Growth Characteristics and Yield of Late-Season Rice under No-tillage and Non-flooded Cultivation with Straw Mulching

Rice Science, 2010, 17(2): 141í148 Copyright © 2010, China National Rice Research Institute. Published by Elsevier BV. All rights reserved DOI: 10.1016/S1672-6308(08)60117-1

Growth Characteristics and Yield of Late-Season Rice under No-tillage and Non-flooded Cultivation with Straw Mulching WANG Dong1, LI Hui-xin1, QIN Jiang-tao1, 2, LI Da-ming1, HU Feng1 (1College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China; 2 Nanjing Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China)

Abstract: A long-term field experiment (started at 2003) was conducted to determine the effects of different rice cultivation methods on growth characteristics and grain yield of late-season rice under double-rice cropping system in seasonal drought region of southeast China (Yujiang County, Jiangxi Province). The rice cultivation methods included no-tillage and flooded rice cultivation (N-F), no-tillage and non-flooded rice cultivation with straw mulching (N-SM), and no-tillage and non-flooded rice cultivation without straw mulching (N-ZM). There was no significant difference in rice grain yield between the N-SM and N-F treatments. However, the rice grain yields in the N-SM and N-F treatments were significantly higher than that in the N-ZM treatment. The late-season rice plants in the N-SM treatment had significantly higher numbers of effective panicles and total grains per hill compared with those in the N-ZM treatment. The above-ground dry matter of late-season rice was similar between the N-SM and N-F treatments. Compared with the N-F treatment, the N-ZM and N-SM treatments significantly decreased the leaf area at the heading stage. Moreover, the N-SM treatment could significantly increase total root length and root tip number at the grain-filling stage compared with the N-ZM treatment. Key words: rice; no-tillage; non-flooded cultivation; straw mulching; growth characteristics; yield

Rice (Oryza sativa L.) is the most luxurious user of water among all the crops and flood-irrigated rice consumes large amounts of total irrigation water with low water use efficiency in China and other Asian countries [1-2]. In the southeast region of China, the major flood-irrigated rice production system is the continuous double-rice cropping system. However, the growth and grain yield of late-season rice (second crop) in this rice cropping system are greatly affected by seasonal drought and scarcity of fresh irrigation water, thereby leading to low crop productivity [3-4]. Thus, it is necessary and important to develop a good agricultural management in terms of increasing water use efficiency and improving the productivity and sustainability of this rice cropping system in the southeast region of China. Non-flooded mulching rice cultivation method, including non-flooded rice cultivation with plastic film and crop straw residue mulching, can save a great amount of fresh irrigation water, maintain or increase rice grain yield compared with the conventional flooded Received: 21 August 2009; Accepted: 10 November 2009 Corresponding author: HU Feng ([email protected]) This is an English version of the paper published in Chinese in Chinese Journal of Rice Science, Vol. 23, No. 5, 2009, Pages 517–522.

rice cultivation method [1-9]. The non-flooded mulching rice cultivation method arises and prevails in single rice cropping system and rice-wheat cropping system in many regions of China where rice production faces the scarcity of water resource [5-6]. However, most previous studies about the impact of this cultivation method on water balance, plant growth and grain yield in ricebased cropping systems are based on the conventional tillage [5-9], whereas studies on the impact of this rice cultivation method based on other tillage (e.g. no tillage) are less reported. As a good agriculture practice, the research and application of conservation tillage (including no tillage, no tillage with straw mulching) in rice-based cropping systems of southern China has been developed since the 1990s [10]. As we know, the conservation tillage can conserve soil and water resources, increase soil fertility, as well as improve plant growth and increase grain yield [10-12]. Therefore, integrated practice involving nonflooded rice cultivation and conservation tillage, a new high-yield and water-saving rice cultivation method, might have a great potential to be applied in the doublerice cropping system in the seasonal drought region of China.

