- Email: [email protected]
Evaporation and evapotranspiration in a watermelon field mulched with gravel of different sizes in northwest China
Agricultural Water Management 81 (2006) 173–184 www.elsevier.com/locate/agwat
Evaporation and evapotranspiration in a watermelon field mulched with gravel of different sizes in northwest China Zhongkui Xie, Yajun Wang *, Wenlan Jiang, Xinghu Wei Cold and Arid Regions Environmental and Engineering Research Institute (CAREERI), Chinese Academy of Sciences, 260 Dongang West Road, 730000 Lanzhou, PR China Accepted 17 April 2005 Available online 10 May 2005
Abstract Trials were conducted to study the effects of decreasing evapotranspiration and evaporation under mulching with coarse sand and gravel of different sizes in a watermelon field in the Loess Plateau of northwest China in 2004. The trials involved four treatments: mulching with coarse sand and gravel of various diameters (2–5, 5–20, and 20–60 mm) and no mulching (control). In addition, the soil surface was mulched with gravel of five size classes in 10 microlysimeters and the same initial water content to determine the relationship between evaporation and gravel size. Ten microlysimeters were filled with six soil samples with different initial water content, and the soil surface was mulched with uniformly sized gravel to study the effect of soil moisture on evaporation. The results showed that there was a significant difference in evapotranspiration and evaporation between treatments: evaporation increased linearly with gravel size. Mulching with 2–5 mm diameter sand and gravel resulted in significantly less evapotranspiration than mulching with 5–20 and 20–60 mm diameter sand and gravel. By comparison, evapotranspiration with 2–5 mm diameter sand and gravel was not significantly different from that with the control. The relationship between evaporation and soil moisture under gravel mulch could be represented mathematically by a cubic curve. Evaporation was decreased little when the soil moisture was reduced from 27% to 8% with gravel mulch. Evaporation and the ratio of evaporation to evapotranspiration (E/ET) increased with the diameter of sand and gravel. The E/ET ratio was 40.7% in the growing period for the control, and it was only 17.8–25.0% for treatments mulched with sand and gravel. Soil evaporation with nonmulching was reduced by 78.0–93.7 mm when plastic film was mulched on the gravel surface and by 16.9–26.3 mm with gravel * Corresponding author. Tel.: +86 931 4967198; fax: +86 931 8273894. E-mail address: [email protected] (Y. Wang). 0378-3774/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2005.04.004
174
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
mulching only. The yield was not obviously different between treatments with gravel of various sizes, but water use efficiency was significantly higher for mulching with 2–5 mm diameter gravel than for mulching with 20–60 mm diameter gravel. In addition, the soluble carbohydrate content decreased for small-diameter gravel. # 2005 Elsevier B.V. All rights reserved. Keywords: Soil evaporation; Crop evapotranspiration; Yield; Gravel size; Mulch
1. Introduction The major objectives of agricultural water conservation practices are to store nongrowing-season precipitation in the soil and to efficiently use it and the water that becomes available during the growing-season for crop production (Unger, 1971). Efficient rainwater use can be achieved by various soil and water conservation practices. In arid/semi-arid regions, mulching is a common and effective practice to reduce evaporation artificially. The mulching materials used have ranged from sand, gravel, and plant and animal residues to synthetic polyethylene (e.g., see Rasiah and Yamamoto, 2002, for a review). Gravel is a preferred material, particularly in developing countries, because of its availability and low cost. In northwest China, gravel mulching has been used to conserve the sporadic and limited rainfall (Gale et al., 1993). Lemon (1956), Corey and Kemper (1968), Unger (1971), Modaihsh et al. (1985), and Groenevelt et al. (1989) have all pointed out that relatively thin surface layers of gravels and coarse sands can reduce evaporation to 10–20% of that occurring from recently wetted unmulched soil surfaces. Kemper et al. (1994) found the effect of evaporation reduction varies with the thickness, color, and particle size of the sand and gravel mulched on the soil surface. Red sandstone and gray granite mulch permitted more water to be lost than white feldspar and quartz mulch. Most studies agree that the greater the thickness of the fragment layer the higher the soil moisture content will be. Corey and Kemper (1968) noted in Colorado that a 12 mm gravel mulch effected greater water savings, by preventing evaporation, than a 6 mm layer, but water conservation increased no further with a 25 mm layer. Yamanaka et al. (2004) showed that gravel mulch increased the resistance to water vapor transfer within the mulch layer. The relationship between the resistance and the thickness of the layer is not linear but exponential, because of air turbulence penetrating the gravel mulch. The size of the particles covering the soil has a strong influence on water budget. Perez (1991) sampled the water content in sandy talus under large single boulders, where moisture was higher than in bare contiguous soil; the difference in water content between the sand and the soil under blocks increased nearly eight times with block size (46–88 cm); this may have resulted from more effective insulation and evaporation reduction by the larger boulders. Corey and Kemper (1968) noted that the grain size of the mulch layer should be significant mainly in relation to the texture of the underlying soil and that evaporation would be reduced only if the gravel particles were bigger than the grains of the soil beneath. When sand particles are <0.1 mm in diameter, they provide sufficient capillary action to maintain liquid-phase continuity at the mulch–air interface during the early stages of the water-loss cycle. Consequently, they are not as effective in reducing water loss as coarser sands and gravels (Modaihsh et al., 1985). Many studies have attempted to evaluate the effect of gravel mulch
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
175
on evaporation by comparing evaporation rate or cumulative evaporation from a mulched soil surface with a bare soil in laboratory experiments (e.g., Hanks and Woodruff, 1958; Groenevelt et al., 1989; van Wesemael et al., 1996; Mellouli et al., 2000; Perez, 2000; Rasiah et al., 2001). However, little attention has been paid to the effect of the particle size of sand and gravel on evaporation from soil. Evaporation from the soil can be measured or estimated in a number of ways (Monteith, 1965; Ritchie, 1972; Arkin et al., 1974; Ashktorab et al., 1989). The microlysimeter method is arguably the simplest and most direct and independent way to measure evaporation. Daamen et al. (1993) showed that the method could provide a simple and accurate measurement of evaporation from sandy soils. The study suggested lysimeters and liners that were constructed of polyvinyl chloride (PVC) pipe with an internal diameter of 50 mm and a length of 100 mm. In sandy soils, the main sources of error were root extraction of water from the lysimeter and impeded drainage at the base of the lysimeter following rain. To decrease the error, a protocol for the use of microlysimeters was developed by Daamen et al. from the results of that study. A number of earlier studies (Jara et al., 1998; Eastham et al., 1999; Jackson and Wallace, 1999) used microlysimeters to measure evaporation.
