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Crop Science 40:148-158 (2000)
© 2000 Crop Science Society of America

CROP ECOLOGY, PRODUCTION, & MANAGEMENT

Postheading Biomass Distribution for Monocrops and Mixtures of Small Grain Cereals

P.E. Juskiwa, J.H. Helma and D.F. Salmona

a Field Crop Development Centre, Alberta Agriculture, Food and Rural Development, 5030 50 Street, Lacombe, AB T4L 1W8, Canada

patricia.juskiw{at}agric.gov.ab.ca


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results
 Discussion
 Conclusions
 REFERENCES
 
Biomass distribution during the harvest period can affect the yield and quality of silage produced from cereal crops. Our objectives were to determine the changes in biomass distribution among morphological structures and how management practices could affect those changes. Three field studies were conducted to evaluate the productivity of barley (Hordeum vulgare L.), oat (Avena sativa L.), triticale (x Triticosecale rimpaui Wittm.), and rye (Secale cereale L.) grown as monocrops and mixtures. Seeding rates ranging from 250 to 750 seeds m-2 were evaluated to determine their effects on biomass distribution from heading to the soft-dough growth stages. While seeding rate had a profound effect on per plant biomass, it had little effect on biomass per unit land area or the distribution of the biomass between leaves, stems, and spikes. During the postheading period for all tests, the leaf component declined and the spike component increased. The stem component declined for all tests, but variation was found for the tests harvested on the basis of the oat and triticale components. Composition biomass weights from our spring cereal tests averaged across the three sampling times (heading to soft dough) were 18% leaf, 50% stem, and 31% head for `Noble' barley; 18% leaf, 44% stem, and 37% head for `AC Mustang' oat; and 22% leaf, 43% stem, and 35% head for `Wapiti' triticale. Plant populations and total, leaf, stem, and spike biomass per plant for mixtures were found to be intermediate to the monocrops. Total biomass quantity and distribution among leaves, stems, and spikes were affected by genotype, production practices, and time of harvest, with the latter having the greatest effect. Understanding cultivar, species, and management effects is important for optimum feed quantity and quality.

Abbreviations: ADF, acid detergent fiber • ADL, acid detergent lignin • CWC, cell-wall content • NDF, neutral detergent fiber


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results
 Discussion
 Conclusions
 REFERENCES
 
WHETHER BAILED OR ENSILED, cereals harvested prior to maturity for their whole-plant biomass is an important portion of livestock diets. For lactating dairy animals, ensuring that these feeds are of top quality, with high protein, low fiber, and high digestibility, is an important consideration (Khorasani et al., 1993). For feedlot animals, high biomass production is an important consideration, as this biomass is used in the diet as the energy and fiber component. Factors that affect feed quality and yield of cereals include plant stage at harvest, species and genotype, and production factors.

Effects of plant stage on quality and biomass yield have been well documented. As cereals mature from the vegetative through boot and dough stages, biomass increases (Cherney and Marten, 1982; Twidwell et al., 1987; Fearon et al., 1990; Bergen et al., 1991; Mislevy et al., 1997) and then declines as physiological maturity approaches (Hunt and Edgington, 1981; Baron and Kibite, 1987). During the time from vegetative to dough stage as stems elongate and secondary cell-wall structures are laid down, whole-plant quality declines (Cherney and Marten, 1982; Twidwell et al., 1987; Brignall et al., 1989; Fearon et al., 1990; Daccord and Arrigo, 1993; Hadjipanayiotou et al., 1996; Mislevy et al., 1997), as does the silage made from it (Acosta et al., 1991; Ben-Ghedalia et al., 1995b). As the grain fills, quality, especially protein, may again improve as the grain makes up more and more of the total biomass (Ben-Ghedalia et al., 1995a, 1995b; Mannerkorpi and Taube, 1995). Although whole-plant fiber digestibility usually continues to decline during grain fill (Mannerkorpi and Brandt, 1993, 1995), in vitro digestibility of the organic matter may not change (Baron et al., 1992) as accumulation of starch in the spike may compensate for the decrease in the degradability of neutral detergent fiber (NDF) polysacharrides (Ben-Ghedalia et al., 1995a). Khorasini et al. (1997) found that fiber concentrations [acid detergent fiber (ADF), NDF, and acid detergent lignin (ADL)] increased, reached a plateau, and then declined from boot to soft-dough stage, reflecting leaf growth, cell-wall development, and finally starch deposition by the seed.

