Low Plant Population Densities Research Articles

Genotype-dependent responses of Andean and Coastal quinoa to plant population density for yield and its physiological determinants in Northwest Argentina

Context In quinoa, similar yields are found under a wide range of plant population densities due to its phenotypic plasticity. Aims This study aimed to identify optimal plant population densities for achieving attainable yields, in relation to the most adapted genotype for a given environment. Methods Andean (RQ252 and RQ420) and Coastal (Titicaca and Puno) genotypes were tested at conventional (14 plants/m2) and low (7 plants/m2) plant population densities, in Dry Valley and Highland mega-environments for 2 years. Key results More than 64% of total variation was explained by genotype, location, and interaction effects for grain yield, biomass, and harvest index. For these variables, the genotype × location × plant population density term presented the highest percentage of variation among triple and quadruple interaction terms. In the Highlands, grain yields decreased with plant population density for Andean genotypes (30–40%), in contrast to lower reductions for Coastal genotypes (9–20%). In the Dry Valleys, no effect of plant population density was found for all genotypes. In the Highlands, reductions in biomass and harvest index explained grain yield response, in parallel with increases in small grain percentage of up to 16% when frosts came early, related to uneven maturity at low plant population density. Conclusions Attainable yields in Northwest Argentina were achieved by exploring local adaptation and response to plant population density of Andean genotypes in the Highlands, in contrast to stable yields of Coastal genotypes through locations and plant population densities. Implications Understanding genotype-dependent responses to plant population density according to Northwest Argentina mega-environments can reduce yield gaps in quinoa production and refine breeding strategies.

Grain yield and kernel setting of multiple-shoot and/or multiple-ear maize hybrids

Rainfed maize ( Zea mays L.) crops in low-rainfall regions are cultivated at very low plant population densities that favor the production of fertile tillers or multiple ears in the main shoot. Little information exists regarding the functional processes governing grain yield and kernel setting on ears of different order of shoots of maize crops. To study these functional processes, field experiments were conducted cultivating two commercial maize hybrids (AX7784 and DM2738) under supplementary irrigation using different plant densities, N rates at sowing, shading around female flowering (silking) and tiller removal treatments. Hybrids differed in the number of tillers per plant at R 1 (AX7784 > DM2738). Early tiller removal increased main shoot growth rate around silking, suggesting competition for light among shoots. Kernel number per plant was positively and curvilinearly related with plant growth rate around silking, i.e. critical period (PGR CP ), in tillered and non-tillered plants of both hybrids. Tillered plants set higher kernel numbers than non-tillered plants at PGR CP > 9 g pl -1 d -1 (AX7784) or 11 g pl -1 d -1 (DM2738), while the opposite trend occurred at PGR CP values < 9 g pl -1 d -1 (both hybrids). In both hybrids, the combination of a higher biomass partitioning to but a lower reproductive efficiency of ears of tillers than of main shoots resulted in a lower kernel number for tillers than for main shoots. Genotypic differences were evident in kernel setting between main shoots (DM2738 > AX7784) and tillers (AX7784 > DM2738). The different pattern of kernel setting between hybrids was explained by differences in the biomass partitioning to tiller ears and the reproductive efficiency of ears of tillers (AX7784 > DM2738), and both the biomass partitioning to and the reproductive efficiency of second and third order ears of main shoots (DM2738 > AX7784). Kernel number per plant was higher for DM2738 due to a higher kernel setting on multiple ears of main shoot plus tillers (more prolific and with lower tiller fertility) than for AX7784 (less prolific and with higher tiller fertility). However, grain yield did not differ between hybrids, because of the higher kernel weight of AX7784. Therefore, this work opens avenues for exploiting higher grain yields in maize crops with low plant population densities through the combination of prolificacy and tillering. Further studies should analyze the impact of reproductive plasticity on kernel weight determination in low-density maize crops. • We studied maize tiller and main shoot grain yield and kernel set determinants. • Tillered plants set more kernels than non-tillered ones at high plant growth rates. • Tillers featured higher biomass partitioning to first order ears than main shoots. • Ears of tillers featured lower reproductive efficiency than ears of main shoots. • The tillering and prolific hybrid featured the highest plasticity, without grain yield differences between hybrids.

