Plant Population Level Research Articles

Influence of Plant Density and Fungicides on Downy Mildew (<i>Peronospora Destructor</i>) and Bulb Yield of Onion in Ethiopia

Onion is a popular vegetable crop, which has been produced for its daily uses and economic benefits. Downey mildew caused by the fungus <i>Peronospora</i> <i>destructor</i> is among the most important yield-reducing factor in onion production. The effect of three different levels of plant population and fungicide frequency with two different fungicides was studied on downy mildew severity and yield of onion. Nineteen treatment of this Experiment included two fungicides mancozeb + metalaxyl and copper hydrox-ide, three different spraying interval with (10 days, 15 days and 21 days) and three level of plant population (0.71, 0.95 and 1.2 million plants/ha). The experiment was laid out in a randomized block design with three replications for two year at Fogera and for one year at Dera districts of South Gondar zone Ethiopia. Data on disease severity, bulb yield, bulb number and bulb size were recorded during the time of harvest. The price of bulb yield was assessed from the local market and the total price of the yield obtained from each treatment was computed on hectare basis. Input costs like seed, fungicides and labor were converted into hectare basis according to their frequencies used. Fungicides cost was estimated based on the price of the local market. Cost of the labor was in Birr per man-days; cost of spray and spray equipment to spray per hectare were also calculated. Based on the obtained data from the above mentioned parameters economic analysis was performed. The lowest disease severity was recorded in treatment were lowest level of plant population (0.71 million plant/hectare) spraying with fungicide mancozeb + metalaxyl within 15days interval. In this treatment bulb yield and bulb weight were the highest. The economic evaluation showed that the highest net benefit with acceptable marginal rate of return was obtained from T3 (0.71million plants/ha spraying with fungicide mancozeb + metalaxyl within 15days interval).

The Populations of Two Differently Medicine-Used Plants of Hedyotis diffusa and Hedyotis corymbosa Shoot-Assembling Rich Bacterial and Fungal Communities with Varied Compositions but Conserved Structures.

The plant-colonized microbial communities have closely micro-ecological effects on host plant growth and health. There are many medicinal plants in the genus Hedyotis, but it is yet unclear about the shoot-assembled bacterial and fungal communities (SBFC) of Hedyotis plants. Hence, eight plant populations of Hedyotis diffusa (HD) and H. corymbosa (HC) were evaluated with 16S rRNA gene and ITS sequences, for comparing the types, abundance, or/and potential functions of SBFC at plant species- and population levels. In tested HD- and HC-SBFC, 682 fungal operational taxonomic units and 1,329 bacterial zero-radius operational taxonomic units were identified, with rich species compositions and varied alpha diversities. Notably, the SBFC compositions of HD and HC plant populations were exhibited with partly different types and abundances at phylum and genus levels but without significantly different beta diversities at plant species and population levels. Typically, the SBFC of HD and HC plant populations were presented with abundance-different biomarkers, such as Frankiaceae and Bryobacteraceae, and with similar micro-ecological functions of microbial metabolisms of lipids, terpenoids,and xenobiotics. Taken together, HD- and HC-SBFC possessed with varied rich compositions, conservative taxonomic structures, and similar metabolic functions, but with small-scale type and abundance differences at plant species- and population- levels.

Improving growth and productivity of chickpea (Cicer arietinum) of south eastern Punjab with optimal plant population and fertility level