2. Materials and methods 2.1. Climate and soil This study was conducted at the Gaolan Research Station of Ecology and Agriculture, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences. The station is located in the Loess Plateau of northwest China (Gaolan County, Lanzhou, Gansu Province, 368130 N, 1038470 E) at an elevation of approximately 1800 m asl. From 30 years of records (1962–1992), mean annual rainfall was calculated as being 263 mm, with nearly 70% falling between May and September. Average annual pan evaporation is 1786 mm. Mean annual temperature is 8.4 8C, with a mean maximum of 20.7 8C in July and a mean minimum of 9.1 8C in January. The depth to the water table is >120 m, which is too deep for the groundwater to be useful. The soil is a silt loam (sand: 123 g kg1; silt: 669 g kg1; clay: 208 g kg1) of loess origin. The measured field capacity and permanent wilting point averaged 24.5 and 9.0% by weight. The bulk density for 1.6 m was 1.33 g cm3. 2.2. Experimental design Three experiments were designed for this study. 2.2.1. Experiment 1 Field studies aiming at examining the response of evapotranspiration (ET) and evaporation to the particle size of sand and gravel mulched in a watermelon field were conducted in 2004. Treatments consisted of a control (CK), which was without mulched sand and gravel, and mulching with sand and gravel in three particle-size ranges: 2–5 mm
176
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
(treatment A), 5–20 mm (treatment B), and 20–60 mm (treatment C). All the treatments were randomized, with three replications. The plots were 2.4 m 7 m, with 50 cm spacing between plots. For mulch treatments, sand and gravel were mulched to 7 cm thickness on the soil surface. On 25 April 2004, watermelon (Xinong-8) was seeded at an in-row spacing of 1.0 m in rows that were 0.6 m apart. During the entire watermelon growing period, 80% of the area of each plot was mulched with plastic film of 0.012 mm thickness and 1.1 m width. In the experimental fields, 30 000 kg of manure, 1500 kg of oil-caked fertilizer, 150 kg of N, 90 kg of P2O5, and 99 kg of K2O were applied per hectare. The gravimetric soil water content was measured at 10 cm intervals in the 0–40 cm soil layer and at 20 cm intervals in the 40–160 cm soil layer in four randomly selected soil cores for each plot. Soil samples were obtained every 10 days between planting and harvesting. The samples of soil were oven-dried at 105 8C for 24 h. The average water content for 0– 160 cm depth for each sampling date was used in the statistical analysis. A standard rain gauge was used to record the amount of rainfall. Evapotranspiration (ET) was determined by the following formula: ET ¼ P þ I D DW
(1)
where P is the watermelon growing-season precipitation (mm); I is the amount of irrigation (mm) measured with a water meter; D is the drainage (mm); and DW is the variation in water content of the soil profile (mm) between planting and harvest or between the growth stages. According to the measurements taken on the experimental site by Li and Gong (2002), during 60% of the rainfall events the total rainfall was <5 mm, and for 79% of the rainfall events, intensities were <5 mm/h. Because the experimental area was level, no surface runoff occurred. The soil moisture measurements indicate that drainage at the site was negligible. Water use efficiency (WUE) was calculated as yield divided by total ET. Measurements of soil evaporation were made with microlysimeters (Fig. 1) containing undisturbed samples (Daamen et al., 1993) at 08:00 every day. The microlysimeter casing and the pipe lining the holes in which the microlysimeter were mounted were both constructed from unplasticised PVC pipe. The microlysimeter was 11 cm in internal
Fig. 1. Microlysimeter in a field mulched with gravel.
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
177
diameter and 15 cm in length. The liner tube was 12 cm in internal diameter and the same length. Care was taken to minimize the gap between the microlysimeter and the liner. The weight loss was recorded by an electric scale (sensitivity, 0.01 g) put into the liner tube. Both tubes were put into the pit where undisturbed soil had been taken. Soil cores were taken manually by alternately inserting the microlysimeter casing 2–3 cm in the soil and then excavating a slightly oversized pillar of soil to a depth 2–3 cm below the base of the core. When the required depth was reached the cores were trimmed flush at the base and were placed on a sheet-metal base plate and sealed with waterproof tape. The microlysimeter was then mounted in a liner tube, with its surface slightly above the soil surface. The microlysimeters on mulch plots were covered to the same thickness with sand and gravel of uniform size. Nylon gauze was placed between the gravel and the soil to prevent them from mixing. The prevention of evaporation by the nylon gauze was far less than from gravel. Therefore, the effect of the nylon gauze on evaporation was negligible. Four lysimeters were installed every treatment to measure evaporation. For gravel-mulched and non-gravel-mulched treatments, 80% of the plot area was covered with plastic film. Therefore, two lysimeters were placed below the plastic film, and others were in place without any plastic film mulch. Lysimeters with undisturbed soil were weighed at 08:00 every morning. Soil core was renewed after 4 days for sand and gravel mulching treatments and after 2 days for control. However, the core was immediately renewed after rainfall events. Evaporation (E) was determined by the following formula, E ¼ 0:8EP þ 0:2EN
(2)
where EP is the evaporation measured from lysimeters with plastic film mulching; and EN is the evaporation measured from lysimeters without mulching. Watermelons were harvested in late July. The total number of melons and their weight were determined for each plot. In addition, five watermelons were randomly selected to determine soluble solids content with a hand-held refractometer (Mu´jica-Paz et al., 2003). All data were subjected to analysis of variance, and means were tested by least significant difference procedures for each experiment. 2.2.2. Experiment 2 Soil samples of the same water content were put into 10 small lysimeters. Gravel of five mean diameters (1.1, 1.7, 2.5, 3, and 4 cm) was mulched on the soil surface in lysimeters. The gravel of each diameter was mulched with two replications and 7 cm thickness. Microlysimeters with undisturbed soil cores were weighed at 08:00 every day from 16 July to 12 August 2004. Lysimeters were installed in the watermelon field after being weighed. Soil core was renewed after 2 days and rainfall events. 2.2.3. Experiment 3 Experiment 3 was designed with six initial soil water contents: 46, 40, 34, 28, 23, and 13% of soil dry weight. Soil of each moisture content was put into two microlysimeters. Dry soil and water weight in each microlysimeter was recorded. The gravel with 2.5 cm diameter was mulched to 7 cm thickness on the soil surface in the microlysimeter. Microlysimeters with undisturbed soil cores were weighed at 08:00 every day from 16 to 31
178
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
August 2004. Lysimeters were installed in the watermelon field after being weighed. Soil water content was calculated as (water weight in microlysmeter weight lost by evaporation)/(soil dry weight).
