Agrometeorological indices of green gram (Vigna radiata L.) varieties under different growing environments in Chhattisgarh plain zone

Introduction

Green gram (Vigna radiata L.) is an important short-duration pulse crop grown under a range of agro-climatic conditions. Its growth and development are closely associated with temperature, sunshine duration and radiation. Changes in sowing time modify the weather conditions experienced by the crop during different phenological stages and consequently alter the accumulation and utilization of thermal and radiative resources. Agrometeorological indices provide a useful way to quantify the weather requirement of a crop. Growing degree days describe accumulated thermal time, while photo-thermal and helio-thermal units incorporate photoperiod and actual sunshine duration, respectively. Radiation use efficiency indicates the efficiency with which intercepted radiation is converted into biomass, whereas heat use efficiency expresses biomass produced per unit of accumulated thermal time. Thermal sensitivity index can further indicate the stability of crop duration under varying thermal environments. Earlier work on summer green gram has shown that sowing time and genotype can influence the accumulation of thermal indices. Tijare et al. (2017) [1] , for example, reported differences in GDD, HTU and PTU among sowing windows and varieties. Studies cited in the present thesis also indicate variation in HUE and RUE among genotypes and growing environments. The present study was therefore undertaken to quantify these indices for green gram varieties under three growing environments at Raipur. replications. The seed rate was 30 kg ha -1 and fertilizer was applied at 25:50:25 kg ha -1 of N:P 2 O 5 :K 2 O, respectively. The crop was planted at a row-to-row and plant-to-plant spacing of 30 × 10 cm. The plot size was 3.5 × 6 m (21 m 2 ).

Agrometeorological indices

Accumulated Growing Degree Days (AGDD) °C day

Growing degree days will be calculated by summation of daily mean temperature above base (T b -10℃) temperature for a corresponding period from sowing as suggested by Monteith (1984) and expressed in degree Celsius using the following formula.

Where, T max = Maximum temperature (℃) of the day. T min = Minimum temperature T b = Base temperature is defined as. "The temperature below which no plant physiological activity takes place'' which is considered 10℃ for green gram.

Accumulated Photo Thermal Unit (APTU) °C day hours

Accumulated photo thermal unit (APTU) is calculated by multiplying AGDD with maximum possible sunshine hours (N).

1. Heat Use Efficiency (HUE) g m -2 °C-1 day -1

Heat use efficiency which indicates the amount of dry matter produced per unit of growing degree days or thermal time.

𝐻𝑈𝐸 ( 𝑔𝑚 -2 / ∘ 𝐶 ) = Biomass (g /m 2 ) AGDD

Where, AGDD = Accumulated growing degree day HUE = Heat use efficiency The values were expressed in grams per square meter per degree Celsius day (g m -2 °C-1 day -1 ).

Thermal Sensitivity index:

𝐴𝐻𝑇𝑈 = 𝐴𝐺𝐷𝐷 × 𝑛

Where, n = actual sunshine hour The values were expressed in degree celsius day hours (°C day hours)

Radiation Use efficiency (RUE) g MJ -1

It is the relationship between the accumulation of biomass relative to the light intercepted by the crop.

𝑅𝑈𝐸 =

Biomass (g/m 2 ) IPAR (MJ/m 2 /day) Where, IPAR is cumulative intercepted photosynthetically active radiation. The photosynthetic active radiation is calculated by using the following formula. [2] .

𝑃𝐴𝑅 = 𝑅𝑠

TSI =

𝑅𝑎𝑛𝑔𝑒 𝑜𝑓 𝐷𝑢𝑎𝑡𝑖𝑜𝑛 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝐷𝑢𝑟𝑎𝑡𝑖𝑜𝑛

Based on TSI the thermal sensitivity index was categorized as follows: TSI Values: Thermal Sensitivity.

2. 5 to 10: Moderately Tolerant.

3. 10 to 15: Moderately susceptible.

4. > 15: Susceptible. [1] . [3] , who observed that sowing time had a significant effect on thermal indices and grain yield of mung bean. under D 1 , D 2 and D 3 , respectively. Thus, RUE increased with delay in sowing within the tested window. Among varieties, V 3 recorded the highest mean RUE (1.105 g MJ -1

Results and discussion

), followed by V 2 (1.013 g MJ -1

) and V 1 (0.928 g MJ -1 ). The maximum individual RUE (1.140 g MJ -1 ) was recorded in V 3 under D 3 , while the minimum (0.892 g MJ -1 ) was recorded in V 1 under D 1 . The higher RUE of V 3 indicates comparatively efficient conversion of available intercepted radiation into biomass under the tested environments. (2020) [4] , who reported differences in radiation use efficiency among mung bean genotypes, and with Kaushik et al. (2015) [5] , who observed variation in RUE among varieties under different growing environments.

Heat Use Efficiency (HUE)

HUE showed a progressive increase from D 1 to D 3 . Mean HUE was 0.464 g m -2 °C-1 day -1 under D 1 , 0.493 under D 2 and 0.541 under D 3 . Among varieties, V 3 recorded the highest mean HUE (0.544 g m -2 °C-1 day -1 ), followed by V 2 (0.499) and V 1 (0.456). The maximum HUE (0.571 g m -2 °C-1 day -1 ) occurred in V 3 under D 3 , whereas the minimum (0.435) occurred in V 1 under D 1 . Higher HUE indicates greater biomass production per unit of accumulated thermal time under the corresponding environment. [6] reported a positive association between HUE and seed yield in green gram. Kumar et al. (2016) [7] also identified HUE as an important index for evaluating terminal heat tolerance.

Thermal Sensitivity Index (TSI) TSI varied from 5.04 to 6.89% among the varieties. V 2 recorded the highest TSI (6.89%), followed by V 1 (6.77%), whereas V 3 recorded the lowest TSI (5.04%). According to the classification used in the study, all three varieties fell in the 5-10% range and were therefore categorized as moderately tolerant. The lower TSI of V 3 indicates comparatively lower variation in crop duration across the tested thermal environments.

Overall discussion

Across the six indices considered, D 3 (21 st March 2026) generally recorded the highest accumulated thermal indices and the highest mean RUE and HUE. V 3 (PDM-139 Samrat) consistently recorded the highest AGDD, APTU and AHTU at physiological maturity and also the highest mean RUE and HUE. These results show that both growing environment and varieties influenced the way the crop accumulated and utilized temperature, sunshine and radiation. The response also demonstrates why agrometeorological indices are useful for comparing crop performance under different growing environments.

Conclusion

The study showed Among the different sowing dates in agrometeorological indices of green gram varieties under different growing environments at Raipur. Accumulated GDD, PTU and HTU increased with crop development, and the highest values at physiological maturity were recorded in PDM-139 Samrat under D 3 (21 st March 2026). Mean RUE and HUE were also highest under D 3 , while PDM-139 Samrat recorded the highest varietal means for both efficiencies. Thermal Sensitivity Index ranged from 5.04 to 6.89%, with all varieties classified as moderately tolerant; PDM-139 Samrat showed the lowest TSI and therefore comparatively greater stability in crop duration. Within the environments and varieties evaluated in this experiment, D 3 (21 st March 2026) and PDM-139 Samrat showed the most favourable response for accumulation and utilization of agro-meteorological resources.

References

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