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Singh, B.P. and W.F. Whitehead 1993. Population density and soil pH effects on vegetable amaranth production. p. 562-564. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.

Population Density and Soil pH Effects on Vegetable Amaranth Production

Bharat P. Singh and Wayne F. Whitehead

  1. SOIL pH
  2. INTRA-ROW PLANT SPACING
  3. CONCLUSIONS
  4. REFERENCES
  5. Table 1
  6. Table 2
The genus Amaranthus consists of nearly 60 species which can be broadly categorized into grain, green leaf vegetable, and weed types. Cultivation of amaranth (Amaranthus spp.) for their leaves dates back to more than 2,000 years. Presently, amaranth is extensively grown as a green leaf vegetable in many tropical countries (National Research Council 1984). The leaves are mostly consumed as pot-herb either alone or in combination with other vegetables and/or meat. Amaranth leaves are good source of dietary fiber and contains high amounts of proteins, vitamins, and minerals (Makus and Davis 1984; Teutonico and Knorr 1985; Willis et al. 1984).

Amaranth species utilized as a vegetable generally have short plants with wide leaves and small inflorescence (Huang 1980). Two species, A tricolor and A. dubius have the desired characteristics for the vegetable type and are commonly grown for this purpose in Asia, West Africa, and the Caribbean. A third species, A. cruentus is grown both for leaves and grain. The production of A. cruentus for leaves is most prevalent in humid tropical Africa (National Research Council 1984).

In the United States, amaranth is seldom used as a vegetable and production is limited to a few ethnic growers. Most greens grown in the United States prefer cool weather and perform poorly during hot summer months. There is a need to introduce leafy vegetables which can successfully be grown during the summer months. Amaranth may be such a candidate to fill this niche. Abbott and Campbell (1982) and Makus and Davis (1984) obtained high green yields from amaranth produced during summer months in Maryland and Arkansas, respectively. Sealy et al. (1990) reported that a West African cultivar 'Ibondwe' yielded 14 t/ha in central Texas and was comparable to spinach in taste. The object of this study was to establish optimum soil pH and intra-row plant spacing for amaranth production.

SOIL pH

The greenhouse experiment was conducted during November-December 1990, to compare the growth of amaranth at 6.4, 5.3, and 4.7 soil pH using Dothan sandy loam soil (fine loamy, siliceous, thermic, Plinthic Paleudult). Seeds of 'Hinchoy' were started in flats and 11-day-old seedlings were transplanted in thirty 3-liter pots, ten of each soil pH. The pots were arranged on the greenhouse benches in a randomized complete block design. The greenhouse was held at 32±3°C day/24±2°C night. Photoperiod was kept at 14 h and supplemental lighting was provided with fluorescent lamps. Five week old plants were harvested and the number of branches and leaves on the plants were counted. Plants were then separated into root, stem, and leaf portions and the fresh weight of plant components were determined. Leaf areas was measured with an area meter (LI-COR Model 3100, Lincoln, Nebraska). All plant parts were dried at 70°C in a forced air oven to a constant weight. The above experiment was repeated during January-February 1991.

Plants grown in pH 6.4 soil were significantly taller and had greater leaf area than plants grown in pH 5.3 or 4.7 soil (Table 1). There was a significant decrease in all above ground plant parts with each increase in soil acidity. The top fresh weight of plants grown in 5.3 and 4.7 pH soil were 27 and 73% lower, respectively, than plants grown in 6.4 pH soil. Campbell and Foy (1987) screened four grain amaranth populations of A. cruentus, A. hypochondriacus, and A. hybridus and also found that each performed poorly in Tatum soil (clayey, mixed, thermic, typic Hapludults) at 4.8 pH. Makus (1989) found that growth of vegetable amaranth was restricted in low pH Enders soil (clayey, mixed, thermic, typic Hapludults).