Impacts of vegetative and reproductive plasticity associated with tillering in maize crops in low-yielding environments: A physiological framework

• Modern maize hybrids sown at low densities tiller in non-restrictive environments. • Light quality and plant growth rate at early stages govern tiller emission. • Tiller fertility would be determined by shoot growth rate around flowering. • Reproductive plasticity is needed to stabilize yields in ultra-low density settings. • The impact of tillering on crop water and nitrogen economies is hypothesized. Selection for maize ( Zea mays L.) grain yield in high-yielding environments at high population densities has favored a compact phenotype tolerant to crowding stress, bearing a single, well-grained ear. However, by contributing to vegetative and reproductive plasticity (i.e., multiple shoots and ears per plant, respectively), tillering may be adaptive in environments with low and variable availability of resources, chiefly water and nutrients, where crops are sown at low plant population density. In this work we present a robust, new conceptual framework for vegetative and reproductive plasticity in maize with direct agronomic applications, combining original data from new experiments and data reviewed from the literature. First, we describe production systems where tillering in maize would be relevant in terms of grain yield. Next, we discuss possible masked effects of genetic selection at high plant densities on tillering and present novel experimental results showing genotypic variation of tillering in modern maize hybrids and genotype x environment x management effects (plant density x location x sowing date) on tillering expression. We follow with a two-part framework to analyze tillering and prolificacy. In the first part (from axillary buds to tillers), we integrate the early effects of the light environment (through photomorphogenesis) and carbon balance on tillering emission, and discuss the environmental factors (temperature, photoperiod, radiation, water, nitrogen) that modulate tiller emission and tiller growth. In the second part (from tillers to kernels), we summarize the functional relationships governing kernel set on the ears of main shoot (apical and sub-apical ears) and tillers, focusing on the growth rate of shoot cohorts, rather than the whole plant. We then provide examples of the diverse patterns of contribution of multiple shoots to crop grain yield for maize husbandry in low-yielding environments. Finally, we address the effect of tillering on resource capture and use efficiency of maize crops by discussing its relationship with biomass and grain yield and provide supportive experimental data. We conclude with identification of knowledge gaps leading to testable hypotheses.

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.

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&amp;lt;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&amp;lt;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.

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.

Allelopathy in jatropha plantation: Effects on seed germination, growth and yield of wheat in north-west India

In-situ and ex-situ allelopathic effects of jatropha (Jatropha curcas L.) were analyzed by studying growth and yield of wheat (Triticum aestivum L.). Ex-situ approach included studying laboratory bioassay of leaf aqueous extract effects on seed germination and seedling growth; and pot experimentation with different jatropha plant parts as soil amendments. Wheat was grown under the jatropha plantation in in-situ approach. To eliminate the shade effects of jatropha, a treatment plot was prepared by cutting jatropha trees to 0.5m above ground level. Bioassay indicated the inhibitory effects of leaf extracts, particularly at high concentrations on seed germination and seedling growth of wheat. In ex-situ pot experiment, soil amendments with different plant parts enhanced biomasses and grain yields of wheat. Increase in yield and biomass was higher in pots amended with jatropha fruit, followed by leaf and stem. When wheat crop was grown with jatropha in in-situ approach, results were more conclusive as the ill effects of jatropha were not seen in pruned plants plots. Grain yield and biomass declined under the standing jatropha cultivation, with lowest reduction in low plant population density plots. Thus, an inhibitory effect of jatropha on wheat was limited to ex-situ bioassay only. Winter shedding of leaves in jatropha could be a boon for the Rabi (winter season) intercrops, and wheat could be an option for its cultivation under low plant population densities of jatropha with limited irrigation in north-west India.

Towards modelling the flexible timing of shoot development: simulation of maize organogenesis based on coordination within and between phytomers.

