Effect of growing environments on agrometeorological indices, heat and radiation use efficiency and yield of rice (Oryza sativa L.) in Raipur District of Chhattisgarh

Introduction

Rice (Oryza sativa L.) is the most important staple food crop of India and plays a vital role in ensuring food security, particularly in Chhattisgarh, popularly known as the "Rice Bowl of India". Climate variability in the form of altered temperature regimes and changing radiation environment significantly affects crop growth duration, phenology and yield. Agrometeorological indices such as growing degree days (GDD), photo-thermal units (PTU) and helio-thermal units (HTU) are widely used to quantify crop-weather relationships. Heat use efficiency (HUE) and radiation use efficiency (RUE) indicate the efficiency of crops in converting thermal and radiant energy into economic yield. Understanding these indices under different growing environments is essential for developing climate-resilient rice production strategies. Climate change models are predicting in general an increase in temperature, variations in precipitation and radiation levels which are likely to influence the crop production. Several studies with crop growth models have predicted cultivation in mean crop yields as a result of the changing crop environment (Rao et al. 2008) [12] . Agriculture will be adversely affected by an increase or decrease in amount of rainfall and shifting of time of rainfall. Ramakrishna et al. (2002) [11] indicated that a temperature increase of 2°C was estimated in Rajasthan to decrease pearl millet production by 10-15%. The rise in mean air temperature over the past 100 years (1850-1899 to 2001-2005) was 0.76°C which will impact the agriculture production.

To evaluate the effects of climate change, different crop models and scenario have been developed and used across the world. The Decision Support System for Agro Technology Transfer (DSSAT) has been found to be most widely used decision support system which included models for cereals, legumes, oilseeds and vegetable crops (Hoogenboom, 2000). DSSAT (Decision Support System for Agro Technology Transfer) is major product of IBSNAT (International Benchmark Sites Network for Agro Technology Transfer).

Methodology

The experiment was conducted during Kharif 2024-25 at the Research and Instructional Farm, IGKV, Raipur (21.16°N latitude, 81.36°E longitude). The experiment was laid out in a factorial randomized block design with three replications. Treatments consisted of three dates of transplanting: D 1 (1st July), D 2 (15th July) and D 3 (30th July), and three rice varieties: MTU-1010, Mahamaya and Vikram TCR. Recommended agronomic practices were followed throughout the crop season. Daily meteorological data were recorded from the agrometeorological observatory located near the experimental site. GDD, PTU and HTU were computed for different phenological stages. Heat use efficiency and radiation use efficiency were calculated using dry matter accumulation and intercepted radiation

Accumulated Growing Degree Days (GDD)

Where, Tx = Daily maximum temperature Tn = Daily minimum temperature The base temperature which is considered 10 ⁰C for Kharif crops

Accumulated Photothermal Unit (PTU)

PTU is calculated by multiplying GDD with maximum possible sunshine hours (N) PTU= GDD X N Where, N =maximum possible sunshine hours.

Accumulated Helio Thermal Unit (HTU)

HTU is calculated by multiplying GDD with actual sunshine hours (n).

HTU = GDD X n

Where, n = actual sunshine hour.

Heat Use Efficiency (HUE)

Heat use efficiency (HUE) for total dry matter was obtained as under Biomass (g/m Mean HUE values ranged from 0.79 to 0.84 g/m 2 /° day across growing environments with the highest mean HUE recorded under D 3 (0.84 g/m 2 /° day). Among varieties, Mahamaya variety recorded the highest mean HUE (0.83 g/m 2 /° day), followed by MTU-1010 (0.82 g/m 2 /°day) and Vikram TCR (0.78 g/m 2 /° day). The maximum HUE (0.87 g/m 2 /° day) was observed in Mahamaya under D 3 . Radiation use efficiency varied from 2.07 to 2.34 gMJ -1 day -1 . The highest mean RUE (2.25 gMJ -1 day -1 ) was recorded under D 3 followed by D 1 (2.16 gMJ -1 day -1 ) and D 2 (2.14 gMJ -1 day -1 ). MTU-1010 variety recorded the maximum RUE of 2.34 gMJ - 1 day -1 under D 1 indicating superior radiation conversion efficiency. e. Grain Yield Grain yield was significantly affected by transplanting dates and varieties. Mean grain yield was highest under D 3 (3962 kg ha⁻¹), followed by D 2 (3548 kg ha⁻¹) and D 1 (3162 kg ha⁻¹). Among varieties, Mahamaya variety recorded the highest mean grain yield (3741 kg ha⁻¹) followed by MTU-1010 (3563 kg ha⁻¹) and Vikram TCR (3468 kg ha⁻¹). Higher yield under early transplanting was attributed to favourable thermal and radiation conditions during critical growth stages.

Conclusion

The study revealed that agrometeorological indices, heat use efficiency, radiation use efficiency and yield of rice were strongly influenced by growing environments and varietal differences. Early transplanting (1st July) resulted in higher accumulation of GDD, PTU and HTUs and produced significantly higher grain yield. Delayed transplanting improved HUE and RUE but reduced overall yield. Among varieties, MTU-1010 performed best in terms of grain yield, while Mahamaya variety showed higher heat and radiation use efficiency. Timely transplanting and appropriate varietal selection can therefore serve as effective adaptation strategies to mitigate the impact of climate variability on rice production in the Raipur district.

References

1. Accumulated PTU required for physiological maturity ranged from 24710 to 25800 °C Day hours in MTU-1010, 26933 to 28701 °C Day hours in Mahamaya and 25216 to 27732 °C Day hours in Vikram TCR. The highest PTU accumulation was observed under D 1 (1st July transplanting) in all varieties indicating better utilization of temperature and day length during crop growth. Table 2: Accumulated Photo Thermal Units (PTU) at different growing stages of different rice varieties under different growing environments Phenological stage MTU-1010 Mahamaya Vikram TCR 2024-25 D1 D2 D3 D1 D2 D3 D1 D2 D3 Tillering 9378 8446 8352 9859 8898 8827 9462 8234 8219 Panicle initiation 14520 12891 12445 15399 14088 13403 14803 14087 12851
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