Critical Period For Yield Determination Research Articles

Modelling phenology to probe for trade-offs between frost and heat risk in lentil and faba bean

Extreme temperatures at critical developmental phases reduce grain yield. Combinations of sowing date and cultivar that favour faster development reduce the likelihood of heat stress but increase the risk of frost at critical phases. Current models are unable to predict pulse yield in response to frost and heat, hence our focus on phenology. Our aim was to model phenological variation with sowing date and cultivar for lentil and faba bean against the climatic patterns of frost and heat in 45 Australian locations that spanned 29 °S-41 °S, 11−340 m.a.s.l., and 1−423 km to the coast.For both crops, modelled mean and standard deviation of time to flowering were close to actuals and mean prediction error was below 5%. Comparison of actual and modelled time to flowering returned: r = 0.89 (n = 121, P < 0.0001) and modelling efficiency = 0.73 for lentil, and r = 0.96 (n = 123, P < 0.0001) and modelling efficiency = 0.84 for faba bean.The critical period for yield determination was assumed to span from flowering to 200 °Cd after flowering. Curves fitted to the time-course of frost (< 0 °C) and heat (> 34 °C) probabilities between 1957 and 2018 were used to estimate the date of 10 % frost probability and the date of 30 % heat probability as the boundaries of a frost-heat risk window for the critical period. Out of the 45 locations, 12 were frost-free but with risk of heat, 7 were heat-free but with risk of frost, 3 were frost- and heat-free, and 23 featured a window defined by both frost and heat boundaries. Frost variables discriminated locations more strongly than heat variables. Geographical patterns in thermal regimes emerged that were associated with latitude, altitude and continentality.Realised warming between 1957 and 2018 advanced the time to 200 °Cd after flowering and shortened the critical period in most locations, particularly in early-sown crops. Comparisons of the probability curves of frost and heat between 1957–1985 and 1986–2018 showed, with few exceptions, an asymmetry between delayed late frost (up to 44 d) and earlier heat onset (up to 11 d), with a narrowing of the frost-heat risk window from 46 to 90 d for the period 1957–1985 to 34–64 d for 1986–2018.We identified a dominant role of frost as (i) the main discriminating factor among geographically distinct locations, (ii) the main source of variation of the frost-heat window, and (iii) a putatively increased risk factor with climate change. Adaptation to frost in the critical period for yield is important for pulses despite warming trends. Increased frost tolerance can directly improve yield and indirectly contribute to reduce risk of heat and drought later in the season.

Deep Soil Water-Use Determines the Yield Benefit of Long-Cycle Wheat.

Wheat production in southern Australia is reliant on autumn (April-May) rainfall to germinate seeds and allow timely establishment. Reliance on autumn rainfall can be removed by sowing earlier than currently practiced and using late summer and early autumn rainfall to establish crops, but this requires slower developing cultivars to match life-cycle to seasonal conditions. While slow-developing wheat cultivars sown early in the sowing window (long-cycle), have in some cases increased yield in comparison to the more commonly grown fast-developing cultivars sown later (short-cycle), the yield response is variable between environments. In irrigated wheat in the sub-tropics, the variable response has been linked to ability to withstand water stress, but the mechanism behind this is unknown. We compared short- vs. long-cycle cultivars × time of sowing combinations over four seasons (2011, 2012, 2015, and 2016) at Temora, NSW, Australia. Two seasons (2011 and 2012) had above average summer fallow (December–March) rain, and two seasons had below average summer fallow rain (2015 and 2016). Initial plant available water in each season was 104, 91, 28, and 27 mm, respectively. Rainfall in the 30 days prior to flowering (approximating the critical period for yield determination) in each year was 8, 6, 14, and 190 mm, respectively. We only observed a yield benefit in long-cycle treatments in 2011 and 2012 seasons where there was (i) soil water stored at depth (ii) little rain during the critical period. The higher yield of long-cycle treatments could be attributed to greater deep soil water extraction (<1.0 m), dry-matter production and grain number. In 2015, there was little rain during the critical period, no water stored at depth and no difference between treatments. In 2016, high in-crop rainfall filled the soil profile, but high rainfall during the critical period removed crop reliance on deep water, and yields were equivalent. A simulation study extended our findings to demonstrate a median yield benefit in long-cycle treatments when the volume of starting soil water was increased. This work reveals environmental conditions that can be used to quantify the frequency of circumstances where long-cycle wheat will provide a yield advantage over current practice.

