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Kappaphycusalvarezii seaweed extract (KSWE), an effective plant biostimulant, was investigated along with its active constituents, namely, glycine betaine (GB), choline chloride (Ch), and zeatin for their role in the alleviation of soil moisture stress subjected at different stages of maize crop at V5, V10, and V15 (i.e. fifth, tenth, and fifteenth leaf with fully emerged leaf collar). This study was undertaken to identify the constituents of KSWE responsible for stress alleviation under soil moisture deficit conditions. Stress was applied by withholding irrigation for 7 days at the three different growth stages of maize. Growth, yield, and antioxidant enzymes were analysed in response to four foliar treatments (viz., T1: water spray, T2: 10% equivalent concentration of zeatin as present in KSWE (Eq-cytokinin), T3: 10% KSWE, and T4: 10% equivalent concentration of GBCh as present in KSWE (Eq-GBCh). Higher yield response over control was obtained by application of Eq-GBCh or Eq-cytokinin when soil moisture stress was applied once at any of the three stages. Yield improvement was obtained only by KSWE or Eq-GBCh when plants were subjected to stress at all three stages. Application of KSWE at V5, V10, V15, and V5 + V10 + V15 stages recorded 20, 9, 18, and 32% higher grain yield over their respective controls, indicating the importance of its application at V5 and V15 stages under drought. Levels of antioxidant enzymes were also elevated under drought by KSWE when compared to its control suggesting that the stress tolerance imparting mechanism of KSWE was through the involvement of antioxidant machinery. It can be concluded from the study that cytokinin increased seed yield under moderate stress conditions, while KSWE was effective even under multiple stress.

Kappaphycus alvarezii seaweed extract (KSWE) is known to enhance crop productivity and impart stress tolerance. Close to one quarter of foliar spray applied to maize falls on the soil, either as drift or from leaf as drip. It was hypothesized that the drift spray would profoundly influence soil microbes under stress. An experiment was conducted with five treatments, with or without KSWE application at critical stages of maize grown under soil moisture stress and compared with an irrigated control. An Illumina platform was employed for the analysis of the V3–V4 region of 16S rRNA gene from the soil metagenome. A total of 345,552 operational taxonomic units were generated which were classified into 55 phyla, 152 classes, 240 orders, 305 families and 593 genera. Shannon’s index and Shannon’s equitability indicated increased soil bacterial diversity after multiple KSWE applications under conditions of abiotic duress. The abundance of the genera Alicyclobacillus, Anaerolinea, Bacillus, Balneimonas, Nitrospira, Rubrobacter and Steroidobacter decreased (49–79%) under drought imposed at the V5,10 and 15 stages of maize over the irrigated control, while it significantly improved when followed by KSWE application under drought. Flavobacterium, Nitrosomonas, Nitrosovibrio, Rubrobacter genera and several other bacterial taxa which are important for plant growth promotion and nutrient cycling were found to be enriched by KSWE application under drought conditions. Treatments having enriched microbial abundance due to KSWE application under stress recorded higher soil enzymatic activities and plant cob yield, suggesting the contribution of altered soil ecology mediated by KSWE as one of the reasons for improvement of yield.

Many countries import potassic fertilizers due to dearth of K-mineral deposits. Therefore processes to obtain K-nutrient sources from sea bittern were developed by our Institute. The present investigation evaluated the fertilizer potential of three different sea bittern-derived (SBD) potassium forms developed viz., potassium schoenite, potassium nitrate and potassium ammonium sulfate on maize productivity in two cropping seasons. The pot and field experiments consisted of four treatments, wherein the three K forms were applied at the recommended rate of 40 kg K O ha and were compared with commercially used sulfate of potash. The effect of these fertilizers on different parameters of plant and soil were evaluated. The application of SBD-potassic fertilizers led to enhancement in growth, productivity and quality of maize which related well with higher photosynthesis, nutrient uptake and soil quality parameters. On an average all the three forms of sea bittern-derived potash enhanced yield of maize over control by 22.3 and 23.8%, respectively, in pot and field trials. The best performance was under SBD-KNO , which also recorded the highest benefit: cost ratio of 1.76. The K-fertilizers derived from sea-bittern-a waste product of salt industry-can thus be economically used to improve crop production sustainably.

