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Lysimetric determination of muskmelon crop coefficients cultivated under plastic mulches
Agricultural Water Management 72 (2005) 147–159 www.elsevier.com/locate/agwat
Lysimetric determination of muskmelon crop coefficients cultivated under plastic mulches S. Lovelli*, S. Pizza, T. Caponio, A.R. Rivelli, M. Perniola Department of Plant Production, University of Basilicata, Viale dell’Ateneo Lucano 10, 85100 Potenza, Italy Accepted 3 September 2004
Abstract A trial was carried out at the lysimeter station in southern Italy on muskmelon crop cultivated with and without plastic mulch during spring–summer in 2001 and 2003. The objective of the experiment was to verify the reliability of the crop evapotranspiration (ETc) estimate by means of the most recent update of the FAO Irrigation and Drainage Paper 56, in comparison with ETc directly measured by two mechanical weighing lysimeters. Crop coefficients (Kc) were determined during different development stages based on lysimetric measures of ETc and of the reference evapotranspiration (ET0) estimated through the Penman Monteith and the Hargreaves methods. On melon crop cultivated without plastic mulch, corrected crop coefficients (Kc) following the last FAO Irrigation and Drainage Paper 56 procedures were well correlated with those measured from lysimeter and were as reliable as the ETc estimate. In contrast, values of Kc proposed by FAO Irrigation and Drainage Paper 56 for crops grown with plastic mulch were meaningfully lowers than those measured from lysimeter, loading to an underestimation of water consumption. On muskmelon, cultivated with and without plastic mulch, it is necessary to adapt development phase duration, suggested by the FAO Irrigation and Drainage Paper 56, to the real phenology of the employed cultivar. An adaptation of the phenology to the real duration of the single phases is essential to avoid error in the estimate of ETc. # 2004 Elsevier B.V. All rights reserved. Keywords: Muskmelon; Crop coefficients; Lysimeter; Crop evapotranspiration; Reference evapotranspiration
* Corresponding author. Tel.: +39 0971 205 384; fax: +39 0971 205 378. E-mail address: [email protected] (S. Lovelli). 0378-3774/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2004.09.009
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1. Introduction Muskmelon (Cucumis melo L. var. Inodorus Naud) is one of the major vegetable crops in Italy, grown on 22 000 cultivated hectares and producing 0.5 million tons. In the last 30 years, the surface area in muskmelon production has almost doubled. The major increase has been recorded in protected cultivation that has reached 3000 ha (Romano and Gennaro, 2000). Irrigation is needed for melon to give satisfactory yields. Yield may vary from 12 to 15 t ha1 without irrigation to 25–30 t ha1 with irrigation (Siviero and Gallerani, 1991). Even though detailed information on irrigation management of this Cucurbitaceae crop is missing or often conflicting in the literature (Bhella, 1985; Lester et al., 1994; Hartz, 1997), it is unanimously accepted that production and its components are highly influenced by the total irrigation volume (Fabiero et al., 2002) and that irrigation requirements are related to the cropping technique like the transplanting time, to the relatively deep preparatory tillage in autumn, to organic matter supply, to the possible use of mulches and to the cultivation environment (Rivelli et al., 2003). The estimate of crop evapotranspiration from meteorological data was introduced in the ’70 by the FAO Irrigation and Drainage Paper 24 (Doorenbos and Pruitt, 1977) and, after the first critical review in 1991, new standards were determined in 1998, as proposed again by the FAO and published in the Irrigation and Drainage Paper 56 (Allen et al., 1998). In their basic formulation, the various proposed models estimate reference evapotranspiration (ET0) and they subsequently derive maximum crop evapotranspiration (ETc) through crop coefficients (Kc) obtained experimentally (Kc = ETc/ET0). This method uses the two steps approach as opposed to the one step approach that evaluates the evapotranspiration rate using directly the Penman–Monteith formula with the specific resistance parameters of the crop. To estimate ET0, the FAO Paper 24 had proposed four methods (Blaney–Criddle, Radiation, FAO modified Penman, Pan evaporation), whereas the more recent FAO 56 Paper is primarily based on the Penman–Monteith method with grass resistance parameters or, in the absence of meteorological data, the new FAO standards refer to the Hargreaves– Samani method (Hargreaves and Samani, 1985). Crop coefficient takes into account the morphological and eco-physiological characteristics of the crop and the adopted cultural practices and though being specific to each crop, evapotranspiration varies in the course of the season because morphological and eco-physiological characteristics of the crop do change over time. The FAO and WMO (World Meteorological Organization) experts have summarised such evolution in the ‘‘crop coefficient curve’’ to identify the Kc value corresponding to the different crop development and growth stages (Tarantino and Spano, 2001). To make the use of Kc operational, research and experiments have been carried out worldwide, and they have led to determination of the average value that Kc may take in the course of the season over the years (Grattan et al., 1998). It is worth highlighting that the Kc is affected by all the factors that influence soil water status, for instance, the irrigation method and frequency (Doorenbos and Pruitt, 1977; Wright, 1982), the weather factors, the soil characteristics and the agronomic techniques that affect crop growth (Stanghellini et al., 1990; Tarantino and Onofrii, 1991; Cavazza, 1991; Annandale and Stockle, 1994).
