In the past V.O. Sadras has collaborated on articles with D.J. Connor and S.P. Milroy. One of their most recent publications is Dynamics of rooting and root-length: leaf-area relationships as affected by plant population in sunflower crops. Which was published in journal Field Crops Research.

More information about V.O. Sadras research including statistics on their citations can be found on their Copernicus Academic profile page.

V.O. Sadras's Articles: (14)

Dynamics of rooting and root-length: leaf-area relationships as affected by plant population in sunflower crops

AbstractCrops of sunflower (Helianthus annuus L.) were grown in a coarse loam Typic Hapludoll to characterize the spatial and temporal development of the root systems, the relationships between root systems and leaf area, and their responses to plant population. Two experiments were carried out, one involving single plant population, the other (using a different cultivar) covering the range of population from 2.04 to 5.10 plants m−2. The trench profile method was used to estimate root density in the row and in the inter-row space. These data were used to estimate root depth and root length on a ground-area basis. The former was defined as the depth which contained 90% of the total root system below the 0-0.2-m layer (D90).Rooting depth (D90) and total root length increased up to anthesis and root length decreased thereafter. Plant population had negligible effects on (D90). The inter-row space was colonized by roots at a slower rate than the within-row space, and after anthesis loss of roots from the former space took place more rapidly. A single allometric function fitted the seasonal changes in the relationship between D90 and leaf area per plant for all crops.The dynamics of roots in the plough and below-plough layers showed different responses to population. Low-population crops had the highest and lowest peak values of root length in the plough and below-plough layers, respectively. In both layers, roots of low-population crops continued to grow until later in the season. Root length and leaf area per plant decreased markedly with population but on a ground-area basis these effects were small. These morphological responses to population are analyzed in relation to their possible effects on crop water use.

Regulation of evapotranspiration, and its partitioning between transpiration and soil evaporation by sunflower crops: a comparison between hybrids of different stature

AbstractThis study investigates the regulation of evapotranspiration (Et) and its partitioning between soil evaporation (E) and transpiration (T) by sunflower (Helianthus annuus L.) crops. A comparison was made of cvs. Cannon (standard height) and Beauty (semi-dwarf) over a full crop season. Three irrigation regimes were established to achieve well irrigated crops (I), and crops stressed before (Dpre) and after anthesis (Dpost). Weekly Et was measured by hydrological balance, E using evaporimeters, and T calculated as the difference. Evaporimeters were renewed each week and calibrated by comparison with evaporation measured using the hydrological balance on bare plots.There was no difference between cultivars in either Et (range from 5 to 64 mm week−1) or the fraction of Et due to soil evaporation, i.e., EEt−1 (range from 0.12 to 0.70).The two cultivars achieved similar partitioning of Et in different ways. Despite smaller leaf area index (L), Cannon crops transpired the same proportion of Et as Beauty because of a compensatory greater TL−1. The greater TL−1 of Cannon was consistent with its greater interception of radiation (ir) per unit L.Irrespective of cultivar, the mechanisms involved in the regulation of transpiration depended on the timing of the water shortage. Lower ir (resulting from reduced leaf expansion) accounted for the smaller T in Dpre crops. Transpiration of Dpost crops was reduced by both smaller canopy conductance and smaller ir caused by greater leaf senescence.

Physiology of yield expression in sunflower

AbstractThis paper evaluates currently available information on the physiology of sunflower (Helianthus annuus L.) in the context of field growth responses and the determination of crop yield. It deals with phenology, water economy, mineral nutrition, carbon fixation and partitioning, yield formation, and seed quality. Attention is drawn to information on intraspecific variation of individual traits to highlight the possibilities that exist for cultivar adaptation and improvement. Properties commonly attributed to this crop such as high photosynthetic capacity, profligate use of water and low water-use efficiency are evaluated.

