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AP®︎/College Environmental science
Course: AP®︎/College Environmental science > Unit 4
Lesson 2: Effects of land and water use IImpacts of agricultural practices
Agricultural practices that can cause environmental damage include tilling, slash-and-burn farming, and the use of fertilizers. Created by Khan Academy.
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- () when we used human labor and big draft animals to till small fields, usually once per year. 1:18
Does anyone else wish that we could go back to that way of life? Simple life?(2 votes)- Ok so.. If we can keep the rights of equality? And the progress we have made? Absolutly REDUCE HUMAN POPULATION(1 vote)
- Why is there so many problems with agriculture?(2 votes)
- do you have any commodities videos?(1 vote)
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Video transcript
- [Voiceover] Hey there. Today I'm gonna cover the impacts
of agricultural practices. And to do so, I'm gonna 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, they're 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, and growing grains typically starts with
tilling in good quality soil with 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, and 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,
usually 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. And 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 top soil to the point that it loses the ability to hold
water and nutrients in place. Tillage also reduces any
leftover crop residue like plant stocks. 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 US where a lot of grains, just
like the ones in my cereal, are grown. No till farming is really
important because the fields are, well, they're really steep and hilly and wind and rain can
cause a lot of erosion when the soil is heavily tilled. 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, cereals aren't
complete without milk. Now, I personally like rice milk because I'm lactose sensitive, and 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? And, 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, 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. And, sometimes too, 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 add
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. And fertilizers help plants grow, but that's not a bad thing, right? And it's not. In fact, we've been using
fertilizers for a 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 use things like leftover crops, manure,
wood ash, ground bones, fish or fish parts, and 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's 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.