Linear Plateau Research Articles

Predicting the Nitrogen Quota Application Rate in a Double Rice Cropping System Based on Rice–Soil Nitrogen Balance and 15N Labelling Analysis

Excessive nitrogen (N) fertilization, low use efficiency, and heavy pollution are the dominant issues that exist in intensively cultivated double rice cropping systems in China. Two-year field and 15N microregion experiments were conducted to evaluate the N fate in a soil-rice system under a series of different N rate treatments from 2020 to 2021. The economic N application rate that simultaneously improved rice yield and N use efficiency in the rotation system was also investigated. Results demonstrated that soil residues and mineralized N accounted for more than 58.0% and 53.2% of the total N input in the early and late rice seasons, respectively. Similarly, most of the total N input was absorbed by rice, ranging from 43.7% to 55.6% in early rice and from 36.8% to 54.7% in late rice. Rice N use efficiency significantly decreased with increasing N application, while rice grain yield and its N uptake increased when the N application rate was below 150 kg ha−1 in early rice and 200 kg ha−1 in late rice. Exceeding this point limited rice N uptake and yield formation. The apparent N recovery rate, N residual rate, and N loss rate were 23.5–34.4%, 17.0–47.1%, and 26.0–47.8% for the early rice, and 32.8–37.3%, 74.2–87.0%, and 71.5–92.1% for the late rice. The linear plateau analysis further indicated that the recommended N application rate (118.5–152.8 kg ha−1 for early rice and 169.9–186.2 kg ha−1 for late rice) can not only maintain a relatively higher rice yield and N utilization but also significantly reduce soil N residue. Our results provide theoretical guidance for improving N management in double-cropping rice fields in southern China.

Rheology and Phase Behavior of Surfactant–Oil–Water Systems and Their Relationship with O/W Nano-Emulsion’s Characteristics Obtained by Dilution

In order to study the relationship between the rheology of a surfactant’s concentrated dispersions and the oil and water liquid crystals from which O/W nanoemulsions (NEs) can be produced by water dilution, the phase diagram of a model SOW (surfactant–oil–water) system was constructed. The dispersion’s compositions to be characterized by rheology were chosen in the diagram’s regions that contain liquid crystal phases. For this, the dilution lines S/O = 25/75, 55/45, and 70/30 with a water content of 20 and 40 wt% (corresponding to surfactant concentrations between 15 and 55 wt%) were chosen. By adding these dispersions to a water pool, NEs were obtained, and it was shown that droplet size distribution depends on the amount of the liquid crystal phase in the initial dispersion and its rheology. The study of the oscillatory amplitude of the dispersion showed a linear viscoelastic plateau (G’ > G”) and a softening deformation region (G” > G’), indicating a viscoelastic behavior of the dispersions. The study was carried out at a constant temperature of 30 °C, and the results show that rheological characterization by itself is not enough to predict that monomodal droplet distributions are obtained. However, the presence and quantity of lamellar liquid crystal phase are important to obtain monodisperse and kinetically stable NEs.

Aluminum foam development by filling architecture techniques and process optimization

The aluminum foam is used in various industrial applications because of its superior strength to weight ratio. The FSP is used here for development of a precursor by processing a foamable mixture into the substrate. The filling of the foamable mixture is done by different techniques named: Buried hole, sandwich, and groove architecture. The developed precursor is then microwave heated for the development of foam. A comparison is made between the different filling techniques, number of passes and composition of the foamable mixture on the distribution of pores, size, porosity, and compressive behavior of the foam. It has been observed that the buried hole is more suitable for foam development owing to less wastage of foaming agent. The decomposed gases were fully utilized by trapping into the substrate. It is also observed that increasing the number of passes and weight % of TiH2, improves the distribution of pores. The buried hole technique shows the linear plateau stress in the compressive test as compared to other techniques. The highest porosity is close to 80% during buried hole technique, and the average pore diameter ranges between 0.4 and 1.69 mm for optimized samples.