The study aimed to investigate the impact of plant populations and fertility levels on growth and yield attributes of chickpea cultivars. For this, a field experiment was conducted with two cultivars (PBG 7 and GPF 2), two levels of plant populations (3.33 and 2.22 lakh plants/ha) and two fertility levels (20:40:20 and 30:60:30 kg NPK/ha) at south-eastern Punjab (Patiala) during the winter season of 2018-2019 following factorial randomized block design. Chickpea cultivar PBG 7 recorded significantly highest growth parameters (plant height, dry weight, branches/plant) and yield attributes (pods/plant, grains/pod, 1000-seed weight and grain yield/plant) and yield as compared to the cultivar GPF 2. The lower plant population (2.22 lakh plants/ha) resulted significant increase in plant height (3.13%), dry weight (22.56%), branches/ plant (25.44%), pods/plant (7.60%), grains/pod (15.62%) over the plant population of 3.33 lakh plants/ha, but considerably higher grain yield (1471 kg/ha) was recorded with 3.33 lakh plants/ha. Higher fertility level (30:60:30 kg NPK/ha) significantly increased growth, yield attributing parameters, grain yield (1476 kg/ha) and net return (INR. 45,036/ha) as compared to low fertility level (20:40:20 kg NPK/ha). Therefore, for obtaining higher yield of chickpea, PBG 7 can be sown at 3.33 lakh plants/ha with 30:60:30 kg NPK/ha under south-eastern Punjab.

Effects of sheep manure, plant population and nitrogen levels on growth and fresh fruit yield of chilli pepper (<i>Capsicum frutescence</i> l.) at Samaru, Zaria, Nigeria

Field experiments were conducted between 2004 and 2006 at the Institute for Agricultural Research Farm, Samaru Zaria in the Northern guinea savannah ecological zone of Nigeria, to study the response of chilli pepper (Capsicum frutescence L.) to sheep manure, plant population and nitrogen levels. Treatments evaluated consisted of four levels of sheep manure rates (0 t, 5 t, 10 t, and15 t ha-1), three plant populations (22,222; 44,444; and 66,666 plants ha1) and four rates of Nitrogen (0kg,60kg 120kg and 180 kg N ha1). The treatments were laid out in a split plot design and replicated three times. Result showed that application of sheep manure produced about significant increase in number of branches by 80%, similarly number of fruits increased by more than 600% and fresh fruit yields (Kg ha-1) recorded 57% increase over the control. Plant population was observed to significantly increase in the number of fruits per plant with 22,222 and 44,444plant/ha recording similar values, but higher number of fruits produced per plant than 66,666 plants ha-1 However, fresh fruit yield of Chilli pepper was not significantly influenced by plant population. The use of 120kgN ha1 resulted in increased number of branches, fruit per plant and fresh fruit yields by 57 and 60% respectively over non fertilized plants. Application of sheep manure at 10 t ha1, +44,444plants ha and 120kgN ha could be recommended for the production of chilli pepper under rain fed condition in Northern Guinea savannah.

Growth and Phenology of Hybrid Maize as Influenced by Different Levels of Nitrogen and Plant Population

Growth and Phenology of Hybrid Maize as Influenced by Different Levels of Nitrogen and Plant Population

Effects of Different Livestock Grazing on Foliar Fungal Diseases in an Alpine Grassland on the Qinghai-Tibet Plateau.

In grassland ecosystems, the occurrence and transmission of foliar fungal diseases are largely dependent on grazing by large herbivores. However, whether herbivores that have different body sizes differentially impact foliar fungal diseases remains largely unexplored. Thus, we conducted an 8-year grazing experiment in an alpine grassland on the Qinghai-Tibet Plateau in China and tested how different types of livestock (sheep (Ovis aries), yak (Bos grunniens), or both)) affected foliar fungal diseases at the levels of both plant population and community. At the population level, grazing by a single species (yak or sheep) or mixed species (sheep and yak) significantly decreased the severity of eight leaf spot diseases. Similarly, at the community level, both single species (yak or sheep) and mixed grazing by both sheep and yak significantly decreased the community pathogen load. However, we did not find a significant difference in the community pathogen load among different types of livestock. These results suggest that grazing by large herbivores, independently of livestock type, consistently decreased the prevalence of foliar fungal diseases at both the plant population and community levels. We suggest that moderate grazing by sheep or yak is effective to control the occurrence of foliar fungal diseases in alpine grasslands. This study advances our knowledge of the interface between disease ecology, large herbivores, and grassland science.

