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Pees seme oe PROCEEDINGS OF THE iW"! INTERNATIONAL SYMPOSIUM ON PAPAYA Convener N. Kumar Madurai, India December 9-12, 2008 ISHS Section Tropical and Subtropical Fruits ISHS Working Group on Papaya Acta Horticulturae 851 January 2010 papay2 Growth in Double-Row Systems Established during the Dry Season T.W. Zimmerman University of the Virgin Islands Agricultural Experiment Station RR | Box 10,000, Kingshill, VI 00850 USA Keywords: Carica papaya, plant density, water usage, plant spacing pstract « Papaya production in the Virgin Islands is hindered by the lengthy dry season in this semi arid environment where fresh water is lacking. Three selected papaya cultivars, ‘Maradol’, ‘Tainung 5’ and ‘Yuen Nong 1° were grown in 1x1, 1x2 or 1x3 m double-row spacing regime randomized block design incorporating drip irrigation with 4 L/h emitters at 1 m intervals and grass-hay mulch. The objective was to determine water usage, plant growth and fruit set during the first six months establishment in the dry season of the U.S. Virgin Islands. Data collected included: rainfall, irrigation water applied, plant height, height to first flower, height to first fruit, stem diameter at 1m and number of fruit set after six months. Plants grown in the 1x1 m double row were taller, had thinner stems and significantly fewer fruit set for all cultivars during the six months of plant establishment and growth. The 1x2 m double row grown papaya were similar to the 1x3 m double row plants for height, stem diameter and fruit set. The 1x2 m double row growing system is recommended to increase production where space and water are limiting factors. A grass/hay mulch is very effective in controlling weeds, conserving soil moisture and protecting the soil from erosion during sudden short heavy tropical rains. INTRODUCTION The crop farms in the U.S. Virgin Islands are mainly comprised of small farmers. The average amount of land for a crop farmer is 4.7 acres (National Agricultural Statistics, 2000). Though this average includes livestock farmers, the crop farmers are less than 2 acres. The small size limits the investment the farmer can make to produce a crop. They have to see a strong benefit to a technology before they invest in it and adapt it to their farming practices. New technologies are being developed for papaya production. Papaya requires nine months from seed, in the early cultivars, to have a marketable crop. To have fruits available during the holiday season and peak tourist season, papayas need to be planted in late February through March. However, February through August are normally the driest months of the year in the U.S. Virgin Islands. Plant spacing from the past project indicated that growth and production were not influenced by plant spacing (Kowalski and Zimmerman, 2006). The plant spacings were 3x3 m, 2x3 m and a double-row 13 m. The double-row provided a higher planting density and a more efficient use of space and irrigation water. Drip irrigation technology permits the resourceful use of water and can help maximize the use of semiarid lands for agricultural use. This technology is particularly suited to widely spaced crops as papaya. Though multiple field trials have shown the economic beneficial use of drip irrigation on vegetable and herb production in the Virgin Islands (Palada et al., 1995; Crossman et al., 1997; Palada and O’Keefe, 2001) limited information is available on the use of drip irrigation for papaya production (Kowalski and Zimmerman, 2001, 2006). It has been suggested that the water needs for papaya in Hawaii are ideally supplied with 100 mm of rainfall each month (Nakasone and Paull, 1998). This amount is seldom encountered in the semiarid climate of the Virgin Islands where erratic rainfall patterns and extended dry periods are the norm. Also, the local preference is for large, greater than one kg, red papayas while most papaya research from Hawaii has focused on smaller, yellow 0.5 kg or smaller fruit. Not only are the cultivars Proc. II"? IS on Papaya Eds.: N. Kumar et al. 263 Acta Hort. 851, ISHS 2010 different between the Virgin Islands and Hawaii but also the soil. The soils of the Virgin Islands are calcareous, having a high pH around 8 versus volcanic base in Hawaii. Breeding