Physiological Challenges for Increasing Crop Yield: Resource Availability and Utilization.

Grain yield of well-adapted cultivars can be described by crop responses to resource availability and the crop’s capacity to utilize these resources. Resources required for crop growth and yield include: water, nutrients, and solar radiation. Likewise, increases in crop yield necessarily require an increase in utilization of those resources most limiting. In most cropping environments, soil moisture during a portion of the growing season limits crop growth and yield. Although progress has been made developing genotypes with improved yield under moderate drought conditions, the prospects of achieving substantial, absolute yield increases under severe drought conditions by either conventional or transgenic technologies are unlikely, particularly for genotypes with high yield potential when grown under optimum conditions. For nutrient resources required by crops, world reserves of P and K are large but costs may limit their use. Since 1980 in the US, the inflation-adjusted costs of K has increased 4- to 6-fold, and the costs of P has approximately doubled. Nitrogen fertilizer costs are closely tied to natural gas prices, and N fertilizer prices have approximately doubled since 1980. In developing countries, where small amounts of fertilizer often result in large yield responses, increasing prices jeopardize use and expansion of fertilizer use. In lower latitudes, for some crops it appears that the cumulative amount of solar radiation available to a crop is often not a limitation to yield. Short-season soybean and maize crops have yields similar to cultivars/hybrids with a longer growth duration and intercept up to 40% less solar radiation during the season. Associated with the decreased cropping cycle and decreased amount of intercepted solar radiation is a proportionate decrease in the amount of water used during the growing season.