Spring Wheat–Summer Maize Annual Crop System Grain Yield and Nitrogen Utilization Response to Nitrogen Application Rate in the Thermal–Resource–Limited Region of the North China Plain

Spring wheat–summer maize (SWSM) annual crop systems were formed to satisfy the maize grain mechanized harvest thermal requirement in the thermal–resource–limited region of the North China Plain. However, the nitrogen (N) application rate effect on SWSM annual yield formation, N accumulation and utilization were barely evaluated. Two–year field experiments were conducted to evaluate the effects of the N application rate on the annual yield of SWSM, observe N accumulation and utilization, and identify the optimized N application. The experiments were conducted under 5 N levels of 0 (N0), 180 (N180), 240 (N240), 300 (N300), and 360 (N360) kg ha−1. The results showed that spring wheat, summer maize and annual cereal yield under the N240 and N480 treatments obtained the highest grain yield (GY) of 5038, 1282 and 16,320 kg ha−1, respectively, and the optimal N application rate was estimated using a linear–plateau model to be 231–307, 222–337 and 463–571 kg ha−1 with maximum GY of 4654–5317, 11,727–12,003 and 16,349–16,658 kg ha−1, respectively. With the increase in the N application rate, the dry matter accumulation (DM) were significantly increased by 16.9–173.5% for spring wheat and 11.1≈–76.8% for summer maize, respectively; and the annual cereal DM was 15.1–179.7% greater than that with N0 treatment, respectively. Spring wheat, summer maize and the annual cereal total N accumulation (TN) under N360 and N720 treatments were significantly increased by 5.4–19.1%, 16.6–32.3% and 11.5–26.2%, respectively, compared to the other treatments; however, N use efficiency for biomass and grain production (NUEbms and NUEg) were decreased significantly by 10.9–13.6% and 8.9–20.7%, 6.8–13.8% and 12.2–15.6%, and 5.5–11.7% and 10.0–16.0%, respectively. Meanwhile, the N partial factor productivity (PFPN), N agronomy use efficiency (ANUE), N recovery efficiency (NRE) and N uptake efficiency (NEupk) under the N240 treatment for spring wheat and summer maize obtained high levels of 20.99 and 47.01 kg−1, 9.27 and 16.35 kg−1, 32.53% and 32.44%, and 0.85 and 0.72 kg−1, respectively. Correlation analysis showed that the N application rate, TN and NEupk played significantly positive roles on GY, spring wheat spilke grain number, summer maize ear grain number and 1000–grain weight, DM LAImax and SPADmax, while NUEbms, NUEg, PFPN and ANUE always played negative effects. These results demonstrate that spring wheat, summer maize and annual cereal obtained the highest GY being 4654–5317, 11,727–12,003 and 16,349–16,658 kg ha−1 with the optimal N application rate 231–307, 222–337 and 463–571 kg ha−1, respectively, which provide N application guidance to farmer for spring wheat–summer maize crop systems to achieve annual mechanical harvesting in the thermal–resource–limited region of the North China Plain.

Characterization of mechanical and metallurgical properties of AA6063 foam developed by friction stir precursor deposition technique

The aim of this work is to develop the precursor-based Al foam by deposition of AA6063-T6 consumable rod, filled with a foamable mixture of titanium hydrate (TiH2) and aluminium powder over a mild steel substrate through friction stir deposition (FSD) technique. The AA6063-T6 consumable rods were drilled with different hole strategies ranging from 1 to 6 holes on the periphery of the rod, which were filled with foaming powder of the same composition. To perform the deposition, a conventional vertical milling machine was used. The deposited material presents a fine equiaxed grain whose size is much lower than the as-received material, indicating dynamic recrystallization during friction stir deposition. The results also show that the foaming particles decrease the hardness values of the produced deposits when compared to those of base material. It has been observed that 4 and 5 numbers of holes in the consumable rod are more suitable for foam development and the foaming particles are more uniform as obtained from energy dispersive spectrum (EDS) and scanning electron microscope (SEM) analysis. It is also observed that by increasing the number of holes in the rod more than 5 promote the formation of defects in the developed foam. The consumable rod with 4 and 5 holes shows the linear plateau stress in the compressive test as compared to 1, 2, 3 and 6 holes.

