winners of the student can competition. recently the bus stopped in massachusetts. the school in foxbo rough for recognizing honorable mention winners and a video called veteran services. they were honored in front of their classmates, family members, and local elected officials are receiving $250 for the winning video. a special thanks to our cable partners. you can view all the winning documentaries at student cam.org. >> on lectures in history, university of colorado boulder teaches a class on how the rise of commercial fertilizer changed

farming. he describes how during the 1800s, farmers look for nitrates, and moving away from traditional methods such as field rotation. this class is about 50 minutes. >> my name is paul. i am a professor. i want to welcome c-span viewers to our history class. this is an environmental history focus. and today, our history is on agriculture and the fertilizer revolution. we began this course talking about agriculture and the frontier the expansion of the agricultural frontier across the world. and the birth of the plantation complex in tropical regions. but another critical storyline of the last few hundred years has been agricultural intensification. the growing, getting more crops

out of those. and this coincides with the industrial revolution. in thereated a real need europe and united states to really concentrate on food ,roduction to escape the trap this notion that population would grow faster than to production. we were talking about something called the green revolution. where a lot of modern industrial agriculture was spread to the rest of the developing world. but today, i want to talk about the 19th century. what i'm going to call the fertilizer revolution. and in the most general sense, a shift away from closed systems of agriculture, where fertility was raised in the farm. and we will talk about that. in whichn system

forms of soil fertility were imported into the farm. they were mined and brought out to the farms, used intensively, and would pull nutrients off the farm, out of soils, and away from the land. this became an open system of nutrient cycling. and i want to use this term metabolic rift. a sociologist going to this term also from karl marx. by metabolic rift i mean a break in the chain of nutrient cycling first on the farm and then between the city and the countryside. with traditional sources of fertilizer becoming waste and new sources of fertilizer needed. what we will see then is the sense of industrialization of soil fertility. the transnational story, i will tell it that way, with a focus

on the united states. ok? before talking about that, let's step back for a minute and look at what soil and soil fertility is. soil is one of the most important natural resources. obviously. it is basically the result of several processes. the first is simply the breakdown of what is called parent material like rock and sediment into loose matter that provides minerals for plants to grow. the second is the breakdown of organic material which combines with this broken down parent material and gives soil its physical, neural structure. and biological structure. and finally, recognize soil as a living thing. there are all sorts of insects, worms, microorganisms at work in soil that are critical to plants and crops' growth. in other words, soil

characteristics are biological, physical, and chemical. now, plants need all sorts of things to grow, it is pretty basic. they need sun, water, carbon dioxide. but they also need nutrients, macronutrients in particular, like nitrogen, phosphorus, and potassium, the holy trinity of effective fertilization. and they also need micronutrients, we won't talk about those as much today. most macronutrients come from the breakdown of soil, but the most troubling one would be nitrogen. that is at the heart of today's story. ok? let's talk about the nitrogen cycle, i know this is a history class, but it turns out it undergoes a dramatic historical change during this period. so, what is the nitrogen cycle?

it is a cycle of nitrogen between land and atmosphere. this is worked out largely in the 19th century. before that, people did not fully understand the nitrogen cycle. but we now know the atmosphere itself is about 79% nitrogen. and that atmospheric nitrogen is a critical source of nitrogen for plants and plant growth. but it is not immediately available to plants. and this is the most critical point we have to make, it is locked up in this n2 at him. plants cannot break it down. they cannot breathe nitrogen, so it has to be made bioavailable to them. i think we talked a little bit about this before. one is a lightning, which can fix nitrogen in the soil, that is an unimportant part of the cycle, but worth knowing. the other two ways are by soil microorganisms. some of which are symbiotic with a type of plant called a legume.