Individual‐plant selectivity by sheep in drylands scales‐up at plant population level and controls the forage supply and its accessibility

Abstract Diet selectivity by domestic herbivores controls plant community structure and dynamics and may induce rangeland degradation, particularly in drylands. However, management decisions frequently ignore herbivore selectivity. Here, we studied how grass morphology controls sheep selectivity for individual plants, and how this selectivity interacts with grazing intensity to determine population plant‐size distributions and the forage supply. In Patagonian steppes, we manipulated the plant morphology (size and standing‐dead proportion) of three dominant grass species differentially preferred by sheep for 4 years. Then, we evaluated how these morphological alterations affected intra‐ and inter‐specific preference patterns. We also evaluated how grazing intensity (ungrazed, moderate grazing and intensive grazing) affected the plant‐size distribution of the three species, the forage supply, and its accessibility. For the highly preferred species, herbivores selected plants that were either naturally or experimentally short, with low proportion of standing‐dead biomass. In contrast, morphological changes did not alter the within‐species selectivity of the least preferred species. Grazing intensity strongly changed the population plant‐size distribution of preferred species in ways that resembled the experimental manipulations of morphology. Moderate grazing showed the greatest morphological heterogeneity among individuals. When integrating the green biomass of forage species' individuals at ecosystem level, we found that the forage supply was the highest in ungrazed sites and decreased as grazing intensity increased. However, considering the dissuading effect of the standing‐dead proportion of plants, the accessible forage was the highest under moderate grazing. Synthesis and applications. Our findings (i) showed that, within preferred species, sheep selectivity at individual‐plant level is controlled by morphological characteristics that determine accessibility to green high‐quality biomass. This effect was as important as that of species identity; (ii) empirically proved plant–animal positive feedback at individual level; and (iii) revealed how the individual‐plant selectivity scales‐up at population level and controls the forage supply, but also its accessibility. Our complementary approach generates critical knowledge for developing management practices to control key forage species defoliation and to adjust the grazing pressure to the offer of accessible forage, avoiding the common carrying capacity overestimation. These aspects are essential for sustainable production in grazed drylands.

Effects of erect panicle genotype and environment interactions on rice yield and yield components

The dense and erect panicle (EP) genotype conferred by DEP1 has been widely used in the high-yield breeding of Chinese japonica rice varieties. However, the breeding value of the EP genotype has rarely been determined at the plant population level. As such, in this study, we aimed to identify the effect of the interaction of EP genotype and environment at different locations and times on rice yield and its various components. We grew two sets of near-isogenic lines (NILs) of EP and non-EP (NEP) genotypes with Liaojing 5 (LG5) and Akitakomachi (AKI) backgrounds in the field in 2016 and 2017 in Shenyang, China, and Kyoto, Japan. In 2018, these sets were grown only in Kyoto, Japan. The average yields of EP and NEP genotypes were 6.67 and 6.13 t ha−1 for the AKI background, and 6.66 and 6.58 t ha−1 for the LG 5 background, respectively. EP genotype positively affected panicle number (PN) and grain number per square meter (GNPM), mostly resulting in a positive effect on harvest index (HI). In contrast, the EP genotype exerted a negative effect on thousand-grain weight (KGW). The ratio of the performance of the EP genotype relative to the NEP genotype in terms of yield and total biomass correlated positively with mean daily solar radiation during a 40-day period around heading. We found the effectiveness of the EP genotype depends on the availability of solar radiation, and its effect is consistently positive for sink formation, conditional in terms of source capacity, and positive in a high-radiation environment.

Plant pathogens as introduced weed biological control agents: Could antagonistic fungi be important factors determining agent success or failure?

