The most sustainable approach to combating malnutrition and undernourishment around the world may be to help local farmers produce adequate quantities of nutritious food. It may also be the most cost-effective approach.

In a 2009 article in the journal Nature, Pedro Sanchez, Director of Tropical Agriculture at Columbia University, compared the cost of three approaches to providing hunger relief in Africa. His comparison was based on the cost of delivering 1 metric ton of corn. As shown in Figure 7.32, buying and shipping corn from the United States is the most expensive way to deliver food aid.

Buying corn in Africa and distributing it locally cost less than half what it would take to buy and ship from the United States. However, providing local farmers with the fertilizer, seed, and technical assistance to produce an extra ton of corn is only one-sixth the cost of shipping from the United States. Sanchez points out that investing in local farmers to help improve their farm production may be the surest and least expensive way to reduce the level of hunger in the world. He notes, encouragingly, that such assistance in some of the regions of Africa most afflicted by hunger has more than doubled corn yields on small farms.

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Intensive agriculture, which was at the center of the Green Revolution, focused on producing food through large-scale monocultures of low genetic diversity, with high production maintained by high inputs of fertilizers, pesticides, and energy. In contrast, many of today’s agricultural scientists are turning back to traditional practices to develop sustainable, high-production systems that require lower inputs of chemicals and energy.

Genetic diversity, one of the basic components of biodiversity (see Chapter 3, page 62), has proved a powerful tool for increasing rice yields in China, echoing the results of Tilman’s study, covered earlier in the chapter. Youyong Zhu of Kunming University in southwestern China led a team that investigated the potential for reducing the loss of rice production—caused by a serious fungal disease called rice blast, Magnaporthe grisea—by increasing the genetic diversity of rice plantings. Sticky or glutinous rice varieties are sought after for making specialty dishes and therefore draw a higher selling price. These sticky varieties seem especially vulnerable to infection by rice blast. To combat rice blast, the researchers copied a traditional planting scheme used by local farmers. They increased the genetic diversity of rice in fields by planting susceptible, tall, sticky rice and resistant, short hybrids in rows in a 1:4 ratio: Two rows of short rice on the left, one row of tall rice in the middle, two rows of short rice on the right.

The reduction in rice blast infection in these mixed fields was dramatic. The rate of infection in monocultures of the sticky rice was 20% compared with 1% in the mixed plantings (Figure 7.33). The increased distance between susceptible plants and modification of temperatures, humidity, and light were likely responsible for creating conditions less favorable for the pathogen than those in monocultures of sticky rice. Furthermore, it was not necessary to spray fungicidal chemicals to control rice blast in the mixed field, thus saving money. Reducing rice blast infections resulted in an 89% increase in yield of the valuable sticky rice varieties and a 40% higher gross economic return per hectare.

Rice farmers across China took notice. In Yunnan and 10 other Chinese provinces, the area in mixed plantings increased to 1.57 million hectares between 2000 and 2004. Across this vast area, rice yields increased by an average of 675 kilograms (1,488 pounds) per hectare, and $259 million were gained either through increased income or reduced costs. Agricultural scientists have demonstrated similar boosts in yield resulting from higher genetic diversity in other crops.

Some of the benefits of biodiversity to crop production can be realized by growing different crops sequentially on the same field generally over a period of three to five years, a practice called crop rotation. For example, a farmer might plant corn in one field, and then plant a different crop in that same field the next year, and the year after. The benefits of crop rotation include increased yields, and lower insect and disease infestations. Crop rotation can also improve soil aeration when deep-rooted crops are part of the rotation, as well as improve soil fertility, as when a nitrogen-fixing legume, such as alfalfa or soybeans, is grown.

Biodiversity can be incorporated into agricultural systems by growing two or more crops in the same field, a technique called intercropping. Intercropping has been practiced for centuries. For example, Native Americans developed a traditional intercropping system in which they grew corn, beans, and squash together, a combination of crops commonly referred to as “the three sisters” (Figure 7.34).

In this system, beans enrich the soil by fixing nitrogen, the corn provides a surface for attachment by the climbing bean plants, and the squash shades the soil, thereby reducing temperature fluctuations and water loss. The three crops also provide complementary sources of nutrition: Combining the amino acids of beans, corn delivers all the essential amino acids required by humans, while squash provides a rich source of vitamin A.

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Modern researchers and farmers are rediscovering the benefits of intercropping. Faced with the daunting task of feeding its 1.3 billion people on limited agricultural lands, China has been investing heavily in agricultural research. The ultimate prize in such research would be the development of low-input (low-cost), high-yield (high-profit) agricultural systems. Examples of Chinese intercropping systems include growing sugarcane and potatoes or wheat and broad beans together on the same field. Intercropping has increased yields from 33% to 84%, reduced the incidence of crop diseases, and increased the income of farmers.