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Fortunately, a long-term field experiment has been conducted since 2003, which was financially supported by the National High-Tech R & D Program of China named ‘Integration and demonstration of water-saving technologies in the seasonal drought area in Southeast China (Yingtan, Jiangxi Province)’, to investigate the effects of non-flooded rice cultivation with or without straw mulching on the water balance and performance of late-season rice under different tillage regimes [3-4]. From 2003 to 2006, field experimental results had shown that non-flooded rice cultivation with straw mulching under either conventional tillage or no tillage applied to late-season rice cropping is a good watersaving rice cultivation with high grain yield in the double-rice cropping system in this region [3-4], owing to alleviating seasonal drought, saving irrigation water and maintaining rice grain yield compared to conventional flooded rice cultivation method. However, the effects of no-tillage and non-flooded rice cultivation with straw mulching on rice growth characteristics are less known. No-tillage and non-flooded rice cultivation with straw mulching (N-SM) is the combination of conservation tillage and non-flooded rice cultivation with straw mulching. When N-SM is applied to paddy system, it has a substantial effect on micro-ecological environments (e.g. soil water content, temperature, and soil fertility) during rice growth period, thereby greatly affecting the characteristics of rice growth and the formation of rice grain yield. Therefore, the objective of this study is to investigate the effects of N-SM on rice grain yield, plant height, tiller number, above-ground dry matter, leaf area, and root traits at different developmental stages of rice.

MATERIALS AND METHODS Experimental site description A field experiment was conducted at the Dengjiapu farm at Yujiang County, Jiangxi Province in southeast

China (28°15ƍN, 116°55ƍE) in 2007, which was initially established in 2003. The experimental area is a representative of a typical subtropical humid climate with a mean annual temperature of 17.6°C, a maximum daily temperature of 40°C in summer, an average of 262 frost-free days and a rainfall of 1750 mm, about 50% of which falls from March to early July. The uneven distribution of rainfall causes strong seasonal drought in summer, and the late-season rice would be affected by drought [3-4]. This was particularly true in 2007 during the experiment (Table 1). The soil was developed from alluvial deposits and used for rice cropping more than 50 years. The soil is anthropogenic soil and the soil horizons include A-P-W1-W2. There was intact ploughpan in this field. The thickness of ploughpan was 7–8 cm at about 15–17 cm under field surface. Groundwater level was at 5.0–6.5 m below soil surface in the experimental area. The soil was sandy soil with sand fraction (0.02–2.00 mm) of 739 g/kg and clay fraction (<0.002 mm) of 73 g/kg. The soil (0–15 cm depth) before the experiment contained soil organic carbon 14.79 g/kg, total N 1.54 g/kg, alkali hydrolyzable N 95.1 mg/kg, Olsen-P 16.1 mg/kg, and exchangeable K 34.2 mg/kg, with pH 5.5 (1.0:2.5, soil: water). Treatments and field management The crop system was early-season rice followed by late-season rice. The rainfall for the early-season rice was plentiful and water management trial was performed only in the late-season rice. To reduce the effect of water management in the early-season rice on the late-season rice, the early-season rice was managed under the controlled flooded cultivation, always keeping a standing water depth in the field before harvest. In the late-season rice, three water managements were set up, including no-tillage and conventional flooded rice cultivation (N-F), no-tillage and non-flooded rice cultivation without mulching (N-ZM), and no-tillage

Table 1. Weather data during the late rice cropping season. Weather factor

Year

Mean air temperature (°C)

2007 Mean value of 41 years (1954–1995) 2007 Mean value of 41 years (1954–1995) 2007 Mean value of 41 years (1954–1995)

Potential evaporation (mm) Rainfall (mm)

July 30.5 29.4 309.1 237.0 42.3 123.0

August 29.0 28.1 243.8 211.4 116.1 118.0

Month September 24.1 24.8 129.9 142.5 115.3 92.6

October 20.1 17.6 159.9 119.0 14.2 71.2

Mean 25.9 25.0 210.7 177.5 72.0 101.2

WANG Dong, et al. Growth Characteristics of Rice under No-tillage and Non-flooded Cultivation with Straw Mulching