Mycoparasitic interactions are common in nature, form part of the microbiota of plants, and are considered significant contributors to fungus-fungus antagonism. Mycoparasites kill plant pathogens, protect the plant from abiotic and biotic stressors, and reduce disease incidence and severity at the plant population level. Their exploitation as biocontrol agents in agriculture is well documented. However, mycoparasites may potentially affect classical fungal biocontrol agents of invasive weed species. Classical biological control, or biocontrol, of invasive weeds involves the intentional introduction of exotic, usually co-evolved plant pathogens and insects, for permanent establishment and long-term control of the target plant. Agent establishment, effectiveness, and safety are the critical elements for a successful weed biocontrol programme. Establishment and effectiveness of agents on the invasive plant often vary throughout the invaded range with about two-thirds of weed biocontrol agents failing to suppress their target weed. There are many documented reasons why weed biocontrol agents do not establish or are ineffective when they do, and the presence and accumulation of natural enemies in the invaded range is one of them. Endophyte-enriched, invasive weeds and those forming mutualistic associations with indigenous, native endophytes could explain the lack of consistency of some classical biological control introductions. However, another variable could be factored into the mix: mycoparasitism, where one fungus parasitises another, the natural enemies of the plant's natural enemies. In this review article, we introduce the concept of invasive weed biocontrol and the history of using plant pathogens as biocontrol agents. We discuss the success and failure of fungal agent programmes and delve into the patterns of success or failure, with a focus on the potential antagonistic role of endophytes and mycoparasites.

Response of Different Levels of Nitrogen and Plant Population to Grain Yield of Winter Hybrid Maize in Chitwan Valley

A field experiment on “Performance of hybrid maize under different levels of nitrogen and plant population” was conducted in Randomized complete block design (RCBD) at the research farm of the National Maize Research Program (NMRP), Rampur, Chitwan during the winter season of 2015/16 to determine the optimum level of nitrogen and plant population for winter season hybrid maize. The grain yield (2.38 Mt ha-1) obtained in control without nitrogen was significantly lower in comparison to its all other levels (70, 140 and 210 Kg N ha-1). Moreover, grain yield (5.45 Mt ha-1) produced by the application 210 Kg N ha-1 was significantly superior over 70 Kg N ha-1 (3.83 Mt ha-1) but remained at par with 140 Kg N ha-1 (5.02 Mt ha-1) which also differed significantly. Moreover, the grain yield (4.98 Mt ha-1) recorded with the population of 101010 plants ha-1 was significantly superior over 55,555 (3.34 Mt ha-1) and 69,444 (3.90 Mt ha-1) plants ha-1 but similar to that of 85,470 plants ha-1 (4.46 Mt ha-1) which was also significantly higher as compared to 69,444 and 55,555 plants ha-1 which were at par with each other. Regression analysis for the effect of nitrogen and plant population on grain yield showed the grain yield was 145 Kg N ha-1 and plant population was 87445 plants ha-1. Thus, hybrid maize (RML95/RML96) can be successfully grown by applying 145 Kg N ha-1 and maintaining a population of 87 thousand plants ha-1 to achieve a higher grain yield during the winter season.

Plant Tissue Nutrient Concentration and Major Soil Nutrients Influenced by NPSB Fertilizer Rates and Plant Population of Maize (Zea Mays L.) at Bako, Oromia National Regional State

Plant nutrients such as nitrogen, phosphorus, potassium and sulfur are the nutrients frequently limit the yields of maize over the world. Nutrient recommendation should be based on the optimum yield and environmental save that can be through plant tissue analysis and soil test. This experiment was conducted at Bako Agricultural Research Center west region of Ethiopia Gobu Sayo using split plot desighn with three levels of plant population 53.333,66,666 and 76,923 plants per hectare on main plot and five level 0,100,150,200,250 kg/ha of NPSB fertilizer rates on sub-plots. Soil sample was taken from the plots pre-harvesting for composite sample and post-harvest from each plot and analyzed at Bako soil laboratory and Ethiopia water work design Addis Ababa for soil fertility management. Nutrient in plant tissue was analyzed at Holota Agricultural Research Center soil laboratory. Collected data was analyzed using Genstat computer statistical soft-ware package. The result of pre planting soil analysis showed soil of the study area was categorized as clay soil with medium and stable organic matter and low organic carbon and low total nitrogen that shows low soil fertility. The ANOVA result showed addition of fertilizer reduced soil pH from 5.7 to 5.47 and bellow. 150 kg/ha of NPSB which gave economically feasible yield 9460kg/ha moderately acidified the soil. This soil analysis result showed that the level at which fertilizer boost yield of maize. Only percent of phosphorus was changed due to plant population density. Plant tissue concentration at silking was significantly influenced by fertilizer rates. Potassium is at sufficiency range for all level of supplied fertilizer. Sufficient range nitrogen at silkin was recorded from the plot received 100-150 kg/ha which gave economically feasible yield. It is better to use fertilizer rate of 150kg/ha which shows sufficiency range for nutrient concentration of soil and plant tissue in leaf at silking stage. This finding is not the end for the area and further research should be carried out for feature. Keywords: plant tissue, soil, Zea mays L., Nitrogen, Phosphorus, Sulfur, potassium DOI: 10.7176/JBAH/12-13-04 Publication date: July 31 st 2022

