Winter Wheat Biomass Research Articles

Modelling the effects of sub‐lethal doses of herbicide and nitrogen fertilizer on crop–weed competition

SummaryThe effects of sub‐lethal dose of herbicide and nitrogen fertilizer on crop–weed competition were investigated. Biomass increases of winter wheat and a model weed, Brassica napus, at no‐herbicide treatment with increasing nitrogen were successfully described by the inverse quadratic model and the linear model respectively. Increases in weed competitivity (β0) of the rectangular hyperbola and parameter B in the dose–response curve for weed biomass, with increasing nitrogen were also successfully described by the exponential model. New models were developed by incorporating inverse quadratic and exponential models into the combined rectangular hyperbola with the standard dose–response curve for winter wheat biomass yield and the combined standard dose—response model with the rectangular hyperbola for weed biomass, to describe the complex effects of herbicide and nitrogen on crop–weed competition. The models developed were used to predict crop yield and weed biomass and to estimate the herbicide doses required to restrict crop yield loss caused by weeds and weed biomass production to an acceptable level at a range of nitrogen levels. The model for crop yield was further modified to estimate the herbicide dose and nitrogen level to achieve a target crop biomass yield. For the target crop biomass yield of 1200 g m−2 with an infestation of 100 B. napus plants m−2, the model recommended various options for nitrogen and herbicide combinations: 140 and 2.9, 180 and 0.9 and 360 kg ha−1 and 1.7 g a.i. ha−1 of nitrogen and metsulfuron‐methyl respectively.

Simulating the response of photosynthate partitioning during vegetative growth in winter wheat to environmental factors

Currently available models of photosynthate partitioning in crops are poorly developed compared to carbon and water balance models. This paper presents a dynamic photosynthate partitioning model (PPModel) that simulates the partitioning of crop biomass to leaf, stem and root through the interaction between carbon gain (assimilation less respiration) and transpiration, in relation to environmental factors. The central concept is the theory of plant functional equilibrium, in which transpirational loss and water uptake are balanced, within acceptable limits, by a dynamic partitioning of assimilates between shoot and root growth. The model was shown to perform effectively against experimental data for growth and partitioning of biomass in winter wheat (collected over a 2-year period), when environmental factors varied daily and water supply was controlled over a wide range.

Evaluation of Green, Red, and Near Infrared Bands for Predicting Winter Wheat Biomass, Nitrogen Uptake, and Final Grain Yield#

Presently normalized difference vegetative indexes (NDVI) based on red (RNDVI) or green (GNDVI) reflectance are commonly used to evaluate plant health, biomass, and nutrient content. This study was conducted to determine which of these two indexes is more correlated with biomass, forage nitrogen (N) uptake, and final grain yield of winter wheat. Three experimental sites were established in Oklahoma in the fall of 2001 at Stillwater. Spectral reflectance measurements were taken at Feekes growth stage 4, 6, and 10.5 followed by winter wheat forage harvest. When evaluated at specific stages of growth, RNDVI was consistently more highly correlated with biomass than GNDVI. Green NDVI and RNDVI were more highly correlated with forage N uptake than with dry biomass at each stage of growth, but neither index appeared to have a comparative advantage over the other. Both indexes were highly correlated with final grain yield and grain N uptake across all locations. Neither index appeared to have a sizeable advantage over the other, suggesting that either will perform equally well when predicting forage N uptake, grain yield, and grain N uptake in winter wheat. Red NDVI does appear to be a better predictor of forage biomass, specifically at earlier stages of growth. #Contribution of Okla. Agric. Exp. Stn.

Diurnal Variation in Hyperspectral Vegetation Indices Related to Winter Wheat Biomass Formation

In this study, a comparison of six vegetation indices derived from hyperspectral reflectance measurements is presented. The aim was to assess the suitability of the indices to detect agronomically relevant crop parameters in the course of a day. Irradiance and reflectance of winter wheat (Triticum aestivum L.) were recorded simultaneously with a portable device, equipped with two spectrometers, on a near-canopy scale in a field trial. Variations in reflection properties of the wheat canopies were induced by (i) growing wheat varieties differing in growth characteristics or leaf colour, and (ii) applying different nitrogen amounts. Biomass samples were taken to determine above-ground biomass yield, N concentration in biomass, and N uptake. The indices were compared by means of analysis of variance and multiple comparisons of means. In winter wheat, considerable differences between the indices were measurable. The red edge inflection point (REIP), and the infrared index (IRI) were least subjected to diurnal variations and simultaneously proved to be most sensitive to N rate. For the REIP, the infrared green index (IRG) and the IRI, no saturation effects were observed for a high N supply. These indices seem to be most advantageous to detect agronomically relevant crop parameters in winter wheat in the course of a day. A practicable concept is proposed for the application of vegetation indices as a tool to optimise N fertilisation.