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The typical empiricism of crop coefficients has been and is still considered to be the major constraint to the estimate of ETc following the ETc = ET0 Kc approach. The applied procedure to determine Kc (Kc = ETc measured by lysimeter/ET0 estimated), assumes that all the environmental, genetic and anthropic factors that affect the measured ETc values inevitably affect Kc. Consequently, the crop coefficient values reported in the literature can vary even significantly from the actual ones if growing conditions differ from those where the said coefficients were experimentally obtained (Tarantino and Onofrii, 1991). Plastic mulches in Italy are widely applied to vegetable crops and to muskmelon in particular. Plastic mulches have numerous advantages, one of them being a reduction in losses by evaporation from bare soil. Associated with the reduction in evaporation losses, transpiration increases because both sensible and radiative heat are transferred from the surface of the plastic cover to adjacent vegetation. Even though the transpiration rates in a muskmelon cantaloupe crop under plastic mulch may increase by 35%, a global reduction in the Kc value of 5–10% is reported in the literature because of reduced soil evaporation estimated to be about 80% (Battikhi and Hill, 1986). Due to the above reasons, in the case of crops under plastic mulches, the FAO Paper 56 suggests that the crop coefficients be reduced by 10–30% if applying the single crop coefficient, and by 5–15% the basal crop coefficients (Kcb) if applying the dual crop coefficient, though highlighting that the effect of this agronomic technique on crop coefficients may be even greater than the reduction suggested in some specific cultural conditions, as in the case of low crop density. However, because experimental evidence is limited, the FAO encourages local calibration of the Kc for the crops cultivated under plastic mulches. The purpose of this work was to check, in the case of muskmelon crop both with plastic mulches and no mulch, the latest update proposed by the FAO to estimate evapotranspiration.
2. Materials and methods The trial was carried out in 2001 and 2003 at the lysimeter station located in southern Italy, at the experimental farm of Basilicata region in the area of Lavello (418030 N and 158420 E), on a 70 cm deep sandy clay soil with a moisture content on weight base of 30.4% at field capacity and 16.7% at wilting point (both determined in the laboratory, respectively at 0.03 and 1.5 MPa). 2.1. Lysimeters The station consists of two mechanical precision weighing lysimeters (resolution 0.05 mm), fully sunken in the soil, whose tanks make no contact with the surrounding soil and resting on a precision balance. Water use is obtained directly by daily measuring all the components of the water balance and, in particular, the variations in soil water storage by difference in weight between two subsequent readings. After heavy rainfall, drainage water was collected by the bottom of lysimeters. The drainage volume was not considered for the
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masurement of daily crop evapotranspiration. Runoff was considered equal to zero because of the flat lying of the land. The lysimeters are metal tanks of a surface area of 4 m2, sunken in the middle of a 650 m2 plot grown with the same crop and the same techniques. Lysimeter, as well as the surrounding plot, was grown with crop cultivated with mulch, whereas the other with no mulch. At the moment of lysimeter installation the tanks were filled with the same soil taken from excavation, maintaining the original stratigraphy. A 30 cm thick layer of gravel and sand was laid at the bottom. The lysimeter depth is 1.20 m and it is enough to prevent any constraint in the development of the crop rooting system. Through a transducer (LVDT connected to the levers of the balance), the weight of the lysimeter was transformed into analogical–digital data continuously transmitted to an electronic measuring and recording system. 2.2. Weather station Both in 2001 and 2003, during the course of the whole growing cycle, climatic data were measured at a meteorological shelter situated on a grass cover adjacent to the experimental plot. The following variables were recorded: global solar radiation, maximum and minimum temperature, air humidity, wind velocity. Data were acquired on 1000 basis, averaged and recorded every 300 through a ‘‘data logger’’ (Mod. Sky DataHog2, type SDL5400). Such data were periodically downloaded from the data logger through a mobile computer and subsequently processed to get daily averages. Additional parameters, such as the saturated vapour pressure, psychometric constant, etc., were estimated from the measured meteorological data. Fig. 1 reports the temperature–rainfall pattern and the daily average pattern of global radiation for both the years of the trial. 2.3. Crop details Both in 2001 and 2003, the experimentation was carried out on ‘‘inodorus’’ group muskmelon crop (cv. Nabucco) transplanted at 2 m 1 m spacing and cultivated with and without mulching. A black plastic film, 1 m holed, was used as mulch. It covered 0.7 m of soil and was placed on the row before muskmelon transplantation. In 2001, transplanting was made on 1st June and harvesting was stepwise until 15th August. In 2003, plants were transplanted on 6th June and harvesting was step-wise until 27th August. The crop was irrigated at a fixed weekly interval, with a watering volume corresponding to full reestablishment of water use, directly measured by the lysimeter. The trickle irrigation method was adopted with dripping lines on the row and 30 cm spaced drippers of 8 l h1. Fertigation, pest and weed control were performed. 2.4. Calculating Kc The daily measurements of evapotranspiration from the lysimeter (ETc) together with reference evapotranspiration (ET0) were used to calculate the crop coefficients (Kc = ETc/ ET0). Reference evapotranspiration was estimated by the Penman–Monteith formula with the typical resistance terms of reference grass (1) (Smith et al., 1990) and (Hargreaves and Samani, 1985) (2).
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Fig. 1. Daily temperature–rainfall and global radiation pattern measured at Lavello in 2001 and 2003 during muskmelon cycle.