Pilot Review Study on Yield Gaps and Cost Benefits of Different Sized Seeds of Bread Wheat (Triticum aestivum L.) Varieties

The main goal of this systematic pilot study is to determine the best plant population rate of bread wheat crop by identifying the most cost-effective varieties depending on their seed size in order to deliver an overview of some other bread wheat production management requirements in general and specifically in Ethiopia, comparing with current research trends as well as to make the appropriate seed rate recommendations for small, medium and large sized seeds reliant varieties, for better yield efficiency, grain quality and cost-effective benefits of bread wheat crop. This paper studied the proper application of the optimum plant-population’s reliant seeding rate under ideal environment availability of which may help in improving the yield capacity gaps by identifying the most cost-effective variety from so far conducted seed rate experiments depending on their seed size of bread wheat varieties. To optimize the plant-population’s dependent seed rate of wheat, some experiments have conducted so far across most wheat growing areas of Ethiopia. The field experiments were conducted in different times at Kulumsa Agricultural Research Center from July to November 2012. Quite similar field experiment was also conducted at Kulumsa Agricultural Research Center from June to 2018 cropping season, Three bread wheat varieties (Hidassie, Dendea and Shorima) representing different seed sizes of large, medium, small, respectively and four plant population levels of 250, 300, 350 & 400 plants m-2 were tested. The interaction effects of varieties seed size and plant population on grain yield showed statistically significant (p<0.01) variation, likewise biomass yield and straw yield indicated significant (p<0.05) variations. The grain yield resulted in (4.309 Ton ha-1), similarly biomass yield and straw yield are (11.00 Ton ha-1) and (5.28 Ton ha-1) respectively, and it suggests that these traits are generally enhanced by the genetic makeups of the variety Hidassie /large seed size. Economic analysis using partial budget procedure was performed on grain yields to determine the treatment with most profitable returns. The beneficial marginal rate of return (8.50) and benefit cost ratio (8.07) was obtained from the variety Hidassie/large seed size at a plant population of 300 seeds m-2 followed by a marginal rate of return (9.55) and benefit cost ratio (8.05) were also recorded again from the variety Hidassie/large seed size at plant population of 250 plants m-2. So the most cost-effective variety and plant population level for farmers with low cost of production and higher benefits were identified to be the variety Hidassie/large seed size at the plant population level of 300 plants m-2 in the rain fed cropping season is identified as low cost of production with highest benefit and can be recommended for the producers of bread wheat crop. The plant-population level of 250 plants m-2 for variety Hidassie/large seed size was also cost-effective with highest netbenefit and can be recommended as another possible choice

A Catalogue of Natural Enemies of Invasive Alien Plants in South Africa: Classical Biological Control Agents Considered, Released and Established, Exotic Natural Enemies Present in the Field, and Bioherbicides