they live on the roots of legumes. they have the capacity to pull nitrogen out of the atmosphere and put it in the soil in ways that make it available to plants. to the planting of leguminous plants like peas, soybeans, peanuts, black-eyed peas, lentils, these were all crops that have the capacity to fix nitrogen from the atmosphere into the soil. there are also non-symbiotic bacteria that can do this, as well. but those legumes are really critical. the earth has a natural nitrogen cycle, nitrogen is constantly cycling in the atmosphere and in the soil. it is a result of decomposers, taking bacteria, and

even denitrifying bacteria. bunnies apparently help in this process. [laughter] so, that is the nitrogen cycle. and what i want to emphasize, one of the products of the metabolic rift i referred to, is the human transformation of the nitrogen cycle into the 20th century. that may not make a lot of sense to you right now, but i promise i will get to it and explain it in some detail. but we're getting ahead of ourselves. so, let's talk about the critical problem here, how do farmers over time maintain soil fertility on the lands they are farming? and before we get to this fertilizer revolution, i want to suggest a of ways in which they did that. perhaps the most important, early on, was shifting cultivation.

by shifting cultivation, the dominant mode of fertilizer management worldwide. it was an approach whereby farmers would clear it a piece of land, usually for us, usually using fire to burn off and make nutrients from organic material immediately available. it turned out that the fire and the ash produced has a basic ph which could correct for acidic soil. farmers would then farm that cleared land for a certain period of time, taking advantage of the natural fertility in the soil. and when that land stopped producing crops, when the fertility began to wane, farmers would move on and clear a new piece of forest and let the old field revert back. they might come back around to it, but decades later when it

had regrown back up and restored its capacity to be fertile as a result of that regrowth. now, practice on a small scale, shifting cultivation, was reasonably sustainable, and not that damaging, ecologically. though it was and still is a land-intensive way of farming. it required a lot of land. maybe another way to think of it, for the little piece being farmed at any moment, there has to be a lot of land available so the farmer can then migrate. does that make sense? ok, so that was one of the most important ways in which farmers managed soil fertility in the past. and typically in tropical regions. we will talk about why that is the case in later lectures. but it turns out tropical soils, burning is a good match for them.

ok, now, having focused on slash and burn as a strategy, a tremendous number of american farmers also practice this, particularly true in the american south. that part of the united states where plantation crops were grown like tobacco and cotton. farmers would farm the land until its productivity was worn out, and then they would move on. and this actually created a caricature of the southern farmer as a soil-miner. someone who did not care for the land, went out and cleared the land, took the nutrients out -- of course, they were growing staple crops like tobacco and cotton -- they would mine the soil nutrients and then move on.

and so, a lot of agricultural farmers and others who valued the stable, sedentary agriculture saw this as a particularly slovenly or wasteful -- they would not say environmentally destructive, but that is what they meant. there was an attachment in places like the american south to being more settled and civilized. and this brand of agriculture seemed messy. it actually seemed a lot like native american agriculture. they practiced slash and burn cultivation for the most part. the other thing southern farmers also did was practice a variation on this called forest fallow. a farmer might own thousands of acres of land, but only farmed a couple of hundred acres at a time. that farm base was there so they could cycle their arable land

through the entirety of that plantation over may be a 20 or 30 year cycle. it did not look good, but it was potentially sustainable. and of course, this land use and soil fertility management system, combined with slavery in in particular ways in the south, southern farmers were particularly interested in maximizing their investment in slaves. and to do that, they had to get as much productivity out of the land as possible. in the context where there was a lot of land to be had, and there was not a lot of labor to be had. so, there was an economic logic rooted in slavery to the upon shiftingnce cultivation of the strategy first soil fertility management. ok, clear so far? questions from anyone? if not, i will charge more to

the interesting stuff. it is yet to come. another way of managing soil fertility, i will mention this quickly and move to another system. it is to manure. manure,use the word what do usually think of, when you hear the word manure? animal manure. it can mean a variety of things. i include fallowing here, you would farm a field for a while and let it rest. letting it rest would return some fertility. probably not enough for agriculture to be sustainable. but a lot of farmers required ground manure. but also nightsoil, and human waste. also, organic materials near the ocean, seaweed, leaves from the forest.

