Tomato Plant Growth during Establishment as ...

Tomato Plant Growth during Establishment as Affected by Root Zone Temperature under Colored Mulches J.C. Diaz-Perez*, D. Granberry, D. Bertrand and D. Giddings Department of Horticulture CPES-Tifton Campus University of Georgia Tifton, GA 31794 USA Keywords: Lycopersicon esculentum, heat stress, transplant shock, plasticulture Abstract Soil warming is one of the benefits associated with the use of plastic film mulches. However, under high temperature and intense solar radiation, further warming of the soil may negatively affect plant growth during establishment. Greenhouse-grown tomato seedlings were transplanted to the field and exposed to a range of root-zone temperatures (RZTs), resulting from growing the plants in different seasons and by utilizing colored mulches that differed in their soil-warming ability. The objective was to determine the relationship of RZT to plant growth during the first 28 days after transplanting (DAT). Experiments were carried out in Fall 1999, Spring 2000, and Fall 2000. Black (n = 2), gray, red, silver (n = 3), and white (n = 2) mulches, and unmulched soil were used. RZT under mulch was measured with copper-constantan thermocouples placed 10 cm below the soil surface. Irrespective of the season, the highest mean RZT (from planting to 28 DAT) occurred under black mulch, and the lowest under white mulch. The mean RZT under black mulch was 4°C greater than under white mulch. In the spring season, vegetative top dry weight (DW) at 28 DAT was higher with increasing mean RZTs. In the fall seasons, vegetative top DW at 28 DAT decreased with increasing mean RZTs. Pooling data from fall and spring seasons, vegetative top DW at 28 DAT was found to fit a quadratic relationship with RZT. From this relationship, optimal RZT for vegetative top growth was calculated to be 25°C. Vegetative top growth during the first 28 DAT was correlated with subsequent vegetative top growth and fruit yield. In conclusion, RZT under colored mulches significantly affected tomato plant growth during the establishment period. INTRODUCTION In the United States, commercially produced fresh market tomato (Lycopersicon esculentum Mill.) are commonly grown on plastic film mulch (Lamont, 1993). The benefits associated with use of plastic mulches include higher yields, earlier harvests, improved weed control, and increased efficiency in the use of water and fertilizers. Increased plant growth, yield and earliness have been attributed to the soil-warming effect of mulches at northern latitudes (Lamont, 1993; Wien and Minotti, 1987). Colored plastic film mulches influence plant growth and yield through modification of the light environment around the plant. Red mulches reflect far red light, resulting in a modified red:far red ratio in plants (Decoteau et al., 1988; Kasperbauer, 1992). Thus, in addition to the light effects of mulches, possibly colored mulches modify RZT in ways that may influence plant growth during the establishment period. Colored mulches have also been shown to affect plant growth and yield by modifying insect behaviour (Schalk and Robbins, 1987; Csizinszky et al., 1995). Under conditions of high ambient temperature and high solar radiation, plants often grow poorly and produce low yields because mulches warm the soil to temperatures that may be deleterious to plant growth (Miller, 1986; Tindall et al., 1991; Díaz-Pérez et al., 2002). Root-zone temperature is important in plant growth and development because it affects physiological processes in roots such as uptake of water and nutrients (Cooper, Proc. XXVI IHC – Transplant Production and Stand Establishment Eds. C.S. Vavrina et al. Acta Hort. 631, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA)

