Muhammad Nazim and Dr. Muqarrab Ali

Climate change and its effect on the variability of weather patterns have a significant impact on agricultural practices, the availability of natural resources, and the nature of the environment. According to the National Climate Assessment climate change will continue to have a significant impact on crop production and agricultural practices over the next few decades and possibly beyond. Because of these issues, climate change will significantly impact global food security and terrestrial ecosystems. The complexity of these problems is shown by the increase in the frequency and intensity of droughts in some regions around the world and the
increase in the intensity of heavy precipitation events on a global scale. The Intergovernmental Panel on Climate Change (2019) has predicted a temperature rise of 1.5 °C between 2030 and 2052, plus a significant change in precipitation patterns, which, together with a greater frequency of extreme weather events, will significantly affect agricultural production. These findings provide strong evidence that human-driven emission of greenhouse gases is causing climate
change risks, which should not be ignored. In this respect, it is important to understand that the global mean land surface air temperature is increasing faster than the global mean surface temperature (combined land surface and sea surface temperature).

Climate variables, such as temperature and precipitation, have direct impact on
crop production because they contribute to crop growth, health, and yield, thus
affecting cropping system efficiency over time. In the future, climate extremes are expected to increase due to the effects of climate change, which may significantly increase the negative impacts on crop production. Given this scenario, it is remarkable that numerous researchers
have studied the effects of climate change on agriculture. However, past studies
have not focused on adaptive changes to improve cropping practices to manage the
impact of drought on crop production. Water stress resulting from drought is known to reduce crop production because of its negative impacts on plant growth. Plants, including crops,
are naturally subjected to a variety of abiotic stresses such as drought, salinity, heat,
and other factors in their life cycle  and are equipped with different resistance mechanisms
for such stresses, the effectiveness of which vary from species to species and even
within species. Particularly, in the context of drought, some crops have high drought tolerance capacity (e.g., pomegranate, sorghum, cassava, millet, sweet potato), while others have low tolerance capacity (e.g., sugarcane, banana, citrus, cotton, rice). Mechanism of drought tolerance in the plant is a complex phenomenon as interactions between stress factors and different
molecular, biochemical, and physiological factors affect crop growth and development. Therefore, it is important to understand the impact of water stress and drought on crop growth and its development, physiological process, morphology, and yields and available genetic and agronomic tools for crop protection from drought.

Drought stress is a critical limiting factor at the initial stage of plant’s physical
growth and development, determining plant height, stem size, number of and size of
leaves, flower and fruit production, root size and distribution, and seed development. Moreover, drought stress causes a change in the physical environment, which
subsequently affects physiological and biochemical processes in plants. Water stress causes negative effects on the overall growth and development of crops, resulting in a significant reduction in crop production, which will contribute to a reduction of global food supplies. However, proper strategies for drought mitigation combined with the best agricultural management practices can reduce the impact of climate extremes on crop production under changing climate effects. These “best management practices” that contribute to drought adaptation due to climate change and which support mitigation processes, include appropriate agronomic and genetic tools for crop protection under drought.

 For example, during drought events, it is important to have planned strategies on how best to

(i)                 utilize available water resources,

(ii)              scale back on acreage to be planted,

(iii)            select early maturing and drought-tolerant crop varieties,

(iv)             select the most effective irrigation practices,

(v)               Use reduced tillage practices.

These strategies are suggested because it has been observed that sustainable agricultural management practices are not widely adopted due to lack of access to resources, knowledge, and practical experiences. In addition, it is necessary to continue our efforts on selecting improved
varieties of all crops for better yield and higher quality and expanded cultivation
environment to enhance their drought tolerance. It is possible to enhance the drought
tolerance limit of a crop by introducing foreign genetic materials that confer added
drought tolerance through genetic transformation. This is a recent biotechnological
approach that shows much promise.

Agronomic Tools To Protect Crops From Drought

Agronomic tools used to mitigate the effects of drought on crops range from variety
selection and the timing of seeding to cultural practices. Cultural practices include
tillage and cultivation, crop production systems, mulching, fallowing, nutrient and irrigation management, and use of soil inoculants such as arbuscular mycorrhizal
fungi (AMF) and plant growth-promoting rhizobacteria (PGPR). In addition, the exogenous
application of protectants like glycine betaine and plant growth regulators has been
useful for protecting crop plants under drought conditions.

Crop and Variety Selection Crop and variety selections most suited to the planting
area are probably the most fundamental decisions to be made for crop production
under drought conditions. Crop and variety selection for drought stress tolerance should be based on the tolerance level of the crop or variety, the time that the crop or variety takes to mature, and the characteristics which favor survival under drought conditions. Early maturing crop varieties typically grow and mature before a drought reaches its peak during the growing season, while varieties with short stems with small leaf surface area can reduce transpiration. Similarly, varieties with deep and extensive root systems improve the capture and use of available soil moisture. Time of Planting It is critical to choose the best time for seeding when cropping under dry conditions, because it helps match water availability to crop demand and
optimizes crop establishment and early plant vigor. Early sowing is encouraged in dry environments because it can improve the water use efficiency of crops and can ensure flowering
and grain filling (both critical growth stages of crops) which occur during periods of
better soil water availability. Early sowing also helps crops to develop deeper roots and avoid early droughts.