and non-flooded rice cultivation with straw mulching (N-SM). The rice straw which harvested from the early-season rice in the same field was applied a week after transplanting at 5000 kg/hm2 in dry weight. There was a strip (2 m wide) between flooded part and nonflooded part. Each treatment was triplicate in the field. In the non-flooded parts, all the treatments were arranged with a randomized design. The plot size was 30 m2 (6 m ×5 m) and the plots were separated by sealed ridge (sealed by double plastic films, the depth was 40 cm under the soil surface) to prevent water exchange among the plots. The two range ridges between conventional flooded part and non-flooded part were also sealed by the same way. As for water management, N-F treatment was submerged by standing water until two weeks before rice harvest, and the N-ZM and N-SM treatments were fully irrigated to over-saturated conditions when the soil water content was about 70% of the field water capacity (volume fraction was 41.3%), and the shallow standing water would disappear in next few hours after irrigation during the rice growing period. The late-season rice variety was Zhongxuan 10 in 2007, the same as in the long-term field experiment from 2003 to 2006. Rice seedlings were transplanted on 25 July at a density of 18 hills/m2 with two or three plants per hill. Rice plants under the N-F treatment were harvested on 2 November, and those under the N-ZM and N-SM treatments were harvested on 6 November. According to the local fertility practice, urea, superphosphate and potassium chloride were applied at the rates of 112.5 kg/hm2 N, 39.3 kg/hm2 P and 62.2 kg/hm2 K as basal fertilizer before transplanting, and thoroughly incorporated into soil by hand. Additional urea was topdressed at the rates of 45.0 and 67.5 kg/hm2 at the tillering and heading stages, respectively after the fields were irrigated. Weeds were controlled by herbicides. Organophosphate insecticides were used to control Chilo suppressalis and Tryporyza incertulas. Measurements Weather data Monthly average values of air temperature, rainfall and potential evaporation during rice growth period in 2007 are presented in Table 1. The average air temperature from transplanting to maturity was 25.9°C, which was

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higher than the 41-year (1954–1995) average of 25.0°C at the same period. Monthly average rainfall from transplanting to maturity in 2007 was 72.0 mm, 29% less than the 41-year average value (101.2 mm). And the monthly average potential evaporation from transplanting to maturity in 2007 was 210.7 mm, 19% higher than the 41-year average value of 177.5 mm. Hence, the growth of late-season rice was affected by drought in this region in 2007. Plant height and tiller number Ten plants were randomly selected along the diagonal of each plot, and tagged to measure the plant height and tiller number at weekly intervals at the tillering stage. The ratio of effective tillers is calculated by dividing the effective panicle number by tiller number at the middle of tillering stage. Above-ground dry matter Three plants of each plot were randomly sampled at the tillering, elongation, heading, grain-filling and ripening stages, respectively. The plant samples were washed with distilled water and oven dried at 70°C to constant weight. Leaf area At the heading stage, ten plants of each plot were randomly selected to determine the areas of flag leaf, the second and the third leaves from the top. Leaf area was obtained through multiplication of the length and width of leaf multiplied by corrected coefficient (0.75). Rice root traits At the grain-filling stage, rice roots (three hills per plot) were randomly sampled and washed with distilled water, and measured by Win RHIZO 2003b. The parameters included total root length, total root surface area, root volume and number of total root tips. Rice yield At the ripening stage, six plants of each plot were randomly sampled to determine yield components (i.e. effective panicle number, total grain number per hill, seed setting rate, 1000-grain weight) and calculate rice grain yield.

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Table 2. Effects of no-tillage and non-flooded rice cultivation with straw mulching on yield and its components of late-season rice. Treatment N-ZM N-SM N-F

No. of effective panicles (×104 /hm2) 206 b 269 a 261 a

No. of total grains per hill 1492.83 b 2079.17 a 1908.44 ab

Seed setting rate (%) 90.20 a 90.35 a 93.43 a

1000-grain weight (g) 24.77 a 25.53 a 25.61 a

Yield (kg/hm2) 6118.98 b 8417.63 a 8222.82 a

N-ZM, No-tillage and non-flooded rice cultivation without straw mulching; N-SM, No-tillage and non-flooded rice cultivation with straw mulching; N-F, No-tillage and flooded rice cultivation. Data followed by the same letters are not significantly different (P>0.05, the Duncan’s method) in the same column.

Data analysis All data were subjected to analysis of variance (ANOVA) using SPSS11.0. And the means of three replicates were compared using the Duncan’s New Multiple Range Test at the 5% level of significance.

