Environmental Problems, Their Causes, and Sustainability 1

1910. People in developing countries typically spendup to 40% of their income on food. And the 1.1 billionof the world’s poor struggling to live on $1 a day orless spend about 70% of their income on food.The industrialization of agriculture has been madepossible by the availability of cheap energy, most of itfrom oil. Putting food on the table consumes about17% of all commercial energy used in the United Stateseach year (Figure 14-6). Good news. The input of energyneeded to produce a unit of food has fallen considerablyand most plant crops in the United States providemore food energy than the energy used to grow them.Bad news. If we include livestock, the U.S. foodproduction system uses about three units of fossil fuelenergy to produce one unit of food energy. That energyefficiency is much lower if we look at the wholeU.S. food system. Considering the energy used togrow, store, process, package, transport, refrigerate,and cook all plant and animal food, about 10 units ofnonrenewable fossil fuel energy are needed to put 1 unit offood energy on the table. By comparison, every unit ofenergy from human labor in traditional subsistencefarming provides at least 1 unit of food energy and upto 10 units using traditional intensive farming.What Growing Techniques Are Usedin Traditional Agriculture? Low-InputAgrodiversity in ActionMany traditional farmers in developing countriesuse low-input agriculture to produce a varietyof different crops on each plot of land.Traditional farmers in developing countries grow aboutone-fifth of the world’s food on about three-fourths ofits cultivated land. Many traditional farmers simultaneouslygrow several crops on the same plot, a practiceknown as interplanting. Such crop diversity reducesthe chance of losing most or all of the year’s food supplyto pests, bad weather, and other misfortunes.Interplanting strategies vary. One type, polyvarietalcultivation, involves planting a plot with severalvarieties of the same crop. Another is intercropping—growing two or more different crops at the same timeon a plot (for example, a carbohydrate-rich grain thatuses soil nitrogen and a protein-rich legume that putsit back). A third type is agroforestry, or alley cropping,in which crops and trees are grown together (see IndividualsMatter, at right).A fourth type is polyculture, in which many differentplants maturing at various times are plantedtogether. Low-input polyculture has a number of advantages.There is less need for fertilizer and waterbecause root systems at different depths in the soilcapture nutrients and moisture efficiently. It providesmore protection from wind and water erosion becausethe soil is covered with crops year-round. There is littleor no need for insecticides because multiple habitatsare created for natural predators of crop-eating insects.Also, there is little or no need for herbicides becauseweeds have trouble competing with the multitude ofcrop plants. The diversity of crops raised provides insuranceagainst bad weather. This is a way of growingfood by copying nature. Wes Jackson is carrying outresearch on polyculture to grow perennial crops onprairie land in the United States (see case study at thebeginning of this chapter).Recent ecological research found that on average,low-input polyculture produces higher yields perhectare of land than high-input monoculture. For example,a 2001 study by ecologists Peter Reich andDavid Tilman found that carefully controlled polycultureplots with 16 different species of plants consistentlyoutproduced plots with 9, 4, or only 1 type ofplant species.Traditional farmers in arid and semiarid areaswith low natural soil fertility have developed innovativemethods to boost crop production. For example, inthe African countries of Niger and Burkina Faso, a4%2% 6% 5%Crops Livestock Food processingFood distribution and preparationFood production17% of total U.S.commercialenergy useFigure 14-6 In the United States, industrialized agriculture uses about 17% of all commercial energy. In theUnited States, food travels an average of 2,400 kilometers (1,500 miles) from farm to table. (Data from DavidPimentel and Worldwatch Institute)278 CHAPTER 14 Food and Soil Resources