Crop harvest management is critical, as amaranth shatters readily (Myers and Putnam 1988). Preliminary studies indicate that losses caused by seed shattering can decrease yields of some cultivars over 1100 kg/ha (Shroyer et al. 1990). Tucker (1986) reported that mechanical harvesting recovered only 50% of the potential yield.
Amaranth is a plant with high plasticity, and adjusts to a range of environmental conditions (Putnam 1990). Plants grown in thin stands branch more, have thick stalks, and mature late while plants grown at high densities are smaller with thin stalks and are better suited for mechanical harvest. Increased lodging often occurs at high plant populations.
Harvesting should begin as soon as practical to minimize grain shattering and losses due to wind. Direct combine harvest of grain amaranth prior to frost can be complicated by variation of grain maturation in the inflorescence and by high stem and leaf moisture at the time of grain maturity (Krishnan et al. 1987). Shattering losses can be severe, particularly when a light frost kills portions of the flower, but does not kill the entire plant (Weber and Kauffman 1990). If plants are harvested while wet, seeds often adhere to wet plant tissue and may be non-harvestable (Tucker 1986).
The seed of most grain amaranth commercially produced are white or light tan. Some immature seeds turn dark brown when harvested or after frost (Baltensperger et al. 1992). The seed has a lenticular shape, with the embryo located in a ring around the perisperm on the longitudinal axis (Bressani 1990). The placement of the embryo around the endosperm makes it vulnerable to mechanical damage during combine harvest. Combine cylinder speed should be reduced to minimize grain damage and loss in seed germination (Weber and Kauffman 1990). Krishnan et al. (1987) reported mechanically harvested seed at a cylinder speed of 437 rpm had 62% germination, while hand-harvested seed had 97% germination.
Before planting, soil fertility of all plot land, based on fall soil tests, was brought to a level suitable for a 5700 kg/ha wheat crop (Danke et al. 1992). Weeds were controlled with sethoxydim and hand weeding when needed.
Amaranth was sown at Prosper, North Dakota, the first week of June, in 1993 and 1994. The soil series at Prosper are Perella (fine-silty, frigid, mixed Typic Haplaquoll) and Bearden (fine-silty, frigid, mixed Aeric Calciaquoll). Each plot consisted of six rows, 6.1-m long at a 30-cm row spacing. Seeds were planted with an Almaco planter at the rate of 3.4 kg/ha. Established plots were thinned, at the three to four leaf stage, to a population of 173 000 plants/ha. The experiment was a randomized complete block design with four replicates. Treatments consisted of five harvest dates at six-day intervals after first seed shatter.
A Hege 125B plot combine was used to harvest the plots. Harvested samples were placed in cloth sacks, weighed before drying, and force air-dried at a temperature <38°C. A 90-g moisture sample was removed before samples were placed in the dryer. The moisture samples were placed in an oven at 110deg.C for approximately 48 h.
Data collected included (1) seed and foreign material moisture content at each harvest, (2) seed yield, (3) seed germination percentage after harvest, and (4) percent dockage at harvest. Moisture was calculated by dividing the moisture loss (g) by the fresh sample weight (g). Percent dockage was calculated by dividing the weight (g) of the dried harvest sample (before cleaning) by the weight (g) of the foreign material removed.
Date 1 was harvested at first seed shatter which occurred on Sept. 15 and Oct. 14, in 1993 and 1994, respectively. Date 2, in 1994, was not harvested due to a heavy (76 mm) rain that did not allow for combine access to the plots. Therefore, date 2 was not included in the analysis. The harvest date-by-environment interaction was significant for grain yield, dockage, seed germination, and moisture.
Grain yields in 1993 were 20% to 40% of those at the same harvest date in 1994. Grain yield decreased significantly after dates 3 and 1, in 1993 and 1994, respectively (Table 1), probably due to seed shatter. Seed loss at date 4 occurred because whole branches of the floral cyme fell off due to plant dry down. Significant differences in grain yield occurred after date 1 in 1994. Grain yields decreased as harvest was delayed beyond first seed shatter.