Responses of winter wheat and diclofop-methyl–sensitive and –resistant Italian ryegrass (Lolium multiflorum) to AE F130060 03

Abstract Greenhouse and laboratory experiments were conducted to investigate the response of winter wheat, and two diclofop-methyl–sensitive (OR and KG) and four diclofop-methyl–resistant (EP, GT, RBG, and JB) Italian ryegrass biotypes to the experimental herbicide mixture AE F130060 03 (an 8.3:1.7 mixture of the experimental sulfonylurea herbicides AE F130060 00 and AE F115008 00). AE F130060 03 at 15 or 18 g ha−1 without the safener AE F107892 reduced biomass of winter wheat 10 to 14%, whereas applications made with AE F107892 did not reduce wheat biomass. AE F130060 03 at 15 or 18 g ai ha−1 was more effective than diclofop-methyl in reducing biomass of one diclofop-methyl–sensitive Italian ryegrass biotype and all four diclofop-methyl–resistant biotypes. However, differential responses to AE F130060 03 at 15 and 18 g ha−1 occurred among diclofop-methyl–resistant biotypes. AE F130060 03 at 15 or 18 g ha−1 reduced biomass of OR, KG, EP, and GT from 61 to 84% but reduced biomass of RBG and JB biotypes onl...

Biomass and nitrogen traits of summer pigeon peas and winter wheat grown for three rotations in containers

Pigeon pea [Cajanus cajan (L.) Millsp.] cultivars, ‘Georgia-1’ and ‘ICPL-87’, were grown without inoculation and with Bradyrhizobium inoculation (multistrain, TAL 1127, or TAL 1132) to evaluate legume dry weight (DW) and nitrogen (N) content, soil mineral N, and subsequent wheat (Triticum aestivum L.) productivity. Pigeon peas were grown during summer and ‘TAM 101’ wheat was grown during winter, along with summer fallow controls fertilized with 0, 45, and 90 kg N ha− 1, in 36-cm diam. 20-L pots from 1992 to 1995. Representative pigeon peas were harvested in the fall and remaining plants were incorporated into the soil. Wheat was planted and soil cores were collected at 35 to 48 d after pigeon pea harvest. Wheat was harvested the following spring. Factors affecting DW and N content of both crops included length of growing season, environmental variation, and contribution of residual N. Among pigeon pea cultivars, Georgia-1 occasionally demonstrated higher DW and N content compared with ICPL-87. Estimation of N provided by pigeon pea to the last wheat crop in the third sequence of yearly rotations was 30 kg N ha− 1. Pigeon pea treatments demonstrating highest DW, N content, and contribution to soil N generally produced winter wheat with higher yield and N content compared with other treatments. While yield and N content of winter wheat fertilized at 90 kg N ha− 1 either decreased or stayed the same from 1993 to 1995, these same measurements in wheat following pigeon peas demonstrated a 3- to 4-fold increase over the same time period and warrant further research in field rotation systems of the southern Great Plains.

Interactive effects of soil temperature, atmospheric carbon dioxide and soil N on root development, biomass and nutrient uptake of winter wheat during vegetative growth.

Nutrient requirements for plant growth are expected to rise in response to the predicted changes in CO(2) and temperature. In this context, little attention has been paid to the effects of soil temperature, which limits plant growth at early stages in temperate regions. A factorial growth-room experiment was conducted with winter wheat, varying soil temperature (10 degrees C and 15 degrees C), atmospheric CO(2) concentration (360 and 700 ppm), and N supply (low and high). The hypothesis was that soil temperature would modify root development, biomass allocation and nutrient uptake during vegetative growth and that its effects would interact with atmospheric CO(2) and N availability. Soil temperature effects were confirmed for most of the variables measured and 3-factor interactions were observed for root development, plant biomass components, N-use efficiency, and shoot P content. Importantly, the soil temperature effects were manifest in the absence of any change in air temperature. Changes in root development, nutrient uptake and nutrient-use efficiencies were interpreted as counterbalancing mechanisms for meeting nutrient requirements for plant growth in each situation. Most variables responded to an increase in resource availability in the order: N supply >soil temperature >CO(2).