The following formulas were used: ET0 ¼
DðRn GÞ þ rCp ðea ed Þ=ra D þ gð1 þ rc =ra Þ
(1)
D is the slope vapour pressure curve (kPa 8C1); Rn the net radiation at the crop surface (MJ m2 s1); G the soil heat flux density (MJ m2 s1); r the mean air density (kg m3); Cp the specific heat (MJ kg1 8C1); ea the saturation vapour pressure (KPa); ed the actual vapour pressure (KPa); ra the aerodynamic resistance (s m1); g the psychometric constant (kPa C1); rc the canopy resistance (s m1). ET0 ¼ 0:0023ðTmean þ 17:8ÞðTmax Tmin Þ0:5 Ra
(2)
Tmean, Tmax, Tmin is the mean, maximum and minimum air temperature (8C); Ra the extraterrestrial solar radiation (mm day1), astronomic tabulated value. The crop coefficients thus measured were related to those proposed by the FAO in the last FAO Irrigation and Drainage Paper 56. The following algorithms were used:
the ‘‘dual approach’’ for the crop under mulch; Kc = Kc basal + Kc soil evaporation, taking Kc soil evaporation = 0; Kc initial = Kc basal tabulated 0.9; Kc mid-season = (Kc basal tabulated + 0.04 (u2 2) 0.004 (RHmin 45))(h/3)0.3 0.9 Kc end = (Kc basal tabulated + 0.04 (u2 2) 0.004 (RHmin 45))(h/3)0.3 0.9
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where RHmin is the minimum relative air humidity (%); h the crop height (m); u2 the wind speed at 2 m above ground surface (m s1). By this approach, the Kc for the crops under mulch is calculated assuming the evaporation losses from bare soil to be zero. The basal crop coefficients, always estimated referring to the bare soil, were further reduced by 10% as they consider minimum losses by evaporation. The basal coefficients thus estimated from the data tabulated in Paper 56 for each growth stage of the melon crop, were also adjusted considering the effect of climatic variables on the ETc/ET0 ratio, referring to the average cropping period values of wind speed (u2), and minimum relative air humidity (RHmin) from a historical thirty-year series measured on site (Tarantino et al., 1997). Finally, a further correction factor suggested by the FAO considers the aerodynamic effect of crop geometry on the evapotranspiration rate versus the canopy height (h). For the crop with no mulch, the Kc values were estimated using the ‘‘single approach’’. More in particular: Kc initial = fw Kc ini, Kc mid-season = (Kc tabulated + 0.04 (u2 2) 0.004 (RHmin 45))(h/3)0.3 Kc end = (Kc tabulated + 0.04 (u2 2) 0.004 (RHmin 45))(h/3)0.3 where Kc ini is tabulated and fw is a storage factor that considers the volume of soil actually wetted depending on the irrigation method and the adopted cropping technique. In the case of trickle-irrigated muskmelon with 2 m spaced dripping lines, the FAO proposes a value of fw equal to 0.3. As previously explained, the tabulated values of mid-season and of the late season Kc were adjusted depending on the climatic variables and the crop height.
3. Results and discussion Fig. 2 reports, for the 2 years of the trial (2001–2003), the daily pattern of maximum evapotranspiration measured by the lysimeter and the estimated one (ETc = ET0 Kc) using the Penman Monteith (Eq. (1)) and Hargreaves (Eq. (2)) methods and the crop coefficients proposed by the FAO Paper 56, respectively for the crop under mulch and no mulch. The evapotranspiration measured from the lysimeter for a muskmelon crop with no mulch (Fig. 2) showed the typical rising pattern at the development stage and a decrease later, as related to leaf area development. At the beginning of the cycle, the average ETc values ranged from a minimum of about 1.2 and 1.5 mm day1, respectively in 2001 and 2003, to an average maximum value in the period of peak vegetative growth of 6.1 and 5.8 mm day1, respectively in the first and the second year. Conversely, in the crop under mulch, the average ETc values at the beginning of the cycle ranged from a minimum of about 1.0 and 0.9 mm day1, respectively in 2001 and 2003 to a maximum of about 6.0 and 7.7 mm day1 during the period of maximum vegetative growth, respectively in the first and the second year. Moreover, for the crop with no mulch, drying cycles of the soil between two successive irrigations were evident at the early stage when, due to limited ground cover, evaporation from bare soil is very high. Although the said drying cycles were not well simulated in the
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Fig. 2. Daily maximum evapotranspiration measured from lysimeter and stimated by ET0 crop coefficients of ID56 Paper on muskmelon crop cultivated with plastic mulch (a) and without (b) in 2001 and 2003.
estimate of ETc (indeed the ‘‘single approach’’ to estimate Kc does not include such type of simulation), as a whole, evapotranspiration estimated by the FAO method was well correlated and corresponded to the measured values. In the case of mulching, evapotranspiration measured from the lysimeter was lower than in the crop with no mulch only during the early 15 days of the cycle, because of reduced evaporation losses from bare soil. Later on, water use suddenly increased and, also, in the period of full development, a higher evaporation rate was observed as compared with the crop with no mulch. As a whole, total water use measured for the crop under mulch (307 and 314 mm, respectively in 2001 and 2003) was higher with respect to the measured one in the crop without mulch (248 and 266 mm, respectively in 2001 and 2003). In fact, plastic mulch, on one hand reduce evaporation losses almost to zero, on the other hand, it create a more favourable growing environment to plant development. Greater availability of water to the plant, modified soil temperature regime, undisturbed rooting system as a result of non tillage on the row, preservation of soil structure thanks to no-trampling near the plant, and no weed competition, are the main reasons for the typical luxuriant vegetative growth of crops under mulch. As a matter of fact, plastic mulches have favoured luxuriant vegetative growth since the maximum measured value of the leaf area index was equal to 2.0 and 1.4, respectively in 2001 and 2003 in the crop under mulch and 1.6 and 1.1, respectively in 2001 and 2003 in the crop with no mulch; this accounts for the greater water use measured in the treatments under mulch. Fig. 3 shows the existing correlation between ETc measured directly through the lysimeters both for the crop under mulching and no mulch, with ETc estimated following the two steps approach, using the Kc values reported in the FAO Irrigation and Drainage
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Fig. 3. Relation between estimated and measured by lisymeter crop evapotranspiration (ETc) of muskmelon crop cultivated with (a) and without (b) plastic mulch.
Paper 56 and calculating ET0 using the Hargreaves (Eq. (2)), Penman–Monteith (Eq. (1)) methods and the average value of ET0 obtained from these two formulas. The results of the statistical regression analysis between the measured and estimated ETc values are reported in Table 1. It is known that the line having a slope not significantly different from 1 and non-significant intercept indicates full agreement between estimated and measured values. The results reported in Table 1 and in Fig. 3 show, in general, a greater correlation in the case of the crop without mulching (r2 = 0.8**) as compared with the crop under mulch (r2 = 0.7**). As again from Fig. 3 and Table 1, despite the good correlation between the values of estimated and measured ETc in the case of the crop cultivated with mulch, a significant underestimate of evapotranspiration of 32% and 22% (Fig. 2) was observed, respectively,
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Table 1 Regression statistics of measured and estimated ETc by various methodsa Estimation method
Regression line slope
Regression line intercept
With plastic mulches
Hargreaves Penman–Monteith Mean
1.34 0.07 1.24 0.07 1.34 0.07
0.11 n.s. 0.31 n.s. 0.05 n.s.
