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NEW CROPS

Row Spacing, Plant Population, and Cultivar Effects on Grain Amaranth in the Northern Great Plains

^a 338 N. Green Bay Rd., #1107, Waukegan, IL 60085 USA
^b Dep. of Plant Sci., North Dakota State Univ., P.O. Box 5051, Fargo, ND 58105-5051 USA

bujohnso{at}plains.nodak.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 
An understanding of plant response to row spacing and plant density is important in developing effective production systems for new crops. Optimum row spacing and plant population for grain amaranth (Amaranthus spp.) production in the northern Great Plains was evaluated at Prosper and Williston, ND, over 6 station-years. Amaranth cultivars K283, K343, K432, and MT-3 were established at populations of 74000, 173000, and 272000 plants ha^-1 in 30- and 76-cm row spacings. Grain and biomass yield, plant height, harvest index, harvested plant population, and plant lodging were measured. Grain yields were similar among plant populations at each of the drier environments, averaging 1050 and 410 kg ha^-1 for Prosper in 1989 and Williston in 1990, respectively. A 12% yield advantage, 160 kg ha^-1, was observed at the lowest compared with the highest plant population at Prosper in 1990, but not in 1992. The main effect of row spacing on grain yield was not significant; however, the interaction of row spacing, plant population, and environment indicated population yield ranking differences at the 30-cm row spacing among environments but not at the 76-cm row spacing. The two A. cruentus L. cultivars, K283 and MT-3, generally produced more grain than the two A. hypochondriacus L. x A. hybridus L. cultivars, K343 and K432, especially in dry environments. When considering yield, plant mortality, and potential harvest difficulties, the moderate population (173000 plants ha^-1), 76-cm row spacing, and generally higher-yielding A. cruentus cultivars would be recommended.

Abbreviations: HI, harvest index

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 
GRAIN AMARANTH is a warm-season annual crop that originated in Central and South America. Amaranth seed is high in protein and lysine, and possesses unique starch and oil properties with potential for industrial use. Yield trials conducted in North Dakota since 1981 indicate certain cultivars of grain amaranth are adapted in the state and exhibit high yield potential, particularly in eastern North Dakota (Henderson et al., 1993).

With any new crop, an understanding of optimal row spacing and crop response to plant density is essential for maximizing yield. Interest in amaranth as a potential specialty crop for the USA was generated in the mid-1970s, and since that time researchers have discussed whether to treat amaranth as a row crop or a solid-seeded crop. Grain amaranth most commonly is grown as a row crop with 70- to 80-cm row widths. Some producers use narrower rows, ranging from 20 to 50 cm (Weber, 1990; Kauffman, 1992).

Research to determine optimal row spacing for maximum amaranth production has been inconclusive. In Minnesota (Robinson, 1986), grain yield was similar from plants grown in 15-, 30-, and 76-cm row spacings at a plant population of 180000 plants ha^-1. Weed control was best with the widest row spacing, irrespective of plant population. At a higher population (470000 plants ha^-1), grain yield was greater at a 15-cm row spacing than at a 76-cm row spacing. Endres (1986) reported a slight yield advantage for narrow rows (36 cm) compared with wide rows (53 cm) in one environment, but observed no differences in another environment. Putnam (1990) reported no evidence of a yield advantage for solid seeding (15-cm rows) compared with 76-cm rows. In contrast, Misra et al. (1985) showed a decline in yield as row spacing increased above 30 cm. In Maryland, row spacing did not affect grain yield, but plant moisture at harvest was lower in narrow (19-cm) than in wide (76-cm) rows, indicating that narrow rows may facilitate faster plant dry-down (Wall, 1986) and harvest.

Other advantages of narrower rows may include reduced erosion potential, earlier canopy closure, and increased ease of harvest (Weber, 1990). The main advantage of wide rows is that cultivation can be used to control weeds. This is an important consideration, as no herbicides are labeled for use on grain amaranth. For this reason, most recommendations suggest that amaranth be seeded in wide rows to facilitate cultivation, with row width based on available cultivation equipment (Myers and Putnam, 1988).

