How Sustain Wheat Yield under Changing Environmental Conditions
Maryam Rafique1*, Sadia Ismail1, Muhammad Sajid2 and Muhammad Amjid2.
1Stress Physiology Lab. Department of Botany, New Science Block, University of Agriculture, Faisalabad
2Postgraduate Lab, Department of Agronomy, University of Agriculture, Faisalabad
*Corresponding author’s email: [email protected]
How Sustain Wheat Yield under Changing Environmental Conditions
Introduction
Climate change is one of the main challenges facing humanity in the future and effect of climate change has been detrimental to agricultural industry. Climate change and its potential impacts has grown in recent decades due to ample research. Climate change impacts cereal production mainly through heat and water stress but is also associated with waterlogging, frost, and disease and pest dynamics.
Climate change factors
Many factor directly or indirectly associated with climatic change pose potential threats to crop yields and economic returns including changes in temperature precipitation within and among growing seasons, atmospheric gas concentrations and severe weather events. Forecasts of climate effects on future crop productivity are based largely on the use of models. For example, urbanization and increasing populations result in increased fossil fuel consumption, while globalization and industrialization result in intensification of agriculture and transportation. These sectors contribute heavily to carbon emissions and resulting atmospheric changes. Model projections are then downscaled to provide a more detailed spatial resolution from the global climate model results to increase relevance to regionally specific forecasts. Temperature and precipitation projections are numerical results of a climate model
Rainfall and temperature influences
Both rainfall and temperature are crucial factors for wheat yield. Uneven rainfall distribution has very bad impact on the wheat growth and yield. Rainfall patterns are less confidently predicted than temperature, although it is likely that the frequency of heavy precipitation (i.e. the proportion of total rainfall from heavy falls) will increase in many regions. Future increases in precipitation of 5-15% during the growing season show a negligible impact on wheat yield.
Winter wheat has gradually reducing resistance to low temperatures after it begins rapid growth in the spring and advances toward maturity. Wheat is most sensitive to low temperatures during the reproductive period, which begins with pollination during the late boot stage. The temperatures required to cause injury throughout the winter wheat life cycle. Both the temperature reached and the duration of the low temperature can be a factor in the amount of damage inflicted. Longer durations of freezing temperatures will cause more damage than a brief exposure. Increased hot and cold spells resulting from climate change could affect bread-making quality or seed quality for growing subsequent wheat crops, depending upon when they occur. Greater temperature variability is expected in future years as a result of climate change. The effects on plants of so-called unseasonal warm and cold periods in the spring are particularly noticeable to gardeners and farmers. Quality of seed to grow later crops was reduced by high-temperature episodes during early seed filling but improved if they occur later during maturation; and vice versa for cool-temperature episodes.
Also, up to a 23% reduction in grain yield has been reported from as little as 4 days exposure to very high temperatures. Periods at such high temperature occur frequently during grain filling in both Mediterranean and continental climates and such extremes may be more frequent throughout Europe in future climates of warmer mean temperatures. Since high temperature episodes appear to be more severe around anthesis these may affect the pollination process and resulting in smaller grain yields. Warmer maximum temperatures over 4 consecutive days close to anthesis directly reduced grain number and as a consequence, grain yield at harvest maturity, while higher mean temperatures reduced root biomass immediately after anthesis. If climates become both warmer and more variable, the occurrence of high temperature during anthesis could reduce wheat grain yields substantially. Deleterious effects of higher temperatures on root growth could pose a further threat to crop production if high temperatures are also associated with periods of drought in future climates.
Greenhouse effect
It is predicted that increases in greenhouse gas concentrations will result in a rise in mean temperatures of about 2°C by the middle of the next century. Although yields of temperate crops increase with enhanced CO2 concentrations, this may be offset by the negative effects of warmer temperatures in determinate crops. The duration of grain filling in cereals is determined principally by temperature. In wheat, high temperatures 31°C after anthesis can decrease the rate of grain-filling whilst high temperatures imposed before anthesis can also decrease yield.
In winter wheat, high temperature episodes occurring near to anthesis can reduce the number of grains per ear and the subsequent rate of increase in harvest index, The effect of short periods of exposure to high temperatures 31 °C on wheat grain yields are thought to be equivalent to a 2±3°C warming in the seasonal mean temperature.
