Farming has changed a lot throughout the course of human history. Technological advances have transformed farming from local family-run farms to primarily large, industrial businesses. This transition is known as the green revolution and it has greatly aided in the ability to address food insecurity and continue feeding a growing population.

Overall, this industrialization of agriculture has led to an increase in efficiency, much higher yields and greater food production, and a more profitable business. However, it comes with a variety of negative effects as well.

There are a variety of practices that are used in modern-day agriculture that have negative, and even disastrous, environmental effects.

With a growing population, there is an increased need for space to grow crops. One method that is used, particularly in tropical forests, is known as slash-and-burn agriculture. This is pretty much exactly what it sounds like. An existing forest is cut down, with any remaining plant life burned. The burning of vegetation returns nutrients to the soil, allowing for increased yields when farming. However, this comes with a variety of issues. The burning releases a variety of greenhouse gases, such as CO2 and N2O. In addition, particulate matter - an air pollutant and respiratory irritant - is released through the burning. The lack of trees lowers the albedo of the area, resulting in warmer temperatures and soil that is more likely to dry out and become susceptible to increased erosion. Deforestation in this manner also removes habitats, decreases biodiversity, and removes the ecosystem services provided by the trees.

Once the land is available for farming, it is increasingly common to grow monocultures. This is when one single species of crop is planted, making it more efficient to farm as all of the crops require the same care and harvesting needs. However, this has ecological impacts as well. It decreases species diversity due to the lack of other plants, which also decreases habitat diversity, as there are no other plants for species to survive on. In addition, as all of the crops will be ready to be harvested at the same time, there will be periods of time when the soil is left bare. Without roots holding in the soil, the frequency and risk of erosion are increased.

In order to more easily plant crops, tilling is used. This is a process that mixes and breaks up the soil, typically by using a machine known as a rototiller. Breaking up the soil significantly reduces the amount of work needed to plant crops, but it also significantly increases the rate of erosion.  This results in the loss of nutrients and organic matter over time as the topsoil erodes away, which typically results in an overreliance of synthetic fertilizers. In addition, particulate matter can pollute the air and the water. PM in the water can increase turbidity, which can lead to a variety of issues. It can directly harm aquatic organisms and decrease the amount of food available in the ecosystem by limiting plant growth.

Once the crops are planted, in order to maximize their growth and yields, synthetic fertilizers are often used. These are manmade fertilizers that add nutrients, particularly nitrate and phosphate, to the soil. Using these as opposed to organic fertilizers such as manure and compost very efficiently increases the growth of plants. However, it requires fossil fuels to produce these, resulting in air pollution and the emitting of greenhouse gases. In addition, they do not return organic matter to the soil as manure and compost do; this returned and broken-down organic matter increases the water-holding capacity of soil and provides a habitat for decomposers. Having excess nutrients due to overuse of fertilizers can result in leaching, where the nutrients run off into groundwater or surface water. This can lead to contaminated drinking water or disrupts aquatic ecosystems via eutrophication.

With the increase in farmland and crop production, there is a greater need to water the crops and to develop more efficient ways to water them. Irrigation is an essential aspect of agriculture that involves the artificial watering of land, and makes up roughly 70% of freshwater use by humans. Surface irrigation, which involves adding water directly to an area of land and distributing it over the surface, is by far the most common worldwide and has been used in some areas for thousands of years.

Water for irrigation comes from a variety of places, including surface water (such as rivers and lakes), treated water (such as wastewater or desalinized water), and groundwater. Aquifers are deposits of groundwater where the water is stored within the pores of permeable rocks underground. They are replenished by infiltration of water into the ground. The water table is the uppermost part of the water-saturated rock which can be raised through the infiltration of more water and lowered from the pumping and removing of water.

There are problems associated with irrigation, particularly as it comes to overwatering crops.

Waterlogging can occur when there is so much water that the soil is completely saturated and the pores are filled with water such that there is no room for air. This has negative effects on plants and can stunt their growth, or drown and kill them. The soil can be aerated to help alleviate the problems from this; soil aeration involves poking holes in the soil in order to provide air to the roots.

The water that is obtained from aquifers and is used in irrigation is freshwater, but it is not 100% pure water; there are small amounts of salt present. As water evaporates, it leaves behind the salt, which builds up in concentration over time. If the concentration becomes high enough, it can reach toxic levels, preventing growth and killing plants by dehydrating their roots. This process is known as soil salinization. There are solutions, such as using more efficient irrigation methods (like drip irrigation), using fresher water, and flushing out or desalinizing the soil, but they are expensive.

