The characteristics of overland ¯ow under varied tillage
and cropping systems in Sichuan Basin, China
$Gangcai Liu
*, Meirong Gao, Bo Zhu
Institute of Mountain Hazards and Environment Chinese Academy of Sciences and Ministry of Water Conservancy, R.d, No. 9, section 4 of Renming South, Chengdu 610041, China
Received 11 November 1998; received in revised form 2 June 1999; accepted 20 October 1999
Abstract
Data from runoff plots operated over a ®ve year period show that signi®cantly less overland ¯ow is generated with a seasonal no-till ridge system than with contour tillage or straight tillage systems. Seasonal no-till ridge is the optimum system for increasing the availability of water for rainfed agriculture on the dryland soils in the hilly area of Sichuan Province, China.
#2000 Published by Elsevier Science B.V. All rights reserved.
Keywords:Overland ¯ow; Tillage; Cropping system
1. Introduction
Seasonal drought is the primary constraint on agri-culture in the sloping drylands of Sichuan Province, China. The climate of the area is subtropical humid monsoon with mean annual rainfall between 800 and 1100 mm. Irrigation facilities are insuf®cient and most farmers rely on rainfed agriculture (Zhongming et al., 1991). However, since the probability of sea-sonal drought exceeds 60% (Gangcai et al., 1997), successful agriculture depends on increasing the pro-portion of rainfall available for crop production and
reducing that running off the land as overland ¯ow. Previous work on overland ¯ow in the area has con-centrated on erosion (Shengwu Lu, 1992; Xianwan et al., 1995) rather than the water balance of the arable land. This paper presents the results of research on overland ¯ow occurring under different tillage and cropping systems.
2. Methodology
Overland ¯ow was measured at ®ve locations: Yanting (YT), Lezhi (LZ), Renshou (RS), Neijiang (NJ) and Jianyang (JY) under three tillage and crop-ping systems with two replications at each site. The soil characteristics of the sites are shown in Table 1. Bulk density was measured with a 50 mm50 mm core sampler. Organic matter content was determined by the dichromate oxidation method. Soil particle size
$
This paper was funded by the key project (No. KZ951-A1-301) and special supported project (No. KZ95T-04) of the Chinese Academy of Sciences.
*Corresponding author. Tel.: 86-28-5235869; fax:
86-28-5235869.
E-mail address: [email protected] (G. Liu)
distribution was determined by pipette analysis (Head, 1980).
The tillage and cropping systems were: (1) contour farming with seasonal no-till ridge (SN); (2) contour tillage (CT); and (3) straight tillage (ST). The SN treatment was established by ploughing the soil to 20 cm depth with a cattle-drawn plough every third year. Hand labour was used to build ridges (100 cm wide) and furrows (also 100 cm wide) along the contour; furrow depth was 30 cm. The furrows were ploughed to a depth of 20 cm before planting each crop. Sweet potato was no-till planted on the ridges and corn was planted in the furrows for the summer± autumn crop. During winter±spring, wheat was planted on the ridges after a shallow tillage and rape was planted in the furrows.
For the CT, the contour strips were established annually. The ridge and furrow design was established each summer according to local custom with 80 cm wide ridges and 70 cm wide furrows; the elevation from the top of the ridge to the base of the furrow is 20 cm. For the winter±spring crop, wheat was planted on the ridges and rape in the furrows after ploughing to a 20 cm depth. For the summer±autunm crop, sweet potato was planted on the ridges and corn in the furrows. The ST treatment followed the same proce-dure as the CT treatment except that the ridges and furrows ran up-and-down slope.
The runoff plots, 20 m long and 4 m wide, were bounded on three sides by concrete borders set to a depth of 0.6 m. A cement ¯oor slab was positioned at the downslope end from which water and sediment were led through a pipe into a collection tank (4 m 2 m1 m). An aliquot of one-tenth of the over¯ow from this tank was separated by a multi-slot divisor and collected in a second tank (2 m2 m1 m). The layout of the collection system is shown in Fig. 1.
The depth of water in each tank was recorded. Rainfall at each site was measured with a daily rain gauge.
The ®eld experiments were carried out from 1989 to 1995 at LZ, NJ, JY and RS on slopes of 10.28, 10.58, 11.28and 11.58, respectively. The experiments at YT were carried out from 1985 to 1989 on a 3.88slope and from 1990 to 1991 on slopes of 3.08, 6.08and 10.28. All the data analysed below are based on averages of the two replicates.
3. Results
3.1. Temporal aspects
Table 2 lists the runoff coef®cients (proportion of rainfall contributing to overland ¯ow), calculated annually for the 3.88slope at YT. The SN treatment yields signi®cantly less runoff than the other treat-ments. There is no signi®cant difference between CT and ST though the runoff coef®cient for the latter is always higher. The effectiveness of SN compared with the CT and ST treatments can be expressed by reduc-tion ratios de®ned respectively asdst(CTÿSN) 100/CT and dct(STÿSN)100/ST. The average reduction ratios are 38.7 and 52.4%, respectively.
Table 1
The main characteristics of soils in experimental sites
Experimental
Plots of the reduction ratios (Fig. 2) indicate that the differences between the treatments are consistent from year to year.
