Vegetation regeneration on natural terrain landslides in Hong Kong: direct seeding of native species as a restoration tool

Landslides are common in tropical and subtropical regions with hilly terrains and heavy rainstorms, which cause significant economic, ecological, and social impacts. Natural forest succession is usually slow on landslide scars due to poor soil structure and the lack of seeds of woody plant seeds, and often comes with a higher risk of repeated landslide. Ecological forest restoration has recently been suggested as an effective alternative to restore the exposed landslide scars, however, a comprehensive study to identify effective landslide restoration strategies remains lacking, particularly associated with seed treatment methods and species selection. Here we evaluated the effectiveness of different seed coating treatments of both pioneer and later successional tree species of different seed sizes on seed germination in a one-year study on three landslides in Hong Kong. Our results show that bare seeds had germination rates of 17 to 67% across all selected species (n=7). Biochar-dominant seed coating formulation boosted an additional 9.33 (SE= 0.04) in seed germination rate, while the clay-dominant seed coating formulation did not show significant effect on germination. Our results also show that medium and large-seeded non-pioneer species have significantly higher germination rates than pioneer species. These results collectively suggest that direct seeding using a biochar seed coat is a manageable and useful method to enhance tree seed germination—an essential first step to restore the forests after landslide disturbances in Hong Kong, with potential to be extended to other humid tropical and subtropical forests.

Response of Rice (Oryza sativa L.) Cultivars to Variable Rate of Nitrogen under Wet Direct Seeding in Temperate Ecology

Transplanting rice appears to pose many problems, including depletion of freshwater reservoirs and competition for labor. Conversely, direct seeding allows us to overcome shortcomings associated with conventional transplanting. Nitrogen is a crucial nutrient needed for plant growth and yield. Therefore, this study was executed to analyze the influence of nitrogen on the performance of rice genotypes grown by direct seeding in wet soil. The experiment comprised various rice cultivars, i.e., Shalimar Rice-1, Shalimar Rice-3, Shalimar Rice-4, and Jhelum, and nitrogen (N) levels, i.e., 0, 90, 120, and 150 kg/ha. Shalimar Rice-4 produced a maximum grain yield (6.39 t/ha), followed by Shalimar Rice-3 and Jhelum). The application of 150 kg N/ha showed maximum values for growth parameters, yield attributing traits, and grain yield (6.68 t/ha); however, it remained at par with 120 kg N/ha. Crop water productivity was highest in Shalimar Rice-4 (0.49 kg/m3), and the same showed a consistent increase with increasing N levels from 0–150 kg/ha, with a comparable value of 0.49 to 0.51 recorded at 120 and 150 kg N/ha. Moreover, the Shalimar Rice-1 variety required the maximum in growing degree days (GDD) and helio-thermal units (HTU) to attain different phenological stages till physiological maturity (131 days). However, the cultivar Shalimar rice-4 (SR-4) performed better by registering significantly higher heat use efficiency (HUE) (4.44 kg/ha °C/day). Additionally, the highest net return and the benefit-cost ratio were registered by Shalimar Rice-4. B:C ratio of 1.75 was realized from application of 150 kg N/ha, which remained very close to that achieved with 120 kg N/ha. In conclusion, the rice cultivar Shalimar Rice-4 with the application of 120 kg N/ha could boost rice production under DSR in water-scarce regions of temperate northern India.

Evaluation of rice genotypes on seed attributes and agronomic performance for developing direct-seeded cultivar

<abstract> <p>Direct seeding of rice (DSR) may give benefit in using water and labor more efficient and reduce production costs. This study purposes to investigate the character of the seeds, their early vigor traits, the growth and development of rice plants for developing DSR cultivar. The research was conducted in four stages: the measurement of the size of the seed, endosperm, and embryo; the germination test in the laboratory; seedling test using experimental pots; and testing the agronomic performance on transplanting and direct seeding methods in a plastic house. Seed material used eight breeding lines of IPB University and two released varieties. The results of study showed that each genotype had different characteristics of seed, endosperm, and embryo in both weight and area. Seed weight becomes the most dominant in the emergence of superior EV traits, whereas the more seed weight indicates faster radicle emergence and more weight of seedling. DSR method compared to transplanting showed performance such as taller plant, higher leaf area and photosynthesis rate at early growth stage, earlier heading time, and higher plant dry weight since early growth until 65 days old. The seed characters have positively correlation to dry weight of seedlings, number of leaves, leaf area, and canopy dry weight. We also found that higher area of endosperm and embryo significantly correlated to have faster plumule emergence, higher leaf area and plant height. Candidate genotypes for DSR would be further investigated in the field trial agronomically.</p> </abstract>

Effect of Nutrient Management and Rice Establishment Methods on Groundnut (Arachis hypogaea L.) in Rice–Groundnut Cropping System