Without plastic mulches
Hargreaves Penman- Monteith Mean
1.00 0.05 0.95 0.04 1.00 0.04
0.17 n.s. 0.25 n.s. 0.09 n.s.
a
Number of observations, n = 150.
with the FAO method in 2001 and in 2003, whereas the estimate was fully reliable in the case of the crop on bare soil. For this reason, contrary to what happened in the crop without mulch, it is thought that some uncertainty does exist in the estimate of ETc by the FAO method in the case of the crop under mulch and this should be mainly be attributed, as we will see later, to the estimate of Kc. Finally, the analysis of the slopes and of the corresponding standard errors reported in Table 1, allows stating that there are no significant differences in the estimate of ETc using the formulas of Hargreaves (Eq. (2)) and Penman–Monteith (Eq. (1)). Therefore, at least in sub-humid climate where the experiment was performed, if meteorological data required to apply the Penman–Monteith method are not available, one may use the Hargreaves method, which only requires maximum and minimum air temperature, without invalidating the estimate of ET0.
Fig. 4. Relation between estimated and measured by lysimeter crop coefficients (Kc) during muskmelon cycle cultivated with (a) and without plastic mulch (b) in 2001 and 2003.
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In the case of muskmelon crop with no mulch, Fig. 4 shows the good reliability of Kc reported in the FAO Paper 56. Fig. 5 highlights a good correlation between estimated Kc values and those really measured by the lysimeter (r2 = 0.8**, slope of the regression line equal to 1.1 statistically not different from 1). Conversely, Fig. 4 shows, for the crop under mulch, a good agreement of the estimated Kc values with the measured ones only at the initial stage of the cycle, followed by a significant underestimate of the FAO crop coefficients at the stage of maximum canopy development. As a matter of fact, despite the good correlation between the estimated and measured Kc values (Fig. 5) (r2 = 0.7**), the slope of the regression line was equal to 1.3, statistically different from 1. In a verification work as this one, we should not neglect the estimate of the length of each single growth stage since Kc pattern over time depends on it and thus, by correctly defining the growth stages, a more accurate estimate of water use is possible.
Fig. 5. Relation between estimated and measured by lysimeter crop coefficients during muskmelon cycle cultivated with (a) and without plastic mulch (b).
Initial 2001
Phenologic phases lengths observed on field (days) FAO phenologic phases lengths (days) M: mulch; NM: no mulch.
2003
Crop development
Mead season
2001
2001
2003
Late season 2003
2001
Total 2003
2001
2003
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
10
20
10
30
41
31
28
21
25
25
19
17
–
–
18
14
76
76
75
82
10
60
25
25
120
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Table 2 Lengths of melon phenologic phases
157
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The FAO Paper 56 proposes a growing cycle of 120 days for muskmelon, this being longer than the length actually observed in the field for the cultivar grown and respectively equal to 76 days in 2001 and to 75 and 82 days in 2003, in the crop under mulching and no mulch (Table 2). The possible use of the Kc values proposed in the FAO Paper 56, making no changes to phenology, would have implied a significant overestimate with respect to the real water use of the crop and no agreement with the actually measured Kc and ETc values (r2 of the regression line between the Kc values estimated according to the FAO growth stages and the measured ones, respectively equal to 0.3 and 0.4 in the case of the crop under mulching and no mulch, data not shown). Table 2 reports the length of each single growth stage measured with respect to those proposed by the FAO, both for the mulched crop and for the one on bare soil; in particular, some reduction in the growing cycle length is highlighted. From that the importance of having more detailed information on the growth stage length of the investigated species, that, in some cases, can vary even greatly between the different cultivars, in order to further improve accuracy in the estimate of ETc.
4. Conclusion From the current research on muskmelon to evaluate the latest update to FAO procedures for estimating crop coefficients, the following conclusions are drawn: The updating of the procedures brought in FAO Irrigation and Drainage Paper 56 allows an accurate ETc estimate in the case of muskmelon cultivated without plastic mulch. Further research is necessary to determine Kc corrections when plastic mulches are used, to avoid underestimating the water consumptions. New algorithms are required to simulate changes in Kc depending on the crop growth stage to further improve accuracy in the ETc estimate.
References Allen, R.G., Pereira, L.S., Raes, D., Smith, M. 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. FAO Irrigation Drainage Paper No. 56, FAO, Rome, Italy, 300 pp. Annandale, J.G., Stockle, C.O., 1994. Fluctuation of crop evapotranspiration coefficients with weather. A sensitivity analysis. Irrig. Sci. 15, 1–7. Battikhi, A.M., Hill, R.W., 1986. Irrigation scheduling and cantaloupe yield model for the Jordan Valley. Agric. Water Manage. 16, 177–187. Bhella, H.S., 1985. Muskmelon growth, yield and nutrition as influenced by planting method and trickle irrigation. J. Am. Soc. Hort. Sci. 110, 793–796. Cavazza, L., 1991. Valutazione dell’evapotraspirazione delle colture. Evapotraspirazione: chiarimenti concettuali preliminari. In: Proceedings of the Meeting ‘‘Irrigazione e Ricerca’’. pp. 97–102. Doorenbos J., Pruitt W.O., 1977. Crop water rquirements. FAO Irrigation Drainage Paper No. 24, FAO, Rome, Italy, 144 pp. Fabiero, C., Martin De Santa Olalla, F., De Juan, J.A., 2002. Production of muskmelon (Cucumis melo L.) under controlled deficit irrigation in a semi-arid climate. Agric. Water Manage. 54, 93–105. Grattan, S.R., Bowers, W., Dong, A., Snyder, R., Caroll, J.J., Gerge, W., 1998. New crop coefficients estimate water use of vegetables, row crops. Calif. Agric. 52 (1), 16–21.