Approaches for retained climate change
Cultivar choice, short duration verities, crop rotation and plant protection were ranked as the most important agronomic management tools for improving yield stability of wheat, followed by mineral fertilization and soil tillage.
Cultivar choice and breeding
Conventionally, breeding efforts have rightly focused on crop yield rather than survival under stresses, but there is an increasing need to identify, develop, and deploy germplasm that can withstand extreme weather events with yield stability in both good and bad years, despite the fact that variability in crop yields may increase due to climate change. Breeding programs aim at improving crop production either within given macro environments (for example rainfed vs. irrigated) or in a wide range of growing conditions. The merit of either strategy depends on the range of testing environments and on the definition of stress environment. When environments with average yields of 3-4 t/ha are defined as ‘stress environments’, selection for stress conditions can be successfully conducted under optimum conditions. However, when the stress environment has a much lower yield potential (0.5-2.0 t/ha), direct selection in the target environment is the most efficient strategy.
Cultivar choice is a very important tool in cereal production and can have positive effects on the yield stability of winter wheat. Advantages in grain yield and better yield stability of hybrids compared to lines could not be seen in low-yielding sites. Furthermore, several farmers and advisors stated that in their opinion, hybrids seem to have a higher drought tolerance due to better vitality, greater rooting system and water uptake efficiency, when compared to line cultivars of winter wheat.
Sowing time
Evolving planting dates could be a good strategy to take advantage of new environmental conditions with prolonged frost-free periods. Potential wheat yields decrease at a rate of 6.5% per °C of mean temperature increase between sowing (July) and harvest (December) due mainly to the shortening of the growth cycle.
Short duration verities
Development and distribution of short duration varieties, which can withstand the climatic anomalies expected in the future, should be given priority in the mountain region. More recent high yielding varieties of the warmer plain areas should also be tested and introduced in the mountain areas because the expected future increases in temperatures caused by global warming would render these varieties suitable for the mountain areas.
Crop rotation
Crop rotations were assumed to have the second greatest effects on the yield stability of crop production systems. The high importance of crop rotations is consistent with the findings of several scientific studies. Favorable, diverse and lengthened crop rotations can improve yield stability of winter wheat. On the other hand, monocultures of wheat lead to enhanced yield variations. Favorable preceding crops, such as oilseed rape and legumes (e.g., peas and field beans) can positively affect the yield stability of winter wheat as the subsequent main crop. Furthermore, crop rotations can break soil pathogen cycles and reduce weed pressure. In the context of crop rotations, farmers also mentioned in the additional free text fields the advantages of cultivating catch crops for the yield stability of winter wheat production.
Surveyed advisors stated the increased importance of favorable crop rotations with regards to the current restrictions on mineral fertilization, the amendment of German governmental fertilization regulations and further prohibition of several active ingredients in chemical plant protection products due to the German Plant Protection Act (GPPA). Overall, crop rotations should not only be planned for monetarily driven factors, but also with regards to soil fertility and environmental sustainability. Therefore, crop rotations should be seen as a systems approach. Some of the respondents stated that favorable crop rotations could react as a buffer for plants in the event of environmental stresses, which could assist in improving yield stability in crop production. However, further investigation is needed to evaluate the effect of different crop rotations on the yield stability of winter wheat under varying environments or agronomic treatments. Optimally, these would be analyses with long-term field trials.
Plant protection
For the surveyed farmers and advisors, plant protection was ranked third highest in importance for yield stable wheat production. Plant health is a decisive criterion to secure wheat yields through reducing biotic stresses (e.g., pathogens). Furthermore, a longer period of photosynthetic active green leaf area has been suggested as the main factor for yield increases obtained with strobilurin and triazole fungicides as the increased photosynthetic period increases the quantity of assimilate available for grain filling. Application of chemical growth regulators could improve root capacities, while a wide range of fungicides led to a retention of green leaf area of wheat plants. Overall it is stated that cultivar adapted plant protection is very important as there is a significant interaction effect between the cultivar and the application of fungicides.
Conclusion
Wheat is a very sensitive crop to environmental changes and its yield significantly reduced due to these stresses on critical stages of the crop. Climate changes are the natural entities which are not under the control of human beings but we mitigates these changes through above mentioned approaches related to environment and crop production.