3. Results and discussions 3.1. Rainfall characteristics Rainfall was 121 mm during the watermelon growing period (from 25 April to 26 July) in 2004. There were 10 rainfall events of >3 mm totaling 114 mm, which amounted to 58.8% of the total rainfall events and 94.2% of the total rainfall (Fig. 2). 3.2. Evapotranspiration and evaporation from the soil surface The results of experiment 1 showed that ET was significantly increased for treatments B and C (gravel of 5–20 and 20–60 mm particle size, respectively) compared with treatments A (gravel of 5–20 mm particle size) and CK (control) (Table 1). However, there was no significant difference between treatments A and CK. The increase in ET was due to more soil water use with mulch of larger diameter gravel than with mulch of small-diameter gravel or with no gravel mulch. Evaporation from the soil surface was significantly higher for the control than for treatments with gravel mulch (Table 1). Gravel mulch in the watermelon field decreased evaporation by 17.7–34.2 mm. Evaporation in treatment C was the highest among mulching treatments, followed by that in treatment B. The minimum value was for treatment A. Thus, the results indicated that evaporation increased with gravel size. Mulch with gravel in the watermelon field reduced the ratio of evaporation to evapotranspiration (E/ET) because of the decrease in E for all mulched treatments and also the increase in ET
Fig. 2. Distribution of rainfall during the watermelon growing period in 2004.
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
179
Table 1 E and ET in watermelon field Gravel size (mm) (treatment)
Rainfall (mm)
CSWC (mm)
ET (mm)
E (mm)
E/ET
2–5 (A) 5–20 (B) 20–60 (C) 0 (CK)
121 121 121 121
26.7 46.7 54.0 27.8
147.7 167.7 171.0 148.8
26.3 32.5 42.8 60.5
0.18 0.19 0.25 0.41
a b b a
a b c d
Note: CK, control; CSWC, change of soil water content during the growing period. Different letters in a column denote significant differences between treatments at p < 0.05.
for treatments B and C. Evaporation was 41% of ET for treatment CK. However, it was only 18% for treatment A. Evaporation was lower in the places with plastic film mulch than where there was no plastic mulch for all gravel-mulched treatments and the control (Fig. 3). Evaporation was 24 mm for soil mulched with both gravel of 2–5 mm diameter and plastic film, which was lower by 94 mm than that for bare soil in the control. The ratio of evaporation mulched with plastic to evaporation without plastic (EP/EN) was found to range from a maximum of 0.65 for the control to a minimum with 0.43 for treatment C. The results showed that the suppressing effect of plastic film on evaporation decreased in the gravel-mulched field, which was due to the increased space between the plastic film and the gravel surface when plastic film was mulched on the larger diameter gravel. The mean rate of evaporation every 10 days was lower for treatment B than with treatment CK (Fig. 4). The maximum rate of evaporation was 0.83 mm day1 for treatment CK and 0.47 mm day1 for treatment B. There was little difference in the rates of ET and evaporation in the first 20 days after sowing. However, the ET rate increased with the growth stages and reached the maximum of 3.06 mm day1 for the control and 3.74 mm day1 for treatment B during 5–15 July, which was 3.7 and 8 times higher than evaporation, respectively. Evapotranspiration was higher for the control than with treatment B at early stages because of high evaporation. The high ET resulted in a low soil water content, which caused a lower ET for the control than for treatment B at the middle and late stages.
Fig. 3. Comparison of evaporation with and without plastic film mulch for all gravel mulching treatments and the control (CK).
180
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
Fig. 4. Comparison of the rate of evaporation (E) and the rate of evapotranspiration (ET) for the mulching treatment with gravel of 5–20 mm particle size and for the control (CK) during the watermelon growing period in 2004.
3.3. Relationship between evaporation and soil moisture under gravel mulch The relationship between evaporation and soil moisture on fine days from 16 to 31 August under gravel mulch (experiment 3) shown in Fig. 5 indicated that the relationship could be represented by a cubic curve. The equation obtained by regression analysis is as follows: E ¼ 0:2114 þ 0:2005m 0:0127m2 þ 0:00024m3
(3)
where E is evaporation (mm/day); m is the soil moisture in experiment 3 (kg kg1); and R2 = 0.915. Fig. 5 shows that evaporation from the soil surface increased when soil water content reached oversaturation and there was water in the mulching layer. However, there was little decrease in evaporation when the soil moisture was reduced from 27% to 8% in gravel mulch treatments.
Fig. 5. Relationship between evaporation and soil moisture under gravel mulch. (The diameter of the gravel was about 25 mm.)
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
181
The total resistance, rt, to evaporation from the bare soil surface is the sum of resistances in the atmosphere (ra) and on the soil surface (rs). However, in the gravel-mulched field, the resistance in the mulch layer (rm) is added as a component of total resistance, rt (Yamanaka et al., 2004); that is, rt ¼ ra þ rm þ rs
(4)
When the soil and mulch layers were saturated by water, rt = ra, because rs = rm = 0. The evaporation from the soil surface approached potential evaporation. Therefore, the value was very high when the soil moisture was at its highest (Fig. 5). When the soil surface is sufficiently wet (i.e., rs = 0), rt ¼ ra þ rm
(5)
The value of rs increased with decreasing soil moisture and with the development of a dry surface layer. The rt of evaporation from a mulched surface varied little when the soil water content change from 27% to 8%; the results showed that the mulch resistance, rm, was far higher than the soil surface resistance, rs. Gravel mulch increased rt and reduced evaporative losses because of extremely low unsaturated hydraulic conductivity at low suctions; the capillary movement of water to the surface of the gravel layer was thus prevented, and upward water transport through the gravel occurred only by vapor diffusion (Poesen and Lavee, 1994). But the evaporation declined when the soil water content was below 8%. That showed that rs was large enough to affect rt of evaporation from a mulched surface. When microlysimeters are used to measure evaporation, errors may occur if the soil within the microlysimeter has a water content or temperature that is significantly different from that of the surrounding soil. To minimize the errors, Daamen et al. (1993) suggested that the ideal renewal schedule should be to extract cores from the soil profile immediately after rain and to renew these cores within 12 h, then remove them daily until root extraction of water from the soil to the microlysimeter depth becomes insignificant (of the order of 4 days after rain). Gravel mulch decreased the difference between the temperature of the microlysimeter and that of the surrounding soil. There was little impact of soil water content on evaporation when the content was reduced from 27% to 8% in the gravel mulch treatments. Thus, temperature and soil water content were not main sources of error. However, disturbance of the soil in the extraction process increased evaporation from the lysimeter. Therefore, renewal of the soil core within 4 days for gravel mulching treatments was appropriate. 3.4. The relationship between evaporation and gravel size The evaporation with every particle-size class was averaged for 10 fine days after 27 July (experiment 2) in mulched soil where the moisture was >8%. The relationship between E and particle size (S) was linear (Fig. 6), and the equation obtained by regression analysis is as follows: E ¼ 0:3587 þ 0:0134S where R2 = 0.99.
(6)
182
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
Fig. 6. Relationship between evaporation and gravel particle size.
Table 2 Watermelon yield, soluble carbohydrate content, and WUE Gravel size (mm) (treatment)
Yield (kg m2)
Soluble carbohydrate content (%)
WUE (kg m2)
2–5 (A) 5–20 (B) 20–60 (C) 0 (CK)
33300 35964 32468 14985
10.0 10.3 11.0 9.0
22.5 21.4 19.0 10.1
a a a b
b b c a
c cb b a
Note: CK, control; WUE, water use efficiency. Different letters in a column denote significant differences between treatments at p < 0.05.
