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Combining Ridge with No-Tillage in Lowland Rice-Based Cropping System: Long-Term Effect on Soil and Rice Yield
Pedosphere 19(4): 515–522, 2009 ISSN 1002-0160/CN 32-1315/P c 2009 Soil Science Society of China Published by Elsevier Limited and Science Press
Combining Ridge with No-Tillage in Lowland Rice-Based Cropping System: Long-Term Effect on Soil and Rice Yield∗1 JIANG Xian-Jun∗2 and XIE De-Ti College of Resources and Environment, Southwest University, 216 Tiansheng Road, Beibei, Chongqing 400716 (China) (Received April 5, 2008; revised March 23, 2009)
ABSTRACT A tillage method of combining ridge with no-tillage (RNT) was employed in lowland rice-based cropping system to study the long-term effects of RNT on soil profile pattern, soil water stable aggregate distribution, nutrients stratification and yields of rice and post-rice crops. After flooded paddy field (FPF) was practiced with RNT for a long time, soil profile changed from G to A-P-G, and horizon G was shifted to a deeper position in the profile. Also the proportion of macroaggregate (> 2 mm) increased, whereas the proportion of silt and clay (< 0.053 mm) decreased under RNT, indicating a better soil structure that will prevent erosion. RNT helped to control leaching and significantly improved total N, P, K and organic matter in soil. The highest crop yields were found under RNT system every year, and total crop yields were higher under conventional paddy-upland rotation tillage (CR) than under FPF, except in 2003 and 2006 when serious drought occurred. RNT was proven to be a better tillage method for lowland rice-based cropping system. Key Words:
aggregate-size distribution, conservative tillage, flooded paddy field, soil profile pattern
Citation: Jiang, X. J. and Xie, D. T. 2009. Combining ridge with no-tillage in lowland rice-based cropping system: Long-term effect on soil and rice yield. Pedosphere. 19(4): 515–522.
INTRODUCTION The area of paddy soils in China is 25 million hectares, which accounts for 25% of the country’s total cultivated area. Although spread throughout China, approximately 93% of the paddy fields in China are located in the tropical and subtropical regions, 1/3 of which are distributed in lowland regions (Li, 1992). According to natural conditions such as sunlight, temperature and rainfall, this land usually yields crops twice a year in southern China. However, because of irrigation problem, farmers in lowland areas traditionally keep their fields permanently flooded to ensure an adequate water supply for the spring rice crop. Water security was seen to outweigh the costs of reduced yields caused by continuous flooding (Liu et al., 2004). Flooded paddy fields were left unplanted throughout the winter, representing an underutilized resource that can be used. Similar to this, there are vast areas of rice land in South and Southeast Asia that remain fallow after rice harvest due to saturated soil conditions limiting establishment of upland crops (Garrity and Liboon, 1995; Wadeet al., 1999; So and RingroseVoase, 2000). The term ‘flooded paddy-field (FPF)’ is used throughout this article to refer this system. Conventional paddy-upland rotation system (CR) is the main alternative to FPF (Li, 1992; Xie and Chen, 2002; Liu et al., 2004). Utilizing this rotation system, farmers double annual productivity by draining their fields after rice harvest to plant another dry crop such as wheat or rape in winter. For rice-based cropping system, soil puddling in advance of transplanting is advantageous for achieving high productivity (Surendra et al., 2001). This involves ploughing the soil when wet, puddling it and ∗1 Project
supported by the National Natural Science Foundation of China (No. 40501033) and the National Key Technologies R&D Program for the 11th Five-Year Plan of China (No. 2007BAD87B10). ∗2 Corresponding author. E-mail: [email protected].
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keeping the area flooded for the duration of rice growth. Puddling breaks down and disperses soil aggregates into micro-aggregates and individual particles (Kirchhof et al., 2000). Thus this practice destroys soil structure and creates a poor physical condition for the following upland crop (Boparai et al., 1992; Mohanty and Painuli, 2004). Attempts have been made to overcome these physical constraints, such as tillage. However, to date, the effects of tillage on yields are unclear (So and Ringrose-Voase, 2000). Additionally, CR poses water risk for the next rice crop after water is drained away for upland crops. It is because of these problems that FPF has remained the primary method of land utilization (Xie and Chen, 2002). Ridge tillage has been proposed as a conservative method (Taylor, 1983; Liebig et al., 1993; Archer et al., 2002) that provides some benefits, such as erosion prevention and leaching control, time savings, soil structure protection, etc. (Behn, 1985; Kaspar et al., 1995; Waddell and Weil, 2006). Furthermore, ridge tillage provides a special benefit of creating a microenvironment of dry-land (ridge top) in flooded paddy fields (Hou, 1983). As a result, dry season crops (wheat or rape) can be planted on the ridge top while water remained in the furrow. This method allows the planting of an upland crop and avoids water risk for the next rice crop in lowland rice-based cropping system. The no-tillage method is considered as one of the most important conservative tillage methods and has been well documented from physical, chemical and biological aspects (Six et al., 1998, 2000; Frey et al., 1999; Jackson et al., 2003; Samarajeewa et al., 2006). However, most of the researches concerning ridge tillage and no-tillage were concentrated on upland crops or post-rice crops (Nachabe et al., 1999; Samarajeewa et al., 2006); little information is available about the effects of ridge or no-tillage on paddy soils (Ambassa-Kiki et al., 