and selection of papayas at the University of the Virgin Islands has resulted in early bearing cultivars that meet the fruit preferences of the Virgin Islanders (Zimmerman and Kowalski, 2004). Water is most often the limiting factor to crop production in the U.S. Virgin Islands. The municipal source of water is from desalination of ocean water. Due to the cost of the desalinated municipal water, farmers use the water sparingly. The most efficient use of water can result in economical gains for the local farmers. The objectives of this research were to develop a commercial papaya producing field plot that incorporates drip irrigation and mulch for growing selected papaya cultivars at multiple double-row spacing regimes and determine water usage during the dry season in the U.S. Virgin Islands. Specifically to integrate water conservation through drip irrigation and mulching into papaya production, determine water requirements of papaya grown under multiple double-row plant spacing regimes and determine the growth and production potential of papaya as influenced by spacing under drip irrigation and biodegradable mulch. MATERIALS AND METHODS Papaya plants were established in double-row spacings during February from greenhouse grown one month old seedlings. The three cultivars used were ‘Maradol’, ‘Tainung 5’ and ‘Yuen Nong 1’. ‘Maradol’ is a compact variety producing red 2 kg fruit. ‘Tainung 5’ and ‘Yuen Nong I ’are standard sized trees that produce large red and yellow fruit respectively. Water usage was recorded over a six month period which corresponds to the annual dry season from March through August. Tensiometers were used to record soil moisture levels and determine when irrigation water needed to be applied. A double-row plant spacing regime was followed. A three meter distance was between double-rows to allow for tractor cultivation until the plants attain one m. Each double-row was 1 m apart. The distance between each plant within a row of the double- row varied from 1, 2 or 3 m which corresponds to 2,400, 1,200, or 800 plants/acre respectively. Each plant spacing was replicated three times and had ten plants of each variety per replication. Guard rows were planted on both sides of the field and between replications. Guard plants were also planted at the end of each row. One drip line of irrigation was installed at the time of transplanting 15-20 cm tall seedlings into the field. The spacing of the orifices in the linear irrigation tubing was | m and exude 4 L/h. The drip lines were placed near the plant base and moved outward to a distance of 0.8 m from the base of the plant. A final drip line was added between the double rows when the plants were 1 m in height. The double rows then had a drip line outside of each row and one between the double-rows for a total of three lines per double- row. Hay mulch was applied to the whole field afier the third drip line was installed. The drip lines were under the mulch and in contact with the soil. The hay mulch was spread to a depth of the 7.5 cm between plants and rows. To determine water requirements of papaya grown under double-row plant spacing regimes soil moisture tensiometers were placed throughout the plots at a depth of 15 and 30 cm. The tensiometers were used to determine soil moisture content. Water meters were installed for each plant spacing plots and the amount of water applied recorded over time. Rainfall information was obtained from the University of the Virgin Islands weather station. Data was collected on plant height, height to first flower, height to first set fruit, stem diameter at 1 m from the soil surface and number of fruit set when the first fruit was ripening. RESULTS AND DISCUSSION ; The first six months of 2007, during the establishment of the papaya plot, a typical dry season was experienced on St. Croix (Fig. 1). Low rainfall started in January an when plant establishment occurred in early February, the soil was dry. There was a sp! xe 264 in rainfall during April. Heavy rains were received that lasted a week and provided seven inches of rainfall. The soil moisture content was at field capacity during these heavy rains causing the tensiometer to read zero for ten days (Fig. 2). The soil tensiometers’ readings increase in value as the soil dries. When the soil is