Katrine A. Stewart

Evaluation of selected warm-season grasses for biomass production in areas with a short growing season

Field studies were conducted in 1994 and 1995 to determine the phenology, leaf and tiller characteristics and yield of 22 warm-season grasses in south western Quebec, Canada. Cordgrass (Spartina pectinata L.), two cultivars of Indiangrass [Sorghastrum nutans L. (Nash)], two cultivars of big bluestem (Andropogon gerardii Vitman), 12 cultivars of switchgrass (Panicum virgatum L.) and five cultivars of prairie sandreed [Calamovilfa longifolia (Hook) Scribn., were included in the study. In terms of initial spring growth, CWNC (cordgrass) and New Jersey 50 (switchgrass) were the earliest and latest, respectively. Initial spring regrowth from sandreeds was predominantly from continued growth of biennial tillers, from rhizomes in cordgrass and from buds on stem bases for the other species. The earliest maturing entries were ND3743, Dakota, Ottawa3 (switchgrasses) and Bison (big bluestem). New Jersey 50 and CWNC were the latest maturing. CWNC had high tiller numbers throughout the season while the rest of the entries showed increases in tiller numbers in summer. There were significant differences among entries in height development across the season. Biomass yields ranged from 65 to 861 g per plant. Lignocellulose concentration was high in all entries with neutral detergent fiber (NDF) and acid detergent fiber (ADF) ranging from 770–860 g kg−1 and 460–540 g kg−1, respectively. Nitrogen and ash concentrations ranged from 4–10 and 40–70 g kg−1, respectively. The results indicate potential for cordgrass (CWNC) and several switchgrasses for biomass production in the short season areas of Quebec.

RELATIONSHIPS BETWEEN EXTRACTABLE CHLOROPHYLL AND SPAD VALUES IN MUSKMELON LEAVES

Chlorophyll content of muskmelon is usually determined by destructively sampling plant leaves. However, a hand-held SPAD-502 Chlorophyll Meter provides rapid and nondestructive measurements of leaf chlorophyll content. This study aims to determine the relationships between extractable chlorophyll and SPAD values in muskmelon leaves. SPAD readings were significantly related to extracted chlorophyll of muskmelon leaves both on a fresh weight and leaf area basis. Quadratic equations best described their relationships. At 10 days after nitrogen (N) fertilization, the r2 values for chlorophyll a, b, and total chlorophyll on a fresh weight basis were 0.84, 0.86, and 0.85, respectively, while on a leaf area basis, r2 values were 0.92, 0.95, and 0.94, respectively. At 17 days after fertilization, the r2 values for chlorophyll a, b, and total chlorophyll on a fresh weight basis were 0.57, 0.49, and 0.56, respectively, while on a leaf area basis, r2 were 0.72, 0.67, and 0.71, respectively. Therefore, the SPAD-502 Chlorophyll Meter can be used to measure chlorophyll content of muskmelon leaves.

Field evaluation of the chlorophyll meter to predict yield and nitrogen concentration of switchgrass

Abstract Chlorophyll meters have been used to estimate leaf chlorophyll content, and therefore nitrogen (N) status and fertilization requirements for several crops. However, until now C4 forage grasses have not been investigated in this regard. A field study was conducted in 1995 and 1996 to evaluate the potential of chlorophyll (SPAD) meter readings to determine switchgrass N concentration and herbage yield. Meter readings were taken on the top most fully expanded leaves of switchgrass grown on a free draining sandy clay loam soil (St Bernard, Typic Hapludalf) fertilized at 0, 75, or 150 kg N ha‐1. The switchgrass was either cut at the end of the season or every four or six weeks. Herbage N concentration in uncut stands declined with time while SPAD readings increased to a mid‐season maximum, beyond which they declined rapidly. The relationship between N concentration and SPAD readings was linear (r2=0.62–0.93; p<0.01) for the cut systems. Exceptforthe 1st cut under the 4‐week harvest regime, there were ...