Elevated temperature altered the reaction norms of stomatal conductance in field-grown grapevine

AbstractWe measured the effect of elevated temperature, and its interaction with fruit load (exp. 1) and water supply (exp. 2), on the stomatal conductance (gs) of Vitis vinifera, cv. Shiraz. Thermal regimes (control vs. elevated temperature using open-top chambers) were initiated in spring, thus affecting leaf development, and were maintained during the whole growing season. We used a top-down approach where reaction norms were derived that relate gs for each treatment and the mean gs across treatments; the slopes of reaction norms quantify phenotypic plasticity.Stomatal conductance responded to neither the interaction between temperature and fruit load (P = 0.37) nor the interaction between temperature and water regime (P = 0.33). We therefore dealt with each factor separately. Reaction norms of gs under elevated temperature and control treatments diverged, i.e. elevated temperature had no effect on gs under conditions conducive to low conductance (below ∼100 mmol m−2 s−1) but increased gs in relation to controls under conditions favouring high conductance. Stomata density was 159 ± 6.7 mm−2, and was unaffected by temperature. Stomata length increased from 20.6 μm in controls to 23.2 μm in the heated treatment (P < 0.0001) and width increased from 14.4 μm in controls to 16.8 μm in the heated treatment (P < 0.0001). Thus, longer and wider stomata contributed to the enhanced plasticity of stomatal conductance under elevated temperature. Consistently, reaction norms of light-saturated photosynthesis were divergent, i.e. elevated temperature did not affect photosynthesis under conditions conducive to low gs and photosynthesis, but increased photosynthesis in relation to controls under more favourable conditions. A high source:sink ratio reduced the plasticity of stomatal conductance. Water regime had a minor effect on the plasticity of stomatal conductance, but the reaction norms for irrigated and water deficit treatments were offset by ∼60 mmol m−2 s−1 thus indicating a consistent effect of water deficit across environmental conditions.We conclude that the responses of stomata derived from transient temperature treatments in fully expanded leaves are unsuitable to model the dynamics of gas exchange in response to projected warming. Our experiments support a conceptual model where current stomatal conductance is a function of (i) the prevailing environmental conditions during early stages of leaf development that set the upper limit of conductance through the modulation of stomatal density and size, (ii) the current environmental conditions and (iii) the source:sink ratio.

Regular ArticleProfiles of Leaf Nitrogen and Light in Reproductive Canopies of Cotton (Gossypium hirsutum)

AbstractDuring vegetative growth, the vertical profile of leaf nitrogen (N) often parallels the profile of light distribution within the canopy. This is more advantageous in terms of canopy photosynthesis than a uniform distribution of leaf N. We investigated the influence of both reproductive growth and N supply on the profiles of N and light in canopies of irrigated cotton crops (Gossypium hirsutum L.). Regular samplings were made from soon after the onset of reproductive growth until crop maturity. Every 2 weeks, a 1 m2sample of the canopy was cut in four successive vertical layers of equal thickness. Leaf area and N concentration (%) in each layer were measured. The vertical N gradient became more marked with ongoing reproductive development. It is hypothesized that because of the high rate of growth after the onset of reproductive development and the long duration of this phase compared to other species, the whole canopy photosynthetic benefit that would accrue from maintaining the N gradient is likely to be accentuated. The rate of decline in leaf N concentration in a layer was not related to either the initial concentration in the leaves nor the boll load within the layer.

On-farm assessment of regional and seasonal variation in sunflower yield in Argentina

