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Withholding of drip irrigation between transplanting and flowering increases the yield of field-grown tomato under plastic mulch
agricultural water management 87 (2007) 285–291
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/agwat
Withholding of drip irrigation between transplanting and flowering increases the yield of field-grown tomato under plastic mulch Mathieu Ngouajio a,*, Guangyao Wang a, Ronald Goldy b a
Michigan State University, Department of Horticulture, 428 Plant and Soil Sciences Building, East Lansing, MI 48824, United States Michigan State University, Southwest Michigan Research and Extension Center, 1791 Hillandale Road, Benton Harbor, MI 49022, United States
b
article info
abstract
Article history:
Experiments were conducted in summer of 2003 and 2004 to study the effect of withholding
Accepted 30 July 2006
irrigation on tomato growth and yield in a drip irrigated, plasticulture system. Irrigation
Published on line 11 September 2006
treatments were initiated at tomato planting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). An additional treatment received only
Keywords:
enough water to apply fertigation (FT). Withholding drip irrigation for a short period (S2–S3)
Withholding drip irrigation
increased tomato marketable yield by 8–15%, fruit number by 12–14% while reducing
Irrigation water use efficiency
amount of irrigation water by 20% compared to the S0 treatment. Withholding drip irrigation
Tomato
also increased irrigation water use efficiency (IWUE). Similar trends were observed in 2003
Plasticulture
and 2004 despite large differences in rainfall, heat units, and tomato yield between years. This suggests that if soil moisture is adequate at transplanting, subsequent withholding of irrigation for 1–2 weeks after tomato transplanting may increase yield while reducing the amount of irrigation water. # 2006 Elsevier B.V. All rights reserved.
1.
Introduction
Tomato (Lycopersicon esculentum) is the largest vegetable crop in the world in terms of acreage (Ho, 1996). Tomatoes require a high water potential for optimal vegetative and reproductive development (Waister and Hudson, 1970). In the United States, over 91% of tomato fields are irrigated (USDA Economic Research Service, 2003). In Michigan, 840 ha of fresh market tomatoes were harvested in 2004 and contributed over US$ 26 million to the state’s economy (MDA, 2005a). Most production is located in southwest Michigan where tomatoes are produced using drip irrigation on raised beds covered with black plastic mulch. Even though in most years total precipitation meets the water requirements for tomato production in Michigan, rainfall varies from year to year and its distribution
is not uniform throughout the growing season. Therefore, irrigation is required for profitable production. However, optimizing water use is an economic and environmental concern for agricultural producers. Recent adoption of the irrigation water use generally accepted agricultural and management practices (GAAMPs) will influence growers to reduce irrigation input in agriculture (MDA, 2005b). Therefore, fresh market tomato growers are interested in developing management strategies that could help reduce total amount of irrigation water without affecting crop yield and fruit quality. Effects of different irrigation intervals, amounts, and techniques on tomato yield and fruit quality have been extensively studied (Dalvi et al., 1999; Harmanto et al., 2005; Kirda et al., 2004; Zegbe-Dominguez et al., 2003). However, identification of the critical irrigation stage and scheduling of
* Corresponding author. Tel.: +1 517 355 5191; fax: +1 517 432 2242. E-mail address: [email protected] (M. Ngouajio). 0378-3774/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2006.07.007
286
agricultural water management 87 (2007) 285–291
irrigation based on crop water status are the most cost efficient way to improve water use efficiency (Simsek et al., 2005). Despite the wide use of plastic mulches for fresh market tomato production, most studies on irrigation have been conducted on bare soil production systems (Kirda et al., 2004; Zegbe-Dominguez et al., 2003). Results from those studies may not apply to plasticulture systems (mainly raised beds covered with black plastic mulch) because the mulch serves as a barrier for water evaporation. Therefore, this study was conducted to determine the effects of delaying the onset of drip irrigation on fresh market tomato growth and yield in a plasticulture system under Michigan growing conditions.
2.
Materials and methods
The experiments were conducted at the Southwest Michigan Research and Extension Center (SWMREC) at Benton Harbor (42.1N, 86.4W; 220 m above sea level) in the summers of 2003 and 2004 on a Spinks loamy fine sand with pH of 6.5, less than 2% organic matter, and an available water holding capacity (AWC) of about 1 mm/cm. Rainfall during the growing season is presented in Fig. 1. The experiment had a randomized complete block design with six treatments and four replications. The treatments consisted of starting irrigation at transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), and at fruit ripening (S4). Another treatment received only enough water to apply fertigation (FT). Randomization of irrigation treatments was achieved by cutting the drip tapes and reconnecting treatments in consecutive blocks with solid tapes (without emitters). Individual plots consisted of one 9.1 m long bed with one row of tomato. Bed spacing was 1.7 m (center to center) and plant spacing within the row was 46 cm. Flow meters were connected to each irrigation line (treatment) to record the amount of water delivered at each irrigation event. Natural rainfall was recorded at the experimental site using a Campbell Scientific weather station Model 012 (Campbell Scientific Inc., North Logan, UT, USA). ‘Mountain Spring’ tomato was transplanted on raised beds covered with black plastic mulch and drip irrigated. Before