Genotype effects on quality and biomass yield have also been documented. Mislevy et al. (1997) concluded that stage of harvest was more important than species on the quality and yield of cereals for forage. For barley, high yields are often associated with late-maturing, tall genotypes (Baron and Kibite, 1987). Good quality is often associated with genotypes that have high leaf to stem ratios. Leaves and heads are known to have better digestibility and higher protein than stems (Baron and Kibite, 1987; Capper, 1988; Goto et al., 1991; Sheaffer et al., 1994). Ohlde et al. (1992) reported that for cereal species at maturity the order of quality by fraction was: leaf blade > leaf sheath> internode.

Differences in quality may be attributed to biomass distribution during growth and differences between genotypes and species in their biomass distribution. Mannerkorpi and Taube (1995) found that the highest nutritive value of barley was measured for the leaf sheath and blade in the uppermost internode and generally declined as senescence began. Brignall et al. (1989) found for rye and triticale that percentage of the plant as leaf sheath and blade fell from jointing to anthesis, while stem and ear percentage increased. Hunt and Edgington (1981) found for winter wheat (Triticum aestivum L.) that rapid spike growth commenced 2 wk after heading and continued to physiological maturity, while leaf weight declined during this period and stem weight increased to 3 wk after heading and then began to decline. Ellen (1993) found that for barley, rye, triticale, and wheat, stems were the largest component of aboveground biomass, but as grains increased they became the next largest component and by maturity they became as large or larger than the stem component in all but rye. Leaf area index and duration was lower in rye, than barley, wheat, and triticale. Petr and Hradecká (1993) also found that leaf area duration was longer in triticale than in rye. Baker and Gebeyhou (1982) found that leaf biomass increased until 7 wk after sowing for wheat and barley and then declined until maturity. Sheaffer et al. (1994) found for barley harvested at the soft-dough stage that conventional cultivars had 20 to 21% leaf blade, 30 to 33% inflorescence, and 46 to 50% stem and leaf sheath, while semi-dwarf lines had 20% leaf blade, 39 to 40% inflorescence, and 39 to 41% stem and leaf sheath. Capper (1988) found that shorter cultivars had higher proportions of leaf blade. Goto et al. (1991) found cultivar differences in barley for leaf blade and sheath content at maturity. Cherney et al. (1983) found that barley had greater in vitro digestibility and higher leaf blade to stem plus sheath ratio and less cell-wall content (CWC), ADF, and ADL than other cereal species. The leaf blade, leaf sheath, and stem of barley were more digestible than oat; however, the inflorescence was less digestible.

Production factors that affect biomass accumulation and its distribution may affect forage yield and its quality. Fearon et al. (1990) found no significant differences for quality and yield of triticale forage with different planting dates. McKenzie et al. (1999) found that for barley, yields and protein content of greenfeed for ensiling responded positively to N fertilization.

The purpose of this study was to document postheading biomass distribution for several cereals and the effects of mixtures and seeding rate on that yield distribution. We wished to determine the patterns of increases and decreases in biomass of morphological structures and how changes in biomass distribution could be related to the value of feedstuffs. Biomass yields and quality potential for silage of these tests are reported in a companion paper (Juskiw et al., 2000).


   Materials and methods
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results
 Discussion
 Conclusions
 REFERENCES
 
Test Treatments and Design
This study consisted of three tests: Test 1, spring barley cultivar mixtures; Test 2, spring cereal mixtures of barley, oat, and triticale; and Test 3, winter cereal mixtures of winter rye and winter triticale. Seeding rates used for Tests 1 and 2 were 250 (standard), 375 (1.5 x), and 500 (2 x) seed m-2. Seeding rates used for Test 3 were 250 (standard), 500 (2 x), and 750 (3 x) seeds m-2. Germination tests were conducted on all seed lots prior to seed setup, and seeding rates were adjusted so rates were based on a live-seed basis. Within Tests 1 and 2, three subtests were run based on the principal component of the test, while within Test 3, two subtests were run. The subtests were run to facilitate harvesting of the crop when the principal-component cultivar was at the heading, milk, or soft-dough stage.