Experimental evidence challenges the approximation, central in crop models, that developmental events follow a fixed thermal time schedule, and indicates that leaf emergence events play a role in the timing of development. The objective of this study was to build a structural development model of maize (Zea mays) based on a set of coordination rules at organ level that regulate duration of elongation, and to show how the distribution of leaf sizes emerges from this. A model of maize development was constructed based on three coordination rules between leaf emergence events and the dynamics of organ extension. The model was parameterized with data from maize grown at a low plant population density and tested using data from maize grown at high population density. The model gave a good account of the timing and duration of organ extension. By using initial conditions associated with high population density, the model reproduced well the increase in blade elongation duration and the delay in sheath extension in high-density populations compared with low-density populations. Predictions of the sizes of sheaths at high density were accurate, whereas predictions of the dynamics of blade length were accurate up to rank 9; moderate overestimation of blade length occurred at higher ranks. A set of simple rules for coordinated growth of organs is sufficient to simulate the development of maize plant structure without taking into account any regulation by assimilates. In this model, whole-plant architecture is shaped through initial conditions that feed a cascade of coordination events.

Adapting maize crop to climate change

AbstractGlobal weather changes compel agriculture to be adequately productive under diverse and marginal conditions. In maize, modern hybrids fail to meet this requirement. Although breeding has achieved spectacular progress in grain yield per area through improved tolerance to stresses, including intense crowding, yields at low plant population densities remain almost unchanged. Stagnated plant yield potential renders hybrids unable to take advantage of resource abundance at lower populations, designating them population dependent. Consequently, the optimum population varies greatly across environments. Generally, the due population increases as the environmental yield potential gets higher. As a remedy, relatively low populations are recommended for low-input conditions leading to inappropriate population in occasional adequacy of resources and considerable yield loss. For example, for a rain-fed hybrid tested at one location across 11 seasons, crop yield potential and optimum population on the basis of the quadratic yield-plateau model varied from 1,890 to 8,980 kg/ha and 4.56 to 10.2 plants/m2, respectively, while 100 % yield loss is computed in the driest season if the optimum population for the most favorable season is used. The article reviews the consequences in terms of crop sustainability under widely diverse environments imposed by climatic changes and proposes crop management strategies to address the situation. The major points are: (1) variable-yielding environments require variable optimum populations, (2) population dependence is an insurmountable barrier in making a decision on plant population, (3) farmers suffer from considerable yield and income loss, (4) estimating the less population-dependent hybrids among the currently cultivated ones is a major challenge for agronomists, and (5) the development of population-neutral hybrids is a fundamental challenge for maize breeding. Honeycomb breeding is a valuable tool to pursue this goal since it places particular emphasis on the so-far stagnated plant yield potential that is essential for population-neutral hybrid development.

Assessment of some major yield-limiting factors on maize production in a humid temperate environment

Despite the availability of modern hybrids and better agronomic practices, there existed large gaps between attainable yield of maize ( Zea mays L.) grown with recommended practices and producers’ harvest yields in the humid temperate regions of eastern Canada. A field experiment was conducted for 3 years in Ottawa, Canada, to determine the most important management yield-limiting factor(s) on rainfed maize grain production. A package of recommended practices (RP) was composed with the recommended levels of nitrogen (N), phosphorus (P), potassium (K), micronutrients, chemical weed control, and plant population density (PPD). Each factor was modified from the RP, making a total of 11 treatments. Under the low occurrence of diseases or insects, weed infestation was the most important yield-limiting factor, which reduced grain yield by 27–38%. While lack of preplant N application (100 kg ha −1) reduced yield by 10–22%, there was no yield increment with additional sidedressing N (50 kg N ha −1). Grain yield was reduced by 8–13% with low PPD (60,000 plants ha −1) in all years, whereas increasing PPD to 90,000 plants ha −1 did not improve yield, compared with the RP. Withhold P application did not affect yield in all years, but yield was reduced by up to 13% in the absence of K, and by 10% and 12% without Zn or Mn, respectively, in 1 year. Our results indicated that lack of weed control (i.e. herbicide use) was the major yield-limiting factor followed by fertilizer N and PPD. The responses of grain yield to K, Zn, and Mn were site and/or year specific. Our study provided experimental data and an insight understanding of yield gap between genotype's yield potential achievable with recommended practices and yields with producers’ practices.