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Hargreaves, G.H., Samani, Z.A., 1985. Reference Crop evapotranspiration from temperature. Appl. Eng. Agric. 1 (2), 96–99. Hartz, T.K., 1997. Effects of drip irrigation scheduling on muskmelon yield and quality. Scientia Horticulturae 69, 117–122. Lester, G.E., Oebker, N.F., Coons, J., 1994. Preharvest furrow and drip irrigation schedule effects on postharvest muskmelon quality. Postharvest Biol. Technol. 4, 57–63. Rivelli, A.R., Lovelli, S., Pizza, S., Perniola, M., 2003. Irrigazione e pacciamatura in coltura di melone: II Consumi idrici e risposta produttiva. Italus Hortus 10 (6), 68–73. Romano, D., Gennaro, L., 2000. Prodotti ortofrutticoli tipici del meridione italiano: caratterizzazione agronomica e nutrizionale. Agricoltura Ricerca 185, 3–46. Siviero, P., Gallerani, M., 1991. Supplemento melone. Inf. Agr. 46, 5–71. Smith, M., Allen, R.G., Pereira, L.S., Perrier, A., 1990. Report of the expert consultation on procedures for revision of FAO guidelines for prediction of crop water requirements. UN-FAO, Rome, Italy, 54 pp. Stanghellini, C., Bosma, A.H., Gabriels, P.C.J., Werkoven, C., 1990. The water consumption of agricultural crops: how crop coefficient are affected by crop geometry and microclimate. Acta Horticulturae 278, 509–516. Tarantino, E., Ferrara, A., Quaglietta Chiaranda`, F., De Franchi, A.S., Perniola, M., Nuzzo, V., 1997. Studio agronomico del comprensorio di bonifica di Bradano e Metaponto per la gestione delle risorse idriche a fini irrigui. D.P.V., R.B., C.B.B.M, Potenza, Italy. Tarantino, E., Onofrii, M., 1991. Determinazione dei coefficienti colturali mediante lisimetri. Bonifica 7, 119–136. Tarantino, E., Spano, D., 2001. La valutazione dei fabbisogni irrigui. Riv. di Irr. e Dren. 48 (4), 21–35. Wright, J.L., 1982. New evapotranspiration crop ceofficients. J. Irrig. Drainage Div. ASCE 108, 57–74.
Lysimetric determination of muskmelon crop coefficients cultivated under plastic mulches S. Lovelli*, S. Pizza, T. Caponio, A.R. Rivelli, M. Perniola Department of Plant Production, University of Basilicata, Viale dell’Ateneo Lucano 10, 85100 Potenza, Italy Accepted 3 September 2004
Abstract A trial was carried out at the lysimeter station in southern Italy on muskmelon crop cultivated with and without plastic mulch during spring–summer in 2001 and 2003. The objective of the experiment was to verify the reliability of the crop evapotranspiration (ETc) estimate by means of the most recent update of the FAO Irrigation and Drainage Paper 56, in comparison with ETc directly measured by two mechanical weighing lysimeters. Crop coefficients (Kc) were determined during different development stages based on lysimetric measures of ETc and of the reference evapotranspiration (ET0) estimated through the Penman Monteith and the Hargreaves methods. On melon crop cultivated without plastic mulch, corrected crop coefficients (Kc) following the last FAO Irrigation and Drainage Paper 56 procedures were well correlated with those measured from lysimeter and were as reliable as the ETc estimate. In contrast, values of Kc proposed by FAO Irrigation and Drainage Paper 56 for crops grown with plastic mulch were meaningfully lowers than those measured from lysimeter, loading to an underestimation of water consumption. On muskmelon, cultivated with and without plastic mulch, it is necessary to adapt development phase duration, suggested by the FAO Irrigation and Drainage Paper 56, to the real phenology of the employed cultivar. An adaptation of the phenology to the real duration of the single phases is essential to avoid error in the estimate of ETc. # 2004 Elsevier B.V. All rights reserved. Keywords: Muskmelon; Crop coefficients; Lysimeter; Crop evapotranspiration; Reference evapotranspiration
* Corresponding author. Tel.: +39 0971 205 384; fax: +39 0971 205 378. E-mail address: [email protected] (S. Lovelli). 0378-3774/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2004.09.009
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1. Introduction Muskmelon (Cucumis melo L. var. Inodorus Naud) is one of the major vegetable crops in Italy, grown on 22 000 cultivated hectares and producing 0.5 million tons. In the last 30 years, the surface area in muskmelon production has almost doubled. The major increase has been recorded in protected cultivation that has reached 3000 ha (Romano and Gennaro, 2000). Irrigation is needed for melon to give satisfactory yields. Yield may vary from 12 to 15 t ha1 without irrigation to 25–30 t ha1 with irrigation (Siviero and Gallerani, 1991). Even though detailed information on irrigation management of this Cucurbitaceae crop is missing or often conflicting in the literature (Bhella, 1985; Lester et al., 1994; Hartz, 1997), it is unanimously accepted that production and its components are highly influenced by the total irrigation volume (Fabiero et al., 2002) and that irrigation requirements are related to the cropping technique like the transplanting time, to the relatively deep preparatory tillage in autumn, to organic matter supply, to the possible use of mulches and to the cultivation environment (Rivelli et al., 2003). The estimate of crop evapotranspiration from meteorological data was introduced in the ’70 by the FAO Irrigation and Drainage Paper 24 (Doorenbos and Pruitt, 1977) and, after the first critical review in 1991, new standards were determined in 1998, as proposed again by the FAO and published in the Irrigation and Drainage Paper 56 (Allen et al., 1998). In their basic formulation, the various proposed models estimate reference evapotranspiration (ET0) and they subsequently derive maximum crop evapotranspiration (ETc) through crop coefficients (Kc) obtained experimentally (Kc = ETc/ET0). This method uses the two steps approach as opposed to the one step approach that evaluates the evapotranspiration rate using directly the Penman–Monteith formula with the specific resistance parameters of the crop. To estimate ET0, the FAO Paper 24 had proposed four methods (Blaney–Criddle, Radiation, FAO modified Penman, Pan evaporation), whereas the more recent FAO 56 Paper is primarily based on the Penman–Monteith method with grass resistance parameters or, in the absence of meteorological data, the new FAO standards refer to the Hargreaves– Samani method (Hargreaves and Samani, 1985). Crop coefficient takes into account the morphological and eco-physiological characteristics of the crop and the adopted cultural practices and though being specific to each crop, evapotranspiration varies in the course of the season because morphological and eco-physiological characteristics of the crop do change over time. The FAO and WMO (World Meteorological Organization) experts have summarised such evolution in the ‘‘crop coefficient curve’’ to identify the Kc value corresponding to the different crop development and growth stages (Tarantino and Spano, 2001). To make the use of Kc operational, research and experiments have been carried out worldwide, and they have led to determination of the average value that Kc may take in the course of the season over the years (Grattan et al., 1998). It is worth highlighting that the Kc is affected by all the factors that influence soil water status, for instance, the irrigation method and frequency (Doorenbos and Pruitt, 1977; Wright, 1982), the weather factors, the soil characteristics and the agronomic techniques that affect crop growth (Stanghellini et al., 1990; Tarantino and Onofrii, 1991; Cavazza, 1991; Annandale and Stockle, 1994).
