THE EFFECT OF TWO DRIP IRRIGATION REGIMES ON THE YIELD OF SWEETPOTATO VINE AND PLUG TRANSPLANTS

VICTOR A. KHAN1, CLAUZELL STEVENS', MACK A. WILSON2, DANIEL J. COLLINS3, ERROL G. RHODEN', JOHN Y. LU', AND JAMES E. BROWN"

'GEORGE WASHINGTON CARVER AGRICULTURAL EXPERIMENT STATION, TUSKEGEE UNIVERSITY, TUSKEGEE INST. AL 36088.

'DEPARTMENT OF AGRICULTURE SOUTHEAST MISSOURI STATE UNIVERSITY, CAPE GIRARDEAU, MO 63701. 'DEPARTMENT OF PLANT PATHOLOGY, AUBURN UNIVERSIT Y, AUBURN AL 36849.

"DEPARTMENT OF HORTICULTURE, AUBURN UNIVERSITY, AUBURN AL 36830.

Abstract: 'Carver', TU-1892, 'Jewel', 'Georgia-Jet' and TU-155 sweetpotato cultivars were planted in a field trial as non-rooted vine and rooted plug transplants during the summer of 1996. Plots were drip irrigated either weekly or biweekly for a maximum of 4 hr (at 1GPM per 100ft of drip tube) after the plants attained maximum growth. Vine transplanted sweetpotatoes had significant total US#1 and canner grades and number of storage roots compared to plug transplanted sweetpotatoes when they were irrigated weekly. Plug transplanted sweetpotatoes had significantly higher jumbo yield when irrigated biweekly compared to the vine transplanted sweetpotato cultivars.

Keywords: Sweetpotatoes, Drip Irrigation, Plugs and Vine Cuttings.

Introduction Sweetpotato is a crop grown by many limited resource farmers in Alabama, however very little

research data on irrigating this crop exists. Early irrigation research was centered on overhead or flood irrigation and was conducted during the very early decades of this century (1,2, 3). The objective of this study was to determine how sweetpotato cultivars would respond to drip irrigation using plug and vine transplants.

Methods and Materials This study was conducted at the George Washington Carver Agricultural Experiment Station,

Tuskgcc Alabama in 1996 on Norfolk Sandy loam soil (Typic Palcudult). Raised bed plots were 20ft long by 2ft wide and placed 4ft apart in a split-split-plot design. Fertilizer was applied at the rate of N 60- 4 80 lbs/acre N-P20,-K20, in a single band-off center of the beds. Beds were sprayed with Dacthal herbicide at the rate of 31bs/acre. Five inch long vine cuttings from the varieties TU-1892, 'Carver', 'Jewel', 'Georgia-Jet' and TU-155 were taken from matured plants in the field which were grown from sweetpotato slips grown in a traditional hot bed. These cuttings were raised in plug trays and kept in the greenhouse for two weeks before planting in the field. After 14 days, a comparable set of non-rooted five inch long vine cutting transplants for all cultivars, were taken from mature plants growing in the field and both type of transplants were planted in beds on July 4, 1996. In-row plant spacing for all treatments was 1 ft.

All plots were drip irrigated weekly (I7) and biweekly (I14) for 1.5 hr when the transplants were 1 -30 days old, 3hr when the transplants were 31 - 55 days old and 4 hr from 55 until harvest at 120 days. Plots were not irrigated whenever the rainfall was over .75 inch. The flow rate of the drip tube used in this study was 1 gallon per per minute per 100 ft of drip tube. At 65 days after transplanting all plots were side dressed with potassium at the rate of 50 lbs K20/acre. Data collected were: US#1, Canner, Jumbo and Total Marketable root weight and numbers. All root yields were expressed as bushels/acre (1 bushel = 50 lbs).

Statistical analysis of all data included analysis of variance (ANOVA) and means were compared

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by orthogonal contrasts (4).

