L. M. Dwyer

Inter-relationships of applied nitrogen, SPAD, and yield of leafy and non-leafy maize genotypes

The SPAD chlorophyll meter was found to be a reliable, quick, and non-destructive tool used for directly measuring leaf chlorophyll and indirectly assessing the proportional parameter of leaf, and by extension, plant nitrogen (N) status. The meter has been used successfully to assess leaf N in conventional maize crops, but it has not been used with new maize (Zea mays L.) genotypes containing leafy (L) and reduced stature (RS) traits. SPAD meter readings were collected on the uppermost fully developed leaves (before silking) and on the ear leaf (after silking) of field grown maize genotypes with and without the L and RS traits. The experiment was conducted during 1996 and 1997 at two sites in Eastern Canada (Ottawa and Montreal). At each site in each year, a split plot arrangement of two treatment factors was used in a randomized complete block design with four blocks. The main plot treatments were levels of N (0, 85, 170, and 255 kg ha−1), with six maize genotypes as subplot treatments. The hybrids included: (i) leafy reduced-stature, LRS, (ii) non-leafy normal stature, NLNS, (iii) leafy normal stature, (LNS), (iv) non-leafy reduced-stature, NLRS, (v) conventional commercial hybrids, Pioneer 3905 as the hybrid check for late maturity, and (vi) Pioneer 3979, a check for early maturity. The hybrids were chosen on the basis of their contrasting canopies and root architecture. The SPAD meter readings were collected on the same five plant genotypes over time (six times per site per year, except four times for the Ottawa site in 1997). All genotypes showed increasing meter reading values as plants aged until silking. In general, SPAD meter readings increased as N fertilization level increased at each measurement date for both sites and years. In general, LNS and P3905 hybrids showed greater SPAD meter readings than other hybrids at all sampling dates for both sites and growing seasons. Applied N rates were significantly correlated with the SPAD meter readings. More highly significant relationships were found for N fertilizer levels and SPAD meter readings for the hybrids in 1997 than for the hybrids in 1996. For the Montreal site in 1997, LRS, LNS and P3905 hybrids were among those showing the highest r values between N level and SPAD readings. The correlation coefficients between SPAD readings and grain yield were generally lower. However, the NLNS hybrid had a high SPAD-yield correlation at the Macdonald site in 1997.

Weed Biomass Production Response to Plant Spacing and Corn (Zea mays) Hybrids Differing in Canopy Architecture1

Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec, Canada, and in 1996 at Ottawa, Ontario, Canada, to quantify the impact of corn hybrids, differing in canopy architecture and plant spacing (plant population density and row spacing), on biomass production by transplanted and naturally occurring weeds. The treatments consisted of a factorial combination of corn type (leafy reduced stature [LRS], late-maturing big leaf [LMBL], a conventional Pioneer 3979 [P3979], and, as a control, a corn-free condition [weed monoculture]), two weed levels (low density [transplanted weeds: common lambsquarters and redroot pigweed] and high density [weedy: plots with naturally occurring weeds]), two corn population densities (normal and high), and row spacings (38 and 76 cm). At all site-years under both weed levels, the decrease in biomass production by both transplanted and naturally occurring weeds was greater due to the narrow row spacing than due to the high plant population density. The combination of narrower rows and higher population densities increased corn canopy light interception by 3 to 5%. Biomass produced by both transplanted and naturally occurring weeds was five to eight times less under the corn canopy than in the weed monoculture treatment. Generally, weed biomass production was reduced more by early-maturing hybrids (LRS and P3979) than by LMBL. Thus, hybrid selection and plant spacing could be used as important components of integrated pest management (weed control) for sustainable agriculture. Nomenclature: Common lambsquarters, Chenopodium album L. #3 CHEAL; corn, Zea mays L.; redroot pigweed, Amaranthus retroflexus L. # AMARE. Additional index words: Competitivness, early maturity, weed management. Abbreviations: LAI, leaf area index; Lfy, leafy; LMBL, late-maturing big leaf; LRS, Leafy reduced stature; P3979, Pioneer 3979; rd1, reduced stature.