The use of thermal time to model common lambsquarters (Chenopodium album) seedling emergence in corn

Abstract A mathematical model was developed to predict common lambsquarters seedling emergence in southwestern Quebec. The model was based on the thermal-time concept, using air temperatures in the double-sine calculation method. The model was built using data from five experiment-years for corn naturally infested with weed populations. Once developed, the model was calibrated using different crop seedbed preparation times. The base temperature was then adjusted for each time of seedbed preparation. A power regression function was used to relate adjusted base temperatures and the accumulated thermal units at seedbed preparation time. A modified Weibull function was then fitted to the field emergence data, expressed as the cumulative proportion of the total seedling emergence over the growing season as a function of cumulative thermal units. The simplicity and accuracy of this model would make it an excellent tool to predict common lambsquarters seedling emergence in field situations, facilitating the determination of the timing of scouting in integrated weed management systems. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; corn, Zea mays L. ‘Pioneer 3921’.

Weed response to flame weeding at different developmental stages.

Abstract Flame weeding is often used for weed control in organic production and other situations where use of herbicides is prohibited or undesirable. Response to cross-flaming was evaluated on five common weed species: common lambsquarters, redroot pigweed, shepherds-purse, barnyardgrass, and yellow foxtail. Dose-response curves were generated according to species and growth stage. Dicot species were more effectively controlled than monocot species. Common lambsquarters was susceptible to flame treatment with doses required for 95% control (LD95) ranging from 0.9 to 3.3 kg/km with increasing maturity stage. Comparable levels of control in redroot pigweed required higher doses than common lambsquarters, but adequate control was still achieved. Flaming effectively controlled shepherds-purse at the cotyledon stage (LD95  =  1.2 kg/km). However, the LD95 for weeds with two to five leaves increased to 2.5 kg/km, likely due to the rosette stage of growth, which allowed treated weeds to avoid thermal injury. Control of barnyardgrass and yellow foxtail was poor, with weed survival > 50% for all maturity stages and flaming doses tested. Flame weeding can be an effective and labor-saving weed control method, the extent of which is partially dependent on the weed flora present. Knowledge of the local weed flora and their susceptibility to flame weeding is vital for the effective use of this method. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; common lambsquarters, Chenopodium album L. CHEAL; redroot pigweed, Amaranthus retroflexus L. AMARE; shepherds-purse, Capsella bursa-pastoris (L.) Medik. CAPBP; yellow foxtail, Setaria pumila (Poir.) Roemer and J.A. Schultes SETLU.

Calibration and validation of a common lambsquarters (Chenopodium album) seedling emergence model

Abstract Studies were conducted to calibrate and validate a mathematical model previously developed to predict common lambsquarters seedling emergence at different corn seedbed preparation times. The model was calibrated for different types of soil by adjusting the base temperature of common lambsquarters seedling emergence to the soil texture. A relationship was established with the sand mineral fraction of the soil and was integrated into the model. The calibrated model provided a good fit of the field data and was accurate in predicting cumulative weed emergence in different soil types. The validation was done using data collected independently at a site located 80 km from the original experimental area. There were no differences between observed and predicted values. The accuracy of the model is very satisfactory because the emergence of common lambsquarters populations was accurately predicted at the 95% probability level. This model is one of the first to take into consideration seedbed preparation time and soil texture. This common lambsquarters emergence model could be adapted to model other weed species whose emergence is limited by low spring temperature. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL.; corn, Zea mays L. ‘Pioneer 3921’.