also, the use of cover crops and legumes, sometimes plowed into the land. all of these were important to return nitrogen and other macronutrients to the soil. but there were two things about them farmers did not always love. one was that they were labor-intensive. if shifting was labor-intensive, applying manure was, too. and it did not allow for the maximization of one land for commercial production. that is an important point. ok, we will feel that works in a minute. it did allow for agriculture to be a more land-indeterminate thing. ok, with this model of soil fertility management, we see in great britain across the 17th and 18th centuries, and emerging revolution that allowed for much more intensive agriculture on

a fixed pieces of land, sustainable over the long-term. i will explain this quickly, it is complicated. but what it involves replacing fallowed land, land out of production, replacing it with a sort of rotation through the farm of improved pasture. with particularly good pasture grasses, some of which were legumious. they were used for human and animal consumption, and grain and other marketable crops. and then pasture. the idea is that you're devoting a substantial part of your form to growing things the animals are going to eat. and that animal digestive process will produce a really high quality manure.

especially if you're using turnips. farmers became very careful stewards of this manure, dung, as they called it. it allowed them, effectively, to within the bounds of a permanent, settled farm, raised sufficient soil fertility as livestock manure to keep those farms producing indefinitely. and they would move past years to farmland to clover, and rotated through the farm, so the nitrogen-fixing of the clover would be used for grain farming later on. ok, this was a very effective system, called convertible husbandry. sometimes called the norfolk system. and it managed to retain soil fertility really effectively. but it was incredibly labor-intensive. and it meant that only a small portion of one plant at any given time could produce crops for market.

and for those reasons -- there is actually a reform in the american south of that tried to get southern farmers and planters to raise more livestock res, and to pastu produce high-quality manure in a way that would allow them to settle in place, and not be constantly engaging in shifting. it did not work, because they were more interested in using fresh land to produce big crops of tobacco and cotton and to maximize their capacity to market these crops. particularly, if they had investment in slate labor. ok. nonetheless, this was a really important, and pretty powerful way, of raising soil fertility in a closed system. be the, this came to best model of the western world

for a closed system for fertility maintenance. make sense? ok. now, we will look at how the system gets cracked open. before doing that, i want to take a quick digression, and that is what happens to fertility management as people urbanized more and more. because as more and more people are concentrated in urban areas, urban areas themselves become places that have a lot of organic nutrients that need recycling. and that happens in a variety of ways. one, this might be from great britain, a figure known as the rag and bone man, they would go around to household and collect any rags that people might have, or bones, as a result of cooking or slaughtering livestock. or whatever. do you know what the rags were used for?

any idea? the rags were the critical resource for papermaking in the 19th century. so, papermaking relied upon rag recycling, but the bones were used for fertilizer. and so, these folks would aggregate huge collections of rags and bones. this is a photograph from baltimore, a figure called the nightsoil man. and he would go around and collect human waste. this was before there was indoor plumbing, so all of these wastes were collected in privies. right? you cannot photograph the smell. it was, perhaps not surprisingly, that this is an african-american worker. this worker would collect the wastes and take them to the

countryside. i will show you that in a minute. do you know what that is? any guess? raise your hand. gets to you.til he this is a street scene in lower manhattan. this is horse manure, one of the greatest sources of fertility. and all of these things, nightsoil, bones, horse manure, would be brought out into the immediate hinterlands, and be dumped on the farmlands. places like long island, brooklyn, queens, those were agricultural hinterlands in new york's early history. they would produce a lot of crops for urban consumption. and they would get the urban waste recycled back to their land. not a metabolic rift.

