Landlords and peasants in Europe & Agricultural expansion; crops 750 -1206

Agricultural expansion; crops HIstory +3 3rd Semester

                           

Introduction

                 The recent intensification of agriculture, and the prospects of future intensification, will have major detrimental impacts on the nonagricultural terrestrial and aquatic ecosystems of the world. The doubling of agricultural food production during the past 35 years was associated with a 6.87-fold increase in nitrogen fertilization, a 3.48-fold increase in phosphorus fertilization, a 1.68-fold increase in the amount of irrigated cropland, and a 1.1-fold increase in land in cultivation. Based on a simple linear extension of past trends, the anticipated next doubling of global food production would be associated with approximately 3-fold increases in nitrogen and phosphorus fertilization rates, a doubling of the irrigated land area, and an 18% increase in cropland. These projected changes would have dramatic impacts on the diversity, composition, and functioning of the remaining natural ecosystems of the world, and on their ability to provide society with a variety of essential ecosystem services. The largest impacts would be on freshwater and marine ecosystems, which would be greatly eutrophied by high rates of nitrogen and phosphorus release from agricultural fields. Aquatic nutrient eutrophication can lead to loss of biodiversity, outbreaks of nuisance species, shifts in the structure of food chains, and impairment of fisheries. Because of aerial redistribution of various forms of nitrogen, agricultural intensification also would eutrophy many natural terrestrial ecosystems and contribute to atmospheric accumulation of greenhouse gases. These detrimental environmental impacts of agriculture can be minimized only if there is much more efficient use and recycling of nitrogen and phosphorus in agroecosystems.

                                                           The agricultural achievements of the past 35 years have been impressive. Grain production, mainly from wheat, rice, and maize, has increased at a rate greater than human population. This has decreased the number of malnourished people even as the earth’s human population doubled to 5.8 billion. Although the estimates vary widely, world population is projected to increase about 75% before leveling off at about 10 billion. In combination with increasing demand for meat in developing countries and the use of grains as livestock feed, this increased population density should cause world demand for grain production to more than double. This raises several important questions. If it is possible for world food production to double, again, within the next four or five decades, what impacts would this doubling have on the functioning of the nonagricultural ecosystems of the world, and on the services they provide to humanity? What routes might be used to decrease such impacts? I explore these questions first by asking what the global ecological impacts of “more of the same” agriculture might be, and then by considering practices that might decrease such impacts. In particular, insights are sought in the parallels between natural and agricultural ecosystems, but no easy answers are uncovered. Rather, a new long-term, multidisciplinary research program is needed to develop agricultural methods that can feed a growing world and still preserve the vital services provided to humanity by the world’s natural ecosystems.

                                                            Current agricultural practices involve deliberately maintaining ecosystems in a highly simplified, disturbed, and nutrient-rich state. To maximize crop yields, crop plant varieties are carefully selected to match local growing conditions. Limiting factors, especially water, mineral nitrogen, and mineral phosphate, are supplied in excess, and pests are actively controlled. These three features of modern agriculture—control of crops and their genetics, of soil fertility via chemical fertilization and irrigation, and of pests (weeds, insects, and pathogens) via chemical pesticides—are the hallmarks of the green revolution. They have caused four once-rare plants (barley, maize, rice, and wheat) to become the dominant plants on earth as humans became the dominant animal. Indeed, these four annual grasses now occupy, respectively, 67 million hectares, 140 million hectares, 151 million hectares, and 230 million hectares, each, worldwide, which is 39.8% of global cropland. For comparison, the total forested area of the United States, including Alaska, is 298 million hectares. Entire regions of the world now are dominated by virtual monocultures of a given crop. These monocultures have replaced natural ecosystems that once contained hundreds to even thousands of plant species, thousands of insect species, and many species of vertebrates. Thus, agriculture has caused a significant simplification and homogenization of the world’s ecosystems.

The Ecology of Doubling Crop Production

                                                                                   The Food and Agriculture Organization (FAO) database provides a wealth of information on agricultural activities for individual nations, regions, and the world from 1961 to the present. Using the FAO data, let’s look at the pattern of world food production during this period and the factors that allowed it to almost double. The majority of the food crops grown on the arable lands of the earth are cereals (barley, maize, rice, and wheat), coarse grains, and root crops. For convenience, I will call the sum of these world food production. In 1996, cereals comprised 57% of this total, coarse grains 25%, and root crops 18%. By using this measure, world food production, as estimated from the FAO database almost doubled (increased 1.97-fold) from 1961 to 1996 Comparable patterns, and comparable ecological implications, occur if just cereal production was considered, or if production for just Europe and the United States, for which better data are available, was considered.