RESULTS Rice yield and its components There was no significant difference in rice grain yield between the N-SM and N-F treatments (Table 2). However, the rice grain yields in both treatments were significantly higher than that in the N-ZM treatment. The effective panicle number was similar between the N-SM and N-F treatments, whereas significantly decreased in the N-ZM treatment. Compared with the N-F treatment, the N-SM treatment had no significant effect on total grain number per hill, whereas the N-ZM treatment slightly decreased the total grain number. In terms of seed setting rate and 1000-grain weight, there was no significant difference among the three cultivation treatments. In the no-tillage and non-

A

flooded rice cultivation treatments, the effective panicle number and total grain number per hill under the N-SM treatment were significantly higher than those under the N-ZM treatment. Analysis of correlation showed that the grain yield was significantly and positively correlated with the effective panicle number, total grain number per hill and 1000-grain weight. And there was a significant and positive correlation of effective panicle number with total grain number per hill. Hence, the high rice grain yield under the N-SM treatment could be likely attributed to the increase of effective panicle number per hill and total grain number compared to the N-ZM treatment. Plant height and tiller number per hill The plant height and tiller number per hill affected by different treatments at the tillering stage are shown in Fig. 1. The plant height in the N-SM treatment was similar with that in the N-F treatment at the tillering stage, and the significantly lower plant height on 1 September in the N-SM treatment was likely related to the effect of decomposed rice straw compared with the N-F treatment (Fig. 1-A). The plant height in the N-ZM treatment was significantly lower

B

Fig. 1. Effects of no-tillage and non-flooded rice cultivation with straw mulching on plant height (A) and tiller number per hill (B) at the tillering stage. N-ZM, No-tillage and non-flooded rice cultivation without straw mulching; N-SM, No-tillage and non-flooded rice cultivation with straw mulching; N-F, No-tillage and flooded rice cultivation.

WANG Dong, et al. Growth Characteristics of Rice under No-tillage and Non-flooded Cultivation with Straw Mulching

than that in the N-F treatment at the tillering stage. The difference of plant height between the N-ZM and N-F treatments might be due to the inhibited rice growth by drought stress in the N-ZM treatment. The plant height in the N-SM treatment was significantly higher than that in the N-ZM treatment from 11 August to 25 August. The results showed that under the no-tillage and non-flooded rice cultivation, the plant height of rice was improved by straw mulching through conserving soil water content. Rice tiller number gradually increased and reached a peak at about 30 days after transplanting, and declined thereafter (Fig. 1-B). The tiller number per hill in the N-SM treatment was slightly higher than those in both N-F and N-ZM treatments, but the difference was not significant. In our study, the N-F and N-SM treatments led to the higher ratio of effective tiller than the N-ZM treatment. As a result, it showed that under the no-tillage and non-flooded rice cultivation conditions, straw mulching could enhance the ability of rice tillering to some extent. Above-ground dry matter The above-ground dry matter increased with the growing stage from tillering to ripening, and maximized at the ripening stage (Table 3). At the tillering stage, the above-ground dry matter was not significantly affected by the treatments. At the elongation, heading,

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grain-filling and ripening stages, the N-F and N-SM treatments significantly increased the above-ground dry matter compared with the N-ZM treatment. The above-ground dry matter accumulated from heading to ripening in both N-F and N-SM treatments were also significantly higher than that in the N-ZM treatment. However, there was no significant difference in aboveground dry matter between the N-F and N-SM treatments at the rice developmental stage mentioned above. Therefore, the disadvantage of lower rice biomass in no-tillage and non-flooded rice cultivation could be overcome by straw mulching. And the N-SM treatment would improve the grain filling resulted from much nutrition, which was provided through the increase of dry matter. Leaf area of the top three leaves at the heading stage Leaf growth of upland rice is most sensitive to water deficit at the heading stage [13]. The lengths, widths and areas of the top three leaves were greatly affected by the treatments (Table 4). Compared with the N-F treatment, the flag leaf and the second leaf from the top in the N-ZM and N-SM treatments were markedly shortened and narrowed. The N-SM treatment led to almost the same length and width of the third leaf from the top as the N-F treatment whereas the N-ZM treatment led to significantly lower width of the third leaf from the top compared with the N-F treatment. In

Table 3. Effects of no-tillage and non-flooded rice cultivation with straw mulching on above-ground dry matter and accumulation at different stages. g/hill Treatment N-ZM N-SM N-F

Above-ground dry matter weight Tillering stage

Elongation stage

Heading stage

10.43 a 11.53 a 12.33 a

28.00 b 31.87 a 32.60 a

40.67 b 48.20 a 49.10 a

Grain-filling stage 50.63 b 55.33 ab 59.23 a

Ripening stage

Dry matter accumulation after heading

62.80 b 79.67 a 86.00 a

22.13 b 31.47 a 36.90 a

N-ZM, No-tillage and non-flooded rice cultivation without straw mulching; N-SM, No-tillage and non-flooded rice cultivation with straw mulching; N-F, No-tillage and flooded rice cultivation. Data followed by the same letters are not significantly different (P>0.05, the Duncan’s method) in the same column. Table 4. Effects of no-tillage and non-flooded rice cultivation with straw mulching on functional rice leaf length, width and area at the heading stage. Flag leaf Treatment N-ZM N-SM N-F

