Forest Ecology and Management 233 (2006) 143–148 www.elsevier.com/locate/foreco
Influence of various in situ rainwater harvesting methods on soil moisture and growth of Tamarix ramosissima in the semiarid loess region of China Xiao-Yan Li a,b,c,*, Pei-Jun Shi a,c, Yong-Liang Sun b, Jia Tang b, Zhi-Peng Yang b a
The Key Laboratory of Environment Change and Natural Disaster, Ministry of Education, Beijing Normal University, Beijing 100875, China b Institute of Land Resources, Beijing Normal University, Beijing 100875, China c College of Resources Science & Technology, Beijing Normal University, No. 19, Xinjiekouwai Street, Beijing 100875, China Received 25 April 2006; received in revised form 8 June 2006; accepted 8 June 2006
Abstract The influence of different in situ rainwater harvesting and moisture conservation methods on soil moisture storage and growth of Tamarix ramosissima was studied in the semiarid loess region of China from 2002 to 2004. The treatments included control (T1), trench (T2), saucer covered by plastic film (T3), bare ridge and bare furrow (T4), plastic-covered ridge and bare furrow (T5), and plastic-covered ridge and gravelcovered furrow (T6). The results indicated that soil water storage for the T5 and T6 was significantly higher than the control. The T6 treatments produced the highest amount of soil water storage, 18–137 mm more than the controls at soil depth of 0–100 cm and 40–75 mm at soil depth of 100–200 cm. No significant differences in soil water storage were found between the T2, T3, T4 and the control treatments at soil depth of 0– 100 cm, but soil water storage at soil depth of 100–200 cm was significantly higher for the T2, T3, T4 treatment than the control. Rainwater harvesting and moisture conservation treatments increased growth of T. ramosissima, tree height was significantly higher for the rainwater harvesting and moisture conservation treatments than the controls. Tree height, crown diameter and collar girth for the T6 treatments increased by 70, 57 and 79% as compared to the controls. No significant differences in crown diameter and collar girth were observed between T1, T2 and T3 or T4 and T5 treatments in some years. The effectiveness of the different treatments for the tree height, crown diameter and collar girth was in the order of T6, T5, T4, T3, T2 and T1. # 2006 Elsevier B.V. All rights reserved. Keywords: Rainwater harvesting; T. ramosissima; Soil water storage; Semiarid
1. Introduction Lack of water is often a critical limiting factor for vegetation establishment in arid and semiarid lands. In the Loess Plateau of China, surface and groundwater resources are often either unavailable or too saline for irrigation, and precipitation is the major water source for plant growth. However, vegetation establishment and growth is slow due to the predominance of severe moisture stress conditions caused by low and sporadic rainfall. Water balance studies on the dry sloping land of the Loess Plateau have shown that about 5–10% of the precipitation is lost as runoff, 45–50% is transpired by plants and 45–50% is
* Corresponding author. Tel.: +86 10 58802716; fax: +86 10 58802716. E-mail address:
[email protected] (X.-Y. Li). 0378-1127/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2006.06.013
evaporated (Zhang and An, 1997). Therefore, to maximize the utilization of rainfall, some more effective practices are necessary to be adopted to retain surface runoff and reduce unproductive evaporation. Microcatchment water harvesting (MCWH) and moisture conservation techniques (e.g., tillage and mulching) are such practices to be used to increase yield of crops (millet, sorghum, corn, wheat, etc.) and tree growth (Hillel, 1967; Tabor, 1995; Gupta, 1995; Ojasvi et al., 1999; Oweis et al., 1999; Prinz, 2001). MCWH can be successful in years of normal or above normal rainfall and are best suited for situations in which drought-resistant trees or other droughthardy perennial species are grown (Aldon and Springfield, 1975; Boers and Ben-Asher, 1982; Sharma et al., 1986; Brooks et al., 1991). Particularly, the microcatchment procedure can be used in complex terrain or on steep slopes, where other waterharvesting techniques may be difficult to install. The effective use of MCWH systems in growing trees and shrubs was