alright, but let's move in that direction. oh, one last thing. anyone know what this is a picture of? zach: american bison. prof. sutter: yes. these are bison bones. people hunted bisons on the american plains almost to extinction. when the bison were all but gone, commercially extinct, the next industry that hit the great plains was an industry to collect bones, which were then ground up into fertilizer. yes, the question? stuart: is the bison species extinct? prof. sutter: no, it is not. but it was the subject of intense market hunting. and they got to the point where there were so few left, there was a growing conservation movement to keep them from going extinct. and now they made a big comeback, although a lot of the bison we see, are crossed with

cattle, so they are beefalos. there is a genetic mix there. that gives you a sense of how w important bones were to the fertilizer trade. well, a quick scientific foray. here, soil science is also critical to the story. and i won't bore you with too many details. but coming into the 19th century, scientists believed in the humus theory of soil fertility, the idea that it was fertile because of the organic matter and manures that were put on the soil and event breakdown into it. this is a model of soil fertility that i think anyone is spent time doing organic farming would be familiar with. it sort of made a bit of a return. but this man, a german chemist, challenged this and opted instead for a reductive soil

chemistry that began to argue that fertile soils relied upon a couple critical nutrients. and again, nitrogen, potassium, phosphorus. npk, that triad. if you go to any fertilizer store, there will be a three number ratio, the ratio of those three elements. he is one of the ones that encourages us to think of fertilizer as more like vitamins then food. the humus theory saw soil as something that needed to be fed. liebig says no. an infusion of these chemical, mineral elements. nitrogen would be the trickiest one. but as luck would have it, just

as liebig was writing his major treatise on the subject in 1840, an industry was beginning to capitalize on a remarkable new sort of concentrated, mineable, nitrogen, that came from an unlikely, remote place. these islands, called the chincha islands. so, let me tell you a little about the chincha islands. anyone know where these islands are? nate? hold on. yeah, i was about to ask where these islands are located? [laughter] prof. sutter: anyone know? >> they're located off the coast of peru. prof. sutter: i will show you a map later. it is a very small island, three of them granite, off the coast of southwest peru. that were best known as hosts

for massive colonies of sea birds, cormorants, pelicans, who would come to these islands, and had been for hundreds of not thousands of years, urinating and defecating on these islands in huge numbers. now, and i have to give you a sense of the magnitude of this because it is actually quite staggering. in some places, and we will see some pictures, people who came to mine these deposits found them to be about 150 feet deep in some places. right? now, how could this be? a couple things important about the ecology of these islands, there was the humboldt current that brought nutrients out of the deep sea water and up to the surface, which fed small fish, in this case, anchovies. huge schools of anchovies around

this area, which allowed the sea birds to feed without abandon on them. and they process this fish fertilizer throughout their digestive tract. now, these islands also exist in a rain shadow from the andean mountains. and the result is that they get about one inch of rain fall a year. and why is that important? skyler, hold on. skyler: no rain shadow means there was no chance to wash it away -- so there is no carbon. family show. in this case, the lack of rainfall effectively means there is no washing away or leaching of this. in most other places, bird guano would've been washed away or leached away. these are almost pure,

geological deposits of bird crap. alright? they were used by peruvian native people for hundreds of not thousands of years. russian great p nationalist humboldt asked, when he made note of these deposits and took peruvian quando back to him with europe where he had chemists test it and found it was incredibly rich in nitrogen. the first deposit to the united states, by order of the editor of "the american farmer," in 1824, and within decades, as others confirmed guano's fertilizing power, an international trade was developed in peruvian guano.

alright, a hugely important thing. alright? sorry i am a little behind there, there is my slide. of course, as always, i will post these, so if you do not get a chance to jot these down now, they will be up on d2l. here are early illustrations of these islands. these are, effectively, guano deposits. and if you don't believe the etching, there is another one. i will show you some photographs in a minute. so, we have already talked about the long history of use. alexander von humboldt, brought it back. the other thing about it, they are light and easy to transport. so, unlike manure or nightsoil, it comes in a light, easy to transport package. now, one of the most important