Fig. 6 indicates that evaporation from the mulched surface increased as gravel size increased from 1.1 to 4 cm. 3.5. Yield, soluble carbohydrate content, and water use efficiency The result of experiment 1 (Table 2) indicated that yield, soluble carbohydrate content, and WUE were significantly lower for the control than for all mulched treatments. Gravel mulch not only increased watermelon yield, but also improved the soluble carbohydrate content and WUE. There was not a significantly difference in yield between the various gravel mulching treatments. However, the soluble carbohydrate content was significantly higher and WUE was significantly lower for the treatment mulched with 20–60 mm diameter gravel than for that with 2–5 mm diameter gravel. Mulching with small sized gravel improved WUE because of decreasing evaporation from the soil surface. The increased soluble carbohydrate content with large-diameter gravel mulch was considered related to the increase difference in the soil temperature.
4. Conclusions Gravel mulch significantly decreased evaporation from the soil surface. Evaporation increased linearly with gravel size. The E/ET ratio also increased with gravel size.
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
183
Evaporation was reduced when the gravel surface in the watermelon field was mulched with plastic film. The relationship between evaporation and soil moisture under gravel mulch could be represented by a cubic curve. There was little reduction in evaporation when the soil moisture decreased from 27% to 8% in the gravel mulch treatments. Evaporation decreased, though, when soil moisture was <8%. Yield, soluble carbohydrate content, and WUE were significantly lower for the control than for all mulched treatments. However, there was no significant difference between treatments mulched with gravel of different sizes. The soluble carbohydrate content was significantly higher and WUE was significantly lower for the treatment mulched with 20– 60 mm diameter gravel than for the treatment mulched with 2–5 mm diameter gravel.
Acknowledgements We are grateful for financial support for the project from the Office of Agricultural Program, Chinese Academy of Sciences (NK15-C-09). We also thank Mrs. Wilson, an English teacher in the ESEC Program, Lanzhou, China, for editing help.
References Arkin, G.F., Ritchie, J.T., Adams, J.E., 1974. A method for measuring first stage soil water evaporation in the field. Soil Sci. Soc. Am. Proc. 38, 951–954. Ashktorab, H., Pruitt, W.O., Paw, U.K.T., George, W.V., 1989. Energy balance determinations close to the soil surface using a micro-Bowen system. Agric. For. Meteorol. 46, 259–274. Corey, A.T., Kemper, W.D., 1968. Conservation of soil water by gravel mulches, Hydrol. Pap. No. 30. Colorado State University, Fort Collins, CO, 23 pp. Daamen, Carl, C., Simmonds, L.P., Wallace, J.S., Laryea, K.B., Sivakumar, M.V.K., 1993. Use of microlysimeters to measure evaporation from sandy soils. Agric. For. Meteorol. 65, 159–173. Eastham, J., Gregory, P.J., Williamson, D.R., Watson, G.D., 1999. The influence of early sowing of wheat and lupin crops on evapotranspiration and evaporation from the soil surface in a Mediterranean climate. Agric. Water Manage. 42, 205–218. Gale, W.J., McColl, R.W., Fang, X., 1993. Sandy fields traditional farming water conservation in China. J. Soil Water Conserv. 48, 474–477. Groenevelt, P.H., Van Straaten, P., Rasiah, V., Simpson, J., 1989. Modifications in evaporation parameters by rock mulches. Soil Technol. 2, 279–285. Hanks, R.J., Woodruff, N.P., 1958. Influences of wind on water vapor transfer through soil, gravel and straw mulches. Soil Sci. 86, 160–164. Jara, J., Stockle, C.O., Kjelgaard, J., 1998. Measurement of evapotranspiration and its components in a corn (Zea Mays L.) field. Agric. For. Meteorol. 92, 131–145. Jackson, N.A., Wallace, J.S., 1999. Soil evaporation measurements in an agroforestry system in Kenya. Agric. For. Meteorol. 94, 203–215. Kemper, W.D., Nicks, A.D., Corey, A.T., 1994. Accumulation of water in soils under sand and gravel mulches. Soil Sci. Soc. Am. J. 58, 56–63. Lemon, E.R., 1956. The potentialities for decreasing soil moisture evaporation loss. Soil Sci. Soc. Am. Proc. 20, 120–125. Li, X.Y., Gong, J.D., 2002. Compacted catchment with local earth materials for rainwater harvesting in the semiarid region of China. J. Hydrol. 257, 134–144.
184
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
Mellouli, H.J., van Wesemael, B., Poesen, J., Hartmann, R., 2000. Evaporation losses from bare soils as influenced by cultivation techniques in semi-arid regions. Agric. Water Manage. 42, 355–369. Modaihsh, A.S., Horton, R., Kirkham, D., 1985. Soil water evaporation suppression by sand mulches. Soil Sci. 139, 357–361. Monteith, J.L., 1965. Evaporation and environment. In: Fogg, G.E. (Ed.), Proceedings of the 19th Symposium of the Society for Experimental Biology, vol. 19, Swansea, Wales. Cambridge University Press, Cambridge, UK, pp. 205–234. Mu´jica-Paz, H., Valdez-Fragoso, A., Lo´pez-Malo, A., Palou, E., Welti-Chanes, J., 2003. Impregnation and osmotic dehydration of some fruits: effect of the vacuum pressure and syrup concentration. J. Food Eng. 57, 305–314. Perez, F.L., 1991. Soil moisture and the distribution of giant Andean rosettes on talus slopes of a desert paramo. Clim. Res. 1, 217–231. Perez, F.L., 2000. The influence of surface volcaniclastic layers from Haleakala (Maui, Hawaii) on soil water conservation. Catena 38, 301–332. Poesen, J.W., Lavee, H., 1994. Rock fragments in top soils: significance and processes. Catena 23, 1–28. Rasiah, V., Yamamoto, T., 2002. Mulching, evaporation, and salinity interrelation in an arid/semi-arid environment. Rural Environ. Eng. 42, 36–43. Rasiah, V., Imai, M., Yamamoto, T., Inoue, M., 2001. Evaporation losses from dune sand: influence of column and gravel mulch size. J. Arid Land Stud. 11, 177–186. Ritchie, J.T., 1972. Model for predicting evaporation from a row crop with incomplete cover. Water Resour. Res. 8, 1204–1213. Unger, P.W., 1971. Soil profile gravel layers effect on water storage distribution and evaporation. Soil Sci. Soc. Am. Proc. 35, 631–634. van Wesemael, B., Poesen, J., Kosmas, C.S., Danalatos, N.G., Nachtergaele, J., 1996. Evaporation from cultivated soils containing rock fragments. J. Hydrol. 182, 65–82. Yamanaka, T., Inoue, M., Kaihotsu, I., 2004. Effects of gravel mulch on water vapor transfer above and below the soil surface. Agric. Water Manage. 67, 145–155.