Length (cm) 35.30 b 37.66 b 44.22 a

Width (cm) 1.75 b 1.79 ab 1.89 a

The second leaf from the top Area (cm2) 46.34 b 50.48 b 62.89 a

Length (cm) 44.84 b 46.85 b 52.53 a

Width (cm) 1.40 b 1.41 b 1.52 a

Area (cm2) 47.11 b 49.55 b 59.76 a

The third leaf from the top Length (cm) 47.53 b 48.69 ab 53.29 a

Width (cm) 1.25 a 1.27 a 1.31 a

Area (cm2) 44.54 b 46.15 ab 52.38 a

N-ZM, No-tillage and non-flooded rice cultivation without straw mulching; N-SM, No-tillage and non-flooded rice cultivation with straw mulching; N-F, No-tillage and flooded rice cultivation. Data followed by the same letters are not significantly different (P>0.05, the Duncan’s method) in the same column.

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Table 5. Effects of no-tillage and non-flooded rice cultivation with straw mulching on rice root traits at the grain-filling stage. Treatment N-SM N-ZM N-F

Total length (cm/hill) 7009.95 b 9115.87 a 8491.78 ab

Total surface area (cm2/hill) 3135.18 a 3649.73 a 3613.12 a

Volume (cm3/hill) 112.37 a 108.71 a 103.88 a

No. of root tips per hill 5742.33 c 8732.33 a 7496.67 b

N-ZM, No-tillage and non-flooded rice cultivation without straw mulching; N-SM, No-tillage and non-flooded rice cultivation with straw mulching; N-F, No-tillage and flooded rice cultivation. Data followed by different letters are significantly different (P<0.05, the Duncan’s method) in the same column.

the no-tillage and non-flooded rice cultivation treatments, the lengths and widths of the top three leaves were similar between the N-SM and N-ZM treatments. The leaf areas of flag leaf and the second leaf from the top in both N-SM and N-ZM treatments were significantly lower than those in the N-F treatment. The leaf area of the third leaf from the top in the N-ZM treatment was significantly lower than that in the N-F treatment, whereas no significant difference was observed between the N-SM and N-F treatments in the leaf area of the third leaf from the top. The results indicate that the growth of the top three leaves at the heading stage under no-tillage and non-flooded rice cultivation was inhibited by water deficit. Rice root system at the grain-filling stage Senescence of upland rice is related with rice root growth at the grain-filling stage [14-15]. The treatments had more effects on the total root length and root tip number than the total root surface area and root volume (Table 5). The total root length and total surface area were similar between the N-SM and N-F treatments, whereas the root tip number was significantly higher in the N-SM treatment than in the N-F treatment. And the N-ZM treatment slightly decreased the total root length and significantly reduced the root tip number compared with the N-F treatment. There was no significant difference in root volume among the treatments. In the no-tillage and non-flooded rice cultivation treatments, the total root length and root tip number were significantly higher in the N-SM treatment than in the N-ZM treatment. The results suggest that straw mulching could promote the growth of rice root under the no-tillage and nonflooded rice cultivation conditions. Moreover, the improved rice root could absorb much soil water and nutrients and thereby contributing to rice growth in the N-SM treatment.

DISCUSSION Rice grain yield and growth characteristics Compared with the N-F treatment, the lower rice grain yield in the N-ZM treatment could be mainly attributed to the decrease of the effective panicle number (Fig. 1-B and Table 2). And the decrease of effective panicle number of late-season rice in the N-ZM treatment might result from lower rice dry matter accumulation (Table 3). In our study, rice plants in the N-ZM treatment exhibited significantly lower plant height, above-ground dry matter accumulation, and leaf area at the heading stage, as well as reduced total root length and root tip number at the grain-filling stage compared with those under the N-F treatment (Fig. 1-A and Fig. 1-B, Tables 3, 4 and 5). The reason was that rice growth could be inhibited by water stress due to low soil water content. Tao et al [7] pointed out that little soil moisture reduction could decrease dry matter production and grain yield in rice. The poor performance of rice in the non-flooded cultivation without mulching was similar between no tillage in our study and conventional tillage [3, 8, 13]. However, the rice grain yield in the N-SM treatment was similar with that in the N-F treatment and significantly higher than that in the N-ZM treatment (Table 2). The difference in rice grain yield might be due to improved rice growth characteristics. In our study, the effective panicle number was similar between the N-SM and N-F treatments, and higher in the N-SM treatment than in the N-ZM treatment (Fig. 1B). The increase of effective panicle number in the N-SM treatment resulted from more tiller number and substantial nutrition supply during tiller formation (Table 3). As for rice grown under the no-tillage condition with straw mulching, more carbohydrate