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The typical empiricism of crop coefficients has been and is still considered to be the major constraint to the estimate of ETc following the ETc = ET0 Kc approach. The applied procedure to determine Kc (Kc = ETc measured by lysimeter/ET0 estimated), assumes that all the environmental, genetic and anthropic factors that affect the measured ETc values inevitably affect Kc. Consequently, the crop coefficient values reported in the literature can vary even significantly from the actual ones if growing conditions differ from those where the said coefficients were experimentally obtained (Tarantino and Onofrii, 1991). Plastic mulches in Italy are widely applied to vegetable crops and to muskmelon in particular. Plastic mulches have numerous advantages, one of them being a reduction in losses by evaporation from bare soil. Associated with the reduction in evaporation losses, transpiration increases because both sensible and radiative heat are transferred from the surface of the plastic cover to adjacent vegetation. Even though the transpiration rates in a muskmelon cantaloupe crop under plastic mulch may increase by 35%, a global reduction in the Kc value of 5–10% is reported in the literature because of reduced soil evaporation estimated to be about 80% (Battikhi and Hill, 1986). Due to the above reasons, in the case of crops under plastic mulches, the FAO Paper 56 suggests that the crop coefficients be reduced by 10–30% if applying the single crop coefficient, and by 5–15% the basal crop coefficients (Kcb) if applying the dual crop coefficient, though highlighting that the effect of this agronomic technique on crop coefficients may be even greater than the reduction suggested in some specific cultural conditions, as in the case of low crop density. However, because experimental evidence is limited, the FAO encourages local calibration of the Kc for the crops cultivated under plastic mulches. The purpose of this work was to check, in the case of muskmelon crop both with plastic mulches and no mulch, the latest update proposed by the FAO to estimate evapotranspiration.
2. Materials and methods The trial was carried out in 2001 and 2003 at the lysimeter station located in southern Italy, at the experimental farm of Basilicata region in the area of Lavello (418030 N and 158420 E), on a 70 cm deep sandy clay soil with a moisture content on weight base of 30.4% at field capacity and 16.7% at wilting point (both determined in the laboratory, respectively at 0.03 and 1.5 MPa). 2.1. Lysimeters The station consists of two mechanical precision weighing lysimeters (resolution 0.05 mm), fully sunken in the soil, whose tanks make no contact with the surrounding soil and resting on a precision balance. Water use is obtained directly by daily measuring all the components of the water balance and, in particular, the variations in soil water storage by difference in weight between two subsequent readings. After heavy rainfall, drainage water was collected by the bottom of lysimeters. The drainage volume was not considered for the
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masurement of daily crop evapotranspiration. Runoff was considered equal to zero because of the flat lying of the land. The lysimeters are metal tanks of a surface area of 4 m2, sunken in the middle of a 650 m2 plot grown with the same crop and the same techniques. Lysimeter, as well as the surrounding plot, was grown with crop cultivated with mulch, whereas the other with no mulch. At the moment of lysimeter installation the tanks were filled with the same soil taken from excavation, maintaining the original stratigraphy. A 30 cm thick layer of gravel and sand was laid at the bottom. The lysimeter depth is 1.20 m and it is enough to prevent any constraint in the development of the crop rooting system. Through a transducer (LVDT connected to the levers of the balance), the weight of the lysimeter was transformed into analogical–digital data continuously transmitted to an electronic measuring and recording system. 2.2. Weather station Both in 2001 and 2003, during the course of the whole growing cycle, climatic data were measured at a meteorological shelter situated on a grass cover adjacent to the experimental plot. The following variables were recorded: global solar radiation, maximum and minimum temperature, air humidity, wind velocity. Data were acquired on 1000 basis, averaged and recorded every 300 through a ‘‘data logger’’ (Mod. Sky DataHog2, type SDL5400). Such data were periodically downloaded from the data logger through a mobile computer and subsequently processed to get daily averages. Additional parameters, such as the saturated vapour pressure, psychometric constant, etc., were estimated from the measured meteorological data. Fig. 1 reports the temperature–rainfall pattern and the daily average pattern of global radiation for both the years of the trial. 2.3. Crop details Both in 2001 and 2003, the experimentation was carried out on ‘‘inodorus’’ group muskmelon crop (cv. Nabucco) transplanted at 2 m 1 m spacing and cultivated with and without mulching. A black plastic film, 1 m holed, was used as mulch. It covered 0.7 m of soil and was placed on the row before muskmelon transplantation. In 2001, transplanting was made on 1st June and harvesting was stepwise until 15th August. In 2003, plants were transplanted on 6th June and harvesting was step-wise until 27th August. The crop was irrigated at a fixed weekly interval, with a watering volume corresponding to full reestablishment of water use, directly measured by the lysimeter. The trickle irrigation method was adopted with dripping lines on the row and 30 cm spaced drippers of 8 l h1. Fertigation, pest and weed control were performed. 2.4. Calculating Kc The daily measurements of evapotranspiration from the lysimeter (ETc) together with reference evapotranspiration (ET0) were used to calculate the crop coefficients (Kc = ETc/ ET0). Reference evapotranspiration was estimated by the Penman–Monteith formula with the typical resistance terms of reference grass (1) (Smith et al., 1990) and (Hargreaves and Samani, 1985) (2).
