High Plant Population Density Research Articles

Effects of mepiquat chloride and plant population density on leaf photosynthesis and carbohydrate metabolism in upland cotton

BackgroundMepiquat chloride (MC) application and plant population density (PPD) increasing are required for modern cotton production. However, their interactive effects on leaf physiology and carbohydrate metabolism remain obscure. This study aimed to examine whether and how MC and PPD affect the leaf morpho-physiological characteristics, and thus final cotton yield. PPD of three levels (D1: 2.25 plants·m−2, D2: 4.5 plants·m−2, and D3: 6.75 plants·m−2) and MC dosage of two levels (MC0: 0 g·ha−2, MC1: 82.5 g·ha−2) were combined to create six treatments. The dynamics of nonstructual carbohydrate concentration, carbon metabolism-related enzyme activity, and photosynthetic attributes in cotton leaves were examined during reproductive growth in 2019 and 2020.ResultsAmong six treatments, the high PPD of 6.75 plants·m−2 combined with MC application (MC1D3) exhibited the greatest seed cotton yield and biological yield. The sucrose, hexose, starch, and total nonstructural carbohydrate (TNC) concentrations peaked at the first flowering (FF) stage and then declined to a minimum at the first boll opening (FBO) stage. Compared with other treatments, MC1D3 improved starch and TNC concentration by 5.4% ~ 88.4%, 7.8% ~ 52.0% in 2019, and by 14.6% ~ 55.9%, 13.5% ~ 39.7% in 2020 at the FF stage, respectively. Additionally, MC1D3 produced higher transformation rates of starch and TNC from the FF to FBO stages, indicating greater carbon production and utilization efficiency. MC1D3 displayed the maximal specific leaf weight (SLW) at the FBO stage, and the highest chlorophyll a (Chl a), Chl b, and Chl a + b concentration at the mid-late growth phase in both years. The Rubisco activity with MC1D3 was 2.6% ~ 53.2% higher at the flowering and boll setting stages in both years, and 2.4% ~ 52.7% higher at the FBO stage in 2020 than those in other treatments. These results provided a explanation of higher leaf senescence-resistant ability in MC1D3.ConclusionIncreasing PPD coupled with MC application improves cotton yield by enhancing leaf carbohydrate production and utilization efficiency and delaying leaf senescence.

Mepiquat chloride application combined with high plant population density promotes carbon remobilization in the roots of upland cotton

Carbon reserves in cotton roots can be remobilized to support reproductive growth, thus potentially affecting cotton yield. However, the regulation of carbon remobilization in cotton roots and its relationship with cotton yield are still poorly understood. Plant population density (PPD) and mepiquat chloride (MC) have been hypothesized to affect the dynamics of nonstructural carbohydrate content and the resulting carbon remobilization in cotton roots through the regulation of carbohydrate metabolism enzyme activities. A mid-maturation cotton line 4003–6 was field-grown in 2019 and 2020. Three different levels of PPD (D1: 2.25 plants m−2, D2: 4.5 plants m−2, and D3: 6.75 plants m−2) and two levels of MC dosage (M0: 0 g hm−2, M1: 82.5 g hm−2) were combined to create six populations differing in terms of the source–sink relationship. The changes in the hexose, sucrose, and starch contents and the key carbon metabolic enzyme activities in cotton roots were examined during peak squaring (PS) to late boll opening (LB). The combination of the PPD of 6.75 plants m−2 and MC application (M1D3) exhibited the greatest cotton yield and reproductive biomass–to–leaf area ratio from peak flowering (PF) onwards. M1D3 presented the greatest total nonstructural carbohydrate (TNC) remobilization amount of 2.96 and 3.80 g m−2, the highest efficiency of 39.11% and 48.39%, and the largest gross contribution to seed cotton yield of 0.66% and 0.79% in 2019 and 2020, respectively. The three parameters were positively correlated with the seed cotton yield except for the remobilization rate in 2019. Unlike the other treatments, the greater carbohydrate content per unit ground area in M1D3 prior to the PF stage was attributed to the higher sucrose phosphate synthase (SPS) and ADP-glucose pyrophosphorylase (AGPase) activities during the PS to first flowering (FF) stages. Conversely, the greater α-amylase and β-amylase activities in M1D3 at the PF stage accounted for the lower starch content at the EB stage, and the smaller vacuolar invertase (VIN) and cell wall invertase (CWIN) activities at the EB stage could be responsible for the lower hexose concentration at that time. The TNC remobilization amount had a positive association with the AGPase and SPS activities at the FF stage and with β-amylase activity at the PF stage in cotton tap roots in 2019 and 2020. This study provides a cotton yield-improving alternative through the promotion of carbon remobilization in roots using certain agronomic practices.

