Plant Density Conditions Research Articles

Accelerated development of maize inbred lines suitable for high density through doubled haploid technology

Aim: Doubled haploid technology was utilized to accelerate the development of maize lines with traits suitable for high planting density, enabling the identification of potential parental lines for hybrid development under these conditions. Methodology: Two F1 populations (PML-119 x PML-185 and PML-95 x PML-172) were used to generate doubled haploid lines, confirmed using polymorphic markers phi115 and umc1887. These lines were phenotypically evaluated under high density (60 cm x 15 cm) and normal density (60 cm x 20 cm) conditions. Results: Using doubled haploid technology, 67 lines were developed from two source populations with traits such as narrow leaf angle, moderate plant height, and sparse tassel for high planting density stress tolerance. Molecular marker screening confirmed the homozygosity of these lines. Agronomic evaluation under narrow plant-to-plant spacing (15 cm) identified eight potential donor lines amenable to high planting density stress, ready for use as parents in breeding high-density tolerant hybrids. Interpretation: Potential donor doubled haploid lines viz. DH2-4, DH2-8, DH2-9, DH2-11, DH2-14, DH2-15 derived from Population-3 X CIM2GTAIL P2 and DH2-4, DH2-23 derived from Population-9 X CIM2GTAIL P2 were identified for utilization as putative parents of hybrids suitable for planting under high planting density conditions. Key words: Doubled haploid, High plant density, Maize, Plant architecture, Yield

Effects of Eucalyptus plantation characteristics and environmental factors on GEDI waveform metrics

ABSTRACT The Global Ecosystem Dynamics Investigation (GEDI) is a high-resolution lidar instrument, facilitating landscape monitoring through forest structure and biomass assessments. Previous research has mainly focused on estimating forest attributes such as height and biomass from GEDI data. In this comprehensive study, we empirically investigate how Eucalyptus plantation characteristics and environmental factors collectively influence GEDI waveform metrics. Using a diverse dataset that includes measurements of canopy height, planting density, foliage characteristics, species composition, understorey presence and environmental conditions such as climate and soil properties, we explore the complex relationships between these attributes and GEDI waveform metrics using a two-step approach that includes assessing the linear relationship between each in-situ parameter and GEDI metrics, and also random forest modelling. Key findings include: 1) While canopy height (Ht) plays a significant role in shaping the GEDI waveform, forest wood volume (Volume), which incorporates height and diameter at breast height (DBH) of the trees and also tree stem density (Ntree/ha), exerts an even greater influence on GEDI metrics, in particular on the waveform extent (WE) and relative heights (RH); 2) The influence of factors such as foliage biomass and wood volume on GEDI waveform varies vertically from the forest floor up to forest top, and the model was more precise to predict the top part of the waveform; 3) No single attribute can solely account for the observed variations in the waveform characteristics, but multiple interactions between different forest and environmental features contribute to the complex patterns in the received waveforms. This research contributes to a deeper understanding of the complex relationships between forest plantation characteristics and GEDI waveform metrics and highlights the need to consider a wide range of forest attributes in the analyse of GEDI waveform to produce more accurate canopy height or volume estimates.

Perda por interceptação em sistemas de produção de erva-mate (Ilex paraguariensis) no Sul do Brasil

ABSTRACT The partitioning of precipitation into interception, throughfall and stemflow is essential for the hydrological balance in forests, particularly in the Brazilian forest system, regulating the amount of water input and leaf distribution in the ecosystem. This study aimed to present the dynamics of interception loss in yerba mate monoculture, agroforestry and native mixed ombrophilous forest systems, in experimental producing areas in the municipality of Guarapuava, Southern Brazil. The total gross rainfall was 788 mm, distributed in 33 events between July 2019 and March 2020. The throughfall, stemfow and interception loss of rainfall were respectively 78.7, 0.2 and 21.1 % in the native mixed ombrophilous forest; 85.3, 0.1 and 14.6 % in the agroforestry system; and 86.1, 0.3 and 13.6 % in the monoculture system. It was observed that diferent canopy characteristics infuence the variability of rainfall partitioning. The mixed ombrophilous forest showed a higher interception capacity, when compared to the monoculture and agroforestry systems, determined by plant density and meteorological conditions.