saturated the readings decrease to zero. Figure 2 also indicates that plant spacing did have an influence on soil moisture available to the plants. The same dripline, with | m emitters, was used for all spacing treatments and the 1x1 m double row spacing configuration had drier soil before and after the heavy April rains. The closer the plant spacing results in more competition from the plants roots for the water available in the soil. The papaya plants in the 1x1 m spacing competed more for the available water, reducing the soil moisture quicker, then was observed for either the 1x2 or 1x3 m double row spacing. During the initial six months of papaya establishment and growth, water was applied as indicated in Figure 3. The wet soils from the heavy April rains resulted in less water being applied to the papayas in April. The mulch was very effective in controlling weeds, conserving soil moisture and protecting the soil from erosion during sudden short heavy tropical rains. However, the straw mulch absorbs the light showers preventing the water from reaching the soil. Most light showers have minimal effect on the soil and availability to plants due to the high evaporation rate (Goenaga et al., 2004). The total amount of water given to each plant was 230 L over eight months for the 1x2 m plant spacing during which plant establishment, floral induction and fruit set occurred. Plant spacing did have an influence on the height of ‘Maradol’ plants over time. After two months of growth, the 1x1 m spacing caused the plants to be taller then the more distant spacings (Fig. 4). ‘Maradol’ is a compact papaya variety that has shorter internodal length but the close plant spacing caused it to stretch to have a difference of 50 cm by the forth month. ‘Maradol’ grew at the same rate for the 1x2 and 1x3 m plant spacing. Both ‘Tainung 5’ and ‘Yuen Nong 1’ are standard sized papaya trees. However, the close 1x1 m spacing had taller plants after one month (Figs. 4 and 5). The leaves start interacting with each other after a month’s growth at the close plant spacing. As the plants became taller with age, the close spacing caused the plants to grow outwards resulting in a ‘V’ shaped double row. This outward leaning was not observed in the 1x2 or 1x3 m spacing which grew perpendicular to the soil. The stem diameter can have an influence on the plants ability to support a column of fruit as well as have tolerance to wind. Thinner stemmed plants tend to snap in wind when carrying a heavy fruit set. These cultivars are grown because they are able to set 30- 50 fruits (Kowalski and Zimmerman, 2001). For all three cultivars the close plant spacing had the thinnest stems (Table 1). The 1x3 m plant spacing resulted in significantly thicker stems then the 1x1 m spacing. With ‘Tainung 5° both the 1x3 and 1x2 m spacing had significantly thicker stems then the 1*1 m spaced plants. The height to first flower and height of the first set fruit indicate how low the fruit is set on the stem. These three cultivars were chosen because they set fruit early. Flowers are present between the first and second of field establishment. Papaya trees that set fruit early have a lower center of gravity and less prone to high winds (Zimmerman and Kowalski, 2004). Both the 1x2 m and the 1x3 m spaced plants had earlier flowering and fruit set lower to the soil surface for all cultivars then the 1x1 m plants (Fig. 7). Lower fruit set also allows more fruit to be within reach for a longer period of time. The main reason for growing papaya is for production. The number of fruit set on a papaya stem column was recorded when the first fruit ripened and indicates expected production for the tree. The 1x1 m double row spacing set significantly less fruit then either the 1x2 or 1x3 m double row spacing (Fig. 7). This indicates that the close plant spacing can’t hold as many fruit and may be influenced by the water availability to the plant previously discussed. The 1x2 and 1x3 m double spaced plants were not significantly different for fruit set. The 1x2 m double row spacing was the most efficient for water usage and land area to produce the most fruit. The papaya plants for ‘Maradol’, ‘Tainung 5’ and ‘Yuen Nong 1’, grown ina 1x1 i) oN Nn m double row system were taller, had thinner stems and significantly