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reported as early as in the nineteenth century for growing olive trees in Tunisia (Pacey and Cullis, 1986). Tamarix ramosissima is an important multipurpose tree species of arid region serving as fodder, fuel, timber and shelterbelt. It is a deep rooted, perennial and drought resistant tree and shows good growth responses when water is available (Devitt et al., 1997). Li et al. (2005) studied response of T. ramosissima growth to microcatchment rainwater harvesting with different size natural loess slope and determined appropriate catchment/planted area ratios, they reported that T. ramosissima is a suitable tree to be established in the loess plateau using MCWH. However, runoff efficiency of the natural loess slope is relatively low and decreases with the size of the catchment, a single T. ramosissima needs 15–30 m2 or more loess catchment to provide runoff water, there is still a need to find other catchment treatments including use of artificial materials to improve runoff efficiency and moisture conservation practices to reduce evaporation in order to improve water use efficiency. Therefore, this study was designed to investigate the effect of some simple in situ mini-dam treatments like trench, saucer, ridge and furrow and their combination with mulching (plastic and gravel) on growth of T. ramosissima. Li et al. (2001) found plastic-covered ridge and furrow method of rainwater harvesting significantly improved water use efficiency and yield of corn in the loess region, so this method is reconsidered to be used to grow T. ramosissima and is included in this study. 2. Materials and methods 2.1. Field site This study was conducted between May and September in growth period of T. ramosissima from 2002 to 2004 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 transitional zone between arid and semiarid regions (Gaolan County, Lanzhou, Gansu Province, 368130 N, 1038470 E) at an altitude of approximately 1780 m. Mean annual precipitation is 263 mm, with nearly 70% falling between May and September. Mean annual temperature is 8.4 8C with a maximum monthly temperature of 20.7 8C (July) and a minimum of 9.1 8C (January). Average annual pan evaporation is 1785 mm. The soil is a silt loam (sand: 12.3%; silt: 66.9%; clay: 20.8%) of loess origin, which can be classified as Calciorthid. The soil is deep (the maximum depth amounts to 300 m) and well developed, the saturated hydraulic conductivity is 19 mm h1 (Li and Gong, 2002) and field water holding capacity amounts to 28% (by volume). 2.2. Experimental design and treatments The experiment comprised of six rainwater harvesting and moisture conservation treatments (Fig. 1), which were: T1, conventional planting of T. ramosissima on flat land (control); T2, trench (1 m wide and 0.3 m deep); T3, saucer (1 m in diameter and 0.3 m in depth) covered by 0.008 mm plastic film. T4, bare ridge and bare furrow (Fig. 2), T5, plastic-covered ridge and bare furrow, T6, plastic-covered ridge and gravelcovered furrow (Fig. 2). The T4, T5 and T6 treatments all consisted of ridges and furrows alternately on the flat land. The ridge (1 m wide, side-slope 408) served as rainwater harvesting zone and furrow (1 m wide) as planting zone; the furrows in the T6 treatment were mulched by a layer of gravel (3–8 cm in diameter). The thickness of the plastic film for the T5 and T6 treatments was 0.20 mm. Each treatment was triplicated and the
Fig. 1. Sketch of different structures of in situ rainwater harvesting and mulching combination for growing T. ramosissima [T1, Conventional planting on flat land (control); T2, Trench; T3, Saucer covered by plastic film; T4, Bare ridge and bare furrow; T5, Plastic-covered ridge and bare furrow; T6, Plastic-covered ridge and gravel-covered furrow].
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Fig. 2. Photographs showing bare ridge and bare furrow structure (T4) (left) and plastic-covered ridge and gravel-covered furrow structure (T6) (right) for rainwater harvesting.
