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A Varietal Comparison of Productivity in the Sweet Potato
A Varietal Comparison of Productivity in the Sweet Potato

A Varietal Comparison of Productivity in the Sweet Potato

by Jeffery Goss, M.H. of Billings, MO and E.O. Brown of Reeds, MO

In 2012 a comparative yield trial involving 38 cultivated varieties of sweet potatoes (Ipomoea batatas) was conducted by Edmund O. Brown II and Pamela Jean Brown at two locations on their farm, known as New Hope Farms in eastern Jasper County, Missouri. The following is a description of the trial, and of which clonal varieties were found by Mr. and Mrs. Brown to yield better and worse.

LOCATION: New Hope Farms is situated near the town of Avilla, on the east side thereof, about ten miles due east of Carthage, and approximately the same distance due north of Sarcoxie. The farm is located in the exact geological boundary between the Osage Plains to the north and the Ozark Plateau to the south. It belongs to the White Oak Creek watershed, and the ecology is intermediate between Prairie and Woodland zones. Last spring frost average is in mid- April, and first autumn frost average is in late October. Soil is mostly a clay-loam complex. Row cropping is widespread in the immediate vicinity.

METHODS: Two sites hereinafter referred to as the Main Plot and East Annex, both being on the selfsame farm, were prepared in rows. Each row consisted of a ridge of loose soil, 8-12 inches high. The sweet potatoes were planted as slips (vegetative outgrowths from a sprouted tuber). Each slip was planted 12-18 inches apart in the row, with the root being pushed down deeply, and the rows were thereafter mulched with straw. The main varieties being grown, i.e., the ones being grown in significant quantity, were assigned to the Main Plot (11 total), while a much wider range of varieties (29 total) were assigned to the East Annex, in small numbers.

The following is a list of the 38 clonal varieties (“cultivars”) of sweet potatoes grown. Those listed without an asterisk were grown at the Main Plot, those which have a single asterisk were grown at the East Annex only, and those which are listed with double asterisks were grown in both fields. There are only two in the last-named category.

Allgold
Amish Bush Porto Rico*
Amish White Bunch*
Apache*
Arkansas Red Leaf*
Beauregard**
Bradshaw
Brinkley*
Carver*
Centennial*
Covington*
Darby
Dingess Old-Time White*
Dingess Pink Tint*
Envy*
Fork Leaf/Malton
Frazier White*
Garnet*
Georgia Yam (not GA Jet)
Gold Star*
Golden Slipper*
Hayman**
Indiana Gold
Jewel*
Korean Purple*
Lace Leaf*
Margaret Bray*
Maryland 810*
Old Fashioned Southern Queen (OFSQ)*
Old Kentucky*
Orange Oakleaf*
Pelican Processor
Porto Rico (Old Fashioned Vining)
Razorback (U-of-A)*
Red Ivy Leaf*
Red Wine Velvet*
Ringley’s Porto Rico*
Theodore Meece

Some notes should here be made concerning the identities of several cultivars named in the foregoing list. The fork-leafed variety is one which was received with no varietal name label, but we believe it to be identical with ‘Malton’, whose description it closely fits and which is known to have been raised by the grower who supplied the slips. Hereinafter it shall be referred to as “Fork Leaf/Malton”. It is a vigorous vining type, having large red-skinned tubers.

The ‘Georgia Yam’ evaluated herein is not, as might be supposed, the same as ‘Georgia Jet’. In fact, the habits and qualities of the Georgia Yam were found to be very different from those of the Georgia Jet, although both of them bear red-skinned tubers containing orange flesh.

The cultivar ‘Razorback’ is also occasionally seen as ‘U of A’. It was developed by the University of Arkansas for farmers in the clay-soil Ozark region, but the university ceased to maintain the cultivar after the sweet potato program ended in the 1990s.

The name Porto Rico is a term for a general variety of sweet potatoes, of which many specific clonal versions exist. Three such clonal versions are evaluated herein: to wit, the ‘Amish Bush Porto Rico’, the ‘Ringley’s Porto Rico’, and the ‘Old Fashioned Vining Porto Rico’. It is generally supposed that this last-named clone is being referenced when the term Porto Rico is used without qualifier, but this is not always the case. Hereinafter the Old Fashioned Vining type shall be listed as ‘Porto Rico (OFV)’. Note also that the spelling “Porto” is considered correct when used in reference to sweet potatoes, whereas the “Puerto” spelling is correct when mentioning the actual island by that name.