1996). Crop yield has been used as the most important indicator to evaluate the sustainability of an agroecosystem. Numerous researches have been done to investigate the effects of various tillage methods on crop yields (Li et al., 2001). Henderson (1979) remarked that most of the studies did not provide an insight into how the procedure influenced crop yield. Moreover, the results obtained were often site and year specific and often contradictory and inconclusive due to variability in soil type, cropping systems, and climate (Wright and Coleman, 1999; Guzha, 2004). Therefore, further research on different types of soil is still required, especially for long-term experiments. The primary objective of the present work was to study the long-term effects of combining ridge with no-tillage (RNT) on soil profile pattern, soil water stable aggregate distribution, nutrients stratification and the yields of rice and post-rice crops in lowland rice-based cropping system. MATERIALS AND METHODS Experimental site A field experiment has been carried out since 1990 at Southwest University, which is located in the Sichuan Basin, southwestern China (latitude 28◦ –32◦ N, longitude 103◦ –108◦ E). The Sichuan Basin covers 165 000 km2 with an annual mean temperature of 14–19 ◦ C and rainfall of 1 000–1 400 mm and naturally yields crop twice a year. The soil used in this study was a Gleyi-Stagnic Anthrosol according to Chinese Soil Taxonomy (CRGCST, 2001), which was developed from purple mudstone. Physical and chemical properties of the soil are listed in Table I. The crops used were wheat (Triticum aestivum L.) TABLE I Physical and chemical properties of the soil used Soil depth
Total N
cm 0–10 10–20 20–30
2.00 1.90 1.87
Available P g kg−1 0.85 0.83 0.79
K 22.4 22.2 23.5
N 165 158 153
Organic matter P
mg kg−1 10.4 9.85 10.8
Clay
pH (H2 O)
250 262 282
6.80 6.70 6.65
K g kg−1 115 120 126
37.4 37.6 37.0
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or rape (Brassica napus L.) in winter and rice (Oryza sativa L.) in summer. Tillage treatments For RNT, ridges were made by manpower in the fields. The ridges were 25 cm wide at the top and the furrows were 30 cm wide and 35 cm deep. Each plot consisted of five rows. From rice transplantation to vegetative stage, the water surface was kept parallel with ridge top in the field, and during other time of a year, water depth in furrow was 25–30 cm, i.e., ridge top was 5–10 cm above water surface. After the harvest of the rice crop, mud from furrow was artificially stacked on the ridge top. Wheat was seeded after the field was covered with rice stubble (50–60 cm). During the wheat growing season, water levels in the furrow were maintained at 5–10 cm depth, i.e., ridge top was 20–25 cm above water surface, thus retaining ridge soakage irrigation. After the harvest of the wheat crop, wheat stubble and weeds were buried in the furrow bottom, and the field was submerged with water up to ridge top for the cultivation of rice. For CR, rice was transplanted in a flooded field with a layer of water until maturation. After rice harvest, the paddy field was drained, ploughed, dried, and harrowed and then wheat was seeded. After wheat was harvested, the soil was puddled and harrowed twice and rice seedlings were transplanted again. For FPF, soil was puddled and harrowed twice before rice-seedlings were transplanted. Rice was planted in a flooded field in summer and land remained fallow in winter. Water was kept flooded in the field throughout the year. Other managements used in the three tillage methods were all the same, including fertilizer application. The annual application of fertilizers was as follows: urea, 270 kg ha−1 ; calcium superphosphate, 500 kg ha−1 ; and potassium chloride, 150 kg ha−1 . The experiment plots, with 4 m × 5 m each, were designed in a complete randomized block with four replicates. Sampling and analyzing Surface soil samples (0–15 cm) were collected in April, 2006. At that time the current crop was rape. Samples were stored at 4 ◦ C for analysis. Fractionation of soil aggregates was achieved using a wet-sieving procedure (Elliott and Cambardella, 1991; Cambardella and Elliott, 1992). Approximately, 100 g soil samples were capillary-wetted to field capacity to prevent slaking following immersion. Wetted soil was immersed in water on a nest of sieves (2, 0.25, and 0.053 mm, respectively) and vertically shaken 3 cm for 50 times within 2 min. Soil aggregates retained on sieves were then backwashed into pre-weighed containers, oven dried at 50 ◦ C for 2–3 d, and weighed. Aggregate-size fractions included macro aggregates (> 2 mm), small macro-aggregates (0.25 to 2 mm), micro-aggregates (0.053–0.25 mm), and silt + clay associated particles (< 0.053 mm). Soil samples were ground to pass a 2-mm sieve and analyzed for soil organic matter, total N, P and K. Soil pH was measured on a 1:2.5 soil-water suspension with a Metrohm 654 pH-meter. Organic carbon (OC) was determined by acid-dichromate wet oxidation procedure (Nelson and Sommers, 1996). Soil organic matter (SOM) was calculated by multiplying OC by 1.724. Total N was determined by Kjeldahl method. Total P was extracted by microwave digestion in sulfuric acid and H2 O2 . Available N was extracted by shaking 20 g of soil in 100 mL of 2 mol L−1 KCl solution for 1 h (Keeney and Nelson, 1982). Available P was determined by the Olsen method (Olsen and Sommers, 1982). Data analysis All analyses were carried out on the four replicates. Data (measured or calculated) were subjected to analysis of variance (ANOVA) and mean values were separated using Duncan’s new multiple range test at P < 0.05. Standard deviations were calculated for mean values of all the determination. All statistical analyses were performed with SPSS statistical package. Total crop yield was calculated by the multiplication of rape yield by 1.5 and then plus rice yield according to their local prices differences in 2006.