Experimental Study on Mechanical Properties of Hemp Fibers Influenced by Various Parameters

Hemp fibers produced by different extraction techniques that were cultivated in the Portuguese districts of Bragança and Mirandela under various nitrogen fertilization and planting density conditions are examined and mechanically described in this paper. The objective of this study is to evaluate the influence of sowing density, nitrogen fertilization, sample location, and extraction method in order to improve the mechanical properties of hemp fibers. To achieve this, we determined the modulus of elasticity, the tensile strength, and the density. The mean value for the modulus of elasticity was 92.44 ± 7.44 GPa, the mean of tensile strength was 564.98 ± 167.03 MPa, and the mean of the density was 1.64 ± 0.24 g cm−3. We performed a statistical analysis of all parameters using ANOVA and found that the retting method had the greatest influence among all parameters. The associated effects of nitrogen fertilization and sowing density revealed an important influence on tensile strength and specific tensile strength, respectively.

Integrated Management Practices for Canopy-Topsoil Improves the Grain Yield of Maize with High Planting Density.

Inappropriate spatial distribution of canopy and roots limits further improvements to the grain yield of maize with increased planting density. We explored an integrated management practice called strip deep rotary with staggered planting (SRS) which includes comprehensive technology for both canopy layers and topsoil. Here, field experiments were conducted under two maize cropping systems (spring maize and summer maize) to evaluate the effect of SRS on the spatial distribution of the canopy and roots for maize under high planting density (90,000 plants ha-1) and to determine the physiological factors involved in yield formation. Compared with conventional management practices (no-tillage with single planting, NTS), SRS decreased the LAI of the middle to top layers while improving the light distribution of the middle and lower layers by 72.99% and 84.78%, respectively. Meanwhile, SRS increased the root dry weight density and root sap bleeding by 51.26% and 21.77%, respectively, due to the reduction in soil bulk density by an average of 5.08% in the 0-40 cm soil layer. SRS improved the SPAD in the ear and lower leaves and maximized the LAD, which was conducive to dry matter accumulation (DMA), increasing it by 14.02-24.16% compared to that of NTS. As a result, SRS increased maize grain yield by 6.71-25.44%. These results suggest that strip deep rotary combined with staggered planting noticeably optimized the distribution of light in the canopy and reduced the soil bulk density to promote root vitality and growth, to maintain canopy longevity, and to promote the accumulation of dry matter, which eventually increased the grain yield of the maize under high planting density conditions. Therefore, SRS can be considered a better choice for the sustainable high yield of maize under high-density planting conditions in the NCP and similar areas throughout the world.

Long-term effects of rootstock and tree type on the economic profitability of ‘Gala’, ‘Fuji’ and ‘Honeycrisp’ orchards performance

Planting a new orchard requires a complex management strategy that involves many factors including cultivar, rootstock, planting density, training system, tree type, climate, and economic conditions that affect orchard profitability. To evaluate the relative importance of each factor, data from long-term field studies is required to analyze their impact on lifetime profitability. Here, we conducted two long-term field studies at two locations in New York State (Dressel farm in South-eastern and VandeWalle farm in Western New York State). The trials were planted in 2006 at a planting density of 3,262 tree/ha and the trees were trained as Tall Spindles. The aim of this study was to compare the impact of tree type (newly bench-grafted trees and large 2-year feathered trees) and rootstock (B.9, M.9, G.11, G.16, G.41) on long-term profitability of three apple cultivars (‘Fuji’, ‘Gala’, and ‘Honeycrisp’). There were important differences in profitability between cultivars, with a higher Net Present Value (NPV) for ‘Honeycrisp’, followed by ‘Gala’ and, finally, for ‘Fuji’. For all the cultivars, the NPV of the feathered trees was substantially higher compared to bench-grafted trees. Furthermore, the highest cumulative NPV's for ‘Honeycrisp’ were on B.9, G.11 and G.16, whereas with ‘Fuji’ the highest NPV's were on G.16, G.11 and M.9 and with ‘Gala’ the highest NPV's were on G.16, G.41 and M.9. The break-even year of a positive NPV for each rootstock, tree type, and cultivar, showed that the fastest investment pay offs were achieved with ‘Honeycrisp’, followed by ‘Gala’ and ‘Fuji’. Feathered trees showed a faster break-even year of a positive NPV compared to bench grafted trees in all cultivars. Our results showed that the key variables that influence orchard profitability were, in descending order, fruit price and yield, followed by discount rate, labor cost, and finally tree price and land cost.

