Choice of planting date is a compromise between targeting time of harvest and maximizing forage yield and nutritive value. Traditionally, planting of small grains for forage occurs later than those harvested for grain because grain maturation is unnecessary and the higher cash value for grain compared to forage. As planting date is delayed from late April to late June the time when forage yield is maximized occurs later in the calendar year. Planting must be early enough to allow sufficient arable growing season to attain an economical forage yield at late milk to hard dough stages (Baron et al., 1992). Extremely late planting that is used in swath grazing may reduce small-grain forage yield and therefore carrying capacity (Baron et al., 2006). Varying planting date may be effective in placing a swath-grazed crop for pasture when other feed sources are not available (e.g., winter or drought). Small grains have been used as emergency feed sources when perennial pastures are unavailable due to dry weather (Kilcher and Heinrichs, 1961). Species and genotypes within species may vary for suitability depending on adaptation to growing conditions created by the late-planting practice.
Swath grazing can reduce costs of winter feeding for beef cows by 40% by eliminating harvesting, hauling, and feeding costs, and reducing manure spreading costs (McCartney et al., 2004). Swath grazing reduced labor costs from $0.29 to $0.18 cow-d−1, feed costs from $0.91 to $0.62 cow-d−1 and equipment costs from $0.34 to $0.04 cow-d−1 when compared to a traditional dry-lot practice (McCartney et al., 2004). However, crop production costs represent 75% of the total cost of swath grazing, and the basic input and operational costs of producing a swath-grazed crop are the same as a crop planted much earlier. Therefore increasing the yield of a swath-grazed crop by choosing a higher yielding variety or species or being able to plant earlier should reduce the cost per unit of dry matter (DM).
Very little information exists on the effects of late planting on forage yield and nutritive value for small grains. Kibite et al. (2002a) estimated a 35% forage yield reduction for oat and barley based on early-May and mid-June planting dates. May et al. (2007) did not find consistent yield reductions for oat and barley cultivars, based on two similar early and late planting dates in Saskatchewan. However, it is widely recognized that small-grain species suffer from reduced grain yield when planted later than the earliest spring date to accommodate seeding operations in Oregon (Ciha, 1983), Alberta (Juskiw and Helm, 2003), and Manitoba and Saskatchewan (May et al., 2004). In Alberta it is recommended to plant small-grain cereals as early as possible to maximize grain yield. For example, barley grain yield was reduced from 4.0 to 3.3 Mg ha−1 on Black Chernozemic (Udic Borroll) soils and 3.2 to 1.6 Mg ha−1 on Gray Luvisolic (Boralf) soils when seeding date was delayed from 7 May until 12 June (Anonymous, 2008). Wheat (Triticum aestivum L.) yields were reduced from 3.3 to 2.6 Mg ha−1 from 7 May to 28 May for Black Chernozemic soils (Anonymous, 2008).
We hypothesize that variation exists among species and possibly cultivars for duration between planting date and dough stage as planting date is delayed from spring to early summer. This might provide flexibility in planting date for systems such as swath grazing. Also, slower maturing genotypes may have lower yield loss as planting date is delayed. The objective of this research was to compare time of harvest, whole-plant yield, nutritive value, and estimated swath-grazing carrying capacity for beef cows among selected small-grain cultivars representing barley, oat, and triticale species when planted over a series of dates from mid-May until late June.