Response of Maize-Hybrids Phenology Under high Plant Population Density in parts of Northern Guinea Savanna of Nigeria

Plant distribution in the field, as affected by plant density, has been one area that has received a great deal of attention over the last several decades. Population density, whether directly on the plant or indirectly on biotic factors associated with plant density is one of the most important factors in determining physiological attributes of a crop. Maize grain yield has a parabolic response to stand density that maximizes yield, which is widely known by the crop managers, physiologists and breeders; together with the concept that this optimum stand density varies with the environment. Development of breeding populations and hybrids with improved tolerance to high plant densities should be an important part of maize breeding programs. A field experiment was therefore conducted during 2015 and 2016 rainy season at Tudun Wada, Kano and Shika, Zaria in the Northern Guinea savanna of Nigeria in order to assess the phenological components of maize-hybrids at high plant population density. The experiment consisted of two plant populations of 53,333 plantha-1 and 88,888 plantsha-1 as main plot and eight recently developed drought–tolerant maize hybrids: M0826-7, M0926-8, M1026-10, M1026-13, M1124-4, M1124-10, M1227-12 and M1227-14 and two widely cultivated commercial hybrids as controls (Oba-98 and Oba super-1) as sub-plots laid out in a randomized split-plot design and replicated three times. Maize-hybrids responded to high plant population density in the two locations. Increasing plant population significantly decreased the phenology of maize-hybrids, which showed better adaptation of hybrids to high plant population density. Hybrids showed shorter days to maturity and shorter anthesis-silking interval. Maize-hybrids performed better at Zaria than at Tudun Wada because rainfall was higher and better distributed in this location. However recent hybrids were more tolerant to high plant population than the commercial hybrids, therefore the recently released maize-hybrids were more adapted to biotic stress.
 Keywords: Biotic stress, Growth, Phenology, Plant population density and Maize-hybrids

Relay Cropping Mung Bean by Plant Density and Row Arrangements with Maize on Yield and Yield Components of Component Crops at Jejebicho, Southern Ethiopia

Maize is among the most important cereal crops in Ethiopia. Rely-intercropping of mung bean between maize enable to get grain yield of maize instead sole alone. Field experiment was conducted to assess the effects of relay intercropping mung bean at different population density and row arrangements with maize yield components and yield of the component crops, to evaluate the productivity and economic value of maize-mung bean intercropping at Sankura Wereda Jejebicho research station in 2019-2021 main cropping season. Three spatial row arrangements (1:1, 1:2 and 1:3) with four population densities (PD) (25%, 50%, 75% and 100%) were intercropped with maize variety ‘Shone’. Each of the component crops were included as a sole for comparison. Randomized complete block design in factorial with three replications was used. days to tasselling, days to physiological maturity, leaf area, leaf area index, hundred kernel weight, grain yield and harvest index of maize significantly affected by the interaction effects of population density and spatial arrangements of mung bean. The highest (8.19 ton/ha) grain yield of maize was obtained from 100% population density and 1:3 spatial row arrangement of mung bean. This may due to the presence of high interspecific competition with related high plant population density per plot area compared to other treatments. Whereas the highest grain yield mung bean (18.54 Quintal/ha) was obtained from when mung rely intercropped with 100% population density and 1:3 row arrangements. The highest thousand seed weight (42.18g) was recorded from 25% population density and 1:1 row arrangements of mung bean. The maximum Land equivalent ration value was calculated from 1.88 from 100% population density in 2019 cropping season. The highest monitory advantage index value 110,280 Ethiopian birr) was obtained from 100% population density with all the three spatial row arrangement of mung bean. Therefore, this experiment could be recommended for mung bean rely cropped with maize by 100% population density and 1:3 row arrangement able the famers to get better grain yield of maize as well as mung bean.