Results Marketable Grades

The significant interaction between sweetpotato cultivars and irrigation showed that the yield of US#1 sweetpotatoes grown from plug transplants was higher at the I14 compared to weekly for all cultivars except TU-1892. Whereas, US#1 yield from vine transplants was significantly higher at weekly rather than biweekly for all cultivars. Canner yield from all sweetpotato cultivars, except TU-1892 that were grown from plug transplants, had higher yields at biweekly compared to weekly. While all cultivars except 'Georgia-Jet' that were grown from vine transplants had significantly higher yields at biweekly (Table 1).

Table 2 shows that TU-1892, and 'Georga-Jet' when grown from plug transplants, had significantly higher jumbo yield at weekly compared to 'Carver1, 'Jewel' and TU-155 which had higher yields at biweekly. Cultivars ('Jewel1, 'Georgia-Jet' and TU-155) when grown from vine transplants, had higher yields at weekly, while TU-1892 and 'Carver' had significantly higher Jumbo yields at biweekly. Total marketable yield of all cultivars grown from vine transplants, were significantly greater at weekly compared to biweekly; while all cultivars grown from plug transplants except TU-1892, had higher yields at weekly compared to biweekly. Market Root Numbers

The number of US#I storage roots obtained from all cultivars except 'Jewel' and TU-1892 when grown from either plug or vine transplants, produced a significantly higher number of storage roots at weekly than at biweekly. However, TU-1892, "Carver* and 'Georgia-Jet', produced a significantly higher number of canner roots when grown from plug transplants at weekly. While 'Georgia-Jet' and TU-155 produced a higher number of canner storage roots, when grown from vine transplants at weekly compared to biweekly (Table 3).

Table 4 shows that the number of jumbo grade storage roots produced from TU-1892 and 'Georgia-Jet' when grown from plug transplants were significantly higher at weekly than at biweekly, and for 'Jewel', 'Georgia-Jet' and TU-155, when grown from vine transplant. All cultivars propagated by either plug or vine transplants except 'Jewel' and TU-1892, produced a greater number of marketable storage roots at weekly compared to biweekly irrigation regime.

Discussion The significant interactions from all of the results indicated that cultivars reacted

differently when they were transplanted as either plug or vine transplants and irrigated either weekly or biweekly. However, certain trends from the study were observed such as higher US#1 and canner yields that were consistently obtained from vine transplants irrigated weekly compared to plug transplants. This trend continued at the biweekly irrigation schedule for the same grades of sweetpotatoes however, there was a significant increase in the jumbo grade of sweetpotatoes when the cultivars were grown from plug transplants. This seems to indicate earliness, and that plug transplants are somewhat more adaptable to drier conditions than vine transplants.

Vine transplants also produced a significantly greater number of US#1 and canner grades of marketable storage roots under both weekly and biweekly irrigation regimes. However, the significant increase in the number of jumbo grade sweetpotatoes from all cultivars grown from plug transplants and irrigated biweekly seems to indicate that storage root initiation took place

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earlier since all plug transplants were rooted 2 wk prior to planting in the field. Subsequently, earlier storage root initiation would lead to early root enlargement.

Since many farmers do not irrigate their sweetpotato crop the data seems to indicate that better yields can be obtained to defray the additional irrigation expenses especially if they use vine transplants. The high jumbo yield obtained at biweekly seems to suggest that plug transplants would be prefered over vine cuttings, if farmers chose not to irrigate and to depend on the limited rainfall. However, more research will be needed before a final determination can be made.

Conclusions 1. Vine transplants produced significantly higher US#1 and canner grade sweetpotatoes at

both weekly and biweekly irrigation schedules. 2. Plug transplants produced significantly higher jumbo yield at both weekly and biweekly

irrigation schedule.

References 1. Boswell, V. R. 1950. Commercial growing and harvesting of sweet potatoes. U.S.

Dept. Agr. Bull. 2020. 2. Hernandez, T. P., Hernandez, E. S., Miller, J. C. and Jones, L. G. 1965. The value of

irrigation in sweet potato production in Louisana. Louisana Agr. Expt. Sta. 607. 3. Hernandez, T. P. Hernandez, T. and Sistrunk, W. A. 1955. Irrigation studies on sweet

potato production. Proc. Assoc. Southern Agr. Workers, 52, 117. 4. Snedecor, W. G. 1966. Statistical Methods. Iowa State University Press, Ames. pp.

