Environmental Problems, Their Causes, and Sustainability 1

AdvantagesT rade-OffsInorganic Commercial FertilizersEasy to transportEasy to storeEasy to applyInexpensive toproduceHelp feed oneof every threepeople in theworldWithoutcommercialinorganicfertilizers, worldfood outputcould dropby 40%DisadvantagesDo not add humus tosoilReduce organicmatter in soilReduce ability of soilsto hold waterLower oxygen contentof soilSupply only 2 or 3 of20 or so nutrientsneeded by plantsRequire largeamounts of energy toproduce, transport,and applyRelease thegreenhouse gasnitrous oxide (N 2 O)Runoff can overfertilizenearby lakesand kill fishFigure 14-15 Trade-offs: advantages and disadvantages ofusing inorganic commercial fertilizers to enhance or restore soilfertility. Pick the single advantage and disadvantage that youthink are the most important.way to reduce such losses is crop rotation. Farmersplant areas or strips with nutrient-depleting crops oneyear. The next year they plant the same areas withlegumes (whose root nodules add nitrogen to thesoil). A typical rotation is corn soybeans (alegume) oats alfalfa (a legume). In additionto helping restore soil nutrients, this method reduceserosion by keeping the soil covered with vegetation. Italso helps reduce crop losses to insects by presentingthem with a changing target.Can Inorganic Fertilizers Save the Soil?A Partial SolutionInorganic fertilizers can help restore soil fertilityif they are used with organic fertilizers and theirharmful environmental effects are controlled.Many farmers (especially in developed countries) relyon commercial inorganic fertilizers. The active ingredientstypically are inorganic compounds containing nitrogen,phosphorus, and potassium. Other plant nutrients mayalso be present in low or trace amounts. These fertilizersaccount for about one-fourth of the world’s cropyield. According to Canadian geographer Vaclav Smil,without synthetic inorganic fertilizer we could onlyfeed 2–3 million people.Figure 14-15 lists the advantages and disadvantagesof using inorganic fertilizers to enhance or restoresoil fertility. Inorganic chemical fertilizers canreplace depleted inorganic nutrients, but they do notreplace organic matter. Thus for healthy soil, both inorganicand organic fertilizers should be used.Bio-Recovery Corporation has developed a bacterialprocess that converts biodegradable human and animalwastes into pathogen free, nutrient rich organicfertilizer in only 72 hours.A second type of organic fertilizer called greenmanure consists of freshly cut or growing green vegetationplowed into the soil to increase the organic matterand humus available to the next crop.A third type is compost, produced when microorganismsin soil break down organic matter such asleaves, food wastes, paper, and wood in the presenceof oxygen.Some farmers also use spores of mushrooms, includingpuffballs and truffles, as organic fertilizer. Thespores take in more moisture and nutrients from thesoil. Unlike typical fertilizers that farmers must applyevery few weeks, one application of mushroom fungilasts all year and costs just pennies per plant.Crops such as corn, tobacco, and cotton can depletenutrients (especially nitrogen) in the topsoil ifplanted on the same land several years in a row. One14-5 FOOD PRODUCTION, NUTRITION,AND ENVIRONMENTAL EFFECTSHow Much Has Food Production Increased?Impressive Gains that Are Slowing DownAfter increasing significantly since 1950, global grainproduction has mostly leveled off since 1985, and percapita grain production has declined since 1978.After almost tripling between 1950 and 1985, worldgrain production has essentially leveled off (Figure14-16, left). And after rising by about 36% between1950 and 1978, per capita food production has declined(Figure 14-16, right). The sharpest drops in percapita food production have occurred in Africa since1970, in the former Soviet Union since 1990, and inChina since 1998.Good news. We produce more than enough food tomeet the basic nutritional needs of every person on theearth. Bad news: one out of six people in developingcountries are not getting enough to eat because food isnot distributed equally among the world’s people. This286 CHAPTER 14 Food and Soil Resources