Amaranth has been described as a plastic plant, able to adjust to a wide range of environmental conditions (Hauptli, 1977). Individual plants tend to branch to fill available space when plant stands are low or uneven (Putnam, 1990; Mnzava and Reuben, 1982; Haas and Kauffman, 1984). The degree of branching varies among cultivars, environments, and plant densities. In general, higher plant densities are more suitable than lower densities for mechanical harvesting of grain amaranth. This is because higher densities promote less branching, fewer secondary seed heads, smaller stalk diameter, and more uniform maturity (Haas, 1983). High populations may be less suitable in more arid climates, due to greater competition for available soil moisture (Haas and Kauffman, 1984). In these areas, soil moisture may be depleted during vegetative growth stages under high plant populations, leaving insufficient moisture for grain production (Weber, 1990). Mnzava and Reuben (1982) observed interplant competition as early as 5 wk after amaranth emergence.

Results of research on the response of grain amaranth to field population vary. Putnam (1990) reported that seeding rate influences grain yield of amaranth less than it influences corn (Zea mays L.), and concluded that precision seeding of amaranth was not advantageous. The effect of plant density on amaranth depends on species, cultivar, and environment (Putnam, 1990; Haas, 1983). An early study showed no effect of field density on grain yield for unselected amaranth populations; selected lines, however, produced higher yields as field density increased up to 60000 plants ha^-1 (Edwards and Volak, 1980). Haas (1983) found the highest grain yields of four amaranth species produced at populations of 320000 to 360000 plants ha^-1.

In Minnesota, Putnam et al. (1990) tested two A. hypochondriacus x A. hybridus cultivars, K343 and K432, with field populations ranging from 62000 to 1975000 plants ha^-1. The optimal density for both cultivars was 272000 plants ha^-1. Cultivar K432 exhibited a greater response to changes in plant density than K343. Robinson (1986), in another Minnesota study, noted greatest amaranth yields at populations between 180000 and 210000 plants ha^-1. Yield was reduced at populations higher than 350000 plants ha^-1 in Maryland (Wall, 1986). Reduced yield at higher populations is often associated with increased plant lodging (Schmidt, 1977; Wall, 1986; Putnam et al., 1990). However, Robinson (1986) noted more lodging at lower populations, because of larger, heavier stems.

Few research data have been published on the response of grain amaranth to the effects of row spacing and plant density. Specific recommendations on optimum field populations have not been published for the northern Great Plains. Our objective was to determine the most desirable combination of row spacing, plant population, and cultivar to maximize yield of grain amaranth in growing regions of the northern Great Plains.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 
Field experiments were conducted at Prosper (46°58' N, 97°4' W; elevation 220 m) in eastern North Dakota during the 1989, 1990, 1991, and 1992 growing seasons, and at Williston (48°9' N, 103°37' W; elevation 573 m) in western North Dakota during the 1990 and 1991 growing seasons. These test sites provide 6 station-years, which are each termed an environment in the combined statistical analysis of the experiment.

Soil types at the Prosper site consist of Perella (fine-silty, mixed, superactive, frigid Typic Endoaquolls) and Bearden (fine-silty, mixed, superactive, frigid Aeric Calciaquolls). Mean annual precipitation at Prosper is approximately 560 mm with an average of 135 frost-free days. Soil N, P, and K were brought to levels suitable for a 5700 kg ha^-1 wheat (Triticum aestivum L.) crop by adding appropriate amounts of fertilizer based on fall-collected soil samples (Fanning et al., 1988). The soil type at Williston is a Max loam (fine-loamy, mixed, superactive, frigid Typic Haplutolls). Williston has a mean annual precipitation of about 354 mm and an average growing season of 131 frost-free days. Fertilizer was applied to obtain soil test levels of 165 and 42 kg ha^-1 N and P, respectively.