Combining ability of S3 maize inbred lines and related contributing traits for high yield under high population density

The productivity of maize may be increased by using maize hybrid ideotype (erect leaves and small leaf angles) which is adaptive under high plant population density. The hybrids maize was desirable in increasing the plant density due to better light interception and space so that it can increase the yield per unit area. The aim of the research was to assess S3 lines that had good combining ability and to determine the traits associated with high yields under high plant population density (83.333 plants/ha). A total of 242 hybrids (F1) were examined from a crossed combination of 121 lines x 2 tester were evaluated with three commercial hybrid varieties such as Bisi 18, P 27, and P 36. The evaluation was carried under high plant population density (83,333 plants/ha) in the rainy season (November 2020 – February 2021). The research used an alpha lattice design with three replications. The results showed that the inbred lines had a greater effect on the yield character and yield components, while the leaf angle and leaf orientation effected by the tester. The lines that had good general combining ability for high yielding were M3B11P27T3-11-3-1, P27M3B11T3-1-4-2, P27M3B11T3-1-2-1, M3B11P27T3-8-4-1, P27M3B11T1-7-1-1, M3B11P27T1-1-1-3. The yield range of the hybrids were 8.43-9.90 t/ha, significantly higher than Bisi 18, P 27, P 36 varieties were 7.13 t/ha. Traits such as small leaf angle, erect leaf, root and stem lodging resistance, stem diameter, leaf length, ear diameter, and kernel row number were significantly correlated with high yield under high plant population density.

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.

Grain Yield, Crop and Basal Evapotranspiration, Production Functions and Water Productivity Response of Drought-tolerant and Non-drought-tolerant Maize Hybrids under Different Irrigation Levels and Population Densities: Part I. In Western Nebraska’s Semi-

Abstract.Grain yield, crop evapotranspiration (ETc), basal evapotranspiration (ETb), ETc-yield production functions (ETYPF), and crop water use efficiency (CWUE) response of three drought-tolerant (DT) and one non-drought-tolerant (NDT) maize ( L.) hybrids to two plant population densities (PPDs) [84,000 plants ha-1 (high PPD) and 59,300 plants ha-1 (low PPD)] and three irrigation levels were researched at two semi-arid locations: North Platte (WCREC) and Scottsbluff (MAL), Nebraska, in 2010, 2011, and 2012. The irrigation levels were fully irrigated (FIT), early cutoff (ECOT), and rainfed (RFT). Precipitation in 2010 was above average, 2011 was a normal year, and 2012 was one of the driest and hottest years in Nebraska’s recorded history. Generally, DT hybrids performed better than the NDT hybrid. The performances of the DT hybrids were stronger in the driest year and driest location (MAL), especially with low PPD. ETc exhibited inter-annual variation for the same hybrid in the same location and between the two locations and also with the PPD and irrigation treatments. There were significant differences (P<0.05) between the ETc values for the same hybrids across three irrigation treatments. The grain yield response to hybrids and treatments also exhibited substantial variation for the same hybrid between the PPDs and had inter-annual variation between the years and locations. The greatest grain yields of 14.6 and 18.0 Mg ha-1 were observed with 548 and 837 mm of ETc, which were recorded for the DT hybrid H3 (high PPD) at WCREC and MAL, respectively. There were significant differences (P<0.05) in performance among the DT hybrids in performance variables (ETc, ETb, ETYPF, CWUE). In most cases, the DT hybrids produced greater grain yield than the NDT hybrid with lower ETc. In terms of ETYPF response for individual hybrids, the slope of the production functions exhibited an inter-annual variation between the hybrids and for the same hybrids between the years and location for both high and low PPDs. All hybrids exhibited a linear yield response to increasing ETc in all years at both locations with positive slopes in all cases with DT hybrids having the greatest slopes. The ETb values also exhibited a substantial variation between the hybrids, years, locations, and PPDs. Generally, DT hybrids had sizably lower ETb values than the NDT hybrid in both PPD levels. It was concluded that DT hybrids increase the grain yield production per unit of ETc in semi-arid regions not only during very dry and hot year, but also during the growing season with favorable rainfall and climate conditions. Keywords: Basal evapotranspiration, Drought-tolerance, Maize, Yield production functions.