Discrepancy between the crop yield goal rate and the optimum nitrogen rates for maize production in Mississippi

AbstractThe varying influence of the environment on N supply and demand dictates the need for annually updated fertilizer N recommendations. Currently, crop yield goal (CYG) methods are used by 34 land grant universities, including Mississippi State University, these do not consider environmental variations. This research tested the efficacy of CYG by determining the agronomic optimum N rate (AONR) and the economic optimum N rate for Mississippi corn (Zea mays L.) production. In total, 12 treatments in 2020 and 11 in 2021 were replicated four times over four locations in a randomized complete block design. The optimum N rates were calculated by fitting linear, quadratic, linear plateau, and quadratic plateau models by means of three different goodness of fit measures. Furthermore, differences between the CYG rate calculated from the Mississippi yield goal equation and AONR were compared at different management levels (14 comparisons) (all data combined, both years combined, sites combined by year, and individual sites). Overall, AONR varied from 134 to 301 kg N ha–1 at different management levels. When we compared the AONR to the CYG rate, the CYG rate over‐recommended N in 12 of the 14 possible comparisons, with differences ranging from 69 kg N ha–1 less to 110 kg N ha–1 greater than the AONR. These differences between AONR values highlight variability caused by factors such as the soil, environment, and their interaction with N supply and demand, which are unaccounted for by the CYG method.

Sample size and Shapiro-Wilk test: An analysis for soybean grain yield

Ignoring the violation of the error normality assumption is a common mistake that can cause inconsistencies in the results of the analysis of variance. To avoid this, normality tests such as the Shapiro-Wilk test can be used to verify whether this assumption is met or violated. However, the test accuracy relies on a representative number of observations sampled in trials, once the calculated W statistic used for the test is considered sensitive or capable of being altered according to the sample size. Therefore, the aims of this study were to analyze the Shapiro-Wilk test response to sample size for soybean grain yield and to define the sample size for optimizing the W statistic estimate, making it more efficient and reliable. For this, the replacement sampling method was applied in trials that measured soybean grain yield per plant. The trials were performed in two locations in the state of Rio Grande do Sul, Brazil, and in each, three sowing dates were assessed, using a total of 30 commercial soybean cultivars. Grain yield per plant was assessed by weighing grains at maturity and correcting the value to 13 % moisture. Posteriorly, thirty-one sample scenarios were simulated per experimental unit, performing an analysis of variance and applying the Shapiro-Wilk test at 5 % error probability to the experimental unit errors in each pre-defined sampling scenario. Also, four methodologies for determining the maximum curvature point to define sample size were compared, which are the general, spline, perpendicular distance, and linear plateau methods. The 95 % confidence interval width of the W statistic had an exponential decreasing response for trials that either meet or violate the error normality assumption. Small sample sizes per experimental unit led to biased estimates of the test, where it was either under or overestimated. The perpendicular distance and linear plateau methods were the most adequate to define the sufficient sample size for the W statistic, and at least 17 plants per experimental unit should be used for estimating error normality for soybean grain yield reliably.

The Effect of Harvest Date on Temporal Cannabinoid and Biomass Production in the Floral Hemp (Cannabis sativa L.) Cultivars BaOx and Cherry Wine

The objectives of this study were to model the temporal accumulation of cannabidiol (CBD) and tetrahydrocannabinol (THC) in field-grown floral hemp in North Carolina and establish harvest timing recommendations to minimize non-compliant crop production. Field trials were conducted in 2020 and 2021 with BaOx and Cherry Wine cultivars. Harvest events started two weeks after floral initiation and occurred every two weeks for 12 weeks. Per-plant threshed biomass accumulation exhibited a linear plateau trend. The best fit model for temporal accumulation of THC was a beta growth curve. As harvest date was delayed, total THC concentrations increased until concentrations reached their maximum, then decreased as plants approached senescence. Logistic regression was the best fit model for temporal accumulation of CBD. CBD concentrations increased with later harvest dates. Unlike THC concentrations, there was no decline in total CBD concentrations. To minimize risk, growers should test their crop as early as possible within the USDA’s 30-day compliance window. We observed ‘BaOx’ and ‘Cherry Wine’ exceeding the compliance threshold 50 and 41 days after flower initiation, respectively.