The significant harvest date-by-environment interaction for percent dockage at harvest was due to the magnitude of differences between 1993 and 1994 (Table 1). In 1993, dockage, across all harvest dates averaged 25% greater than in 1994. This change may have been due to loss of seed to shattering and the ability of the plot combine to remove the empty floral parts from the cyme. The unusually long growing season in 1994 may have increased the seed:foreign material ratio by allowing more seed to mature before harvesting.
Germination percentages differed among environments for seed harvested at different dates. Germination decreased as harvest date was delayed, in 1993. Germination of seed harvested at dates 1 and 3 were significantly higher than seed from dates 4 and 5. Germination of seed from harvest date 1 in 1994 was significantly lower than that of seed from dates 3, 4, and 5. This may have been due to higher seed injury by the plot combine, as seed had not been frosted and may have been at a more immature state. Germination of seed from harvest date 3 was significantly higher than from dates 4 and 5. Seed weathering and seed injury during threshing may have reduced seed germination at the later harvest dates.
Percent moisture of the harvested samples, including seed and plant material, from Prosper in the 1993 and 1994 growing seasons. In 1993, a killing frost occurred before seed shatter was observed. A significant decrease in percent seed moisture for dates 1, 3, and 4 in 1993 was observed. This was probably due to the periodic occurrence of frost and a dry fall, both of which encourage plant dry down.
Percent moisture of the harvested sample did not differ significantly for dates 1 and 3 during the 1994 harvest. Frost had not occurred before date 3, and plant material had not dried down. The lush vegetative plant material in the harvest sample provided an explanation for the high moisture values for dates 1 and 3. A killing frost occurred after date 3, and the moisture values for dates 4 and 5 decreased significantly.
In 1994, comparisons were made between hand-harvest and plot combine harvest. Grain yield and percent seed germination were compared at each date. Mean values for harvest date effect are presented in Table 2. Plot combine harvested plots yielded 70% to 75% of the hand-harvested plots. Although considerable (25% to 30%) seed loss occurred due to mechanical harvesting, this loss was less than the 50% reported by Tucker (1986). This difference may be due to the use of a plot harvester rather than a commercial harvester.
Percent seed germination after harvest was significantly higher in hand-harvest plots than in combine harvested plots. Germination of hand-harvested grain ranged from 82% to 93% across harvest dates while combine harvested seed ranged from 58 to 74% across harvest dates. The decrease in percent germination was probably due to seed damage caused by the plot combine.
Percent dockage was high at all harvest dates. Seed germination was found to decrease with the later harvest dates, possibly due to weathering and mechanical damage. Percent moisture of the harvested sample was very high before a killing frost and decreased rapidly after a killing frost.
Amaranth should be harvested as soon as possible after a killing frost to reduce yield losses and maximize seed germination. Harvest before a killing frost was not feasible due to a high moisture content of the harvest sample that makes storage difficult and increases drying costs. Arrangements must be made to remove plant material to avoid grain spoilage. The harvest sample may need to be dried so seed can be separated from wet plant tissues.
Hand-harvested plots yielded 25% to 30% higher than plot combine harvest yields, due to seed losses caused by mechanical harvesting. Germination was approximately 20% higher for hand-harvest seed than for plot combine harvest seed.
|Harvest||Grain yield (kg/ha)||Dockage (%)||Germination (%)||Moisture (%)|
|1||Sept. 15||Oct. 14||480ay||1346a||64ab||35b||86a||58c||32a||60a|
|3||Sept. 27||Oct. 20||425ab||1131c||66a||42a||85a||74a||16b||60a|
|4||Sept. 31||Nov. 1||376a||1248b||63b||42a||74b||68b||10c||21b|
|5||Oct. 6||Nov. 7||253c||1191bc||62b||37b||69c||65b||11c||18c|
|Harvest||Grain yield (kg/ha)||Germination (%)|
|1||Sept. 15||Oct. 14||1346ay||1890a||58c||93a|
|3||Sept. 27||Oct. 20||1131c||1616b||74a||85b|
|4||Sept. 31||Nov. 1||1248b||1634b||68b||91a|
|5||Oct. 6||Nov. 7||1191c||1640b||65b||82b|