The experiment design was a randomized complete block in a split-split plot arrangement with four replications. Row spacings, plant populations, and cultivars were the main, sub,-and sub-subplots, respectively. Cultivars were established at three plant populations at each of two row spacings, 30 and 76 cm. Plant populations were 74000, 173000, and 272000 plants ha^-1. Four cultivars adapted to the northern Great Plains were grown: A. cruentus cv. K283 and cv. MT-3, A. hypochondriacus x A. Hybridus cv. K343 (also known as Plainsman), and cv. K432 (Schulz-Schaeffer et al., 1989; Weber and Reider, 1989; Baltensperger et al., 1992). Cultivars K283 and MT-3 are tall types with little tendency to branch; cultivars K343 and K432, tall and semidwarf types, respectively, are more highly branched types.

In the combined analyses, environment (env) was considered a random effect, while all other effects (row spacing, plant population, and cultivar) were considered fixed. The model statement (SAS Inst., 1979, p. 119–131) was

dependent variables = env rep(env) rowspacing env*rowspacing rep*rowspacing(env) population env*population rowspacing*population env*rowspacing*population rep*population(env*rowspacing) cultivar env*cultivar rowspacing*cultivar env*rowspacing*cultivar population*cultivar env*population*cultivar rep*cultivar(env*rowspacing*population)

Test statements for effects were

Test H = rowspacing E = env*rowspacing; Test H = env*rowspacing E = rep*rowspacing(env); Test H = population E = env*population; Test H = rowspacing*population E = env*rowspacing*population; Test H = env*population env*rowspacing*population

E = rep*population(env*rowspacing); Test H = cultivar E = env*cultivar; Test

H = rowspacing*cultivar E = env*rowspacing*cultivar; Test H = env*cultivar env*rowspacing*cultivar E = rep*cultivar(env*rowspacing*population).

Means separation was performed using an F-protected LSD at the P = 0.05 level of significance. Least significant differences were calculated using the method of Carmer et al. (1989).

Seed of all cultivars was sown 13 to 15 cm deep with a double-disk-opener drill on 8, 14, 17, and 4 June at the Prosper site in 1989, 1990, 1991, and 1992, respectively, and on 31 May and 3 June at the Williston site in 1990 and 1991, respectively. Plots were 4.6 m in length and consisted of six rows spaced 30 cm apart or three rows spaced 76 cm apart. Plot stands were oversown and hand-thinned at approximately the four-leaf stage to plant populations of 74000, 173000, and 272000 plants ha^-1 in both narrow (30-cm) and wide (76-cm) row spacings. Plots were hand-weeded as necessary since labeled herbicides were not available. Plants were also hand-harvested shortly after the first frost in September by cutting stalks just above the soil line. In the narrow-row (30-cm) plots, a 3.05-m section of the center two rows was harvested. A 2.43-m length of the center row was harvested in each wide-row (76-cm) plot. The harvested area was equivalent (1.86 m²) for plots at narrow and wide row spacings.

Grain yield and aboveground biomass yield, harvest index (HI), and average plant height at harvest were determined for each plot at all environments. Harvest index was calculated as the ratio of grain yield to aboveground biomass yield on a dry weight basis. Final population was recorded at Prosper during the 1990, 1991, and 1992 growing seasons and at Williston during the 1991 growing season by counting plants within each plot at harvest. Lodging percentage was recorded at Prosper during the 1989, 1990, 1991, and 1992 growing seasons. Lodging was determined on an individual plot basis as the number of plants not harvested, due to stalk breakage, divided by the final population. Precipitation and maximum and minimum temperatures were recorded daily at all environments.

	Results and discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 
During the 1991 growing season, low seed quality resulted in extremely poor and variable stands at both Prosper and Williston; therefore, the experiment data from 1991 were not included in the statistical analysis. Consequently, only four environments were included in the combined study analysis.

Climatic Conditions at Tested Environments
Growing season precipitation and temperature were quite variable among the three Prosper environments. Precipitation amounts were 42 and 14 mm below average for the 1989 and 1990 environments, respectively, and 117 mm above average for the 1992 environment (Table 1) . In addition to below-average precipitation at the Prosper 1989 environment, high temperatures 30°C were recorded on 21 days during July (Table 2) . In 1990 at Prosper, precipitation was high in June, followed by considerably below-average precipitation in July and another below-average amount in August (Table 1). Temperatures at this environment were near normal each month with the exception of July, which was cool (Table 2). Similarly, rainfall was greater than average in June at Prosper in 1992, followed by considerably below-average precipitation in July and slightly below-average precipitation in August (Table 1). Temperatures were very cool throughout the growing season at Prosper in 1992, perhaps delaying plant development (Table 2).