For Test 1, the three subtests were based on `Kasota', an early, semi-dwarf, six-rowed spring barley; `AC Lacombe', a mid-maturing, six-rowed spring barley; and `Seebe', a late, two-rowed spring barley. Within each subtest of Test 1, the treatments were each cultivar as a monocrop and the mixtures of the principal component with the two other cultivars in the ratios 1:1, 3:1, 1:1:1, and 3:1:1, making a total of nine treatments.

For Test 2, the three subtests were based on Noble, a mid-maturing, six-rowed spring barley; AC Mustang, a late, spring oat; and Wapiti, a late spring triticale. Within each subtest of Test 2, the treatments were each species as a monocrop and mixtures of the principal component with the two other species in the ratios 1:1 and 3:1, making a total of seven treatments.

For Test 3, the two subtests were based on `Prima', a winter rye, and `Pika', a winter triticale. Within each subtest of Test 3, the treatments were each species as a monocrop and 1:1 mixture, for a total of three treatments in 1994-1995, and mixtures of the principal component with the other species in the ratios 1:1, 2:1, and 3:1, for a total of five treatments in 1995-1996.

The experimental design for each subtest was a split-plot design with three replicates for Tests 1 and 2, and four replicates for Test 3. Main plots were the rate of seeding and subplot treatments were the mixture and monocrop treatments. While plots were separated into cultivar and species for the purposes of this study, analyses were based on plot means. Seeding rate and cultivar and mixture treatments were treated as fixed effects and time of sampling was treated as a random effect. Errors appropriate to this model were used to test effects (Steel and Torrie, 1980). Each subtest was analyzed across years using the GLM procedure (SAS Institute, 1988). Plant number was included as a covariant in the analyses of leaf, stem, spike, and total plant biomass.

Field Techniques and Trait Measurements
Plots were established from 1994 to 1996 at Lacombe, AB, on a Penfold loam [orthic Black Chernozem (coarse loamy, frigid Typic Haplustoll)] and for Test 3 only, in 1994 and 1995 at Botha, AB, on a Daysland loam [60% orthic Black Solod (coarse loamy, Typic Argiustoll with a natric horizon) and 40% thin orthic Black Chernozem (coarse loamy, frigid Typic Haplustoll)]. Due to hail in June 1996 at Botha, data were not collected from that location–year. For more detailed information on field techniques, refer to the companion paper (Juskiw et al., 2000).

For the spring cereal tests, components were analyzed in 1994 and 1995 only. For the winter cereal tests components were analyzed in 1995 and 1996 only. Subtests were harvested when the principal cultivar was at the heading, milk, and soft-dough stage as outlined in Table 1 . Plots were sampled by pulling one 0.5-m row by hand. Samples were separated into their component cultivars. Each sample was subdivided into spikes, leaves, and stems. Roots were removed from the stems. Leaves were just the leaf blades, with leaf sheaths remaining with the stem material. Subsamples were dried (<60°C, >24 h) and weights recorded.


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  		Table 1 Sampling dates for biomass determinations of small grain cereals by growth stages during two cropping years, 1994 and 1995 for spring cereal tests, and 1995 and 1996 for the winter cereal tests

 

   Results
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results
Discussion
 Conclusions
 REFERENCES
 
Test 1 — Spring Barley Mixtures
Seeding rates, monocrop and mixture treatments, and sampling time had significant effects on leaf, stem, spike, and total plant biomass (Table 2) . As plant populations increased with higher seeding rates, per plant weight for leaves, stems, and spikes declined (Table 3) . Across the three sampling times at all seeding rates, leaf weight declined, while spike weight increased (Table 3). Stem weight was relatively stable with a small increase with the second sampling time on a per plant weight basis, and a decline with the final sampling (Table 3). The percentage of components as leaves, stems, and spikes was relatively stable across these seeding rates and tests, changing only with sampling time (Table 4) .