A catalogue of natural enemies considered and released as biological control (biocontrol) agents against invasive alien plants in South Africa has been maintained for many years, and is updated here to include the period 2011-2020. The current catalogue reorders and separates data for exotic natural enemies that have been approved as classical biocontrol agents, from those on exotic natural enemies that have been considered but not released, exotic natural enemies that have been inadvertently introduced into South Africa with host plants that include target weed species, and locally sourced natural enemies that have been considered as bioherbicides. Ninety weed species have been targeted for biocontrol, with 310 exotic natural enemies considered, 136 classified as de jure or de facto classical biocontrol agents, and 92 established in the field on 66 target weeds. Ten of these species were found to have established independently of being released while research on them was in progress. An additional six exotic species have been found established on target weeds, and 11 locally sourced natural enemies have been considered for inundative or augmentative biocontrol, of which two have been developed commercially. Of the exotic natural enemies deliberately established, 35% inflict extensive damage to their host plants. Insects make up the majority of biocontrol agents (90%), with the balance of 8% being fungi and 2%, mites. Both establishment rates and damage levels vary between taxa. Five biocontrol agents previously considered established, have not been found in the field for several years and their persistence is in doubt. Outcomes of biocontrol at a plant population level are indicated for 54 target weeds on which agents have been established for over a decade. The increase in numbers of target weeds considered, as well as biocontrol agents released, over the past decade, has been enabled by continued generous funding and an efficient release-approval process.

Long‐term heavy grazing increases community‐level foliar fungal diseases by shifting plant composition

Abstract In grasslands, the interactions of foliar fungal diseases and their host plants are largely dependent on grazing by large herbivores. However, the relative importance of direct (i.e. pathogen removal) and indirect effects (i.e. via changes in plant community composition) of long‐term grazing on foliar fungal diseases remains largely unexplored, especially under varied grazing intensities. We conducted a 13‐year experiment to explore the effects of grazing intensity on foliar fungal diseases at both plant population and community levels in a semi‐arid grassland. We quantified the contributions of direct and indirect effects of long‐term grazing on community pathogen load. At the population level, the severity of five rusts and five powdery mildews decreased significantly as grazing intensity increased, whereas two leaf spots increased significantly in severity with increasing grazing intensity. Similarly, at the community level, the pathogen load of rusts and powdery mildews was negatively related to the increase in grazing intensity, whereas the pathogen load of leaf spots was positively related to grazing intensity. Overall, heavy grazing (i.e. 8.7 sheep/ha) significantly increased community pathogen load. Our SEM analysis showed that grazing indirectly increased the pathogen load of leaf spots by increasing disease proneness. Grazing decreased the pathogen load of rusts, but this could not be explained by changes in disease proneness. Overall, the indirect effects via changes in community composition of hosts resulting in the increase in community disease proneness outweighed the direct effect of grazing on community pathogen load. Synthesis and applications. Our study provides the first evidence that long‐term heavy grazing can indirectly increase community pathogen load by increasing the abundances of grazing‐tolerant hosts and decreasing the abundances of grazing‐intolerant hosts. These results provide empirical evidence that the pathogen load of foliar fungal diseases in grasslands can depend on the community context of hosts, which can, in turn, be controlled by large herbivores. We recommend that infectious diseases are considered when predicting the responses of grassland ecosystems to anthropogenic activities. Maintaining light to moderate grazing intensity or establishing an appropriate non‐grazing period could be an effective way to control foliar fungal diseases in grasslands.

Effect of Blended (NPSB) Fertilizer Rates and Plant Population on Yield and Yield Components of Maize (Zea mays L.) at Bako, Oromia National Regional State, Ethiopia

