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A field investigation was made at the Tamil Nadu Agricultural University farm in Coimbatore during the late Kharif 2019 and late Rabi 2019-20 seasons to quantify the impact of induced moisture stress (MS) at critical stages (10, 15, 20, & 25 days from panicle initiation and flowering) on physiological traits and yield of rice. The experiment was laid-out in randomized complete block design (RCBD) with three replications. During both seasons, physiological traits (photosynthetic rate, stomatal conductance, transpiration rate and chlorophyll index) were recorded after the MS period (10, 15, 20 and 25 days) at both critical stages. The experimental results revealed that MS of any period and any stage (panicle initiation and flowering) reduced the values of all physiological traits, grain and straw yields in both seasons. The MS period of 25 days from panicle initiation significantly reduced all physiological parameters, including rice yield.

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Rice (Oryza sativa L.) grain yield is reduced by drought stress during reproductive stages. In this work, the effects of foliar selenium (Se) spray on the reduction of drought stress are measured and the most critical stage of rice is identified. Three field experiments were carried out. In experiments I and II, the sensitive stage was determined by imposing drought stress at the panicle initiation and flowering stages by withholding irrigation for 10, 15, 20, and 25 days. In experiment III, drought stress was induced by depriving plants of moisture for 20 or 25 days. Se spray was then applied at rates of 0, 10, and 20 mg L−1 to alleviate the drought, and its effects were evaluated. Overall, it was reported that the panicle initiation stage was more vulnerable to drought stress than the flowering stage, as evidenced by a larger reduction in grain yield. Employing Se as a foliar spray at a rate of 20 mg L−1 under drought stress enhanced the number of filled grains m−2, the total number of grains m−2, and grain yield ha−1 by 22.0, 4.3, and 11.0%, respectively, over water spray. This shows a positive interaction or synergistic interaction between drought tolerance and selenium application. These results demonstrate that foliage supplementation of Se at a dosage of 20 mg L−1 alleviate the adverse effects of drought stress at the panicle initiation stage in rice cultivation. Se mitigated the negative effects of drought by improving the membrane stability index, relative water content, and proline content.

A field study was conducted to quantify the effect of moisture stress on nutrient uptake and post-harvest available soil nutrient status of rice in Tamil Nadu Agricultural University, Coimbatore during Kuruvai (July-November) 2019 and Navarai (December-March) 2019-20 seasons. Nine treatments, viz., Moisture stress at panicle initiation stage for 10 days (T 1 ), 15 days (T 2 ), 20 days (T 3 ) and 25 days (T 4 ), moisture stress at flowering stage for 10 days (T 5 ), 15 days (T 6 ), 20 days (T 7 ) and 25 days (T 8 ) along with control -maintaining saturation (T 9 ) were tested under randomized complete block design with three replications. Moisture stress was imposed by withdrawing water and not irrigating in the defined period. The result showed that significantly higher total drymatter production and N, P and K nutrient uptake (grain, straw and total) during both the seasons were observed in T 9 treatment than all other moisture stress imposed treatments. The least uptake of N, P and K in grain, straw and total was recorded in T 4 and was statistically at par with T 3 . There was reverse trend on post-harvest soil nutrient status (NPK). The study revealed that moisture stress was more sensitive during panicle initiation stage than flowering stage, which directly influenced the uptake of nutrients in rice and there was a reverse trend on post-harvest soil available nutrients (NPK).