Evaporation and evapotranspiration in a watermelon field mulched with gravel of different sizes in northwest China Zhongkui Xie, Yajun Wang *, Wenlan Jiang, Xinghu Wei Cold and Arid Regions Environmental and Engineering Research Institute (CAREERI), Chinese Academy of Sciences, 260 Dongang West Road, 730000 Lanzhou, PR China Accepted 17 April 2005 Available online 10 May 2005
Abstract Trials were conducted to study the effects of decreasing evapotranspiration and evaporation under mulching with coarse sand and gravel of different sizes in a watermelon field in the Loess Plateau of northwest China in 2004. The trials involved four treatments: mulching with coarse sand and gravel of various diameters (2–5, 5–20, and 20–60 mm) and no mulching (control). In addition, the soil surface was mulched with gravel of five size classes in 10 microlysimeters and the same initial water content to determine the relationship between evaporation and gravel size. Ten microlysimeters were filled with six soil samples with different initial water content, and the soil surface was mulched with uniformly sized gravel to study the effect of soil moisture on evaporation. The results showed that there was a significant difference in evapotranspiration and evaporation between treatments: evaporation increased linearly with gravel size. Mulching with 2–5 mm diameter sand and gravel resulted in significantly less evapotranspiration than mulching with 5–20 and 20–60 mm diameter sand and gravel. By comparison, evapotranspiration with 2–5 mm diameter sand and gravel was not significantly different from that with the control. The relationship between evaporation and soil moisture under gravel mulch could be represented mathematically by a cubic curve. Evaporation was decreased little when the soil moisture was reduced from 27% to 8% with gravel mulch. Evaporation and the ratio of evaporation to evapotranspiration (E/ET) increased with the diameter of sand and gravel. The E/ET ratio was 40.7% in the growing period for the control, and it was only 17.8–25.0% for treatments mulched with sand and gravel. Soil evaporation with nonmulching was reduced by 78.0–93.7 mm when plastic film was mulched on the gravel surface and by 16.9–26.3 mm with gravel * Corresponding author. Tel.: +86 931 4967198; fax: +86 931 8273894. E-mail address: [email protected] (Y. Wang). 0378-3774/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2005.04.004
174
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
mulching only. The yield was not obviously different between treatments with gravel of various sizes, but water use efficiency was significantly higher for mulching with 2–5 mm diameter gravel than for mulching with 20–60 mm diameter gravel. In addition, the soluble carbohydrate content decreased for small-diameter gravel. # 2005 Elsevier B.V. All rights reserved. Keywords: Soil evaporation; Crop evapotranspiration; Yield; Gravel size; Mulch
1. Introduction The major objectives of agricultural water conservation practices are to store nongrowing-season precipitation in the soil and to efficiently use it and the water that becomes available during the growing-season for crop production (Unger, 1971). Efficient rainwater use can be achieved by various soil and water conservation practices. In arid/semi-arid regions, mulching is a common and effective practice to reduce evaporation artificially. The mulching materials used have ranged from sand, gravel, and plant and animal residues to synthetic polyethylene (e.g., see Rasiah and Yamamoto, 2002, for a review). Gravel is a preferred material, particularly in developing countries, because of its availability and low cost. In northwest China, gravel mulching has been used to conserve the sporadic and limited rainfall (Gale et al., 1993). Lemon (1956), Corey and Kemper (1968), Unger (1971), Modaihsh et al. (1985), and Groenevelt et al. (1989) have all pointed out that relatively thin surface layers of gravels and coarse sands can reduce evaporation to 10–20% of that occurring from recently wetted unmulched soil surfaces. Kemper et al. (1994) found the effect of evaporation reduction varies with the thickness, color, and particle size of the sand and gravel mulched on the soil surface. Red sandstone and gray granite mulch permitted more water to be lost than white feldspar and quartz mulch. Most studies agree that the greater the thickness of the fragment layer the higher the soil moisture content will be. Corey and Kemper (1968) noted in Colorado that a 12 mm gravel mulch effected greater water savings, by preventing evaporation, than a 6 mm layer, but water conservation increased no further with a 25 mm layer. Yamanaka et al. (2004) showed that gravel mulch increased the resistance to water vapor transfer within the mulch layer. The relationship between the resistance and the thickness of the layer is not linear but exponential, because of air turbulence penetrating the gravel mulch. The size of the particles covering the soil has a strong influence on water budget. Perez (1991) sampled the water content in sandy talus under large single boulders, where moisture was higher than in bare contiguous soil; the difference in water content between the sand and the soil under blocks increased nearly eight times with block size (46–88 cm); this may have resulted from more effective insulation and evaporation reduction by the larger boulders. Corey and Kemper (1968) noted that the grain size of the mulch layer should be significant mainly in relation to the texture of the underlying soil and that evaporation would be reduced only if the gravel particles were bigger than the grains of the soil beneath. When sand particles are <0.1 mm in diameter, they provide sufficient capillary action to maintain liquid-phase continuity at the mulch–air interface during the early stages of the water-loss cycle. Consequently, they are not as effective in reducing water loss as coarser sands and gravels (Modaihsh et al., 1985). Many studies have attempted to evaluate the effect of gravel mulch
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
175
on evaporation by comparing evaporation rate or cumulative evaporation from a mulched soil surface with a bare soil in laboratory experiments (e.g., Hanks and Woodruff, 1958; Groenevelt et al., 1989; van Wesemael et al., 1996; Mellouli et al., 2000; Perez, 2000; Rasiah et al., 2001). However, little attention has been paid to the effect of the particle size of sand and gravel on evaporation from soil. Evaporation from the soil can be measured or estimated in a number of ways (Monteith, 1965; Ritchie, 1972; Arkin et al., 1974; Ashktorab et al., 1989). The microlysimeter method is arguably the simplest and most direct and independent way to measure evaporation. Daamen et al. (1993) showed that the method could provide a simple and accurate measurement of evaporation from sandy soils. The study suggested lysimeters and liners that were constructed of polyvinyl chloride (PVC) pipe with an internal diameter of 50 mm and a length of 100 mm. In sandy soils, the main sources of error were root extraction of water from the lysimeter and impeded drainage at the base of the lysimeter following rain. To decrease the error, a protocol for the use of microlysimeters was developed by Daamen et al. from the results of that study. A number of earlier studies (Jara et al., 1998; Eastham et al., 1999; Jackson and Wallace, 1999) used microlysimeters to measure evaporation.