AbstractUsing an on-farm approach, we investigated constraints to actual yield of sunflower in six agroecological zones within the Argentine Pampas during three growing seasons. In 249 large, grower-managed paddocks, we quantified a series of variables related to: (1) crop phenology, growth, and yield; (2) the physical and biological environment; and (3) management practices. Variation in yield among zones and seasons was analysed on the basis of four biologically-founded assumptions: (1) grain number accounts for a large proportion of the variation in yield; (2) grain number is associated with a photothermal coefficient, Q=R (T-Tb)−1, where R and T are average solar radiation and air temperature respectively, during the 50-day period bracketing anthesis; and Tb is a base temperature; (3) crop growth and yield are proportional to light interception, and therefore proportional to canopy ground cover; and (4) yield is proportional to the fraction of seasonal rainfall that occurs after anthesis. Average yield ranged from 1.1 to 2.7 t ha−1, grain number from 2400 to 5400 m−2, individual grain mass between 40 and 69 mg and grain oil concentration between 42 and 52%. Grain number accounted for 43% of the variation in average yield while Q accounted for 23% of the variation in grain number. Low yield was associated with deficient ground cover in 25% of the crops; part of the remaining variation in yield was accounted for by sets of measured variables particular to each zone, including soil shallowness, low available P, low initial water content, weeds and diseases — chiefly Verticillium wilt (Verticillium dahliae) and Sclerotinia head rot (Sclerotinia sclerotiorum). Across zones and seasons, the proportion of seasonal rainfall occurring after anthesis accounted for 28% of the variation in crop yield. A trade-off is highlighted whereby beneficial effects of rainfall that favours growth and yield may be offset by the detrimental effect of abundant moisture that favours major fungal diseases. We emphasised the value of combining experimental studies — which provide biological background in the form of working hypotheses — with on-farm research that realistically quantifies yield response to key factors.

Response of maize kernel number to plant density in Argentinean hybrids released between 1965 and 1993

AbstractWe investigated the response of maize kernel number to plant density in four hybrids released in Argentina between 1965 and 1993. Assuming kernel number is the main yield component, and using as a framework the relationship between kernel number per plant (KNP) and plant growth rate bracketing silking (PGRs), we tested the alternative hypotheses that modern hybrids produce more kernels because they have (a) greater PGRs or (b) more kernels per unit PGRs than their older counterparts. Three experiments were carried out including a range of plant densities from 3–5 to 15–18 plants m−2. PGRs was calculated from shoot dry matter measured 10 days before and 20 days after silking. Shoot dry matter, grain yield and its components were measured at physiological maturity. Grain yield of the oldest hybrid averaged 7.7 t ha−1, and increased with year of release at a rate of 173 kg ha−1 per year. The response of grain yield to plant density was curvilinear. Kernel number per square meter accounted for most of the variation in yield with both year of release and plant density. For both sources of variation, there was a trade-off between kernel number and mass. Both PGRs and KNP decreased with increasing plant density in all four hybrids. Whereas variation in PGRs among hybrids was small, the oldest hybrid set 93 (low density) and 113 (high density) kernels per unit PGRs in comparison to the newest that set 167 and 193. We conclude that more kernels per unit PGRs, rather than greater PGRs, accounted for the genetic improvement of yield potential in the hybrids investigated.

Environmental risk analysis of farming systems in a semi-arid environment: effect of rotations and management practices on deep drainage