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  		Table 2 Mean squares from the analysis of variance for plant numbers, and biomass of leaves, stems, spikes, and the total plant of barley monocrops and mixtures grown in 2 yr at three seeding rates, and sampled at heading, milk, and soft-dough growth stages of the principal component

 

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  		Table 3 Effect of seeding rate and sampling time on component biomass yields of barley grown at Lacombe, AB in 1994 and 1995.{dagger}

 

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  		Table 4 Percentage composition of biomass distribution averaged across three post heading harvests of annual cereals, three seeding rates, and monocrops and mixtures. Where time of sampling was based on the growth stage of the principal cultivar (heading, milk, soft dough)

 
For all three tests, the Kasota monocrop had lower per plant leaf and stem biomass and higher per plant spike biomass than the AC Lacombe and Seebe monocrops (Table 5) . While separation of the mixtures into their component cultivars was done, for this study, only the mean weights for the treatment were compared. The mixtures were intermediate to the monocrops, and those with a greater proportion of Kasota tended to have less leaf and stem and more spike biomass, while those with a greater proportion of Seebe tended to have more leaf and stem and less spike biomass. Where exceptions occurred, they could in part be due to variation from the targeted plant population. The Seebe-based test, the mixtures with three parts Seebe to either Kasota or AC Lacombe, tended to have less leaf and stem biomass than the 1:1 mixtures.


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  		Table 5 Treatment effects on component biomass yields of barley grown at Lacombe, AB in 1994 and 1995.{dagger}

 
Test 2 — Spring Cereal Mixtures (Barley, Oat, and Triticale)
Seeding rate and sampling time had significant effects on leaf, stem, spike and total biomass of the barley, oat, and triticale (Table 6) . As for the barley-based tests, weight per plant declined with increased seeding rates (Table 7) , but leaf, stem and spike components remained stable relative to one another. Stem weight differences between the Noble barley-based test and the oat- and triticale-based tests were noted. For the Noble barley-based test, stem weights declined on a per plant basis with the later sampling times (Tables 4, 7). For the oat-based tests, stem weight increased with the second sampling prior to a decline with the third sampling. For the triticale-based test, change in stem weight with sampling depended on the seeding rate, declining with the second sampling at the higher seeding rates but not the standard (250) rate, leading to an overall low stem weight percentage at the second sampling for the triticale-based test (Table 4). Biomass distribution on a percentage basis varied across the sampling times for the subtests (Table 4).


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  		Table 6 Mean squares from the analysis of variance for plant numbers, and biomass of leaves, stems, spikes, and the total plant of barley, oat, and triticale monocrops and mixtures grown in 2 yr at three seeding rates, and sampled at heading, milk, and soft-dough growth stages of the principal species

 

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  		Table 7 Seeding rate and sampling time effects on component biomass yields of barley, oat, and triticale monocrops and mixtures grown in Lacombe, AB in 1994 and 1995.{dagger}

 
For the Noble barley-based test, Noble had significantly higher spike biomass than the AC Mustang and Wapiti (Table 8) . While for the same test, both leaf and stem biomass for Noble and AC Mustang were lower than for Wapiti. With the tests sampled later, total biomass had increased for all three species. Total biomass for AC Mustang was similar to that for Noble and lower than that for Wapiti, perhaps due to differences between plant populations for the samples. All traits (plant population, leaf biomass, stem biomass, spike biomass, and total biomass) for the mixtures were intermediate to the monocrop components (Table 8). Again, differences from this generalization could be attributed to plant population effects.


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  		Table 8 Treatment effects on component biomass yields of barley, oats, and triticale monocrops and mixtures grown at Lacombe, AB in 1994 and 1995.{dagger}

 
Test 3 — Winter Cereal Mixtures (Rye and Triticale)
Seeding rate and sampling time effects on leaf, stem, spike, and total biomass of the winter cereals were significant (Table 9) . Plant populations for the winter cereals at the two higher seeding rates were generally lower than expected (Table 10) . However, as expected and as found in the other tests, on a per plant basis, the higher seeding rates resulted in lower total plant biomass (Table 10). The crop was more mature by the harvests for the Pika triticale-based tests, so stem and spike weights were greater and leaf biomass was lower (Table 9). As for the earlier tests, biomass distribution on a percentage basis varied across the sampling times for both subtests (Table 3).