Ecological Impacts of Doubling Global Food Production

                                                                                         If these simple extrapolations of past practices are any indication, doubling global food production will triple the annual rates of nitrogen and phosphorus release to the globe. Current rates of agricultural nitrogen production, via both production of fertilizer and cultivation of legume crops, already approximately equal the natural (preindustrial) rate of addition of biologically active nitrogen to the globe (4). Point-source releases of phosphorus are tightly regulated in developed nations because phosphorus is a major limiting nutrient in aquatic ecosystems and increases in its supply rate harm water quality and aquatic foodweb structure. A tripling of global phosphorus supply rates is likely to adversely impact many aquatic ecosystems, especially those that have significant inputs of eroded agricultural soils or phosphorus-rich wastes from livestock and poultry. Nitrogen is much more motile in soil than phosphorus because soil bacteria can convert ammonia to nitrate and nitrite, which are readily leached from soil  Denitrification by bacteria also can convert nitrate into nitrous oxide, a potent greenhouse gas. In addition, ammonia, which is both directly applied as fertilizer and created via bacterial degradation of animal waste and other organic compounds, is highly volatile. It is transported via air and deposited on other ecosystems with precipitation. These numerous modes of transport mean that agricultural nitrogen, less than half of which stays in a field or is harvested with a crop, impacts both terrestrial and aquatic ecosystems as a eutrophier, and impacts global climate because of is role as a greenhouse gas. Indeed, there is a direct and quantitative link between the amounts of nitrogen in the major rivers of the world and the magnitude of agricultural nitrogen inputs to their watersheds.

Agriculture and the Loss of Ecosystem Services

                                                                                     A doubling of global food production would have major impacts on the ability of nonagricultural ecosystems to provide services .vital to humanity. Existing nonagricultural ecosystems provide, at no cost, pure, drinkable water. In contrast, the groundwater associated with intensive agricultural ecosystems often contains sufficiently high concentrations of nitrite and nitrates or of pesticides and their residues as to be unfit for human consumption. Expensive treatment is required to make it potable. The biodiversity of nonagroecosystems provides many services to agriculture. For instance, the genetic diversity of both wild relatives of crop plants and unrelated organisms is used to increase yields and to reduce impacts of agricultural pests and pathogens. However, the maintenance of the wild biodiversity needed for future development of crops and medicines occurs mainly in nonagricultural ecosystems, the very ecosystems threatened by agricultural expansion and nutrient release. Agriculture depends on soil fertility, fertility created by the ecosystems destroyed when lands are converted to agriculture. Especially on sandy soils, the best way to regain soil fertility lost because of tilling is to allow re-establishment of the native ecosystems. Many agricultural crops depend on the pollination services provided by insects, birds, or mammals that live in nearby nonagricultural ecosystems.Similarly, agricultural crops benefit from biocontrol agents, such as parasitic and predatory insects, birds, and bats, that live in neighboring nonagricultural ecosystems and that decrease outbreaks of agricultural pests. Nonagricultural ecosystems, such as forests on slopes and wetlands, help meter the release of water into streams and rivers, and thus help in flood control. If properly managed, natural ecosystems also can produce a sustainable supply of goods used by society, including timber and fiber, fish, and game.

Ecological Insights into Agricultural Impacts and Sustainability

                                                                                                                      What might be done to decrease the environmental impacts of agriculture while maintaining or improving its productivity, stability, or sustainability? This major challenge will have no single, easy solution. Partial answers will come from increases in the precision and efficiency of nutrient and pesticide use, from advances in crop genetics including advances from biotechnology, and from a variety of engineering solutions. Some additional insights may come from a consideration of the principles that govern the functioning of all ecosystems, including agroecosystems. Ecosystem functioning is known to depend on the traits of the species ecosystem’s contain (their composition), the number of species they contain (their species diversity), and the physical conditions they experience, especially disturbance regimes. A consideration of the principles governing the impacts of composition, diversity, and disturbance on ecosystems may suggest ways to decrease impacts of agriculture or to make it more productive, stable, or sustainable. It is critical to realize that these principles apply within a given ecosystem type. They describe differences in functioning of otherwise identical ecosystems that share the same species pool and differ only in which and how many species they contain. These principles were not derived from, and do not apply to, comparisons among different ecosystem types, such as cattail swamps versus prairies, or mangrove versus upland forest, or tropical versus temperate forests.

Conclusions

                       A hallmark of modern agriculture is its use of monocultures grown on fertilized soils. Ecological principles suggest that such monocultures will be relatively unstable, will have high leaching loss of nutrients, will be susceptible to invasion by weedy species, and will have high incidences of diseases and pests—all of which do occur. Although ecological principles may predict these problems, they do not seem to offer any easy solutions to them. Agriculture, and society, seem to be facing tough tradeoffs. Agricultural ecosystems have become incredibly good at producing food, but these increased yields have environmental costs that cannot be ignored, especially if the rates of nitrogen and phosphorus fertilization triple and the amount of land irrigated doubles. The tradition in agriculture has been to maximize production and minimize the cost of food with little regard to impacts on the environment and the services it provides to society. As the world enters an era in which global food production is likely to double, it is critical that agricultural practices be modified to minimize environmental impacts even though many such practices are likely to increase the costs of production.