Maize (Zea mays L.) is the major cereal crop in Ethiopia and plays a crucial role in ensuring food security. However, its productivity is constrained by a number of problems, among which use of high or low plant population and poor soil fertility management are the most critical once. Therefore, a field experiment was undertaken to determine the optimal NPSB fertilizer rate and plant population for maize at Bako. The experiment was laid out in split plot design distributing three levels of plant population [53,333 plants ha -1 (25 x75 cm), 66,666 plants ha -1 (60x25cm) and 76923 plants ha -1 (65x20cm)] in the main plots and five levels of NPSB fertilizer rates (0,100,150,200 and 250 kg NPSB ha -1 ) and recommended NP rates as sub-plots. The interaction of plant population and NPSB rates influenced significantly (P<5 %) leaf area index, number of cobs plot -1 , number of kernel cob -1 , dry biomass and thousand kernel weight. The highest leaf area index 6.661 was recorded on the combination of 66,666 plants ha -1 with 200 kg NPSB fertilizer rate. The highest number of cob plot -1 (115.3) and dry biomass yield 28,299 kg ha -1 were recorded from 66,666 plant ha -1 with 150 kg NPSB ha -1 , and 53,333 plant ha -1 with standard check 92/69 kg NP ha -1 , respectively. The highest grain yield 9954 kg ha -1 with net profit of 76,038 Birr with marginal rate of return 598% was obtained from 150 kg NPSB ha -1 with 66666 plants ha -1 (60 cmx25 cm). Therefore, application of 150 kg NPSB ha -1 with 66666 plants ha -1 for farmers in the study area and with similar agro-ecology can use and can improve maize productivity. However, the experiment need to be further verified in multi-locations for better usage at different agro-ecologies. Keywords: plant population, blended fertilizer, maize, yield DOI: 10.7176/JNSR/12-21-04 Publication date: November 30 th 2021

Kin discrimination in allelopathy and consequences for agricultural weed control.

Among all biotic stress types (i.e. pathogens, pests and weeds), weeds have the largest potential for yield reduction (larger than the other two combined) (Oerke, 2006). Chemical control of weeds is coming under increasing pressure due to concerns about their health- and environmental impacts and increasing herbicide resistance of weeds. As a consequence there is an increased interest in ecological weed control, of which development of weed-suppressive crops can be an important part (Bastiaans, Paolini, & Baumann, 2008). In the current issue, Xu, Cheng, Kong, and Meiners (2021) for the first time, show that kin recognition (the ability of plants to distinguish genetically related individuals from strangers) can make rice plants more competitive against weeds potentially being a new strategy in ecological weed control. This article is protected by copyright. All rights reserved.

Maize-soybean intercrop silage yield and quality with different nitrogen levels and plant population

This study hypothesizes that maize-soybean intercrop with lower maize plant population and nitrogen levels can allow better soybean development and yield, which may offset lower maize biomass and silage crude protein yield. Experiment was carried out in a randomized complete block design arranged in a 2 x 5 factorial scheme, with three replications. Treatments consisted of two different maize-soybean plant stand (40,000 and 60,000 plants ha-1) and five nitrogen fertilization levels (0, 50, 100, 150, and 200 kg ha-1). As a result, soybean biomass yield increased at the lower maize plant stand, although, maize and total (maize + soybean) biomass yield were higher at the greater maize plant stand. Thus, individual maize plants and total dry matter yield increased as nitrogen levels were increased. However, there was no effect of the studied factors on the silage crude protein yield per area, indicating a great potential of soybean to offset biomass yield reduction trough silage quality improvement. Moreover, since there was no difference on total silage crude protein yield per hectare, it is suggested that the adoption of maize-soybean intercrop with lower maize plant stand (40 thousand maize plants ha-1) and with lower nitrogen values is a more environmentally friendly approach to increase farmland sustainability while decreasing environmental and productivity costs. Intermediate levels may be evaluated in future studies

Attaining higher biomass and steviol glycosides yields of Stevia rebaudiana through adjustment of plant population and nitrogen rate

Stevia rebaudiana is being cultivated in many parts of the world for its industrial uses as a low-caloric natural sweetener. However, the effects of plant population and nitrogen (N) levels and their interactions on biomass yield and steviol glycosides accumulation are not properly known in the mild-temperate conditions. Therefore, an experiment was laid out with ten treatment combinations having two plant densities (50,000 and 100,000 plants ha−1) and five N levels (0 to 160 kg ha−1). The overall dry leaf yield of stevia ranged from 1.74 to 3.35 Mg ha−1, while total steviol glycosides (SGs) concentration of the stevia leaf varied from 7.6 to 9.3%. The dense population (100,000 plants ha−1) registered about 64.9 and 71.8% higher dry leaf yields compared with thin population (50,000 plants ha−1) during 2014 and 2015, respectively. Irrespective of plant density, N at 120 kg ha-1 recorded significantly (P ≤ 0.05) higher dry leaf yields (3.35 and 2.83 Mg ha−1) compared with control during both the experimental years. However, substantially higher apparent N-recovery and agronomic N-efficiency were registered with lower doses (40−80 kg ha−1) of N. The total SGs yield (g plant−1) was not reduced with dense plantation. Similarly, the significantly higher total SGs yield was recorded with the application of N at 120 kg ha−1. The response curve suggests that the dense plantation and N up to 143 kg ha−1 can be practiced to increase dry leaf yield of stevia without sacrificing the production of total SGs under mild temperate conditions.