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RESULTS AND DISCUSSION Effects of RNT on morphological profile patterns of the Gleyi-Stagnic Anthrosol Morphological profile patterns of the Gleyi-Stagnic Anthrosol under RNT, CR and FPF are listed in Table II. Three horizons A, P and G were identified in RNT and CR profiles, but only one horizon G for flooded soils (Table II). The horizon composition of soil profile in paddy soil is often determined by topographic conditions and ground water tables. Common horizons are cultivated horizon (horizon A), plow pan or percogenic horizon (horizon P), gley horizon (horizon G), and perco-submergic horizon (horizon W). Horizon G is usually formed under strongly reduced conditions, and is considered as an obstacle horizon for plant growth. The position and thickness of horizon G directly affect soil fertility and crop yields (Li, 1992). TABLE II Tillage effects on morphological profile patterns of the Gleyi-Stagnic Anthrosol Tillage method
Horizona)
Depth
Color
Structure
Mottle
Flooded paddy field Combining ridge with no-tillage
G A P G A P G
cm 0–80 0–18 18–30 > 30 0–20 20–35 > 35
5BG 3/1 5RP 5/1 7.5Y 7/2 N 3/0 5P 3/1 5RP 3/1 N 3/0
Muddy clay and occlusion Granular, loose and soft Granular Occlusion and soft Massive, subangular blocky Massive, angular blocky Occlusion and soft
5Y 7/6 7.5Y 7/6 10YR6/6 -
Conventional paddy-upland rotation
a) Horizon
A stands for cultivated horizon, horizon P for plow pan or percogenic horizon, and horizon G for gley horizon.
Horizon G was identified from surface to bottom under FPF. Horizons A and P were formed above horizon G under CR system mainly because the field was drained after rice harvest and the upper portion of the soil profile oxidized. As a result, the morphological profile pattern changed with tillage method. However, a similar change was observed for RNT system (Table II). Although water was kept in the field after rice harvest, micro-relief was altered by ridge tillage and it directly exposed surface horizon to air. As a result the upper portion of the soil profile oxidized. Therefore, horizon G was shifted deeper in the soil profile and horizon A was formed under RNT system without drainage. The soil morphological profile pattern of A-P-G is much better than G not only for rice growth but also for post-rice crops (Li, 1992). Pan (1996) studied characteristics of gleyization of paddy soils and found that the values of redox potential, the percentage of active Fe and Mn in surface soil increased as the location of horizon G shifted deeper and its thickness decreased. Our results showed that soil profile pattern was changed from G to A-P-G through water regime change by RNT system, and thus favors post-rice crops. Furthermore, water is still kept to ensure water security for the next rice crop. Effects of RNT on water-stable soil aggregate distribution RNT, in comparison with FPF and CR systems, increased the proportion of macro-aggregates (> 2 mm) by 120% and 50%, respectively (Table III). This may be due to soil puddling or tillage, which disrupts soil macro-aggregates into micro-aggregates or individual particles (Kirchhof et al., 2000). Another reason may be that mulch cover under RNT increases organic C, as it plays an important role in the formation of macro-aggregates (Tisdall and Oades, 1982). The proportions of water-stable aggregates in soil often change very rapidly when tillage practices and crop rotations are modified (Angers et al., 1997). Angers et al. (1988) reported that the aggregate content of a marine clay soil increased by up to 50% under barley and alfalfa compared to a fallow control or corn. Beare et al. (1997) reported that there were fewer water-stable macro-aggregates in the 0–5 cm layer soil from CR
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plots than from adjacent plots under RNT. You et al. (2006) received similar results in a four-year field study and suggested that no-tillage increased soil aggregation compared to CT system. Our study agreed with their reports, although our experiment was performed in a rice-based cropping system. TABLE III Effects of tillage methods on water-stable soil aggregates distribution Tillage method
> 2 mm
2–1 mm
1–0.25 mm
0.25–0.053 mm
< 0.053 mm
Recover rate
Combining ridge with no-tillage Conventional paddy-upland rotation Flooded paddy field
26.1aa) 18.2ab 12.0b
1.6a 0.5b 1.9a
10.6a 10.0a 11.1a
% 35.8a 28.7a 34.2a
31.9b 42.6a 40.9a
96.9 98.5 96.7
a) Means
followed by the same letter within each column are not different at P < 0.05 by Duncan’s multiple range test.