MATERIALS AND METHODS
The experiment was established in the spring of 2005, 2006, and 2007 on different fields that were previously planted to barley at Lacombe, AB, Canada (52°28’ N, 113°45’ W, 847 m) on an Orthic Black Chernozemic ‘Ponoka’ clay loam soil (Udic Boroll). The experiment was a randomized complete block design with a split-plot arrangement of treatments. Main plots were planting dates and subplots were small-grain species–cultivars treatments with three replicates. AC Lacombe (Kibite, 1994) and Vivar (Helm et al., 2003) barley, Murphy oat (Kibite et al., 2002b), and Wapiti triticale (Salmon et al., 1988) were planted on seven dates. The number of entries for the species effect is limited due to the total size of the experiment and by the relatively scant number of triticale varieties available. The barley varieties were chosen because they are representative of standard (AC Lacombe) and semi-dwarf (Vivar) stature types commonly grown in the area and have been used in related research (Chow et al., 2008). Murphy oat is a forage oat adapted to the region (Kibite et al., 2002b). The planting dates were almost identical among years. In 2005 planting dates were 12, 19, 26 May; 1, 9, 16, and 23 June; in 2006 planting dates were 10, 17, 24, and 31 May; 7, 14, and 21 June. The 2007 planting dates differed from 2006 only in that the third planting date was 23 May. Subplots for small grain species consisted of six rows, 25 cm apart, planted with a double disk drill at a rate of 300 seeds m−2. Nitrogen, P, and K fertilizer were broadcast at rates of 100, 13, and 25 kg ha−1, respectively, at one time before the first planting date and incorporated with a light cultivator and mounted harrow. Dicot weeds were controlled chemically by applying 0.56 kg ha−1 MCPA (2-methyl-4-clorophenoxyacetic acid) herbicide. Other weeds were controlled by hand.
Heading date and canopy height were recorded as heads emerged (stage 55 after Tottman and Makepeace, 1979). Leaf area index (LAI) was measured after heading using a LAI-2000 plant canopy analyzer consisting of a LAI-2050 optical sensor (Li-Cor Ltd., Lincoln, NE). The LAI measurements were made between the centermost rows of each subplot.
Whole-plant harvest of each subplot occurred when barley and triticale reached the soft dough stage (stages 83–85) (Baron et al., 1992) and oats reached the milk stage (stages 77–79) (McElroy and Gervais, 1983). The periods from planting to heading and heading to harvest are referred to as the vegetative and filling periods, respectively (Fig. 1 and 2). Filling period, in the context of forage production, was the difference between harvest date and heading date. Heading and harvest dates were recorded as a calendar date (Fig. 1). Accumulated growing degree days > 0.0°C from planting (i.e., GDD = ∑ Daily Mean Temperature > 0.0°C) until harvest (Fig. 2) and for vegetative and filling periods were also estimated.
At harvest, the inner-most four rows of each small grain plot were cut with a flail mower at a height of 5 cm. Two 250-g subsamples of cut and chopped material were taken to determine DM concentration and nutritive value. Dry matter concentration was determined from dry weight after drying at 80°C for at least 72 h divided by 250 g of fresh material. The second subsamples were used for nutritive value determinations and were dried at 55°C for at least 72 h. Nutritive value subsamples were ground using a Wiley mill (Model 4; Arthur H. Thomas Co., Philadelphia, PA), equipped with a 2-mm screen. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations were determined separately (Van Soest and Robertson, 1980), using procedures modified for a filter bag system (ANKOM Technology Corp., Fairport, NY) similar to that described by Vogel et al. (1999). Alpha amylase (ANKOM Technology–FAA) and sodium sulfite (ANKOM Technology–FSS) were used to determine NDF as described in ANKOM Technology 8/98. In vitro true digestibility (IVTD) was determined using 30 h for Stage 1 of the procedure described by Marten and Barnes (1980), then, undigested residues were treated with NDF solution. Crude protein concentration (6.25 × N concentration) was measured by the Dumas combustion method (Etheridge et al., 1998) with a Leco CN analyzer (Model CN 2000 analyzer, Leco Corp., St. Joseph, MI). Subsamples used to determine starch concentration were gelatinized with sodium hydroxide and then measured with an enzymatic method (Karkalas, 1985). Glucose concentration was measured using a glucose oxidase/peroxidize enzyme (No. P7119, Sigma, St. Louis, MO) and dianisidine dihydrochloride (No. F5803, Sigma). A plate reader was used to determine absorbance (SpectraMax 190, Molecular Devices Corp., Sunnyvale, CA).