Long-term assessments of cotton fiber quality in response to plant population density: Reconciling fiber quality and its temporal stability

Regulation of plant population density is crucial for optimizing cotton fiber quality. However, the relationship between plant density and fiber quality stability under contrasting climatic conditions remains unclear, and the compromise between fiber quality and temporal stability is unknown. In this study, based on a long-term field experiment with various plant densities (1.5–10.5 plants m–2) conducted from 2008 to 2021, cotton fiber quality variability, including fiber length, fiber strength, elongation, uniformity index, and micronaire, and their temporal stability, were evaluated. We determined the optimal plant density for cotton cultivation and elucidated the contributions of plant density and climatic conditions to the variability of cotton fiber quality and its temporal stability in China’s Yellow River Valley. The results revealed that cotton maintained its upper-intermediate quality throughout the study period, with fiber length, strength, elongation, uniformity index, and micronaire values ranging between 28.04 and 30.03 mm, 26.15–30.05 cN tex–1, 5.90–6.83%, 83.85–85.44%, and 4.24–5.14, respectively. An increase in plant density improved fiber quality but impaired temporal stability (P < 0.01), and slight increases in stability at lower plant densities resulted in substantially decreased probabilities of years with major declines in fiber quality class. Plant density and climatic conditions regulated the quality traits (23.5% and 69.3% of the explained variance, respectively), including fiber length, fiber strength, and micronaire, while climate was the most important factor (75.9% of the explained variance) in determining their temporal stability. Photosynthetically active radiation and maximum and mean temperature exhibited significant positive effects on fiber quality, whereas mean diurnal temperature range had the opposite effect. A plant density of 3.3–5.1 plants m–2 ensures the highest temporal stability of cotton fiber quality without declines in the fiber quality class. This study first provides insights into balancing cotton fiber quality and temporal stability through agronomic interventions, with implications for the quantitative prediction of future crop quality changes owing to climatic variation.

The taming of the weed: Developmental plasticity facilitated plant domestication.

Our experiments with crop progenitors have demonstrated that these species exhibit dramatic plasticity in key traits that are affected by domestication, including seed and fruit morphology. These traits can be altered by cultivating crop progenitors for a single season, in the absence of any selection for domesticated phenotypes. We hypothesize that cultivation caused environmental shifts that led to immediate phenotypic changes in crop progenitors via developmental plasticity, similar to tameness in animals. Here we focus on the loss or reduction of germination inhibitors in an annual seed crop because seeds with high dormancy are undesirable in crops, and also present a serious barrier to selective pressures that arise from seed-saving and planting by humans. Data from four seasons of observation of the crop progenitor Polygonum erectum L. suggest that the low plant density conditions of an agroecosystem trigger a phenotypic response that reduces germination inhibitors, eliminating a key barrier to further selection. The timing of the harvest can also be used to manipulate the germinability of seed stock. These observations suggest that genetic assimilation may have played a role in the domestication of this plant. More experimental work with crop progenitors is needed to understand whether or not this phenomenon played a part in the domestication of other plants, and to accurately interpret the significance of ancient plant phenotypes in the archaeological record.