Defining relative yield for soil test correlation and calibration trials in the Fertilizer Recommendation Support Tool

AbstractThe Fertilizer Recommendation Support Tool (FRST) will perform correlations between soil nutrient concentrations and crop response to fertilization from user‐selected datasets in the FRST national database. Yield response for the nutrient of interest in a particular site‐year is presented as relative yield (RY), a ratio of unfertilized yield to the maximum attainable yield (A). Several methods exist in the literature for estimating A and calculating RY but the effect of method choice on soil test correlation outcomes is undocumented. We used six published methods to calculate RY from site‐year yield data for five published correlation datasets, and fit a generalized linear plateau (LP) model to each. The critical soil test value (at the LP join point) and RY intercept coefficients were not significantly affected by RY method for any of the datasets, and RY plateau was significantly affected by method for only one dataset. The top options after robust group discussions were the so‐called MAX and FITMAX methods. We selected the MAX method, which defines A as the numerically highest treatment yield mean, as the most appropriate method for FRST because MAX represents maximal yield in responsive sites, is inclusive of trial data having a range of treatment numbers, limits RY to 100% (which allows options for transforming data), and is simpler to implement than FITMAX, which requires a decision tree to calculate RY for diverse trials.

The Effects of Weather and Fertilization on Grain Yield and Stability of Winter Wheat Growing on Orthic Luvisol-Analysis of Long-Term Field Experiment.

Based on a long-term experiment in Prague, established in 1954, we analyzed the effect of weather and seven fertilization treatments (mineral and manure treatments) on winter wheat grain yield (GY) and stability. In total, 23 seasons were analyzed, where a wheat crop followed a summer crop of potatoes. A regression analysis showed that, since the experiment started, there has been a significant increase in the annual daily maximum, average, and minimum temperature of 0.5 °C, and an increase in annual rainfall of 0.3 mm. Grain yield was positively associated with April precipitation, mean daily temperature in October, and daily maximum temperature in February. Yields were most stable between years with two fertilizer treatments that supplied a mean of 47 kg N ha−1yr−1, 54 kg P ha−1yr−1, and 108 kg K ha−1yr−1. The rate of N at which grain yield was optimized was determined according to the linear-plateau (LP) and quadratic response models as 44 kg N ha−1yr−1 for the long-strawed varieties and 87 kg N ha−1yr−1for short-strawed varieties.A gradual increase in yields was observed in all treatments, including the unfertilized control, which was attributed to improved varieties rather than to a changing climate.

Dietary effect of energy levels on growth performance and carcass characteristics of White Pekin duck over 21 days.

This experiment was conducted to determine the maximum dietary energy levels on growth performance and carcass characteristics of White Pekin duck. the Six dietary treatments were formulated based on their apparent metabolizable energy (AME) concentrations from 2,700 to 3,200 kcal/kg with a 100 kcal/kg gap to evaluate the accurate dietary AME requirement to address current knowledge and further issues for fulfilling the genetic potential of meat-type white Pekin ducklings. A total of 432 one-day-old male White Pekin ducklings were randomly allocated into one of six dietary treatments with six replicates (12 birds per pen). The diets were formulated as corn-soybean meal-based diets to meet or exceed the Nutrient Requirement of Poultry specification for meat-type ducks. Growth performance indices (i.e. average daily gain [ADG], average daily feed intake, feed conversion ratio) were measured weekly. Medium body weight (BW) ducklings from each pen were sacrificed to analyze the carcass traits and abdominal fat content on day 21. Obtained data were analyzed to estimate significant effect using the one-way ANOVA of IBM SPSS Statistics (Version, 25). If the p-value of the results were significant, differences in means among treatments were separated by Tukey’s post hoc test. Significant differences were then analyzed with a linear and quadratic broken model to estimate the accurate concentration of AME. Ducklings fed higher dietary AME diets increased (p < 0.05) BW, ADG. Ducklings fed higher AME than 2,900 kcal/kg diets increased abdominal fat accumulation and leg meat portion. The estimated requirement by linear plateau method showed from 3,000.00 kcal/kg to 3,173.03 kcal/kg whereas the requirement by quadratic plateau method indicated from 3,100.00 kcal/kg to 3,306.26 kcal/kg. Collectively, estimated dietary requirements exhibit diverse results based on the measured traits and analysis methods. All the estimated requirements in this experiment present higher than previous research, the maximum requirement for the next diet formulation should be selected by the purpose of the diet.