Calculations of the monthly runoff coef®cients (Table 3) indicate that most overland ¯ow occurs in July and August during which the rainfall intensity is highest. The ranking of SN (lowest), CT and ST (highest) is the same for all months and con®rms the annual rankings. Plots of the reduction ratios (Fig. 3) indicate that the SN treatment is most effective in June and in August.
The SN treatment is the optimum system for redu-cing overland ¯ow which is in line with other research. Contour tillage is known to diminish runoff and retain soil water (Yoo et al., 1995; Dana et al., 1996; Singh et al., 1996). On top of this, the SN treatment of no-tillage on the ridges and retaining crop residues leads to an improvement in soil structure (Xianwan et al., 1995) and greater in®ltration.
3.2. Spatial aspects
The results from the experimental sites on steeper slopes at LZ, RS, NJ and JY (Table 4) also show that the SN treatment results in signi®cantly less runoff. Again the differences between the CT and ST treat-ments are small. The rankings of the treattreat-ments are consistent with those observed at YT. The differences in runoff coef®cients between the sites can be attrib-uted to differences in soil properties.
Table 2
The runoff coef®cients of varied tillage and cropping systems for various years for 3.88at YT
Crop system 1985 1986 1987 1988 1989 Average value LSD Test
SN 0.076 1.062 0.13 0.158 0.069 0.099 a A LSD0.01, 120.07
CT 0.129 0.136 0.165 0.266 0.132 0.166 b AB LSD0.05, 120.05
ST 0.164 0.176 0.207 0.279 0.188 0.230 c B
Fig. 2. The reduction ratio of runoff for SN against CT and ST.
Table 3
The runoff coef®cients of varied tillage and cropping systems for various months with 3.88at YT
Crop system 5 6 7 8 9 10
SN 0.102 0.048 0.144 0.102 0.092 0.098
CT 0.148 0.082 0.201 0.243 0.158 0.118
ST 0.304 0.201 0.362 0.453 0.252 0.336
The data obtained at YT for different slopes shows that the runoff coef®cients increase with slope steep-ness for all treatments, indicating that contour plough-ing becomes more important with increasplough-ing slope gradient (Table 5). Calculations of the reduction coef®cient show thatdstincreases with slope whereas dctdecreases (Table 6).
3.3. In¯uence of rainfall
Calculations of the runoff coef®cients and reduction coef®cients with classes of rainfall amount (Table 7) con®rm the treatment rankings of SN < CT < ST. The
SN treatment is most effective in rainstorms of less than 100 mm. The highest reduction coef®cients are found for rainstorms of 50±100 mm.
4. Conclusions
The seasonal no-till ridge system is the most effec-tive of the three cropping systems investigated for rainfed agriculture in the hilly drylands of Sichuan Province. It consistently leads to less runoff over a range of soil types and slopes.
References
Dana, I., et al., 1996. The relationship between conservation and sustainability. J. Soil Water Conservation 51 (4), 292±295. Gangcai, Liu, et al., 1997. The mechanism of bearing drought for
contour tillage system in Sichuan Basin, China. Chinese J. Soil Sci. 28 (6), 248±250 (in Chinese).
Head, K.H., 1980. Manual of Soil Laboratory Testing. Pentch Press, London.
Shengwu, Lu, 1992. The effect of rainfall and moisture on erosion. Chinese J. Soil Sci. 29 (1), 94±103 (in Chinese).
Table 4
The runoff coef®cients of varied tillage and cropping systems at various sites
Site SN CT ST LSD Test dct(%) dST(%)
LZ 0.175 0.205 0.370 a A LSD0.05, 100.036 14.6 52.7
JY 0.179 0.248 0.300 a A LSD0.01, 100.052 27.8 40.3
NJ 0.094 0.128 0.220 b B 26.6 57.6
RS 0.128 0.164 0.196 b B 22.0 34.7
Average value 0.144 0.186 0.272 22.8 46.3
a b c
LSD A A B
Test LSD0.05,100.036
LSD0.01,100.052
Table 5
The runoff coef®cients of varied tillage and cropping systems at various slope at YT
The equation of relationship between runoff coef®cient (Y) and slope gradient (X) for YT
The runoff coef®cient of contrasting tillage and cropping system under varied rainfall at YT for 3.88
Rainfall (mm) SN CT ST dct(%) dst(%)
l0±20 0.10 0.18 0.22 44.4 53.9
20±50 0.35 0.56 0.66 37.6 47.3
50±100 0.28 0.58 0.87 51.6 67.3
l00±200 0.22 0.33 0.39 33.5 43.7
Singh, B., et al., 1996. Soil hydraulic properties of an Orphic Black Chemozum under long term tillage and residue management. Can. J. Soil Sci. 76 (1) 63±71.
Xianwan, Zhang, et al., 1995. Seasonal no-tillage ridge cropping system: a multiple objectives tillage system for hilly land management in south China. In: SA. EL-swaify, et al. (Eds.),
Multiple Objectives Decision Making for Land, Water and Environmental. CRC Press, Boca Raton, FL, pp. 564±575. Yoo, K., et al., 1995. Soil-water content changes under three tillage
systems used for cotton. J. Sustainable Agric. 7 (2/3), 53±56. Zhongming, Li, et al., 1991. Purple Soils in China. Chinese Science