INTRA-ROW PLANT SPACING

A field experiment to compare the performance of amaranth at six intra-row plant spacings was conducted during summer of 1990. The genotype, RRC 241 was planted on a Dothan sandy loam soil (fine loamy, siliceous, thermic, Plinthic Paleudult) in 5 m long and 90 cm wide rows at six plant spacing of 4, 8, 16, 24, 32, and 40 cm in completely randomized blocks with three replications. Weeding was done mechanically and plots were irrigated as needed. The crop was harvested 40 days after planting. Data on plant height, branch number, and leaf number were obtained from five random plants from each plot. Plants were then separated into stem, petiole, and leaf parts. Plant component fresh weight was recorded and leaf area of two plants/plot was measured. Holes were made by a cork borer in the leaf blades of two random plants and 50 leaf discs were collected. The cumulative leaf area of the discs were measured and the leaf discs were dried to a constant weight at 70°C to calculate the specific leaf weight (unit dry weight/unit leaf area).

The tallest plants were produced in the closest spacing (Table 2). The relationship of plant height to intra-row spacing was quadratic in nature. The highest leaf number and maximum leaf area were obtained with the widest spacing. The regression of specific leaf weight on intra-row spacing was non-significant indicating that intra-row spacing did not affect leaf thickness. The maximum stem, petiole, and leaf fresh weights were produced in the widest spacing; minimum values were produced in closest spacing. As a result, the widest spacing had the highest and the closest spacing the lowest per plant fresh weight among the six intra-row spacings. On an unit area basis, however, green yield increased quadratically as intra-row spacing decreased. The coefficient of determination (R2) of green yield with intra-row spacing was 0.96, indicating that 96% of the total variation in the mean yields could be explained by the quadratic regression equation.

CONCLUSIONS

Our results show that growth of vegetable amaranth was adversely affected by soil pHs of 5.3 and 4.7. A soil with pH of 6.4 could produce high yielding vegetable amaranth. Green yield increased quadratically as intra-row spacing decreased. Maximum yield at 4 cm spacing within row was 1.50 kg/m2.

REFERENCES

Table 1. Growth parameters of amaranth at three soil pH levelsz

Plant weight (g/plant)
Top Root
Soil pH Plant height (cm) Branch (no./plant) Leaf (no./plant) Leaf area (cm2/plant) Fresh Dry Fresh Dry
6.4 18.3ay 8.5a 47.1a 1343a 49.5a 3.8a 19.8a 2.3a
5.3 16.0b 7.2b 42.4a 1011b 36.3b 2.8b 16.6b 1.8a
4.7 10.2c 5.3c 28.5b 412c 13.3c 1.0c 4.2c 0.6b
zExperiments 1 and 2 combined.
yMean separation within column by Duncan's multiple range test, P = 0.05.

Table 2. Growth parameters of amaranth at six intra-row plant spacings.

Plant fresh wt (g/plant)
Intra-row spacing (cm) Plant height (cm) Branch (no./plant) Leaf (no./plant) Leaf area (cm2/plant) Specific leaf weight (mg/cm2) Stem Petiole Leaf Yield (kg/m2)
4 29.3 5.3 35.3 873 4.43 18.9 6.0 24.2 1.50
8 23.0 6.7 56.3 1420 5.54 21.2 8.9 51.9 1.15
16 21.7 8.0 69.7 1598 6.10 25.4 10.9 55.9 0.66
24 15.3 6.0 63.7 1370 3.05 18.4 8.2 52.4 0.41
32 16.0 7.0 65.7 1368 4.16 19.5 8.5 49.4 0.29
40 20.7 6.7 70.0 1882 4.16 27.7 14.5 65.7 0.35
Significancez Q**y NSx C**w C**v NSu NSt C**s C**r Q**q
zC = cubic, Q = quadratic, L = linear
yR2 = 0.71
xR2 = 0.03
wR2 = 0.59
vR2 = 0.80
uR2 = 0.04
tR2 = 0.06
sR2 = 0.75
rR2 = 0.66
qR2 = 0.96
NS, *, ** Nonsignificant or significant at P = 0.05 or 0.01, respectively.

Last update April 29, 1997 aw