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  		Table 9 Mean squares from the analysis of variance for plant numbers, and biomass of leaves, stems, spikes, and the total plant of winter rye and triticale monocrops and mixtures grown in three locations and years at three seeding rates, and sampled at heading, milk, and soft-dough growth stages of the principal species

 

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  		Table 10 Effect of seeding rate and sampling time on component biomass yields of winter cereals grown at Botha, AB in 1994–1995 and Lacombe, AB in 1994–1995 and 1995–1996.{dagger}

 
When sampled for the Prima rye-based test, biomass did not differ between the two monocrops and the mixtures (Table 11) . However, by the sampling for the Pika triticale-based test, Pika had less leaf biomass than Prima at Lacombe, but not at Botha, and lower stem, spike, and total biomass than Prima at Lacombe and Botha in 1995 (Table 11). At Lacombe in 1996, for the Pika-based test, the 1:1 and 3:1 Prima–Pika treatments had lower than expected biomass yields, although this was not the case for the 2:1 mixture.


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  		Table 11 Treatment effects on component biomass yields of winter cereals grown at Botha in 1994–1995 (B95) and Lacombe in 1994–1995 (L95) and in 1995–1996 (L96).{dagger}

 

   Discussion
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results
 Discussion
Conclusions
 REFERENCES
 
Cultivar, species, and production practices all had an effect on biomass distribution, with the greatest effect on biomass in these studies being time of sampling or growth stage of the plants. Leaf biomass declined during the period of this study (from shortly before heading for some cultivars to the late dough stage for other cultivars), stem biomass remained relatively constant, increased, or declined but tended to be highest at the second sampling date, and spike biomass increased. The increase and decline in stem weights over the three sampling times was probably due to remobilization and redistribution of leaf and stem reserves to the filling grain. As leaves are associated with better whole-plant quality, producers must decide whether to harvest at an early maturity stage for optimum forage quality or to delay harvest until later when yield is higher but quality lower (Twidwell et al., 1987). A major consideration in this decision is the nutritional needs of the class of livestock being fed.

For these tests, sampling was timed to reflect heading, milk, and soft-dough stages of the major component. Under our conditions, anthesis for barley occurs 3 to 4 d before heading, while in oat, triticale, and rye, anthesis occurs 5 to 7 d after heading. For the barley test, averaged across cultivars, the composition on a dry matter basis was: leaves and sheaths 28% at heading and 12% at soft-dough stage; stems 58% at heading and 39% at soft-dough stage; and spikes 14% at heading and 49% at soft-dough stage. These figures are comparable with those found for wheat by Ben-Ghedalia et al. (1995a): (on a dry matter basis) leaves and sheaths 26% at anthesis and 18% at soft-dough stage; stems 54% at anthesis and 44% at soft-dough stage; and spikes 20% at anthesis and 38% at soft-dough stage. The higher leaf content and lower stem content of the barley may mean slightly better quality for barley vs. wheat, but most probably reflects differences in stages between the two studies; heading vs. anthesis and the soft-dough stage can last for an extended period of time (10–14 d under our conditions). Khorasani et al. (1997) determined the composition of cereals at harvest for silage as: 27% leaf, 24% stem and 49% head for barley; 26% leaf, 31% stem, and 43% head for oat; and 24% leaf, 35% stem and 41% head for triticale. Composition biomass weights from our spring cereal tests averaged across the three sampling times (heading to soft dough) from our tests were 18% leaf, 50% stem, and 31% head for barley; 18% leaf, 44% stem, and 37% head for oat; and 22% leaf, 43% stem, and 35% head for triticale. Because the averages from our tests were across an earlier period of growth than the Khorasani et al. (1997) study, the lower proportion of spike and higher proportion of stem was expected. The lower proportion of leaf biomass found in our study was not expected but may reflect differences in cultivars, production practices, precipitation, temperature, and locations between the two studies.