Yield and growth characteristics of a high oil–protein soybean with enhanced diacylglycerol acyltransferase

AbstractIntroduction of the VgDGAT1A gene in soybean [Glycine max (L.) Merr.] genotypes increased both protein and oil content and resulted in earlier maturation compared with commonly cultivated soybean genotypes (i.e., Jack). However, the effect of VgDGAT1A gene on the length of the vegetative, reproductive, and the overall growth period of soybean has not been thoroughly evaluated. A randomized complete block design consisting of two transgenic soybean genotypes with VgD1‐1 and VgD1‐2 highly active acyl‐CoA: diacylglycerol acyltransferase (DGAT) from ironweed [Vernonia galamensis (Cass) Less.] and nontransgenic control (Jack) was evaluated in field studies in 2015 and 2016 in Lexington, Kentucky. Levels of sucrose accumulation and seed weight were calculated for the three genotypes. Soybean grain yield, seed weight, and seed number were similar among all genotypes in both years. Modified genotypes reached the R7 (beginning of physiological maturity) stage earlier, and the rate of dry weight accumulation in individual seeds ranged between 2.8 to 4.4 mg seed−1 day−1 and was not different in comparison with the control (range: 3.4–4.7 mg seed−1 day−1). While days to reach R7 was shorter in VgD, there were no differences among genotypes for pod weight (PW), seed weight (SW), pod sucrose (PS), or seed sucrose (SS) concentrations. Linear plateau and cubic models were the best fit for seed weight for both years. These results indicated that despite earlier maturation in VgD genotypes, seed growth, and final soybean yield were similar among VgD and Jack.

Improving wheat yield by optimizing seeding and fertilizer rates based on precipitation in the summer fallow season in drylands of the Loess Plateau

Precipitation has been recognized as the dominant factor driving crop grain yields and large yield variations in drylands, which suggests that some agricultural management practices can be optimized to achieve high yields and benefits. In this study, we investigated 804 farmers' wheat fields from 2015 to 2018 in the dryland area of the Loess Plateau in China and analyzed the relationships between wheat yield and the influence factors (including precipitation, wheat sowing rate, fertilizer inputs, and soil nutrients) to propose optimized agricultural management practices for wheat production. The results showed that wheat grain yield followed a linear plateau pattern relative to the precipitation in the summer fallow season, with a yield of 5344 kg ha−1 obtained at a precipitation of 203 mm. In the L203 group (precipitation in the summer fallow season less than 203 mm), the Low-yield subgroup (0–33th in grain yield group (in order from low to high)) had a lower sowing rate, kernel weight, kernel number and spike number than the High-yield subgroup (68–100th in grain yield group); different levels of phosphorous (P) and potassium (K) fertilizer overuse were found among the three yield subgroups. However, in the H203 group (precipitation in the summer fallow season greater than 203 mm), differences in only kernel and spike numbers and nitrogen (N) fertilizer application rate were observed among the Low-, Moderate-, and High-yield subgroups. Additionally, there were no differences in the soil organic matter (SOM), total N or pH in the three subgroups in either L203 or H203, but significant differences in soil mineral N, available P and K were observed among the three subgroups (except mineral N in L203). Based on these results, the wheat sowing rate and fertilizer input rates can be optimized to increase wheat yield and farmers’ income and promote agricultural management for dryland wheat production on the Loess Plateau.

Qual é a melhor maneira para definir o tamanho amostral para mudas de couve-flor?

