Agronomy Journal 94:1437-1443 (2002)
© 2002 American Society of Agronomy
WATER USE EFFICIENCY
Water Use Patterns of Grain Amaranth in the Northern Great Plains
Burton L. Johnson*,a and
Tracey L. Hendersonb
a Dep. of Plant Sci., North Dakota State Univ., Fargo, ND 58105
b 268 1st Ave., Waynesburg, PA 15370
* Corresponding author (burton.johnson{at}ndsu.nodak.edu)
Received for publication March 7, 2002.
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ABSTRACT
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An understanding of water use is essential for evaluating the potential of new crops in areas where water is a limiting factor. This study was conducted to determine water use efficiency (WUE), depth of soil water extraction, and other agronomic characters of grain amaranth (Amaranthus spp.) produced in the northern Great Plains. Field experiments were conducted with four grain amaranth cultivars at Prosper, ND, during the 1989 through 1992 growing seasons. Volumetric soil water content was monitored with a neutron probe at eight soil profile depths during each growing season. Significant differences among cultivars were observed for biomass yield, biomass WUE, plant height, and harvest index (HI). The year x cultivar interaction was significant for grain yield, grain WUE, plant height, and HI. Maximum effective depth of soil water extraction was 122 cm in the less water-stressed years, 1990 and 1992, and 154 cm in the more water-stressed years, 1989 and 1991. Cultivars did not differ significantly for depth of soil water extraction or total water use (TWU). Maximum effective rooting depth occurred at early to full anthesis in 1989, 1990, and 1991 and at the late anthesis to grain fill stages in 1992. Approximately 70 to 75% of TWU occurred by the end of anthesis. Mean TWU and grain WUE values were 267 mm and 5.9 kg ha-1 mm-1, respectively. Amaranth's apparent ability to respond to water stress by increasing rooting depth makes it a potentially useful crop in North Dakota where soil moisture conditions vary considerably among growing seasons.
Abbreviations: CWU, cumulative water use • HI, harvest index • SWD, soil water depletion • TWU, total water use • WUE, water use efficiency
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INTRODUCTION
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GRAIN AMARANTH is a warm-season annual crop that produces small, high-protein seed with high lysine content and unique starch and oil characteristics. Grain amaranth is unusual as a dicotyledonous food crop possessing the C4 photosynthetic pathway (El-Sharkawy et al., 1968). Amaranth has been considered a drought-tolerant species; however, little research exists on water requirements of the crop (Weber, 1990; Kauffman and Haas, 1983). Amaranth has been observed to withstand drought stress better than corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and cotton (Gossypium spp.) (Kauffman and Haas, 1983; Putnam, 1990; Jiayi et al., 1989). The drought-tolerant characteristic of amaranth has been attributed to water efficiency of the C4 pathway, indeterminate flowering habit, long taproot, and extensive lateral root system (Hauptli, 1977; Putnam, 1990). Research in China indicates the main taproot may grow as long as 2.45 m (Jiayi et al., 1989; Shaoxian and Hongliang, 1990).
Water use efficiency has been defined as the ratio of economic yield to TWU or evapotranspiration (Zaffaroni and Schneiter, 1989; Copeland et al., 1993). In greenhouse experiments, amaranth had higher WUE than the C3 crops sunflower (Helianthus annuus L.), cotton, cowpea [Vigna unguiculata (L.) Walp.], and rice (Oryza sativa L.) but lower WUE than the C4 crops corn and sorghum (Morison and Gifford, 1984). In another study, the amaranth species A. hypochondriacus had significantly higher WUE than two C3 species grown for comparison under the same water-stressed conditions (Miller et al., 1984). Amaranthus cruentus produced the highest seed yield of four grain amaranth species grown under artificially induced water stress in greenhouse conditions (Cavagnaro and Jain, 1985). Average grain WUE values for A. cruentus and A. hypochondriacus ranged from 4.02 to 6.08 kg ha-1 mm-1 under nonstress and severe-stress conditions, respectively.