Kappaphycus seaweed extract (KSWE) has been reported to enhance the yield of several crops under normal conditions. The detection of the quaternary ammonium compounds (QACs) glycine betaine and choline chloride (GBCh) in KSWE impelled us to explore its efficacy on growth and yield under soil moisture deficit conditions. Another objective was to elucidate the extent to which the QACs have a role in mitigating drought stress, if at all. Thus, a factorial experiment was carried out on maize plants, wherein five foliar treatments (KSWE at 10 and 15%; GBCh at equivalent concentration to that found in 10 and 15% KSWE, respectively, designated as 10 and 15% Eq-GBCh; and water spray control) were subjected to three soil moisture stress levels (well-watered, WW; moderately stressed, MS; and severely stressed, SS). Observations were recorded for growth and yield parameters, pigments, photosynthetic attributes, antioxidant enzymes, and quality of grains. The results revealed the ability of KSWE to alleviate soil moisture stress, 10% KSWE being effective in increasing the seed yield under WW and MS conditions while 15% being optimal under SS condition. The percent increases in seed yield over their respective controls under WW, MS, and SS conditions at the optimal KSWE concentrations were 13.5, 21.7, and 36.4%, respectively, indicating higher grain yield response to KSWE treatments at higher stress levels. The yield advantage under stress could be attributed to minimal damage of photosystem in KSWE-treated plants as evidenced by higher pigment content, photosynthetic rate, reduced photoinhibition, and lipid peroxidation by enhanced protection against reactive oxygen species. The protein content in grains was enhanced by KSWE application under all stress groups compared to their respective controls. Although the predominant role of GBCh in KSWE towards drought mitigation and yield response was apparent, the results also connoted towards the role of other constituents in KSWE acting in unison along with GBCh, which should be investigated further.

High volumes of lipid extracted microalgal biomass residues (LMBRs) are expected to be produced upon commencement of biodiesel production on a large scale, thus necessitating its value addition for sustainable development. LMBRs of Chlorella variabilis and Lyngbya majuscula were employed to substitute the nitrogen content of recommended rate of fertilizer (RRF) for Zea mays L. The pot experiment comprised of 10 treatments, i.e., T1 (No fertilizer); T2 (RRF-120 N: 60 P2O5: 40 K2O kg ha(-1)); T3 to T6-100, 75, 50, and 25% N through LMBR of the Chlorella sp., respectively; T7 to T10-100, 75, 50, and 25% N through LMBR of Lyngbya sp., respectively. It was found that all LMBR substitution treatments were at par to RRF with respect to grain yield production. T10 gave the highest grain yield (65.16 g plant(-1)), which was closely followed by that (63.48 g plant(-1)) under T5. T10 also recorded the highest phosphorus and potassium contents in grains. T4 was markedly superior over control in terms of dry matter accumulation (DMA) as well as carbohydrate content, which was ascribed to higher pigment content and photosynthetic activity in leaves. Even though considerably lower DMA was obtained in Lyngbya treatments, which might have been due to the presence of some toxic factors, no reduction in grain yield was apparent. The length of the tassel was significantly higher in either of the LMBRs at any substitution rates over RRF, except T6 and T7. The ascorbate peroxidase activity decreased with decreasing dose of Chlorella LMBR, while all the Lyngbya LMBR treatments recorded lower activity, which were at par with each other. Among the Chlorella treatments, only T5 recorded significantly higher values of glutathione reductase activity over RRF, while the rest were at par. There were significant increases in carbohydrate and crude fat, respectively, only in T4 and T3 over RRF, while no change was observed in crude protein due to LMBR treatments. Apparently, there was no detrimental effect on soil properties, suggesting that both the LMBRs can be employed to reduce the usage of chemical fertilizers, thus promoting maize crop production in a sustainable manner.

Burgeoning population demands increased agricultural production; however, the climate change impact being currently experienced necessitates sustainable crop intensification. In this context, Kappaphycus alvarezii seaweed extract has potential to increase the crop productivity in an environmentally friendly way. Since K. alvarezii or rather any seaweed extract contains several beneficial constituents, we hypothesized that not all the stages of crop would respond identically upon its application. A literature survey indicated that there was no concrete rationale behind the frequency and application time of seaweed extract as it arbitrarily varied across the studies. Therefore, a field experiment was designed to evaluate the effect of seaweed extract at select crop growth stages of maize. The application time included ten different combinations chosen among V3, V5, V10, V15, and grain filling stages. The results corroborated our hypothesis, and it was demonstrated that application of a Kappaphycus seaweed-based bio-stimulant at the V10 stage was not effective in significantly influencing productivity. However, in contrast, when applied earlier at V5 or later at the V15 stage, a yield improvement of 13.7 and 11.1% was recorded over their respective controls. We also showed that application of the extract at V5 along with V15 elicited the best yield response (32%) and no further significant gains accrued with higher number of applications. In addition, there was a decline in the benefit-to-cost ratio from 1.7 recorded at V5 + V15 to less than or equal to 1 in other treatments. Consecutive application at V5 and V15 stages also showed a net 20% diminution in the climate change impact category compared to control, and this treatment resulted in savings of 35.7 kg CO 2 -equivalents per tonne of maize grain production compared to that where one application was done at the V10 stage only. Thus, the experimental result highlights the pre-eminence of the crop application stage at which seaweed bio-stimulants can influence yield and profitability and also minimize environmental impacts. However, further trials are needed to validate the findings of this study.