Calculation of Potential Swath Grazed-Carrying Capacity for Beef Cows
The following variables were calculated from measured parameters:
Total digestible nutrients (TDN [%]) = 104.96 – (ADF % × 1.302);
Digestible feed energy [DE (Mcal kg−1)] = 4.4 Mcal kg−1 × (TDN/100);
Metabolizable energy of feedstuff [ME (Mcal kg−1)] = 0.82 × DE;
Net energy of maintenance of feedstuff [Nem (Mcal kg−1)] = 1.37 × ME– 0.138 × ME2 + 0.0105 × ME3 – 1.12);
Net energy required by cow for maintenance; [Ner (Mcal hd-d−1)] = (0.077 × (680 kg hd−1) 0.75) + 1.782 Mcal hd-d−1);
Dry matter intake required by cow at < –15°C [FR-15 (kg hd-d−1)] = (NEr/NEm) × 1.16);
Carrying capacity (hd-d ha−1) = (DM yield (kg ha−1) × (80/100))/FR-15.
Digestible feed energy (DE) of harvested forage was based on ADF content using Steps 1 and 2 as described by Bull (1981). The ME and NEm determinations for feedstuffs were calculated for individual subplots using Steps 3 and 4 according to National Research Council (1996). Maintenance energy requirements (Ner) for a 680 kg nonlactating cow at approximately 210 d of pregnancy carrying a calf with 38-kg birth weight were calculated with Steps 5 and 6 using dry matter intake for maintenance at temperatures < –15°C (National Research Council, 1996). The projected environment would be a cow grazing in late January and calving in March in a Canadian Prairie environment. Potential carrying capacity allowing for 80% consumption (20% loss due to grazing and weathering) of available forage (Step 7) was estimated. The estimated loss rate is within the range shown in previous (Baron et al., 2006) and current research (8–25%) at Lacombe, AB and was determined from dry weight of residue and stubble left after grazing as a percentage of aboveground yield. The cow size (680 kg) used in the calculation of potential carrying capacity is similar to that used in actual grazing studies which facilitates comparison of estimated carrying capacity to previous results from research performed under field conditions (Baron et al., 2006).
The statistical analyses considered the regression of crop responses against planting date, expressed as days after 10 to 12 May (first seeding date). The regression (data combined over all years) was conducted using a random coefficient model with the PROC MIXED procedure from SAS (Littell et. al., 1996; SAS Institute, 2004). The linear effect of delayed seeding (slope coefficient), its quadratic form (delayed seeding squared), and the corresponding intercept coefficient were modeled as fixed effects cross-classified with the applied treatments (small-grain species and cultivar combinations). Variance estimates (random effects) for the intercept and linear effect of delayed seeding were estimated across years with a variance component covariance structure. Regression coefficients, corresponding variance estimates, and interactions with the applied treatments were declared significant at P ≤ 0.05. Where a species difference among means or trends is discussed in terms of size this probability of significance exists. Trends for species over planting date delay were described by coefficients and the differences among the coefficients.
Growing season temperature and rainfall (Table 1) were conducive for normal small-grain forage production during the 3 yr of the study. The 2006 and 2007 growing seasons were generally warmer than the long-term average, and 2005, 2006, and 2007 had greater growing season precipitation than the long-term average, and precipitation in 2006 and 2007 were greater than in 2005. Average mean monthly temperatures of June, August, and September in 2005 were at least 1°C cooler than the long-term average.
|Month||2005||2006||2007||Long term||2005||2006||2007||Long term|
Timing of Heading and Harvest Dates
To meet any specific swathing date target triticale and oat should be planted earlier than barley. As planting date was delayed, timing of heading and harvest stages became later for all species (Fig. 1) and were affected by interaction terms between planting date and small-grain species (Table 2), indicating significant trends for one or more species (Table 3). Heading moved later, linearly, for barley and triticale and curvilinearly for oat with delay in planting (Table 3, Fig. 3a). The average heading date for oat was at least 6 d later than the other species (Table 2). Harvest time for both barley cultivars was affected by identical linear and quadratic terms (Table 3, Fig. 3b). Harvest time for oat and triticale was affected by the linear term, only. For every day planting was delayed harvest time was delayed more for triticale > oat > barley (Fig. 1 and 3b) as indicated by the relative size of coefficients (Table 3).