The water requirement of grain amaranth was reported as 42 to 47% that of wheat (Triticum aestivum L.), 51 to 62% that of corn, and 79% that of cotton, based on observations in China (Weber, 1990). Adequate soil moisture during emergence and early vegetative growth is essential for amaranth production, but little quantitative information is available about amaranth water requirements and utilization patterns later in the season. The objectives of this study were to evaluate the water requirement, water use patterns, depth of soil water extraction, and other agronomic characters of grain amaranth produced in the northern Great Plains.
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MATERIALS AND METHODS
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Field experiments were conducted at Prosper, ND (46°58' N, 97°4' W; elevation 220 m), during the 1989, 1990, 1991, and 1992 growing seasons. Four amaranth cultivars previously shown to be adapted in the northern Great Plains were grown: A. cruentus cv. K283 and MT-3 and A. hypochondriacus x A. hybridus cv. K343 (also known as Plainsman) and K432 (Schulz-Schaeffer et al., 1989; Baltensperger et al., 1992; Weber and Reider, 1989). 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.
Soil series at the trial site consisted of Perella (fine-silty, mixed, superactive, frigid Typic Endoaquolls) and Beardon (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 a level suitable for a 5700 kg ha-1 wheat crop by adding appropriate amounts of fertilizer based on fall-collected soil samples (Fanning et al., 1988). Wheat was the previous crop each year the study was conducted. Reliance on cultural weed control practices, in the absence of labeled herbicides, included selection of fields with low weed pressure and supplemental hand weeding of plots.
The experimental design was a randomized complete block with four replicates. The four cultivars were considered a fixed effect in the analysis. Plots consisted of six rows spaced 30.5 cm apart and 6.1 m in length. Seeding was performed with a plot planter with double-disk openers and press wheels at a depth of 15 to 25 mm. Seeding dates were 8, 14, 13, and 4 June for 1989, 1990, 1991, and 1992, respectively. Stands were oversown and hand-thinned at the two- to three-leaf stage to a uniform population of 173 000 plants ha-1. A 4.6-m section of the center two rows of each plot was hand-harvested by cutting stalks just above the soil surface after the first killing frost in mid- to late September. Grain and aboveground biomass yield (dry weight basis), HI, and average plant height at harvest were determined for each plot. Daily precipitation and maximum and minimum temperatures were recorded and reported as monthly averages.
Soon after emergence, access tubes were installed vertically into the soil profile to a depth of 2.13 m between two amaranth plants in one of the center two rows of each plot. As a check to monitor soil water content without plant transpiration, an additional access tube was installed in an area of bare fallow adjacent to the experiment. Volumetric soil water content was determined using a neutron moisture meter (Model 503 Hydroprobe Moisture Depth Gauge, Campbell Pacific Nuclear Corp., Pacheco, CA). Soil water readings were taken every 10 to 14 d in 1990, 1991, and 1992 for a total of eight readings each season. In 1989, soil water readings were determined only four times during the growing season.
In all years, the first soil water data were collected about 2 wk after emergence with subsequent neutron readings taken at approximately 4, 5, 7, 8, 10, 12, and 14 wk. The final data were collected at harvest, which occurred at about 14 wk after emergence in 1989, 1990, and 1991 and 15 wk after emergence in 1992. Only four neutron probe readings taken in 1989; these were at 2, 4, 8, and 14 wk. Soil water data were recorded at soil profile depths of 0.15, 0.30, 0.61, 0.91, 1.22, 1.52, 1.83, and 2.14 m. Plant height and stage of plant development were recorded at each soil moisture reading. After harvest TWU, soil water depletion (SWD) at each depth, cumulative water use (CWU) over the growing season, and WUE were determined for each plot. Runoff, deep percolation, and lateral and upward soil water movement were assumed to be negligible.
Volumetric soil water content was analyzed as a split plot in space (soil profile depth) and time (sampling date) (Steel and Torrie, 1980). The maximum depth of soil water extraction was assumed to be the maximum effective rooting depth and was determined as the maximum effective depth at which significant positive differences in soil water content were observed among successive reading dates.
Profile SWD was calculated as the difference between profile soil water content values on the initial and final moisture reading dates of the growing season. Soil water depletion values at different soil depths were analyzed using a split plot in space arrangement. Total water use was considered the sum of evaporation and transpiration and was calculated as the sum of profile SWD and precipitation from the time of initial to final soil moisture readings. Water use from emergence to the initial soil moisture reading was assumed to be negligible. Water use efficiency was calculated for both grain and aboveground biomass yields as the ratio of yield (kg ha-1) to TWU (mm).
