Increasing the appropriate seedling density for higher yield in dry direct-seeded rice sown by a multifunctional seeder after wheatstraw return

Dry direct-seeded rice(DDR) sown using a multifunctional seeder that performs synchronous rotary tillage and sowing has received increased attention because it is highly efficient,relatively cheap,and environmentally friendly.However,this method of rice production may produce lower yields in a rice–wheat rotation system because of its poor seedling establishment.To address this problem,we performed field experiments to determine the rice yield at five seedling density levels(B1,B2,B3,B4,and B5=100,190,280,370,and 460 seedlings m-2,respectively) and clarify the physiological basis of yield formation.We selected a representative high-quality rice variety and a multifunctional seeder that used in a typical rice–wheat rotation area in 2016 and 2018.The proportion of main stem panicle increased with increasing seedling density.There was a parabolic relationship between yield and seedling density,and the maximum yield(9.34-9.47 t ha-1) was obtained under B3.The maximum yield was associated with a higher total spikelet number m-2 and greater biomass accumulation from heading to maturity.The higher total spikelet number m-2 under B3 was attributed to an increase in panicle number m-2 compared with B1 and B2.Although the panicle numbers also increased under B4 and B5,these increases were insufficient to compensate for the reduced spikelet numbers per panicle.Lower biomass,smaller leaf area,and lower N uptake per plant from the stem elongation stage to the heading stage were partially responsible for the smaller panicle size at higher seedling density levels such as B5.The higher biomass accumulation under B3 was ascribed to the increases in the photosynthetic rate of the top three leaves m-2 of land,crop growth rate,net assimilation rate,and leaf area index.Furthermore,the B3 rice population was marked by a higher grain–leaf ratio,as well as a lower export ratio and transport ratio of biomass per stem-sheath.A quadratic function predicted that 260-290 seedlings m-2 is the optimum seedling density for achieving maximum yield.Together,these results suggested that appropriately increasing the seedling density,and thereby increasing the proportion of panicles formed by the main stem,is an effective approach for obtaining a higher yield in DDR sown using a multifunctional seeder in a rice–wheat rotation system.

Study on the Relationship of Seedling Density and Line Spacing to Leaf-stem Ratio, DW/FW Ratio and Grass Yield of Forage Sweet Sorghum

[ Objectives ] The aim was to optimize the configuration of seedling density and line spacing of forage sweet sorghum （ Sorghum blcolor （ L. ） Moench） and explore its high-yield cultivation techniques. [ Methods] Effects of such two influencing factors as line spacing and seedling density on the leaf-stem ratio, DW/FW ratio and grass yield of forage sweet sorghum were analyzed by using split-plot experiment design experiment method and LSD method of IBM. SPSS. Statis- tics. v22 stati, stics software. [ Results ~ Seedling density and line spacing had no obvious effect on the leaf-stem ratio and DW/FW ratio of forage sweet sorghum but had obvious influences on the grass yield. Moreover, the optimal combination of seedling density and line spacing for high yield of forage sweet sorghum was A2 B4, that is, seedling density was 225 000 plants/hm2, and line spacing was 40 cm. [ Conclusions] The results provided a theoretical basis and technical support for high-yield cultivation techniques of forage sweet sorghum.

A Study on Seedlings' Density of Aralia elata

Aralia clata is an important economic species in northeast China. The experiments for determung optimum seedlings density were made in the nursery of Experimental Forest Farm of Liaoning Province. Qingyuan County, in 1997. The results of 4 repeating experiments for six densities were analyzed using variance analysis by single factor. Seedling density has great effects on growth of diameter(at foot) and height. The proper seedlings density forAralia elata was determined to be 55–65 stems/m2, or 330000 390000 hm2. Thus density can insure individual seedling’s quality and the maximum productivity of seedlings.