ABSTRACT: This study compared four methods for defining the ideal sample size per experimental unit to estimate the overall experimental mean for the total length, shoot length, root length, and the number of leaves of cauliflower seedlings. An experiment was carried out where the number of leaves, shoot, root, and total length were measured, and the general, perpendicular distance, linear response plateau, and spline methods were tested. While the general method may under or overestimate sample size and the sampling of 10 seedlings suggested by the spline method is still too far from the stabilization point of the curve, the perpendicular distance and linear plateau response methods are recommended to obtain results corresponding to narrower confidence interval widths. Therefore, according to the perpendicular distance method, at least 15 seedlings per experimental unit are required to estimate the overall experimental mean of cauliflower seedlings reliably for the traits here measured.

Modeling analysis of the growth of a cubic crystal in a finite space.

The applications of semiconductor nanocrystals in optoelectronics are based on the unique characteristic of quantum confinement. There is great interest to tailor the performance of optoelectronic nanodevices and systems through the control of the sizes of nanocrystals. In this work, we develop a general mathematical formulation for the growth of a crystal/particle in a liquid solution, which takes account of the combinational effect of diffusion-limited growth and reaction-limited growth, and formulate the growth equations for the size of a cubic crystal grown under three different scenarios - isothermal and isochoric conditions, isothermal growth with the evaporation and/or extraction of the solvent and isochoric growth with continuous change in temperature. For the growth of a cubic crystal under isothermal and isochoric conditions, there are three growth stages - linear growth, nonlinear growth and plateau, and the growth rate in the stage of linear growth and the final size of the cubic crystal are dependent on the degree of supersaturation. For the growth of multi-crystals with a Gaussian distribution of crystal sizes, the change of the monomer concentration in a liquid solution is dependent on the change rates of average size and the standard deviation of the crystal sizes.

Evaluation of Soil Test Phosphorus Extractants and Tissue Analysis for Corn

The objective of this study was to evaluate the relationship of four different soil test phosphorus methods (Mehlich 3, Bray 1, Bray 2, and Haney H3A) for corn production, and determine critical P tissue concentration at different growing stages. The experiment was conducted at 12 locations, and the fertilizer treatments consisted of five phosphorus fertilizer rates applied by broadcast pre-plant. Soil samples were collected at 0- to 6-in. depth, then samples were collected before treatment application by block. Tissue samples were collected at the V6 and R1 growth stages. The relationship between the different soil test phosphorus methods and the R2 varies between 0.24–0.93. Mehlich 3 and Bray 1 have a higher correlation, and Bray 1 and Bray 2 have a lower correlation. Linear plateau determined the critical phosphorus levels for the V6 growth stage was 0.42%, and for the R1 stage was 0.22%. The relationship between the concentration at V6 and R1 was moderately correlated with R2 = 0.62, having a higher phosphorus concentration in the early stage.

Exploring the nitrogen source-sink ratio to quantify ear nitrogen accumulation in maize and wheat using critical nitrogen dilution curve

Ear nitrogen (N) accumulation plays an imperative role in ear photosynthesis and the formation of grain yield and quality of maize and wheat. However, the mechanism governing ear N accumulation (NAe) especially under different N levels is not yet clear. For this purpose, this study endeavored to describe the N source-sink ratio of NAe by developing a model using ear critical N concentration (%Nc) dilution curves of maize and wheat. The data obtained include ear dry matter (DMe), NAe, ear N nutrition index (NNIe), ear N accumulation rate index (NARIe), post-anthesis N uptake (PANU), grain number (GN), and thousand-grain weight (TGW) were collected from 12 varied N rates (0–300 kg N ha−1) field experiments conducted using four wheat and three maize cultivars. Integrated models were developed to show the effect of N source and sink on NAe in maize and wheat. The ratio between PANU and NAe was used to represent the post-anthesis supply capacity of N source, while DMe was used as the storage capacity of N sink in these models. Robust relationships of NARIe with the ratio between PANU and NAe in maize and wheat indicated that NAe was controlled by N source from N-limiting to non-N-limiting levels. The relationship between the rate of ear dry matter accumulation (DMRe) and NNIe showed a linear plateau model across different N levels due to the similar DMe under non-N-limiting levels, indicating that ear N status was regulated by DMe (N sink) under N-limiting levels. Therefore, NAe under N-limiting levels was co-regulated by N source and sink. Besides, the temporal effect of plant N status before anthesis on NAe was also observed. The close relationship between DMe and plant N status at anthesis across different N levels in maize and wheat indicated that the potential ear N sink was controlled by the pre-anthesis supply capacity of plant N source. Consequently, pre-anthesis plant N status was imperative for quantifying potential ear N sink. This was the first-ever attempt to investigate the N source-sink ratio of NAe using ear %Nc curve and highlighted the effect of pre-anthesis plant N status on NAe. The findings will contribute towards a better understanding of the process of NAe under different N levels for developing a judicious N management strategy for improving the N use efficiency of wheat and maize.