Identifying optimal sowing and flowering periods for barley in Australia: a modelling approach

Frost, drought and heat are key abiotic constraints to barley production in Australia. To maximise grain yield, crop life-cycle needs to be timed to minimise growth stresses associated with insufficient radiation, frost, heat and drought stress during the critical period for yield determination that occurs prior to and during flowering. To identify optimal flowering times for commercial Australian barley genotypes, we conducted a genotype (G) × environment (E) × management (M) analysis using climate data from locations distributed throughout the Australian barley growing regions. Prior to conducting the G×E×M, we parameterised key phenological variables in the APSIM-Barley module for all genotypes using photoperiod and vernalisation data from experimental treatments, then we verified the model using seven independent field experiments. The verification process showed an average RMSE of 1.4–7.2 days and R2 values of 0.83–1.00 depending on genotype, indicating reasonable performance of the model in simulating phenology. Using the parameterised model, we then characterised water, frost and heat stress patterns for a range of sowing date × genotype combinations. The G×E×M showed that optimal flowering period (OFP) was a function of the environment more so than the genotype, and the relative importance of insufficient radiation, frost, heat and water stress varied signficantly with location. OFP was earlier (mid August to late September), in Western Australia and South Australia, while OFP was later (mid-October to mid-November) in Tasmania and Victoria. In low rainfall environments, the duration of the OFP was shorter in most cases than in high rainfall environments. In general, earlier sowing (1 April to 22 April) resulted in lower yield across sites, and this was more pronounced for fast developing genotypes La Trobe, Fathom, Compass and Alestar. Later sowing (1 June to 30 June) at Condobolin (NSW), Hopetoun (WA) and Loxton (SA) also resulted in a lower yield for all genotypes. Knowledge of OFPs based on long-term abiotic stresses will allow breeders to develop genotypes with phenological durations that are pertinent to each location. This will also allow farmers to select sowing dates according to genotype duration and thus minimise the combined risk of frost, heat and water stresses, which collectively should allow yield to approach its maximum potential.

The critical period for yield determination in common buckwheat (Fagopyrum esculentum Moench)

The aim of this study was to identify the critical period for yield determination in buckwheat by applying successive shading periods (of 14-days duration) throughout the crop cycle, from nine days after emergence to crop maturity. Experiments were carried out under field conditions during the 2017 and 2018 growing seasons. The critical period was defined as the interval when crop yield was significantly reduced by the shading treatments. This period extended from 74 °C days after the first open flowers to the first brown fruits stage (i.e. 390 °C days duration). Aerial biomass and its partitioning to the achenes (i.e. harvest index) were also reduced by shading. Achene number was reduced in a similar way to that of yield, and crop yield was highly associated with this yield component, while the shading treatments did not affect achene weight. The main cause of achene number reduction was the lower number of achenes per raceme, as the number of racemes was not affected. It is possible to speculate that radiation restriction imposed during the critical period could have increased floret mortality and thereby the number of achenes per raceme. However, further studies are required to determine the causes of reductions in the number of achenes per raceme during the critical period.

Yield determination and the critical period of faba bean (Vicia faba L.)