parts of the story and i can only talk a little bit about it, but it is important to talk to understand, to mine these guano deposits would be incredibly awful work. have any of you ever cleaned out a chicken coop? magnify that about 100 annual and you get an idea. this guano was incredibly acrid and dusty and get into people's lungs and make them sick. it was not work anyone wanted to do. not surprisingly, the earliest guano farmers were slaves. sometimes african, sometimes native to south america. after peru outlawed slavery in the 1850's, and it was increasingly fed by a trade in chinese labor. some of it coming from the fujian coast. that we talked about earlier in the semester. about 100,000 laborers from china, semi-free labor was

brought over to peru. many of them ended in the chincha islands where they had to effectively work off the cost of their transport, mining guano. it was awful work, they got paid very little. but it was to feed the fertility revolution in the developed world. alright, it is also a story partly about the decline of slavery and the rise of other types of global labor and migration. alright, suicide was also a really major problem, particularly among the chinese workers, who often kill themselves because the work was so awful. what happened was, and here's a look at one of the sheds, and these are the deposits. another look.

again, these are people here with guano carts there filling. they would then put them in these canvas chutes, to take to the united states and europe. ok. will just show i you. there is an ad for pacific guano. and just a look at the period of guano export, really peaking and in the 1870's. a little decline there, and then going down again after that. in this period, exports were more than 12.6 million metric tons. totaling about $750 million in value. talk about mining. i think you should think about this in relationship to our lecture on coal mining. because i think there is a real

analog here between tapping into these fossil forms of soil fertility and the shift in organic to fossil fuel regime. now, the peruvians retained control of the islands, but it was dominated by british trade houses. w.j. myers out of liverpool, and another ad from london that had a motto applied to them, "the house of gibbs made its dibs selling the turds of foreign birds." that is how this works. i will mention this quickly, and there is a chapter in the mann book that i almost had you read, but it was almost certainly the case that the potato blight that would undo the irish potato crop in 1840's and prompting massive wave of irish immigration, would walk from south america to

europe. ok, so there is another little interesting tidbit of the columbian exchange. now, a lot of this guano was sold to french sugarbeet farmers. fromlp ween themselves caribbean sugar. but probably half of it went to british agriculture to help grow food for the industrialization of britain. about a quarter of it went to the united states. not surprisingly, a lot of it went to the american south, to help sort of restore the fertility that some planters had worn out. and increasingly, the importance of guano to american farmers led to political calls to break the peruvian monopoly. president millard fillmore, one of the less memorable presidents in our history, dedicated a substantial part of his annual address, the state of the union, in 1850, to the need for the united states to find strategic

guano reserves. it almost was to mid-19th century politics with oil is today. and then, in 1856, and i should get my slide here, congress passed and the president signed something called the guano islands act of 1856. and what this act effectively did, it allowed american citizens who might be searching for new guano islands in the pacific or caribbean, if they found a new islands covered in guano and were otherwise unclaimed, to claim these islands a sovereign territory of the united states. ok, the guano islands act of 1856. and this huge guano island rush. it began. it is important to point out that those really particular

conditions did not replicate themselves. most of the other guano islands had much smaller deposits and were much less rich in nitrogen because of rain leaching. alright? nonetheless, there was a rush to find a sovereign territory. and one of the important things, at least in u.s. history, this is a bit of a digression, it did not articulate comfortably with the u.s. system of incorporating into nations. that system have been defined as a process whereby westward moving americans usually would settle a territory, and it would be incorporated into the nation as a territory and then estate. ok? but these guano islands would never become part of the united states, like states. they would just be islands connected in formally. let me read the language of the act. "whenever a citizen of the u.s.

discovers guano not within the lawful jurisdiction of any other government or occupied by the citizens of any other government, and takes peaceable possession thereof and occupies, such island, rock, or key may, at the discretion of the president, be considered as appertaining to the united states." that phrase, appertaining, would become absolutely critical at the turn of the 20th century when the united states becomes a colonial nation. when it takes some colonies like the philippines, guam, puerto rico, etc. but does not create mechanisms allowing them to become part of the united states. there are a series of supreme court cases, insular cases, that sort of create the legal justification for the taking of colonies. and what others rooted in? the guano islands act of 1856.

