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

Abstract

Bolinder, M. A., Angers, D. A., Bélanger, G., Michaud, R. et Laverdière, M. R. 2002. Root biomass and shoot to root ratios of perennial forage crops in eastern Canada. Can. J. Plant Sci. 82: 731-737. 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 (0-45 cm) in the 0-to 15-cm layer increased from 54 to 71% while that in the 15-to 30-cm layer decreased from 37 to 21%; the proportion of roots in the 30-to 45-cm layer remained constant at about 10% in both years. The S:R of alfalfa for the 0-15 cm depth was significantly higher than that for most of the grasses. No significant difference in S:R was observed among grass species. Recognizing that S:R may vary with locations and climatic conditions, our results suggest that average S:R of about 1.30 (values ranged from 1.01 to 1.72) in the first production year and 0.60 (values ranged from 0.43 to 0.87) in the second production year could be used as a first approximation to estimate the amount of root biomass left in the soil to a depth of 45 cm from forage crops in eastern Canada. The S:R of forage crops, particularly grasses, were lower than those of annual crops such as small-grain cereals and corn. Le rapport biomasse aérienne : biomasse racinaire (BA:BR) mesuré lorsque les cultures sont à maturité est souvent utilisé pour estimer les apports annuels de C laissés dans le sol par la BR des plantes. Cependant, la BR a souvent été négligée dans les études au champ et il n'existe pas d'estimé du rapport BA:BR pour plusieurs espèces de plantes fourragères. Notre objectif était de déterminer la BR au champ et le rapport BA:BR pour différentes espèces de plantes fourragères pérennes sous les conditions climatiques et édaphiques de l'est du Canada. Des mesures de la BR ont été effectuées pour trois couches de sol (0-15, 15-30 et 30-45 cm) et ce, pendant deux années consécutives (la première et la deuxième année de production) quelques jours après la deuxième coupe pour sept espèces de graminées et deux de légumineuses. Une variation importante dans la BR a été observée entre la première et la deuxième année de producti...

Effect of Alfalfa Grown for Forage on Soil Fertility Related to Mineral and Organic Fertilization

“…Our results showed the Root mass of 1214 kg/ha was recorded by Hakl et al (2008) in the first growing year of alfalfa. Bolinder et al (2002) measured root mass in the 15-to 30-cm layer in the first year of production of alfalfa (range of 1900 to 3580 kg/ha, average of 2450 kg/ha) and in the second year (range of 1920 to 3660 kg/ha, average of 2800 kg/ha). Biederbec et al (2005) found significant less ammount of 928 -1556 kg/ha dry root mass accumulated in alfalfa after 5 year growing.…”

Root biomass, root/shoot ratio, and soil water content under perennial grasses with different nitrogen rates

“…The reason is that perennial grasses have higher root biomass that contributes more C to the soil than cereal crops (Paustian et al, 1997;Bollinder et al, 1997Bollinder et al, , 2002. Furthermore, the relatively undisturbed soil condition under perennial grasses reduces mineralization of soil organic matter and therefore favors soil C accumulation.…”

“…Furthermore, the relatively undisturbed soil condition under perennial grasses reduces mineralization of soil organic matter and therefore favors soil C accumulation. Because of the difficulty of accurately measuring root biomass in the field due to high variability and tedious work of separating roots from the soil, measurement of root biomass, especially for perennial grasses, is often neglected (Bollinder et al, 2002). Other sources of variation in the measurement of root biomass include the soil sampling strategy employed, different sieve size used to separate roots from the soil affecting the quantification of root biomass, variation in root growth during the crop growing season making the sampling time critical, and age of the grass establishment (van Nordwijk et al, 1987;Amato and Pardo, 1994).…”

Reed canarygrass crop biomass and silage as affected by harvest date and nitrogen fertilization

“…In a study conducted in Nova Scotia with one cut taken in the fall, switchgrass outyielded reed canarygrass in the second post-seeding year but not in the third post-seeding year (Wile et al 2014). In a two cut-system, the DM yield of switchgrass was less than that of reed canarygrass in the first two post-seeding years in New Brunswick (Bolinder et al 2002). Although switchgrass and reed canarygrass were not compared directly, our results and those obtained in other studies conducted in eastern Canada suggest that the potential yield of reed canarygrass in the first two or three post-seeding years is close to that of switchgrass in areas with around 1700 growing degree-days (5°C basis) or less.…”