Water-stable macro-aggregates are the most important structure for soil fertility and plant growth (Oades, 1984; Hillel, 2004). Increases in aggregation concomitant with increases in organic C have been observed in no-tillage systems (Six et al., 2000). Our results also indicated that higher contents of soil organic matter were sequestrated under RNT than those under CR and FPF systems, as supported by data shown in Table III. The proportion of silt and clay associated particles (< 0.053 mm) represented the greatest fraction of whole soil in all three tillage regimes (Table III). A significant decrease of silt and clay contents was found under RNT. Change in clay content was related to decreasing soil leaching. Therefore, RNT may provide benefits of controlling erosion and leaching in this cropping system. Effects of RNT on soil nutrients and organic matter contents The main effects of this tillage system on nutrients are shown in Table IV. Generally, total N, P, K and organic matter contents in soil were improved significantly after RNT has been continuously practiced for 17 years. Many studies reported similar results that C, N, K, Ca and Mg tended to accumulate near the surface in no-tillage culture (Triplett and Van Doren, 1969; Lal, 1976; Dick, 1983; Edwards et al., 1992; Rhoton et al., 1993; Bauer et al., 2002). Beare et al. (1997) reported that total C and N concentrations in soil were higher under no-tillage than those from adjacent plots under conventional tillage (CT) in a 13-year experiment. Limousin and Tessier (2007) also found that no-tilled soil had greater organic C and exchangeable cations than tilled soil, and the differences were concentrated in the upper 5 cm layer. Besides the effects of tillage, the amount of residue being returned to the soil is another reason to explain the results. Plant residue is very important for the regeneration and maintenance of soil fertility within this cropping system (Verma and Bhagat, 1992). In the present long-term experiment, the amounts of plant residue were much higher under RNT than those under CT system because the yields of rice and wheat (or rape) were much higher under RNT (Fig. 1). However, total N and P in soil decreased after FPF turned into CR system (Table IV). TABLE IV Effects of different tillage on soil nutrients and organic matter contents Tillage method
Total N
Total P
Total K g
Conventional paddy-upland rotation Combining ridge with no-tillage Flooded paddy field a) Means
1.47ca) 2.59a 2.10b
0.59c 1.21a 1.07b
Organic matter
kg−1 17.8b 24.1a 18.7b
32.06b 47.52a 34.83b
followed by the same letter within each column are not different at P < 0.05 by Duncan’s multiple range test.
Effects of RNT on crop yields Effects of tillage on rice grain yields were proved the greatest under RNT system from 2001 to 2006,
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Fig. 1 Effects of different tillage methods on rice and total crop yields from 2001 to 2006. Total yields were calculated by the multiplication of rape yield by 1.5 and then plus rice yield. RNT stands for combining ridge with no-tillage, CR for conventional paddy-upland rotation and FPF for flooded paddy field. Vertical bars represent standard deviation.
though rice yields significantly varied over years (Fig. 1). Rice yields under FPF were always higher than those under CR. In 2003 and 2006, rice yields deceased due to serious drought, especially under CR system. Since field had been drained to plant rape in winter, rice yield decreased from 6 800 kg ha−1 in 2002 to 3 500 kg ha−1 in 2003 and 2 100 kg ha−1 in 2006 under CR regime due to water deficiency. Compared to this, rice yields under RNT and FPF were almost 2 times higher than CR system in 2003 and more than that in 2006, regardless of yields experiencing decreases in 2003 and 2006. Fig. 1 also shows total crop yields under different tillage methods from 2001 to 2006. The total crop yields were found to be highest under RNT system in all the years and were higher under CR than FPF except in 2003 and 2006. Since rice yields sharply deceased under CR system in 2003 and 2006, total crop yields were lower than those under FPF. This is exactly the reason why farmers traditionally prefer FPF to CR system. Since RNT provides a way to satisfy both water security and another dry season crop, it has been proven to be a better method in lowland rice-based cropping system. CONCLUSIONS Combining ridge with no-tillage (RNT) method could create ridges and furrows, and alternate micro-relief that enables farmers to plant another dry crop in winter, doubling annual productivity without draining water away. High-yield soil profile pattern of A-P-G was formed, and the location of horizon G became deeper and thinner after RNT was practiced. RNT increased the proportion of macro-aggregate while decreased the proportion of silt and clay, indicating the formation of a better soil structure. Additionally, RNT may provide protection against erosion and control leaching. Finally, RNT improved total nutrients in surface soil and increased crop yields. So, RNT proved to be a better tillage method in lowland rice-based cropping system compared to CR or FPF. REFERENCES Ambassa-Kiki, R., Aboubakar, Y. and Boulama, T. 1996. Zero-tillage for rice production on Cameroonian Vertisols. Soil Till. Res. 39: 75–84. Angers, D. A., Nadeau, P. and Mehuys, G. R. 1988. Determination of carbohydrate composition of soil hydrolysates by high-performance liquid chromatography. J. Chromatogr. 454: 444–449. Angers, D. A., Recous, S. and Aita, C. 1997. Fate of carbon and nitrogen in water-stable aggregates during decomposition of 13 C, 15 N-labelled wheat straw in situ. Eur. J. Soil Sci. 48: 295–300. Archer, D. W., Pikul, J. L., Jr. and Riedell, W. E. 2002. Economic risk, returns and input use under ridge and conventional tillage in the northern Corn Belt, USA. Soil Till. Res. 67: 1–8. Bauer, P. J., Frederick, J. R. and Busscher, W. J. 2002. Tillage effect on nutrient stratification in narrow- and wide-row cropping systems. Soil Till. Res. 66: 175–182. Beare, M. H., Hu, S., Coleman, D. C. and Hendrix, P. F. 1997. Influences of mycelial fungi on soil aggregation and organic matter storage in conventional and no-tillage soils. Appl. Soil Ecol. 5: 211–219.
