L18. Let's Talk Corn

Welcome to the next unit of our course! You are now an expert in growing, harvesting, processing, and using wood for building or for paper. You have also learned that wood may not be perfect, but is environmentally better than other construction materials. There is always more to learn but it is time to move on.

This lesson begins our next unit where we discuss emerging bioproducts made from herbaceous plants and algae.

Herbaceous Crops

If you remember from Lesson 7, herbaceous crops are different from wood. The primary difference is that the leaves and stems of herbaceous plants die off each year while wood stems continue to grow - adding to the diameter of the stem each year. Herbaceous crops include grasses (e.g switchgrass), cereal grains (e.g wheat, oats), and roots/tubers (e.g. potatoes, taro). Bioproducts and bioenergy can be made from almost any plant, and can be derived from the stems, leaves, fruits, or seeds. Remember that each plant species will have different amounts of molecules like starch, cellulose, protein, and oil, so the crops we choose to grow depend on the end product we seek to make.

Let's begin by reviewing how herbaceous crops are grown. Understanding this will help us think later about a bioproduct's Life Cycle Assessment. Growing plants can be thought of as the "extraction phase" of the LCA.

Most of the herbaceous crops we use for bioproducts are annual crops - planted and harvested every year. Corn and soybeans are the most common crops used for bioproducts, but they are mainly produced to grow food for humans or animals. Corn and soybeans are row crops - meaning they are planted in rows. Grain crops like wheat and oats or grasses are not grown in rows. Producing any annual crop requires the following steps:

Tilling and preparing the soil for the seeds. This involves a tractor and an implement to break up the soil to allow good contact between the soil and the seed. Tillage can also be used to mix in the dead plant material from the previous year (called residual) into the soil. There is a variety of different tillage equipment used to accomplish this soil preparation.
Planting the seeds. With annual crops seeds are planted every year. This is done with special equipment designed to accurately place seeds at the appropriate depth and spacing between plants.
Fertilizing. Plants require a variety of nutrients to grow properly. The most necessary nutrients are nitrogen, phosphorus, and potassium. Soils are tested each year and assessed for available nutrients. If the crop needs more nutrients to grow properly, fertilizer will be applied to meet these needs. Corn plants require lots of nitrogen. This nitrogen (and phosphorus) can come from manure or from can be made chemically. The production of chemical fertilizers (also called synthetic) requires significant energy inputs.
Weed and pest control. Weeds and pests can significantly reduce the efficiency of crop production. In conventional agriculture the weeds and pests are controlled through the application of pesticides and herbicides (chemicals used to kill pests and weeds). Weeds can also be controlled with mechanical tillage.
Irrigation. Crops need water to grow. Growing crops in geographic regions that do not have enough rainfall requires irrigation. Irrigation water can come from rivers or groundwater.
Harvest: Crops are seasonal with harvest in the fall. Harvest season is very short because the crops can easily spoil in the field.
Transportation and Storage: Crops are harvested in the fall but animals and people require food throughout the year. Hence there is a need to store the crops and also transport them to where the animals or people are.

Depending on the type of plant grown or farming method (conventional or organic), these production steps will vary.

From storage, the harvested fruit or grain from the plant is further processed or packaged. With bioproducts, there are a variety of ways that the crop is processed. As we move into specific products, we will outline these steps. The important thing to remember is that each of these production steps involves energy inputs (e.g. tractors using fuel, chemical production) that would be included in an LCA.

One other important consideration in agriculture is the reliance on a monoculture. Monoculture means that we're growing just one thing on any plot of land at time. A corn field is ONLY corn. A soybean field is ONLY soybeans - there is not a mix on the same field. Most agriculture rotates what crops are grown each year. For instance, corn and soybeans are often grown in the same field on alternative years (i.e. corn in 2017 and soybeans in 2018). This is referred to as crop rotation. All of these production steps, including the use of monoculture and crop rotations, are extremely specialized and efficient which has resulted in very cheap fruits, grains, and fiber that can be used for food and fuel.

All About Corn

To provide an example of the agriculture process from preparing the soil to the final use of the crop we will begin with an example - corn.

Corn grain is the most important feedstock for bioproducts and biofuels in the United States and across the world. Remember that a feedstock is the raw material to supply an industrial process. Corn grain and stover, sugarcane, wood chips, sugar beets, and wheat straw are all examples of feedstocks. Corn grain is valuable because of the amount we can produce per acre (yield), but also because of its composition. About 62% of the corn grain is starch - an important component of biofuels and bioproducts. Corn is currently grown on 90 million acres in the US (compare this to the approximate 750 million of forestland in the US).

In 2017, corn production was 14,604 million bushels (about 408 million tons) or about 4.5 tons per acre. For those doing the math, bushels is a volume measurement. Properly dried corn will weigh 56 lbs per bushel. Both the amount produced per acre (yield) and the total amount produced has been generally increasing over time (Figure 1). You can see the dramatic production increases from 1937 to about 2007. The most recent trend is an increase of about 1.2% per year. These increases come from improvements in plant genetics, fertilization, and management.

combined

Figure 1. History of US corn yield total production (World of Corn, 2018)

The lesson video (How Stuff Works) provides an overview of corn production and the use of corn as a food, fuel, and bioproduct. The video is a bit longer than most (42 minutes). Please watch the entire video. Quiz questions will be based on the first 10 minutes of the video. The reflection question will focus on the different video segments. You may want to write down when each of these segments starts so you can find them quickly for your reflection question. The first 10 minutes is alla bout production. The next section is on oil drilling and xanthun gum, etc. The sections are pretty easy to identify.

Summary of Corn

As we have seen, we grow and use a lot of corn in the US. This corn has many uses, as shown in Figure 2. In the figure, "FSI" represents fuel and industrial uses (e.g. sweeteners, bioproducts), "Feed and Residuals" is the amount fed to animals, "Exports" is what is sent to other countries, and "Carry-Out" is the end of year surplus. About 30% of corn grain is used for biofuel production and another 1.6% (about 6 million tons) goes into bioproducts. (World of Corn Links to an external site.). As you can see, this 6 million tons for bioproducts is very small when compared with total amount of corn produced. However, the value of these products is significant.

Figure 2. Corn Processed by Market Segment (World of Corn).

Conclusions

In future lessons, we will spend more time discussing other crops and provide more details on how these crops are made into products.