|Heading date||Harvest date||Period from planting to harvest
|Julian||d||Growing degree days > 0.0°C|
|Source||Probability of significance‡|
|Planting delay (PD)||***||***||***||*||***||***||ns§||ns|
|PD × TR||ns||***||**||***||***||**||***||***|
|PD × PD||ns||***||***||ns||***||***||ns||***|
|PD × PD × TR||*||***||***||***||***||***||***||***|
|Coefficients and Significance levels
|Fig. 3a–Heading date (Julian)|
|Fig. 3b (° C)–Harvest date (Julian)|
Duration from Planting to Harvest
The vegetative and filling periods represented approximately 80 and 20% of the planting to harvest period, respectively, for barley and oat, but approximately 60 and 40%, respectively for triticale in days (Fig. 1) or GDD units (Fig. 2). On average, the vegetative period for barley and triticale was similar in length, while oat was longer than the others (Table 2). The trends for length of the vegetative period as planting date was delayed differed among the species and between barley cultivars (Table 4). The vegetative period was not affected by planting date for Vivar barley and Wapiti triticale, but it decreased linearly for A. C. Lacombe barley (Fig. 4a). The vegetative period for oat responded curvilinearly, beginning with a reduction, then, increased when planted after the first week in June (Fig. 4a). On average the filling period for barley was 6 and 21 d shorter than oat and triticale, respectively (Table 2). The trend for filling period with delay in planting date was dramatically different for triticale than the other species, although some variation occurred among all of them (Table 4, Fig. 4b). At the earliest planting date triticale's filling period was at least 10 d longer than other species as indicated by the intercept, then increased linearly with delayed planting (Table 4, Fig. 4b).
|Coefficients and significance levels
|Fig. 4a–Vegetative period, d|
|Fig. 4b–Filling period, d|
|Fig. 4c–Planting to harvest, d|
|Fig. 4d–Vegetative period, GDD|
|Fig. 4e–Filling period, GDD|
|Fig. 4f–Planting to harvest, GDD|
The planting-to-harvest period trends with delayed planting represented the combination of vegetative and filling period trends. For barley, initially, planting to harvest decreased linearly, then leveled out curvilinearly as planting date was delayed (Table 4, Fig. 4c). By contrast, planting to harvest for triticale increased linearly with delayed planting. Planting to harvest for oat was unaffected with delay in planting date as vegetative and filling period responses were offsetting. On average the length of the planting-to-harvest period for barley was 12 and 21 d (161 and 365 GDD) shorter than oat and triticale, respectively (Table 2).
When expressed as GDD small-grain species and planting date interactions were highly significant for the vegetative, filling, and planting to harvest date periods (Table 2). The GDD of the vegetative period was constant for oat (Table 4) and curvilinear for the others over a relatively small range (Fig. 4d). By contrast the filling period GDD accumulation for triticale was constant, but curvilinear for the others over a small range (Fig. 4e).
A constant GDD accumulation between planting and harvest was required for any barley planting date (Fig. 4f). However, the GDD between planting and harvest increased for triticale and oat until dates in early June and then leveled off or decreased slightly. Thus, while constant in GDD (Fig. 4f), the planting to harvest period became shorter in days with delay in planting (Fig. 1 and 4c) for barley, illustrating the role of temperature in the maturation process. Also, the role of temperature in extending the filling period (Fig. 4e) for triticale was important in explaining the longer planting to harvest period in triticale compared to oat and barley.
Generally, small-grain species was more important than delayed planting in effecting nutritive value, although interactions between main effects did occur. Murphy oat had lower IVTD concentration than all other species (Table 5). Small differences in crude protein were exhibited among species, with AC Lacombe barley greater than triticale. Nutritive value parameters for Vivar barley and triticale were generally unaffected by delayed planting (Table 6).