transplanting, 224 kg/ha of 0–0–60 (N–P2O5–K2O), 168 kg/ha of 33–0–0 (N–P2O5–K2O), and 11 kg/ha of Solubor (20.5% B) were broadcasted and disked in late April of each year. The field was then fumigated with 392 kg/ha of methyl bromide and covered with black plastic. Trifluralin and Sencor were applied on 14 May 2003 for weed control before tomato transplanting. Tomato was transplanted on 24 May 2003 and 20 May 2004 when the soil was well irrigated in all treatments. During the growing season, the insecticides (Thiodan, Asana, or Provado) and fungicides (Bravo plus Champ or Penncozeb plus Champ) were applied according to commercial recommendations. All plots were fertigated weekly between mid June and first week of September of each year with 4 kg of 4–0–8–2 (N–P2O5–K2O– Ca). Thus, even the no irrigation treatment received some water during fertigation. Access tubes were installed in each treatment for weekly monitor of soil moisture content at 30, 60, and 90 cm using a capacitance probe (Troxler 200AP from Troxler Electronic Laboratories Inc., Research Triangle Park, NC) connected to a portable data logger precision irrigation scheduling method (PRISM) from Irrigation Scheduling Methods Inc. (4147 Hamlin Road Malaga, WA 98). Leaf water potential was measured using the third leaflet of the third fully expanded leaf. Leaves were collected prior to sunrise (Rudich et al., 1981), enclosed in zip lock bags and put in a cooler. Leaf water potential was measured after leaf collection in all treatments using a pressure chamber (Model 600 Pressure Chamber Instrument, PMS Instrument Company, Albany, OR, USA). Tomato height was measured 7 August 2003 and 2 August 2004. Additionally, a trench was dug in each treatment on 23 September 2004 to measure root depth. Tomatoes were harvested five times in 2003 (from 7 August to 18 September) and seven times in 2004 (from 7 August to 23 September). Tomato fruits were graded into no. 1 large (>5.4 cm), no. 1 (<5.4 cm) small, no. 2, and Cull according to standards for fresh market grades (USDA, 1991). Fruit number and weight in each grade category were determined. Irrigation water use efficiency was calculated by the following equation (Hillel and Guron, 1975): IWUE ¼
Y I YFT WI WFT
(1)
where IWUE is irrigation water use efficiency (kg tomato1 ha 1 mm), YI is tomato yield with irrigation, YFT tomato yield in FT (fertigation only) treatment, WI the amount of water applied in irrigation treatments, and WFT is the amount of water applied in FT treatment.
2.1.
Statistical analysis
All data on soil water content, leaf water potential, tomato height, root depth, and tomato yield were subjected to ANOVA and means were separated using Fisher protected L.S.D. at 5% level of probability. Tomato fruit number and marketable yield were fitted to the following quadratic equation: Y ¼ aX2 þ bX þ c Fig. 1 – Weekly rainfall during the tomato-growing season in 2003 and 2004.
(2)
where Y is fruit number or marketable yield in percentage of the treatment with no irrigation withholding (S0), X the logarithm
agricultural water management 87 (2007) 285–291
transformation of the length of irrigation withholding in days after transplanting (DAT) (ln(DAT)), a, b, and c are regression parameters. The DAT at which highest values of fruit number and yield occurred were calculated by setting the first derivative of Eq. (1) to zero and solving for X. Then, the resulting value of X was put into Eq. (2) to calculate highest fruit number and yield predicted by the regression. Eq. (2) was also set equal to 100 to calculate the maximum length of time when irrigation can be withheld without reduction in fruit number and yield compared with the S0 treatment.
rainfall in 2004, there was also a more uniform rain distribution compared to 2003. Therefore, 2003 was a dry year and 2004 a more normal year in terms of rainfall. Total water applied (mm) in 2003 to S0, S1, S2, S3, S4, and FT were, respectively, 1122, 902, 773, 705, 557, and 100. The corresponding values for 2004 were: 957, 839, 770, 728, 584, and 106. In 2004, the amount of water applied was reduced by about 20% early in the season (treatment S0) because of more rainfall. However, the amount of water applied in other treatments was similar to the 2003 value.
3.2.
3.
Results
3.1.
Rainfall and amount of irrigation water applied
Natural rainfall varied greatly between the 2003 and 2004 seasons (Fig. 1). Total rainfall during the growing season was 162.3 mm in 2003 and 412.5 mm in 2004. In addition to greater
287
Soil moisture during the growing season
In 2003, there were significant differences among the irrigation treatments at all depth and throughout the growing season (Fig. 2). Generally, the longer irrigation was withheld, the lower the soil moisture content. The FT treatments maintained the lowest throughout the growing season. Soil moisture declined progressively especially at 60 and 90 cm depths.
Fig. 2 – Soil moisture content at 30, 60, and 90 cm (percent of available water holding capacity) in tomato field in 2003 and 2004 under different irrigation regimes. Irrigation treatments were initiated at tomato transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). The FT treatment received only enough water for fertigation. Asterisks indicate significant difference between treatments at the specific dates. DAT is days after tomato transplanting.
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agricultural water management 87 (2007) 285–291
In 2004, all treatments had similar soil moisture content in the depths of 30 and 90 cm because of more frequent rainfall (Fig. 2). However, irrigation treatments resulted in significant differences in soil moisture content at the depth of 60 cm, with S2 having higher soil moisture content than S4 and FT treatments. The decline in soil moisture content observed in 2003 (dry year) was less in 2004 (wet year).
3.3.
Leaf water potential
Leaf water potential was measured eight times in 2003 and nine times in 2004 (Fig. 3). Values varied from 100 to 1100 kPa in 2003 and from 100 to 750 kPa in 2004. Delaying the onset of irrigation had little effect on leaf water potential in both years. The only significant differences among treatments were found between 82 and 96 DAT in 2003 (following a long period of no rainfall) and at 77 DAT in 2004 (following 2 weeks of no rainfall). Even at those dates, the only treatment that had significantly lower leaf water potential was the FT treatment.
3.4.
Tomato height and root depth
Irrigation withholding after transplanting had no significant effect on tomato height in 2003. Tomato height was 113.7, 113.0, 110.5, 102.2, 101.6, and 96.5 cm for S0, S1, S2, S3, S4, and FT, respectively. In 2004; however, initiating irrigation before first flower (S2) or after fruit set (S3) produced shorter plants. Plant height was 85.0, 86.0, 96.5, 89.0, 83.3, and 84.5 cm. Also, delaying irrigation increased root depth in 2004. Roots were deepest (145 cm) when irrigation was initiated at fruit ripening in 2004 (wet year). Tomato roots were shallowest (90 cm) when irrigation was initiated immediately after transplanting (S0).