Remote Sensing of Biomass and Yield of Winter Wheat under Different Nitrogen Supplies

Vegetation indices derived from reflectance data are related to canopy variables such as aboveground biomass, leaf area index (LAI), and the fraction of intercepted photosynthetically active radiation (fIPAR). However, under N stress the relationships between vegetation indices (VI) and these canopy variables might be confounded due to plant chlorosis. We studied the relationships between reflectance-based VI and canopy variables (aboveground biomass, LAI canopy chlorophyll A content [LAI X Chl A], and fIPAR) for a wheat (Triticum aestivum L.) crop growing under different N supplies. Nitrogen fertilization promoted significant increases in radiation interception (plant growth) and, to a lesser extent, in radiation use efficiency (RUE). The VI vs. LAI relationships varied significantly among treatments, rendering the VI-based equations unreliable to estimate LAI under contrasting N conditions. However, a single relationship emerged when LAI X Chl A was considered. Moreover, VI were robust indicators of fIPAR by green canopy components independently of N treatment and phenology. Aboveground biomass was poorly correlated with grain yield, whereas cumulative VI simple ratio (SR) was a good predictor of grain yield, probably because cumulative SR closely tracked the duration and intensity of the canopy photosynthetic capacity.

Effect of proximity factors on competition between winter wheat (Triticum aestivum) and Italian ryegrass (Lolium multiflorum)

Density and spatial arrangement (rectangularity) effects on the competitive relationships, yield performance, and dynamics in canopy dominance of winter wheat and Italian ryegrass were evaluated using two addition series experiments. In experiment 1, combinations of six densities of each species formed the treatment matrix of addition series. In experiment 2, each species was tested at four densities and three rectangularities (RE) of winter wheat. In monocultures, crop density (plants per square meter) explained 82 to 85% of the total variation in the per-plant biomass of winter wheat in experiment 1. In mixtures of crop and weed, initial wheat density (N1) and initial ryegrass density (N2) and interaction of N1and N2explained 74 to 80% of the total variation in the per-plant biomass of winter wheat and 68 to 79% of Italian ryegrass in experiment 1. Intraspecific competition was apparent between 15 and 90 days after emergence (DAE) in winter wheat and between 90 and 170 DAE in Italian ryegrass. In mixtures, RE influenced plant size of Italian ryegrass up to 50 DAE only. Maximum winter wheat intraspecific competition occurred at 170 DAE, but maximum interspecific competition occurred during reproductive stages in mixtures. High RE increased seed yield, seed size, and harvest index of winter wheat and reduced biomass of Italian ryegrass. Grain yield of winter wheat was reduced up to 92% by competition from ryegrass. Even nine ryegrass plants in 100 winter wheat plants m−2reduced winter wheat grain yield by 33%. However, the extent of loss in winter wheat grain yield was less in RE 16 (wider spacing) than in RE 1 (square planting) or 4 (close row spacing). Winter wheat was the stronger competitor during vegetative stages, but Italian ryegrass became the stronger competitor during the reproductive stages of development. Winter wheat leaves dominated at the top canopy during the vegetative stage, but ryegrass dominated at the top canopy during the reproductive stages. In the top canopy of mixtures at 200 DAE, the leaf area indices (LAI) of ryegrass was 6.6 times greater than winter wheat at RE 1 compared to only 1.6 times at RE 16. Greater LAI of Italian ryegrass in the top canopy reduced photosynthetically active radiation available to winter wheat by 68% at booting stage.

Winter wheat biomass and nitrogen dynamics under different fertilization and water regimes: application of a crop growth model

Growth, nitrogen uptake and nitrogen allocation between roots, stems, leaves and grains were measured and simulated in winter wheat on a clay soil in three treatments including daily irrigation and fertilization. Special emphasis was placed on biomass and nitrogen allocation within the crop and on the availability of soil nitrogen for crop growth. The model used for the simulations of growth (SOILN-CROP), which was driven by a hydrological model, is based on the light interception concept and empirical allometric functions. Growth is the driving force for nitrogen uptake, which is limited by the availability of mineral N in the soil. The model was calibrated for one treatment. Thereafter, the same parameter set was used to simulate the other two treatments. Frequent irrigation in combination with single-dose fertilization increased crop growth and N leaching compared with the non-irrigated but single-dose fertilized control, whereas irrigation together with daily fertilization increased crop growth and N uptake but not N leaching. Simulated soil mineral N levels agreed well with measurements on a 1-year time scale. Assimilate allocation to roots decreased logarithmically with total crop biomass in all treatments. Allocation to leaves decreased linearly with total above-ground crop mass. The crop availability of mineral N differed considerably between treatments. The model parameter defining the proportion of soil mineral N available for plant uptake had a strong influence on model behaviour. This proportion is indicated to depend on soil water content and the mechanisms of this relation need to be considered in future work to improve our predictions of N uptake.