HARVEST: The sweet potatoes were measured by weight at harvest, with the yields per row and per hill being calculated (with “hill” being interpreted as a single cluster, deriving from a single slip).

The crop from the Main Plot was harvested over an 11-day period, between Sept. 26th and Oct. 7th. This was in cool weather and after the rapid growth season of the tubers had ended, but it should be noted that the last-harvested varieties may have grown slightly larger having had the opportunity to benefit from a rain shower on the 28th of September (the cultivar ‘Beauregard’ being harvested first, not having had that chance). But in any case the differences so wrought in yield cannot be great.

The results of the yield comparison in the Main Plot are as follows, with poundage per vine being the measure of productivity (rather than tuber count).

TABLE I. Per Capita Yield in the Main Plot

Row(s)Cultivar NameNo. of hillsLbs./vine
1-4Beauregard2003.75
5Darby85
5Fork Leaf/Malton143.5
5Hayman153
5Pelican Processor52
6Indiana Gold153
6Porto Rico (OFV)244.17
6Theodore Meece31
7Bradshaw22.5
7Georgia Yam33.3
8Allgold501.5

Row numbers proceed upward in a general west-to-east direction. Total tuber yield from the Main Plot was estimated at 1,132 pounds, with an all variety average of 3.34 pounds of tubers per surviving vine. Since ‘Beauregard’ was the main variety grown, it has a much larger sample size than the others. (The number of “hills”, i.e. surviving vines that bore tubers, is listed above for each cultivar in order to give an indication of the comparative statistical sample size, which differed widely. This is largely a result of differing numbers of available slips to begin with, as well as the Beauregard’s status as the main cultivar grown for production at New Hope Farms.)

Within the Beauregard section, it was observed that the westernmost row got an average of 4.5 pounds per hill, while the other three planted to that cultivar yielded about 3.5 pounds per hill. This can probably be ascribed to the well-known “end row effect”, in which plants in an end row are exposed to more sunlight and have more root space, and therefore appear to be higher-yielding or faster-growing. Nevertheless, for the purposes of this study the west end row was computed into the general yield figures for ‘Beauregard’.

The following table will deal with the results obtained in the other field, the East Annex, which more precisely approximates scientifically controlled conditions. This plot has a wider range of cultivars, as it was prepared especially for comparative evaluation of the “minor” ones, that is to say, the ones which the growers did not intend to plant en masse, or else did not have large quantities of slips on hand. However, it is not larger than the Main Plot: the Main Plot yielded 339 hills or clusters in totality, whereas the East Annex had only 301 hills. The East Annex sweet potato planting consisted of 6 rows.

TABLE II. Per Capita Yield in the East Annex

Row(s)Cultivar NameNo. of HillsLbs./vine
1Centennial502
1Covington42
1 & 5Jewel430.26
2Amish Bush Porto Rico91
2Amish White Bunch141.5
2Arkansas Red Leaf101.7
2Apache92
2Brinkley72.86
2Carver41
3Dingess Old-Time White61.5
3Dingess Pink Tint42
3Envy33.33
3Frazier White62.5
3Garnet41
3Golden Slipper70.86
3Gold Star141
3Hayman50.5
3 & 4Old Kentucky121.21
4Korean Purple70.72
4Lace Leaf70.72
4Margaret Bray60.83
4Maryland 81031.67
4OFSQ50.4
4Orange Oakleaf1est 0.2
4Red Ivy Leaf60.17
4Red Wine Velvet60.33
4Ringley’s Porto Rico70.72
5Razorback100.5
6Beauregard260.25

All of the sweet potatoes in the East Annex were harvested within a 48-hour period of one another, mostly on the 8th of October, 2012. Total poundage of tubers in this plot was approximately 296 pounds, but may be slightly more since the weights were in some cases rounded to the nearest half pound down. Of the 295 surviving vines (six Hayman vines in Row 1 of the East Annex failed to mature), the East Annex has an all-variety yield average of almost exactly one pound per hill. The much lower average yields in the East Annex as compared to the Main Plot may be in part cultural and site-specific, but also in part because the Main Plot was planted mostly in cultivars already reputed to be higher yielding.