The field experiments were conducted at Agronomy Main Research Farm, Odisha University of Agriculture and Technology, Bhubaneswar, Odisha, India during rabi (November–March) seasons of 2019–2020 and 2020–2021 to evaluate direct and residual effect of nutrient management and rice establishment methods on phenology, growing degree days, growth, yield and economics of groundnut in rice–groundnut cropping system. The experiments were laid out in split-plot design with three replications. Carryover effect of direct seeding rice favourably influenced the succeeding groundnut crop as compared to that grown after transplanting which had superior growth parameters resulting in 25.7% higher pod yield, oil yield (1.24 t ha-1), gross return (` 136612.7 ha-1) and net return (` 63965.0 ha-1). Residual effect of organic management to preceding rice significantly increased growth, yield attributes, growing degree days at physiological maturity and net return, resulted in highest pod yield of 2.48 t ha-1 in groundnut which was at par with that grown after INM in rice, but was on an average, 17.0% higher than inorganic practice in rice. INM to groundnut increased yield parameters and economics of the crop resulting in 19.7 and 39.3% higher pod yields than 100% and 75% soil test based fertiliser, respectively. Hence, INM under direct seeding to kharif rice benefits the succeeding groundnut crop and direct application of 75% STBN (inorganic)+25% STBN (FYM)+0.2 LR+biofertilisers to groundnut proved beneficial for improving phenology, growing degree days, growth, yield and economics of groundnut in rice–groundnut cropping system.

Direct and Residual Effect of Nutrient Management and Rice Establishment Methods on Productivity, Profitability, Nutrient Uptake and Resource Use Efficiency in Rice (Oryza sativa L.)-Groundnut (Arachis hypogaea L.) Cropping System

Background: Rice and rice based cropping systems are of prime importance in global food production but continuous rice mono cropping and excessive dependence on chemical fertilisers degrade the soil quality, which can be partly solved by changing into rice-legume system. Methods: The field experiment was conducted during kharif and rabi of 2019-2020 and 2020-2021 at Odisha University of Agriculture and Technology, Bhubaneswar to evaluate direct and residual effect of nutrient management and rice establishment methods on productivity, profitability, nutrient uptake and resource use efficiency in rice-groundnut system. Result: Transplanted rice increased the yield attributes of rice in both the years resulting in 6.0-8.1% higher grain yield than direct seeding. Integrated nutrient management (INM) significantly improved the growth and yield of rice as compared to sole organic and inorganic. Carryover effect of direct seeding increased growth and yield of succeeding groundnut. Residual effect of organic in preceding rice increased pod yield of groundnut. INM to groundnut increased yield parameters of the crop resulting in 19.7-20.2 and 38.9-40.0% higher pod yields than 100% and 75% soil test based fertiliser, respectively in both the years. Direct seeding of rice with INM practice in both the crops performed superior in rice-groundnut cropping system.

Genome-Wide Association Study (GWAS) of Mesocotyl Length for Direct Seeding in Rice

Direct seeding is considered an efficient cultivation technology that reduces water use and labor costs. Mesocotyl length is one of the significant traits in cultivation; long mesocotyl is beneficial for the rate and uniformity of seedling emergence. In this study, we used a core collection of 137 rice accessions to identify quantitative trait loci (QTL) for mesocotyl elongation. A genome-wide association study (GWAS), combined with a principal component analysis (PCA) and a kinship matrix analysis, was conducted for the genotype analysis of 2 million, high-quality single nucleotide polymorphisms (SNPs). Through this GWAS analysis, 11 lead SNPs were confirmed to be associated with mesocotyl length, and a linkage disequilibrium (LD) decay analysis identified the 230 kb exploratory range for the detection of QTLs and candidate genes. Based on the gene expression database and haplotype analysis, five candidate genes (Os01g0269800, Os01g0731100, Os08g0136700, Os08g0137800, and Os08g0137900) were detected to be significantly associated with phenotypic variation. Five candidate gene expressions are reported to be associated with various plant hormone responses. Interestingly, two biotic stress response genes and two copper-containing redox proteins were detected as the candidate genes. The results of this study provide associated SNPs in candidate genes for mesocotyl length and strategies for developing direct seeding in breeding programs.

Increased Number of Spikelets per Panicle Is the Main Factor in Higher Yield of Transplanted vs. Direct-Seeded Rice

With increasing water shortages and labor costs, rice planting is gradually undergoing a transformation from traditional transplanting to direct seeding. However, the yield of direct-seeded rice is unstable and the reasons for this instability are disputed. Therefore, we established a field experiment conducted over 3 years to investigate the reasons for the difference in rice yield under different planting methods. The planting methods compared were transplanting (TR), broadcast sowing (BS), and sowing in line (SL). The yield of rice under TR was higher (10,390 kg ha−1) than that of BS (7790.7 kg ha−1) and SL (9105.2 kg ha−1). Given that the harvest index showed little variation among the three planting methods, the yield differences reflected that shoot dry matter production under TR was higher. Two reasons for the latter observation are suggested: (1) the planting density under TR was lower than that under BS and SL, thus competition for nutrient resources would have been reduced; (2) the growth period of TR was longer. The higher shoot dry matter accumulation under TR contributed to enhanced panicle number per m2 and number of spikelets per panicle than under BS. A significant correlation between number of spikelets per panicle and yield was observed. Although yield was highest under TR, the costs under TR were the highest among the three planting methods. In contrast, the benefit-to-cost ratio under SL was higher than that of TR and BS. The higher yield under TR reflected the production of larger spikelets per panicle than those produced under direct-seeding methods. However, the benefits of SL are conducive to enhanced profitability of rice production.