Faba bean is a cool-season, indeterminate grain legume grown in Mediterranean and temperate environments where yield loss associated with abiotic and biotic stress is common. Yield responses depend on the timing of stress relative to the species-specific vulnerable stages in the crop lifecycle. To determine the critical period for yield determination in faba bean, we used sequential 14-d shading periods in locally-adapted varieties grown in five environments with yield of unshaded controls from 2.3 to 6.8 t ha−1.Yield of shaded treatments diverged from the controls around 450 °Cd before flowering, reached the largest difference around 100 °Cd after flowering, and converged with controls towards 700–800 °Cd after flowering; the most critical stage aligned with pod emergence. Seed number accounted for most of the variation in yield response to shading. Shading increased seed size when stress severely reduced seed number. Pod number accounted for most of the variation in seed number for shading before flowering, and both pod number and seeds per pod contributed to the reduction in seed number in crops shaded after flowering. The defined critical period is a useful reference for breeding and agronomic solutions to improve yield under stress.

Canopy development and grain yield of dryland wheat is modified by strategic nitrogen supply and stubble management

Abstract Yield in dryland wheat could be improved through a better understanding of crop responses to no-till (NT), stubble retention and nitrogen (N). Field experiments were established at Roseworthy and Karoonda in South Australia to evaluate wheat crop responses to contrasting tillage systems, different amounts of stubble and N timing. Canopy development regulated grain yield. No-till crops produced more biomass compared with conventional tillage while large amounts of stubble (5 t ha−1) reduced biomass at harvest compared with both moderate amounts of stubble (2.5 t ha−1) and bare ground. The application of N at sowing produced large vegetative biomass compared with delayed N supply. However, delayed N supply allowed more rapid accumulation of biomass between stem elongation and flowering, the critical period for yield determination in wheat. Crop growth rate during this period positively correlated with grain number (R = 0.44) but negatively with tiller numbers (R = 0.66). Grain yield declined with the retention of more than moderate amounts of stubble, irrespective of whether the stubble was applied as mulch or left standing; similarly, additional stubble did not improve water conservation benefits. Results demonstrate that the strategic supply of N under stubble retention can increase crop growth rate during the critical period between stem elongation and flowering.

The critical period for yield and quality determination in canola (Brassica napus L.)

Despite its global significance as an edible oil and biofuel, the critical period for yield determination in canola (edible oilseed rape – Brassica napus L.) has not been determined in the field. Field experiments were conducted at two contrasting sites in southern Australia where 100 °Cd shading periods (15% PAR transmitted) were applied from early vegetative growth until maturity to identify the developmental period when the crop was most sensitive to stress. Despite the significant difference between the two sites for yield in the unshaded control (450 g m−2 in New South Wales, and 340 g m−2 in South Australia), the critical period was consistent at both sites extending from 100 to 500 °Cd after the start of flowering (BBCH60), and centred 300 °Cd after BBCH60. Seed number (seed m−2) was reduced by an average of 48% in the critical period, generated in equal parts by reduced pod m−2 in the early part of the period, and reduced seed pod−1 in the latter part. Reduced seed number was partially compensated by an increase in seed size of 29%. These trends were similar on the branches and main stem. On the main stem, the timing of the critical period moved from earlier to later from lower to upper pods linked to the timing of their development. Seed oil content declined and protein content increased under shading in the critical period, while both oil and protein yield (kg m−2) were reduced by 40–50% and 30–40% respectively. The critical period is coincident with the greatest number of near-open buds and newly opened flowers, which are highly sensitive to assimilate supply for ovule development. Both pod abortion and restricted capacity for compensatory growth of surviving pods are consequences of assimilate restriction on developing ovules. Identification of the critical period provides a useful target for breeding and management strategies to maximize productivity.

The critical period for yield determination in chickpea (Cicer arietinum L.)

Chickpea seed yield is highly variable as a result of biotic, mostly fungal, and abiotic stresses including extreme temperatures and water stress. The effect of stress on yield depends on its intensity, timing and duration, hence the importance of knowing the critical window of yield formation and stress vulnerability. This window has not been determined in chickpea. To fill this gap, we compared the effect of sequential 14-d shading periods on the yield and yield components of two chickpea varieties, PBA Boundary and PBA Slasher, in three environments where unshaded controls yielded between 2880 and 3130kgha−1. Unlike other species which do not respond to stress early in the season, shading reduced yield from emergence until the beginning of the critical period, 300°Cd before flowering (base temperature=0°C). The critical period was found to be at least 800°Cd long centred 100°Cd after flowering. Seed number accounted for most of the variation in yield, which was unrelated to seed size. Pod number accounted for most of the variation in seed number prior to the critical period, while pod number and seeds per pod contributed to seed number within the critical period. After 400°Cd post flowering, seeds per pod was the main variable affecting seed number. This information can be used in breeding and agronomy to improve stress adaptation.