fewer fruit set then the 1x2 or 1x3 m double row spacing regime during a normal dry season of six months for plant establishment and growth. The 1x2 m double row grown papaya were similar to the 1x3 m double row plants for height, stem diameter and fruit set. The 1x2 m double row growing system is recommended to increase production where space and water are limiting factors. A grass/hay mulch is very effective in controlling weeds, conserving soil moisture and protecting the soil from erosion during sudden short heavy tropical rains. ACKNOWLEDGEMENTS The research on which this report is based was financed in part by the USDI- USGS through the Virgin Islands Water Resources Research Institute and by USDA- Hatch. The assistance provided by Jacqueline Kowalski, Willie Ventura and James Gordon was graciously appreciated. Literature Cited Crossman, S.M.A., Palada, M.C. and Kowalski, J.A. 1997. Comparison of mulch type effect on yield of parsley in the Virgin Islands. Carib. Food Crops Soc. 33:216-220. Goenaga, R., Rivera, E. and Almodovar, C. 2004. Yield of papaya irrigated with fractions of class A pan evaporation in a semiarid environment. J. Agri. Univ. Puerto Rico 88:1- 10. Kowalski, J.A. and Zimmerman, T.W. 2001. Evaluation of papaya germplasm in the U.S. Virgin Islands. Carib. Food Crops Soc. 37:24-28. Kowalski, J.A. and Zimmerman, T.W. 2006. Papaya production under different spacing regimes. Carib. Food Crops Soc. 42:399-402. Nakasone, H.Y. and Paull, R.E. 1998. Tropical Fruits. CAB International, New York, NY National Agricultural Statistics. 2000. Virgin Islands of the United States 1998 Census of Agriculture. http://www.nass.usda.gov/census/census97/vi/vi.htm Palada, M.C. and O’Keefe, D.A. 2001. Response of hot pepper cultivars to levels of drip irrigation. Caribbean Food Crops Society 37:190-196. Palada, M.C., Crossman, S.M.A. and Kowalski, J.A. 1995. Water use and yield of basil as influenced by drip irrigation levels and mulching. Caribbean Food Crops Society 31:143-149. Zimmerman, T.W. and Kowalski, J.A. 2004. Breeding and selection for early bearing papayas. Acta Hort. 632:53-55. Tables Table 1. Diameter (cm) of papaya stems taken at a one meter height for three cultivars as influenced by plant spacing in a double row system. Variety Spacing (m)* 1x] 1x2 1x3 Maradol 6.70 a 7.80 ab 9.01b Tainung 5 6.49 a 8.67 b 9.36b Yuen Nong | 7.01 a 8.35 ab 9.86 b *Mean separation within rows conducted using LSD P=0.05. 266 Table 2. Number of fruit set at the time of the first ripe fruit for three papaya cultivars as influenced by plant spacing in a double row system. Variety Spacing (m)* 1x1 1x2 1x3 Maradol 23.34 35.9 b 38.8 b Tainung 27.9 a 46.1b 49.0b 23.1a 36.5 b 39.1b Yuen Nong | *Mean separation within rows conducted using LSD P=0.05. Figures — Sate eso pe ice coe. ie Jan Feb Mar Apr May Jun Jul Aug Month Fig. 1. Average monthly rainfall during 2007. 267 60 40 Centibars 20 10 0 50 + 30 + --«-3x --e-- 3x6 23x99 fee 1 n \ e o-6 \ / \ “| f 4 7 4 eh | Pho Piet \ / AR vi | USE GE, t T v | Ny x \ / \ 1 1 < ite | Vj Ly oN é 1 | # VS AL ® mM & oy \ yo 4 7\ Winder vb T / + 1/ nae? ope Be es eg iW a er ales yf ‘ [Rene | 4 > Tate. | eign ieee | T T i wiper 3/9 3/16 3/23 3/30 4/6 4/13 4/20 4/27 5/4 5/11 Days Fig. 2. Soil tensiometer readings over time for each papaya spacing. Gallons 16 14 12 10 + 8 +4 6 5 23-4 Feb March April May June Aug Month July Fig. 3. Average gallons of water applied to each papaya plant. 268 250 O3x3 O3x6 200 O3x9 ft 150 100 50 lle = 1 Month Fig. 4. Plant height of the ‘Maradol’ papaya plants during the first four months. 300 a3x3 o3x6 250 ya3x9 == — ee ae 200 at 150 100 [aie hare = 50 pean Month Fig. 5. Plant height of the ‘Tainung 5’ papaya plants during the first four months. 269 300 03x3 O3x6 B 250 4o3x9 Month Fig. 6. Plant height of the ‘Yuen Nong 1” papaya plants during the first four months. 75 O First Flower Zz - | O First Fruit 3 80 | ‘a ae - lo | 1] 4) @l E 45-4 — oo -— al t— C= = cl — = ie 2 ; ‘ o = = = = }— | }— an = Lt = 30 4 j 15 +4 Ea J [I —— cay I -— ro z 0 : 3x3 3x6 3x9 3x3 3x6 | 3x9 3x3 | 3x6 3x9 | Maradol | Marado!| Maradol| TNGS | TNGS TNG5 YN1 | YN1 YN1 Variety and Spacing Fig. 7. Effect of plant spacing on the initiation of the first flower and setting of the first fruit for three papaya cultivars. 270