3.5.
Tomato yield
Tomato fruit number and marketable yield in all treatments was smaller in 2004 compared to 2003 (Table 1). In 2004, the S1 treatment had the highest tomato fruit number and marketable yield but fruit size was similar across treatments. In 2004; however, fruit number and marketable yield was similar among treatments, and the S2 treatment had larger fruits compared to S3, S4, and FT treatments. When compared with the S0 treatment, S1 treatment in 2003 and
Fig. 3 – Tomato leaf water potential during growing season in 2003 and 2004 as affected by the irrigation regime. Irrigation treatments were initiated at tomato transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). The FT treatment received only enough water for fertigation. Asterisks indicate significant difference between treatments at the specific dates. DAT is days after tomato transplanting.
S2 treatment in 2004 increased tomato yield by 8.4 and 14.8%, respectively, with 19.6 and 21.1% less irrigation water input, respectively. Tomato fruit number and marketable yield presented as percentage of S0 was regressed against logarithm transforma-
Table 1 – Tomato fruit number, fruit size, and marketable yield in 2003 and 2004 as affected by the timing of irrigation initiation Timing of irrigation initiationa S0 S1 S2 S3 S4 FT a
2003
2004
Counts (1000/ha) 399.8 449.2 422.9 402.3 391.9 384.1
abb a ab b b b
Weight (tonnes/ha) 106.5 115.4 108.3 103.2 100.8 86.5
ab a ab b b c
Fruit size (g/fruit) 266.3 257.0 256.1 256.5 257.3 225.9
a a a a a b
Counts (1000/ha)
Weight (tonnes/ha)
193.9 219.1 220.1 210.5 210.9 200.3
59.2 66.3 67.9 62.4 61.1 56.5
Fruit size (g/fruit) 305.2 302.5 308.9 296.5 289.6 282.0
ab ab a bc cd d
Irrigation treatments were initiated either at tomato transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). The FT treatment received only enough water for fertigation. b Values with same letters are not significantly different at 5% level of probability.
agricultural water management 87 (2007) 285–291
tion of DAT. A quadratic function adequately was used to describe the relationship (Fig. 4). The regression for fruit number had R2 values of 0.81 and 0.97 for 2003 and 2004 data, respectively. For marketable yield, the R2 of the regression was 0.99 in 2003 and 0.92 in 2004. The quadratic function was used to calculate the highest fruit number and yield predicted by the model and the DAT at which starting irrigation would produce the highest fruit number and yield. Starting irrigation at about 6–8 DAT would increase fruit number and yield by 9.9 and 10.6%, respectively in a dry year like 2003. Starting irrigation at 10–13 DAT would increase fruit number and yield by 14.1 and 15.9%, respectively in a wet year like 2004. The
optimal DAT to start irrigation for fruit number is later than that for yield in both situations indicating water withholding may result in more fruits but of smaller size.
3.6.
Irrigation water use efficiency
IWUE estimates the contribution of irrigation to tomato fruit yield. Although there was large variation in the observations, a short delay in the onset of irrigation seemed to increase IWUE in both years (Table 2). The highest IWUE was obtained when irrigation was initiated after transplant establishment (S1) in 2003 and at first flower (S2) in 2004. Withholding irrigation until the stages produced the most tomatoes per unit of irrigation water. Beyond those stages, further delay in the onset of irrigation reduced IWUE.
4.
Fig. 4 – Fruit number and yield of tomato in percentage of full irrigation. Tomato fruit number and marketable yield were fitted to Eq. (2) (Y = aX2 + bX + c) where Y is fruit number or marketable yield in percentage of the treatment with no irrigation withholding (S0), X the logarithm transformation of the length of irrigation withholding in days after transplanting DAT (ln(DAT)), a, b, and c are regression parameters. The highest fruit number (% of S0) was 109.9 in 2003 and 114.1 in 2004 and was achieved at 7.7 and 13.3 DAT in 2003 and 2004, respectively. The highest yield (% of S0) was 110.6 in 2003 and 115.9 in 2004 and was achieved at 5.9 and 9.6 DAT in 2003 and 2004, respectively.
289
Discussion
The experiments were conducted in 2 years with different rainfall amount and distribution. The 2003 season was dry and the 2004 season wet. Variability between the two seasons was ideal to test how rainfall can affect tomato response to drip irrigation under plasticulture. Measurement of soil moisture under the plastic showed that under conditions of low rainfall (2003), irrigation treatments have a significant effect in the entire soil profile (up to 90 cm). However, when rainfall was adequate in 2004, soil water content was different at the depth of 60 cm. This is an indication that irrigation water in the 30 cm was enough for plant growth in all treatments and the rainfall provided sufficient water at the depth of 90 cm. Work conducted by Machado and Oliveira (2005) showed that most tomato roots were concentrated in the first 40 cm in the soil profile. The lack of difference in soil moisture content at 30 cm among treatments in 2004 was probably due to cooler conditions the uniform application of irrigation after the treatments were initiated. Although leaf water potential showed large differences between years, it was not a good indicator for water status among treatments. Leaf water potential was generally similar despite significant differences in soil water potential. Rudich et al. (1981) showed tomato leaf water potential was more affected by atmospheric factors than by soil water availability. In this work, leaf water potential decreased following long periods of drought stress and increased after rainfall. However, differences due to the irrigation treatments were less apparent. Tomato fruit number and marketable yield in all treatments was much smaller in 2004 compared to 2003 because of heavy rain and cloudy weather. This suggests fresh market tomato grown using plasticulture and drip irrigation perform better under dry and sunny conditions (Zegbe-Dominguez et al., 2003, 2006). Despite the large differences in rainfall and total yield between years, the effect of withholding irrigation on tomato growth and yield showed similar trends. This study shows that after transplanting, it was possible to withhold irrigation (except for weekly fertigation) for 35 days in 2003 (dry year) and 95 days in 2004 (wet year) without yield losses. As long as there is adequate moisture in soil at transplanting, withholding irrigation for 1–2 weeks would increase tomato fruit number and marketable yield. However, withholding
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agricultural water management 87 (2007) 285–291
Table 2 – Irrigation water use efficiency in 2003 and 2004 for tomato grown under different irrigation regimesa Timing of irrigation initiationa
S0 S1 S2 S3 S4 FT
2003
2004
Mean
Standard error
Mean
Standard error
17.4 33.4 29.2 24.0 26.6 17.4
6.0 4.1 5.9 3.7 11.2 6.0
3.1 5.3 17.2 9.5 9.6 3.1
4.0 5.8 8.2 8.4 5.5 4.0
a
Irrigation treatments were initiated either at tomato transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). The FT treatment received only enough water for fertigation.