Absorbed radiation and radiation use efficiency as affected by foliar diseases in relation to their vertical position into the canopy in wheat

The impact of foliar diseases on crop yield losses is better understood if considering ecophysiological variables together with pathological variables. Although wheat crop losses due to foliar diseases have already been studied with an ecophysiological approach, none of these studies analyzed the vertical diseases distribution into the canopy leaf layers in relation to the canopy size (leaf area index—LAI) and its architecture (light extinction coefficient- k value). Thus, the objectives of the present study were: (i) to understand the importance of the vertical distribution of the foliar diseases in relation to radiation absorption efficiency (RAE) for different LAI levels and canopy architectures and; (ii) to analyze and compare two ways of radiation capture estimations, considering LAI as a total or LAI of each leaf layer separately. The wheat cultivar Klein Pegaso was grown in plots under field conditions during three growing seasons using different nitrogen supply levels and a wide range of severity diseases by using protected and unprotected crops (applying or not fungicides, respectively). Unprotected plots were inoculated with biotrophic and/or necrotrophic pathogens. Biotrophic ( Puccinia triticina-leaf rust) and necrotrophic pathogens ( Drechslera tritici- repentis-tan spot; Alternaria triticina-leaf blight) constituted the “diseases complex” with different levels and proportions depending on the year and N treatment. Results showed that foliar diseases reduced LAI and GLAI (green leaf area index). GLAI was not only diminished by LAI reductions, but also by increases in NGLAI (non-green leaf area index) due to lesion coverage which reduced light absorption. In spite of the differences observed in LAI between protected and unprotected crops, radiation interception was not affected until LAI dropped down its critical value (i.e. when crop intercept 95% of the maximum radiation possible to be intercepted). The results demonstrated that assuming a uniform distribution of the diseases, lead to underestimations of accumulated absorbed radiation up to 21%, and as a consequence to overestimations of radiation use efficiency (RUE) up to 29% when diseases were concentrated in the lower leaf layers into the canopy. Together with the severity of the pathogen, at the time to decide controlling diseases, farmers should take into account: (i) LAI level, mainly in those crop situations where, during the critical period for yield determination, the LAI is close to or below the critical value; (ii) canopy architecture ( k) associated with light distribution into the canopy and (iii) vertical diseases distribution into the crop.

Determination of grain number in sorghum

Grain number is an important component of grain yield in sorghum. Research in wheat and maize has indicated a dependency of grain number on the crop or panicle growth rate around anthesis (CGR a and PGR a respectively), but little quantitative information is available for sorghum. The aim of this paper was firstly to quantify the effect of CGR a and PGR a on grain number and secondly, to identify other parameters that could be used as substitutes for PGR a. Analyses included data from a number of experiments, covering a range in nitrogen and drought treatments and including both tall (single dwarf) and short (triple dwarf) hybrids. CGR a and SGR a (stem growth rate) were calculated from the derivative of a curvilinear function fitted to experimental data, and PGR a was obtained by subtraction of SGR a from CGR a. Results indicated a linear relationship between grain number and CGR a, but the slope differed for tall and short hybrids. This was due to a difference in the proportion of dry matter allocated to the reproductive organs around anthesis ( P r), as PGR a was closely related to grain number, irrespective of crop height. Since panicle dry mass at maturity (excluding grain) was closely correlated with reproductive biomass shortly after anthesis, this indicator represents an integration of panicle growth during the critical period for yield determination in sorghum (i.e. flag leaf until start of grain filling). Panicle biomass at maturity (excluding grain) was thus also linearly related to grain number, and the relationship was independent of crop height and of the timing, severity, or type of stress. Our results indicate that panicle mass at maturity could provide an alternative to PGR a for the estimation of grain number.