Grain Yield, Crop and Basal Evapotranspiration, Production Functions, and Water Productivity Response of Drought-tolerant and Non-drought-tolerant Maize Hybrids under Different Irrigation Levels, Population Densities, and Environments: Part II. In South-c

Abstract. Information and data on newer drought-tolerant maize hybrid response to water in different climates are extremely scarce. This research quantified the performance of non-drought-tolerant (NDT) (H1) and drought-tolerant (DT) (H2, H3, and H4) maize ( L.) hybrids response to grain yield, crop evapotranspiration (ETc), basal evapotranspiration (ETb), ETc-yield production functions (ETYPF), and crop water use efficiency (CWUE) at three irrigation levels and two plant population densities (PPDs) at two locations (transition zone between sub-humid and semi-arid climates at Clay Center (SCAL), Nebraska, in 2010 and 2012; and in a sub-humid climate at Concord (HAL), Nebraska, in 2010, 2011, and 2012). Irrigation treatments were: fully irrigated (FIT), early cutoff (ECOT) (i.e., no irrigation after blister stage), and rainfed (RFT) under two PPDs of 59,300 plants ha-1 (low PPD), and 84,000 plants ha-1 (high PPD). Generally, DT hybrids performed superior to NDT hybrid consistently at both locations, treatments, and years. DT H3 and DT H4 had highest grain yield consistently at SCAL and HAL, respectively. DT H3 and H4 hybrids’ productivity was not only superior in the RFT, but also in FIT. The highest yield of 16.3, and 15.3 Mg ha-1 were achieved by DT H3 (high PPD) and DT H2 (high PPD), respectively, associated with 471 and 590 mm of ETc in the FIT in 2012 at SCAL, and HAL, respectively. In most cases, all hybrids had highest grain yield under low PPD than high PPD at the RFT. All hybrids exhibited a linear yield response to increasing ETc in all years at both locations with positive slopes in all cases. The individual ETYPF response for individual hybrids had inter-annual variation in slopes between the hybrids and for the same hybrids between the years and location for both low and high PPDs. The ETYPF slopes ranged from 0.004 to 0.102 Mg ha-1 mm-,1 including all treatments (i.e., irrigation and PPDs) at SCAL for 2010 and 2012; and they ranged from 0.008 to 0.057 Mg ha-1 mm-1 including all treatments at HAL for 2010, 2011, and 2012. The ETb values exhibited inter-annual variation for the same hybrid between the irrigation levels, PPDs, and locations and they also exhibited an inner-annual variation between the hybrids and treatments in a given year with DT hybrids having consistently lower ETb values than the NDT hybrid. The greatest CWUE values were found in DT hybrids consistently at both locations. The DT hybrids can significantly increase yield productivity as well as crop water productivity per unit of ETc with respect to conventional hybrids not only in dry conditions, but also in average or above average years in terms of precipitation. Keywords: Basal evapotranspiration, Crop evapotranspiration, Drought-tolerance, Efficiency, Maize, Production functions.

SUNFLOWER OIL YIELD RESPONSES TO PLANT POPULATION AND ROW SPACING: VEGETATIVE AND REPRODUCTIVE PLASTICITY

Attempts have not been made to increase the potential yield of sunflower via the combined use of high plant populations and crowding-tolerant cultivars, an approach that has been successful in maize -another strong apical dominance crop. This may be due to the negative effects of increased disease pressure and increased susceptibility to lodging at high sunflower plant populations. Information on crop yield responses to plant populations higher than usual recommended commercial plant populations is also limited. Wide inter-row spacing could shift crop water consumption towards later developmental stages with positive effects on yield in seasons of low rainfall, but might also limit crop yields in years with good rainfall. Here we report on studies aimed at examining yield (both oil and total biomass) responses to changes in plant population at two inter-row spacings: 0.7 and 1.4 m, in crops grown without restrictions due to water or nutrients, and protected from insects and diseases. Oil yields in the 0.7 m row spacing treatments increased over the whole of the 2.0-14.3 plants m-2 range, reaching values much greater than those obtainable at the current commercial plant population of around 5.1 plants m-2. This increase reflected a continuous increase with increased plant population for total crop biomass, together with an unchanging harvest index. Over the 2-7 plant m-2 range of plant populations shared between the two row spacing treatments yields were not affected by spacing. Vegetative and reproductive plasticities, as reflected in the responses of biomass and plant leaf area at mid-anthesis to ground surface area per plant (vegetative plasticity indicators) and oil yield per plant to ground surface area per plant (reproductive plasticity indicator) did not vary over the 2.0-14.3 plant m-2 plant population range in either row spacing. In the 0.7-m row-spaced crops, reproductive plasticity was less than vegetative plasticity and a similar tendency was observed at the 1.4-m row spacing. Floret number and achene number per plant together with unit achene weight decreased over the 2.0-14.3 plant m-2 range for both row spacings, while fertility ratio over the same range was stable. Over the same range of plant population, achene oil concentration fell slightly, while achene oil content increased slightly and then stabilised. The study of the genetic basis of the plasticities found in this work should contribute to breeding programs aimed at increasing crop tolerance to high plant population densities.