WANG Dong, et al. Growth Characteristics of Rice under No-tillage and Non-flooded Cultivation with Straw Mulching

was transported from culm to grain, which was suggested to improve the traits of rice panicles [12]. Besides, improved root traits (total length, tip number) and more rice above-ground dry matter in the N-SM treatment could also contribute to high rice grain yield to some extent (Tables 3 and 5). Furthermore, in nontillage and non-flooded rice systems, lots of earlyseason rice stubbles were remained due to no-tillage and were ratooned in the late-season rice fields, and weed biomass was greatly increased because of nonflooded rice cultivation. Thus, the ratooned rice and weed would compete for soil nutrients and water with late-season rice, which would affect late-season rice yield. However, straw mulching was effective in suppressing the growth of weed flora [16]. Therefore, it may be another reason why the rice yield in the N-SM treatment was significantly higher than that in the N-ZM treatment. According to the results, sufficient water should be supplied to maintain green leaf areas at the heading stage, and subsequently enhance active photosynthesis available for grain filling in no-tillage and nonflooded rice cultivation. In the study, higher total root length, root tip number and total surface area in the N-SM treatment were observed compared with other treatments (Table 5), suggesting that numerous lateral roots were induced by drought stress and the environment of rhizosphere were improved by straw mulching [17-18], thus improving rice root traits in the N-SM treatment. Prospects and development of the adoption of no-tillage and non-flooded rice cultivation with straw mulching The results from this study together with those from Qin et al [3-4] indicate that N-SM may be an alternative option for farmers in double-rice cropping system in the southeast of China for the maintenance of late-season rice yield, and also highlight some constraints requiring more detailed research. Firstly, it is clear that rice plants can be successfully grown under no-tillage and non-flooded rice cultivation with straw mulching in double-rice cropping system in the southeast of China. As a water-saving irrigation technique for alleviating seasonal drought and increasing water use efficiency [3-4], the N-SM treatment could obtain similar grain yield as the N-F treatment and

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local traditional flooding rice cultivation. The increased grain yield achieved in the N-SM treatment might provide an incentive for farmers to adopt this practice. Secondly, the N-SM treatment, applied to late-season rice cropping system, is a good soil and rice straw residue management. It can increase soil organic matter and some nutrients, improve soil microbial biomass and enhance soil enzyme activities (data not shown), as well as the expected environmental benefits. Because of the short turn-around time between early-season rice harvest and late-season rice transplanting, local farmers used to burn the early-season rice stubbles, thereby leading to large losses of organic C and N as well as significant air pollution. Thirdly, for local farmers, the N-SM treatment had more benefit in saving labors and agricultural cost (plough, irrigation). The first area for further research is to evaluate the physiological traits of rice and its contribution to grain yield under no-tillage and non-flooded rice cultivation. The second area of concern is how to control the weed biomass in no-tillage and non-flooded rice cultivation. Some studies showed that weed biomass was enhanced under non-flooded condition [16]. So it is necessary to investigate the structure and dynamics of weed communities in the non-flooded rice cultivation system, especially under no-tillage condition, and to adopt sound weed management strategies. The third area of concern is how long the no-tillage and non- flooded rice cultivation was applied to the rice-based rotation system. Is it a good agriculture practice, continuous no-tillage and non-flooded rice cultivation, or alternative stratagem of conventional tillage after long-term no-tillage under non-flooded rice cultivation? Therefore, performance of the new system needs to be monitored over a long period, in terms of crop productivity, soil quality and biology process.

ACKNOWLEDGEMENT We are grateful to the National High-Tech Research and Development Program of China (Grant No. 2002AA2Z4331) for generous financial support.

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