THE EFFECT OF FOUR PLASTIC MULCHES ON THE TOP SOIL TEMPERATURE AND ITS RELATIONS WITH THE GROWTH AND YIELD OF MUSKMELON

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1 THE EFFECT OF FOUR PLASTIC MULCHES ON THE TOP SOIL TEMPERATURE AND ITS RELATIONS WITH THE GROWTH AND YIELD OF MUSKMELON Alejandro Zermeño and Rafael Martinez Departamento de Riego y Drenaje U.A.AA.N. Saltillo, Coahuila, Mexico. Juan Munguia Departamento de Agroplasticos C.I.Q.A. Blvd Enrique Reina Hermosillo No 149 Saltillo, Coahuila, Mexico Abstract. The effect of four plastic mulches on the soil temperature and its relations to the growth and yield of a muskmelon crop was evaluated. The plastic films studied were: black polyethylene at 37.5 and 20.0 pm, and transparent polyethylene at 37.5 and 20.0 pm. As a control, a treatment with no plastic film was included. These plastic films were evaluated at 40% and 60% of soil water content. The soil temperature was measured at a soil depth of 25, 50 and 100 mm, using copper-constantan thermocouples attached to a microdatalogger. The results of this study showed that the highest fruit yields were obtained with the plastic films of black polyethylene. These films induced an average soil temperature of C during the crop season, which was around 3 C higher than the soil temperature were no plastic film was used and around 4 C lower than those under films of transparent polyethylene. Keywords: muskmelon, plastic film, mulch, soil temperature Introduction Muskmelon is a very important crop for Mexico because it demands a considerable amount of labor for its growth and harvest and is a very important source of income for the farmers in the national market as well as the international markets. In Mexico, the use of plastic mulches in the growth of vegetables crops has increased considerably in the last few years. This is because it has been shown that the use of plastic mulches induces an early harvest, increases yields, improves the quality of the fruits, reduces the soil water evaporation, increases the soil temperature were the roots develop, and reduces the incidence of weeds The effect of a plastic film in the net radiation at the soil surface and its effects on the soil temperature depends on the spectral properties of the plastic film. These plastic films can transmit, absorb or reflect radiation in different proportions as a function of wavelength. For instance, the transparent films transmit most of the incident short wave radiation, while the black films absorb most of the incident short wave radiation. Recent studies have shown that due to the increase in the soil temperature and the reduction in the soil surface evaporation by the plastic mulches, the yield and harvest quality of some crops were 112

2 increased and harvest maturity advanced (Bhella, 1988; Maiero et al., 1987; Wien and Minotti, 1988). Other studies have found that the spectral characteristics of the reflected radiation for some plastic films may affect the temperature of the plant leaves which may have an effect on the crop water use (Hametal., 1991). Martinez (1985) conducted a field study to analyze the water use of a melon crop with and without a plastic mulch. This study was conducted at the Comarca Lagunera of Torreon Coahuila Mexico. He found that the soil water at a depth of m was 10.8% higher in the plots with black plastic films than those with no plastic mulch. Battikhi and Ghawi (1987) reported that the yield of melon was higher using a black plastic mulch than that using a transparent film. The yield with both plastic films was higher than the yield with no plastic mulch. They did not find any difference in évapotranspiration among the treatments. Most of the conducted studies have measured the soil temperature in a discrete form at time intervals of one hour or larger. This may result in errors in determining the average low or high soil temperatures at different depths. The objective of this study was to analyze the effect of four plastic films on the soil temperature at various soil depths under two soil water content levels. The relationship of the treatments on growth and yield of muskmelon crop was measured. Materials and Methods The field study was conducted on the agricultural experiment station of the plasticulture department of the research center for applied chemistry (CIQA) at Saltillo, Coahuila, Mexico, located at 25 27' of north latitude and ' of west longitude and 1610 m above sea level. A factorial randomized block with subdivided plots with 10 treatments and 4 replications was adapted as the experimental design. As the whole plots, a 40% and 60% of soil water content at the first 0.40 m of soil depth was used, while as the sub plots 4 plastic films and a control, no plastic mulch, were used. The plastic films evaluated were: black polyethylene of 37.5 and 20.0 pm, and transparent polyethylene of 37.5 and 20.0 pm. Each experimental plot consisted of three beds of 0.8 m wide by 5 m length. Only the plants at the central bed were used for growth and yield analysis. All plots were fertilized with kg/ha of N,P, an K. All fertilizer was applied by hand before seeding. The irrigation system used T-Tape with drippers spaced each 0.20 m and a flow of 250 LPH for each 100 m of tape length. The tapes were place under the plastic films at the center of the beds. Sowing was established on May 15, 1996 using the variety Crusier Fl. The seeds were placed on the beds in two rows separated 0.60 m and at a distance of 0.35 m between seeds to give a population of plants per hectare. Instrumentation and Measurements. Soil water was measured with a neutron probe. For the access of the probe, an aluminum tube of 50 mm of diameter and 1.5 m of length was buried at a depth of 1.2 m at the middle of the central beds of each treatment of two blocks. Irrigation was applied to sustain a soil water content of 40% and 60%. To measure the soil temperature, at the west part of the experimental site, 10 beds of 0.8 by 5 m were made. On these beds the 10 treatments were distributed. These beds received the same management as the beds in the experimental site. At the middle of each of these beds, copperconstantan thermocouples were placed at 25, 50 and 100 mm of soil depth, to give a total of 30 thermocouples. These thermocouples were connected to a datalogger and a multiplexer of 25 channels (Model 21X of the Campbell Sci. Inc.). The soil temperature at the three depths was scanned at a frequency of 10 seconds to obtain an average soil temperatures every 30 minutes. These measurements were taken in a continuous manner (day and night) during the crop season. 113

