Abstract
Heat and soil moisture stress account for serious abiotic constraint in black gram (Vigna mungo (L.) Hepper) production during spring–summer under Gangetic plains of Eastern India. Concurrence of these two can bring about early completion of phenophases that hampers normal metabolism of legumes by disrupting their defense mechanism, leading to poor seed set. The field experiment was conducted with two different sowing dates as the main plot, soil application of cobalt (Co) as subplots and foliar sprays of potassium (K) and boron (B) either alone or in combination as sub–sub plot treatment in a split–split plot design during spring–summer seasons of 2020 and 2021 with black gram (variety: Pant U 31). The study was aimed at evaluating the impact of sowing time and nutrients application alleviating adversities of abiotic stress during reproductive development of black gram. The March first week sown crop took significantly higher days to complete its life cycle compared to March third week sown one (82.0 vs. 78.2 and 81.8 vs. 78.8). This in turn relatively allowed a broader window for leaf area expansion, flowering, and seed filling in the first crop compared to the second one leading to the attainment of superior yield in the normal sown crop during the consecutive years. Crop growth rate (CGR), net assimilation rate (NAR), pod number per plant, seed yield, and harvest index were significantly higher (p ≤ 0.05) with soil Co @ 4 kg ha−1 and foliar 1.25% K + 0.2% B applications through stress mitigation by stimulating chlorophyll biosynthesis, nitrate reductase activity, proline accumulation, and cell membrane stability, irrespective of the years. Fluctuations in per plant pod number explained about 96 and 94% variations in seed yield through linear regressions in respective years. Optimum sowing date along with soil Co application combined with foliar K+B sprays manifested immense potential to achieve higher black gram production. In addition, this nutrient schedule proved to be efficient enough to promote satisfactory growth and optimum seed yield of late sown blackgram through relief of stress during the spring–summer season.
Highlights
The phenological behavior and yield formation of any crop have a strong correspondence with the prevailing weather conditions throughout its growing period irrespective of the region [1]
Heat stress coupled with moisture stress during the reproductive stage of the delayed sown black gram crop (March third week) compelled it to complete the phenophases to some extent earlier than the normal sown one (March first week)
Stress-induced reduction in yield owing to restricted photosynthetic activity and nitrogen assimilation were evident from reduced chlorophyll contents and nitrate reductase activity respectively
Summary
The phenological behavior and yield formation of any crop have a strong correspondence with the prevailing weather conditions throughout its growing period irrespective of the region [1] In this context, rising atmospheric temperature and water scarcity are some of the major constraints for developmental aspects of pulse crops in Eastern India [2]. The exposure to elevated air temperature well above the optimum during the window of February end to mid-June is extremely severe in terms of crop growth. This season invariably lags in soil moisture reserve due to continuous evapotranspiration accompanied by insufficient and erratic rainfall [4]. This in turn necessitates switching to more efficient and economical agronomic strategies in crop management, largely mitigating the climatic adversities through reduction of intercellular oxidative damage by triggering enzymatic and non-enzymatic antioxidant defence mechanism, induction of osmotic adjustment by accumulating osmotically active substances such as proline and sustaining the whole photosynthetic activity [10]
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