water further may decrease fruit number and size because of drought stress. Such a practice requires monitoring soil moisture status, especially during excessively dry seasons. It has long been asserted that excessive soil moisture during the first couple of days (or weeks) following planting may have adverse effects on crop yield (Phene and Sanders, 1976; Sezen et al., 2006; Dalvi et al., 1999). This is clearly supported by results in this trial. Although irrigation during the whole growing period (S0) increased yield compared to fertigation only treatment (FT), it had lower or equivalent yield than withholding irrigation until the end of the transplant establishment stage (S1) in 2003 or until first flower (S2) in 2004. Results of this study suggest growers could save up to 40% irrigation water input and improve tomato yield by up to 15% simply by withholding irrigation for a few weeks after transplanting. Excess irrigation not only reduces crop yield, but also increases nutrient leaching (Moreno et al., 1996; Pang et al., 1997; Zegbe-Dominguez et al., 2003, 2006). In most vegetable crop fields, extensive irrigation water is applied and nitrogen left over is much higher than cereal crops (Greenwood et al., 1996). Withholding irrigation or reduced irrigation in the early stage of crop growth enhanced a deeper and more extensive root system in this study and elsewhere (Pace et al., 1999; Ludlow and Muchow, 1990; Marouelli and Silva, 2005; De Costa and Shanmugathasan, 1999). This would allow plants to use water and nutrients from deeper soil, thus increase IWUE and nutrients use efficiency, and reduce nitrogen leaching. This study shows that delaying onset of drip irrigation after tomato transplanting improves fresh market tomato growth and yield while reducing the total amount of water applied under plasticulture. These combined factors could increase profitability of tomato production. However, the soil should be moist at transplanting, and the exact duration of irrigation withholding depends on natural rainfall and other environmental factors. This period could range from 1 to 2 weeks or more after transplanting. The price of tomato fruit, irrigation cost, as well as the effect of water on fruit quality, should be considered to maximize the profit of irrigation management.
Acknowledgements This work was supported in part by GREEEN Project (Generating Research and Extension to meet Environmental and Economic Needs) No GR04-008, SWMREC (Southwest Michigan
Research and Extension Center), and the Michigan Vegetable Council. Dave Francis provided technical assistance on this project and the summer student Adrianne helped in experiment set-up and data collection. Thanks to all growers in Southwest Michigan who contributed to the design of this experiment by sharing their ideas and experience, and Trevor Meachum for providing transplants in 2003.
references
Dalvi, V.B., Tiwari, K.N., Pawade, M.N., Phirke, P.S., 1999. Response surface analysis of tomato production under microirrigation. Agric. Water Manage. 41, 11–19. De Costa, W.A.J.M., Shanmugathasan, K.N., 1999. Effects of irrigation at different growth stages on vegetative growth of mung bean, Vigna radiata (L.) Wilczek, in dry and intermediate zones of Sri Lanka. J. Agron. Crop Sci. Zeitschrift Fur Acker Und Pflanzenbau 183, 137–143. Greenwood, D.J., Rahn, C.R., Draycott, A., Vaidyanathan, L.V., Paterson, C.D., 1996. Modelling and measurement of the effects of fertilizer-N and crop residue incorporation on Ndynamics in vegetable cropping. Soil Use Manage. 12, 13–24. Harmanto, Salokhe, V.M., Babel, M.S., Tantau, H.J., 2005. Water requirement of drip irrigated tomatoes grown in greenhouse in tropical environment. Agric. Water Manage. 71, 225–242. Hillel, D., Guron, Y., 1975. Relation between evapotranspiration rate and maize yield. Water Res. 9, 743–748. Ho, L.C., 1996. Tomato. In: Zemaski, E., Schaffer, A.A. (Eds.), Photoassimilate Distribution in Plants and Crops: Source– Sink Relationships. Marcel Dekker, NY, USA, pp. 709–728. Kirda, C., Cetin, M., Dasgan, Y., Topcu, S., Kaman, H., Ekici, B., Derici, M.R., Ozguven, A.I., 2004. Yield response of greenhouse grown tomato to partial root drying and conventional deficit irrigation. Agric. Water Manage. 69, 191–201. Ludlow, M.M., Muchow, R.C., 1990. A critical evaluation of traits for improving crop yields in water-limited environments. Adv. Agron. 43, 107–153. Machado, R.M.A., Oliveira, M.D.G., 2005. Tomato root distribution, yield and fruit quality under different subsurface drip irrigation regimes and depths. Irrig. Sci. 24, 15–24. Marouelli, W.A., Silva, W.L.D.E., 2005. Drip irrigation frequency for processing tomatoes during vegetative growth stage. Pes. Agropec. Brasil. 40, 661–666. MDA (Michigan Department of Agriculture), 2005a. Michigan agricultural statistics 2004–2005, Michigan Department of Agriculture, Lansing, MI, USA, p. 81.