experiment plots were laid out in a randomized pattern. Tenmonth-old seedlings of T. ramosissima were planted in April 2002 in pits of 50 cm 50 cm 50 cm at 2 m 1 m spacing in all the treatments. There were 20 plants per plots. Rainwater harvesting structures and mulching were made before planting. A supplemental watering of 0.02 m3 was given to each tree immediately after tree planting in April 2002. A standard rain gauge and a siphon-type recording rain gauge were used to obtain the amount and intensity of rainfall. Soil moisture in the plant area was measured using TDR each month to a 2-m soil depth in 20-cm depth increments. Tree height of T. ramosissima was measured after planting and yearly thereafter in September. The crown diameter, and collar girth at the tree base were also measured in September each year from 2002 to 2004. 3. Results and discussion 3.1. Rainfall characteristics Rainfall between May and September was 228, 255 and 172 mm in 2002, 2003 and 2004, respectively, which was 5.2, 4.7 and 5.6 times less than the corresponding pan evaporation (Fig. 3), thus giving a net water deficit of 959, 950, 796 mm, respectively; this suggests that rainfall can not meet demands of
evaporation and deficit prevails throughout the growth period of T. ramosissima. Compared to the average, the year 2002 and 2003 were relative wet years, and 2004 was a dry year. Rainfall was erratic and 60–76% was received between June and August. Seventy-five percent of the rainfall events were of less than 5 mm, 15% were in the range of 5–10 mm; 9% in the range of 10–20 mm, the highest daily rainfall of 32 mm only accounted for 1% of the rainfall events (Fig. 4). It has been found that a rainfall event of 8.5 mm or more and a rain intensity of 3 mm h1 (I10) or more is capable of generating the measurable runoff from the undisturbed loess soil surface (Li et al., 2004). The data analysis also indicated that about 60% of the total amount of the annual rainfall resulted from rains exceeding 10 mm. A rainfall intensity of 5 mm h1 (I10, maximum rain intensity in 10 min) was recorded for 58% of the rainfall events, 23% were in the range of 5–10 mm h1 and 11% in the range of 10–20 mm h1, whereas rainfall intensity exceeded 20 mm h1 for only 8% of the storm. Rainfall intensity was generally higher for high values of rainstorms, the correlation coefficient of rainfall and rain intensity was 0.587 (F(1, 67) = 37.72, P < 0.0001). The results suggest that most storms were of small size with low intensity, but the total amount of annual rainfall mainly depended on a few of lager size storms. The latter typically occurred during the monsoon period in the region. 3.2. Soil water storage
Fig. 3. Monthly rainfall and evaporation during growth period of the T. ramosissima.
Fig. 5 shows soil moisture storage at soil depth of 0–100 and 100–200 cm for the different rainwater harvesting and moisture conservation treatments from 2002 to 2004. Variation of soil moisture storage corresponded well with the pattern of rainfall distribution (Figs. 4 and 5). Soil moisture storage was higher for the plastic-covered ridge and furrow methods of rainwater harvesting treatments (T5 and T6) than the trench, saucer, bare ridge and bare furrow, and the control treatments; particularly for soil moisture at soil depth of 100–200 cm, suggesting that more water was recharged into the deeper soil layer by the plastic-covered ridge treatments. This is due to the fact that
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Fig. 4. Daily rainfall distributions from 2002 to 2004 during tree growth period at the experimental site.
plastic-covered ridge has a low rainfall threshold for generating runoff, and more water can be harvested in the tree area. Li et al. (2000) reported that runoff efficiency (runoff/rainfall) of the plastic-covered ridge was 87% in the study area, and it could
Fig. 5. Variation of soil moisture storage in soil layer of 0–100 cm depth (A) and 100–200 cm depth (B) for the different treatments in the tree-growing seasons between 2002 and 2004 (T1, Control; T2, Trench; T3, Saucer covered by plastic film; T4, Bare ridge and bare furrow; T5, Plastic-covered ridge and bare furrow; T6, Plastic-covered ridge and gravel-covered furrow).