Особливості технології вирощування гібридів соняшнику кондитерського типу в умовах східної частини Лісостепу України

Purpose. To evaluate the effects of the plant density and fertilizer dose on the yield and thousand seed weight in F1 confectionary sunflower hybrids. Methods. Field, laboratory and mathematical statistical methods were used. Results. The average yield of confectionery sunflower hybrids grown at a density of 28,600 plants/ha exceeded their yield at a density of 20,400 plants/ha by 0.01–0.43 t/ha, depending on the study year and fertilizer dose. The average thousand seed weight at the density of 20,400 plants/ha exceeded that at the density of 28,600 plants/ha by 6.0–14.8 g. The greatest increase in the yield and thousand seed weight was achieved when fertilizers were applied at a dose of N45P45K45: +0.21 t/ha and +6.5 g to the control (without fertilizers), respectively, at the density of 28,600 plants/ha; +0.18 t/ha and +5.4 g to the control, respectively, at the density of 20,400 plants/ ha. The maximum seed yield was produced by hybrid Forsazh: 3.97 t/ha (2016, 28,600 plants/ ha, N45P45K45). Confectionery hybrids Hudvin and Nasoloda had the maximum values of the thousand seed weight: 123.0 and 121.2 g, respectively (2018, 20,400 plants/ha, N45P45K45), which exceeded the thousand seed weight of the check large-fruited variety by 7.2 and 5.4 g, respectively. In the dry year (2017), the thousand seed weight in Hudvin and Nasoloda grown at the density of 20,400 plants/ha was higher than 95.6 g. In the wet year (2020), the thousand seed weight in Hudvin and Nasoloda, even at the density of 57,100 plants/ha, amounted to 88.6–92.5 g. Conclusions. The seed yield and thousand seed weight of the confectionary sunflower hybrids are significantly influenced by plant density, fertilizer dose and weather conditions during the growing period. The highest yield and thousand seed weight were recorded when fertilizers were applied at the dose of N45P45K45: 3.97 t/ha (at 28,600 plants/ha) and 123 g (at 20,400 plants/ha), respectively. The confectionery sunflower hybrids ensured high yields and high-quality confectionary seeds in Eastern Forest-Steppe of Ukraine.

Modeling maize water consumption and growth under plastic film mulch using an agro–hydrological model: Searching for the optimal plant density in different hydrological years

Appropriate plant density is essential for crop production in rainfed areas. However, it is quite difficult to obtain the optimal plant density under plastic film mulch in different hydrological years through field experiments due to its limited treatments, and time and labor costs. Therefore, mathematical models are generally used for searching the optimal alternatives. In this paper, the Agro–Hydrological & chemical and Crop systems simulator (AHC) was adopted to model soil water dynamics, rainfed maize growth, and yield under plastic film mulch and various plant density conditions in Northeast China for different hydrological years. The results showed that the AHC model can simulate rainfed maize water use and growth under plastic film mulch and various plant density conditions, i.e., 60,000 (D1), 67,500 (D2), 75,000 (D3), 82,5000 (D4) and 90,000 plants ha−1 (D5). The average maize yields of all treatments in the severely dry (SD), moderately dry (MD), normal (N), moderately wet (MW), and severely wet (SW) years were 11440.3, 13685.4, 13821.5, 14704.8, and 14014.3 kg ha–1, respectively. Compared with non–mulch, plastic film mulch increased the maize basal crop coefficient by 0.08–0.11 and decreased the soil evaporation coefficient by 0.26–0.32, from SD and SW years, respectively. Thus, plastic film mulch augmented maize transpiration by 46.2–76.8 mm, while reduced evaporation by 163.5–186.8 mm across the simulated years. Ultimately, the maize yield under plastic film mulch was 5.9–17.4% higher than that without mulch. From D1 to D5 treatments, the decrease of soil evaporation coefficient was within 0.02 under plastic film mulch and was over 0.05 without mulch. Under plastic film mulch, the relations between plant density and net profit could be well described by the parabolic curves, and the recommended optimal plant densities of maize in the study area were 91, 101, 101, 105, and 101 thousand plants ha–1 in the SD, MS, N, MW, and SW years, respectively. Our findings provide management implications for maize cultivation in the rainfed areas of Northeast China.