Determination of Optimum Seed Rate of Hybrid Rice (Oryza sativa L.) Varieties in Mat-Type Seedling Raising for Mechanical Transplanting

Rice is the most important and crucial to ensuring food and dietary energy security in most developing countries and is the staple food of more than half of the world’s population. This study was conducted to identify the seed rate of hybrid rice varieties for mechanical transplanting during Boro (irrigated dry season), 2021-22 season at BRRI research field, Gazipur. Slender grain type BRRI hybrid dhan3, BRRI hybrid dhan5, Ishpahani hybrid dhan6, and BRRI dhan89 were used in the study. The same growth medium was used to establish mat-type seedlings on plastic trays (280 × 80 × 25 mm) at seed rates of 80, 90, 100, 110, and 120 g∙tray−1. Walk-behind type 04 rows rice transplanter (Daedong, model-DP 488) was used during transplanting in the field at the set of the plant to plant spacing of 140 mm while line-to-line spacing was fixed to 300 mm. The result depicted that regardless of the variety, seedling density increased linearly as seed rate increased, except for the 21 days following sowing. However, the seedling density of BRRI dhan89 decreased after the seed rate of 100 g∙tray−1 due to mortality. The seedling height of the BRRI hybrids dhan5 and Ishpahani hybrid dhan6 was significantly higher than that of the BRRI hybrid dhan3 and BRRI dhan89. After 21 days, the seedling height decreased significantly with the increase in seed rate. For the seed rates of 100, 110, and 120 g∙tray−1, identical numbers of hills per unit area and plants per hill were observed. On the other hand, regardless of the variety, the percentage of missing hills considerably decreased with the increased seed rate. The yield of the BRRI hybrid dhan5 variety was significantly higher at the seed rates of 100 and 110 g∙tray−1, although the yield of the Ishpahani hybrid dhan6 variety was comparable. In terms of yield among the four varieties, BRRI hybrid dhan5 gave a higher yield followed by Ishpahani hybrid dhan6 while BRRI dhan89 gave a lower yield compared to the hybrid varieties irrespective of the seed rate. However, a seed rate of 110 g∙tray−1 gave a significantly higher yield followed by 120 g∙tray−1 while 80 and 90 g∙tray−1 gave lower grain yield. Generally, mat type seedling of inbred rice varieties is used in Bangladesh. The determination of seed rate of hybrid rice varieties may be increased by the use of rice transplanter in mechanical transplanting of hybrid rice varieties reducing the seed loss and increasing the grain yield.

Impact of invasive Ageratina adenophora on relative performance of woody vegetation in different forest ecosystems of Kumaun Himalaya,India

Invasive plant Ageratina adenophora(Sprengel)R.King&H.Robinson has invaded majority of the temperate forests in Kumaun,Central Himalaya.Information on A.adenophora invaded forest types,their structural attributes,population demography and regeneration status are still at rudimentary level.Considering this,the present study was conducted to assess the impacts of A.adenophora on vegetational attributes and regeneration status of three forest types,viz.,Oak(Quercus oblongata D.Don),Pine(Pinus roxburghii Sarg.)and Cypress(Cupressus torulosa D.Don).We selected three sites for each forest type and each site was further purposively stratified into paired sampling plots of 1 ha each i.e.,A.adenophora invaded and uninvaded sites.Our results showed large densities of cut stumps or felled trees throughout invaded sites,but with fewer fire signs in comparison to uninvaded sites.In uninvaded sites,total density and basal area calculated for woody species were relatively higher than those in invaded sites,although results were insignificant(p>0.05).With the exception for Cypress forests,vegetation indices showed low woody species richness and diversity in invaded Oak and Pine forests.Also,regeneration of Q.oblongata,P.roxburghii and C.torulosa tree species did not differ significantly(p>0.05)between invaded and uninvaded sites.These insignificant differences clearly imply that A.adenophora's presence has not entirely changed the perennial plant communities in terms of composition,structure and natural regeneration.However,tree species with poor or no regeneration status requires special attention and needs management strategies involving control of invasive species in forest ecosystems.