Cumulative water use over the growing season was determined by adding the sum of profile SWD and precipitation over successive time increments throughout the growing season. Values for CWU were analyzed using a split plot in time arrangement. In all cases, cultivar, soil depth, and weeks after emergence were considered fixed effects and year a random effect. Since time increments between neutron probe readings were different in 1989 than the other years, the analysis for CWU was performed across 1990, 1991, and 1992.
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RESULTS AND DISCUSSION
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Climatic Conditions during Tested Years
Precipitation at the Prosper research site was below average in the 1989, 1990, and 1991 growing seasons and above average in the 1992 growing season (Table 1). June and July during 1989 were dry. The maximum daily temperature was 31°C or higher for 21 d in July 1989, during which only 25% of the average precipitation was received (Table 2). Below-average precipitation in May 1990 and hot, dry conditions in the 1989 season likely reduced initial soil profile water status in 1990. Timely precipitation, however, in the seeding month (June) of both years enabled good stand establishment. Above-average precipitation occurred in mid- to late August 1989. In 1990, rainfall conditions were favorable for plant growth early in the growing season as June rainfall was 87.4 mm above average. Rainfall was below average during the rest of the 1990 growing season. Average precipitation was received in June 1991, but the remainder of the growing season was drier than average, especially during August. In 1992, the excessive rainfall in June (162 mm above average) and cool temperatures throughout the growing season slowed amaranth development.
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Table 1. Total monthly precipitation and departure from average monthly precipitation during 1989, 1990, 1991, and 1992 at Prosper, ND.
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Table 2. Mean monthly temperature and departure from average mean monthly temperature during 1989, 1990, 1991, and 1992 at Prosper, ND.
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Cultivar and Year x Cultivar Effects
Significant main-effect differences among cultivars were observed for biomass yield, biomass WUE, HI, and plant height (Table 3). The year x cultivar interaction was significant for grain yield, grain WUE, HI, and plant height. The greatest grain yields were produced in the 1990 and 1992 growing seasons, which received above-average early-season precipitation (Table 4). Grain yield and HI were highest for K283 and K432 in 1992 as these two cultivars appeared to tolerate the cool, wet 1992 conditions better than MT-3 or K343. When averaged across years, cultivars K283 and K432 produced significantly less biomass than MT-3 or K343. The two A. cruentus cultivars (K283 and MT-3) appeared to be more suited for grain production under dry conditions such as those that prevailed in 1989. Cultivar MT-3 produced 66% greater yield than the mean yield of K343 and K432 in 1989 (Table 4). Although K283 and K343 yields were not statistically different, a general assignment would classify K283 with MT-3 in the high-yield category and K343 in the low-yield category with K432 in 1989.
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Table 3. Levels of significance of main effects and the year x cultivar interaction for several agronomic characters of grain amaranth produced during the 1989, 1990, 1991, and 1992 growing seasons at Prosper, ND.
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Table 4. Influence of the cultivar main effect and year x cultivar interaction on several agronomic characters of grain amaranth produced during 1989, 1990, 1991, and 1992 at Prosper, ND.
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Although not statistically tested, TWU and biomass yield were lower in 1992 than in previous years (Table 4). These effects can be attributed to decreased evapotranspiration and reduced vegetative growth resulting from unusually cool temperatures in 1992. Total water use ranged from an average of 164 mm in 1992 to 322 mm in 1989. A C4 plant such as amaranth grows well under conditions of high temperature and sunlight and dry conditions. Although growing conditions were cool and moist during 1992, yield performance was high for K283 and K432, with cultivars K343 and MT-3 producing lower yields comparable to their performance in 1989 and 1990 (Table 5). Slightly later maturity for K343 and MT-3 may have limited their yield performance in the cooler year 1992.
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Table 5. Average growth stages of four grain amaranth cultivars produced during 1989, 1990, and 1991, and growth stages of the same cultivars produced during 1992 at Prosper, ND.