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Fig. 1. Daily temperature–rainfall and global radiation pattern measured at Lavello in 2001 and 2003 during muskmelon cycle.
The following formulas were used: ET0 ¼
DðRn GÞ þ rCp ðea ed Þ=ra D þ gð1 þ rc =ra Þ
(1)
D is the slope vapour pressure curve (kPa 8C1); Rn the net radiation at the crop surface (MJ m2 s1); G the soil heat flux density (MJ m2 s1); r the mean air density (kg m3); Cp the specific heat (MJ kg1 8C1); ea the saturation vapour pressure (KPa); ed the actual vapour pressure (KPa); ra the aerodynamic resistance (s m1); g the psychometric constant (kPa C1); rc the canopy resistance (s m1). ET0 ¼ 0:0023ðTmean þ 17:8ÞðTmax Tmin Þ0:5 Ra
(2)
Tmean, Tmax, Tmin is the mean, maximum and minimum air temperature (8C); Ra the extraterrestrial solar radiation (mm day1), astronomic tabulated value. The crop coefficients thus measured were related to those proposed by the FAO in the last FAO Irrigation and Drainage Paper 56. The following algorithms were used:
the ‘‘dual approach’’ for the crop under mulch; Kc = Kc basal + Kc soil evaporation, taking Kc soil evaporation = 0; Kc initial = Kc basal tabulated 0.9; Kc mid-season = (Kc basal tabulated + 0.04 (u2 2) 0.004 (RHmin 45))(h/3)0.3 0.9 Kc end = (Kc basal tabulated + 0.04 (u2 2) 0.004 (RHmin 45))(h/3)0.3 0.9
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where RHmin is the minimum relative air humidity (%); h the crop height (m); u2 the wind speed at 2 m above ground surface (m s1). By this approach, the Kc for the crops under mulch is calculated assuming the evaporation losses from bare soil to be zero. The basal crop coefficients, always estimated referring to the bare soil, were further reduced by 10% as they consider minimum losses by evaporation. The basal coefficients thus estimated from the data tabulated in Paper 56 for each growth stage of the melon crop, were also adjusted considering the effect of climatic variables on the ETc/ET0 ratio, referring to the average cropping period values of wind speed (u2), and minimum relative air humidity (RHmin) from a historical thirty-year series measured on site (Tarantino et al., 1997). Finally, a further correction factor suggested by the FAO considers the aerodynamic effect of crop geometry on the evapotranspiration rate versus the canopy height (h). For the crop with no mulch, the Kc values were estimated using the ‘‘single approach’’. More in particular: Kc initial = fw Kc ini, Kc mid-season = (Kc tabulated + 0.04 (u2 2) 0.004 (RHmin 45))(h/3)0.3 Kc end = (Kc tabulated + 0.04 (u2 2) 0.004 (RHmin 45))(h/3)0.3 where Kc ini is tabulated and fw is a storage factor that considers the volume of soil actually wetted depending on the irrigation method and the adopted cropping technique. In the case of trickle-irrigated muskmelon with 2 m spaced dripping lines, the FAO proposes a value of fw equal to 0.3. As previously explained, the tabulated values of mid-season and of the late season Kc were adjusted depending on the climatic variables and the crop height.
3. Results and discussion Fig. 2 reports, for the 2 years of the trial (2001–2003), the daily pattern of maximum evapotranspiration measured by the lysimeter and the estimated one (ETc = ET0 Kc) using the Penman Monteith (Eq. (1)) and Hargreaves (Eq. (2)) methods and the crop coefficients proposed by the FAO Paper 56, respectively for the crop under mulch and no mulch. The evapotranspiration measured from the lysimeter for a muskmelon crop with no mulch (Fig. 2) showed the typical rising pattern at the development stage and a decrease later, as related to leaf area development. At the beginning of the cycle, the average ETc values ranged from a minimum of about 1.2 and 1.5 mm day1, respectively in 2001 and 2003, to an average maximum value in the period of peak vegetative growth of 6.1 and 5.8 mm day1, respectively in the first and the second year. Conversely, in the crop under mulch, the average ETc values at the beginning of the cycle ranged from a minimum of about 1.0 and 0.9 mm day1, respectively in 2001 and 2003 to a maximum of about 6.0 and 7.7 mm day1 during the period of maximum vegetative growth, respectively in the first and the second year. Moreover, for the crop with no mulch, drying cycles of the soil between two successive irrigations were evident at the early stage when, due to limited ground cover, evaporation from bare soil is very high. Although the said drying cycles were not well simulated in the
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Fig. 2. Daily maximum evapotranspiration measured from lysimeter and stimated by ET0 crop coefficients of ID56 Paper on muskmelon crop cultivated with plastic mulch (a) and without (b) in 2001 and 2003.
estimate of ETc (indeed the ‘‘single approach’’ to estimate Kc does not include such type of simulation), as a whole, evapotranspiration estimated by the FAO method was well correlated and corresponded to the measured values. In the case of mulching, evapotranspiration measured from the lysimeter was lower than in the crop with no mulch only during the early 15 days of the cycle, because of reduced evaporation losses from bare soil. Later on, water use suddenly increased and, also, in the period of full development, a higher evaporation rate was observed as compared with the crop with no mulch. As a whole, total water use measured for the crop under mulch (307 and 314 mm, respectively in 2001 and 2003) was higher with respect to the measured one in the crop without mulch (248 and 266 mm, respectively in 2001 and 2003). In fact, plastic mulch, on one hand reduce evaporation losses almost to zero, on the other hand, it create a more favourable growing environment to plant development. Greater availability of water to the plant, modified soil temperature regime, undisturbed rooting system as a result of non tillage on the row, preservation of soil structure thanks to no-trampling near the plant, and no weed competition, are the main reasons for the typical luxuriant vegetative growth of crops under mulch. As a matter of fact, plastic mulches have favoured luxuriant vegetative growth since the maximum measured value of the leaf area index was equal to 2.0 and 1.4, respectively in 2001 and 2003 in the crop under mulch and 1.6 and 1.1, respectively in 2001 and 2003 in the crop with no mulch; this accounts for the greater water use measured in the treatments under mulch. Fig. 3 shows the existing correlation between ETc measured directly through the lysimeters both for the crop under mulching and no mulch, with ETc estimated following the two steps approach, using the Kc values reported in the FAO Irrigation and Drainage
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Fig. 3. Relation between estimated and measured by lisymeter crop evapotranspiration (ETc) of muskmelon crop cultivated with (a) and without (b) plastic mulch.