2. Materials and methods 2.1. Climate and soil This study was conducted at the Gaolan Research Station of Ecology and Agriculture, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences. The station is located in the Loess Plateau of northwest China (Gaolan County, Lanzhou, Gansu Province, 368130 N, 1038470 E) at an elevation of approximately 1800 m asl. From 30 years of records (1962–1992), mean annual rainfall was calculated as being 263 mm, with nearly 70% falling between May and September. Average annual pan evaporation is 1786 mm. Mean annual temperature is 8.4 8C, with a mean maximum of 20.7 8C in July and a mean minimum of 9.1 8C in January. The depth to the water table is >120 m, which is too deep for the groundwater to be useful. The soil is a silt loam (sand: 123 g kg1; silt: 669 g kg1; clay: 208 g kg1) of loess origin. The measured field capacity and permanent wilting point averaged 24.5 and 9.0% by weight. The bulk density for 1.6 m was 1.33 g cm3. 2.2. Experimental design Three experiments were designed for this study. 2.2.1. Experiment 1 Field studies aiming at examining the response of evapotranspiration (ET) and evaporation to the particle size of sand and gravel mulched in a watermelon field were conducted in 2004. Treatments consisted of a control (CK), which was without mulched sand and gravel, and mulching with sand and gravel in three particle-size ranges: 2–5 mm
176
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
(treatment A), 5–20 mm (treatment B), and 20–60 mm (treatment C). All the treatments were randomized, with three replications. The plots were 2.4 m 7 m, with 50 cm spacing between plots. For mulch treatments, sand and gravel were mulched to 7 cm thickness on the soil surface. On 25 April 2004, watermelon (Xinong-8) was seeded at an in-row spacing of 1.0 m in rows that were 0.6 m apart. During the entire watermelon growing period, 80% of the area of each plot was mulched with plastic film of 0.012 mm thickness and 1.1 m width. In the experimental fields, 30 000 kg of manure, 1500 kg of oil-caked fertilizer, 150 kg of N, 90 kg of P2O5, and 99 kg of K2O were applied per hectare. The gravimetric soil water content was measured at 10 cm intervals in the 0–40 cm soil layer and at 20 cm intervals in the 40–160 cm soil layer in four randomly selected soil cores for each plot. Soil samples were obtained every 10 days between planting and harvesting. The samples of soil were oven-dried at 105 8C for 24 h. The average water content for 0– 160 cm depth for each sampling date was used in the statistical analysis. A standard rain gauge was used to record the amount of rainfall. Evapotranspiration (ET) was determined by the following formula: ET ¼ P þ I D DW
(1)
where P is the watermelon growing-season precipitation (mm); I is the amount of irrigation (mm) measured with a water meter; D is the drainage (mm); and DW is the variation in water content of the soil profile (mm) between planting and harvest or between the growth stages. According to the measurements taken on the experimental site by Li and Gong (2002), during 60% of the rainfall events the total rainfall was <5 mm, and for 79% of the rainfall events, intensities were <5 mm/h. Because the experimental area was level, no surface runoff occurred. The soil moisture measurements indicate that drainage at the site was negligible. Water use efficiency (WUE) was calculated as yield divided by total ET. Measurements of soil evaporation were made with microlysimeters (Fig. 1) containing undisturbed samples (Daamen et al., 1993) at 08:00 every day. The microlysimeter casing and the pipe lining the holes in which the microlysimeter were mounted were both constructed from unplasticised PVC pipe. The microlysimeter was 11 cm in internal
Fig. 1. Microlysimeter in a field mulched with gravel.
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
177
diameter and 15 cm in length. The liner tube was 12 cm in internal diameter and the same length. Care was taken to minimize the gap between the microlysimeter and the liner. The weight loss was recorded by an electric scale (sensitivity, 0.01 g) put into the liner tube. Both tubes were put into the pit where undisturbed soil had been taken. Soil cores were taken manually by alternately inserting the microlysimeter casing 2–3 cm in the soil and then excavating a slightly oversized pillar of soil to a depth 2–3 cm below the base of the core. When the required depth was reached the cores were trimmed flush at the base and were placed on a sheet-metal base plate and sealed with waterproof tape. The microlysimeter was then mounted in a liner tube, with its surface slightly above the soil surface. The microlysimeters on mulch plots were covered to the same thickness with sand and gravel of uniform size. Nylon gauze was placed between the gravel and the soil to prevent them from mixing. The prevention of evaporation by the nylon gauze was far less than from gravel. Therefore, the effect of the nylon gauze on evaporation was negligible. Four lysimeters were installed every treatment to measure evaporation. For gravel-mulched and non-gravel-mulched treatments, 80% of the plot area was covered with plastic film. Therefore, two lysimeters were placed below the plastic film, and others were in place without any plastic film mulch. Lysimeters with undisturbed soil were weighed at 08:00 every morning. Soil core was renewed after 4 days for sand and gravel mulching treatments and after 2 days for control. However, the core was immediately renewed after rainfall events. Evaporation (E) was determined by the following formula, E ¼ 0:8EP þ 0:2EN
(2)
where EP is the evaporation measured from lysimeters with plastic film mulching; and EN is the evaporation measured from lysimeters without mulching. Watermelons were harvested in late July. The total number of melons and their weight were determined for each plot. In addition, five watermelons were randomly selected to determine soluble solids content with a hand-held refractometer (Mu´jica-Paz et al., 2003). All data were subjected to analysis of variance, and means were tested by least significant difference procedures for each experiment. 2.2.2. Experiment 2 Soil samples of the same water content were put into 10 small lysimeters. Gravel of five mean diameters (1.1, 1.7, 2.5, 3, and 4 cm) was mulched on the soil surface in lysimeters. The gravel of each diameter was mulched with two replications and 7 cm thickness. Microlysimeters with undisturbed soil cores were weighed at 08:00 every day from 16 July to 12 August 2004. Lysimeters were installed in the watermelon field after being weighed. Soil core was renewed after 2 days and rainfall events. 2.2.3. Experiment 3 Experiment 3 was designed with six initial soil water contents: 46, 40, 34, 28, 23, and 13% of soil dry weight. Soil of each moisture content was put into two microlysimeters. Dry soil and water weight in each microlysimeter was recorded. The gravel with 2.5 cm diameter was mulched to 7 cm thickness on the soil surface in the microlysimeter. Microlysimeters with undisturbed soil cores were weighed at 08:00 every day from 16 to 31
178
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
August 2004. Lysimeters were installed in the watermelon field after being weighed. Soil water content was calculated as (water weight in microlysmeter weight lost by evaporation)/(soil dry weight).
3. Results and discussions 3.1. Rainfall characteristics Rainfall was 121 mm during the watermelon growing period (from 25 April to 26 July) in 2004. There were 10 rainfall events of >3 mm totaling 114 mm, which amounted to 58.8% of the total rainfall events and 94.2% of the total rainfall (Fig. 2). 3.2. Evapotranspiration and evaporation from the soil surface The results of experiment 1 showed that ET was significantly increased for treatments B and C (gravel of 5–20 and 20–60 mm particle size, respectively) compared with treatments A (gravel of 5–20 mm particle size) and CK (control) (Table 1). However, there was no significant difference between treatments A and CK. The increase in ET was due to more soil water use with mulch of larger diameter gravel than with mulch of small-diameter gravel or with no gravel mulch. Evaporation from the soil surface was significantly higher for the control than for treatments with gravel mulch (Table 1). Gravel mulch in the watermelon field decreased evaporation by 17.7–34.2 mm. Evaporation in treatment C was the highest among mulching treatments, followed by that in treatment B. The minimum value was for treatment A. Thus, the results indicated that evaporation increased with gravel size. Mulch with gravel in the watermelon field reduced the ratio of evaporation to evapotranspiration (E/ET) because of the decrease in E for all mulched treatments and also the increase in ET
Fig. 2. Distribution of rainfall during the watermelon growing period in 2004.