Critical period for grain number establishment of near isogenic lines of two- and six-rowed barley

In barley no studies have attempted to pinpoint the critical period for grain number determination, and it is frequently stated that the critical period is similar to that of wheat. However, there are important differences between the species and among barley genotypes (i.e. two- and six-rowed types) suggesting that this assumption requires testing. The objectives of this paper were (i) to determine the critical period for grain number determination in two- and six-rowed barleys, and (ii) to identify which yield components were more sensitive to changes in incident radiation during that period. Two field experiments were conducted using two pairs of near isogenic lines differing only in the spike type. Shading was imposed at different periods throughout the crop cycle (from 60 days before heading to 15 days after) to reduce incident solar radiation approximately 70%. The critical period for grain number determination tended to be slightly earlier in two- (ca. between 40 and 10 days before heading) than in six-rowed barleys (ca. between 30 days before heading until that stage). In terms of the external phenology, the beginning of the critical period for setting grains was 10 days after the beginning of stem elongation, and 10 days before flag leaf appearance in two- and six-rowed lines, respectively. Changes in the number of grains per unit area were correlated with crop growth rate during the critical period for yield determination.

Radiation effects on potential number of grains per spike and biomass partitioning in two- and six-rowed near isogenic barley lines

The critical period for yield determination in barley ( Hordeum vulgare L.) is situated in the pre-heading phases. During the latest part of the critical period one of the most important yield components (i.e. the number of grains per spike) is set in two- and six-rowed barley. In wheat, much is known about the role of the spike in assimilate acquisition for the establishment of grains per spike, but not in barley. This paper evaluates how biomass partitioning between vegetative and reproductive organs impacts floret development and primordia survival in response to radiation during different periods in the crop cycle, in barley lines. Field experiments were carried out using two- and six-rowed near isogenic barley lines differing only in spike type. Shading treatments were applied at different periods during the crop cycle (from 60 to 15 days before and after heading) reducing the intercepted radiation (ca. 70%). Dynamics of floret primordia initiation and mortality and of floret development for different spikelet positions along the spike were measured, and biomass partitioning between vegetative and reproductive structures was calculated. Pre-heading shading reduced fertile florets per spike ( P < 0.001). In the immediate pre-heading treatment, distal floret primordia could not reach a fertile floret stage due to a low rate of floral development. The amount of assimilates partitioned to the spike at heading affected the number of fertile florets per spike in both barley types. However, when spike biomass at heading was corrected by nitrogen concentration, the fitness of the relationship did not improve in relation to the first one. In relative terms, radiation restrictions during the immediate pre-heading phase increased the amount of biomass partitioned to the growing spike.

Yield Responsiveness in Two‐ and Six‐Rowed Barley Grown in Contrasting Nitrogen Environments

AbstractTwo‐ and six‐rowed barley with different intrinsic ability to produce tillers and kernels per ear, would differ in responsiveness to nitrogen availability with environmental improvements. Two field experiments were carried out to elucidate how nitrogen supply (N40 and N150) affects yield and its components in two‐ and six‐rowed barley. High nitrogen increased aboveground dry matter at anthesis, by improving cumulative solar radiation intercepted by the crop, determining an increased dry‐matter production at maturity without changes in harvest index. In both barley types, variations in grain yield were explained by changes in kernels per unit land area rather than by differences in the average kernel weight. However, changes in the number of kernels were due to variations in the number of ears per m2 in two‐rowed barley and the number of kernels per ear in six‐rowed barley. Ears per unit area showed a greater responsiveness in two‐ than in six‐rowed barley due to a higher nitrogen supply treatment, associated with their intrinsic higher tillering capacity, while the number of kernels per ear was more responsive in six‐ than in two‐rowed types. The fact that responses to nitrogen by the number of kernels per unit land area in two‐ and six‐rowed barley is better explained by different yield sub‐components, allows the speculation that the critical period for yield determination would differ between barley types.