Paper 56 and calculating ET0 using the Hargreaves (Eq. (2)), Penman–Monteith (Eq. (1)) methods and the average value of ET0 obtained from these two formulas. The results of the statistical regression analysis between the measured and estimated ETc values are reported in Table 1. It is known that the line having a slope not significantly different from 1 and non-significant intercept indicates full agreement between estimated and measured values. The results reported in Table 1 and in Fig. 3 show, in general, a greater correlation in the case of the crop without mulching (r2 = 0.8**) as compared with the crop under mulch (r2 = 0.7**). As again from Fig. 3 and Table 1, despite the good correlation between the values of estimated and measured ETc in the case of the crop cultivated with mulch, a significant underestimate of evapotranspiration of 32% and 22% (Fig. 2) was observed, respectively,
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Table 1 Regression statistics of measured and estimated ETc by various methodsa Estimation method
Regression line slope
Regression line intercept
With plastic mulches
Hargreaves Penman–Monteith Mean
1.34 0.07 1.24 0.07 1.34 0.07
0.11 n.s. 0.31 n.s. 0.05 n.s.
Without plastic mulches
Hargreaves Penman- Monteith Mean
1.00 0.05 0.95 0.04 1.00 0.04
0.17 n.s. 0.25 n.s. 0.09 n.s.
a
Number of observations, n = 150.
with the FAO method in 2001 and in 2003, whereas the estimate was fully reliable in the case of the crop on bare soil. For this reason, contrary to what happened in the crop without mulch, it is thought that some uncertainty does exist in the estimate of ETc by the FAO method in the case of the crop under mulch and this should be mainly be attributed, as we will see later, to the estimate of Kc. Finally, the analysis of the slopes and of the corresponding standard errors reported in Table 1, allows stating that there are no significant differences in the estimate of ETc using the formulas of Hargreaves (Eq. (2)) and Penman–Monteith (Eq. (1)). Therefore, at least in sub-humid climate where the experiment was performed, if meteorological data required to apply the Penman–Monteith method are not available, one may use the Hargreaves method, which only requires maximum and minimum air temperature, without invalidating the estimate of ET0.
Fig. 4. Relation between estimated and measured by lysimeter crop coefficients (Kc) during muskmelon cycle cultivated with (a) and without plastic mulch (b) in 2001 and 2003.
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In the case of muskmelon crop with no mulch, Fig. 4 shows the good reliability of Kc reported in the FAO Paper 56. Fig. 5 highlights a good correlation between estimated Kc values and those really measured by the lysimeter (r2 = 0.8**, slope of the regression line equal to 1.1 statistically not different from 1). Conversely, Fig. 4 shows, for the crop under mulch, a good agreement of the estimated Kc values with the measured ones only at the initial stage of the cycle, followed by a significant underestimate of the FAO crop coefficients at the stage of maximum canopy development. As a matter of fact, despite the good correlation between the estimated and measured Kc values (Fig. 5) (r2 = 0.7**), the slope of the regression line was equal to 1.3, statistically different from 1. In a verification work as this one, we should not neglect the estimate of the length of each single growth stage since Kc pattern over time depends on it and thus, by correctly defining the growth stages, a more accurate estimate of water use is possible.
Fig. 5. Relation between estimated and measured by lysimeter crop coefficients during muskmelon cycle cultivated with (a) and without plastic mulch (b).
Initial 2001
Phenologic phases lengths observed on field (days) FAO phenologic phases lengths (days) M: mulch; NM: no mulch.
2003
Crop development
Mead season
2001
2001
2003
Late season 2003
2001
Total 2003
2001
2003
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
M
NM
10
20
10
30
41
31
28
21
25
25
19
17
–
–
18
14
76
76
75
82
10
60
25
25
120
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Table 2 Lengths of melon phenologic phases
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The FAO Paper 56 proposes a growing cycle of 120 days for muskmelon, this being longer than the length actually observed in the field for the cultivar grown and respectively equal to 76 days in 2001 and to 75 and 82 days in 2003, in the crop under mulching and no mulch (Table 2). The possible use of the Kc values proposed in the FAO Paper 56, making no changes to phenology, would have implied a significant overestimate with respect to the real water use of the crop and no agreement with the actually measured Kc and ETc values (r2 of the regression line between the Kc values estimated according to the FAO growth stages and the measured ones, respectively equal to 0.3 and 0.4 in the case of the crop under mulching and no mulch, data not shown). Table 2 reports the length of each single growth stage measured with respect to those proposed by the FAO, both for the mulched crop and for the one on bare soil; in particular, some reduction in the growing cycle length is highlighted. From that the importance of having more detailed information on the growth stage length of the investigated species, that, in some cases, can vary even greatly between the different cultivars, in order to further improve accuracy in the estimate of ETc.
4. Conclusion From the current research on muskmelon to evaluate the latest update to FAO procedures for estimating crop coefficients, the following conclusions are drawn: The updating of the procedures brought in FAO Irrigation and Drainage Paper 56 allows an accurate ETc estimate in the case of muskmelon cultivated without plastic mulch. Further research is necessary to determine Kc corrections when plastic mulches are used, to avoid underestimating the water consumptions. New algorithms are required to simulate changes in Kc depending on the crop growth stage to further improve accuracy in the ETc estimate.
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