|Probability of significance§|
|Planting delay (PD)||ns¶||ns||*||***||***||*||ns|
|PD × TR||ns||ns||ns||ns||ns||ns||ns|
|PD × PD||ns||ns||***||***||***||***||***|
|PD × PD × TR||ns||ns||ns||ns||ns||ns||ns|
|Coefficients and Significance levels
|Fig. 5a–Starch, g kg−1|
|Fig. 5b–NDF, g kg−1|
|Fig. 5c–CWD, g kg−1|
|Fig. 5d–ADF, g kg−1|
|Fig. 5e–TDN, g kg−1|
The trends in starch, NDF, cell wall digestibility, ADF, and TDN (Fig. 5a–5e) were significantly affected by planting date delay, but were unique to AC Lacombe barley and Murphy oat (Table 6). Values for starch, NDF, and cell wall digestibility concentrations for AC Lacombe barley fluctuated with planting date delay, but may have been offsetting resulting in a constant IVTD concentration that was similar to triticale. Oat had a low starch (Fig. 5a) content which was unaffected by planting date delay, but trends in NDF (Fig. 5b) and ADF (Fig. 5d) concentration increased with delayed planting, supporting the low IVTD concentration (Table 5). Acid detergent fiber and TDN trends were mirror images of each other as TDN is a function of ADF (Bull, 1981). Both were affected by delayed planting and small-grain species (Table 5). Oat-ADF increased (Fig. 5d) and TDN decreased (Fig. 5e) at increasing rates as planting was delayed (Table 6). Acid detergent fiber (ADF) and TDN for other small-grain treatments were unaffected by planting date.
Whole-Plant Yield and Carrying Capacity
Whole-plant yield and beef cow carrying capacity were impacted by all of the interaction terms (Table 7), but canopy height and LAI, were affected by small-grain species only. Maximum barley yields occurred at the first planting date (approximately 9.6 Mg ha−1) and then AC Lacombe and Vivar barley decreased linearly (Table 8, Fig. 6a) by 35 and 39%, respectively. For oat, yield increased marginally (8%) until a first week in June planting, while triticale yield increased with an additional planting delay (10%). After maximizing yield, both decreased at a relatively slow rate compared to barley. For maximum whole-plant yield barley should be planted as early as possible, while triticale and oat should be planted approximately 31 May. However, yield maxima may not coincide with the target harvest date for swath grazing.
|Cultivar||Species||DM Yield||Height||LAI||Carrying capacity|
|Mg ha−1||cm||Cow-d ha−1|
|Source||Probability of significance¶|
|Planting delay (PD)||ns#||ns||ns||ns|
|PD × TR||***||ns||ns||***|
|PD × PD||***||ns||ns||***|
|PD × PD × TR||***||ns||ns||***|
|Coefficients and significance levels
|Fig. 6a–Dry matter yield, Mg ha−1|
|Fig. 6b–Carrying capacity, cow-d ha−1|
Barley cultivars were shorter than oat and triticale, and, triticale was shorter than oat (Table 7). Oat had the largest LAI after heading, significantly greater than triticale; barley was intermediate. At initial planting dates beef cow carrying capacities for barley and triticale were at approximately similar levels (785–822 cow-d ha−1; Fig. 6b). However, carrying capacity of barley declined linearly (Table 8) as planting date was delayed to June 23 (550–570 cow-d ha−1). Carrying capacity for triticale increased curvilinearly, peaking at 935 cow-d ha−1 when planted over a period beginning the last week in May to second week in June, then decreased to approximately 804 cow-d ha−1. Oat had a beef cow carrying capacity about 23% lower than the others (618 cow-d ha−1) at the first planting date, increased to 663 cow-d ha−1 when planted during the last week of May, then decreased to a level similar to barley (515 cow-d ha−1) at the last planting date. In terms of beef cow carrying capacity, an optimum planting date for triticale was approximately 31 May and for oat 24 May; barley should be planted as early as possible. However, as with whole-plant yield, optimum planting dates for maximum carrying capacity may not be ideal for targeting swathing in September.
Late planting of small-grain species is deemed an acceptable practice to meet the fall harvest date for swath grazing (Entz et al., 2002). Barley has been the species of choice because of rapid maturity. However, low yield and beef carrying capacity were associated with this extremely late planting date.