Irrigation rate and plant density effects on yield and water use efficiency of drip-irrigated corn

The efficient use of water by modern irrigation systems is becoming increasingly important in arid and semi-arid regions with limited water resources. This study was conducted for 2 years (2005 and 2006) to establish optimal irrigation rates and plant population densities for corn ( Zea mays L.) in sandy soils using drip irrigation system. The study aimed at achieving high yield and efficient irrigation water use (IWUE) simultaneously. A field experiment was conducted using a randomized complete block split plot design with three drip irrigation rates ( I 1: 1.00, I 2: 0.80, and I 3: 0.60 of the estimated evapotranspiration), and three plant population densities ( D 1: 48,000, D 2: 71,000 and D 3: 95,000 plants ha −1) as the main plot and split plot, respectively. Irrigation water applied at I 1, I 2 and I 3 were 5955, 4762 and 3572 m 3 ha −1, respectively. A 3-day irrigation interval and three-way cross 310 hybrid corn were used. Results indicated that corn yield, yield components, and IWUE increased with increasing irrigation rates and decreasing plant population densities. Significant interaction effects between irrigation rate and plant population density were detected in both seasons for yield, selected yield components, and IWUE. The highest grain yield, yield components, and IWUE were found for I 1 D 1, I 1 D 2, or I 2 D 1, while the lowest were found for I 3 D 2 or I 3 D 3. Thus, a high irrigation rate with low or medium plant population densities or a medium irrigation rate with a low plant population density are recommended for drip-irrigated corn in sandy soil. Crop production functions with respect to irrigation rates, determined for grain yield and different yield components, enable the results from this study to be extrapolated to similar agro-climatic conditions.

AN EMPIRICAL MODEL TO PREDICT YIELD OF RAINFED DRY BEAN WITH MULTI-YEAR DATA

The prediction of crop yield and harvest volume of about 700 thousand ha planted to dry bean in Zacatecas State will enable the implementation of strategies to decrease the degree of uncertainty of decisions pertaining to agriculture. The purpose of the present study was to predict bean yield under rainfed conditions using leaf area index (LAI), light interception (LI) by the canopy, and rainfall. LAI and LI of both black-grain and light-colored grain beans were determined at the beginning of flowering, at pod formation, at the beginning of pod filling, and at intermediate pod filling. The relationship yield: LAI/LI/rainfall as well as the verification of a model were examined by linear least-square regression. Maximal LI and its LAI for the various years were 70 % and 1.6 for 2002 and 75 % and 2.5 in 2003. For these years, LI as a function of LAI could be described by an exponential model. LAI and LI at pod formation and the beginning of pod filling were the phenological stages that better explained bean yield for all varieties. The empirical model relating bean yield: LAI/LI/rainfall accounted for 71 % of the variability of light-colored grain bean yield. The corresponding percentages of the variability in measured yields for black-grain beans were 68 % for Emiliano Zapata and Progreso and 74 % for Zaragoza and Miguel Auza. Even though the relationship LAI/LI/rainfall was affected due to the low plant population density, the many varieties employed, and the agroecological sites, the information from this kind of studies will be useful to decision makers and farmers to make decisions.

Frost damage to winter wheat in the UK: the effect of plant population density

One winter wheat variety, Soissons, suffered extensive frost damage in a plant population density (PPD) and sowing date (SD) experiment in 1997/1998. Another variety, Cadenza, did not incur any frost damage, even though it was at a similar developmental stage to Soissons when the damaging frosts (minimum grass temperatures of −8 and −9 °C) occurred. Therefore, in addition to rapid development, other physiological characteristics of Soissons, such as the presence of awns and weak glaucosity must be important in determining its susceptibility to frost damage. When sown on 23 September, the low PPD crops suffered the most frost damage but when sown on 25 October the high PPD crops suffered the most. This challenges the assumption that low PPDs are more resistant to frost than high PPDs. No frost damage was observed in the crop sown on 16 December. Frosts killed spikelets, restricted internode extension (stem growth) and reduced yield. Frosts in April and May, after growth stage (GS) 33, appeared responsible for the damage symptoms observed in the crop. Minimum temperatures in April and May were similar to those recorded in the previous season when no frost damage was observed. There had been a cooler winter in 1996/1997, allowing slower crop development and more cold hardening, therefore the frosts in the spring of 1997 did not inflict obvious damage.