AbstractWe investigated the impact of crop rotations and management practices on the water balance of farming systems in a semi-arid region of south-eastern Australia, where drainage beyond the root zone and rising water tables contribute to salinisation of soils and water streams. The CropSyst model was locally tested and used with long-term weather data to analyse the risk of deep drainage associated with alternative farming practices; water balances were estimated using both cascade and finite difference approaches. Model estimates were compared with (a) yield, biomass, phenology, soil water content and water use measured in a 5-year experiment involving two rotations, i.e. FWP (fallow-wheat–pea) and MWP (mustard–wheat–pea) and (b) yield measured in grower-managed wheat crops encompassing three seasons and broad ranges of weather, rotations, management practices and soils. In the rotation experiment, the simulations of yield were close to measured yield for wheat (observed range from ≈0 to 2.4 t ha−1; R2 = 0.78; RMSE = 0.42 t ha−1), mustard (range from ≈0 to 0.6 t ha−1; R2 = 0.57; RMSE = 0.20 t ha−1) and field pea (range from ≈0 to 1.4 t ha−1; R2 = 0.72; RMSE = 0.29 t ha−1). Simulated wheat yield also compared well with on-farm measurements (observed range from ≈0 to 3.5 t ha−1; R2 = 0.72, RMSE = 0.21 t ha−1). The model provided reasonable estimates of crop biomass, phenological development, soil water content and water use. Water use tended to be overestimated in some cases using the finite difference approach, but soil water content was well simulated in the presence of crop residues. The use of a finite-difference approach highlights the need to account for upward movement of water in the soil and its consequences on deep drainage.Median annual drainage simulated at 1.5 m was +9.1 mm for the fallow-wheat rotation, −5.4 mm for fallow-wheat–pea, −8.4 mm for mustard–wheat–pea, and +0.6 mm for wheat–wheat. The 3-year rotations (FWP and MWP) had the lowest median drainage and lowest probability of large drainage events in wet years. In the fallow-wheat rotation, median annual drainage was 24.8 mm with stubble retention and zero tillage, compared to −2.8 mm for stubble burnt and conventional tillage. Whilst the median response is indicative of comparative system performance, large episodic drainage events can be expected to be more frequent under fallow-wheat and even larger events with stubble retention and zero tillage. Stubble retention and zero tillage might be justified to increase and stabilise crop yield and reduce soil erosion but they do need to be assessed against the requirement to reduce deep drainage that is implicated in rising river and soil salinisation.

Phenotypic plasticity of yield and agronomic traits in cereals and rapeseed at high latitudes

AbstractIn the northernmost European environments of Finland, large variability in the yield and quality of crops is a critical source of uncertainty for growers and end-users of grain. The aims of this study were (i) to quantify and compare the plasticity, i.e., cultivar responsiveness to environment, in yield of spring oat, spring wheat, six-row barley, two-row barley, winter rye, winter wheat, turnip rape and oilseed rape, (ii) to explore the existence of hierarchies or positive correlations in the plasticity of agronomic, yield and quality traits and (iii) to probe for trends in yield plasticity associated with different eras of breeding for yield potential and agronomic traits. Plasticities of yield, agronomic and quality traits were derived as slopes of norms of reaction using MTT Agrifood Research Finland data sets combining long-term (1970–2008 for cereals and 1976–2008 for rapeseed) results from 15 to 26 locations. Plasticity of yield ranged typically between 0.8 and 1.2, was smallest for six-row barley (0.84–1.11) and largest for winter rye (0.72–1.36). We found two types of associations between plasticity of yield and yield under stressful or favourable conditions for cereals but none for rape. In spring wheat, oat and six-row barley, high yield plasticity was associated with crop responsiveness to favourable conditions rather than yield reductions under stressful conditions. Modern spring wheat cultivars had higher maximum grain yields compared to older ones at the same level of plasticity. In winter wheat and rye, high yield plasticity resulted from the combination of high yield in favourable conditions and low yield in stressful environments. Many associations between yield plasticity and other traits were identified in cereals: e.g., high yield plasticity was often associated with higher grain weight, more grains per square meter, later maturity (contrary to turnip rape), shorter plants, less lodging and lower grain protein content and in winter cereals with higher winter damage.

Screening field pea for adaptation to water and heat stress: Associations between yield, crop growth rate and seed abortion

Highlights•Twenty-nine pea lines compared in environments spanning a 3-fold range in yield.•Environmental variation in yield was related to water availability and maximum temperature from 400 °Cd before to 200 °Cd after flowering.•No trade-offs between yield in favourable and stressful conditions.•Crop growth rate in a critical window accounted for 50% of the variation in seed number and for 44% of the variation in yield.•Genotype-dependent increase in yield of 73 kg ha−1 per 1% reduction in pod wall ratio.

Synergy between breeding for yield in winter wheat and high-input agriculture in North-West China

Highlights•The interactions between varieties and supply of resources were analysed from the perspective of phenotypic plasticity.•Plasticity of yield increased with year of cultivar release.•Newer varieties had better stability in harvest index under high inputs.•Selection for yield has improved the ability of winter wheat to capture the benefits of higher inputs.