Effects of plant density on the aboveground dry matter and radiation-use efficiency of field corn.

The amount of solar radiation intercepted by the plant canopy drives crop plant photosynthesis and the formation and development of plant organs. Radiation-use efficiency (RUE) is an index used to quantify the relationship between solar radiation and biomass, and crop yield can be increased by increasing RUE. The main goals of this study were to initially investigate the effects of plant densities on the aboveground dry matter of corn, and subsequently examine the effects of plant densities on RUE and leaf area index (LAI), and the effects of LAI on RUE. Finally, we provide a comparative assessment of the approaches used to determine RUE. Analyses were conducted using growth and meteorological data obtained for two field corn varieties (TNG1 and TNG7) grown under four different plant density conditions in central Taiwan in 2017. The RUE values obtained in this study were primarily estimated from the slope of the linear relationship between aboveground dry matter measured at periodic harvests and the corresponding cumulative intercepted photosynthetically active radiation up to the time of harvest. TNG1 and TNG7 with a row spacing of 37.5 cm × 20 cm had the largest amounts of aboveground dry matter and highest RUE values of 4.41 and 4.55 g MJ-1, respectively. We established that the higher the plant density, the higher were the values obtained for RUE and LAI. We also compared the different methods of estimating RUE and make recommendations in this regard. Our findings in this study will enable farmers to gain information on the dynamics of crop yield variation at an early stage of growth, and also provide reference values that can be incorporated in future crop yield models.

Maize hybrid yield and physiological response to plant density across four decades in China

AbstractThe popularity of density‐tolerant maize (Zea mays L.) hybrids greatly increased the yield of maize hybrids in China in recent years. Clarifying trends in yield and plant density responses of agronomic characters of maize hybrids released in different years can provide theoretical and practical guidance for breeding high‐yield and density‐tolerant maize hybrids. The results showed grain yield (GY) of maize hybrids released in the 1970s and 1980s decreased with increased plant density. But GY of maize hybrids released in the 1990s and 2000s increased with a plant density increase. The GY gains from the low to high plant density plots were 86, 135, and 198 kg ha–1 per year, respectively. In all plant density treatments, yield and biomass of newer hybrids (2000s) were significantly higher than those of older hybrids (1970s). The leaf area index (LAI) of maize hybrids released in different years (1970s ∼ 2000s) increased with plant density, whereas the extinction coefficient decreased. Compared with the old hybrids, new hybrids have larger population sink capacity and stronger source supply ability, which is more prominent under high density. Population sink capacity is the main factor limiting maize yield. The key to maize hybrid improvement is to increase the population sink capacity. Breeders should continue to select for hybrids under stressful and high plant density conditions to increase seed setting rate and decrease empty ear rate of maize hybrids.

Grain Dehydration Characteristics of Old and Modern Maize Hybrids and Their Response to Different Planting Densities

High grain water content at harvest stage is the main limiting factor for realizing mechanized maize grain harvest in China. Under the background of yield gain by density increase, it is necessary to clarify the effect of planting density increase on maize grain dehydration characteristics, which would provide theoretical support for realizing mechanized grain harvest under high planting density conditions. Therefore, this study selects five main hybrids, ZD2, DY13, YD13, XY335, and DH618, released in different eras that were widely promoted in Inner Mongolia from the 1970s to 2010s. The experiment was conducted in the Chilechuan Modern Agriculture Expo Park, Tumed Right Banner, Baotou city, Inner Mongolia, in 2018 and 2019. Under the three densities of 45,000 plants ha−1 (low density), 75,000 plants ha−1 (medium density) and 105,000 plants ha−1 (high density), the indexes of grain dehydration, leaf stay-green, bract and cob dehydration of the different maize hybrids were measured and analyzed. The results show that MCpm (moisture content at physiological maturity) of hybrids in the 1970s and 1990s was significantly reduced by 1.57 and 1.14 percentage points, respectively, and MCh (moisture content at harvest time) in the harvest period of hybrids in the 1970s was significantly reduced by 0.99 percentage points, from a low to medium density. The GDRbm (rate of grain dehydration before maturation) and the GDRam (rate of grain dehydration after maturation) showed an increasing trend from a low to medium density. From a medium to high density, the MCpm from the 1980s to 2000s could be significantly reduced by 1.78, 1.53 and 1.88 percentage points; the MCh from the 1980s could be significantly reduced by 1.77 percentage points; and the GDRbm from the 1970s was significantly increased by 0.101%/d, but the improvement of GDRam was not significant. With the planting density increase, the decreased ratios of relative GLAD (green leaf area duration) and leaf SPAD (soil and plant analyzer development) per plant of old maize hybrids were more than that of modern maize hybrids, which promoted the decrease in grain water content and the rate increase in grain dehydration for old maize hybrids. There was a direct positive correlation between the bract and grain dehydration rates, but the cob dehydration rate had no significant effect on the grain dehydration rate. With the increase in planting density, the relative GLAD and leaf SPAD values of plants decreased, and the stay-green of plants worsened, and a significant increase in the dehydration rate of bracts in old and modern eras was an important reason for the decrease in grain moisture content and increase in dehydration rate.