american imperialism springs then.hese bed of guano, at any rate, guano is hugely important for these industrial centers in the united states and europe. but eventually it plays out. and the search for concentrated nitrate fertilizer shifts to another really interesting place. in this case, a place called the atacama desert in chile. atacamaver been to the desert. casey? want to say anything? casey: it is one of the world's highest deserts, and one of the driest places as well. prof. sutter: is one of the driest places on earth, that is important. it has incredibly rich sodium

nitrate deposits, nearly pure. kalish there. a rock-like layer found under a gravel surface. very quickly, this becomes the next site for mining nitrate fertilizer. it was mined here by peruvians, bolivians, and chileans, and there was a system which was a form of sort of debt-peonage labor. it was incredibly brutal work in this arid desert. it was mostly underwritten by british and american capital. a guy known as john thomas north became known as the nitrate king and dominates the

system, owning 70% of the industry. these chilean nitrates effectively replaced peruvian guano, and they also rely on huge numbers of jute sacks, most of which are grown and processed in bengal. ,n modern india and bangladesh ok? again, to feed the market. this slide is a little blurry, but the atacama desert is here. and like the chincha islands, it is the andean rain shadow that makes for this particularly rich ecology. most of these nitrates went to britain and germany. though, in the united states, they particularly fed the growth of the citrus industry in california. going up the coast. chilean nitrates going up the pacific coast and feeding california agriculture. the nitrates trade would last into the 1930's.

i think i have a similar slide here. this is from a great article by a scholar named ted mellilo. gives you an idea of the spiking in the early 1930's. i will explain that cut off in a minute. yes, liam? liam: were companies and governments actively looking for these huge deposits of nitrates, or were they kind of just stumbled upon them? prof. sutter: a combination. so, i quickly went through that story about urban fertilizers. and one of the important things about that, horse manure, nightsoil, bones, that created a fledgling commercial fertilizer industry and got people in the habit of thinking about fertilizer as being something they don't necessarily raise on the farm but can purchase in commercial marketplaces.

and as those supplies, like bones from bison, proved increasingly inadequate. people looked elsewhere to find those things. and i focused particularly on nitrates, but phosphates are analogous, but slightly less interesting. so, some of it was dumb luck. like humboldt stumbling upon it. some of it was urban trade at cause people to think about fertilizer as a commercial commodity. some of it was liebig and is reductive chemistry. said, wegly, people know we need nitrogen, where can we find it? under the humus theory, this approach might not have made quite as much sense. does that answer the question? good question. ok. so, in the u.s. south, they did not use a tremendous number of

these chilean nitrates. they actually ended up, here are a couple of other ads, european. they ended up shifting to a different source of fertilizer. and this is a fish called the menhaden. and it is like an anchovy, a very small fish. it is a plankton feeder. it exists in huge schools in the atlantic ocean. today, is mostly -- does anyone know what it is harvested for today, it is controversial? there is a company called omega that harvested these for fish oil, or supplements for human ingestion. but early on, menhaden came to the late 19th century to replace

, as whales were increasingly extinct or hard to find as a major source of oil. . once at oil was pressed out of them, and they are fish that are not good for eating, their bony and oily. once they were pressed, they became an important source for commercial nitrates. so, now we are mining the seas to find nitrogen fertilizer to feed, in this case, mostly tobacco and cotton farming. now, under the tenant system, instead of slaves. still, one in which very poor southerners are trying to bring crops of cotton from increasingly degraded land. usually they are in land, one of the reasons, because they are buying a lot of fertilizer. also, phosphate fertilizer being mined from south carolina, and later, tennessee. and florida.