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Cultivar grain WUE was generally higher in the cooler year 1992 (7.2–11.8 kg ha-1 mm-1) compared with other years, with the exception of similar WUE for MT-3 in 1992 and 1990 (Table 4). Cultivar differences for WUE were not apparent in the drier years 1989 and 1991 where values ranged from 2.8 to 4.3 and 3.8 to 4.6 kg ha-1 mm-1, respectively. In 1990, MT-3 had higher WUE than the other cultivars because of high grain yield. The main effect of cultivar and year x cultivar interaction for TWU was not significant. Cultivar K343, which is tall and branching, had the highest biomass yield and biomass WUE when averaged across years. Mean TWU, grain WUE, and biomass WUE values averaged across cultivars and years were 267 mm, 5.9 kg ha-1 mm-1, and 31.9 kg ha-1 mm-1, respectively. The mean grain WUE value is similar to that observed by Cavagnaro and Jain (1985) for grain amaranth under severe, artificially induced water stress. In their study, however, grain WUE increased in response to drought stress, whereas the opposite was observed in our study. Observed grain WUE for sunflower, safflower (Carthamus tinctorius L.), canola (Brassica spp.), and crambe (Crambe abyssinica Hochst.) grown in the same area was 6.7 to 7.5, 6.9 to 9.1, 4.3 to 5.9, and 6.7 kg ha-1 mm-1, respectively (Schneiter et al., 1993; Henderson et al., 1993). Total water use for sunflower (Schneiter et al., 1993) and wheat (Bauder, 2002) grown in the northern Great Plains was reported at 350 to 440 and 290 to 365 mm, respectively. In general, this shows amaranth and wheat comparable in TWU but sunflower having a higher TWU than amaranth. Water use efficiency reported for wheat ranged from 8.8 to 11.7 kg ha-1 mm-1 (Bauder, 2002; Dalal et al., 1998; Tanaka, 1990) and is higher than amaranth's WUE when averaged across years. However, amaranth WUE in the cooler year 1992 ranged from 7.2 to 11.8 kg ha-1 mm-1, which is comparable to WUE previously reported for wheat.
Plant Rooting Depth
The maximum depth of soil water extraction, which may be interpreted as maximum effective rooting depth, was 122 cm in 1990 and 1992 and 152 cm in 1989 and 1991 (Fig. 1)
. The 1989 data for soil water content by depths and weeks were analyzed separately from the 1990, 1991, and 1992 data because soil water readings were taken at just four dates in 1989. The results suggest that water stress, such as that observed in 1989 and 1991, stimulates deeper root penetration in grain amaranth. A similar response has been observed in sunflower where effective rooting depth was 1.8 and 1.5 m during a wet and dry year, respectively (Schneiter et al., 1993).
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Fig. 1. Depth of soil water extraction by grain amaranth at Prosper, ND, based on the maximum depth at which positive significant differences in volumetric soil moisture content at successive reading dates were observed (LSD 0.05 = 10.5 mm for 1989 and 13.8 mm for the combined analysis across years 1990, 1991, and 1992).
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In 1989, 1990, and 1991, maximum effective rooting depth occurred 8 wk after emergence (Fig. 1), corresponding to early anthesis in K343 and MT-3 and full anthesis in K283 and K432 (Table 5). In 1992, rooting depth continued to increase after completion of most anthesis until the maximum effective depth was reached at approximately 12 wk after emergence (Fig. 1). This corresponded with the late anthesis to grain fill stages (Table 5). In 1992, cool temperatures and subnormal rainfall in July and August delayed phenological development. This may have promoted more root penetration later in the season than in the other years.
Cumulative Water Use
Analysis showed that about 70 to 75% of TWU occurred by the end of anthesis, which occurred for most plants about 10 wk after emergence in 1990 and 1991 and 12 wk after emergence in 1992 (Fig. 2)
. Beginning 5 wk after emergence, CWU was significantly lower in 1992 than in the two previous years, possibly due to the decreased vegetative growth associated with cool temperatures. Water use was negligible during the full-anthesis stage in 1992 (10–12 wk after emergence), whereas CWU continued to increase during anthesis in the other years. This may have been due to the effects of shallow rooting depth and water stress in July and August 1992 or to a near cessation in vegetative growth. Amaranth plants continued to use water until the first killing frost in both 1990 and 1992. In 1991, measurable water use ceased 12 wk after emergence during the grain fill stage. At this time, the available water in the root zone had been reduced because of the hot, dry conditions in August and September 1991, and further root penetration did not occur at this stage. Volumetric moisture values for the 15- and 30-cm soil depths were near the permanent wilting point at 0.25 and 0.29%, respectively. Soil water content at deeper profile depths indicated plant available water, but change in volumetric soil moisture was not noted between 12 and 14 wk (data not shown).
