**2. Corn productivity**

available soil nutrients. As a C4 plant, corn has some photosynthetic advantages in capturing solar energy in warm weather compared to C3 crops such as wheat, rice and soybean. Due to its high productivity under various climate conditions, corn is now the largest grain crop in the world [1]. Favorable agro-climatic conditions in the US "Corn Belt" have made the US the largest corn producer. In 2017, corn production in the US accounted for 35% of world corn

The rise of corn as the most important cereal in the world has been associated with important improvements in its productivity [5]. **Figure 1** illustrates the evolution of the average corn yield on US farms from 1870 to 2017 [6]. **Figure 1** shows that corn productivity was basically stagnant before 1940: during the period 1870–1940, US average corn yields stayed

in 1940, a period of fast and steady rise in corn productivity began and continues to this time. US average corn yield increased from 28.9 bu/acre (1.81 metric tons/ha) in 1940 to 176.6 bu/acre (11.1 metric tons/ha) in 2017 [6]. This amazing achievement means that a given area of land can produce 6.1 times more corn in 2017 than in 1940, which corresponds to an average annual growth rate of 2.35%, reflecting the rapid technological progress sustained over the last seven decades. This achievement raises two questions. First, what are the sources of this growth in corn productivity? Second, is it likely to continue in the future? Below, we discuss the role played by two key drivers of corn productivity: improved genetics and improved management. We also consider the corn market and its evolving prices. Finally,

Starting

within a narrow range between 20 and 30 bu/acre. (between 1200 and 1900 kg/ha)<sup>1</sup>

1 bushel of corn equals 25.40 kg and 1 acre of land equals 0.4047 hectare. Thus, 1 bu/acre = 62.77 kg/hectare.

**Figure 1.** Historical corn yield, US. Source: The corn yield is measured in dollar per bushel, as reported by USDA-NASS [6].

production [1].

14 Corn - Production and Human Health in Changing Climate

1

Genetic selection has been a very important driver of agricultural productivity. The process started some 9000 years ago in Mexico when corn was first "selected" and evolved from its wild ancestor [2]. Over the centuries, accidental mutations and some intentional selections contributed to beneficial changes [3]. But as **Figure 1** indicates, the rate of genetic improvement was very slow before 1940. Genetic selection was then based mostly on traditional breeding methods trying to combine desirable characteristics of each parent into the progeny. Applied to crops, farmers used selective breeding to pass on desirable traits while omitting undesirable ones. The desirable traits included higher yield and better quality as well as improved adaptation to local agro-climatic and ecological conditions. When applied by farmers, the selection intensity was low, generating slow genetic changes.

The early part of the twentieth century saw the rise of modern genetics and its applications to plant breeding. The discovery of hybrid vigor led to the development of hybrid seed corn and rapid improvements in corn productivity [5, 8]. The higher corn yields stimulated the rapid adoption of hybrid seed corn among US farmers [8, 9]. The new corn hybrids also contributed to the development of a seed corn industry that focused on refined genetic selection [10]. The increased intensity of genetic selection contributed to the development of improved varieties that were better at capturing soil nutrients and more resistant to diseases [5]. As **Figure 1** shows, the result has been decades of genetic improvements and rapid and sustained growth in corn yields.

Starting in the 1980s, progress in biotechnology revolutionized genetic selection. The identification of genes and the refinements in gene transfer<sup>2</sup> technologies opened new opportunities for genetic selection. Eventually, this process led to the development of genetically engineered (GE) corn hybrids that, along with the patenting of GE seeds, stimulated the growth of biotechnology in agriculture. The first GE corn hybrids became commercially available in the US in 1996, with US farmers rapidly adopting the technology. In 2017, more than 90% of all corn planted in the US was GE [12]. The rapid adoption of GE corn in the US led to significant productivity improvements [13]. Over the last two decades, the adoption of GE seed in agriculture has proceeded around the world, though at different rates depending on each country's regulations [14].

Two major types of GE traits are currently available in the hybrid seed corn market: those providing insect resistance (IR) (commercially available in corn in 1996) and those providing herbicide tolerance (HT) (commercially available for corn in 1998). Hybrid seed corn contains these traits either singly or combined as stacks or pyramids, so that a single hybrid is both IR to multiple pests and HT to more than one herbicide.

<sup>2</sup> We now know that horizontal gene transfers across species are not uncommon and that they played an important role in the evolution of life (e.g., [11]).

