Reorient farming to build heat tolerance

VS Sohu and BS Dhillon

WHEAT is the second most important staple food of Indians, after rice. In Punjab, it is the most important rabi crop and a major contributor to the economy of the state and its farmers. The wheat crop is facing a major challenge due to early heatwaves. During the 2021-22 rabi season, extraordinary spikes in temperatures were witnessed. This coincided with grain development, when wheat is very sensitive to high temperatures. It adversely impacted ear length, grain number and grain boldness as well as forced advanced maturity by about 10 days. As a result, wheat yield dropped from 4,868 kg/ha (hectare) during 2020-21 to 4,216 kg/ha during 2021-22 in the state. Besides the grain produced had lower quality because of shrivelling and poor lustre. The national wheat yield dropped marginally from 3,521 kg/ha during 2020-21 to 3,484 kg/ha during 2021-22 due to erratic weather (high temperatures).

During the current rabi season, the unusual rise in temperature started even earlier. During February 5-11, 2023, the maximum and minimum weekly temperatures were 3°C above normal (recorded at PAU, Ludhiana); in the succeeding week, the maximum temperature was 3.3°C above normal (though the deviation of the minimum temperature was not as pronounced). On February 20, the maximum as well as minimum temperatures were markedly above normal (5.1°C or more) at many places in north India.

Anticipating adverse effects of an impending early heatwave on wheat yield and its consequences for food security, committees have been constituted at the national level to monitor the situation. The Punjab Government and PAU are also keeping a watch. PAU and other agricultural research institutions are issuing advisories for mitigating heat stress:

• Increase the frequency of light Irrigations: If the temperature rises above normal, frequent light irrigation should be applied up to March-end. However, care should be taken to avoid heavy irrigation as it results in stress due to flooding.
• Spray potassium nitrate or salicylic acid: Apply 2% KNO3 (4 kg potassium nitrate, 13:0:45, in 200 litres of water) or salicylic acid at the rate of 75 ppm (15 gm salicylic acid dissolved in 450 ml of ethyl alcohol using 200 litres of water) per acre at ear emergence and early milk stage in the evening hours.

For rabi 2023-24, the following points should be taken care of before the advent of the season:

• Heat-tolerant wheat varieties: The high temperatures during 2021-22 provided an opportunity to assess the performance of heat-tolerant varieties in the farmers’ fields across the state. The surveys revealed that PBW 766 (Sunehri) was the best, having higher yield with minimum reduction in yield under heat stress. Other varieties such as PBW 824, PBW 869, DBW 187 and PBW 677 also performed well. Further, in the all-India coordinated research trials conducted at the national level, PBW 826 ranked first for grain yield in the north-western plains zone (Punjab, Haryana, Delhi, and parts of Rajasthan, Uttar Pradesh, Jammu, Himachal Pradesh and Uttarakhand) during all three years of testing, including the heat stress season of 2021-22. Furthermore, the heat tolerance capability of PBW 826 was confirmed by its release in the north-eastern plains zone (eastern Uttar Pradesh, Bihar, Jharkhand, Odisha, West Bengal, Assam and plains of NE states) which is warmer than the western zone.
• Sowing date-dependent varietal choices: Appropriate wheat varieties are available for normal and late sowings. But there is a tendency to sow varieties suitable for normal sowing because of their higher yield potential, even under delayed sowing. These varieties have longer duration and when sown late, suffer more due to heat stress. Thus, varietal choice should be based on the sowing date.
• Long-duration rice varieties: The cultivation of long-duration rice varieties such as Pusa 44 and Pusa Dogar, besides causing ill effects (depletion of groundwater, pollution due to straw burning), delay wheat sowing, making wheat more vulnerable to heat stress. The cultivation of such varieties should be prohibited.
• Conservation agriculture: Sowing wheat using Happy Seeder in rice residue-retained fields provides a mulch on the soil surface. This mulch keeps soil and canopy temperatures mild during March-April and enables the crop to bear high temperature stress.

The wheat crop is exposed to temperature fluctuations during almost the entire season. Thus, the ability of the varieties of variable durations (for different sowing times) to withstand heat stress during all growth stages needs to be improved. The ICAR’s All-India Coordinated Wheat and Barley Improvement Project and agricultural universities in Punjab and other states are alive to this situation, but need more resources to strengthen these activities so as to face the emerging challenge of high temperatures.

To reap the full harvest of improved practices, the extension system must run campaigns to make farmers aware of the latest products and technologies and their relevance to different agro-ecologies, and also create awareness among the masses on the impending climate change chaos.

Sohu is HoD, Plant Breeding & Genetics, and Dhillon is former VC, PAU, Ludhiana

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