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1973; Dodd et al., 2000; Tindall et al., 1990; Zobel, 1992). Root-zone temperature may also be critical for plant survival, because roots have a lower temperature optimum and are less adapted to extreme fluctuations than shoots (Paulsen, 1994). Root zone temperature plays a significant role in tomato plant growth. The optimal RZT for growth and yield of mature tomato plants under field conditions is between 25.4 and 26.3°C (DíazPérez and Batal, 2002). The objective of the present study was to determine the relationship of root zone temperature, as affected by the various plastic mulches, with growth during plant establishment, and how that plant growth is related with subsequent plant growth and yield of mature plants. MATERIALS AND METHODS Experiments were carried out at the Horticulture Farm, Tifton Campus, University of Georgia in Fall 1999, Spring 2000 and Fall 2000 on a Tifton Sandy Loam (a fine loamy, siliceous thermic Plinthic Paleudults) with a pH of 6.3-6.7. Fall 1999. The experimental design was a randomized complete block with five treatments (plastic mulch) and 10 replications. The mulches were gray-on-black (‘gray’) (Leco, Montreal, Canada), silver-on-black (Clarke Ag Plastics, Greenwood Va.), whiteon-black (Leco), black mulch painted with white latex paint, and no mulch. ‘Sun Chaser’ (Petoseed, Saticoy, Ca.) tomato plants were transplanted on 3 Aug. 1999. Spring 2000. The experimental design was a split plot with three replications, with plastic mulches (n = 8) as the main plot and three tomato cultivars as the subplot. The mulches were black, black-on-silver (Sonoco Products Co., Hartsville, S.C.), gray-onblack (Leco), red (Sonoco), silver-on-black (Sonoco), black mulch painted with silver paint (‘silver-painted’), white-on-black (Leco), and bare soil. The tomato cultivars used were ‘Florida-91’ (Seminis, Oxnard, Calif. ), ‘BHN-444’ (BHN Research, Bonita Springs, Fla.) and ‘Sun Chaser’ (Seminis). Transplanting was on 5 Apr. 2000. Fall 2000. The experimental design was a split plot with three replications, with plastic mulches (n = 4) as the main plot and tomato cultivars (n = 3) as the subplot. The mulches were black-on-silver, gray-on-black, silver-on-black, and bare soil. The tomato cultivars used were ‘Heat Master’, ‘Heat Wave’ (Seminis), and ‘Sun Chaser’ Transplanting was on 1 Aug. 2000. The various colored mulches were expected to differ in their light reflectance and light transmittance and thus to result in a range of soil temperatures (Díaz-Pérez et al., 2002; Ham et al., 1993). The effect of the mulches on air temperature was assumed to be minimal (Ham et al., 1993). In all three experiments, the experimental plot consisted of an 8-m long section on a 0.9-m wide bed formed on 1.8-m centers, having a 3-m separation between plots within the same bed. Before laying the mulches with a tractor, the soil was fertilized with N, P, and K at 90, 90 and 54 kg ha-1 broadcast, respectively. The soil was fumigated with a mixture of 70% methyl bromide + 30% chloropicrin (by weight) at 250 kg ha-1. Drip irrigation tape (T-Tape; T-Systems Intl., San Diego), with 30.5-cm emitter spacing and a 17 mL min-1 emitter flow, was placed manually on the surface of the soil in the center of the bed. Six-week old tomato transplants were planted to the field in a single row per bed at a 60-cm spacing. After transplanting, 250 mL of starter fertilizer solution was applied directly to the base of each transplant. The starter fertilizer solution consisted of 0.72 kg of an 18N-20.2P-0K fertilizer mixed in 100 L of water. Beginning two weeks after transplanting, plants were fertilized weekly for 8 weeks with N and K. For both, N and K, the actual rate was 1.4 kg ha-1 d-1 at early stages, 2.0 kg ha-1 d-1 during fruit development, and 1.4 kg ha-1 d-1 at late stages of development. For the 8-week period, plants received a total of 116 kg ha-1 N and 116 kg ha-1 K. Root-zone temperature (RZT) and air temperature. RZT was measured by determining soil temperature midway between the plants at 10 cm below the mulch and the soil surface. RZT over the growing season was measured with copper-constantan thermocouples (Model 105, Campbell Scientific, Logan, Utah) connected to a data logger (CR10X, Campbell Scientific) and an AM416 Relay Multiplexer (Campbell Scientific). 120