Gap characteristics and their effects on regeneration,dominance and early growth of woody species

Aims We aim to examine the canopy gap characteristics and evaluate their influence on regeneration,dominance and the early growth of woody species in seasonally dry Shorea robusta forests(Sal forests).Methods Sixty canopy gaps were surveyed in six randomly located transects belts in seasonally dry subtropical Sal forests of central Nepal.Each transect belt was followed until 10 gap sites were encountered.The equation for the area of an ellipse was used to calculate the size of canopy gap,measuring the longest axis and its perpendicular shorter axis.Number,sizes,ages and causes of tree falls creating canopy gaps along with number and sizes of border trees were identified and recorded.Detailed gap inventories were carried out using square 25-m2 quadrats placed in the middle of each gap.All individuals>2 m in height within the quadrat were identified at the species level and their diameter at breast height was measured.We assigned a nested 4-m2 quadrat to the corner of each 25-m2 quadrat,within which all woody individuals>10 cm tall were identified at the species level,and counted them and their regeneration mechanisms were identified.The height and collar diameter of the tallest individuals were measured.Descriptive statistics was calculated for the variables of interests and Pearson correlation,linear regression,independent-sample t-test and chi-square test were used to relate them and to test for their associations.Important Findings The study found mean gap size of 283 m2 and;50%gaps of 10–15 years old.Gaps created by natural single-tree falls were significantly more numerous,and their mean size was significantly smaller than those resulting from artificial causes or multiple-tree falls.Gap size correlated with the basal area of felled trees,but it did not correlate with the number of tree falls.While tree fall basal area was significantly positively correlated to the seed-originated seedling to resprout ratio,it was negatively correlated,along with gap area and the basal size of retained trees,to seedling growth.The relative seedling density of Terminalia alata increased with increases in gap areas,while that of S.robusta decreased with increases in tree fall basal area,thereby lowering the plot-level dominance.However,the relative seedling densities of Eugenia operculata and Syzigium cumini were negatively and positively correlated,respectively,with tree fall basal area.

Tree species determine soil seed bank composition and its similarity with understory vegetation in a semi-arid African savanna

Introduction:The presence of larger trees in semi-arid African savannas creates sub-habitats,which influences on herbaceous plant communities grown under their canopies differently from opened areas.Knowledge of seed banks accumulated in the soils over time beneath larger trees could facilitate the recovery of plant communities that might disappear due to sustained heavy grazing,prolonged fire,or other anthropogenic factors in semi-arid African savannas.However,the impact of larger trees on soil seed bank composition and its similarity with plant communities grown under their canopies are less understood in semi-arid African savannas.Therefore,we studied the effect of leguminous and non-leguminous tree species and their canopies on soil seed bank(SSB)composition and its similarity with understory vegetation(USV)in a semi-arid savanna of Ethiopia.Methods:We selected 20 matured trees from 3 dominant tree species,representing one leguminous(Acacia robusta Burch)and 2 non-leguminous tree species(Ziziphus spina-Christi and Balanites aegyptiaca(L.)Del),found in isolation,a total of 60 trees for this study.Under each selected individual tree,the species composition of USV were recorded using 1-m2 quadrat in four directions(north,south,east,and west)under the inside and outside tree canopies during the flowering stage.Similarly,soil samples in a 1-m2 quadrat were also collected under the inside tree canopies and their corresponding outside canopies,in each individual tree,for the determination of SSB composition,using a seed emergence method.Then,the soil was thoroughly mixed after removal of all roots and plant fragments,and spread over sand in plastic pots to a depth of 20 mm.The pots were placed at random in a glasshouse,examined every 3 days,for the first 2 months,and thereafter weekly for 6 months.A total of 960 soil samples were used for the determination of SSB composition during this study.Results:A total of 64 species were emerged from the SSB samples,of which 27 were grasses(19 annual and 8 perennial grasses),35 annual forbs and 2 woody species.Acacia robusta had a higher seedling density in the SSB compared to other tree species,whereas Z.spina-Christi had higher species diversity in the SSB than other tree species.Moreover,seedling density and species diversity were higher under the inside canopies than outside tree canopies.The mean similarity in species composition between the SSB and USV was low.However,it was higher under the leguminous trees than non-leguminous trees,and under the inside tree canopies than outside canopies.Conclusions:We found that mature tree species maintained a higher SSB species diversity and abundance under their canopies than the surrounding opened areas.Therefore,conservation of mature dominant tree species is of paramount importance for ecological stability and possible restoration of degraded semi-arid savannas under the changing climate and global warming.