Quantifying contributions of leaf area and longevity to leaf area duration under increased planting density and nitrogen input regimens during maize yield improvement

Leaf area and its longevity are the key factors driving dry matter accumulation and yield formation in maize (Zea mays. L). Both factors are influenced by cultivation management measures. The objective of this study was to utilize a quantitative framework to better understand the contribution of leaf area and longevity to leaf area duration (LAD) and yield in maize plants at varying plant densities and nitrogen application rates. A two-year field experiment was conducted using a factorial combination of two plant densities and four nitrogen levels. Leaf area and longevity were measured at each leaf position in two different maize cultivars. We calculated the LAD at the single-leaf, individual-plant, and whole-population scales and quantitatively analyzed the contribution of leaf area and longevity to LAD. The results showed that in the upper leaves, leaf area had a larger proportional contribution to LAD (54.1–95.7%), whereas in the lower leaves, leaf longevity contributed more to LAD (51.8–74.1%). Both were greatly affected by variations in plant density and nitrogen application. At the individual-plant scale, the proportional contribution of leaf area to LAD (57.3%) was similar to that of leaf longevity (57.2%); at the whole-population scale, leaf area accounted for a larger contribution to LAD (87.0%). The increase in LAD (which integrating increases in leaf area and longevity) was positively associated with an increase in dry matter at maturity and grain yield. Yield gain was achieved by reasonable increases in density and nitrogen fertilizer application to promote LAD. The quantitative evaluation of leaf area and longevity described in this study provides a theoretical basis for increasing maize yield under increased plant density and nitrogen input conditions.

Evaluation of Electrostatic Spraying Equipment in a Greenhouse Pepper Crop

Greenhouse vegetable production is of great importance in southern Europe. It is a cultivation system characterised by a high planting density and environmental conditions that favour the development of pests and diseases. Although alternatives to chemical pest and disease control have been used over recent years in greenhouse crops, it is still mostly plant protection products that are used to protect crops and prevent crop losses. Hand-held spraying equipment is mainly used to apply plant protection products to this type of crop. This equipment is technologically basic, offering low deposition efficiency in the plant canopy, high losses to the ground, and a high risk of worker exposure. In this context, it is important to utilise technologies that reduce the problems associated with using the conventional hand-held sprayers in greenhouses. This study evaluated the deposition and uniformity in the plant canopy and the losses to the ground when applying plant protection products with an electrostatic hand-held sprayer; the results were then compared with applications carried out using a conventional hand-held sprayer. For this purpose, a colorimetric method has been used based on the application of a tartrazine solution. The tests showed that the electrostatic spraying equipment increased the plant canopy deposition by 1.48 times that of the hand-held spray gun, resulting in a 48% reduction in the application rate. There was also a 1.78-times increase in deposition on the underside of the leaves and a 36.36% reduction in losses to the ground. In general, the electrostatic hand-held sprayer improves the effectiveness of the plant canopy deposition and reduces losses to the ground compared to the hand-held spray gun commonly used in pest and disease control.

