R. 2006. Winter damage to perennial forage crops in eastern Canada: Causes, mitigation, and prediction. Can. J. Plant Sci. 86: 33-47. 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 and the identification of molecular markers may facilitate the future development of winter-hardy cultivars. Crop management practices required for good winter survival are now better defined, particularly those involving cutting management and the interval between harvests. Simulation models and climatic indices derived from our current knowledge of the causes of winter damage provide general indications on the risk of winter damage but their degree of precision and accuracy is still not satisfactory. Further improvements in winter survival require a more thorough understanding of the different causes of winter damage and, primarily, of their complex interactions with genetic, climatic, and management factors.

Total nonstructural carbohydrates (TNC) provide readily fermentable energy to rumen microbes and their increased concentration in forages improves N use efficiency in dairy cows (Bos taurus). This study was conducted to compare TNC concentration of grass and legume forage species and to determine how variations of TNC concentration caused by time of cutting during the day differ among forage species and how these variations are related to other attributes of forage nutritive value. Six grass and two legume species were cut at 0900 h (AM) and 1530 h (PM) in the spring growth and summer regrowth of two harvest years. The TNC concentration was estimated by the sum of sucrose, glucose, fructose, pinitol, fructans, and starch. Red clover (Trifolium pratense L.) and tall fescue [Schedonorus phoenix (Scop.) Holub] had the greatest TNC concentration [94.2 g kg−1 of dry matter (DM) across time of cutting and growth periods] whereas reed canarygrass (Phalaris arundinacea L.) had the lowest TNC concentration (65.5 g kg−1 DM). Concentration of TNC of all species increased with PM cutting but the extent of this increase varied among forage species. This increase, averaged across growth periods, went from 13% in smooth bromegrass (Bromus inermis Leyss; 67.0–73.9 g kg−1 DM) to 68% in reed canarygrass (49.6–81.4 g kg−1 DM). Increased TNC concentration with PM‐cutting resulted in significant but small decreases in N, acid detergent fiber (ADF), and neutral detergent fiber (aNDF) concentrations and a small increase in in vitro true digestibility (IVTD). Both species selection and PM cutting can be used to increase forage total nonstructural carbohydrates (TNC) concentrations.

The effectiveness of forages to prevent post-calving hypocalcaemia, when used as a feed source for nonlactating dairy cows, can be predicted by the dietary cation-anion difference (DCAD). Three to four weeks before calving, the ration of non-lactating dairy cows should have a DCAD around )50 mmol c kg )1 DM. In an experiment, swards, based on Timothy (Phleum pratense L.), were used to (i) evaluate the impact of two types (CaCl 2 and NH 4 Cl) and four application rates of chloride fertilizer per season (0, 80, 160 and 240 kg Cl ha )1 ) in combination with two N application rates (70 and 140 kg N ha )1 ) on mineral concentrations and DCAD in the herbage, and (ii) determine the economically optimal rate of chloride fertilizer (Cl op ) for DCAD in herbage. Chloride and N fertilizers were applied in the spring and, after the first harvest in 2003 and 2004 at four locations that differed in K content of their soils. Two harvests were taken during each year. Averaged across N-fertilizer application rates, harvests and locations, the highest rate of chloride fertilizer increased chloride concentration in herbage by 8AE5 g kg )1 dry matter (DM) and decreased DCAD in herbage by 190 mmol c kg )1 DM to values as low as )9 mmol c kg )1 DM. Both types of chloride fertilizer had the same effect on chloride concentration and DCAD in herbage and had no effect on DM yield. When no chloride fertilizer was applied on soils with a high content of available K, application of N fertilizer increased DCAD in herbage by 47 mmol c kg )1 DM at both harvests. Herbage DCAD was lower in summer than in spring by 47-121 mmol c kg )1 DM depending on the location. Application of chloride fertilizer can effectively lower the DCAD of Timothybased herbages; the economically optimal rate of chloride fertilizer in the spring varied from 78 to 123 kg Cl ha )1 , depending on soil K and chloride contents and expected DM yield.

Crop composition at harvest affects the ensiling process and the resulting silage quality. The objectives of this study were to determine: (i) the effect of annual N-fertilizer application (0, 60, 120 and 180 kg N ha )1 ) and developmental stage (stem elongation, early heading, late heading and early flowering) on the ensiling properties and silage quality of the spring regrowth of timothy (Phleum pratense L.) at two sites for 1 or 2 years, and (ii) the relationship between ensiling properties of the forage and the quality of the resulting silage. Laboratory silos with wilted forage at approximately 350 g dry matter (DM) kg )1 of fresh matter were prepared at each harvest and opened 150 d later for silage analysis. Higher rates of N-fertilizer application decreased the concentration of water-soluble carbohydrates (WSC), increased the buffering capacity (BC) and nitrate concentration, and decreased the ratio of WSC:BC, primarily in the early stages of development. The ensiling properties of timothy were, therefore, less favourable when high rates of N fertilizer were applied. Silage pH generally increased with increasing rates of Nfertilizer application; this increase was particularly evident at the first three developmental stages at one site in 1 year. Non-protein N (NPN) and soluble N concentrations of the silages increased with increased rates of N-fertilizer application at the first three developmental stages but decreased at early flowering. Ammonia-N concentration in the silages increased by 0AE85, 0AE56 and 0AE67 when rates of N-fertilizer application were 60, 120 and 180 kg ha )1 , respectively, compared with that when no N fertilizer was applied. Significant correlations between the composition of the forage ensiled and silage quality variables were found at sites in individual years but, when all data were combined, WSC concentration and BC, and their ratio in the forages, were not correlated with pH, and soluble-N and ammonia-N concentrations of the silages, and were weakly correlated with NPN and free amino acid-N concentrations of the silages. Silage quality was reduced by increased N-fertilizer application, primarily at the early developmental stages, and this can be attributed to a reduction in WSC concentration and an increase in BC of the forage. Water-soluble carbohydrate concentration, BC, and their ratio, however, were poor predictors of silage quality.

An untimely autumn defoliation of alfalfa reduces root accumulation of specific N reserves such as proline, arginine, histidine and vegetative storage proteins that are positively related to the vigour of spring regrowth but poorly related to winter survival.