Geographically weighted regression estimation of the linear response and plateau function

Geographically weighted regression estimation of the linear response and plateau function

Potato Yield, Net Revenue and Specific Gravity Responses to Nitrogen Fertilizer under Different Canadian Agroecozones

Applying higher nitrogen (N) rates than required for optimum potato (Solanum tuberosum L.) growth leads to economic and environmental losses. The extent to which the N rate associated with maximum potato yields differs from that maximizing net revenue (NR) or potato specific gravity is not fully understood. The objectives of this three-year study (2013–2015) conducted at five sites in three Canadian provinces (MB-1; MB-2; QC-1; QC-2; PEI) (15 site-years) were to: (i) assess potato marketable yield, NR, and specific gravity responses to increasing N application; (ii) calculate the N rate maximizing marketable (Nmax) yield and NR using different statistical models. The year, N fertilizer, and their interaction were significant on marketable yield and NR except at the MB-1 site where no significant effect of N was observed. No significant yield increases were observed at a N rate above 60 kg N ha−1 at four site-years and above 120 kg N ha−1 at five site-years, implying that the current recommended N rate could be reduced. All models fitted the marketable and NR data equally based on R2, mean bias error or root mean square error and resulted in comparable predicted yield and NR values. However, Nmax values were different depending on the model with higher values being predicted by the quadratic- (161.4 to 191.9 kg N ha−1) and the quadratic plateau models (60 to 191.9 kg N ha−1), while lower Nmax values were obtained with linear plateau- (60.6 to 129.8 kg N ha−1) and Mitscherlich–Baule plateau models (60.9 to 130. 9 kg N ha−1). Nitrogen rate maximizing NR was on average 4% lower than the N rate maximizing marketable yields, except at one site where it was higher by 26 kg N ha−1 when the quadratic plus plateau model was used. Specific gravity tended to decrease with the N rate. Our study confirms trade-offs between the N rate maximizing yields or NR with that maximizing specific gravity. Nitrogen rate maximizing marketable yield and NR varies depending on the selected model.

Constitutive Modeling of the Densification Behavior in Open-Porous Cellular Solids.

The macroscopic mechanical behavior of open-porous cellular materials is dictated by the geometric and material properties of their microscopic cell walls. The overall compressive response of such materials is divided into three regimes, namely, the linear elastic, plateau and densification. In this paper, a constitutive model is presented, which captures not only the linear elastic regime and the subsequent pore-collapse, but is also shown to be capable of capturing the hardening upon the densification of the network. Here, the network is considered to be made up of idealized square-shaped cells, whose cell walls undergo bending and buckling under compression. Depending on the choice of damage criterion, viz. elastic buckling or irreversible bending, the cell walls collapse. These collapsed cells are then assumed to behave as nonlinear springs, acting as a foundation to the elastic network of active open cells. To this end, the network is decomposed into an active network and a collapsed one. The compressive strain at the onset of densification is then shown to be quantified by the point of intersection of the two network stress-strain curves. A parameter sensitivity analysis is presented to demonstrate the range of different material characteristics that the model is capable of capturing. The proposed constitutive model is further validated against two different types of nanoporous materials and shows good agreement.