Quantitative Relationship Between Solar Radiation and Grain Filling Parameters of Maize.

A quantitative understanding of the factors driving changes in grain filling is essential for effective prioritization of increasing maize yield. Grain filling is a significant stage in maize yield formation. Solar radiation is the energy source for grain filling, which is the ultimate driving factor for final grain weight and grain filling capacity that determine maize yield. Here, we first confirmed the quantitative relationships between grain filling parameters and photosynthetically active radiation (PAR) by conducting field experiments using different shading and plant density conditions and cultivars in 2019 and 2020 in Xinjiang, China. The results showed that with every 100 MJ m−2 increase in PAR, the average grain filling rate (Gave), maximum grain-filling rate (Gmax), and the kernel weight at the time of maximum grain-filling rate (Wmax) increased by 0.073 mg kernel−1 day−1, 0.23 mg kernel−1 day−1, and 0.24 mg kernel−1, and the time of maximum grain-filling rate (Tmax) delayed by 0.91 day. Relative changes in PAR were significantly and positively correlated with relative changes in yield and Gave. With every 1% change in PAR, yield and Gave changed by 1.16 and 0.17%, respectively. From the perspective of grain filling capacity, DH618 was a more shade-resistant cultivar than XY335 and ZD958. It is urgent to breed maize cultivars with low light tolerance and high grain yield in the face of climate change, particularly the decrease in solar radiation.

Plant topping effects on growth, yield, and earliness of field-grown cotton as mediated by plant density and ecological conditions

Manual removal of the main-stem growth tip is traditionally used to break the apical dominance of cotton ( Gossypium hirsutum L.). Chemical topping with plant growth regulators also effectively inhibits apical dominance. However, the effect of chemical topping on yield increases and whether plant density or ecological conditions affect its efficacy are unclear. Therefore, a three-year field experiment with a split-plot design was conducted to determine the effects of plant topping, plant density, and their interactions on cotton yield and related physiological and agronomical parameters at three sites with different ecological conditions in China. In each site, the main plots were assigned low, moderate, or high plant density and the subplots were assigned no topping, manual topping, or chemical topping. Growth, yield, yield components, earliness, and late-season leaf photosynthesis as well as labor and material inputs were examined each year. Compared with no topping, both chemical and manual topping greatly reduced plant height at all sites. Manual topping increased seed cotton yield and earliness in all tested plant densities and sites. However, plant density but not ecological condition greatly mediated the effect of chemical topping on yield. At low plant density, the yields with chemical topping were 4–6% lower than those with no topping and 5.5–10.8% lower than those with manual topping at the three sites. Although yields with chemical topping were comparable with those of manual topping at moderate and high plant densities, they were 8.6–12.8% higher at moderate density and 13.8–16.4% higher at high plant density than those with no topping across years and sites. Averaged across the sites, chemical topping reduced biological yield by 12.7% at low plant density. Although biological yield decreased slightly, chemical and manual topping increased the harvest index by 12.4% and 13.3% at moderate density and by 15.6% and 17.4% at high density, respectively. In comparison with no topping, the reduction in seed cotton yield with chemical topping at low plant density was attributed to insufficient biological yield, whereas the increase in yield at moderate and high plant densities was mainly due to greater partitioning of assimilates to reproductive tissues. Compared with manual topping, chemical topping produced 23.2% lower net returns as a result of lower seed cotton yield at low plant density but produced 8.1% and 20.9% higher net returns at moderate and high plant densities, respectively, because of savings in labor inputs and comparable seed cotton yields. In addition, chemical topping increased the earliness percentage compared with that of no topping. Overall, this study demonstrates that chemical topping is a promising alternative to traditional manual topping under moderate or high cotton plant density. • Manual topping increased cotton yield regardless of plant densities and ecological conditions relative to non-topping. • Chemical topping decreased yield at low plant density relative to non-topping because of greater biomass reduction. • Chemical topping increased cotton yield at moderate and high plant densities via greater assimilates partitioning to fruits. • Chemical topping could replace manual topping at moderate and high plant densities without ecological dependence.

