Impacts of Agricultural Practices| Land and water use| AP Environmental science| Khan Academy

Hey there! Today I'm going to cover the impacts of agricultural practices. To do so, I'm going to take you through my morning ritual. It sounds weird, but my bowl of multigrain Cheerios and rice milk and relaxing in my super comfy pajamas are all connected to intensive agricultural practices; in particular, tilling, slash and burn farming, and fertilizers.

So let's take a closer look at the Cheerios in my bowl. Most of my cereal here is actually composed of grains like oats, corn, and barley. Growing grains typically starts with tilling and good quality soil, which has lots of nutrients. But what is tilling? In short, tilling is the process of turning soil, and it’s really useful because loosening the soil allows farmers to easily control weeds and other pests at the surface of the soil. It helps them to prepare the soil for seeding.

Sometimes in areas that have been heavily farmed, the soil can become compacted over time. Here, tilling can help to break down the soil into smaller pieces called soil aggregates and allow for easier crop planting. Now, tillage has been done for thousands of years, but it's changed a lot from the past. When we used human labor and big draft animals to till small fields, this was usually done once per year. Nowadays, in the era of industrialized agriculture, large-scale farmers use heavy mechanized equipment that can till thousands of acres multiple times per year.

Okay, we're growing more, so we're tilling more—a lot more. While soil tillage can help to loosen and aerate soil, what do you think happens when heavy machinery passes over the land and tears up the surface multiple times per year? This practice of repeated intensive tilling compacts the lower layers of the soil and loosens the topsoil to the point that it loses the ability to hold water and nutrients in place. Tillage also reduces any leftover crop residue like plant stalks.

So, in turn, the exposed soil surface becomes really vulnerable to wind and rain because nothing is really holding the soil down or providing cover. So, what happens next? Loose soil can start to collect in surface runoff and become displaced through erosion. When this happens, soil organic matter and nutrients are literally washed or blown away. Who would have thought that these Cheerios were doing so much damage?

But there's some good news here too. Low-till or no-till farming alternatives can alleviate some of these problems. Thankfully, in the Palouse, a huge agricultural area in the western U.S., where a lot of grains just like the ones in my cereal are grown, no-till farming is really important. Because the fields are really steep and hilly, wind and rain can cause a lot of erosion. By not tilling the fields, farmers can prevent soil erosion and, more importantly from my perspective, make sure that they can grow lots of grains for my Cheerios.

But wait! Cereal isn't complete without milk. Now, I personally like rice milk because I'm lactose sensitive. Rice is commonly grown in temperate and tropical regions, oftentimes in areas where soil quality isn't the best and nutrients are lacking. So how do farmers get nutrients back into the soil? More importantly, how do they grow rice for my rice milk at breakfast? Well, they often use slash and burn farming.

So, like the name suggests, forest plots are slashed or cut, left to dry, and then burned. The ash left over from the burning fertilizes the soil, but it's only a temporary benefit. After about three to five years, the productivity of slashed and burned plots goes down really quickly due to the loss of nutrients and as weeds start to grow again. When this happens, farmers simply abandon the field, move over to a new area, and repeat the process.

But it can take decades for these plots to recover once they've been slashed, burned, and farmed, and this practice can become a vicious cycle. In the Amazon, for example, people in rural areas rely on slash and burn so that they can make money selling the crops they grow or create open pastures for animals to graze. In the process, thousands of acres are burned each year, and as these trees and plants burn, enormous amounts of greenhouse gases, mainly carbon dioxide, are produced, which contribute to climate change.

Sometimes, fires may not be well managed and can burn out of control, causing huge, costly wildfires. But it's not all doom and gloom when it comes to my tasty rice milk. There are alternatives to slash and burn, which include applying animal fertilizer like manure on used plots to bring nutrients back to the soil or using alley cropping, in which trees or other vegetation are planted between crops to help keep nutrients and moisture in the soil.

All right! By now, I've eaten my breakfast and I'm relaxing in my super comfy cotton pajamas. But turns out that cotton is actually a really finicky crop to grow, and it requires a lot of fertilizers. Fertilizers help plants grow, but that's not a bad thing, right? It's not! In fact, we've been using fertilizers for millennia.

For thousands of years, people have used natural fertilizers to replenish or increase nutrients in the soil and promote plant growth. Natural fertilizers meant that farmers used things like leftover crops, manure, wood ash, ground bones, fish or fish parts, and even bird and bat poop. In the early 1800s, though, scientists discovered that nitrogen, phosphorus, and potassium were key to plant growth, and in time, many farmers began to switch from natural fertilizers to artificial fertilizers with higher concentrations of these nutrients, which greatly increased crop yields.

In other words, farmers could grow more, and that means more cotton and more comfy pajamas. But there's a catch! Now that farmers are growing more crops than any time in history, we've learned that there are impacts to using large amounts of very concentrated fertilizers. Applying too much fertilizer can pollute runoff water with excess fertilizer and pollute local surface waters.

As nutrient-rich materials like fertilizer make their way into nearby rivers, lakes, and oceans, they can cause major problems in the balance of nutrients in marine ecosystems. When too many nutrients from fertilizers saturate a body of water, called eutrophication, these nutrients feed the rapid growth of algae. In turn, these massive algae blooms can suck up all the oxygen in bodies of water and lead to enormous fish die-offs called dead zones. Quite a morbid situation and very different from the happy unicorns of my pajamas!

But there are ways to reduce the amount of fertilizers released into waterways. Farmers can limit the amount of fertilizer that they apply or use compost, which is decomposed organic material as a fertilizer, which tends to have lower and safer levels of nitrates and phosphates.

And there you have it! Common agricultural practices and their impacts in a nutshell—or really a bowl of cereal.