Effects of plant population density and root-induced cytokinin on the corn compensatory growth during post-drought rewatering

The effect of plant population density (PPD) and root-induced leaf cytokinin on the compensatory growth of potted corn seedlings during post-drought rewatering was investigated. The study design comprised four treatments: (1) wetness with low PPD, (2) wetness with high PPD, (3) rewatering with low PPD, and (4) rewatering with high PPD. Results showed that drought stress restrained the growth of corns. By contrast, rewatering enhanced the net photosynthetic rate and growth of corns. During the 8 days of rewatering, compensatory growth during post-drought rewatering occurred in corns with high PPD; however, such compensatory growth did not occur in corns with low PPD. Zeatin riboside concentrations in leaves and xylem saps were significantly higher under rewatering treatment than those under wet treatment. High leaf cytokinin concentration accelerated corn growth. The coefficients of variation and Gini-coefficient of wet treatment were significantly higher than those of rewatering treatment under high PPD, demonstrating that intense intraspecific competition occurred in the wet treatment. Extreme intraspecific competition negatively affected net photosynthetic rate. In brief, the interactions between root-induced leaf cytokinin and weak intraspecific competition promoted the compensatory growth under high PPD.

Physiological differences between sugar beet varieties susceptible, tolerant or resistant to the beet cyst nematode, Heterodera schachtii (Schmidt) under uninfested conditions

The beet cyst nematode (BCN) is a problem to sugar beet growers around the world and can cause severe yield losses. Recently, varieties of sugar beet have been developed which are either tolerant to damage caused by BCN, or alternatively are resistant to BCN. Little is understood about these varieties and how they may have different physiological characteristics when compared with varieties of sugar beet that are susceptible to BCN. This study assessed a range of nine varieties, which were tolerant, susceptible or resistant to BCN, in pot and hydroponic tank investigations to measure differences in their canopy, early rooting and yield traits in the absence of BCN. Two field experiments, using four varieties which were susceptible, resistant or tolerant to BCN, then followed to test the hypothesis that increasing the plant population density (PPD) allows a BCN resistant variety to achieve a greater yield. In the pot and hydroponic experiments, it became clear that the varieties had different growth habits. The resistant variety yielded the least sugar and had the smallest canopy per plant. In the field experiments, which were not infested with BCN, in both years the resistant variety also showed a delayed canopy expansion compared to the other varieties. The rate of expansion could be increased by increasing the PPD. In 2016 this increased PPD resulted in higher yields of the resistant variety. However, due to better canopy development in the following year, a yield penalty was found in 2017 at higher PPDs. Understanding how different varieties need different PPDs may make resistant varieties a more economical option to cultivate in the future. However, the levels of impurities, particularly sodium impurities, in the resistant plants may still make them a less favourable choice to grow. The light tolerant varieties showed a distinct increased rooting and canopy expansion rate compared to the other variety types, while the tolerant varieties showed similar rooting and canopy traits to the susceptible varieties but had different yield responses to increased seed rate.

Maize Yield Potential and Density Tolerance

Maize (Zea mays L.) yield potential has not undergone genetic improvement during the hybrid era, yet substantial genetic improvement has occurred for tolerance to high plant population densities. As many crops including maize are approaching yield plateaus, it may be necessary to exploit other means of increasing grain yields. In this study, we examine potential reasons for why this occurred. Using a four‐way breeding cross representing the commercial germplasm pool, we demonstrate that the lack of genetic improvement in yield potential is not due to the two attributes being antagonistic. We then demonstrate that the lack of genetic improvement in yield potential is not due to density‐tolerant genotypes being higher yielding at modern conventional plant densities. We show that physiological differences in partitioning dry matter to the grain (i.e., harvest index [HI]) are present in a set of genotypes with contrasting yield potential and density tolerance genotypes. However, a higher or a lower HI is not associated with yield potential either. Finally, we show that the density‐tolerant genotypes exhibit a static kernel set efficiency (KSE), meaning that regardless of the plant growth rate at silking (pGRS), the number of kernels formed per unit dry matter fixed is constant. Surprisingly, the hybrids with high yield potential possess a dynamic KSE and are capable of sustaining kernel set at higher levels when pGRS is low. Given our findings, there is no apparent biological or genetic explanation for genetic improvement in only density tolerance during the hybrid era.