366-368.

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Table 1. Mean yield of US# 1 and canner grade of five sweetpotato cultivars irrigated weekly and bi-weekly.

Market grades US#l(bu/acre) Çanngr$(bu/acrç)

Weeklv Irrigation Bi-weeklv irrigation Weeklv Irrigation Bi-weeklv irrigation Cultivars Plugs Vines Plugs Vines Plugs Vines Plugs Vines TU-1892 333 467 268 303 319 362 271 465 Carver 195 427 212 388 167 428 185 570 Jewel 225 651 276 564 144 456 367 624 Ga-Jet 410 511 501 434 261 474 267 459 TU-155 377 608 381 456 235 527 318 609 Significance of F test From AQV Cultivars Irrigation Plugs vs Vines Cultivars X Irrigation Cultivars X (Plugs/vines) Irrigation X (Plugs/vines) Irrigation X Cultivars X Plugs/vines

NS significant at the 1%, 5% and not significant, respectively.

Table 2. Mean yield of Jumbo and total marketable grade of five sweetpotato cultivars irrigated weekly and bi-weekly.

Market grades Jumbofbu/acre) Total marketable (bu/acre)

Weekly Irrigation Bi-weeklv irrigation Weekly Irrigation Bi-weekly irrigation Cultivars Plugs Vines Plugs Vines Plugs Vines Plugs Vines TU-1892 196 33 92 73 848920 632 460 Carver 10365 169 76 465 946 565 545 Jewel 48 98 76 44 418 1198 719 721 Ga-Jet 91 58 83 22 762 1076 851 591 TU-155 72 120 80 22 684 1227 778 613 Significance of F test From AOV Cultivars ** ** Irrigation ** ** Plugs vs Vines ** ** Cultivars X Irrigation ** ** Cultivars X (Plugs/vines) ** ** Irrigation X (Plugs/vines) ** ** Irrigation X Cultivars X Plugs/vines !! HI

**, *, NS significant at the 1%, 5% and not significant, respectively.

Table 3. Mean number/acre of US#1 and canner sweetpotatoes of five sweetpotato cultivars irrigated weekly and bi-weekly.

Market grades US#1 COOO/acre) Canner COOO/acre)

Weekly Irrigation Bi-weeklv irrigation Weekly Irrigation Bi-weeklv irrigation Cultivars Plues Vines Plugs Vines Plugs Vines Plugs Vines TU-1892 14 11 10 18 3 5 2 8 Carver 5 17 4 8 4 7 2 7 Jewel 9 19 10 16 2 7 4 8 Ga-Jet 15 20 13 13 7 8 6 7 TU-155 12 9 4 5 4 9 4 5

CJ1 o

Significance of F test From AOV Cultivars Irrigation Plugs vs Vines Cultivars X Irrigation Cultivars X (Plugs/vines) Irrigation X (Plugs/vines) Irrigation X Cultivars X Plugs/vines

* *

* *

* *

* *

NS **

# *

NS **

* *

NS **

**, *. NS significant at the 1%, 5% and not significant, respectively.

Table 4. Mean number/acre of Jumbo and total marketable sweetpotatoes of five sweetpotato cultivars irrigated weekly and bi-weekly.

Market grades Jumbo COOO/acrei Total marketable COOQ/acrel

Weekly Irrigation Bi-weekly irrigation Weekly Irrigation Bi-weekly irrigation Cultivars Plues Vines Plugs Vines Plues Vines Plugs Vines TU-1892 6 1 4 2 23 17 16 28 Carver 2 3 5 7 12 27 11 22 Jewel 3 5 4 1 14 31 18 26 Ga-Jet 6 4 5 3 28 33 24 23 TU-155 4 7 4 2 20 25 13 12 Significance of F test From AOV

Irrigation X Cultivars X Plugs/vines HI

**, *, NS significant at the 1%, 5% and not significant, respectively.