Development, growth and yield of late-sown soybean in the southern Pampas

AbstractSoybean/wheat double cropping is becoming a key component of farming systems in the southern Pampas. In contrast to milder environments, where reduced seed number and shorter duration of early reproductive stages (between R1, one open flower at any node, and R5, 3 mm-long seed in a pod at one of the four uppermost nodes) account for most of the variation in the yield of late-sown soybean, it is proposed that seed weight and duration of later stages (R5 to R7, physiological maturity) are also important in a cooler environment. To evaluate this hypothesis, the yield and yield components of late-sown soybean, as if double-cropped after wheat, were measured in an environment where radiation and temperature fall sharply in late summer (37°S). We carried out a factorial experiment that combined seasons (dry, 1998 and wet, 1999), sowing dates (mid December and early January), cultivars (maturity group II and III), inter-row spacings (0.19 and 0.38 m) and water regimes (dryland and irrigated).This research established a new environmental boundary for soybean performance in soybean/wheat double cropping, moving into temperatures 2 to 4 °C below those in the cooler environments reported in the literature. Yield ranged from 3.7 t ha−1 in irrigated, early sown crops to 2.2 t ha−1 in late-sown dryland crops. Significant interactions between sowing date and other experimental sources of variation were detected that highlight the complex process involved in yield determination. Averaged over all sources of variation, delayed sowing reduced yield at a rate about 2% d−1 from mid December. Seed number accounted for 86, shoot biomass for 66 and harvest index for 56% of the variation in yield. Early-sown crops had heavier seed than their late sown counterparts, i.e. 136 vs. 118 mg seed−1. The decline in crop biomass, harvest index, seed number and individual seed weight with delayed sowing can be attributed to three main factors: (i) shorter season length, (ii) slow growth rate associated with short days, and low temperature and radiation, and (iii) a dramatic reduction in the relative duration of key phenostages, chiefly the period from R5 to R7 which accounted for 77% of the variation in yield, 56% of the variation in seed number and 62% of the variation in seed weight. Crop management practices for late sown soybean are discussed.

Nitrogen and water-use efficiency of Australian wheat varieties released between 1958 and 2007

AbstractWe used a collection of Australian wheats released between 1958 and 2007 to probe for time trends in evapotranspiration and nitrogen uptake, and the efficiencies in the use of water and nitrogen to produce grain yield. Yield increased linearly with year of cultivar release at a rate of 18 kg ha−1 y−1; this rate aligned with the relationship between rate of genetic gain and environmental yield from breeding programs worldwide. No time trend was apparent for seasonal evapotranspiration, hence the linear increase in yield per unit evapotranspiration with year of release which was fully accounted for by yield improvement. Under our experimental conditions, yield per unit transpiration of current varieties was ∼24 kg ha−1 mm−1, highlighting the need to update the 20 kg ha−1 mm−1 ratio commonly used in agronomic benchmarking.Yield per unit nitrogen uptake was largely unchanged as a consequence of increased nitrogen uptake that paralleled the increase in yield, and a secondary contribution of reduced grain protein concentration particularly under environmental conditions that favoured high protein. The nitrogen nutrition index, accounting for the effect of biomass on nitrogen uptake, increased linearly with year of cultivar release, hence supporting the conclusion that breeding for yield improved the nutrition status of wheat in association with an increased capacity to uptake nitrogen in equal-sized crops.

Precision agriculture based on crop physiological principles improves whole-farm yield and profit: A case study

Highlights•Precision agriculture should account for the physiological processes underlying the relationship between environment and crop development, growth and yield.•Crop choice and practices were tailored to each zone based on ecophysiological principles.•Zone management increased production and profit, and reduced risk.•It is possible to achieve the yield gain rates required to meet projected grain demand in 2050.

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