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MDA (Michigan Department of Agriculture), 2005b. Generally accepted agricultural and management practices for irrigation water use, Michigan Department of Agriculture, Lansing, MI, USA, p. 21. Moreno, F., Cayuela, J.A., Fernandez, J.E., Fernandez-Boy, E., Murillo, J.M., Cabrera, F., 1996. Water balance and nitrate leaching in an irrigated maize crop in SW Spain. Agric. Water Manage. 32, 71–83. Pace, P.F., Cralle, H.T., El-Halawany, S.H.M., Cothren, J.T., Senseman, S.A., 1999. Drought-induced changes in shoot and root growth of young cotton plants. J. Cotton Sci. 3, 183–187. Pang, X.P., Letey, J., Wu, L., 1997. Irrigation quantity and uniformity and nitrogen application effects on crop yield and nitrogen leaching. Soil Sci. Soc. Am. J. 61, 257–261. Phene, C.J., Sanders, D.C., 1976. High-frequency trickle irrigation and row spacing effects on yield and quality of potatoes. Agron. J. 68, 602–607. Rudich, J., Rendon-Poblete, E., Stevens, M.A., Ambri, A.I., 1981. Use of leaf water potential to determine water stress in field-grown tomato plants. J. Am. Soc. Hort. Sci. 106, 732–736. Sezen, S.M., Yazar, A., Eker, S., 2006. Effect of drip irrigation regimes on yield and quality of field grown bell pepper. Agric. Water Manage. 81, 115–131.
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Simsek, M., Tonkaz, T., Kacira, M., Comlekcioglu, N., Dogan, Z., 2005. The effects of different irrigation regimes on cucumber (Cucumbis sativus L.) yield and yield characteristics under open field conditions. Agric. Water Manage. 73, 173–191. USDA Economic Research Service, 2003. U.S. Tomato Statistics (92010), http://usda.mannlib.cornell.edu/data-sets/ specialty/92010. USDA (United States Department of Agriculture), 1991. United States Standards for Grades of Fresh Tomatoes, United States Department of Agriculture Agricultural Marketing Service, Fruit and Vegetable Division, Fresh Products Branch, p. 13, http://www.ams.usda.gov/standards/ tomatfrh.pdf. Waister, P.D., Hudson, J.P., 1970. Effect of soil moisture regimes on leaf deficit, transpiration and yield of tomatoes. J. Hort. Sci. 45, 359–370. Zegbe-Dominguez, J.A., Behboudian, M.H., Lang, A., Clothier, B.E., 2003. Deficit irrigation and partial rootzone drying maintain fruit dry mass and enhance fruit quality in ‘Petopride’ processing tomato (Lycopersicon esculentum Mill.). Sci. Hort. 98, 505–510. Zegbe-Dominguez, J.A., Behboudian, M.H., Clothier, B.E., 2006. Responses of ’Petopride’ processing tomato to partial rootzone drying at different phenological stages. Irrig. Sci. 24, 203–210.
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/agwat
Withholding of drip irrigation between transplanting and flowering increases the yield of field-grown tomato under plastic mulch Mathieu Ngouajio a,*, Guangyao Wang a, Ronald Goldy b a
Michigan State University, Department of Horticulture, 428 Plant and Soil Sciences Building, East Lansing, MI 48824, United States Michigan State University, Southwest Michigan Research and Extension Center, 1791 Hillandale Road, Benton Harbor, MI 49022, United States
b
article info
abstract
Article history:
Experiments were conducted in summer of 2003 and 2004 to study the effect of withholding
Accepted 30 July 2006
irrigation on tomato growth and yield in a drip irrigated, plasticulture system. Irrigation
Published on line 11 September 2006
treatments were initiated at tomato planting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). An additional treatment received only
Keywords:
enough water to apply fertigation (FT). Withholding drip irrigation for a short period (S2–S3)
Withholding drip irrigation
increased tomato marketable yield by 8–15%, fruit number by 12–14% while reducing
Irrigation water use efficiency
amount of irrigation water by 20% compared to the S0 treatment. Withholding drip irrigation
Tomato
also increased irrigation water use efficiency (IWUE). Similar trends were observed in 2003
Plasticulture
and 2004 despite large differences in rainfall, heat units, and tomato yield between years. This suggests that if soil moisture is adequate at transplanting, subsequent withholding of irrigation for 1–2 weeks after tomato transplanting may increase yield while reducing the amount of irrigation water. # 2006 Elsevier B.V. All rights reserved.
1.
Introduction
Tomato (Lycopersicon esculentum) is the largest vegetable crop in the world in terms of acreage (Ho, 1996). Tomatoes require a high water potential for optimal vegetative and reproductive development (Waister and Hudson, 1970). In the United States, over 91% of tomato fields are irrigated (USDA Economic Research Service, 2003). In Michigan, 840 ha of fresh market tomatoes were harvested in 2004 and contributed over US$ 26 million to the state’s economy (MDA, 2005a). Most production is located in southwest Michigan where tomatoes are produced using drip irrigation on raised beds covered with black plastic mulch. Even though in most years total precipitation meets the water requirements for tomato production in Michigan, rainfall varies from year to year and its distribution
is not uniform throughout the growing season. Therefore, irrigation is required for profitable production. However, optimizing water use is an economic and environmental concern for agricultural producers. Recent adoption of the irrigation water use generally accepted agricultural and management practices (GAAMPs) will influence growers to reduce irrigation input in agriculture (MDA, 2005b). Therefore, fresh market tomato growers are interested in developing management strategies that could help reduce total amount of irrigation water without affecting crop yield and fruit quality. Effects of different irrigation intervals, amounts, and techniques on tomato yield and fruit quality have been extensively studied (Dalvi et al., 1999; Harmanto et al., 2005; Kirda et al., 2004; Zegbe-Dominguez et al., 2003). However, identification of the critical irrigation stage and scheduling of
* Corresponding author. Tel.: +1 517 355 5191; fax: +1 517 432 2242. E-mail address: [email protected] (M. Ngouajio). 0378-3774/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2006.07.007
286
agricultural water management 87 (2007) 285–291
irrigation based on crop water status are the most cost efficient way to improve water use efficiency (Simsek et al., 2005). Despite the wide use of plastic mulches for fresh market tomato production, most studies on irrigation have been conducted on bare soil production systems (Kirda et al., 2004; Zegbe-Dominguez et al., 2003). Results from those studies may not apply to plasticulture systems (mainly raised beds covered with black plastic mulch) because the mulch serves as a barrier for water evaporation. Therefore, this study was conducted to determine the effects of delaying the onset of drip irrigation on fresh market tomato growth and yield in a plasticulture system under Michigan growing conditions.
