Crop productivity is ultimately controlled by the environmental resources that support plant growth and the ability of the plant to convert these resources into economic yield. The basic resource is the solar radiation available when conditions are suitable for plant growth. The availability is determined by a rate (solar radiation per day) and by time (the period when conditions are suitable for plant growth). Economic yield of a crop is also a function of a rate of growth expressed over time. Fundamental aspects of crop growth are often presented as rates in the literature (e.g., crop growth rate, single leaf or canopy photosynthesis rate), but more detailed analysis of crop productivity integrates rates over time to produce the final yield.
Time has always been an important consideration when matching crop cultivars to the production environment, whether the length of the growing season was limited by temperature or water availability. Historically, however, plant processes associated with rates probably received more research attention than processes involving time, but both are important and must be included in any analysis of the yield production process.
There are two aspects of the effect of time on the productivity of agricultural systems. First, the total time required for the growth of the crop (planting to maturity) as well as the time devoted to various activities or growth phases may affect yield, but these effects are not always intuitively obvious. Second, the time available for plant growth in any environment, usually defined by temperature or water availability, determines the potential resource capture by the crop. Time, therefore, plays a role in defining the available resources and how effectively these resources are converted into yield.
Dennis B. Egli, with the Dept. of Plant and Soil Sciences, University of Kentucky, seeks to evaluate the role that time plays in determining agricultural productivity and to attempt to identify aspects of the use of time by grain crops that can be exploited to increase food production in the future.
Time influences crop productivity in two ways; the time devoted to the growth of the crop can affect yield, and the time available for plant growth in any environment determines the potential resource capture by the crop.
In this research, these relationships were investigated using data describing the length of the vegetative and reproductive growth phases of major grain crops. The total growth duration (TGD) of six crop species (n = 83) varied from 62 to 185 d. Vegetative growth averaged 67% of TGD while the reproductive phase accounted for 33%. Total biomass was related to the TGD, and seed yield was related to the length of the reproductive phase.
There was a curvilinear relationship between TGD and reproductive phase duration with the maximum reproductive phase occurring at a TGD of ~110 d. Consequently, selecting a longer TGD cultivar does not necessarily increase seed yield, making it difficult to convert the extra resources available in long growing seasons into seed yield. The length of the vegetative phase can be manipulated to enhance yield or production efficiency by, for example, shortening it to place reproductive growth in a more favorable environment or to reduce the irrigation requirement.
Crops that grow longer produce more biomass and those with longer seed-filling periods produce more seed yield when environmental conditions permit extended growth. The data presented and discussed in this research suggests that these generalizations may apply to all agronomic crops.
Manipulating the plant to extend the duration of growth in these situations will increase biomass and grain yield, all other factors constant. The failure of reproductive growth and total growth duration to always increase in tandem limits the ability of a single grain crop to effectively use environmental resources in environments with long growing seasons based on temperature or moisture availability.
On the other hand, this disconnect allows manipulation of the duration of vegetative growth of a crop without affecting seed yield, providing unique opportunities to improve the efficiency of cropping systems and to develop systems that convert more of the natural resources to seed yield in environments with longer growing seasons.
Involving time as well as rate in efforts to improve yield provides more opportunities to increase food supplies in the future.
Summary adapted from:
Time and the Productivity of Agronomic Crops and Cropping Systems
Dennis B. Egli
Published in Agron. J. 103:743-750(2011)
Published online 10 Mar 2011