particularly for dryland planting, it is time to prepare for soybean planting. Last week the ANR agent for the extension district posted information from K-State regarding fertilizers and corn. Good information but maybe a bit of an explanation of the why regarding in-row and banded fertilizer applications at planting may be helpful. This is the Readers’ Digest version.

• There are two types of nutrients plant roots can take up – anions and cations. Anions such as nitrate, phosphate, chloride, and sulfate are negatively charged. Soil colloids, small mineral and organic fractions in the soil, possess a net negative charge. Like charges repel each other so these ions, especially nitrate, sulfate, and chloride are mobile and can move with water in the soil. This can be toward roots or with heavy rainfall, out of the root zone or even into ground water. Cations such as ammonium, potassium, calcium, magnesium, iron, and zinc are positively charged so they can be held on the soil colloids and exchanged into the soil solution for plant uptake. They move less easily to the roots and are less likely to move out of the root zone.

• Plant roots take up nutrients in three ways. Mass flow means the nutrient is carried to the plant in water taken up by the plant – nitrate and sulfate for example. Diffusion is the second way. Here the nutrients, phosphorus for example, move along a concentration gradient from higher to lower concentration. As the root removes the nutrient the concentration near the root decreases and causes the ion to move there from an area of higher concentration. This process is slow with drier soils and is slower under cool soil temperatures such as early spring. Finally, there is root interception, which is just like it sounds. The root grows and “runs into” the nutrient. Roots only take up nutrients from young actively growing root tissue, which is why roots must constantly be exploring the soils and producing root hairs on older roots.

• This relates to practices such as in-row fertilizer placement and banding near the seed trench. A newly emerged seedling has a small root system so where possible, fertilizer in the row makes uptake of nutrients easier. Banding near the seed allows the seed to quickly intercept a concentrated source of nutrients, especially those moving by diffusion. Banding also helps in cooler soil such as no-till where diffusion is slower. Also mentioned is split fertilizer application for things like nitrogen which helps when the nutrient can move easily in soil water and be lost to leaching.


Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207.