Effects of shading in different developmental phases on biomass and grain yield of winter wheat at ambient and elevated CO2

ABSTRACTWinter wheat (Triticum aestivuin cv. Mercia) was grown in a controlled‐environment facility under simulated Held conditions at ambient (360μmol mol−1) and elevated (690 μmol mol−1) CO2 concentrations. Some of the plants were shaded to mimic cloudy conditions during three periods of about 20d duration between terminal spikelet and start of grain‐fill, giving 16 treatments in all. Elevated CO2, increased grain yield by about 20%, while shading in any period decreased yield, with the greatest effect in the last period, encompassing anthesis. No interactions between these effects were significant for grain yield, but there were complex interactions for mean grain size. Observed effects of shading and elevated CO2 on biomass production were well predicted by a simulation model. Observed effects of treatments on yield could be related to effects on biomass using a simple model which assumes that yield is proportional to biomass production, with coefficients of 0.42 (g grain yield g−1 biomass) for the first two periods and 0.74 for the last period. Wheat models should therefore include developmental changes in sensitivity of yield to biomass production, but biomass changes induced by different CO2 concentrations or light environments can be treated as having equivalent effects on grain yield.

CropSyst, a cropping systems simulation model: Water/nitrogen budgets and crop yield

In agriculture, water and nitrogen are two critical resources for growing a crop. However, their management cannot be analyzed independently of weather, soil characteristics, field hydrology, crop characteristics, crop rotation, and management factors. This paper describes the water, nitrogen, and crop growth components of CropSyst, a comprehensive cropping systems simulation model, and provides preliminary verification of these components. The water budget of the model properly describes crop water use. Predicted nitrogen contents throughout the soil profile did not exactly match the measured values from leaching experiments, but they did follow the general trends of the data. The agreement between simulated and observed biomass and yield of corn, winter wheat and spring wheat grown in two locations with a total of 77 data points was good as shown by several statistical indicators. Based on this preliminary validation, CropSyst appears promising as a tool to analyze management practices for water and nitrogen. Additional validation of model components, including a wide range of crops and conditions, should be conducted in the future.

Downy Brome (Bromus tectorum) Density and Relative Time of Emergence Affects Interference in Winter Wheat (Triticum aestivum)

Field experiments over 3 yr at Lethbridge, Alberta, determined the effect of various downy brome densities and times of its emergence on winter wheat biomass and seed yield. Downy brome reduced wheat biomass up to 59% and seed yield up to 68%. Time of downy brome emergence relative to wheat affected the magnitude of these yield reductions more than the density of downy brome. At comparable densities, downy brome caused 2- to 5-fold greater reductions in yield when it emerged within 3 wk after winter wheat than when it emerged 6 wk after wheat or in early spring. Late-emerging downy brome caused significant wheat yield or biomass losses only at densities of 200 to 400 plants m-2. Late-emerging downy brome plants were strongly shaded (70 to 90%) by winter wheat throughout much of the growing season.

Growth promotion of winter wheat by fluorescent pseudomonads under growth chamber conditions

The efficacy of Pseudomonas cepacia R85, P. putida R104 and R105, and P. fluorescens R111 and their rifampicin-nalidixic acid resistant (Rif r Nal r) counterparts to enhance the growth of winter wheat ( Triticum aestivum L. var Norstar) was assessed in two soils under simulated fall conditions (at 5°C) in a growth chamber. Bacterial colonization and survival on wheat roots, and the effects of inoculation on plant yield, total-P, total-Fe and 15N-uptake from fertilizer were determined. Introduced Rif r Nal r pseudomonads colonized and survived on the plant roots throughout the 150-day study. Some wild-type and their Rif r Nal r mutants enhanced early plant biomass of winter wheat in a low-fertility Dark Brown Chernozemic soil, whereas grain yield was enhanced by 46–75% in a more fertile Ortho Black Chemozemic soil. Inoculation also affected the uptake of fertilizer N and soil Fe by winter wheat in both soils. Our results show that some fluorescent pseudomonads and their Rif r Nal r mutants stimulated growth and nutrient uptake of vernalized winter wheat, although the response to inoculation was dependent on soil characteristics. The use of Rif r Nal r marked bacteria allowed root colonization and population dynamics of inoculants in the rhizosphere of winter wheat to be studied, and may facilitate plant-inoculant studies under field conditions.

DEFOLIATION EFFECTS ON BIOMASS YIELD COMPONENTS OF WINTER WHEAT

Short duration, high intensity grazing is often used to maximize production of grazed forage crops. Relatively little information is currently available for this practice on dual purpose cereal crops such as wheat. Components of soft white winter wheat biomass yield were studied during the 1979 and 1980 crop years near Corvallis, Oregon. Treatments were a factorial arrangement of two defoliation times (mid-April and mid-May) and three defoliation intensities (undefoliated and clipped to either an 8-cm or 4-cm stubble). All defoliation regimes reduced grain yields compared to undefoliated controls. However, biomass yields of 8-cm vs. 4-cm treatments were similar within defoliation dates. Grain yields primarily reflected the most recent defoliation event, suggesting that plant phenological stage and/or the length of the regrowth period following defoliation was more important than the intensity of the defoliation event in determining plant yield.Key words: Short duration grazing, grazing wheat