2.
Materials and methods
The experiments were conducted at the Southwest Michigan Research and Extension Center (SWMREC) at Benton Harbor (42.1N, 86.4W; 220 m above sea level) in the summers of 2003 and 2004 on a Spinks loamy fine sand with pH of 6.5, less than 2% organic matter, and an available water holding capacity (AWC) of about 1 mm/cm. Rainfall during the growing season is presented in Fig. 1. The experiment had a randomized complete block design with six treatments and four replications. The treatments consisted of starting irrigation at transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), and at fruit ripening (S4). Another treatment received only enough water to apply fertigation (FT). Randomization of irrigation treatments was achieved by cutting the drip tapes and reconnecting treatments in consecutive blocks with solid tapes (without emitters). Individual plots consisted of one 9.1 m long bed with one row of tomato. Bed spacing was 1.7 m (center to center) and plant spacing within the row was 46 cm. Flow meters were connected to each irrigation line (treatment) to record the amount of water delivered at each irrigation event. Natural rainfall was recorded at the experimental site using a Campbell Scientific weather station Model 012 (Campbell Scientific Inc., North Logan, UT, USA). ‘Mountain Spring’ tomato was transplanted on raised beds covered with black plastic mulch and drip irrigated. Before
transplanting, 224 kg/ha of 0–0–60 (N–P2O5–K2O), 168 kg/ha of 33–0–0 (N–P2O5–K2O), and 11 kg/ha of Solubor (20.5% B) were broadcasted and disked in late April of each year. The field was then fumigated with 392 kg/ha of methyl bromide and covered with black plastic. Trifluralin and Sencor were applied on 14 May 2003 for weed control before tomato transplanting. Tomato was transplanted on 24 May 2003 and 20 May 2004 when the soil was well irrigated in all treatments. During the growing season, the insecticides (Thiodan, Asana, or Provado) and fungicides (Bravo plus Champ or Penncozeb plus Champ) were applied according to commercial recommendations. All plots were fertigated weekly between mid June and first week of September of each year with 4 kg of 4–0–8–2 (N–P2O5–K2O– Ca). Thus, even the no irrigation treatment received some water during fertigation. Access tubes were installed in each treatment for weekly monitor of soil moisture content at 30, 60, and 90 cm using a capacitance probe (Troxler 200AP from Troxler Electronic Laboratories Inc., Research Triangle Park, NC) connected to a portable data logger precision irrigation scheduling method (PRISM) from Irrigation Scheduling Methods Inc. (4147 Hamlin Road Malaga, WA 98). Leaf water potential was measured using the third leaflet of the third fully expanded leaf. Leaves were collected prior to sunrise (Rudich et al., 1981), enclosed in zip lock bags and put in a cooler. Leaf water potential was measured after leaf collection in all treatments using a pressure chamber (Model 600 Pressure Chamber Instrument, PMS Instrument Company, Albany, OR, USA). Tomato height was measured 7 August 2003 and 2 August 2004. Additionally, a trench was dug in each treatment on 23 September 2004 to measure root depth. Tomatoes were harvested five times in 2003 (from 7 August to 18 September) and seven times in 2004 (from 7 August to 23 September). Tomato fruits were graded into no. 1 large (>5.4 cm), no. 1 (<5.4 cm) small, no. 2, and Cull according to standards for fresh market grades (USDA, 1991). Fruit number and weight in each grade category were determined. Irrigation water use efficiency was calculated by the following equation (Hillel and Guron, 1975): IWUE ¼
Y I YFT WI WFT
(1)
where IWUE is irrigation water use efficiency (kg tomato1 ha 1 mm), YI is tomato yield with irrigation, YFT tomato yield in FT (fertigation only) treatment, WI the amount of water applied in irrigation treatments, and WFT is the amount of water applied in FT treatment.
2.1.
Statistical analysis
All data on soil water content, leaf water potential, tomato height, root depth, and tomato yield were subjected to ANOVA and means were separated using Fisher protected L.S.D. at 5% level of probability. Tomato fruit number and marketable yield were fitted to the following quadratic equation: Y ¼ aX2 þ bX þ c Fig. 1 – Weekly rainfall during the tomato-growing season in 2003 and 2004.
(2)
where Y is fruit number or marketable yield in percentage of the treatment with no irrigation withholding (S0), X the logarithm
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transformation of the length of irrigation withholding in days after transplanting (DAT) (ln(DAT)), a, b, and c are regression parameters. The DAT at which highest values of fruit number and yield occurred were calculated by setting the first derivative of Eq. (1) to zero and solving for X. Then, the resulting value of X was put into Eq. (2) to calculate highest fruit number and yield predicted by the regression. Eq. (2) was also set equal to 100 to calculate the maximum length of time when irrigation can be withheld without reduction in fruit number and yield compared with the S0 treatment.
rainfall in 2004, there was also a more uniform rain distribution compared to 2003. Therefore, 2003 was a dry year and 2004 a more normal year in terms of rainfall. Total water applied (mm) in 2003 to S0, S1, S2, S3, S4, and FT were, respectively, 1122, 902, 773, 705, 557, and 100. The corresponding values for 2004 were: 957, 839, 770, 728, 584, and 106. In 2004, the amount of water applied was reduced by about 20% early in the season (treatment S0) because of more rainfall. However, the amount of water applied in other treatments was similar to the 2003 value.