before i moved to mine conclusion, any questions? yeah. nate. in the back. nate: how long did they use the menhaden fertilizer? prof. sutter: they still do, to a certain degree. though, the end of my story here would shift that menhaden fertilizer to animal feed. because it was increasingly necessary for fertilizer, because of these. alright, and these two guys are fritz haber and carl bosch. hisuly 3, 1909, haber told superiors in germany that he had perfected a reaction capable of generating ammonia, creating --

he had figured out how to mine the air of nitrogen. and then later, this chemical engineer by the name of carl bosch standardized it into an industrial process. we know it as the haber-bosch. industrial production of nitrates mind from the air began in 1913. what else are nitrates used for? rachel, hold your thought until we get the mic over there. rachel: explosives, like for a war. ? prof. sutter: munitions. we were just about to enter into world war i. this process would prove really critical to the german capacity to fight world war i. and this process would prove really critical to the german capacity to fight world war i. and then, after world war i,

there were all these industrially produced nitrates hanging around as farmers would then begin to turn to them. and here, in a sense after all of this 19th century searching around the globe for nitrates, we have a fully industrialized process for producing nitrogen. alright, the haber-bosch process after the 1930's, and incredibly energy-intensive process, we would not need guano or menhaden anymore. at least for people who could afford to buy fertilizer on the open market. bringhis helps to really to a conclusion these various metabolic rifts occurring throughout this period. now, i had talked about the urban fertilizer market. what happens to the rest of the

world with the use of nightsoil and horse manure? well, cities, these organic places cease to be so organic, increasingly we have indoor plumbing, that takes our waste away into natural systems, where these critical nutrients become what we call pollution. we also cease to have so many horses in cities, and cease to have the manure problems as well. that is one of the metabolic risk. another, having to travel the world over to find these really concentrated forms of nitrogen pollution. but let me end by pointing out, sorry again, a slide behind, how the haber-bosch process , again this will be up so do not scramble to write all this down, this week my last point today, transforms the nitrogen cycle. today, industrial nitrogen fix

ed through the haber-bosch process, produces about 32 million metric tons. and the intentional cultivation of legumes, we also get nitrogen oxide from bosch, another 25 million metric tons. and combined, and you can do the math here, we are looking at about over 157 million metric tons of nitrogen that is human produced. the natural nitrogen cycle itself only cycles about 110 million metric tons between land and air. so, the human nitrogen cycle has become bigger than the natural one. josh, quick question. we will get the boom back to you. josh: what industrialization would that affect, the changing diet, outdating nightsoil -- with the change of the diet of

people during industrialization, of america, would that change the viability of nightsoil? prof. sutter: all of this fertilizer would be critical to raising the foods that support one of the other critical things, the huge bison population growth. now, again, in the 19th century, century, this kind of fertilizer was being used only in very particular paces. the vast majority relied upon shifting cultivation or our organic nutrient cycling, some manure. increasingly, they turned to this. what you get is a result, my final slide. metabolic rift, this is a map of the mississippi-missouri -ohio watershed, which has become a huge source of nitrogen pollution. all of which runs downstream and

has created a hypoxic dead zone. nothing really can live in the gulf of mexico here because so much nitrogen fertilizer is being pushed into the gulf, creating huge plankton blooms, and, you know, sucking all the oxygen out of the water. effectively, right? i would just leave you with that, in terms of what the end result of all of this is. last question, because we do have to end. nate: what sort of long-term solutions do they have for this? can they remove nitrogen from the water and restore it, while also reusing the nitrogen? prof. sutter: my understanding, i think that is very difficult. it would be a very energy-intensive process. the much more important thing is to get farmers to use nitrogen

and less likely to leech large amounts out into aquatic ecosystems. alright, thanks all, see you next time. see you. >> join us saturday evening as we join students in college classrooms to hear lectures ranging in topics from the american revolution, to 9/11. lectures in history are also available as podcasts. visit our website, or download them from itunes. >> next on american history tv, a panel of vietnam war veterans, including two prisoners of war and an army nurse, discuss the grim reality of life, death, and suffering in vietnam. the discussion was moderated by the national endowment for