The data logger was programmed to record readings every 10 min and store hourly averages for each plot. Air temperature data were obtained from a University of Georgia weather station located within 200 m of the plots. Plant growth. On day 28 after transplanting (DAT), five randomly-selected plants (vegetative top) from each replication were excised at the soil level. Vegetative tops were dried at 70°C and dry weights (DW) recorded. Harvest. Once-over harvest was made 9 weeks after transplanting. Plants were excised at the soil level and their vegetative top fresh weight (FW) and fruit yield were determined within 24 h. Fruit yield was measured as total fruit FW per plant. Statistical analysis. Data were analyzed using the Mixed Procedure of SAS (SAS Inst. Inc., 2000). RESULTS AND DISCUSSION Tomato plant growth during the establishment period (first 28 DAT) was highly related to RZT. In the spring, vegetative top DW at 28 DAT was greater with increasing mean RZTs (Fig. 1). In the fall seasons, vegetative top DW at 28 DAT decreased with increasing mean RZTs. Pooling data from fall and spring seasons, vegetative top DW during the establishment was found to fit a quadratic relationship with RZT (Fig. 1). From this relationship, optimal RZT for vegetative top growth was calculated to be 25.0°C. This estimation of the optimal RZT during establishment will require corroboration with further studies which include a wider range in RZTs, because in the present study no data between 24 and 29°C were included. The majority of studies on the effect of RZT on plant growth is conducted under controlled conditions. Under controlled-temperature conditions, optimal RZT for tomato shoot growth and fruiting is 30°C (Cooper, 1973). However, plant responses under constant RZT may differ from the responses of plants grown under the dynamic RZTs that occur in the field (Voorhees et al., 1981). Under field conditions, Díaz-Pérez and Batal (2002) recently reported that growth and yield of mature tomato plants fit a quadratic relationship with the mean seasonal RZT, with an optimum RZT of 25.4 to 26.3°C. Vegetative top growth during the establishment was related with subsequent plant growth and fruit yield of mature tomato plants (Fig. 2). During the first 28 DAT, mean RZTs in the fall were about 9°C higher than in the spring (Table 1). Mature plants grew more and had higher yields in the spring than in the fall because RZTs in the spring were closer to the optimal RZT for mature plant growth than in the fall (Table 1). Root zone temperatures above the optimal dramatically reduce growth of mature tomato plants (Díaz-Pérez and Batal, 2002). Dark mulches (black, red and gray) had higher soil-warming ability than lightcolored mulches, as indicated by their higher RZT values. In Fall 1999, RZT ranged from 29.4°C (bare) to 31.9°C (gray), while in Fall 2000 it ranged from 31.1°C (silver, bare) to 32.4°C (black-on-silver). In Spring 2000, RZT ranged from 20.5 (white) to 23.7°C (black). Depending on the mulch and the season, mean RZT was from 1.2°C to 6.4°C greater than mean air temperature. The increased soil-warming ability of dark mulches was beneficial in the spring when RZT under all mulches was lower than the optimal RZT (25°C) but detrimental in the fall when RZTs (> 31°C) under dark mulches negatively affected plant growth. The color of a mulch determines its energy-radiating behavior and its influence on the microclimate around the plant (Lamont, 1993). Mulch color also determines root zone temperature underneath the mulch. Mulches of the same color and different manufacturer differed in their soil-warming ability (i.e. RZT), as shown for white compared to whitepainted mulch (Fall 1999, Table 1) and black compared to black-on-white mulch (Spring 2000). Thus, mulch color as determined visually was an inaccurate predictor of the thermal properties of the mulch. In addition to soil warming, colored plastic mulches also modify the light environment of crop plants affecting plant growth and morphogenesis (Decoteau et al., 1988) and insect behavior (Csizinszky et al., 1995). However, the influences of mulch color on plant growth have been inconsistent because plant responses 121

may be affected by geographic location and season (Csizinszky et al., 1995). CONCLUSIONS The ability of mulches to increase RZT and promote plant growth under cool conditions has been recognized for many years (Lamont, 1993). However, there are few reports on the effects of plastic film mulches under warm conditions. This study shows that root zone temperature under colored mulches significantly influenced tomato plant growth and that excessive soil warming (i.e. mean daily RZT above 25°C) was detrimental to tomato plant growth during the establishment. Dark mulches typically produce RZTs greater than those in unmulched soil, while light-colored mulches will result in RZTs lower than those in unmulched soil. Mulch selection should consider information on thermal and optical properties of the mulch and the temperature conditions under which the crop will grow. ACKNOWLEDGEMENTS We are graciously thankful to B. Mullinix for statistical assistance, to E. Folds for secretarial support, and to G. Acuña for help with field and laboratory tasks. We acknowledge support of the following donors: Asgrow, BHN, and Peto Seed for tomato seeds; United Irrigation and Roberts Irrigation Products Inc., for drip tape; Hydro Agri North America, Inc., for calcium nitrate liquid fertilizer; and Green-Tek and Sonoco for plastic film mulches. Literature Cited Cooper, A.J. 1973. Root temperature and plant growth - A review. Commonwealth Agr. Bureaux, Slough, United Kingdom. Csizinszky, A.A., Schuster, D.J. and Kring, J.B. 1995. Color mulches influence yield and insect pest populations in tomatoes. J. Amer. Soc. Hort. Sci. 120:778-784. Decoteau, D.R., Kasperbauer, M.J., Daniels, D.D. and Hunt, P.G. 1988. Plastic mulch color effects on reflected light and tomato plant growth. Scientia Hort. 34:169-175. Díaz-Pérez, J.C. and Batal, K.M. 2002. Colored mulches affect tomato growth and yield via changes in root zone temperature. J. Amer. Sci. Hort. Sci. 127:127-136. Dodd, I.C., He, J., Turnbull, C.G.N., Lee, S.K. and Critchley, C. 2000. The influence of supra-optimal root-zone temperatures on growth and stomatal conductance in Capsicum annuum L. J. Expt. Bot. 51:239-248. Ham, J.M., Kluitenberg, G.J. and Lamont, W.J. 1993. Optical properties of plastic mulches affect the field temperature regime. J. Amer. Soc. Hort. Sci. 118:188-193. Lamont, W.J.Jr. 1993. Plastic mulches for production of vegetable crops. Hort. Technol. 3:35-39. Miller, D.E. 1986. Root systems in relation to stress tolerance. Hort. Sci. 21:963-970. Paulsen, G.M. 1994. High temperature responses of crop plants. p.365-389. In: K.J. Boote, J.M. Bennett, T.R. Sinclair and G.M. Paulsen (eds.), Physiology and determination of crop yield, Amer. Soc. of Agron., Madison, Wis. SAS Institute Inc. 2000. SAS / C OnlineDocTM. Release 7.00. SAS Inst. Inc., Cary, N.C. Schalk, J.M. and Robbins, M.L. 1987. Reflective mulches influence plant survival, production, and insect control in fall tomatoes. Hort. Sci. 22:30-32. Tindall, J.A., Beverly, R.B. and Radcliffe, D.E. 1991. Mulch effect on soil properties and tomato growth using micro-irrigation. Agron. J. 83:1028-1034. Tindall, J.A., Mills, H.A. and Radcliffe, D.E. 1990. The effect of root-zone temperature on nutrient uptake of tomato. S. Plant Nutr. 13:939-956. Voorhees, W.B., Allmaras, R.R. and Johnson, C.E. 1981. Alleviating temperature stress, p.217-266. In: G.F. Arkin and H.M. Taylor (eds.), Modifying the root environment to reduce crop stress. Monogr. 4 Amer. Soc. of Agr. Eng., St. Joseph, Mi. Wien, H.C. and Minotti, P.L. 1987. Growth, yield, and nutrient uptake of transplanted fresh-market tomatoes as affected by plastic mulch and initial nitrogen rate. J. Amer. Soc. Hort. Sci. 112:759-763. 122