Mepiquat Chloride Effects on Castor Growth and Yield: Spraying Time, Rate, and Management

The use of plant growth regulators on castor (Ricinus communis L.) plants may be an alternative to reduce excessive vegetative growth, which would ease harvest and even increase seed and oil yield. This study aimed to evaluate the effects of both spraying time and rate of the plant growth regulator mepiquat chloride (MC) on growth parameters, yield components, seed yield, and seed oil content of castor cultivar IAC 2028 cultivated under high plant population density conditions in a spring–summer growing season in Botucatu, southeastern Brazil. One greenhouse experiment and two field experiments were performed. Mepiquat chloride application reduced leaf growth, height, and dry matter (DM) and increased the shoot/root ratio of castor plants. When sprayed during the vegetative phase (expanded leaf at nodes 6–8 of the primary stem), MC reduced the height and DM of castor plants; however, application during the first raceme flowering or at two sequential times (expanded leaf at the eighth node of the primary stem and third expanded leaf on a secondary stem) was more effective at reducing plant height and increasing seed yield. Spray rates between 100 and 200 g a.i. ha−1 of MC resulted in lower plant height and a greater number of filled fruits per raceme (24.0–38.8%), seed weight (2.6% in one experiment), and seed yield (17.4–33.1%). The increased number of filled fruits per raceme in response to MC application influenced seed yield. Mepiquat chloride spraying did not affect castor seed oil content.

Optimizing nitrogen application rate and plant density for improving cotton yield and nitrogen use efficiency in the North China Plain.

Plant population density (PPD) and nitrogen (N) application rate (NAR) are two controllable factors in cotton production. We conducted field experiments to investigate the effects of PPD, NAR and their interaction (PPD × NAR) on yield, N uptake and N use efficiency (NUE) of cotton using a split-plot design in the North China Plain during 2013 and 2014. The main plots were PPDs (plants m−2) of 3.00 (low), 5.25 (medium) and 7.50 (high) and the subplots were NARs of 0 (N-free), 112.5 (low), 225.0 (moderate) and 337.5 (high). During both 2013 and 2014, biological yield and N uptake of cotton increased significantly, but harvesting index decreased significantly with NAR and PPD increasing. With NAR increasing, internal nitrogen use efficiency(NUE) decreased significantly under three PPDs and agronomical NUE, physiologilal NUE, nitrogen recovery efficiency(NRE) and partial factor productivity from applied nitrogen (PFPN) also decreased significantly under high PPD between two years. Lint yield increment varied during different PPDs and years, but NAR enhancement showed less function under higher PPD than lower PPD in general. Taken together, moderate NAR under medium PPD combined higher lint yield with higher agronomic NUE, physiological NUE, and NRE, while low NAR with high PPD would achieve a comparable yield with superior NRE and PFPN and high NAR under high PPD and medium PPD produced higher biological yield but lower harvest index, lint yield and NUE compared to moderate NAR with medium PPD. Our overall results indicated that, in this region, increasing PPD and decreasing NAR properly would enhance both lint yield and NUE of cotton.

Plant anatomy as a tool for evaluating the effect of different levels of nitrogen, plant population density, row spacing and irrigation on kenaf (Hibiscus cannabinus) fibre development

Kenaf (Hibiscus cannabinus) provides high-quality fibre that is used in papermaking, building materials and absorbents. The study aims were to conduct a proper anatomical study of fibre development in kenaf stems, and to investigate if the number of fibre wedges, fibre rings (layers) and fibre bundles can be used as a tool to determine fibre development response to different agronomic practices. The practices evaluated included different nitrogen levels (0, 50, 100 and 150 kg N ha−1) under both rainfed and irrigated conditions, as well as different combinations of plant population densities (300 000, 400 000, 500 000 and 600 000 plants ha−1) and row spacing (0.17, 0.34 and 0.50 m) under rainfed conditions. In most cases N, water and plant population density were the principal factors affecting the number of fibre rings and fibre bundles, but not the number of fibre wedges. Higher levels of N and more water increased the number of fibre rings and fibre bundles, whereas at higher plant population densities, these decreased. No clear trends were observed with regards to row spacing. The results of this study suggested that under local conditions, 150 kg N ha−1 applied in two splits, 300 000 plants ha−1 and 0.50 m row spacing was the optimal combination of agronomic practices in terms of fibre development per plant. This paper gives a more complete explanation of fibre development in kenaf and shows how plant anatomy can be used as a tool to assess fibre development.