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Combining Ridge with No-Tillage in Lowland Rice-Based Cropping System: Long-Term Effect on Soil and Rice Yield∗1 JIANG Xian-Jun∗2 and XIE De-Ti College of Resources and Environment, Southwest University, 216 Tiansheng Road, Beibei, Chongqing 400716 (China) (Received April 5, 2008; revised March 23, 2009)
ABSTRACT A tillage method of combining ridge with no-tillage (RNT) was employed in lowland rice-based cropping system to study the long-term effects of RNT on soil profile pattern, soil water stable aggregate distribution, nutrients stratification and yields of rice and post-rice crops. After flooded paddy field (FPF) was practiced with RNT for a long time, soil profile changed from G to A-P-G, and horizon G was shifted to a deeper position in the profile. Also the proportion of macroaggregate (> 2 mm) increased, whereas the proportion of silt and clay (< 0.053 mm) decreased under RNT, indicating a better soil structure that will prevent erosion. RNT helped to control leaching and significantly improved total N, P, K and organic matter in soil. The highest crop yields were found under RNT system every year, and total crop yields were higher under conventional paddy-upland rotation tillage (CR) than under FPF, except in 2003 and 2006 when serious drought occurred. RNT was proven to be a better tillage method for lowland rice-based cropping system. Key Words:
aggregate-size distribution, conservative tillage, flooded paddy field, soil profile pattern
Citation: Jiang, X. J. and Xie, D. T. 2009. Combining ridge with no-tillage in lowland rice-based cropping system: Long-term effect on soil and rice yield. Pedosphere. 19(4): 515–522.
INTRODUCTION The area of paddy soils in China is 25 million hectares, which accounts for 25% of the country’s total cultivated area. Although spread throughout China, approximately 93% of the paddy fields in China are located in the tropical and subtropical regions, 1/3 of which are distributed in lowland regions (Li, 1992). According to natural conditions such as sunlight, temperature and rainfall, this land usually yields crops twice a year in southern China. However, because of irrigation problem, farmers in lowland areas traditionally keep their fields permanently flooded to ensure an adequate water supply for the spring rice crop. Water security was seen to outweigh the costs of reduced yields caused by continuous flooding (Liu et al., 2004). Flooded paddy fields were left unplanted throughout the winter, representing an underutilized resource that can be used. Similar to this, there are vast areas of rice land in South and Southeast Asia that remain fallow after rice harvest due to saturated soil conditions limiting establishment of upland crops (Garrity and Liboon, 1995; Wadeet al., 1999; So and RingroseVoase, 2000). The term ‘flooded paddy-field (FPF)’ is used throughout this article to refer this system. Conventional paddy-upland rotation system (CR) is the main alternative to FPF (Li, 1992; Xie and Chen, 2002; Liu et al., 2004). Utilizing this rotation system, farmers double annual productivity by draining their fields after rice harvest to plant another dry crop such as wheat or rape in winter. For rice-based cropping system, soil puddling in advance of transplanting is advantageous for achieving high productivity (Surendra et al., 2001). This involves ploughing the soil when wet, puddling it and ∗1 Project
supported by the National Natural Science Foundation of China (No. 40501033) and the National Key Technologies R&D Program for the 11th Five-Year Plan of China (No. 2007BAD87B10). ∗2 Corresponding author. E-mail: [email protected].
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keeping the area flooded for the duration of rice growth. Puddling breaks down and disperses soil aggregates into micro-aggregates and individual particles (Kirchhof et al., 2000). Thus this practice destroys soil structure and creates a poor physical condition for the following upland crop (Boparai et al., 1992; Mohanty and Painuli, 2004). Attempts have been made to overcome these physical constraints, such as tillage. However, to date, the effects of tillage on yields are unclear (So and Ringrose-Voase, 2000). Additionally, CR poses water risk for the next rice crop after water is drained away for upland crops. It is because of these problems that FPF has remained the primary method of land utilization (Xie and Chen, 2002). Ridge tillage has been proposed as a conservative method (Taylor, 1983; Liebig et al., 1993; Archer et al., 2002) that provides some benefits, such as erosion prevention and leaching control, time savings, soil structure protection, etc. (Behn, 1985; Kaspar et al., 1995; Waddell and Weil, 2006). Furthermore, ridge tillage provides a special benefit of creating a microenvironment of dry-land (ridge top) in flooded paddy fields (Hou, 1983). As a result, dry season crops (wheat or rape) can be planted on the ridge top while water remained in the furrow. This method allows the planting of an upland crop and avoids water risk for the next rice crop in lowland rice-based cropping system. The no-tillage method is considered as one of the most important conservative tillage methods and has been well documented from physical, chemical and biological aspects (Six et al., 1998, 2000; Frey et al., 1999; Jackson et al., 2003; Samarajeewa et al., 2006). However, most of the researches concerning ridge tillage and no-tillage were concentrated on upland crops or post-rice crops (Nachabe et al., 1999; Samarajeewa et al., 2006); little information is available about the effects of ridge or no-tillage on paddy soils (Ambassa-Kiki et al., 1996). Crop yield has been used as the most important indicator to evaluate the sustainability of an agroecosystem. Numerous researches