3.2.
3.
Results
3.1.
Rainfall and amount of irrigation water applied
Natural rainfall varied greatly between the 2003 and 2004 seasons (Fig. 1). Total rainfall during the growing season was 162.3 mm in 2003 and 412.5 mm in 2004. In addition to greater
287
Soil moisture during the growing season
In 2003, there were significant differences among the irrigation treatments at all depth and throughout the growing season (Fig. 2). Generally, the longer irrigation was withheld, the lower the soil moisture content. The FT treatments maintained the lowest throughout the growing season. Soil moisture declined progressively especially at 60 and 90 cm depths.
Fig. 2 – Soil moisture content at 30, 60, and 90 cm (percent of available water holding capacity) in tomato field in 2003 and 2004 under different irrigation regimes. Irrigation treatments were initiated at tomato transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). The FT treatment received only enough water for fertigation. Asterisks indicate significant difference between treatments at the specific dates. DAT is days after tomato transplanting.
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In 2004, all treatments had similar soil moisture content in the depths of 30 and 90 cm because of more frequent rainfall (Fig. 2). However, irrigation treatments resulted in significant differences in soil moisture content at the depth of 60 cm, with S2 having higher soil moisture content than S4 and FT treatments. The decline in soil moisture content observed in 2003 (dry year) was less in 2004 (wet year).
3.3.
Leaf water potential
Leaf water potential was measured eight times in 2003 and nine times in 2004 (Fig. 3). Values varied from 100 to 1100 kPa in 2003 and from 100 to 750 kPa in 2004. Delaying the onset of irrigation had little effect on leaf water potential in both years. The only significant differences among treatments were found between 82 and 96 DAT in 2003 (following a long period of no rainfall) and at 77 DAT in 2004 (following 2 weeks of no rainfall). Even at those dates, the only treatment that had significantly lower leaf water potential was the FT treatment.
3.4.
Tomato height and root depth
Irrigation withholding after transplanting had no significant effect on tomato height in 2003. Tomato height was 113.7, 113.0, 110.5, 102.2, 101.6, and 96.5 cm for S0, S1, S2, S3, S4, and FT, respectively. In 2004; however, initiating irrigation before first flower (S2) or after fruit set (S3) produced shorter plants. Plant height was 85.0, 86.0, 96.5, 89.0, 83.3, and 84.5 cm. Also, delaying irrigation increased root depth in 2004. Roots were deepest (145 cm) when irrigation was initiated at fruit ripening in 2004 (wet year). Tomato roots were shallowest (90 cm) when irrigation was initiated immediately after transplanting (S0).
3.5.
Tomato yield
Tomato fruit number and marketable yield in all treatments was smaller in 2004 compared to 2003 (Table 1). In 2004, the S1 treatment had the highest tomato fruit number and marketable yield but fruit size was similar across treatments. In 2004; however, fruit number and marketable yield was similar among treatments, and the S2 treatment had larger fruits compared to S3, S4, and FT treatments. When compared with the S0 treatment, S1 treatment in 2003 and
Fig. 3 – Tomato leaf water potential during growing season in 2003 and 2004 as affected by the irrigation regime. Irrigation treatments were initiated at tomato transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). The FT treatment received only enough water for fertigation. Asterisks indicate significant difference between treatments at the specific dates. DAT is days after tomato transplanting.
S2 treatment in 2004 increased tomato yield by 8.4 and 14.8%, respectively, with 19.6 and 21.1% less irrigation water input, respectively. Tomato fruit number and marketable yield presented as percentage of S0 was regressed against logarithm transforma-
Table 1 – Tomato fruit number, fruit size, and marketable yield in 2003 and 2004 as affected by the timing of irrigation initiation Timing of irrigation initiationa S0 S1 S2 S3 S4 FT a
2003
2004
Counts (1000/ha) 399.8 449.2 422.9 402.3 391.9 384.1
abb a ab b b b
Weight (tonnes/ha) 106.5 115.4 108.3 103.2 100.8 86.5
ab a ab b b c
Fruit size (g/fruit) 266.3 257.0 256.1 256.5 257.3 225.9
a a a a a b
Counts (1000/ha)
Weight (tonnes/ha)
193.9 219.1 220.1 210.5 210.9 200.3
59.2 66.3 67.9 62.4 61.1 56.5
Fruit size (g/fruit) 305.2 302.5 308.9 296.5 289.6 282.0
ab ab a bc cd d
Irrigation treatments were initiated either at tomato transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). The FT treatment received only enough water for fertigation. b Values with same letters are not significantly different at 5% level of probability.
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tion of DAT. A quadratic function adequately was used to describe the relationship (Fig. 4). The regression for fruit number had R2 values of 0.81 and 0.97 for 2003 and 2004 data, respectively. For marketable yield, the R2 of the regression was 0.99 in 2003 and 0.92 in 2004. The quadratic function was used to calculate the highest fruit number and yield predicted by the model and the DAT at which starting irrigation would produce the highest fruit number and yield. Starting irrigation at about 6–8 DAT would increase fruit number and yield by 9.9 and 10.6%, respectively in a dry year like 2003. Starting irrigation at 10–13 DAT would increase fruit number and yield by 14.1 and 15.9%, respectively in a wet year like 2004. The
optimal DAT to start irrigation for fruit number is later than that for yield in both situations indicating water withholding may result in more fruits but of smaller size.
3.6.
Irrigation water use efficiency
IWUE estimates the contribution of irrigation to tomato fruit yield. Although there was large variation in the observations, a short delay in the onset of irrigation seemed to increase IWUE in both years (Table 2). The highest IWUE was obtained when irrigation was initiated after transplant establishment (S1) in 2003 and at first flower (S2) in 2004. Withholding irrigation until the stages produced the most tomatoes per unit of irrigation water. Beyond those stages, further delay in the onset of irrigation reduced IWUE.