Mechanisms of adjustment by different pearl millet plant types to varying plant population densities

Pearl millet (Pennisetum glaucum (L.) R. Br.) is commonly grown at a wide range of plant population densities, both by design and as a consequence of stand establishment problems. High tillering genotypes are known to compensate effectively for lower plant population densities through their tillering capacity; less is known about the ability of naturally low tillering genotypes to adjust to low plant population densities. This is a particular concern in the case of the Iniadi landrace materials which are currently widely used in breeding programmes in both India and Africa. This research was done to determine how effectively the low tillering Iniadi types adjust to low plant population densities and how their mechanism(s) of adjustment compares to those of higher tillering materials. Two high and two low tillering genotypes were grown over a period of 5 years at plant population densities ranging from 12 to 2 plants/m2, under both high and low fertility regimes at the ICRISAT Centre, India. Both the high and low tillering types adjusted equally well to the reduced plant population densities, as judged by grain yield, but differed in their mechanism of adjustment. The high tillering genotypes adjusted, as expected, primarily by increasing productive tiller numbers, with only small changes in individual tiller productivity. The Iniadi genotypes increased productive tiller numbers in response to decreasing plant population densities to a limited degree, but increased panicle productivity to a much greater degree than the high tillering types. There was no differential effect on adjustment ability between the two types as a consequence of increased fertility, despite the stimulating effect of fertility on productive tiller numbers. The results are discussed in terms of generalized mechanisms of response to changing individual plant environmental resources (fertility and space), and in terms of the use of Iniadi germplasm in pearl millet breeding programmes.

Plant Population Density x Sowing Date Interaction in Wheat

Wheat yield response to sowing date is very well known in Northwest of Mexico; however, sowing date x plant population density has not been studied before. The objective of this work is to set wheat performance at early sowing date when using low plant population density. Six experiments were carried out during two years (1994-96) planting in three different sowing dates (November 15, December first and January 10). Each of these experiments contained five plant population densities treatments (13.5, 24.1, 54 and 217 thousand plants/ha plus a check with 120 kg seed/ha) with three cv: Bacanora T88, Oasis F86 and Tepoca T67. Plant population densities x sowing date interaction was significant. This was due to a higher yield with 117 thousand plants/ha than the check in early dates (end of November) and the opposite in later dates. Plant population density x sowing date x variety interaction was also significant. This was due to the fact that Tepoca T87 response to any increment in seed dosage even in early sowing date. The optimum plant population density was 200 thousand plants/ha for November 15 and 260 for December first. Plant population density response was explained mainly by the tillering capacity of wheat, and sowing date response was mainly due to kernel weight.

Panicle emergence of tiller types and grain yield of tiller order for direct-seeded rice cultivars

Grain yield of rice ( Oryza sativa, L.) tillers is critical to rice crop yield and quality but relatively little is known about variations that occur among panicles and grains for tiller types and emergence orders of direct-seeded rice cultivars. The objective of research was to examine how tillering may affect yield and quality at low plant population densities with profuse tillering. Single rice plants were grown in pots in a greenhouse in 1990 and in 1992 and in the field in 1991. The aim was to maximize tillering and thus better see effects of tiller emergence order and type on yield and panicle emergence. Culm and panicle emergence dates were successively later for primary, secondary, and tertiary tillers but with a smaller delay among panicle emergence dates than was observed for tiller emergence. Grain yield of tillers was related more to emergence order than to tiller type. Secondary and tertiary tillers in sufficient numbers could cause delays in crop grain maturity. Specifically, the beginning of grain-filling (closely following top anthesis) was 1 to 5 d later for primary tillers and 3 to 9 d later for secondary tillers, compared to main stems. These data indicate direct-seeded rice cultivars have partial but not complete synchrony of panicle emergence. Consequently, production strategies that increase preflood N to increase tillering in thin (sparsely populated) rice stands, could potentially delay maturity of the crop as well as increase yields.

