A field experiment was conducted during the rainy (kharif) season in Indian in 2006 to study the effects of foliar applications of different concentrations of seaweed extract (prepared from Kappaphycus alvarezii) on nutrient uptake, growth and yield of soybean [Glycine max (L.) Merr.] grown under rainfed conditions without the application of chemical fertilizers. The foliar spray was applied twice at seven concentrations (0; 2.5; 5; 7.5; 10; 12.5 and 15% v/v) of seaweed extract. Foliar applications of seaweed extract significantly enhanced yield parameters. The highest grain yield was recorded with applications of 15% seaweed extract, followed by 12.5% seaweed extract that resulted in 57% and 46% increases respectively compared to the control. The maximum straw yield was also achieved with 15% seaweed extract application. Improved nutrient uptake (N, P, K and S) was also observed with seaweed extract applications. Thus, under rainfed soybean production, foliar applications of seaweed extracts could be a promising option for yield enhancement

Microalgae accumulate a considerable amount of lipids and carbohydrate under nutrient-deficient conditions, which makes them one of the promising sustainable resources for biofuel production. In the present study, to obtain the biomass with higher lipid and carbohydrate contents, we implemented a short-term nitrogen starvation of 1, 2, and 3 days in a green microalga Acutodesmus dimorphus. Few recent reports suggest that oxidative stress-tolerant microalgae are highly efficient for biofuel production. To study the role of oxidative stress due to nitrogen deficiency, responses of various stress biomarkers like reactive oxygen species (ROS), cellular enzymatic antioxidants superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and non-enzymatic scavengers proline and polyphenols were also evaluated. Further, the endogenous levels of phytohormones abscisic acid (ABA) and indole-3-acetic acid (IAA) were also determined to study their response to nitrogen deficiency. We observed that nitrogen starvation of 2 days is effective to produce biomass containing 29.92% of lipid (comprising about 75% of neutral lipid) and 34.80% of carbohydrate, which is significantly higher (about 23 and 64%, respectively) than that of the control culture. Among all nitrogen-starved cultures, the accumulations of ROS were lower in 2 days starved culture, which can be linked with the several folds higher activities of SOD and CAT in this culture. The accumulations of proline and total polyphenols were also significantly higher (about 4.7- and 1.7-folds, respectively, than that of the control) in 2 days nitrogen-starved culture. The levels of phytohormones once decreased significantly after 1 day, increased continuously up to 3 days of nitrogen starvation. The findings of the present study highlight the interaction of nitrogen starvation-induced oxidative stress with the signaling involved in the growth and development of microalga. The study presents a comprehensive picture of the adaptive mechanisms of the cells from a physiological perspective along with providing the strategy to improve the biofuel potential of A. dimorphus through a short-term nitrogen starvation.