3 The effect of the plastic mulches on the growth and crop yield was evaluated by taking periodic measurements of leaf area index, shoot growth and dry matter production. At the end of the crop season, the total yield of fruits of each treatment was obtained. Harvest was accomplished from August 2 to September 13, Results and Discussion. Table 1 presents the mean and standard deviation (Sx) of the soil temperature at the three soil depths under the different plastic films for 40% and 60% of soil water content at the first 10 days after sowing. Note that the highest soil temperatures occur in the transparent polyethylene of 37.5 pm of all plastic films in the two soil water content. Note also that the difference in mean soil temperature between the 40% and 60% of soil water content for all treatments is very small (< 1.0 C), indicating that the difference in soil water content had no effect on the soil temperature. It can also be observed that the standard deviation at 25 mm of soil depth is the highest in all treatments which indicates that the amplitude of the soil temperature variations is larger at this depth. Thus, the highest and lowest soil temperatures occur at this depth. The Sx decreases with depth in all treatments at the two soil water content, which indicates that the amplitude of the soil temperature decreases with depth. Table 1 also shows that the mean soil temperature under all plastic films at the three depths is higher than the mean soil temperature of the control. Table 2 shows the same values of mean soil temperature and standard deviation as in Table 1 but for the time interval of 40 to 50 days after sowing. Note that the values of mean soil temperature and standard deviation are smaller in this time interval. This is due to the growing of foliage which was intercepting more solar radiation. This table also shows that the highest values of standard deviation occur at 25 mm of soil depth and that Sx decrease with depth at all treatments. Note that at this time range the mean soil temperature at 100 mm of soil depth is slightly higher than that at 25 mm of soil depth for most of the treatments at the two soil water contents. This indicates that the soil was slightly warmer at this depth. It was also observed that the mean temperature of the soil profile with the plastic films was higher than the mean temperature of the soil profile in the control. This shows that the plastic films induced a warming in the top soil profile. By looking at the values of mean soil temperature of tables 1 and 2, we can observe that the transparent films of 37.5 pm induced a higher mean soil temperature than the transparent films of 20.0 pm; while for the black plastic films, the sheets of 20.0 pm induced a higher mean soil temperature than the sheets of 37.5 pm. Similar patterns were observed at other times of the crop season. The mean soil temperature and standard deviation showed decreasing values as the crop was growing. To evaluate the effect of the plastic films on the crop growth, leaf area index, dry mater production and shoot growth were measured at different times during the crop season. At the end of the crop season the total yield of fruits were obtained (Table 3). No significant difference between the two soil water contents was observed for any variable evaluated. This indicates that the difference in soil water content had no effect on the growth and crop yield. However, significant difference between the plastic mulches and the control for all variables was observed. The highest fruit yield on the 40% of soil water content was from the black polyethylene, 20 pm with a value of 75.9 Ton/ha; while for the 60% of soil water content the highest yield was observed with the black polyethylene, 37.5 pm, with a value of 66.6 Ton/ha. From tables 1 and 2 it can be observed that the temperature of the soil profile under the black plastic films for the two soil water contents was between 25 and 27 C in the first 10 days after sowing and between 24 and 26 C from 40 to 50 days after sowing. These temperature ranges are smaller than those observed with the transparent polyethylene and higher than 114