generate runoff at a threshold value of 0.8 mm rainfall. So we can estimate that plastic-covered ridge would bring about 198, 222 and 150 mm additional runoff into the T. ramosissima growing furrows than the controls in 2002, 2003 and 2004, respectively. In this study, plastic-covered ridge and bare furrow treatments had 11–114 mm more water than the controls at soil depth of 0–100 cm, and 24–55 mm at soil depth of 100– 200 cm; while plastic-covered ridge and gravel mulched furrow treatments had 18–137 mm more water than the controls at soil depth of 0–100 cm, and 40–75 mm at soil depth of 100– 200 cm. This suggests that a layer of gravel can reduce about 16–23 mm soil evaporation. Soil water storage for the trench, saucer and bare ridge and bare furrow treatments tended to be higher than the control treatments. This trend is obvious for soil water storage at soil depth of 100–200 cm (Fig. 5). We did not measure runoff amount concentrating into the tree planted area for the different microcatchment treatments, but Li et al. (in press) measured runoff efficiency of the undisturbed loess slope with gradient of 58 and 1 m in length in the study area at the same experimental period, the runoff efficiency was 13.7, 8.9 and 3.1% in 2002, 2003 and 2004, respectively. So we can roughly estimate that the trench and bare ridge and bare furrow treatments would bring about 31, 23 and 5 mm additional water to the tree than the controls. Lower soil water storage for the saucer treatment than the trench and bare ridge and bare furrow treatments may be attributed to the fact that although surface plastic cover can concentrate rainwater and reduce soil evaporation but meantime it can retard infiltration. There was only small opening between trunk and plastic cover at the tree base, rainwater ponded on top of the plastic film cannot infiltrate immediately and most water evaporated.
X.-Y. Li et al. / Forest Ecology and Management 233 (2006) 143–148 Table 1 Tree growth parameters for the different rainwater harvesting and moisture conservation treatments from May to September during the growth period of the T. ramosissima between 2002 and 2004 T1
T2
T3
T4
T5
T6
111b 141b 167b
132c 156c 197c
150d 187d 212d
167e 200e 226e
180f 213f 242f
Crown diameter (cm) 2002 47a 69b 2003 92a 121b 2004 117a 124a
96c 118b 157b
108d 131b 171c
109d 137c 186d
112d 145c 209e
Tree height (cm) 2002 93a* 2003 127a 2004 142a
Collar girth (cm) 2002 0.7a 2003 1.1a 2004 1.4a
0.8a 1.2a 1.5a
0.9b 1.2a 1.6a
1.0b 1.6b 2.0b
1.0b 1.6b 2.0b
1.2c 1.7b 2.2c
T1, conventional planting on flat land (control); T2, trench; T3, saucer covered by plastic film; T4, bare ridge and bare furrow; T5, plastic-covered ridge and bare furrow; T6, plastic-covered ridge and gravel-covered furrow. * Means in the same row followed by the same letter are not significantly different at P = 0.05 as determined by Fisher’s protected least significant difference test.
3.3. Growth of T. ramosissima T. ramosissima showed an obvious improvement in growth as a result of the various rainwater harvesting and moisture conservation treatments (Table 1). The plastic-covered ridge and gravel mulched furrow treatments (T6) caused maximum growth increase. Compared with tree height of 142 cm, crown diameter of 117 cm and collar girth of 1.4 cm in the control, T. ramosissima in the T6 treatment were 70% taller and had 57% thicker collar girth and 79% wider crown size in a period of 3 years. Tree height were significantly higher (P < 0.05) for the rainwater harvesting and moisture conservation treatments than the controls, indicating rainwater harvesting and moisture conservation treatments were effective for T. ramosissima growth and the effectiveness was in the order of T6, T5, T4, T3 and T2. No significant difference in crown diameter and collar girth were observed between T1, T2 and T3 or T4 and T5 treatments in some years, but the trend of crown diameter and collar girth in response to rainwater harvesting treatments was the same as the tree height, crown diameter and collar girth were highest for the T6, followed by T5, T4, T3, T2 and T1. 4. Implications Rainwater harvesting in arid and semiarid regions is an old yet an effective way of establishment and subsequent growth of trees. This study demonstrated the potential of rainwater harvesting and conservation methods in enhancing growth of tree under arid conditions. However, the application of various rainwater harvesting methods is site-specific and depends on local rainfall characteristics, construction materials, site conditions, installation methods and labor cost. Table 2 shows construction cost for the different treatments. The plasticcovered ridge and gravel mulched furrow treatments (T6) had
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Table 2 Construction cost (US$ ha1) for various rainwater harvesting and moisture conservation treatments T1
T2
T3
T4
T5
T6
Labor cost Gravel cost Plastic film cost
113 – –
188 – –
338 – 109
300 – –
375 – 2250
563 427 2250
Total cost
113
188
446
300
2625
3240
T1, conventional planting on flat land (control); T2, trench; T3, saucer covered by plastic film; T4, bare ridge and bare furrow; T5, plastic-covered ridge and bare furrow; T6, plastic-covered ridge and gravel-covered furrow.