Time of Swathing or Harvest
For swath-grazed barley the relationship between rate of maturation and delayed planting is so strong that planting dates late enough to target swathing in September may have to occur in July, especially at warmer locations in western Canada. For any projected harvest date, triticale and oat could be planted earlier than barley as the whole-plant maturation rate was slower in days and GDD. In previous research a planting date delay from early May to mid-June, reduced time from planting until physiological grain maturity by 13 d in barley (Juskiw and Helm, 2003) and by 14 d in oat (May et al., 2004).
The time of whole-plant harvest was likely affected by differential responses among species to temperature and photoperiod. As photoperiod lengthens leaf appearance rate increases; interval from planting-to-spikelet formation, heading, and numbers of leaves and tillers decrease in quantitative long-day cereal species, such as wheat (Allison and Daynard, 1976), oat (Sampson and Burrows, 1972), and barley (Fairey et al., 1975). At Lacombe, AB daylength increased from 15.5 h on 12 May to 16.4 on 16 June, then decreased to 16.2 h by 30 June. Although variability for photoperiod sensitivity exists among genotypes within species (Sampson and Burrows, 1972; Allison and Daynard, 1976; Juskiw and Helm, 2003) the trait plays a role in the adaptation for successful grain maturation in northern latitudes.
Triticale and barley had opposite trends for duration between planting to harvest with delayed planting (Fig. 4c); barley decreased from 75 to 64 d and triticale increased from 84 to 90 d. For barley the period was constant in length in terms of GDD (Fig. 4f). The filling period for barley was placed during weeks of relatively warm temperature (July–early August; Table 1). This may have exacerbated rapid maturation. In the case of triticale delayed planting moved the filling period into time-frames when temperatures were cooler, (late August and September), which would lengthen the heading to harvest period (Fig. 4c). The impact was that the filling period for triticale increased from 21 d with no delay in planting to 44 d with a 6-wk delay in planting (Fig. 4b).
Delay in planting date did not result in substantive negative trends in nutritive value for barley and triticale. However, as planting date was delayed an increasing NDF, low cell wall digestibility and increasing ADF concentration for oat did influence nutritive value. The differences in IVTD shown among species is generally supported by previous research conducted in Minnesota (Cherney and Marten 1982) where oat cultivars had lower in vitro digestible DM than barley, while triticale was intermediate. General trends in fiber levels were also similar to Cherney and Marten (1982).
Forages grown under higher than lower temperatures have resulted in increased lignification of cell walls (Fahey and Hussein, 1999). This was a possibility due to the temporal position of some delayed-planting treatments in the current study. Chow et al. (2008) observed a negative relationship between IVTD for whole-plant barley and mean daily temperature during the grain-filling period. However, this trend was not consistent for both barley cultivars and triticale in the current study (Fig. 5c). Cell wall digestibility (Fig. 5C) did exhibit a curvilinear decrease with delayed planting for oat and AC Lacombe barley, and the minimum values occurred when filling periods were exposed to relatively higher temperatures compared to initial and final planting dates. However, ADF concentration did not increase with delayed planting for AC Lacombe barley and oat cell wall digestibility improved at the later planting dates when NDF (Fig. 5b) and ADF (Fig. 5d) concentrations continued to increase. Cherney and Marten (1982) showed that whole-plant acid detergent lignin increased throughout the grain maturation process (4 wk post heading) even though NDF and ADF concentrations remained constant
Whole-Plant Yield and Carrying Capacity
Potential beef cow carrying capacity is the integration of yield and nutritive value for gestating cows in winter. We concluded that for barley and triticale beef cow carrying capacity was largely a function of delayed planting impacts on forage yield. Oat and triticale were more resistant to delayed-planting yield loss than barley. Determining why forage DM yield decreased with delayed planting date is speculative. It can be concluded that average crop growth rate decreased from 12.6 to 9.4 g m−2 d−1 in barley as both DM yield (Fig. 6a) and time from planting to harvest (Fig. 4c) decreased with planting date delay. Leaf area index was unaffected by planting date delay (Table 7), therefore daily DM assimilation in barley may have been impaired by increasing temperatures to which the later planting dates were exposed. By contrast DM yield in triticale and oat was only moderately, negatively impacted by the latest planting dates (Fig. 6a); duration from planting to harvest increased in triticale and was unaffected in oat (Fig. 4c); while LAI was unaffected by planting date delay. Therefore, in oat a slight reduction in average crop growth rate from a peak of 12.5 to 10.9 g m−2 d−1 may have occurred due to maturation under slightly cooler temperatures of late summer and early fall at the later planting dates. For triticale, the reduction from a peak average crop growth rate of 12.9 to 11.2 g m−2 d−1 at the latest planting date may have been offset by a longer filling period (Fig. 4d). In general, LAI and plant height were correlated to yield (e.g., r = 0.65 between LAI and yield and r = 0.55 for canopy height and yield), but delayed planting did not appear to impact yield through effects on LAI and canopy height per se.