English

Haricot beans are the most important food and cash crop for most of the Ethiopian farmers. However, bean stem maggot (BSM) (Ophiomyia species) is limiting the production of the crop particularly in dry areas. Three species are involved in the infestation: Ophiomyia phaseoli, Ophiomyia spencerlla and Ophiomyia centrosematis. Two decades ago, two management options of BSM were developed and used for the last twenty years. However, there is a tendency of decline in effectiveness. Hence, the current experiment was conducted to see the age effect  on the efficacy of BSM resistant varieties (Beshbesh and Melkae) and  high bean plant population density (400,000 plants ha-1) (narrow spacing). The experiments were conducted at Shalla (southern Ethiopia) and Omonada (Jimma). Randomized Complete Block Design (RCBD) in three replications was used as the experimental design. The plot size was 10 m × 10 m. The experiment was conducted in 2014 and 2015. The treatments were BSM resistant varieties (Beshbesh and Melkae), high bean plant population, standard check (Awash-1) and Imdalem (seed dressing chemical). For plant population treatment and Imdalem 70% WS seed treatment a bean variety Awash-1 was used as a planting material. Data collected include stand count, seedling percent mortality by BSM, vigorously score, number of larva per plant and grain yield. The data were analyzed using SAS software and mean separation was done by Tukey Standardized Range Test (p<0.05). In all parameters measured, Melkae bean variety become susceptible to BSM and cannot be used any more as a resistant variety. From the result of the experiment, it can be concluded that Beshebeshe bean variety, high plant population and Imdalem seed dressing can be used as integrated management of BSM in Ethiopia in general and study sites in particular.   Key words: Bean stem maggot, Imdalem 70% WS (Imdachloprid), seed dressing, plant population, resistant variety, two decades, proven technology.

Does increasing plant population density alter sugar yield in high stalk-sugar maize hybrids?

Escalating demands for food and green energy have renewed interest in the dual-purpose use of maize (Zea mays L.) for a biofuel and high-energy forage crop. Recently, maize hybrids with high stalk-sugar (sugarcorn) have been developed. It is important to determine how agronomic practices, for example altering plant population density (PPD), affect stalk-sugar yields of these newly developed hybrids and to advance knowledge required for producing sugarcorn as a dual-purpose bioenergy–high energy silage crop in short-season regions unable to grow sugarcane. A field experiment was conducted for 3 years to assess the effect of PPD on stalk-sugar accumulation, dry matter production, silage and sucrose yields of sugarcorn compared with two commercial silage hybrids. Targeted PPD ranged from 75 000 to 150 000 plants ha–1 in increments of 25 000 plants ha–1. We found that increasing PPD from 75 000 to 125 000 plants ha–1 increased stalk sugar concentrations by up to 25% in some of the sugarcorn hybrids, with minimum change in the conventional check hybrids. The sugarcorn hybrid CO348 × C103 had the highest stalk sugar concentration (128 g kg–1) and sucrose yield of up to 3.8 Mg ha–1 at the targeted PPD of 125 000 (or actual 118 000 ± 7000) plants ha–1. By contrast, the check silage hybrids produced at most 2.0 Mg ha–1 of sucrose yield with much lower stalk sugar concentrations (53–65 g kg–1). Sugarcorn hybrids had generally lower grain yield with greater plant barrenness (the failure of a plant to produce a normal ear) and severer head smut infestation than the conventional silage hybrids. Our results suggest that as a silage crop, the current recommended PPD of 75 000–85 000 plants ha–1 for commercial silage maize production in the region is likely suitable for sugarcorn, and a higher PPD is required if sugarcorn hybrids are designated as a biofuel crop or for dual-purpose use.

Transforming the Plasticulture Production System through Novel Bed Geometry Design