View this table: [in this window] [in a new window]   Table 1 Total monthly precipitation and departure from the long-term average during the 1989, 1990, and 1992 growing seasons at Prosper, and the 1990 growing season at Williston, ND.

View this table: [in this window] [in a new window]   Table 2 Mean monthly temperature and departure from the long-term average during the 1989, 1990, and 1992 growing seasons at Prosper, and the 1990 growing season at Williston, ND.

Effect of Row Spacing
Plant height and lodging were significantly affected by the main effect of row spacing, but grain yield, biomass yield, HI, and final plant population were not (Table 3) . Closer plant spacings in 76-cm spaced rows than 30-cm spaced rows increased interplant competition and resulted in taller plants (Table 4) with visibly thinner and perhaps weaker stalks that contributed to greater lodging (Table 4). The F-test for final plant population had 1 degree of freedom for both numerator and denominator, resulting in a calculated F-value that was greater than the tabulated F-value of 161.4 for significance. Consequently, row spacing was not significant for final plant population; however, a substantially lower final population was observed at the 76-cm than at the 30-cm row spacing. This may be due to increased interplant competition and greater plant mortality at the wider row spacing, where within-row plant spacings are much closer than at the narrower row spacing.

Final plant population at harvest indicated increasing plant mortality as plant population increased (Table 4). Approximately 11 and 25% of the plants were lost at the moderate, 173000 plants ha^-1, and highest, 272000 plants ha^-1, established plant populations, respectively. Reduced interplant competition and plant mortality were observed at the lowest plant population, compared with the higher plant populations. The final plant population was slightly higher than the established plant population of 74000 plants ha^-1, probably because of continued seedling emergence after thinning (Table 4). This was particularly evident at Prosper in 1992, when continued emergence after thinning would have been encouraged by precipitation amounts being 163% of normal during June (Table 5) . Seedlings would also be subject to less interplant competition at this population and more likely to survive. The row spacing x plant population interaction was not significant for any of the characters evaluated (Table 3).

Main Effect Interactions
The row spacing x plant population and row spacing x cultivar interactions were not significant for any of the characters evaluated (Table 3). The only character influenced by the plant population x cultivar interaction was final plant population. This interaction is associated with magnitude differences in final plant population that are directly related to the plant populations at which the cultivars were initially established (data not shown).

Main Effect Interactions
Environmental conditions influenced plant response to row spacing, plant population, and cultivar for certain characters (Table 3). These environmental interactions with main effects, for grain yield and biological yield, are largely affected by magnitude differences among environments (Tables 5, 6, and 7) . These differences are caused by very low values for grain and biological yield at the Williston 1990 environment. Growing conditions at the Williston 1990 environment were very dry and severely limited grain and biological yield expression. Consequently, grain yield and biomass yield were much lower than those under the Prosper environments.

Environment influenced the effect of plant population on grain yield, HI, and final population (Table 5). Magnitude and ranking differences for grain yield were observed among environments. Plant population did not influence grain yield at the Prosper 1989 and Williston 1990 environments. Yield was markedly reduced at the Williston 1990 environment compared with the Prosper environments. The greatest yields occurred at the Prosper 1990 environment and were associated with the low and moderate plant populations. The high and moderate plant populations at this environment produced equivalent grain yield. Growing conditions for the Prosper 1990 environment were perhaps the most normal among all the tested environments. At Prosper in 1992, which was characterized by unusually cool temperatures that resulted in low biomass yields, more grain was produced at the highest than at the moderate population. The greater number of plants at the high population in 1992 could explain this result. There was less interplant competition at any population for the Prosper 1992 environment than in other environments, because plants were smaller due to the quite cool temperatures that reduced plant development. Without warm temperatures, little compensatory growth and grain yield occurred at the low population. Less plant attrition (higher final population) occurred at the two higher populations in 1992 than in 1990, because the smaller plants in 1992 resulted in less interplant competition.