4.
Fig. 4 – Fruit number and yield of tomato in percentage of full irrigation. Tomato fruit number and marketable yield were fitted to Eq. (2) (Y = aX2 + bX + c) where Y is fruit number or marketable yield in percentage of the treatment with no irrigation withholding (S0), X the logarithm transformation of the length of irrigation withholding in days after transplanting DAT (ln(DAT)), a, b, and c are regression parameters. The highest fruit number (% of S0) was 109.9 in 2003 and 114.1 in 2004 and was achieved at 7.7 and 13.3 DAT in 2003 and 2004, respectively. The highest yield (% of S0) was 110.6 in 2003 and 115.9 in 2004 and was achieved at 5.9 and 9.6 DAT in 2003 and 2004, respectively.
289
Discussion
The experiments were conducted in 2 years with different rainfall amount and distribution. The 2003 season was dry and the 2004 season wet. Variability between the two seasons was ideal to test how rainfall can affect tomato response to drip irrigation under plasticulture. Measurement of soil moisture under the plastic showed that under conditions of low rainfall (2003), irrigation treatments have a significant effect in the entire soil profile (up to 90 cm). However, when rainfall was adequate in 2004, soil water content was different at the depth of 60 cm. This is an indication that irrigation water in the 30 cm was enough for plant growth in all treatments and the rainfall provided sufficient water at the depth of 90 cm. Work conducted by Machado and Oliveira (2005) showed that most tomato roots were concentrated in the first 40 cm in the soil profile. The lack of difference in soil moisture content at 30 cm among treatments in 2004 was probably due to cooler conditions the uniform application of irrigation after the treatments were initiated. Although leaf water potential showed large differences between years, it was not a good indicator for water status among treatments. Leaf water potential was generally similar despite significant differences in soil water potential. Rudich et al. (1981) showed tomato leaf water potential was more affected by atmospheric factors than by soil water availability. In this work, leaf water potential decreased following long periods of drought stress and increased after rainfall. However, differences due to the irrigation treatments were less apparent. Tomato fruit number and marketable yield in all treatments was much smaller in 2004 compared to 2003 because of heavy rain and cloudy weather. This suggests fresh market tomato grown using plasticulture and drip irrigation perform better under dry and sunny conditions (Zegbe-Dominguez et al., 2003, 2006). Despite the large differences in rainfall and total yield between years, the effect of withholding irrigation on tomato growth and yield showed similar trends. This study shows that after transplanting, it was possible to withhold irrigation (except for weekly fertigation) for 35 days in 2003 (dry year) and 95 days in 2004 (wet year) without yield losses. As long as there is adequate moisture in soil at transplanting, withholding irrigation for 1–2 weeks would increase tomato fruit number and marketable yield. However, withholding
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Table 2 – Irrigation water use efficiency in 2003 and 2004 for tomato grown under different irrigation regimesa Timing of irrigation initiationa
S0 S1 S2 S3 S4 FT
2003
2004
Mean
Standard error
Mean
Standard error
17.4 33.4 29.2 24.0 26.6 17.4
6.0 4.1 5.9 3.7 11.2 6.0
3.1 5.3 17.2 9.5 9.6 3.1
4.0 5.8 8.2 8.4 5.5 4.0
a
Irrigation treatments were initiated either at tomato transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). The FT treatment received only enough water for fertigation.
water further may decrease fruit number and size because of drought stress. Such a practice requires monitoring soil moisture status, especially during excessively dry seasons. It has long been asserted that excessive soil moisture during the first couple of days (or weeks) following planting may have adverse effects on crop yield (Phene and Sanders, 1976; Sezen et al., 2006; Dalvi et al., 1999). This is clearly supported by results in this trial. Although irrigation during the whole growing period (S0) increased yield compared to fertigation only treatment (FT), it had lower or equivalent yield than withholding irrigation until the end of the transplant establishment stage (S1) in 2003 or until first flower (S2) in 2004. Results of this study suggest growers could save up to 40% irrigation water input and improve tomato yield by up to 15% simply by withholding irrigation for a few weeks after transplanting. Excess irrigation not only reduces crop yield, but also increases nutrient leaching (Moreno et al., 1996; Pang et al., 1997; Zegbe-Dominguez et al., 2003, 2006). In most vegetable crop fields, extensive irrigation water is applied and nitrogen left over is much higher than cereal crops (Greenwood et al., 1996). Withholding irrigation or reduced irrigation in the early stage of crop growth enhanced a deeper and more extensive root system in this study and elsewhere (Pace et al., 1999; Ludlow and Muchow, 1990; Marouelli and Silva, 2005; De Costa and Shanmugathasan, 1999). This would allow plants to use water and nutrients from deeper soil, thus increase IWUE and nutrients use efficiency, and reduce nitrogen leaching. This study shows that delaying onset of drip irrigation after tomato transplanting improves fresh market tomato growth and yield while reducing the total amount of water applied under plasticulture. These combined factors could increase profitability of tomato production. However, the soil should be moist at transplanting, and the exact duration of irrigation withholding depends on natural rainfall and other environmental factors. This period could range from 1 to 2 weeks or more after transplanting. The price of tomato fruit, irrigation cost, as well as the effect of water on fruit quality, should be considered to maximize the profit of irrigation management.
Acknowledgements This work was supported in part by GREEEN Project (Generating Research and Extension to meet Environmental and Economic Needs) No GR04-008, SWMREC (Southwest Michigan
Research and Extension Center), and the Michigan Vegetable Council. Dave Francis provided technical assistance on this project and the summer student Adrianne helped in experiment set-up and data collection. Thanks to all growers in Southwest Michigan who contributed to the design of this experiment by sharing their ideas and experience, and Trevor Meachum for providing transplants in 2003.
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