Raised-bed plasticulture with drip irrigation is used worldwide for growing high-value crops, especially vegetables. This high-input, intensive system must become more efficient to meet food demands while reducing its environmental footprint. Futuristic tall and narrow compact beds were designed with an aim to improve the plasticulture system by increasing or maintaining yield while decreasing system input requirements. Using a whole-systems approach, compact geometries were evaluated on an example crop, eggplant ( L.), in the ecologically sensitive but highly productive sub-tropical Everglades region of Florida. Two compact beds, 61 cm (width) x 25 cm (height) and 45 cm x 30 cm, were evaluated against a conventional short and wide bed, 91 cm x 15 cm. The conventional bed used two drip tapes for irrigation and fertigation. The compact beds needed only one tape but produced equivalent yields as the conventional bed. Irrigation, nitrogen, and phosphorus application rates were respectively reduced by 50%, 14%, and 19% in the compact beds. Water and nutrient productivities with the compact beds increased by at least $43 per 10 kL irrigation, $6 per kg nitrogen, and $8 per kg phosphorus applied, representing respective gains of 92%, 11%, and 8% over the conventional bed. Productivity increases highlight how compact beds can make plasticulture more efficient. Shifting to compact beds also brings non-water co-benefits, including reductions in the system‘s production costs by $560 to $670 ha -1 , carbon footprint by 5% to 10% (reduced fumigant and plastic usage), agricultural plastic waste, and potential detrimental impacts from changed climate. Compact beds provide flood and disease protection by decreasing impervious (mulched) surface area and having extra bed height above the ground. Use of compact beds at the study farm would decrease rainfall intensity in the row middles by 34% and increase the farm‘s soil water storage capacity by 52% (1.4 cm). Increased storage and infiltration of rainfall will decrease flooding frequency and runoff volume, thereby reducing peak flows in downstream environments. Compact beds also have an added economic benefit for farmers who pay to lease land, as production can be increased through a higher plant population density without changing total mulched surface area. A cultural shift to taller and narrower compact beds makes plasticulture more sustainable as water, nutrient, cost, and energy inputs are reduced without sacrificing yields. Compact beds provide the impetus to transform plasticulture to a futuristic, further-optimized system that is more automated (e.g., chemigation), less labor intensive, and better adapted to climate change for continued economic and environmental viability.

Cropping systems and the prevalence of giant ragweed (Ambrosia trifida): From the 1950’s to present

Over the course of the past two decades, giant ragweed (Ambrosia trifida L.) has become an important weed of arable lands in many parts of the United States and Canada. Its shift from a primarily ruderal weed to one commonly found in row crop production has coincided with advancements in maize and soybean production practices and the associated fluctuations in the area seeded to each of these major crops. A field trial was conducted over three years to explore how cropping systems practices representative of distinct eras of maize and soybean production (i.e., the 1950s, 1980s and 2000s) influenced giant ragweed’s ability to grow, develop and successfully reproduce within a crop field. Maize hybrids and soybean cultivars bred in each era were seeded in separate split plot designs with era of production practices as the whole plot and time of giant ragweed transplanting (i.e., at crop emergence or 14 days after) as the split plot. Results of this study indicate that historic changes brought about through maize breeding and shifts in cropping systems practices have increased the capacity of this crop to suppress the growth and reproduction of giant ragweed. Conversely, the phenotypic shift of soybean from a vine to a more upright row crop, coupled with the relative lack of change in production practices, has had little impact on its weed suppressive capacity. Giant ragweed’s ability to overtop soybean, even when placed at a competitive disadvantage by delayed emergence, creates a situation where the control of giant ragweed seed production is almost exclusively dependent on the availability and efficacy of in-crop herbicide options. In contrast, there is a clear potential for the suppression of giant ragweed fecundity when modern maize hybrids, planted at high plant population densities, are provided a 14d weed-free window following emergence.

Genomewide Selection to Introgress Semidwarf Maize Germplasm into U.S. Corn Belt Inbreds

ABSTRACTSemidwarf maize (Zea mays L.) could be grown in new areas of production or in alternative crop rotations. Our objectives were to determine (i) if genomewide selection is useful for the rapid improvement of an exotic × adapted cross, (ii) if genomewide selection is more effective than phenotypic backcrossing for a trait with major genes, and (iii) the extent to which the high grain yield of nondwarf maize can be combined with the reduced stature and adaptability to high plant population densities of semidwarf maize. We conducted four cycles of genomewide selection in two semidwarf × adapted crosses. Phenotypic backcrossing was also done until the BC4 with selection for short plants. The accuracy of genomewide predictions in Cycle 0 was 0.67 to 0.70 for plant height and 0.57 to 0.70 for grain yield. Genomewide selection from Cycle 1 until Cycle 5 either maintained or improved on the gains from phenotypic selection achieved in Cycle 1. Observed gains generally agreed with predicted gains. Cycle 5 did not always have the best mean performance. Unfavorable genetic correlations made it difficult to select for short plants with high grain yield. Linkage disequilibrium between markers declined as selection progressed. Compared with phenotypic backcrossing, genomewide selection led to better mean performance and a higher proportion of exotic germplasm introgressed. To our knowledge, this is the first empirical study on genomewide selection to improve an exotic × adapted cross.