Special attention should be paid to the only two varieties grown at both locations, for they are helpful bellwethers to indicate the rate of difference between the expected yields at either. “Hayman” (the surviving five vines thereof, in row 3 of the East Annex) yielded 0.5 lbs./vine according to Table II, while in the Main Plot it yielded 3 lbs./vine (see Table I). Meanwhile ‘Beauregard’ yielded 3.75 lbs. /vine in the Main Plot and 0.25 lbs. /vine in the East Annex. Thus ‘Hayman’ yielded 6 times better in the Main Plot than in the East Annex, while ‘Beauregard’ yielded 15 times better there (or 14 even if we correct for the “end-row advantage” of Row 1 in the Main Plot). Thus, it can be said that most of the difference in outcomes at the two plots is non-genetic in origin. We can even note that the relative superiorities are switched: while Beauregard outperforms Hayman in the Main Plot, Hayman outperforms Beauregard in the East Annex. Therefore the following table should be read with that in mind, considering the Main Plot more likely to represent rich garden-type soil, and the East Annex to represent prairie-type cropland soils.

TABLE III. Comparative Yields in Both Plots, in Descending Order

Main PlotEast Annex
5 – Darby3.33 – Envy
4.17 – Porto Rico (OFV)2.86 – Brinkley
3.75 – Beauregard2.5 – Frazier White
3.5 – Fork Leaf/Malton2 – Centennial, Covington, Apache
3.3 – Georgia Yam1.7 – Arkansas Red Leaf
3 – Hayman, Indiana Gold1.67 – Maryland 810
2.5 – Bradshaw1.5 – Amish White Bunch, Dingess Old-Time White
2 – Pelican Processor1.21 – Old Kentucky
1.5 – Allgold1 – Amish Bush Porto Rico, Carver, Garnet, Gold Star
1 – Theodore Meece0.86 – Golden Slipper
0.83 – Margaret Bray
0.72 – Korean Purple, Lace Leaf, Ringley’s Porto Rico
0.5 – Hayman, Razorback
0.4 – OFSQ
0.33 – Red Wine Velvet
0.26 and below – Jewel, Beauregard, Orange Oakleaf, Red Ivy Leaf

We should here note some of the specific limitations and peculiarities of this table. The placement of cultivars high on the list for either location suggests that they are good producers in these conditions, but the placement of cultivars low on the list – especially on the East Annex list – should not necessarily be interpreted as meaning they are extremely bad. The sample size is an important clue to the reliability of the data for each cultivar. For example, only one vine of ‘Orange Oakleaf’ was grown, and it bore only a very small tuber, but a larger sample of the same clonal variety would likely have yielded higher amounts.

Dingess Pink Tint is known for its habit of sending down tubers at nearly every node, and in a straw-mulched system such as that used here; there are very few opportunities for the vines to root at the nodes (adventitiously). Consequently it is likely that ‘Dingess Pink Tint’ would yield better in a situation where it was allowed to root freely, perhaps even with the nodes being carefully buried. Most often these tubers are borne 3 to a node.

Some of the varieties listed also have synonyms. ‘Porto Rico (OFV)’ is sometimes sold as ‘Running Porto Rico’. Likewise, ‘Garnet’ is either a synonym or very nearly so of ‘Dianne’ and ‘Cuban Red’.

The general uniformity of conditions and therefore the general reliability of data taken from the East Annex is confirmed by the yield of ‘Carver’ being intermediate between its parents (it is a cross of Centennial x Jewel). We must also consider, however, the effects of differing viral loads on each of the slip samples being propagated, which may account for a great deal of low-yielding. For example, trials at the Sand Hill Preservation Center in Calamus, Iowa have indicated that ‘Orange Oakleaf’ gives “above-average yields”.

Some noteworthy clonal varieties have not been included in the trials at New Hope Farms, and some that would be beneficial for farmers to include in future trials would include:

GEORGIA JET, the most commonly grown variety in the U.S.

IVIS WHITE CREAM, a white-fleshed cultivar reported to be high-yielding.

JERSEY YELLOW, for reference, since it is a very old standard (dated to 1780 or prior).

NEMAGOLD, a University of Oklahoma commercial variety bred for high beta carotene content and nematode resistance.

OZARK COUNTY, a strain not currently commercially sold, but long grown in the region.

STEVENSON’S, a 100-year-old variety which southeast Tennessee farmer Nick Alley compared with ‘Beauregard’ and reported it “produced double what Beauregard did, with more evenly sized tubers”, in 2011.

A final word is to remember that yield is not the sole important quality to consider. For example, ‘Allgold’ has 50% more vitamin C and over 300% more vitamin A than ‘Porto Rico’.