Within plot variability in available soil mineral nitrogen in relation to leaf greenness and yield

Abstract Available soil mineral nitrogen (N) varies both temporally and spatially. These variations affect field‐scale N‐use efficiency. A field study was conducted for three years to investigate spatial variability in available soil mineral N within uniform research plots in relation to leaf greenness or chlorophyll content (plant N sufficiency) and yield. Variations within the plot in available soil mineral N sampled at the 6‐ligule stage was related to N fertility: the higher the fertilizer N levels, the higher the variability. The standard deviation for the 200 kg N ha‐1 treatment was up to five times higher than the unfertilized control treatment. The nitrate (NO3)‐N accounted for 70 to 80% of soil mineral N in fertilized plots compared to 50 to 60% in unfertilized control plots. The variability in grain yield of individual maize (Zea mays L.) plants within a plot was inversely related to soil N fertility: the higher the fertilizer N levels, the lower the yield variability (at 100 or 200 kg N ha‐1, y...

Leafy reduced-stature maize for short-season environments: morphological aspects of inbred lines

Development of maize (Zea mays L.) types that produce leaf area rapidly and finish vegetative development quickly would increase production of maize in mid- to short-season areas. The Leafy (Lfy1) and reduced-stature (rd1) traits each make contributions to this end. However, these two traits have not previously been combined. Our objective was to evaluate the morphological aspects of non-leafy normal-stature (NLNS), leafy reduced-stature (LRS), non-leafy reduced-stature (NLRS), and leafy normal-stature (LNS) maize inbreds. Two traits, Lfy1 and rd1, were incorporated into a series of inbreds, resulting in a range of canopy architectures. Twelve variables were recorded for each of 30 inbreds over three years. The 12 variables were: seed emergence, above-ear leaf number, below-ear leaf number, dead leaf number at tasselling, live leaf number at tasselling, total leaf number, above-ear leaf area, ear leaf length, ear leaf width, ear height, internode length, and plant height. Inbreds containing the Lfy1 trait had more above-ear leaf area, above-ear leaf number, dead leaf number at tasselling, total leaf number and number of live leaves at tasselling than non-leafy inbred lines. Below-ear leaf number was not different among LRS, LNS, and NLNS inbred lines. LRS and NLRS inbred lines were also not different for below-ear leaf number. Plant height, ear height, and ear leaf length and width were higher in normal-stature than reduced-stature plants. The proportion of the seeds which emerged was higher for LRS inbreds than the other trait groups.

Timing and method of 15nitrogen-labeled fertilizer application on grain protein and nitrogen use efficiency of spring wheat

ABSTRACT Grain protein content is one of the most important quality constraints for bread wheat (Triticum aestivum L.) production in eastern Canada. A field experiment was conducted for two years (1999 and 2000) on the Central Experimental Farm, Ottawa, Canada, to study whether split application of nitrogen (N) fertilizer improved grain protein content and nitrogen-use efficiency (NUE). Two cultivars (‘Celtic,’ as N-responsive and ‘Grandin’, as N-non-responsive) were grown using three different N doses and application methods: (1) 100 kg N ha−1 as NH4NO3, soil-applied at seeding with 15N2-labeled NH4NO3 to microplots, (2) 60 kg N ha−1 soil-applied at seeding plus 40 kg N ha−1 foliar-applied at the boot stage with 15N2-labeled urea to microplots, and (3) 90 kg N ha−1 as soil-applied at seeding plus 10 kg N ha−1 foliar-applied at the boot stage with 15N2-labeled urea to microplots. Plants were sampled at heading and maturity. While dry-matter production and grain yields were not affected by the treatments in either year, N application methods influenced tissue N concentration and NUE. In 1999, extended drought stress led to significant yield reduction; in 2000, foliar application of 10 kg N ha−1 at the boot stage significantly increased grain N concentration when grain protein was under the limit for bread quality, suggesting that later-applied N can contribute to grain protein content. At maturity, the average NUE was 22.3% in 1999 and 34.5% in 2000, but was always greater when all N was applied at seeding (42.5%) than when N was foliar-applied at the boot stage (18.5% to 24.5%). We conclude that application of a small amount of fertilizer N at the boot stage can improve the bread-making quality of spring wheat by increasing grain protein concentration.

Leafy reduced-stature maize for short-season environments: Yield and yield components of inbred lines