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Fig. 2. Mean cumulative water use of grain amaranth during 1990, 1991, and 1992 at Prosper, ND (LSD 0.05 = 11.8 mm).
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Soil Water Depletion
Significantly more water was extracted from shallow subsurface profile depths (30, 61, and 91 cm) in 1990 than in 1989 or 1991 (Fig. 3)
. The high rainfall in June 1990, which increased soil water at shallow depths and provided adequate water for early vegetative growth and faster early root development, may explain this effect. Dry conditions followed in July and August 1990, during which the surface soil water was depleted. The abundance of water in the upper profile in June 1990 did not promote the deeper root penetration observed in response to drier early-season conditions in 1989 and 1991. Excess water in the upper profile and high early-season soil water conditions also resulted in shallower depths of soil water extraction in 1992.
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Fig. 3. Mean soil water depletion by grain amaranth at eight depths in the soil profile during 1989, 1990, 1991, and 1992 at Prosper, ND (LSD 0.05 = 17.9 mm).
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Significantly more water was extracted at the 122-cm depth in 1989 than in 1990. Soil water depletion at the 152-cm depth occurred in both 1989 and 1991 but not in 1990 or 1992. Although soil water extraction did occur at both 91 and 122 cm in 1992, it occurred later in the season, starting approximately 8 wk after emergence. The negative SWD values at 91 and 122 cm in 1992 occurred because the influx of water from the excessive precipitation in June exceeded the amount of water extracted after root penetration to these depths in August and September. The more pronounced water deficit in 1989 and 1991 apparently led to deeper root penetration and, therefore, greater SWD at lower soil depths in these environments. Khan (1987) reported SWD at deeper profile depths in the drier year of a 2-yr study with wheat. Soil water depletion occurred at 122 cm in the drier year and at 91 cm in the wetter year. Khan suggested that SWD would correspond with the effective rooting depth for wheat. Effective rooting depths for safflower, canola, and crambe of 183, 122, and 122 cm, respectively, indicate amaranth having a similar or greater effective rooting depth compared with canola and crambe but a lower effective rooting depth than safflower (Henderson et al., 1993).
While the cultivar main effect was not significant for grain yield or grain WUE, year influenced cultivar response for these characters. Early-season rainfall and soil water during vegetative development appears to be a critical factor influencing grain yield. Before the grain fill stage, grain amaranth appears to respond to mild to moderate soil water stress by increased root penetration and water extraction at lower soil profile depths. Additional research is necessary to evaluate amaranth's response to severe drought conditions.
High early-season available soil water and cool temperatures appear to inhibit deep root penetration and vegetative growth of amaranth, but not grain yield, thereby improving HI and grain WUE. Such responses make amaranth a potentially useful crop in the northern Great Plains where soil water conditions may vary from year to year. Amaranth water use in the northern Great Plains appears to be similar to wheat and less than sunflower. Effective rooting depth for amaranth ranged from 122 to 152 cm and increased with less seasonal precipitation. This is comparable to reported effective rooting depths for canola, crambe, and wheat but less than the deeper-rooted crops safflower and sunflower. Amaranth should not deplete soil water more for subsequent crops than cereals and cool-season oilseed crops commonly grown in the region. This is an important factor when considering cropping options from season to season in the more arid areas of the northern Great Plains. Cultivar grain yield response varied from year to year and was largely influenced by seasonal climatic conditions, indicating the importance for producers to select cultivars that have the best adaption for their region. Cultivar K283 was consistently in the high cultivar group for yield and HI each season of the study, whereas the other cultivars exhibited a more varied response among seasons for these characters. Harvest index for amaranth is lower than crops that have been domesticated and improved for yield performance by many decades of plant breeding. Future increases in grain yield are likely to increase HI and grain WUE.
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REFERENCES
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ABSTRACT
INTRODUCTION