Use of Perennial Legumes Living Mulches and Green Manures for the Fertilization of Organic Broccoli

Fertilization of organic horticultural crops is often problematic due to a scarcity of manure and nutrient sources. Field experiments were conducted in Sainte-Anne-de-Bellevue, Québec, Canada, to evaluate red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.) as perennial living mulches and green manures for the fertilization of broccoli (Brassica oleracea var. italica Plenk). Yield, broccoli N uptake, incidence of hollow stem, and available soil N were increased by both red clover and alfalfa green manures. Available soil N was also increased by alfalfa living mulch. However, competition in living mulch treatments led to equal or reduced yields and broccoli N uptake compared to the unfertilized control. Application of mulch clippings directly on the crop row did not increase nitrogen transfer to broccoli. Living mulches have the potential to supply N but should be mown more frequently to reduce competition with the main crop.

Row Covers Reduce Insect Populations and Damage and Improve Early Season Crisphead Lettuce Production

Insect damage on cripshead lettuce (Lactuca sativa L.) can reduce its marketability and cause significant crop losses. There is increasing interest in using alternative control strategies to replace or reduce pesticide use for this purpose. Crisphead lettuce cv. Ithaca grown under two densities 10 (ARC10) and 17 (ARC17) g/m2 of polypropylene applied as floating covers or low tunnels were compared with an uncovered control. Effects on tarnished plant bugs and aphids, air and soil temperature, and lettuce growth and development were recorded. Aphids and tarnished plant bug were almost completely excluded by covers. Once removed, insect population in the covered treatments increased but was 5.5 times less than in uncovered control. Covered plots had higher air and soil temperatures than uncovered plots. Air temperatures were higher under the floating covers than tunnels. ARC17 had higher soil temperatures than ARC10. Row covers promoted earlier growth and maturity. Head weights of lettuce covered with ARC17 were 1.4 times heavier than those of ARC10, which in turn were heavier than the control. Head weights were similar for floating covers and low tunnel treatments.

Reduction of Insect Damage in Radish with Floating Row Covers

ABSTRACT Radish (Raphanus sativus L.) is a short season direct seeded crop with multiple seedlings starting as soon as the ground has thawed to ensure continuous supply. Floating row covers can be used to protect crops from low temperature to stimulate germination and to exclude insect pests. There is a need to optimize the use of floating row covers for early and mid-season radish production with floating row covers of different weave and weight. Two types of floating row covers (Agryl P10 and Agryl P17) and an uncovered treatment were compared in a randomized block design experiment with four replicates in the muck soil region of southwestern Quebec. The floating row covers completely excluded cabbage maggots (Delia radicum L.) and significantly reduced beetle (Phyllotreta spp.) damage by 60% compared to control plots. Both floating row covers increased daytime temperatures relative to the control, with Agryl P17 producing the warmest microclimate. Covering the seeded plots increased total emergence by 19% and decreased mean emergence time by 1.3 days but did not affect the uniformity of seed germination as expressed by the spread of emergence. For the three sowing dates, the floating row covers accelerated growth relative to the control, resulting in heavier leaf weight and larger root diameter at harvest. Radish plants covered with Agryl P17 in the late season showed a decrease in foliage health, which likely resulted from excessive heat. Plants covered with Agryl P17 and Agryl P10 were harvested respectively 10 days ± 4 days and 7 days ± 5 days earlier than the control.

Plastic Mulches and Low Tunnels to Reduce Bolting and Increase Marketable Yield of Early Celery

Abstract Canadian celery (Apium graveolens L. var. duke) growers are transplanting crops earlier to lengthen the growing season. This increases the risks of vernalization (exposure to temperatures <14°C), which induces bolting and makes the plants unmarketable. Combinations of mulches and low tunnels were tested in 1999 and 2000 to determine whether they could increase air and/or soil temperatures to inhibit bolting. Mulches increased maximum soil temperatures by up to 10°C compared with the control. Low tunnels, particularly polyethylene tunnels combined with clear mulch, increased both air and soil temperatures. In 1999, few if any plants bolted. In 2000, covering celery with tunnels significantly reduced bolting. Covering celery with a single layer of spunbonded polyester produced the most consistent benefits in terms of reducing bolting and increasing marketable yield.