Development of maize (Zea mays L.) types that produce leaf area and mature quickly would increase production of maize in mid- to short-season areas. The leafy (Lfy1) and reduced-stature (rd1) traits both make contributions to this end. However, these two traits have not previously been combined. Our objective was to evaluate the yield and yield components of non-leafy normal-stature (NLNS), leafy reduced-stature (LRS), non-leafy reduced-stature (NLRS), and leafy normal-stature (LNS) maize inbred lines. The two genes, ‘Lfy1’ and ‘rd1’, were incorporated into a series of inbred lines resulting in a range of canopy architectures. Ten variables were recorded for each of 30 inbred lines over three years. The 10 variables were: corn heat unit requirement from planting to tasselling, corn heat unit requirement from planting to silking, days between tasselling and silking, grain moisture content, husk dry weight, cob dry weight, ear length, maximum ear circumference, grain yield and ratio of grain yield to moisture content. Reduced-stature inbred lines reached anthesis more quickly than normal-stature inbred lines. Grain moisture content was less in reduced-stature inbred lines than normal stature trait groups. Leafy-reduced stature plants had the highest ratio of grain to moisture content and the lowest grain moisture content at harvest. Inbred lines containing the rd1 trait matured more rapidly than other trait groups. The LRS trait group yielded more than the other groups, and showed great potential for use in mid- to short-season environments.

Use of nitrogen‐15 microplots for field studies of maize nitrogen‐use efficiency

Abstract Choice of minimum size of nitrogen (15N) microplots is essential in studies of maize (Zea mays L.) N uptake, translocation, assimilation, and accumulation patterns using the 15N isotopic technique. The objectives of this field experiment were to determine if: i) plants adjacent to restricted 15N microplots (0.76 m × 0.23 m × 0.25 m deep, centred on a plant) were 15N‐enriched, ii) growth of plants in microplots was hampered, and iii) the estimated fertilizer N recovery (FNR) was lower than that previously reported. There was no detectable enrichment by applied 15N in maize plants adjacent to the microplots. Root and aboveground biomass and N content of plants in the microplots were similar to plants in the main plot at harvest (P>0.1). The FNR in the aboveground plants was 29% for 200 kg N ha‐1 and 38% for 100 kg N ha‐1 treatment with 18 and 26% in the corresponding grains. These values were similar to those reported in the literature where larger non‐restricted or restricted microplots were used....

Plant sample nitrogen-15 measurement response to tube pressure with optical emission spectroscopy

Abstract Optical emission spectroscopy provides a rapid and relatively precise method for determining 15N/14N ratios of 15N‐enriched plant and/or soil samples. The objectives of this study were to determine the optimum amount of nitrogen (N) in measurement tubes which would generate a usable operating pressure range after baking and to measure N enrichment of plant samples with a large range of N concentrations and % atom 15N enrichment using a commercial emission spectrometer. Ten plant samples with large ranges of N concentration of 0.1 to 3.5% and % atom 15N enrichment of 0.37 to 3.54% were used to determine the optimum amount of N in the tube. Another 350 plant samples contributed to a comparison of success rate of tube lighting during emission spectroscopy and of determination of the 15N baseline at normal (7 μg) and low (3.5 μg) N levels in the tube. Results of our analysis of plant samples suggest that for routine 15N analysis by emission spectrometer, tubes (1 mL internal volume) containing 3 to 4...

Distillation solution with and without indicator for nitrogen-15 measurement by optical emission spectrometry

Abstract Optical emission spectroscopy provides a rapid and precise method for determining 15N/14N ratios of 15N‐enriched plant and/or soil samples. The objective of this study was to determine the effect of an indicator added in the distillation solution on the success rate of tube lighting in the optical emission spectrometer over a large range of N concentration in 15N enriched plant samples. One‐hundred‐eighty plant samples with large ranges of N concentration (4 to 30 g.kg‐1 dry weight) and 15N atom enrichment (0.368 to 1.635%) were analyzed. Our data suggest that there was no difference in the success rate of tube lighting in emission spectroscopy and in 15N/14N ratio measured between samples prepared with and without addition of indicator in the distillation solution.

Effect of peduncle‐perfused nitrogen, sucrose, and growth regulators on barley and wheat amino acid composition

Abstract Nitrogen (N) or growth regulator application to small grain cereals near anthesis has been demonstrated to alter grain fill and grain yield, the protein yield and nutritional quality may also be modified by these management factors. The objective of this study was to determine whether delivery of N, growth regulator, or sucrose solutions into greenhouse‐grown barley (Hordeurn vulgare L. cv. Leger) or wheat (Triticum aestivum L. cv. Katepwa), plants through peduncle perfusion altered the amino acid composition of the grain. The following treatments were tested: N (25 and 50 mM), chlormequat (30 μM), ethephon (15 μM), N + chlormequat, N + ethephon, detillering + N, sucrose (250 mM), distilled water check, and non‐perfused check. Perfusion lasted 30 d beginning 5 to 8 d after spike emergence. Addition of N via peduncle perfusion increased protein concentrations and concentrations of all amino acids in both barley and wheat when expressed in terms of grain dry matter. Protein yield and lysine content...