The relatively high yield of oat was negated by a low IVTD (Table 5) and an increasing ADF (Fig. 5d) with planting date delay. This resulted in a carrying capacity for oat that was lower than any other small-grain treatment regardless of planting time (Fig. 6b). However, nutritive value (Fig. 5a–5e) of oat was low in general and fiber levels tended to increase with delayed planting, causing the estimated daily DM requirement for cow maintenance to increase with delayed planting.
Previous studies have shown mixed results for whole-plant cereal yield trends with delayed planting (Kibite et al., 2002a; May et al., 2007). However, estimates of beef cow carrying capacity in the current study are in general agreement and verifiable at field scale. Although in different years, yield in swath-grazed field-scale studies using barley varied from 8.3 Mg ha−1 planted on 15 June to 6.5 Mg ha−1 planted on 8 July and resultant actual carrying capacity during winter on the same fields ranged from 829 to 481 cow-d ha−1 for respective planting dates (Baron et al., 2006).
Optimizing a Planting Date for Swath Grazing
Species and target date for swathing have implications on choice of the best planting date. A traditional late-June planting date may result in lower carrying capacities than necessary if the species choice is barley or oat. For barley, delaying planting until 23 June resulted in an average harvest date of 27 August, (Fig. 1) forage yield of 6.0 Mg ha−1 (Fig. 6a) and beef cow carrying capacity of 561 cow-d ha−1 (Fig. 6b). Planting on 23 June for Oat and 7 June for triticale resulted in a harvest on the same date, 7 September (Fig. 1). On 7 September forage yield (Fig. 6a) was 11.1 and 8.6 Mg ha−1 for triticale and oat, respectively and beef cow carrying capacity (Fig. 6b) was 920 and 515 cow-d ha−1, respectively.
When planted on 23 June, the latest date in the current study, triticale yielded 46% more than barley and 22% more than oat, with beef cow carrying capacities 30% greater than barley and 35% greater than oat. For triticale three planting dates ranging from 7 to 23 June could be swathed from 7 to 25 September , ranging from 2.0 to 14% lower than maximum carrying capacity. Thus, triticale provided the most flexibility for planting date and highest carrying capacity for swathing within a targeted zone of September. Barley would have to be planted later than 23 June to be swathed in September.
The current study used a limited number of genotypes within each species. This study has shown that variability exists for the relationships for yield and carrying capacity with delayed planting and that this may impact management decisions relative to swath grazing. It is possible that more variation exists within adapted oat, barley, and triticale cultivars that would make them more or less suitable for swath grazing in winter or for use as emergency forage at different times of the year in similar or other agroclimatic regions. Thus, more research in this area is required to fine tune the management system. In the context of a Northern Prairie climate of western Canada and swath-grazing systems, it can be concluded that triticale provided the most flexibility and highest potential carrying capacity across a range of relatively late planting dates compared to oat and barley. This occurred because both forage yield and nutritive value for triticale remained relatively high as planting date was delayed to allow attainment of the dough stage in concert with a high potential carrying capacity in September. Time until maturity decreased as planting was delayed for barley and this rapid maturation was accompanied by yield loss which reduced potential carrying capacity by at least 33% when late June planting dates were compared to initial planting dates. In fact, barley could not be targeted for a September harvest, while maximizing yield and carrying capacity within the range of planting dates tested. The low nutritive value of oat negated a yield advantage over barley as planting date was delayed, resulting in approximately similar potential carrying capacity as barley when planted in late June.