The Down and Dirty of Soil Fertility

— Written By Katie Carter
en Español / em Português

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Soil is more than just dirt, it is a living substance and when balanced, exchanges nutrients, stores and drains water, and provides a healthy environment for crops and forages to produce realistic yield expectations (RYE). So, what is soil fertility, and how do we get soil to a healthy place where crops and forages will thrive?

A fertile soil will contain all the major nutrients for basic plant nutrition, such as nitrogen, phosphorus, and potassium, as well as other nutrients needed in smaller quantities like calcium, magnesium, sulfur, iron, zinc, copper, boron, molybdenum, nickel. Most fertile soils will also have a component of organic matter which improves soil structure, moisture and nutrient preservation, and a pH between 6-7. Unfortunately, many soils around ENC do not have adequate nutrient levels and have little organic matter, because we have very sandy soils which allows leaching of nutrients.

Some things that can be done to strengthen soil fertility are applying commercial fertilizers, manures, waste products, and composts to add nutrients and organic matter to the soil. Lime can be added to bring the pH up to accepted levels of 6-7. It’s important to be careful when applying nutrients to soil and to ensure that practices are environmentally sustainable. Inappropriate management of nutrients can lead to contamination of lakes, rivers, streams, and groundwater.

There are 17 essential plant nutrients. Three of these essential nutrients come from air and water (carbon, oxygen, and hydrogen) and 14 come from the soil. Macronutrients are needed in high quantity, whereas micronutrients are needed in pH chartsmall amounts. pH plays a huge role in nutrient up take. If pH is too high, some nutrients become unavailable and the same situation happens if the pH is to low.

When a crop or forage is deficient in a nutrient it can be hard to identify what nutrient deficiency symptom is showing, but the problem needs to be addressed to reach RYE. Some of the macronutrients that we are most commonly concerned with are Nitrogen, Phosphorus, and Potassium. Nitrogen (N) is absorbed by the plant in forms of NO3- and NH4+. The function of N are protein and enzyme competent. Deficiency symptoms are general yellowing of leaves, stunted growth and often the older leaves are affected first. Phosphorus (P) is absorbed by the plant in forms HPO4- and HPO42-. The function of P is used for membranes, energy, and DNA. Deficiency is difficult to visualize until it’s severe, dwarfed or stunted plants and older the leaves turn dark green or a reddish-purple. Potassium (K) is absorbed by the plant in the form of K+. The function of K is for Osmotic balance. K deficiency looks like wilting in older leaves or they will look burnt. Another symptom is yellowing between veins and begins at the base of leaf and goes inward from the leaf edges.

N, P, and K are the three nutrients that we oftentimes are the most concerned with. But how do we know before a crop or forage is planted, what the soil is lacking? Soil samples of course! A soil sample test tells us what is in the soil and also what the soil needs to be adequate enough to promote healthy growth of crops and forages. Soil sample boxes along with the soil sample report form can be picked up at your local Extension office.

Now that you have your boxes, it’s time to start taking samples. The best way to take soil samples is at random. The number of samples varies on the size of land that your wanting to sample. The bigger the area, the more samples you’ll need. You can ask at time of soil sample box pick up, how many samples will need to be taken. After your random samples have been taken and mixed into a clean plastic bucket, a few handfuls of the mixed sample need to be placed in the soil sample box, filling to the red line. Once the soil sample sheet is filled out with the forage or crop that is being grown everything can be returned to the N.C. Cooperative Extension of Craven County office where it will be sent off to N.C. Department of Agriculture and Consumer Services. When filling out the soil sample form be sure to write in the correct code for what is being grown. Different forages/crops require different amounts of nutrients. It will take a few weeks to get sample reports back, and if you need help reading the report, your local Crops, Horticulture, or Livestock agent will be happy to help.