Review Study on the Effect of Different Varieties Seed Size to Yields and Economic Benefits of Bread Wheat (<i>Triticum aestivum</i> L.) Crop

The main goal of this study is to determine the best plant population level of bread wheat crop by identifying the most economic-effective variety’s seed size and to deliver an overview of wheat production management requirements in general and specifically in Ethiopia, comparing with current research trends as well as to make some recommendations on the appropriate seed rates for yields, and economic benefits of bread wheat. This paper reviewed that application of the optimum seed rate under ideal environment availability of which may help in improving yield and yield components of bread wheat. To optimize seed rate and plant density of wheat, some experiments have conducted so far across most wheat growing areas of Ethiopia. The field experiments were conducted in different times at Kulumsa Agricultural Research Center from July to November 2012. Quite similar field experiment was also conducted at Kulumsa Agricultural Research Center from June to 2018 cropping season, Three bread wheat varieties (Hidassie, Dendea and Shorima) representing different seed sizes of large, medium, small, respectively and four plant population levels of 250, 300, 350 & 400 plants m^-2 were tested. The interaction effects of varieties seed size and plant population on grain yield showed statistically significant (p<0.01) variation, likewise biomass yield and straw yield indicated significant (p<0.05) variations. The grain yield resulted in (4.309 Ton ha^-1), similarly biomass yield and straw yield are (11.00 Ton ha^-1) and (5.28 Ton ha^-1) respectively, and it suggests that these traits are generally enhanced by the genetic makeups of the variety Hidassie /large seed size. Economic analysis using partial budget procedure was performed on grain yields to determine the treatment with most profitable returns. The beneficial marginal rate of return (8.50) and benefit cost ratio (8.07) was obtained from the variety Hidassie/large seed size at a plant population of 300 seeds m^-2 followed by a marginal rate of return (9.55) and benefit cost ratio (8.05) were also recorded again from the variety Hidassie/large seed size at plant population of 250 plants m^-2. So the most cost-effective variety and plant population level for farmers with low cost of production and higher benefits were identified to be the variety Hidassie/large seed size at the plant population level of 300 plants m^-2 in the rain fed cropping season is identified as low cost of production with highest benefit and can be recommended for the producers of wheat crop.

Implementing a system in South Africa for categorizing the outcomes of weed biological control

The biological control of weeds, i.e. invasive alien plant species, depends on the release and establishment of host-specific plant-damaging insect, mite, or pathogen species from the country of origin of the target weed. These ‘natural enemies’ (agents) variously damage their target hosts and may reduce their vigor and invasiveness. Over time, populations of the target weed may be influenced and these outcomes can be observed and/or measured. The impacts of biocontrol agents and the outcomes of biological control are usually summarized using brief descriptive terms which have been previously defined and widely applied but are unsatisfactory from several viewpoints. Recently, a conceptual model was put forward that illustrates and categorizes the possible results of agent impacts at a plant population level. The details of releases of agents and their impacts against 54 species of target weeds in South Africa, since 1913, are given as elaborations of that system. Outcomes are categorized for different regions and habitats, according to measures of changes in density, biomass, area occupied, and rate of spread of the targeted weed species. The categorizations have been updated and verified through extensive consultations with local experts. The traditional descriptive assessments of outcomes in weed biological control have now been replaced in South Africa by implementing this more-rigorous system which may, with modifications, have wider applicability, in other regions or countries.