the highest cost, partly because we used 0.20 mm radiation resistant plastic film, which has a long life span and can be used for 5–8 or more years. The general type of 0.008 mm plastic film has a longevity of 5–6 month or 1 year but the cost is just 8% of the 0.18 mm radiation resistant plastic film. To offset high cost, it might be possible to grow fruit trees (apple, grape and Jujube). Or, another means of replacing plastic film covering with low cost soil-hardening agent which would be imperious to both liquid and vapor movement of water. Li et al. (2001) reported that the plastic-covered ridge and furrow system had some advantages: First, it can make better use of light rain by harvesting rainwater from plastic-covered ridges, thus improving the availability of water to crops. Second, plastic-covered ridges can increase soil temperature. Third, this system can reduce wind velocity for controlling wind erosion. Fourth, the ridge and furrow configuration can improve aeration and light radiation. Fifth, it can improve the effectiveness of fertilizer utilization. The disadvantage of the plastic-covered ridge and furrow system for crop is that ridges must be rebuilt after each cultivation or tillage operation (Li et al., 2001); however, this is not a problem for growing tree because there is no need to cultivate soil every year. The ridge and furrow can be permanently used. This system may be better to be used in the place where small rain dominated and irrigation is costly or difficult to install, but afforestation is necessary, e.g., city park, greenbelt along highway. Stone and straw are in abundance and available in many arid areas and they can be combined with plastic-covered ridge system to reduce evaporation (Li et al., 2001). There is less risk of waterlogging and overtopping for this ridge system in the dry semiarid region of China (Li et al., 2001), but it should be considered in the other high rainfall area. The cost of trench, saucer and bare ridge and bare furrow treatments is relatively low, it is suitable to be used in various situations and has a great potential to develop. Particularly, it can be used in remote poor area where manual labor is cheaper and easily available. Acknowledgments This study was partly supported by the National Science Foundation of China (NSFC 40571023, 40599423), the Foundation for the Author of National Excellent Doctoral Dissertation of PR China for Dr. Xiao-Yan Li (Grant No. 200426), the National Science Fund for Distinguished Young
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Scholars (NSFC 40425008) and the Ministry of Science and Technology, China (Grant No. 2005BA517A11). Special thanks are owed to two anonymous reviewers for their fruitful suggestions to the improvement of the manuscript. Mr. XiZhong Lu is appreciated for his help in establishing field experiment and observations. References Aldon, E.F., Springfield, H.W., 1975. Using paraffin and polyethylene to harvest water for growing shrubs. In: Frasier, G.W. (Ed.), Symposium on Water Harvesting, Phoenix, AR, ARSW-22, USDA, pp. 251–257. Boers, Th.M., Ben-Asher, J., 1982. A review of rainwater harvesting. Agric. Water Manage. 5, 145–158. Brooks, K.N., Ffollott, P.F., Gregersen, H.M., Thames, J.L., 1991. Hydrology and the Management of Watersheds. Iowa State University Press, Ames, Iowa 50014, pp. 307. Devitt, D.A., Sala, A., Mace, K.A., Smith, S.D., 1997. The effect of applied water on the water use of saltcedar in a desert riparian environment. J. Hydrol. 192, 233–246. Gupta, G.N., 1995. Rainwater management for tree planting in the India desert. J. Arid Environ. 31, 219–235. Hillel, D., 1967. Runoff inducement in arid lands. Final Tech. Rep. USDA Project A 10-SWC-36. Rehovot, Israel, 142 pp. Li, X.Y., Gao, S.Y., Xu, H.Y., Liu, L.Y. Growth of Caragana korshinskii using runoff-collecting microcatchments under semiarid condition. J. Hydrol., in press. 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 (1–4), 134–144.
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