 

 

Stand Density

Reducing stand density is another agronomic tool often explored for
water saving in cropping systems situated in moisture-deficient environments
Though this practice tends to

(i)                 lower crop interception of solar radiation,

(ii)              increase evaporation losses of water and runoff

(iii)            Increase weed competition, especially for crops with wide rows, it appears to be very effective at water savings and hence yield optimization under intermittent terminal stress
levels.

Tillage Practices

Tillage practices impact on soil hydraulic properties, including soil hydraulic conductivity, implying that these practices can affect moisture storage in the soil. Influence of tillage on soil hydraulic properties revealed that reduced tillage tends to increase water storage in the soil through higher storage in fine pores in spite of reduced total porosity and
macropore volume (Hydrological regimes and different soil textures).

Crop Production Systems

 Polyculture or multiple crop production systems that
control erosion, increase water and nutrient retention, and also have a potential to
increase yield, should be employed for crop production under dry environments.
Examples of these systems include crop rotation and strip cropping. Though crop
rotation is typically more commonly practiced in humid regions, it can be useful in
dry regions if crop rotations are planned around crop moisture requirements. Crop rotations in these environments should also focus on selecting crops that help improve soil structure and the addition of organic matter to the soil to minimize soil erosion. These are typical in dry
cropping environments. Such planning can also maintain and/or improve the nutrient levels of soils in these environments. Strip cropping essentially involves planting crops in alternate strips which are usually planted perpendicular to slopes or the direction of prevailing winds to
control erosion problems. Strip cropping also incorporates elements of crop rotation, contour cultivation, and stubble mulching, which are all good farming practices. Hence, the soil water storage potential of this approach is attributable to the combined benefits of all of these advantageous practices.

Fallowing

Fallowing involves keeping the land free of vegetation for at least one growing season, with the intention of storing moisture gained from rainfall in the soil for use by a subsequent crop. Mulching And Stubble Tillage

This technique involves covering up the soil surface with a protective layer, which may be organic or inorganic. Mulching helps hold moisture in the soil by reducing evaporation and runoff, which protects the soil and enhances its condition for supporting crop growth. Stubble tillage is also aimed at improving soil moisture storage and soil protection. However, it is more of a postharvest measure used during fallow periods between successive crops.

Nutrient Management Studies

P nutrient management (at both macro and micro levels) can improve water use efficiency and promote crop yield. Macronutrients include phosphorus and potassium, while important micronutrients include selenium, silicon, zinc, iron, and boron. Under drought stress most of the plant increased root growth. Similarly, an adequate supply of potassium for grain legumes during drought conditions improved their tissue water potential and maintained photosynthesis at expected levels. Selenium is reported to increase the ability of roots to uptake water under drought conditions, silicon addition to drought-stressed plants increased their relative water content through increases in proline and glycine betaine. The application of silicon alone or in combination with potassium to drought-stressed chickpea plants resulted in dry matter yield increases.

Irrigation

Since irrigation in cropping systems is not efficient and water wasted in
the process is estimated to be over 50% of the amounts applied in some regions of
the world, it is imperative that water use in crop production systems in dry environments is optimized. Water waste typically stems from technical issues associated with the distribution and inadequate maintenance of irrigation systems. This is often compounded by the high evapotranspiration and usually infertile fragile soils in dry environments that are prone to degradation and salinization. Efficiency strategies include scheduling irrigation at night to reduce evapotranspiration, limiting overdependence on aquifers, and upgrading traditional irrigation systems to precision types coupled with Crop Protection under Drought Stress
precision agriculture. Another technique that has some documented success is partial root-zone irrigation or drying in which case irrigation is applied alternately to different sides of the root zone.

Plant Growth Regulators (PGR)

Inoculating Soil with Arbuscular Mycorrhizal Fungi (AMF) and Plant GrowthPromoting Rhizobacteria (PGPR) Arbuscular mycorrhizal fungi (AMF) help
plants resist drought through many mechanisms. First, they enhance water uptake
from the soil through their extensive extra-radical mycelia. Second, AMF increases the antioxidant potential of plants under drought reducing lipid peroxidation in addition to producing more osmoprotectants The mechanisms by which plant growth-promoting rhizobacteria assist with plant drought stress resistance include solubilization of phosphorus, siderophore production, nitrogen fixation, and production of organic acids and plant growth enhancing substance.Plant growth regulators such as salicylic acid, cytokinins, and ABA are all reported to be involved in plant drought tolerance. They help increase water potential and chlorophyll contents
of plants under drought stress, which can all lead to crop yield increases.

Conclusion

The aim of this Article is to provide a critical and comprehensive examination of
studies related to the impact of climate extremes, such as drought, on crop
physiology, crop morphology, and crop yields. It will also investigate issues of
global food security and available genetic and agronomic tools in addressing
drought stress and the protection of crops under drought conditions. Furthermore,
this article is focused on adaptation strategies to mitigate the effects of drought and
to augment crop management for sustainable and climate-smart agriculture. This
assessment will provide a technical study of climate-smart agriculture, which may
assist farmers and growers to better understand crop needs under changing climate
conditions.

About the Author:

Muhammad Nazim, Assistant Agronomist in the office Director Agriculture (Extension) Disvision Bahawalpur.

Dr. Muqarrab Ali, Supervisor/ Assistant Professor Department of Agronomy, HOD, Department of AgroForestry, Muhammad Nawaz Sharif, University of Agriculture Multan.