4 Table 1. Mean and standard deviation of the soil temperature C at the three depths in the different plastic films in the first 10 days after sowing, at 40% and 60% of soil water content. TREATMENTS DEPTH SOIL WATER 40 % CONTENT 60 % (mm) Mean Sx Mean Sx Transparent polyethylene of 37.5 (im Transparent polyethylene of 20.0 nm Black polyethylene of 37.5 jxm Black polyethylene of 20.0 nm Control h. Table 2. Mean and standard deviation of the soil temperature C at the three depths in the different plastic films from days after sowing, at 40% and 60% of soil water content. TREATMENTS DEPTH SOIL WATER CONTENT 40 % 60 % (mm) Mean Sx Mean Sx Transparent polyethylene of 37.5 (un Transparent polyethylene of 20.0 (am Black polyethylene of 37.5 nm Black polyethylene of 20.0 urn Control

5 Table 3. Leaf area index (LAI), dry matter (DM), shoots growth (SG) and total fruit yield for the different plastic films for various days after sowing for 40% and 60% of soil water content. TREATMENTS DAYS AFTER SOWING LAI DM (g.) SG (m) TOTAL FRUIT YIELD t/ha 40% water Content Black of 37.5 um Black of 20.0 um Transparent of 37.5 um Transparent of 20.0 um Control % Water Content Black of 37.5 ^m Black of 20.0 im Transparent of 37,5 im Transparent of 20.0 um Control Significance Soil water content Treatments NS ** NS NS NS ** NS. Significant at 1 % of confidence Significant at 5 % of confidence Not significant 116

6 those observed in the control. These results indicate that the black plastic mulches gave an adequate temperature of the top soil profile which enhanced crop growth and fruit yield. Conclusions The temperatures of the top soil profile were higher with the plastic mulches of transparent polyethylene than those with black polyethylene. Both plastic films (transparent and black) induced a soil temperature higher than the soil temperature in the controls. The transparent films of 37.5 pm induced a higher soil temperature than the transparent films of 20.0 pm, while in the black films, the sheets of 20.0 pm induced a higher soil temperature than the sheets of 37.5 pm. No significant differences in the growth analysis and fruit yield were observed between the soil water content of 40% and 60%. However significant differences were observed with the same variables between the plastic films and the controls. The highest fruit yields were observed with the black plastic films in the two soil water content studied. These films induced an average soil temperature higher than the controls and smaller than the transparent films. Literature Cited Battikhi, A.M. and Y. Ghawi Muskmelon production under mulch and trickle Irrigation in the Jordan Valley. Hort Sci. 22(4): Bhella, H.S Tomato response to trickle Irrigation and black polyethylene mulch. J. Amer. Soc. Hort. Sci. 113: Ham, M.J., Kluitenberg, and W.J. Lamont Potential impact of plastic mulches on the above ground plant environment Proc. Nat. Agr. Plastics Cong. 21: Kansas State University, Manhattan. Maiero, M., F.D. Schales and T.J. Ng Genotype and plastic mulch effects on earliness, fruit characteristics and yield in muskmelon. Hort. Sci. 22(5): Martínez, S.J. (1985) Frecuencia del riego en el cultivo de melón (Cucumis meló L.) por transplante con y sin acolchado con plástico. Tesis Ingeniero Agrónomo. UAAAN. Saltillo, Coahuila México. 51 p. Wien H.C. and P.L. Minotti Increasing yield of tomato with plastic mulch and apex removal. J. Amer. Soc. Hort. Sci. 113: