Gilles Bélanger

Root biomass and shoot to root ratios of perennial forage crops in eastern Canada

Shoot to root ratios (S:R) at peak standing crop are commonly used to estimate the annual crop residue C inputs to the soil from the root biomass left in the soil at harvest. However, root biomass has often been neglected in field studies and estimates of S:R for many commonly grown forage species are not available. Our objective was to determine root biomass and S:R of seven perennial grass species and two perennial legume species under eastern Canadian soil and climatic conditions. Root biomass in three soil layers (0–15, 15–30 and 30–45 cm) was measured shortly after the second harvest in the first (1995) and second (1996) year of production. Two harvests of aboveground DM were taken each year. The total root biomass (0–45 cm) in the second year of production (average of 1437 g m-2) was twice that measured in the first year of production (average of 683 g m-2). This temporal variation was mainly explained by the increase of root biomass in the 0- to 15-cm layer. The proportion of total root biomass (0–...

Ecosystem function enhanced by combining four functional types of plant species in intensively managed grassland mixtures: a 3‐year continental‐scale field experiment

1.A coordinated continental-scale field experiment across 31 sites was used to compare the biomass yield of monocultures and four species mixtures associated with intensively managed agricultural grassland systems. To increase complementarity in resource use, each of the four species in the experimental design represented a distinct functional type derived from two levels of each of two functional traits, nitrogen acquisition (N2-fixing legume or nonfixing grass) crossed with temporal development (fast-establishing or temporally persistent). Relative abundances of the four functional types in mixtures were systematically varied at sowing to vary the evenness of the same four species in mixture communities at each site and sown at two levels of seed density. 2.Across multiple years, the total yield (including weed biomass) of the mixtures exceeded that of the average monoculture in >97% of comparisons. It also exceeded that of the best monoculture (transgressive overyielding) in about 60% of sites, with a mean yield ratio of mixture to best-performing monoculture of 1·07 across all sites. Analyses based on yield of sown species only (excluding weed biomass) demonstrated considerably greater transgressive overyielding (significant at about 70% of sites, ratio of mixture to best-performing monoculture = 1·18). 3.Mixtures maintained a resistance to weed invasion over at least 3 years. In mixtures, median values indicate

Critical Nitrogen Curve and Nitrogen Nutrition Index for Potato in Eastern Canada

Plant diagnostic methods of N deficiency should be based on the definition of a critical N concentration, that is the minimal N concentration required to achieve maximum growth. The critical N concentration (Nc) of potato was determined from six on-farm field trials in which two cultivars (Russet Burbank and Shepody) were grown under three or four N rates with and without irrigation. Dry matter yield and N concentration of shoots and tubers were determined approximately weekly during the growing season. The Nc was determined by selecting data points for which the highest total biomass comprised of shoots and tubers was obtained, and by expressing N concentration (N) as a function of total biomass (W). The N nutrition index (NNI), calculated as the ratio between measured N concentration and predicted Nc during the growing season, was then related to the relative yield measured at harvest. Under non-limiting water conditions, the allometric relationship between Nc and total biomass for Russet Burbank (Nc = 4.57W-0.42) was different from that of Shepody (Nc = 5.04W-0.42), indicating that Shepody had a greater N concentration than Russet Burbank. The N concentration of Shepody was also greater than that of Russet Burbank under limiting water conditions. These results suggest that there is intra-specific variability in potato for the relationship between N concentration and biomass. The NNI ranged from 0.50 to 1.4. The relationship between relative yield and NNI expressed by a quadratic function accounted for a greater proportion of the variability with irrigation (71% for Russet Burbank and 82% for Shepody) than without irrigation (65% for Russet Burbank and 32% for Shepody). Our results suggest that the NNI could be a reliable indicator of the level of N stress during the growing season, particularly under non-deficient water conditions.ResumenLos métodos de fitodiagnóstico de deficiencia de N deben basarse en la definición de una concentración crítica de N, es decir, la concentración mínima requerida para alcanzar el crecimiento máximo. La concentración critica de N (Nc) en la papa fue determinada en seis campos experimentales de agricultores, en los cuales crecieron dos cultivares (Russet Burbank y Shepody) bajo tres o cuatro niveles de N con y sin irrigación. Los rendimientos en materia seca y la concentración de N en las yemas y tubérculos se determinaron aproximadamente cada semana durante la temporada de crecimiento. La Nc se determinó seleccionando los datos por los cuales se obtuvo la biomasa total más alta, que incluía yemas y tubérculos, y expresando la concentración de N (N) como una función de la biomasa total (W). El índice de nutrición de N (NNI, en inglés) calculado como la relación entre la concentración medida de N y hl Nc pronosticada durante la temporada de crecimiento, se relacionó entonces con el rendimiento relativo medido y cosechado. Bajo condiciones de abundancia de agua, la relación alométrica entre Nc y la biomasa total para Russet Burbank (Nc = 4.57W-0.42) fue diferente que para Shepody (Nc = 5.04W-0.42), indicativo de que Shepody tiene una mayor concentración de N que Russet Burbank. La concentración de N de Shepody fue también mayor que la de Russet Burbank bajo condiciones limitadas de agua. Estos resultados sugieren que hay una variabilldad intraespecíflca en la papa en la relación entre la concentración de N y la biomasa. El índice de nutrición de N (NNI) osciló entre 0.50 a 1.4. La relación entre el rendimiento relativo y el NNI, se expresó por una función cuadrática contabilizada por una mayor proporción de la variabilidad con irrigación (71% para Russet Burbank y 82% para Shepody) que sin irrigación (65% para Russet Burbank y 32% para Shepody). Nuestros resultados sugieren que el NNI podría ser un indicador confiable del nivel de estrés de N durante la temporada de crecimiento, particularmente bajo condiciones no deficientes de agua.

Yield response of two potato culivars to supplemental irrigation and N fertilization in New Brunswick

Nitrogen and water are important factors influencing potato production, and crop response to these two factors may vary with cultivars. The yield response of two potato cultivars (Russet Burbank and Shepody) to six rates of N fertilization (0-250 kg N ha-1) with and without supplemental irrigation was studied at four onfarm sites in each of three years, 1995 to 1997, in the upper St-John River Valley of New Brunswick, Canada. On average, irrigation increased total yield from 31.9t ha-1 without irrigation to 38.41 ha-1 with irrigation and marketable yield from 25.61 ha-1 without irrigation to 30.71 ha-1 with irrigation. Potato yields were increased by irrigation at nine out of the 12 sites, and the irrigation response was similar for both cultivars. Nitrogen fertilization significantly increased both total and marketable yields at all sites except one. The yield response to N fertilization was greater with irrigation. The N fertilization rate (Nmax) required to reach maximum total and marketable yield, however, was similar with and without irrigation. A large variation in Nmax was observed among sites. With irrigation Nmax varied between 158 and 233 kgN ha-1 for total yield, and between 151 and 250 kg N ha-1 for marketable yield. There was no interaction between N fertilization and potato cultivar for both total and marketable yields. The two cultivars had similar total yields (35 t ha-1). Shepody, however, had a greater marketable yield (28.9 t ha-1) than Russet Burbank (27.4 t ha-1). Our results indicate that the response to two of the most significant factors of potato production, irrigation and N fertilization, varies greatly with sites and climatic conditions, and that field specific recommendations are required for the optimum management of N and irrigation.ResumenEl nitrógeno y el agua son factores importantes que influyen en la producción de la papa, y la reacción de la cosecha antes estos dos factores puede variar con diferentes cultivares. La reacción de rendimiento de dos cultivares de papa (Russet Burbank y Shepody) antes seis medidas de fertilizante N (0-250 kg N Ha-1) con y sin irrigación suplementaria se estudió en dos lotes en granja durante cada uno de los tres años, 1995–1997, en la parte superior del Valle del Río St-John en New Brunswick, Canadá. En un p romedio, la irrigación aumentó el rendimiento total de 31.91 ha-1 sin irrigación a 38.4 t ha-1 con irrigación y al rendimiento comerciable de 25.61 ha- 1 sin irrigación a 30.71 t ha-1 con irrigación. Los rendimientos de la papa aumentaron a causa de la irrigación en 9 de los 12 lotes, y el resultado de la irrigación fue similar para los dos cultivares. La fertilización con nitrógeno aumentó notablemente tanto los rendimientos totales y comerciables en todos los lotes menos uno. El rendimiento ante la fertilización N fue mayor con irrigación. La tasa de fertilización N (Nmax) que es necesaria para alcanzar el rendimiento total y comerciable, sin embargo, fue similar con y sin irrigación. Se observó una gran variación en Nmax en los lotes. Con irrigación, Nmax varió entre 158 y 233 kg N ha-1 en el rendimiento total, y entre 151 y 250 kg N ha-1 en el rendimiento comerciable. No había ninguna interacción entre la fertilización N y el cultivar de la papa para los rendimientos tanto totales como comerciables. Los dos cultivares tuvieron rendimientos totales similares 35 t ha-1). Shepody, sin embargo, tuvo un rendimiento comerciable mayor (28.9 t ha-1) que Russet Burbank (27.4t ha-1). Nuestros resultados indican que la respuesta a dos de los factores más significativos en la producción de la papa, la irrigación y la fertilización N, varía mucho entre lotes y condiciones climáticas, y que unas recomendaciones de campo específicas son necesarias para el manejo óptimo de N y de la irrigation.

Nitrogen fertilization and irrigation affects tuber characteristics of two potato cultivars

Nitrogen fertilization, irrigation, and cultivars affect tuber characteristics such as tuber size, specific gravity, and N concentration. Few studies, however, have investigated the interaction of irrigation and N fertilization on the tuber characteristics of potato cultivars, particularly in Atlantic Canada. The objective of this on-farm study, conducted at four sites in each of three years, 1995 to 1997, was to determine the effects of supplemental irrigation and six rates of N fertilization (0-250 kg N ha-1) on the number of tubers per plant, the average fresh tuber weight, tuber N concentration, nitrate (NO3-N) concentration, and specific gravity of the cultivars Shepody and Russet Burbank. Nitrogen fertilization increased the average fresh tuber weight, tuber N and N03-N concentrations, and decreased specific gravity. Effects of increasing N fertilization on tuber characteristics were often more pronounced for Shepody than for Russet Burbank, and for irrigated than for non-irrigated conditions. Shepody had greater average fresh tuber weight and tuber N concentration, lower specific gravity, and fewer tubers per plant than Russet Burbank. Supplemental irrigation increased the average fresh tuber weight and the number of tubers per plant, but it had a limited effect on specific gravity and tuber N and NO3-N concentrations. Tuber NO3-N con centration and specific gravity were strongly related to tuber N concentration, which in turn depended primarily on N fertilization. Incidents of lowest specific gravity and highest NO3-N concentration occurred with a relative yield close to or equal to 1.0. We conclude that the risks of low specific gravity and high tuber NO3-N concentration are greater when fertilization exceeds the N requirements to reach maximum tuber yield.

Winter damage to perennial forage crops in eastern Canada : Causes, mitigation, and prediction

Harsh winter climate results in frequent losses of stands and yield reduction in many forage-growing areas of Canada and other parts of the world. Climatic conditions and crop management both affect the winter survival of perennial forage crops. In this review, we present the main causes of winter damage in eastern Canada and we discuss crop management practices that help mitigate the risks of losses. Predictive tools available to assess the risks of winter damage both spatially and temporally are also presented. Our understanding of the causes of winter damage and of the plant adaptation mechanisms to winter stresses, particularly the role of N and C organic reserves, has improved. Forage species commonly grown in eastern Canada differ in their tolerance to subfreezing temperatures and to anoxia caused by the presence of ice on fields. Some improvement in winter hardiness of forage legume species has been achieved through breeding in eastern Canada but new technologies based on laboratory freezing tests ...

Methane yield from switchgrass harvested at different stages of development in Eastern Canada.