have been done to investigate the effects of various tillage methods on crop yields (Li et al., 2001). Henderson (1979) remarked that most of the studies did not provide an insight into how the procedure influenced crop yield. Moreover, the results obtained were often site and year specific and often contradictory and inconclusive due to variability in soil type, cropping systems, and climate (Wright and Coleman, 1999; Guzha, 2004). Therefore, further research on different types of soil is still required, especially for long-term experiments. The primary objective of the present work was to study the long-term effects of combining ridge with no-tillage (RNT) on soil profile pattern, soil water stable aggregate distribution, nutrients stratification and the yields of rice and post-rice crops in lowland rice-based cropping system. MATERIALS AND METHODS Experimental site A field experiment has been carried out since 1990 at Southwest University, which is located in the Sichuan Basin, southwestern China (latitude 28◦ –32◦ N, longitude 103◦ –108◦ E). The Sichuan Basin covers 165 000 km2 with an annual mean temperature of 14–19 ◦ C and rainfall of 1 000–1 400 mm and naturally yields crop twice a year. The soil used in this study was a Gleyi-Stagnic Anthrosol according to Chinese Soil Taxonomy (CRGCST, 2001), which was developed from purple mudstone. Physical and chemical properties of the soil are listed in Table I. The crops used were wheat (Triticum aestivum L.) TABLE I Physical and chemical properties of the soil used Soil depth
Total N
cm 0–10 10–20 20–30
2.00 1.90 1.87
Available P g kg−1 0.85 0.83 0.79
K 22.4 22.2 23.5
N 165 158 153
Organic matter P
mg kg−1 10.4 9.85 10.8
Clay
pH (H2 O)
250 262 282
6.80 6.70 6.65
K g kg−1 115 120 126
37.4 37.6 37.0
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or rape (Brassica napus L.) in winter and rice (Oryza sativa L.) in summer. Tillage treatments For RNT, ridges were made by manpower in the fields. The ridges were 25 cm wide at the top and the furrows were 30 cm wide and 35 cm deep. Each plot consisted of five rows. From rice transplantation to vegetative stage, the water surface was kept parallel with ridge top in the field, and during other time of a year, water depth in furrow was 25–30 cm, i.e., ridge top was 5–10 cm above water surface. After the harvest of the rice crop, mud from furrow was artificially stacked on the ridge top. Wheat was seeded after the field was covered with rice stubble (50–60 cm). During the wheat growing season, water levels in the furrow were maintained at 5–10 cm depth, i.e., ridge top was 20–25 cm above water surface, thus retaining ridge soakage irrigation. After the harvest of the wheat crop, wheat stubble and weeds were buried in the furrow bottom, and the field was submerged with water up to ridge top for the cultivation of rice. For CR, rice was transplanted in a flooded field with a layer of water until maturation. After rice harvest, the paddy field was drained, ploughed, dried, and harrowed and then wheat was seeded. After wheat was harvested, the soil was puddled and harrowed twice and rice seedlings were transplanted again. For FPF, soil was puddled and harrowed twice before rice-seedlings were transplanted. Rice was planted in a flooded field in summer and land remained fallow in winter. Water was kept flooded in the field throughout the year. Other managements used in the three tillage methods were all the same, including fertilizer application. The annual application of fertilizers was as follows: urea, 270 kg ha−1 ; calcium superphosphate, 500 kg ha−1 ; and potassium chloride, 150 kg ha−1 . The experiment plots, with 4 m × 5 m each, were designed in a complete randomized block with four replicates. Sampling and analyzing Surface soil samples (0–15 cm) were collected in April, 2006. At that time the current crop was rape. Samples were stored at 4 ◦ C for analysis. Fractionation of soil aggregates was achieved using a wet-sieving procedure (Elliott and Cambardella, 1991; Cambardella and Elliott, 1992). Approximately, 100 g soil samples were capillary-wetted to field capacity to prevent slaking following immersion. Wetted soil was immersed in water on a nest of sieves (2, 0.25, and 0.053 mm, respectively) and vertically shaken 3 cm for 50 times within 2 min. Soil aggregates retained on sieves were then backwashed into pre-weighed containers, oven dried at 50 ◦ C for 2–3 d, and weighed. Aggregate-size fractions included macro aggregates (> 2 mm), small macro-aggregates (0.25 to 2 mm), micro-aggregates (0.053–0.25 mm), and silt + clay associated particles (< 0.053 mm). Soil samples were ground to pass a 2-mm sieve and analyzed for soil organic matter, total N, P and K. Soil pH was measured on a 1:2.5 soil-water suspension with a Metrohm 654 pH-meter. Organic carbon (OC) was determined by acid-dichromate wet oxidation procedure (Nelson and Sommers, 1996). Soil organic matter (SOM) was calculated by multiplying OC by 1.724. Total N was determined by Kjeldahl method. Total P was extracted by microwave digestion in sulfuric acid and H2 O2 . Available N was extracted by shaking 20 g of soil in 100 mL of 2 mol L−1 KCl solution for 1 h (Keeney and Nelson, 1982). Available P was determined by the Olsen method (Olsen and Sommers, 1982). Data analysis All analyses were carried out on the four replicates. Data (measured or calculated) were subjected to analysis of variance (ANOVA) and mean values were separated using Duncan’s new multiple range test at P < 0.05. Standard deviations were calculated for mean values of all the determination. All statistical analyses were performed with SPSS statistical package. Total crop yield was calculated by the multiplication of rape yield by 1.5 and then plus rice yield according to their local prices differences in 2006.