The Effect of Plant Density, Zinc Added to Phosphorus Fertilizer Sources and Location on Selected Yield Parameters of Soybean

Background: Soybean [Glycine max (L.) Merrill] is an annual herbaceous leguminous grain crop which is cultivated mainly for its oil and protein. The objective of the study was to determine the effects of plant density and zinc added to phosphorus fertilizer sources on soybean yield performance under different environmental conditions. Methods: A field trial was executed in two sites during the 2018/19 and 2019/20 summer planting seasons. The experimental design involved a 2 × 2 × 5 factorial fitted into a randomized complete block design (RCBD) with four replications. The experiment consisted of two plant densities, a lower plant density of 66 666 plants/ha and a higher plant density of 111 111 plants/ha. The five different types of fertilizer treatments were single superphosphate, monoammonium phosphate, zinc sulphate added to single superphosphate, zinc sulphate added to monoammonium phosphate and control. Result: The results showed that plant density has a significant effect (P less than 0.05) on soybean number of pods per plant and the field biomass yield. Soybean planted under lower plant density conditions produced a significantly larger number of pods per plant during both planting seasons, whereas higher plant density conditions resulted in a higher soybean field biomass yield during the 2018/19 planting season. It was observed that soybean treated with monoammonium phosphate had higher seed mass.

Partial exclusion of precipitation: throughfall, stemflow and canopy interception in Eucalyptus plantations in southern Brazil

Hydrological behavior in reforested watersheds is different from that under other forms of cover. The variation may be related to aspects intrinsic to species, planting density, physiological maturity, management system and climatic conditions. Periodically, climatic anomalies such as the case of La Ninã are observed, and these are responsible for the alteration of the rainfall regime and consequently generate water deficits in the southern region of Brazil. Water deficit is responsible for reducing growth and productivity for the Eucalyptus genus, in addition to causing changes in hydrological behavior in reforested watersheds. Accordingly, this study compared the partition of rainfall in throughfall, stemflow and canopy interception of eucalyptus trees submitted or not to partial exclusion of precipitation. In the open field, 3 rainfall collectors were installed, and in the stand, for each rain exclusion treatment, 9 throughfall collectors and 9 stemflow collectors were installed. Every two weeks for 12 months, the volume of the collectors was measured. The quantified precipitation was 1627 mm over a year. In the treatment without exclusion, 84.8, 2.9 and 12.3% referred to throughfall, stemflow and canopy interception, respectively, while in the treatment excluding rainfall 80.6, 2.3 and 17.2% referred to throughfall, stemflow and canopy interception. The regression adjustments for throughfall and stemflow showed satisfactory R2 coefficients.

Grain yield gains and associated traits in tropical × temperate maize germplasm under high and low plant density

Development of ideal breeding and crop management strategies that can improve maize grain yield under tropical environments is crucial. In the temperate regions, such yield improvements were achieved through use of genotypes that are adapted to high plant population density stress. However, tropical germplasm has poor tolerance to high plant population density stress, and thus it should be improved by introgressing temperate maize germplasm. The aim of this study was to estimate the genetic gains and identify traits associated with such gains in stable and high yielding temperate × tropical hybrids under low and high plant population densities. A total of 200 hybrids derived from a line × tester mating design of tropical × temperate germplasm were developed. These hybrids were evaluated for grain yield and allied traits under varied plant population densities. High yielding and stable hybrids, such as 15XH214, 15XH215 and 15XH121, were resistant to lodging and had higher number of leaves above the cob. The high genetic gains of 26% and desirable stress tolerance indices of these hybrids made them better performers over check hybrids under high plant population density. At high plant population density yield was correlated to stem lodging and number of leaves above the cob. Future gains in grain yield of these hybrids derived from temperate × tropical maize germplasm can be achieved by exploiting indirect selection for resistance to stem lodging and increased number of leaves above the cob under high plant density conditions.