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
179
Table 1 E and ET in watermelon field Gravel size (mm) (treatment)
Rainfall (mm)
CSWC (mm)
ET (mm)
E (mm)
E/ET
2–5 (A) 5–20 (B) 20–60 (C) 0 (CK)
121 121 121 121
26.7 46.7 54.0 27.8
147.7 167.7 171.0 148.8
26.3 32.5 42.8 60.5
0.18 0.19 0.25 0.41
a b b a
a b c d
Note: CK, control; CSWC, change of soil water content during the growing period. Different letters in a column denote significant differences between treatments at p < 0.05.
for treatments B and C. Evaporation was 41% of ET for treatment CK. However, it was only 18% for treatment A. Evaporation was lower in the places with plastic film mulch than where there was no plastic mulch for all gravel-mulched treatments and the control (Fig. 3). Evaporation was 24 mm for soil mulched with both gravel of 2–5 mm diameter and plastic film, which was lower by 94 mm than that for bare soil in the control. The ratio of evaporation mulched with plastic to evaporation without plastic (EP/EN) was found to range from a maximum of 0.65 for the control to a minimum with 0.43 for treatment C. The results showed that the suppressing effect of plastic film on evaporation decreased in the gravel-mulched field, which was due to the increased space between the plastic film and the gravel surface when plastic film was mulched on the larger diameter gravel. The mean rate of evaporation every 10 days was lower for treatment B than with treatment CK (Fig. 4). The maximum rate of evaporation was 0.83 mm day1 for treatment CK and 0.47 mm day1 for treatment B. There was little difference in the rates of ET and evaporation in the first 20 days after sowing. However, the ET rate increased with the growth stages and reached the maximum of 3.06 mm day1 for the control and 3.74 mm day1 for treatment B during 5–15 July, which was 3.7 and 8 times higher than evaporation, respectively. Evapotranspiration was higher for the control than with treatment B at early stages because of high evaporation. The high ET resulted in a low soil water content, which caused a lower ET for the control than for treatment B at the middle and late stages.
Fig. 3. Comparison of evaporation with and without plastic film mulch for all gravel mulching treatments and the control (CK).
180
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
Fig. 4. Comparison of the rate of evaporation (E) and the rate of evapotranspiration (ET) for the mulching treatment with gravel of 5–20 mm particle size and for the control (CK) during the watermelon growing period in 2004.
3.3. Relationship between evaporation and soil moisture under gravel mulch The relationship between evaporation and soil moisture on fine days from 16 to 31 August under gravel mulch (experiment 3) shown in Fig. 5 indicated that the relationship could be represented by a cubic curve. The equation obtained by regression analysis is as follows: E ¼ 0:2114 þ 0:2005m 0:0127m2 þ 0:00024m3
(3)
where E is evaporation (mm/day); m is the soil moisture in experiment 3 (kg kg1); and R2 = 0.915. Fig. 5 shows that evaporation from the soil surface increased when soil water content reached oversaturation and there was water in the mulching layer. However, there was little decrease in evaporation when the soil moisture was reduced from 27% to 8% in gravel mulch treatments.
Fig. 5. Relationship between evaporation and soil moisture under gravel mulch. (The diameter of the gravel was about 25 mm.)
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
181
The total resistance, rt, to evaporation from the bare soil surface is the sum of resistances in the atmosphere (ra) and on the soil surface (rs). However, in the gravel-mulched field, the resistance in the mulch layer (rm) is added as a component of total resistance, rt (Yamanaka et al., 2004); that is, rt ¼ ra þ rm þ rs
(4)
When the soil and mulch layers were saturated by water, rt = ra, because rs = rm = 0. The evaporation from the soil surface approached potential evaporation. Therefore, the value was very high when the soil moisture was at its highest (Fig. 5). When the soil surface is sufficiently wet (i.e., rs = 0), rt ¼ ra þ rm
(5)
The value of rs increased with decreasing soil moisture and with the development of a dry surface layer. The rt of evaporation from a mulched surface varied little when the soil water content change from 27% to 8%; the results showed that the mulch resistance, rm, was far higher than the soil surface resistance, rs. Gravel mulch increased rt and reduced evaporative losses because of extremely low unsaturated hydraulic conductivity at low suctions; the capillary movement of water to the surface of the gravel layer was thus prevented, and upward water transport through the gravel occurred only by vapor diffusion (Poesen and Lavee, 1994). But the evaporation declined when the soil water content was below 8%. That showed that rs was large enough to affect rt of evaporation from a mulched surface. When microlysimeters are used to measure evaporation, errors may occur if the soil within the microlysimeter has a water content or temperature that is significantly different from that of the surrounding soil. To minimize the errors, Daamen et al. (1993) suggested that the ideal renewal schedule should be to extract cores from the soil profile immediately after rain and to renew these cores within 12 h, then remove them daily until root extraction of water from the soil to the microlysimeter depth becomes insignificant (of the order of 4 days after rain). Gravel mulch decreased the difference between the temperature of the microlysimeter and that of the surrounding soil. There was little impact of soil water content on evaporation when the content was reduced from 27% to 8% in the gravel mulch treatments. Thus, temperature and soil water content were not main sources of error. However, disturbance of the soil in the extraction process increased evaporation from the lysimeter. Therefore, renewal of the soil core within 4 days for gravel mulching treatments was appropriate. 3.4. The relationship between evaporation and gravel size The evaporation with every particle-size class was averaged for 10 fine days after 27 July (experiment 2) in mulched soil where the moisture was >8%. The relationship between E and particle size (S) was linear (Fig. 6), and the equation obtained by regression analysis is as follows: E ¼ 0:3587 þ 0:0134S where R2 = 0.99.
(6)
182
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
Fig. 6. Relationship between evaporation and gravel particle size.
Table 2 Watermelon yield, soluble carbohydrate content, and WUE Gravel size (mm) (treatment)
Yield (kg m2)
Soluble carbohydrate content (%)
WUE (kg m2)
2–5 (A) 5–20 (B) 20–60 (C) 0 (CK)
33300 35964 32468 14985
10.0 10.3 11.0 9.0
22.5 21.4 19.0 10.1
a a a b
b b c a
c cb b a
Note: CK, control; WUE, water use efficiency. Different letters in a column denote significant differences between treatments at p < 0.05.