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RESULTS AND DISCUSSION Effects of RNT on morphological profile patterns of the Gleyi-Stagnic Anthrosol Morphological profile patterns of the Gleyi-Stagnic Anthrosol under RNT, CR and FPF are listed in Table II. Three horizons A, P and G were identified in RNT and CR profiles, but only one horizon G for flooded soils (Table II). The horizon composition of soil profile in paddy soil is often determined by topographic conditions and ground water tables. Common horizons are cultivated horizon (horizon A), plow pan or percogenic horizon (horizon P), gley horizon (horizon G), and perco-submergic horizon (horizon W). Horizon G is usually formed under strongly reduced conditions, and is considered as an obstacle horizon for plant growth. The position and thickness of horizon G directly affect soil fertility and crop yields (Li, 1992). TABLE II Tillage effects on morphological profile patterns of the Gleyi-Stagnic Anthrosol Tillage method
Horizona)
Depth
Color
Structure
Mottle
Flooded paddy field Combining ridge with no-tillage
G A P G A P G
cm 0–80 0–18 18–30 > 30 0–20 20–35 > 35
5BG 3/1 5RP 5/1 7.5Y 7/2 N 3/0 5P 3/1 5RP 3/1 N 3/0
Muddy clay and occlusion Granular, loose and soft Granular Occlusion and soft Massive, subangular blocky Massive, angular blocky Occlusion and soft
5Y 7/6 7.5Y 7/6 10YR6/6 -
Conventional paddy-upland rotation
a) Horizon
A stands for cultivated horizon, horizon P for plow pan or percogenic horizon, and horizon G for gley horizon.
Horizon G was identified from surface to bottom under FPF. Horizons A and P were formed above horizon G under CR system mainly because the field was drained after rice harvest and the upper portion of the soil profile oxidized. As a result, the morphological profile pattern changed with tillage method. However, a similar change was observed for RNT system (Table II). Although water was kept in the field after rice harvest, micro-relief was altered by ridge tillage and it directly exposed surface horizon to air. As a result the upper portion of the soil profile oxidized. Therefore, horizon G was shifted deeper in the soil profile and horizon A was formed under RNT system without drainage. The soil morphological profile pattern of A-P-G is much better than G not only for rice growth but also for post-rice crops (Li, 1992). Pan (1996) studied characteristics of gleyization of paddy soils and found that the values of redox potential, the percentage of active Fe and Mn in surface soil increased as the location of horizon G shifted deeper and its thickness decreased. Our results showed that soil profile pattern was changed from G to A-P-G through water regime change by RNT system, and thus favors post-rice crops. Furthermore, water is still kept to ensure water security for the next rice crop. Effects of RNT on water-stable soil aggregate distribution RNT, in comparison with FPF and CR systems, increased the proportion of macro-aggregates (> 2 mm) by 120% and 50%, respectively (Table III). This may be due to soil puddling or tillage, which disrupts soil macro-aggregates into micro-aggregates or individual particles (Kirchhof et al., 2000). Another reason may be that mulch cover under RNT increases organic C, as it plays an important role in the formation of macro-aggregates (Tisdall and Oades, 1982). The proportions of water-stable aggregates in soil often change very rapidly when tillage practices and crop rotations are modified (Angers et al., 1997). Angers et al. (1988) reported that the aggregate content of a marine clay soil increased by up to 50% under barley and alfalfa compared to a fallow control or corn. Beare et al. (1997) reported that there were fewer water-stable macro-aggregates in the 0–5 cm layer soil from CR
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plots than from adjacent plots under RNT. You et al. (2006) received similar results in a four-year field study and suggested that no-tillage increased soil aggregation compared to CT system. Our study agreed with their reports, although our experiment was performed in a rice-based cropping system. TABLE III Effects of tillage methods on water-stable soil aggregates distribution Tillage method
> 2 mm
2–1 mm
1–0.25 mm
0.25–0.053 mm
< 0.053 mm
Recover rate
Combining ridge with no-tillage Conventional paddy-upland rotation Flooded paddy field
26.1aa) 18.2ab 12.0b
1.6a 0.5b 1.9a
10.6a 10.0a 11.1a
% 35.8a 28.7a 34.2a
31.9b 42.6a 40.9a
96.9 98.5 96.7
a) Means
followed by the same letter within each column are not different at P < 0.05 by Duncan’s multiple range test.