One thing that can worsen this problem, as it makes groundwater saltier, is saltwater intrusion. When water is pumped out of aquifers, the water table is lowered. If it is lowered too much near the coast, salt water can begin to seep in, increasing the salinity of the groundwater in the aquifer.

With increased agricultural productivity, the threats posed by pests that can destroy crops increasingly need to be addressed. 

One of the biggest things that can be done to address pests is the use of pesticides. These are chemicals that are toxic to and can kill pests. The root "-icide" means that it is killing something; insecticides kill insects, herbicides kill plants, rodenticides kill rodents, and fungicides kill fungi. These can be sprayed on the crops in order to prevent pests from eating or disturbing them, which results in greater yields from the crops. These come with two major issues, though. One is that pests can evolve to become pesticide-resistant through natural selection. If there are pests that happen to have a variation that makes them more resistant than others, they will be more likely to survive and reproduce, making the resistance a higher proportion in the next generation. The pesticides act as a selective pressure and cause the population to evolve towards resistance due to natural selection. The other is the threat of non-target killings, where the pesticide harms unintended species, such as pollinators.

A second large method, and one that is being increasingly used, is genetically modified crops. The two major strategies for this are making crops that are resistant to pests (such as Bt corn which produces its own pesticide) and making crops that are herbicide resistant (such as 'RoundUp Ready' crops).  While it may sound scary to be eating a corn that essentially produces its own poison, it's actually perfectly safe! Think about how you can eat chocolate, grapes, or garlic but it's dangerous for your dog; the toxicity of a substance depends on the species.

Bt corn has been found to have significantly fewer environmental impacts, such as killing non-target species and the risk of water contamination, and reduces overall pesticide use. Of course, however, if there are organisms such as predators that rely on the pests, they may be negatively affected due to the reduction in pest populations. In addition, there is concern about pesticide resistance evolving from this as well.

Herbicide-resistant crops result in an increase in herbicide use. As the crops are resistant to the herbicides, herbicides can be used with much less care and more frequency to kill and prevent weeds from growing, which compete for resources with the crops and can limit or impede their growth.

We started talking about it with IPM and drip irrigation, but there are a variety of ways to maintain agriculture that are not as damaging to the environment. One strategy is to focus on preventing soil degradation. 

Currently, soil erosion is a major problem as it leads to a loss of nutrients and moisture, along with causing other damage such as increased water turbidity. This is particularly an area of concern in America, as we lose topsoil to erosion roughly 10x the speed that new topsoil is made. As such, soil conservation centers around agricultural techniques that minimize topsoil erosion.

Along with erosion, another risk that soil is facing is nutrient depletion. Nutrients are lost overtime as crops pull them from the soil, and many modern agricultural practices such as monocropping amplify these problems. Strategies to retain or improve soil fertility that do not rely merely on the use of synthetic fertilizers (which cause their own issues) are an essential part of sustainable agriculture.

One of the most well-known methods for improving soil fertility is crop rotation. Planting different crops on the same plot of land sequentially works to prevent the depletion of soil nutrients. Growing the same type of plant over and over in the same area will gradually deplete specific nutrients. In addition, it will also allow for specific weeds or pests that thrive well with that certain crop to take over. By rotating through different plants, with each having different nutrient needs, it reduces the risk of a specific nutrient being depleted and allows more time for the soil to recover its nutrient levels. Some crops are even very helpful at actively improving nutrient levels. Legumes, for example, have nitrogen-fixing bacteria in their root nodules and help to increase the levels of nitrate in the soil.

The use of cover crops and green manure can help as well. Oftentimes, there is a period of time between harvest and replanting where the soil is bare. Cover crops such as fast-growing grasses can be planted that will grow over and cover the soil, without the intention of ever being harvested; they are typically used to protect soil health. Their roots will work to prevent erosion and water loss from the soil. In addition, legumes such as clover can be planted to increase soil fertility (although they typically need to be grown for an entire season rather than just the off-season for this purpose). The cover crops will be clipped, mulched, and churned so that their remains can create a "green manure." It will be decomposed to improve the nutrient content of the soil. Along with helping with soil fertility, while the cover crops are present, they can also suppress weeds, provide habitats, attract pollinators, and reduce erosion.

When soil becomes more acidic, it reduces the availability of nutrients. A lower pH means there is an increased amount of hydrogen ions (H+), which displaces the nutrients. A common technique for increasing the soil pH is adding limestone, which releases calcium carbonate and neutralizes the soil. This increases nutrient availability in the soil and improves plant growth and health.