Far‐red enrichment and photosynthetically active radiation level influence leaf senescence in field‐grown sunflower

Basal leaves frequently senesce before anthesis in high population density crops. This paper evaluates the hypothesis that quantitative and qualitative changes in the light environment associated with a high leaf area index (LAI) trigger leaf senescence in sunflower (Helianthus annuus L.) canopies. Mean leaf duration (LD, time from achievement of maximum leaf area) of leaf 8 was significantly (P &lt; 0.05) reduced from 51 to 19 days as crop population density was increased from 0.47 to 4.76 plants m−2. High compared to low plant population density was associated with earlier reduction in the photosynthetically active radiation (PAR) and red/far‐red ratio (R/FR) reaching the target leaf. However the changes in R/FR preceded those in PAR. When the light environment of individual leaves of isolated plants growing under field conditions was manipulated using filters and FR‐reflecting mirrors, LD was positively and linearly related with the mean daily PAR (MDR) received in the FR‐ (no FR enrichment) treatments. FR enrichment of light reaching the abaxial surface of the leaf significantly (P &lt; 0.05) reduced LD by 9 days at intermediate PAR levels with respect to FR‐controls, but did not affect LD at the maximum PAR used in these experiments. However, when light reaching both leaf surfaces was enriched with FR, LD (for leaves receiving maximum PAR) was 13 days shorter than that of the FR‐ control. These results show that basal leaf senescence in sunflower is enhanced both by a decrease in PAR and by a decrease in R/FR.

Comparison of swathing and desiccation of borage (Borago officinalis) and estimation of optimum harvest stage

SummaryIn trials of borage (Borago officinalis L.) between 1988 and 1991, swathing resulted in substantially higher yields than desiccation with diquat or glyphosate. Earlier harvest resulted in slightly lower seed oil content. Optimum swathing stage for uniform crops was estimated as that in which youngest flowers on apical cymes with shed or mature seed were the first to the third from the cyme base (i.e. stage 5,1 to 5,3). In crops with low plant population density, in which production of lowest branches is not suppressed, assessment of swathing stage is likely to be difficult and may require sampling from lower cymes.

Yield Contribution of Apical and Subapical Ears in Prolific and Nonprolific Corn

AbstractPrevious studies have demonstrated higher corn (Zea mays L.) yield potential for prolific corn hybrids (more than one ear) compared to nonprolific hybrids (one ear). However, little is known about the relative contribution of the second ear to total yield at various N levels. This study compared yield responses to N rates of 56, 140, and 224 kg N ha−1 of prolific Hybrids A (I202 × Mo17) and B (I117 × B73) with responses of nonprolific Hybrid C (Pioneer 3320) at a uniform low plant population density. All three hybrids gave a positive yield response to N applications. The prolific hybrids increased both in apical ear weight and in subapical ear weight and number in response to N rate. Averaged over N rates, Hybrid A yielded 24% and Hybrid C 14% higher than Hybrid B in 1987. In 1988, they yielded 13 and 10% higher than Hybrid B. Yield of single ears of nonprolific hybrid was higher than that of the apical ears in the prolific hybrids. Total potential yield in response to N application appears to be highest in Hybrid A because of second ear formation. Factors contributing to to yield increases from N applications in prolific Hybrid A included, in order of importance, an increase in the number of subapical ears, an increase in apical ear weight, and an increase in the subapical ear weight. Contrary to previous reports, apical and subapical ear weight increased simultaneously, with increasing N rates

Effects of seed ageing on growth and yield of spring wheat at different plant-population densities

When seed samples of spring wheat ( Triticum aestivum L., cv. Timmo) were aged they showed delayed field emergence and slower seedling growth. However, their subsequent relative growth rate was not deleteriously affected and, at a low plant-population density, on one occasion there was even evidence of some compensatory increase in growth rate, though not sufficient to overcome the disadvantages of poor initial seedling growth. Since poor seed vigour mainly affected early growth, it was argued that its deleterious effect would be minimised at high population densities where the potential advantage of high-vigour seeds would be partially counteracted by earlier competition. Experiments carried out over a wide range of population densities supported this proposition. They also showed that, if direct effects of poor vigour seed on yield through reduced establishment are avoided by adjusting sowing rates so that recommended rates of establishment are achieved, then there will probably be little or no effect of seed vigour in final yield, providing normal germination in the laboratory test is 85% or more, and sowing in the spring is not delayed. However, if these conditions are not met, then significant yield reductions can be expected which could not be overcome by increasing sowing rate.