The environment x cultivar interaction was significant for all characters evaluated except final population (Table 6). In the two drier environments, Prosper 1989 and Williston 1990, the two A. cruentus cultivars (K283 and MT-3) produced higher grain yields than the two A. hypochondriacus x A. hybridus cultivars (K343 and K432). The semidwarf cultivar, K432, had poor yields in the driest environments, but produced the highest grain yield in the unusually cool and moist environment of Prosper 1992. The cultivar K343 produced high grain yields in Prosper 1990, which had high early-season moisture and warm temperatures, but appeared to be more sensitive to the conditions of drought stress, excess moisture, and cool temperatures that occurred in the other environments. The A. cruentus cultivars had the highest HI in all environments except Prosper 1992, where cool temperatures and high moisture resulted in the highest HI values for K432 and K283.

Grain and biomass yield and HI were affected by the environment x row spacing x plant population interaction. This interaction for grain yield is associated with yield ranking differences for plant populations at the 30-cm row spacing among environments (Table 8) . Plant population did not influence grain yield at the 76-cm row spacing at any of the environments. Lack of biomass yield response to plant population at the 76-cm row spacing at any environment but a variable response at the 30-cm row spacing for plant population at the Prosper environments contributed to the environment x row spacing x plant population interaction.

	Summary

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

With uniform stands, there appeared to be no problem with harvestability at the lowest plant population. Where stands were uneven or poor, however, stalk diameter appeared greater and could cause difficulties during harvest. Therefore, although the lowest population tested had a slight yield advantage in one environment, the moderate population, 173000 plants ha^-1, is recommended as the target population for grain amaranth production in the northern Great Plains. The moderate population also has the advantages of reducing seed costs relative to the highest population and providing a more dense crop canopy for competition with weeds. Higher populations had no yield advantage in any environment except the very cool 1992 season in Prosper.

Although equivalent grain yield was produced from narrow and wide row spacings, wide row spacings are recommended because they facilitate cultivation for weed control. Use of narrow rows resulted in less plant mortality and associated stand losses during the growing season and less plant lodging. Severe lodging was only observed for one cultivar, K343, and only during the unusually cool, moist environment Prosper 1992.

The A. cruentus cultivars produced the highest grain yields over the range of conditions represented by the four tested environments. The semidwarf cultivar, K432, produced low grain yield in the dry environments but produced the highest grain yield under cool and moist conditions. Producers should consider seasonal moisture availability when choosing cultivars for their production region. Selecting more than one potentially good-yielding cultivar for production may improve and stabilize season and season-to-season production.SAS Institute 1979

Received for publication December 2, 1998.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Summary REFERENCES

 

• Baltensperger D.D., Weber L.E., Nelson L.A. Registration of `Plainsman' grain amaranth. Crop Sci. 1992;32:1510-1511.[Free Full Text]
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• Edwards, A.D., and B. Volak. 1980. Grain amaranth: Optimization of field population density. p. 91–94. In Proc. Amaranth Conf., 2nd, Rodale Res. Cent., Kutztown, PA. 13–14 Sept. 1979. Rodale Press, Emmaus, PA.
• Endres, C.S. 1986. Influence of production practices on yield and morphology of Amaranthus cruentus and Amaranthus hypochondriacus. M.S. thesis. Univ. of Arkansas, Fayetteville.
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• Robinson, R.G. 1986. Amaranth, quinoa, ragi, tef, and niger: Tiny seeds of ancient history and modern interest. Stn. Bull. AD-SB-2949. Agric. Exp. Stn., Univ. of Minnesota, St. Paul.
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This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (10) Citing Articles via Google Scholar Google Scholar Articles by Henderson, T. L. Articles by Schneiter, A. A. Search for Related Content PubMed Articles by Henderson, T. L. Articles by Schneiter, A. A. Agricola Articles by Henderson, T. L. Articles by Schneiter, A. A. Related Collections Crop Growth and Development Other Cropping Systems Other Grain Crops Other Oil Crops