New eUpdate series on agriculture, climate, and change - Part 1
A new series of articles will be featured in the eUpdate in coming weeks. The theme of the series centers on agriculture, climate, and change. Dr. Xiaomao Lin, State Climatologist, and Dr. Rob Aiken, Crops Research Scientist, are the contributing authors on this 4-part series.
Is Kansas agriculture likely to be affected by a changing climate? If so, are there ways to adapt?
In the semi-arid Central High Plains, crop systems contend with heat stress, desiccating winds, lack of rainfall, flood-generating rains, and unexpected arctic air masses, inducing winter-kill or bringing the season to a chilling conclusion. Are producers in Kansas adapting to these changes? In a sense, we prepare by helping farmers adjust to the challenges of the current growing season.
Our growers recognize long-term warming trends and shifts of weather patterns. A recent report (1), prepared by the State Climatologists of Texas, Oklahoma and Kansas, indicates climate change has been written into the historical weather record.
“Both temperature and precipitation have increased across the Southern Plains since the beginning of the 20th century. Temperature increases so far have averaged about 1.5 degrees F over the 20th century, and precipitation has increased by as much as 5%, albeit with large variations from year-to-year and decade-to-decade. Heavy rainfall events have increased in frequency and magnitude. Historical data for tornadoes and hail are not reliable enough to be used to determine whether a trend is present in these types of severe weather.”
“Variations in drought conditions from year-to-year and decade-to-decade are triggered by changes in sea surface temperature patterns in the Pacific and Atlantic oceans. The Dust Bowl drought is thought to have been exacerbated by poor land use practices, while precipitation may have been enhanced in recent decades by growth in irrigated agriculture and surface water.”
“It is clear that temperatures will continue rising over the long term, as carbon dioxide and other greenhouse gases continue to become more plentiful in the atmosphere. By the middle of the 21st century, typical temperatures in the Southern Plains are likely to be 4 to 6 degrees F warmer than the 20th century average, making for milder winters (with less snow and freezing rain), longer growing seasons, and hotter summers. Rainfall trends are much less certain. The majority of climate models favor a long-term decrease, but most projected changes are small compared to natural variability. Extreme rainfall is expected to continue to become more intense and frequent.”
Specific concerns that come from these warming trends include:
- Declining yield potential as a consequence of increased night temperatures
- Diminished photo-protection systems of plants under persistent heat stress
- Increased risk of reproductive failure with heat stress at critical development stages
- Increased crop water requirements
- Degradation of soil with intensive rainfall events
- Increased potential for large-scale methane emissions unleashed by thawing permafrost (2)
These concerns emerge as potential climate change impacts.
Crop productivity is expected to benefit from historic and on-going annual increases in global CO2 concentrations. Assimilation rates can be maintained with modestly reduced crop water requirements. Cool-season grass crops and broadleaf crops will likely gain photosynthetic efficiencies. However, warming trends can detract from the beneficial effects of elevated CO2 levels.
“When elevated temperatures exceed optimal conditions for assimilation, stress responses can include damage to the light-harvesting complex of leaves, impaired carbon-fixing enzymes, thereby reducing components of yield including seed potential, seed set, grain fill rate and grain fill duration. Field studies conducted under conditions of elevated CO2 indicate that benefits of elevated CO2 are reduced by heat-induced stress responses (3)”.
Warmer temperatures, the most reliable feature of climate change, can extend the growing season, but also impair plant productivity. Persistent heat stress pushes plant metabolism to the edge of toleration. The complexity of plant metabolic processes can be astounding. Many of these processes are temperature-sensitive, with optimum temperatures for photosynthesis ranging from 77 to 86 degrees F for winter wheat (4), up to 90 degrees F for soybean (5), and up to 100 degrees F for corn (6). Chronic heat stress, with daily temperatures exceeding this range, can accelerate breakdown of protective mechanisms and can result in permanent damage to crop canopies.
Hot conditions prior to and during flowering can result in crop failure. Grain production requires effective pollination of ovules for ‘seed set’, followed by development and growth of the kernels, harvested as grain. Excessive temperatures (i.e., daily mean temperatures > 77 degrees F for grain sorghum (7) and wheat (8)) for a few days in the approximate 15 day period around flowering can decrease yield potential due to impaired pollination and seed-set; complete failure can occur with daily mean temperatures of 95 degrees F wheat or 99 degrees F sorghum.
Night temperatures drive the metabolic rates of plants. In a sense, plant respiration depletes the supply of carbohydrates available for plant growth and development (9, 10). As a long-term trend, warmer night temperatures can reduce crop productivity.
In summary, chronic high temperatures add to the evaporative demand on crop systems. This increases the water requirement for crop growth. Warmer temperatures can reduce yield potential by impairing heat-tolerance protective mechanisms; by shortening the duration of grain-filling; and by increasing the respiratory cost, the water requirement for growth, and the risk of reproductive failure of cereal crops. Warmer temperatures carry a complex drumbeat of warnings for crop productivity. Needed research is underway to adapt crop cultural practices to avoid heat stress; and to seek genetic advances for crop varieties that are capable of tolerating or resisting effects of warming temperatures.
Xiaomao Lin, State Climatologist
Rob Aiken, Crops Research Scientist, Northwest Research-Extension Center
1) “Climate Considerations.” John Nielsen-Gammon, Gary McManus, Xiaomao Lin and David Brown. White paper developed for “Resilient Southern Plains Agriculture and Forestry in a Varying and Changing Climate: Conference Report” July 18-19, 2017; El Reno, OK. http://twri.tamu.edu/el-reno
3) Aiken, R. “Climate change impacts on crop growth in the Central High Plains.” Proceedings of the 21st Annual Central Plains Irrigation Conference. Colby, Kansas, February 24-25, 2009.
4) Yamasaki, T., T. Yamakawa, Y. Yamane, H. Koike, K. Satoh and S. Katoh. 2002. Temperature acclimation of photosynthesis and related changes in photosystem II electron transport in winter wheat. Plant Physiol. 128:1087-1097.
5) Vu, J.C.V., L.H. Allen, Jr., K.J. Boote and G. Bowes. 1997. Effects of elevated CO2 and temperature on photosynthesis and Rubisco in rice and soybean. Plant, Cell and Environment 20:68-76.
6) Crafts-Brandner, S.J. and M.E. Salvucci. 2002. Sensitivity of photosynthesis in a C4 plant, maize, to heat stress. Plant Physiol. 129:1773-1780.
7) Prasad, P.V.V., M. Djanaguiraman, R. Perumal and I.A. Ciampitti. 2014. Impact of high temperature stress on floret fertility and individual grain weight of grain sorghum: sensitive stages and thresholds for temperature and duration. Front Plant Sci. 6:820.
8) Prasad, P.V.V. and M. Djanaguiraman. 2014. Response of floret fertility and individual grain weight of wheat to high temperature stress: sensitive stages and thresholds for temperature and duration. Functional Plant Biology 41:1261-1269.
9) Tan, K.Y., G.S. Zhou and S.X. Ren. 2013. Response of leaf dark respiration of winter wheat to changes in CO2 concentration and temperature. Chines Science Bulletin 58(15):1795-1800.
10) Narayanan, S., P.V.V. Prasad, A.K. Fritz, D.L. Boyle, B.S. Gill. 2014. Impact of high night-time and high daytime temperature stress in winter wheat. J. Agronomy and Crop Science 201(3):206-218.