Fig. 6 indicates that evaporation from the mulched surface increased as gravel size increased from 1.1 to 4 cm. 3.5. Yield, soluble carbohydrate content, and water use efficiency The result of experiment 1 (Table 2) indicated that yield, soluble carbohydrate content, and WUE were significantly lower for the control than for all mulched treatments. Gravel mulch not only increased watermelon yield, but also improved the soluble carbohydrate content and WUE. There was not a significantly difference in yield between the various gravel mulching treatments. However, the soluble carbohydrate content was significantly higher and WUE was significantly lower for the treatment mulched with 20–60 mm diameter gravel than for that with 2–5 mm diameter gravel. Mulching with small sized gravel improved WUE because of decreasing evaporation from the soil surface. The increased soluble carbohydrate content with large-diameter gravel mulch was considered related to the increase difference in the soil temperature.
4. Conclusions Gravel mulch significantly decreased evaporation from the soil surface. Evaporation increased linearly with gravel size. The E/ET ratio also increased with gravel size.
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
183
Evaporation was reduced when the gravel surface in the watermelon field was mulched with plastic film. The relationship between evaporation and soil moisture under gravel mulch could be represented by a cubic curve. There was little reduction in evaporation when the soil moisture decreased from 27% to 8% in the gravel mulch treatments. Evaporation decreased, though, when soil moisture was <8%. Yield, soluble carbohydrate content, and WUE were significantly lower for the control than for all mulched treatments. However, there was no significant difference between treatments mulched with gravel of different sizes. The soluble carbohydrate content was significantly higher and WUE was significantly lower for the treatment mulched with 20– 60 mm diameter gravel than for the treatment mulched with 2–5 mm diameter gravel.
Acknowledgements We are grateful for financial support for the project from the Office of Agricultural Program, Chinese Academy of Sciences (NK15-C-09). We also thank Mrs. Wilson, an English teacher in the ESEC Program, Lanzhou, China, for editing help.
References Arkin, G.F., Ritchie, J.T., Adams, J.E., 1974. A method for measuring first stage soil water evaporation in the field. Soil Sci. Soc. Am. Proc. 38, 951–954. Ashktorab, H., Pruitt, W.O., Paw, U.K.T., George, W.V., 1989. Energy balance determinations close to the soil surface using a micro-Bowen system. Agric. For. Meteorol. 46, 259–274. Corey, A.T., Kemper, W.D., 1968. Conservation of soil water by gravel mulches, Hydrol. Pap. No. 30. Colorado State University, Fort Collins, CO, 23 pp. Daamen, Carl, C., Simmonds, L.P., Wallace, J.S., Laryea, K.B., Sivakumar, M.V.K., 1993. Use of microlysimeters to measure evaporation from sandy soils. Agric. For. Meteorol. 65, 159–173. Eastham, J., Gregory, P.J., Williamson, D.R., Watson, G.D., 1999. The influence of early sowing of wheat and lupin crops on evapotranspiration and evaporation from the soil surface in a Mediterranean climate. Agric. Water Manage. 42, 205–218. Gale, W.J., McColl, R.W., Fang, X., 1993. Sandy fields traditional farming water conservation in China. J. Soil Water Conserv. 48, 474–477. Groenevelt, P.H., Van Straaten, P., Rasiah, V., Simpson, J., 1989. Modifications in evaporation parameters by rock mulches. Soil Technol. 2, 279–285. Hanks, R.J., Woodruff, N.P., 1958. Influences of wind on water vapor transfer through soil, gravel and straw mulches. Soil Sci. 86, 160–164. Jara, J., Stockle, C.O., Kjelgaard, J., 1998. Measurement of evapotranspiration and its components in a corn (Zea Mays L.) field. Agric. For. Meteorol. 92, 131–145. Jackson, N.A., Wallace, J.S., 1999. Soil evaporation measurements in an agroforestry system in Kenya. Agric. For. Meteorol. 94, 203–215. Kemper, W.D., Nicks, A.D., Corey, A.T., 1994. Accumulation of water in soils under sand and gravel mulches. Soil Sci. Soc. Am. J. 58, 56–63. Lemon, E.R., 1956. The potentialities for decreasing soil moisture evaporation loss. Soil Sci. Soc. Am. Proc. 20, 120–125. Li, X.Y., Gong, J.D., 2002. Compacted catchment with local earth materials for rainwater harvesting in the semiarid region of China. J. Hydrol. 257, 134–144.
184
Z. Xie et al. / Agricultural Water Management 81 (2006) 173–184
Mellouli, H.J., van Wesemael, B., Poesen, J., Hartmann, R., 2000. Evaporation losses from bare soils as influenced by cultivation techniques in semi-arid regions. Agric. Water Manage. 42, 355–369. Modaihsh, A.S., Horton, R., Kirkham, D., 1985. Soil water evaporation suppression by sand mulches. Soil Sci. 139, 357–361. Monteith, J.L., 1965. Evaporation and environment. In: Fogg, G.E. (Ed.), Proceedings of the 19th Symposium of the Society for Experimental Biology, vol. 19, Swansea, Wales. Cambridge University Press, Cambridge, UK, pp. 205–234. Mu´jica-Paz, H., Valdez-Fragoso, A., Lo´pez-Malo, A., Palou, E., Welti-Chanes, J., 2003. Impregnation and osmotic dehydration of some fruits: effect of the vacuum pressure and syrup concentration. J. Food Eng. 57, 305–314. Perez, F.L., 1991. Soil moisture and the distribution of giant Andean rosettes on talus slopes of a desert paramo. Clim. Res. 1, 217–231. Perez, F.L., 2000. The influence of surface volcaniclastic layers from Haleakala (Maui, Hawaii) on soil water conservation. Catena 38, 301–332. Poesen, J.W., Lavee, H., 1994. Rock fragments in top soils: significance and processes. Catena 23, 1–28. Rasiah, V., Yamamoto, T., 2002. Mulching, evaporation, and salinity interrelation in an arid/semi-arid environment. Rural Environ. Eng. 42, 36–43. Rasiah, V., Imai, M., Yamamoto, T., Inoue, M., 2001. Evaporation losses from dune sand: influence of column and gravel mulch size. J. Arid Land Stud. 11, 177–186. Ritchie, J.T., 1972. Model for predicting evaporation from a row crop with incomplete cover. Water Resour. Res. 8, 1204–1213. Unger, P.W., 1971. Soil profile gravel layers effect on water storage distribution and evaporation. Soil Sci. Soc. Am. Proc. 35, 631–634. van Wesemael, B., Poesen, J., Kosmas, C.S., Danalatos, N.G., Nachtergaele, J., 1996. Evaporation from cultivated soils containing rock fragments. J. Hydrol. 182, 65–82. Yamanaka, T., Inoue, M., Kaihotsu, I., 2004. Effects of gravel mulch on water vapor transfer above and below the soil surface. Agric. Water Manage. 67, 145–155.