Ecological intensification of cereal production systems: Yield potential, soil quality, and precision agriculture

K. G. Cassman
1999 Proceedings of the National Academy of Sciences of the United States of America  
Wheat (Triticum aestivum L.), rice (Oryza sativa L.), and maize (Zea mays L.) provide about two-thirds of all energy in human diets, and four major cropping systems in which these cereals are grown represent the foundation of human food supply. Yield per unit time and land has increased markedly during the past 30 years in these systems, a result of intensified crop management involving improved germplasm, greater inputs of fertilizer, production of two or more crops per year on the same piece
more » ... f land, and irrigation. Meeting future food demand while minimizing expansion of cultivated area primarily will depend on continued intensification of these same four systems. The manner in which further intensification is achieved, however, will differ markedly from the past because the exploitable gap between average farm yields and genetic yield potential is closing. At present, the rate of increase in yield potential is much less than the expected increase in demand. Hence, average farm yields must reach 70-80% of the yield potential ceiling within 30 years in each of these major cereal systems. Achieving consistent production at these high levels without causing environmental damage requires improvements in soil quality and precise management of all production factors in time and space. The scope of the scientific challenge related to these objectives is discussed. It is concluded that major scientific breakthroughs must occur in basic plant physiology, ecophysiology, agroecology, and soil science to achieve the ecological intensification that is needed to meet the expected increase in food demand. This paper explores biophysical constraints to global food security in the next century. Emphasis is placed on wheat, rice, and maize, because these three plant species account for the majority of calories in human diets (http:͞͞apps.fao.org͞, agricultural production, November 1998), and they are likely to remain the mainstay of human nutrition in the foreseeable future. Intensification of wheat, rice, and maize cropping systems was largely responsible for averting a shortfall in food supply during the past three decades-a 30-year period marking the advent of the so-called "green revolution." The most salient feature of these intensified systems was greater yield per unit land and time. Although appropriate government policies and social conditions also were required to promote intensification, three production factors were largely responsible for the increased production achieved by farmers. These factors were: (i) new "miracle" varieties of wheat and rice released in the mid to late 1960s, which had a higher harvest index (HI; the ratio of grain to total crop biomass), shorter stature, and increased stalk strength that reduced susceptibility to lodging, as well as steady improvement in maize hybrids; (ii) increased application of N fertilizer, which allowed greater net primary production with-
doi:10.1073/pnas.96.11.5952 pmid:10339523 pmcid:PMC34211 fatcat:p4tgxj47urfmtmj2blhhqkafiy