Water-stable macro-aggregates are the most important structure for soil fertility and plant growth (Oades, 1984; Hillel, 2004). Increases in aggregation concomitant with increases in organic C have been observed in no-tillage systems (Six et al., 2000). Our results also indicated that higher contents of soil organic matter were sequestrated under RNT than those under CR and FPF systems, as supported by data shown in Table III. The proportion of silt and clay associated particles (< 0.053 mm) represented the greatest fraction of whole soil in all three tillage regimes (Table III). A significant decrease of silt and clay contents was found under RNT. Change in clay content was related to decreasing soil leaching. Therefore, RNT may provide benefits of controlling erosion and leaching in this cropping system. Effects of RNT on soil nutrients and organic matter contents The main effects of this tillage system on nutrients are shown in Table IV. Generally, total N, P, K and organic matter contents in soil were improved significantly after RNT has been continuously practiced for 17 years. Many studies reported similar results that C, N, K, Ca and Mg tended to accumulate near the surface in no-tillage culture (Triplett and Van Doren, 1969; Lal, 1976; Dick, 1983; Edwards et al., 1992; Rhoton et al., 1993; Bauer et al., 2002). Beare et al. (1997) reported that total C and N concentrations in soil were higher under no-tillage than those from adjacent plots under conventional tillage (CT) in a 13-year experiment. Limousin and Tessier (2007) also found that no-tilled soil had greater organic C and exchangeable cations than tilled soil, and the differences were concentrated in the upper 5 cm layer. Besides the effects of tillage, the amount of residue being returned to the soil is another reason to explain the results. Plant residue is very important for the regeneration and maintenance of soil fertility within this cropping system (Verma and Bhagat, 1992). In the present long-term experiment, the amounts of plant residue were much higher under RNT than those under CT system because the yields of rice and wheat (or rape) were much higher under RNT (Fig. 1). However, total N and P in soil decreased after FPF turned into CR system (Table IV). TABLE IV Effects of different tillage on soil nutrients and organic matter contents Tillage method
Total N
Total P
Total K g
Conventional paddy-upland rotation Combining ridge with no-tillage Flooded paddy field a) Means
1.47ca) 2.59a 2.10b
0.59c 1.21a 1.07b
Organic matter
kg−1 17.8b 24.1a 18.7b
32.06b 47.52a 34.83b
followed by the same letter within each column are not different at P < 0.05 by Duncan’s multiple range test.
Effects of RNT on crop yields Effects of tillage on rice grain yields were proved the greatest under RNT system from 2001 to 2006,
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Fig. 1 Effects of different tillage methods on rice and total crop yields from 2001 to 2006. Total yields were calculated by the multiplication of rape yield by 1.5 and then plus rice yield. RNT stands for combining ridge with no-tillage, CR for conventional paddy-upland rotation and FPF for flooded paddy field. Vertical bars represent standard deviation.
though rice yields significantly varied over years (Fig. 1). Rice yields under FPF were always higher than those under CR. In 2003 and 2006, rice yields deceased due to serious drought, especially under CR system. Since field had been drained to plant rape in winter, rice yield decreased from 6 800 kg ha−1 in 2002 to 3 500 kg ha−1 in 2003 and 2 100 kg ha−1 in 2006 under CR regime due to water deficiency. Compared to this, rice yields under RNT and FPF were almost 2 times higher than CR system in 2003 and more than that in 2006, regardless of yields experiencing decreases in 2003 and 2006. Fig. 1 also shows total crop yields under different tillage methods from 2001 to 2006. The total crop yields were found to be highest under RNT system in all the years and were higher under CR than FPF except in 2003 and 2006. Since rice yields sharply deceased under CR system in 2003 and 2006, total crop yields were lower than those under FPF. This is exactly the reason why farmers traditionally prefer FPF to CR system. Since RNT provides a way to satisfy both water security and another dry season crop, it has been proven to be a better method in lowland rice-based cropping system. CONCLUSIONS Combining ridge with no-tillage (RNT) method could create ridges and furrows, and alternate micro-relief that enables farmers to plant another dry crop in winter, doubling annual productivity without draining water away. High-yield soil profile pattern of A-P-G was formed, and the location of horizon G became deeper and thinner after RNT was practiced. RNT increased the proportion of macro-aggregate while decreased the proportion of silt and clay, indicating the formation of a better soil structure. Additionally, RNT may provide protection against erosion and control leaching. Finally, RNT improved total nutrients in surface soil and increased crop yields. So, RNT proved to be a better tillage method in lowland rice-based cropping system compared to CR or FPF. REFERENCES Ambassa-Kiki, R., Aboubakar, Y. and Boulama, T. 1996. Zero-tillage for rice production on Cameroonian Vertisols. Soil Till. Res. 39: 75–84. Angers, D. A., Nadeau, P. and Mehuys, G. R. 1988. Determination of carbohydrate composition of soil hydrolysates by high-performance liquid chromatography. J. Chromatogr. 454: 444–449. Angers, D. A., Recous, S. and Aita, C. 1997. Fate of carbon and nitrogen in water-stable aggregates during decomposition of 13 C, 15 N-labelled wheat straw in situ. Eur. J. Soil Sci. 48: 295–300. Archer, D. W., Pikul, J. L., Jr. and Riedell, W. E. 2002. Economic risk, returns and input use under ridge and conventional tillage in the northern Corn Belt, USA. Soil Till. Res. 67: 1–8. Bauer, P. J., Frederick, J. R. and Busscher, W. J. 2002. Tillage effect on nutrient stratification in narrow- and wide-row cropping systems. Soil Till. Res. 66: 175–182. Beare, M. H., Hu, S., Coleman, D. C. and Hendrix, P. F. 1997. Influences of mycelial fungi on soil aggregation and organic matter storage in conventional and no-tillage soils. Appl. Soil Ecol. 5: 211–219.
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