In the US, currently available IR traits involve gene transfers from the soil bacterium *Bacillus thuringiensis* (Bt) so that hybrids express insecticidal proteins in their tissues that help control specific insect pests. Bt corn hybrids in the US focus on two pests that have had significant adverse effects on corn yield: European corn borer (*Ostrinia nubilalis*) and corn rootworm, a complex of four closely related species (*Diabrotica* spp.). European corn borer larvae feed on corn plant tissues, including tunneling through corn stalks and ear shanks, which not only disrupts plant functions and so causes direct yield loss, but also causes plant lodging and ear drops, causing additional yield loss. Corn rootworm larvae feed on corn roots, which disrupts water and nutrient uptake by the plant and so causes direct yield loss, and also causes plant lodging. Both pests have historically caused significant damage to corn plants, reduced corn yield and are somewhat difficult to control using conventional insecticides [15].

been selected to be more resistant to lodging and more tolerant of biotic stress (pest damage, weed competition, disease) and abiotic stress (adverse weather, poor soil conditions). These genetic changes have interacted with improved management practices, including fertilizer use, irrigation, tillage system, weed control, pest management and crop rotation. Fertilizer applications remedy soil nutrient scarcity, as corn yield is very responsive to nitrogen [5]. When available, irrigation alleviates soil water scarcity and drought. Pest and weed populations can be (at least partially) controlled and suppressed by tillage, crop rotations and by the use of pesticides (insecticides and herbicides). Crop rotation had been used by farmers for

Corn Productivity: The Role of Management and Biotechnology

http://dx.doi.org/10.5772/intechopen.77054

17

The hypothesis that management and genetic biotechnology interacted in generating recent corn productivity gains have been investigated by Chavas and Shi [22] and Chavas et al. [23]. They found evidence of the important role of management and of interaction effects between technology and management. First, they documented how biotechnology has been a major driver of improved corn productivity over the last decade. They also explored how the benefit of GE traits can vary with agro-climatic conditions. Second, they showed how GE hybrids provide enhanced control of pest damages, thus reducing exposure to both risk and downside risk (the provability of facing low yields). Reducing risk exposure is a major part of the benefits of GE technology [24]. Importantly these GE benefits can go beyond the farm if the suppression of pest population is regional [25]. Third, Chavas and Shi [22] and Chavas et al. [23] showed how crop rotation and GE technology provide alternative ways to control pest populations, indicating that they behave as substitutes in the corn production process. Fourth, they reported the presence of synergy between biotechnology and plant density as they affect corn productivity. By improving pest control, GE hybrids make it possible to obtain greater productivity from higher plant density, evidence that the observed growth in corn productivity has been the outcome of important synergies between genetics and improved management.

In a market economy, technological progress affects producers, consumers and prices. **Figure 2** presents the evolution of US corn prices (\$/bu) over the period 1947–2017, reporting both nominal prices and real prices [6]. Real prices are nominal prices adjusted for inflation by dividing by the US Consumer Price Index (CPI), in this case with 1983 normalized to 1. **Figure 2** shows that the nominal price of corn has gone from \$1.52/bu (\$59.8/metric ton) in 1950 to \$3.36/bu (\$132.3/metric ton) in 2017, corresponding to an average increase of +1.19% per year. It also shows that the real price of corn has gone from \$6.30 to \$1.37/bu, correspond-

holding purchasing power constant, an individual can buy 4.6 times more corn in 2017 than in 1950. This dramatic change mostly arises from productivity gains. Indeed, the rate of change in the real corn price (−2.25% per year) almost perfectly matches the rate of change in yield

The difference is due to inflation, the average US inflation rate between 1950 and 2017 being +3.44% per year.

This sharp decline in real price means that,

centuries to reduce pest and weed infestation and to restore soil fertility [19–21].

**4. Corn markets**

ing to an average decline of −2.25% per year.<sup>3</sup>

reported earlier (+2.35% per year).

3

Bt corn has proven more effective in controlling European corn borer and corn rootworm than conventional insecticides, thus increasing harvested yields. In addition, farmer adoption in the US of Bt corn has reduced the aggregate use of insecticides [16]. The rapid adoption of IR Bt corn in the US reflects that US farmers have obtained significant productivity benefits from this technology [12, 13].

HT corn hybrids simplify herbicide-based weed management by allowing application of herbicides on the crop without causing crop damage. Weed management without HT hybrids is managerially more complicated since several weed species look similar when they are small at the time when farmers must make herbicide decisions, but different species commonly require different herbicides for effective control. The earliest and still most popular HT hybrid is tolerant of the herbicide glyphosate, though other types of HT hybrids have been available. As a broad-spectrum herbicide, glyphosate controls a wide range of weed species, so that farmers do not need to know the specific weed species in their fields and which herbicides provide effective control. As a result, farmers rapidly adopted glyphosate tolerant corn hybrids and glyphosate quickly become the most commonly used corn herbicide, with glyphosate used on approximately 75% of US corn acres since 2008 [17]. In US, farmer adoption of HT hybrids has reduced the aggregate use of herbicides [16]. In addition, HT varieties facilitate farmer adoption of reduced tillage and no-till systems, which not only reduces soil erosion, but also lowers labor and fuel requirements [18]. Features such as these have made GE corn attractive to US farmers, contributing to their rapid adoption [12, 13].
