Background Information
We are fortunate to live in a society with abundant food, but the challenge for the future is simple. We must feed a population that grows by 80 million people each year, using the same amount of farmland and depleting natural resources. Clearly, the farming practices of the past are not going to be able to sustain us in the future. Our response to this challenge involves making difficult decisions about land use, fertilizers, pesticides, and genetic engineering, among others. As a society, we will have to decide how agriculture can economically feed our growing population while at the same time help us protect our environment.
Soil Triangle
During soil formation, inorganic material is broken down by weathering into particles of various sizes. Soil texture refers to the relative proportions of different-sized particles found in the soil. Scientists classify soil particles into three categories: clay, silt, and sand. Because soils vary in their proportions of these, soil scientists classify different soil types using the soil triangle. Each side of the soil triangle represents the amount of a particle of a certain size—clay, silt, or sand. The relative amounts of these three soil components intersect within the triangle and determine what type of soil those proportions correspond.
Nourishing Crops with Fertilizers
Fertilizer is essentially “plant food.” It is added to replenish nutrients that people indirectly extract from the soil by harvesting plants. In non-agricultural ecosystems, the nutrients removed by plants are returned to the soil after the plants die and decompose. On farms, some of these nutrients are removed in the form of harvested crops,
so it is often necessary to replace them with fertilizers. The essential components of most fertilizers in nitrogen, phosphorus, and potassium, which are macronutrients. All three of these elements play essential roles in allowing plants to access the free energy of the sun through photosynthesis and must be present in adequate amounts to
ensure healthy crop growth.
Organic and Commercial Fertilizers
Farmers who fertilize their crops have the choice of using either organic or commercial fertilizers, or a combination of the two types. As the name suggests, organic fertilizers come from once-living material, such as plants or animal manure. Commercial fertilizers consist of natural ingredients that have been subjected to a chemical process to make a fertilizer with increased and uniform nutrient content. Commercial fertilizers come either from natural mineral deposits or, in the case of nitrogen, from the Earth’s atmosphere. Chemically, there is no difference between the nitrogen atoms that come from fertilizer, animal manure, a compost pile, or the atmosphere. Provided they are in the same form (e.g., ammonium, nitrate, or urea), they are the same as far as the plants are concerned. Yet, there are differences in the rate at which the nitrogen from each of these sources is made available to plants and in the ratio of nitrogen to other elements such as phosphorus.
Meeting Crops’ Nutrient Needs
Fertilizers can be applied as liquids, solids or, as in the case of anhydrous ammonia, a pressurized gas that is injected into the soil. Bagged fertilizers are sold in a wide variety of mixtures. It is easy to read their contents from the fertilizer label. The percentage by weight of the three macronutrients—nitrogen, phosphorus, and
potassium—is listed as the fertilizer’s NPK ratio. For example, a label with an NPK ratio of 26-6-6 means that the fertilizer contains 26 percent nitrogen, 6 percent phosphorus, and 6 percent potassium. Some fertilizers also contain micronutrients, which are nutrients needed in smaller amounts for plant health and growth. Fertilizer
labels also indicate the amounts of micronutrients as well as any inert ingredients, such as sand, that are included to provide bulk and make the fertilizer easier to apply.
Farmers use scientific methods to determine the appropriate nutrient balance for their crops. Because every farm field is different, farmers need to be able to select best management practices (BMPs) that are suited to their growing conditions. Factors that may influence BMP selection include soil, climate, topography, and crop nutrient requirements. Often, farmers work with a certified crop adviser, a trained nutrient management professional, to assess growing and environmental conditions and develop a nutrient management plan based on soil needs determined by soil tests.
Free Educational Resources
Science and proper soil nutrition will be critical to helping with not only feeding our world but doing so sustainably. This background information serves as a basic understanding to this complex subject. Free Nourishing the Planet in the 21st Century high school curriculum is available for teachers to use. Teaching the curriculum prior to teaching the breakout box will provide the background information needed for the students to be successful at the lesson. To view other free educational resources, visit www.nutrientsforlife.org and www.kansascornstem.com.