Mesophilic methane yield of ensiled switchgrass grown in Eastern Canada was assessed. Switchgrass was harvested at three stages of development, corresponding to mid-summer, late summer and early fall in 2007. The regrowth of plots harvested in mid-summer was also harvested in early fall as a two-cut strategy. Specific methane yields decreased significantly with crop maturity from 0.266 to 0.309 (N)L CH(4)g(-1) VS in mid-summer to 0.191-0.250 (N)L CH(4)g(-1) VS in early fall; values were similar for the first harvest in late July and the second harvest (regrowth) in October. Approximately 25% more methane was produced by hectare for the two-cut strategy (2.90-3.44 x 10(6)(N)L CH(4)ha(-1)) compared to the one-cut strategy with a harvest in late summer (2.28-2.77 x 10(6)(N)L CH(4)ha(-1)). Methane yields from switchgrass grown under the cool humid climate of Eastern Canada suggest that this crop remains an interesting renewable alternative energy source.

Improving the nutritive value of timothy through management and breeding

Timothy (Phleum pratense L.) is a widely grown fo rage grass species in cool and humid regions of the world including northeastern and northwestern North America, Nordic countries, Russia, and Japan. The nutritive value of timothy decreases with time, phenological development, and increasing forage yield. This review paper summarizes methods of controlling or improving the nutritive value of timothy through management practices and genetic selection, while keeping in mind the importance of forage yield. Consequently, the nutritive value of timothy is considered in relation to the accumulation of forage yield. The ecophysiological basis for the decrease in nutritive value with increasing forage yield during a growth cycle is presented with the assumption that the forage is made of two components: metabolic and structural. The decrease in the proportion of the metabolic component with increasing forage yield reduces the nutritive value of timothy. The nutritive value is also affected by the N concentration ...

Timothy Yield and Nutritive Value by the CATIMO Model

The Canadian Timothy Model (CATIMO) is a mechanistic simulation model of timothy (Phleum pratense L.) growth and nutritive value that features radiation interception and use efficiency, leaf and stem growth, leaf senescence, a N function based on the critical N concentration of whole plants, and cell wall (CW) concentration and digestibility of leaves and stems; the model was calibrated with measurements of timothy primary growth from one location (Fredericton, NB, Canada). In this paper, we compare the predictions of the CATIMO model with measurements from a total of six experiments conducted at four locations that cover the pedo-climatic conditions of eastern Canada (Levis, QC; Nappan, NS; Normandin, QC; St. Johns, NF). Across experiments, the root mean square errors (RMSE) for dry matter (DM) yield varied from 30.9 to 265.9 g DM m -2 and averaged 123.9 g DM m -2 . Omitting one experiment in 1999, however, reduced the overall RMSE to 72.6 g DM m -2 , which is very close to the 65.9 g DM m -1 reported for calibration. The RMSE values across experiments for N concentration (0.013 g g -1 DM), in vitro true dry matter digestibility (0.052 g g -1 DM), CW concentration (0.104 g g -1 DM), and CW digestibility (0.064 g g -1 CW) were higher than those obtained at the calibration site. At three of four locations, however, RMSE values were close to those of the calibration site. The CATIMO model seems robust enough to apply to situations different than those used for calibration, at least within eastern Canada.

Predicting nitrogen fertilizer requirements of potatoes in Atlantic Canada with soil nitrate determinations

Nitrogen greatly affects potato ( Solanum tuberosum L.) yield, but excess N can result in environmental degradation. In this study soil nitrate (NO3-N) content was determined pre-plant to predict fertilizer N requirements of potatoes in Atlantic Canada and in mid-season to adjust N fertilization during the growing season. Soil NO3-N contents were measured to a 0.30-m depth in spring prior to planting at four on-farm sites in each of 3 yr (1995 to 1997) in the upper St. John River Valley of New Brunswick, Canada. Mid-season soil NO3-N contents at a 0–0.30 m depth were also determined (32–47 days after planting) at two sites in three N treatments in 1995 (0, 50, and 250 kg N ha-1) and in four N treatments in 1996 and 1997 (0, 50, 100, and 250 kg N ha-1). The yield response of potatoes to six rates of N fertilization (0–250 kg N ha-1) with and without supplemental irrigation was used to determine the economically optimum N application (Nop). The pre-plant spring soil NO3-N test alone could not adequately pre...