Zobel, R.W. 1992. Soil environment constraints to root growth. Adv. Soil Sci. 19:27-51.

Tables Table 1. Root zone temperature (RZT) as affected by plastic film mulch and air temperature during the first 28 days after transplanting in the fall (1999 and 2000) and spring (2000) seasons in Tifton, Ga. Temperature (°C) Mulch No mulch Gray Silver White White-painted Average for mulches Air4 Mulch No mulch Black-on-silver Gray Silver Average for mulches Air Mulch No mulch Black Black-on-silver Gray Red Silver Silver-painted White Average for mulches Air

Mean (°C)1

Maximum (°C) 2

Minimum (°C) 3

29.4 d 31.9 a 30.6 b 29.8 c 30.5 b

Fall 1999 33.7 b 36.3 a 32.8 e 33.5 d 34.5 c

25.0 e 27.5 b 28.4 a 26.1 d 26.6 c

30.4

34.2

26.7

28.2

33.7

22.7

31.1 b 32.4 a 31.3 b 31.1 b

Fall 2000 37.7 a 37.9 a 35.6 b 35.4 b

26.2 c 28.0 a 27.9 a 27.5 b

31.5

36.7

27.4

27.2

33.0

21.4

21.6 f 23.7 a 23.0 c 22.3 d 23.3 b 22.0 e 22.3 d 20.5 g

Spring 2000 28.3 c 30.1 a 28.9 b 27.0 d 29.8 a 26.2 e 26.4 e 24.6 f

15.7 f 18.0 b 17.7 cd 17.8 bc 17.6 d 17.9 bc 18.3 a 16.5 e

22.3 17.3

27.7 24.1

17.4 10.4

1

Mean RZT for data collected hourly for 28 d with four sensors per mulch. Average of the daily maximum RZT for the first 28 d after transplanting. 3 Average of the daily minimum RZT for the first 28 d after transplanting. 4 Air temperatures were collected from the Univ. of Ga. Weather Monitoring System. 2

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Figurese

25

Top DW at 28 DAT (g)

Fall Spring

20

15

10

5 2

y = -0.33 x + 16.48 x - 187.73 2 R = 0.73

0 20

22

24

26

28

30

32

34

o

Root zone temperature ( C) Fig. 1. Vegetative top dry weight of tomato plants 2828days aftertransplanting transplanting as a Figure 1. Vegetative top dry weight of tomato plants days after function of the root zone temperature under colored mulches. Each point as a function of the root zone temperature under colored mulches. Each point represents the treatment mean. Data were pooled for mulches and seasons. represents the treatment mean. Data were pooled for mulches and seasons.

2.0

3.5 3.0

Fruit FW (kg)

Top FW (kg)

1.6 y = 0.077x R2 = 0.70; P < 0.01

1.2 0.8 Fall 0.4

y = 0.124 x R2 = 0.55; P < 0.01

2.5 2.0 1.5 1.0 0.5

Spring 0.0

0.0 0

5

10

15

20

25

0

5

10

15

20

25

Vegetative top DW 28 days after transplanting (g) Figure Relationship ofofthethe vegetative top fresh fruit yield mature tomato plants with Fig. 2.2.Relationship vegetative topweight freshand weight andoffruit yield of mature tomato the plantplants size 28 with days after transplanting. the plant size 28 days after transplanting.

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