The consistently lower yields of Kasota compared with Seebe (Juskiw et al., 2000) may be due to consistently lower per plant biomass as found in this study. The greater proportion of Kasota as spike and lower proportion of Seebe as spike, reflect their relative maturities at the sampling times. The lower ADF and NDF levels in Seebe and its mixtures compared with Kasota and AC Lacombe as reported in our companion paper (Juskiw et al., 2000) may be attributed to the greater proportion of biomass that was leaf material.

As reported in our companion paper (Juskiw et al., 2000), the AC Mustang oat monocrop had low biomass yields when harvested early, but was similar to Wapiti with later harvests. Petr and Hradecká (1993) found total biomass for triticale was higher from the end of the vegetative period to maturity than for wheat or rye, and attributed this to the overall longer growth period of triticale. The decline in quality of Noble with the later-harvested tests (Juskiw et al., 2000) could be associated with the decline in leaf biomass reported here.

The higher fiber content of the Pika monocrop compared with Prima (Juskiw et al., 2000) was not associated with any reduction in leaf vs. stem and spike biomass.

As seeding rate increased for all tests, the leaf, stem, and spike weights on a per plant basis declined. This decline was expected due to restricted tillering at the higher plant densities. However despite this pronounced effect of plant densities on a per plant basis, little effect on quality due to distribution of leaves, stems, and spikes or on total biomass yields on a land basis were found. The lower quality at higher seeding rates reported in Juskiw et al. (2000) was not associated with any reduction in the proportion of the biomass as leaf structure.

There was a tendency for population numbers of the samples from the spring cereal tests to be consistently higher than the desired population projection. As seeding rates were adjusted based on germination tests, it was possible that under field conditions more seed was viable than under cabinet conditions. As seed is often not uniformly distributed in the field while seeding (awns can clog chutes and rocks and soil aggregates can prevent seed from being dropped uniformly into the soil), plant populations can vary within and between rows. There was a tendency when sampling to pick areas of the row with good plant distribution, and this probably led to selection of rows with higher than expected plant numbers. For the winter cereal test, population numbers were generally lower than expected based on seeding rates, especially for the higher seeding rates. Death of plants due to winterkill under the severe conditions of Canadian winters could have led to these lower plant numbers.


   Conclusions
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results
 Discussion
 Conclusions
REFERENCES
 
Total biomass per plant and distribution of that biomass to leaves, stems, and spikes were affected by genotype, production practice, and time of harvest, with the latter being of greatest magnitude. Biomass increased with time of harvest from heading to soft-dough stage, with the leaf component decreasing and the spike component of biomass increasing during this time. Changes in the stem component were variable depending on the test.

Cultivar differences found in partitioning of biomass were generally associated with relative maturities. Seebe, a late-maturing cultivar, had a high proportion of biomass as leaf, while Kasota, an early-maturing cultivar, had a high proportion as spike. Noble, an early-maturing cultivar, had a high proportion of biomass as spike, while AC Mustang and Wapiti, late-maturing cultivars, had a higher proportion as leaf and stem.

Per plant weights for all components decreased with increased seeding rates, but seeding rate had little effect on the relative proportions as leaf, stem, and spike. Plant populations and mean total, leaf, stem, and spike biomass per plant for mixtures were found to be intermediate to the monocrops.

The higher quality associated with early postheading harvest of cereals can be linked the high proportion of biomass as leaf material. When late-maturing cultivars or species are grown as monocrops or in mixtures, they can improve overall quality of early harvests by contributing a high proportion of leaf material to the harvest.


   ACKNOWLEDGMENTS
 
The technical assistance of Donna Westling, Dave Dyson, Susan Lajeunese, Deanna Runge, and Tom Zatorski is gratefully acknowledged. A portion of this research was funded by Alberta Agricultural Research Institute.

Received for publication December 22, 1998.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results
 Discussion
 Conclusions
 REFERENCES
 




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