Field Crops Research 129(2012)28–38
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Field Crops
Research
j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /f c
r
Effect of tillage on soil and crop properties of wet-seeded ?ooded rice
Min Huang a ,Yingbin Zou a ,b ,?,Peng Jiang a ,Bing Xia a ,Yuehua Feng a ,Zhaowei Cheng a ,Yali Mo a
a College of Agronomy,Hunan Agricultural University,Changsha 410128,China b
State Key Laboratory of Hybrid Rice,Changsha 410125,China
a r t i c l e
i n f o
Article history:
Received 10November 2011
Received in revised form 17January 2012Accepted 19January 2012
Keywords:
Crop biomass production Direct seeding No-tillage
Paddy soil properties
Physiological characteristics Super hybrid rice
a b s t r a c t
No-tillage (NT)is an alternative cropping system for saving costs and conserving soils relative to conven-tional tillage (CT).However,NT effects on paddy soil and rice growth are still controversial or not fully understood.A ?xed ?eld experiment was conducted to compare soil and crop properties between NT and CT wet-seeded ?ooded super hybrid rice in Changsha,Hunan Province,China.After 6years of continuous cropping,NT had higher contents of active organic carbon,NaOH hydrolysable N and NH 4OAc extractable K and higher activities of invertase,urease and acid phosphatase at 0–5cm soil depth,higher bulk density at 5–10cm soil depth,and higher contents of double acid P at 5–10cm and 10–20cm soil depths.NT or associated soil compaction caused an adverse root environment for NT rice at early growth stage,which resulted in a lower capacity of photosynthetic carbon metabolism and consequent reductions in number of tillers and aboveground biomass accumulation before heading.However,no reductions were observed in total aboveground biomass and grain yield in NT rice,because the negative effects of NT or associated soil compaction on aboveground biomass production before heading were compensated for by its posi-tive effects on aboveground biomass accumulation after heading.On one hand,the reduction in growth before heading of NT rice made its population density lower but more suitable during heading to 20days after heading,which led to a more appropriate leaf area index,a lower leaf senescence and a consequent increase in net assimilation rate.On the other hand,N uptake was delayed in NT rice,which was another critical factor in determining its low leaf senescence.Our study suggests that the negative effects of NT or associated soil compaction on crop growth at early growth stage do not necessarily become concerns in NT wet-seeded ?ooded rice production.
?2012Elsevier B.V.All rights reserved.
1.Introduction
No-tillage (NT),a combination of ancient and modern agricul-tural practices (Phillips et al.,1980),has potential bene?ts including reduced production costs though saving in fuel,equipment and labor (Allmaras and Dowdy,1985)as well as soil conservation (Uri,1997).NT can work in a wide range of climates,soils and geographic areas (Huggins and Reganold,2008).In 1999NT was adopted on about 45million ha worldwide,growing to 72million ha in 2003and to 105million ha in 2009(Derpsch and Friedrich,2009).It is considered that the development of NT agriculture is one of the revolutions that have greatly impacted agriculture throughout the world (Triplett and Dick,2008).However,NT adoption rates are still low in European,Africa and most parts of Asia.About 85%of NT land lies in North and South America (Huggins and Reganold,2008).
Paddy ?elds account for approximately 15%of the world’s arable land (Xiao et al.,2005),and more than 90%of them are located
?Corresponding author.Tel.:+8673184618758;fax:+8673184673648.E-mail address:ybzou123@https://www.doczj.com/doc/3b10696104.html, (Y.Zou).
in Asia.In order to produce enough food for the rapidly growing population,agriculture land use in Asia has become very intense (Bronson et al.,1997).In the past 40years,intensi?cation of rice-based cropping systems has helped ensure production of suf?cient rice and other food crops (Buresh et al.,2005).However,contin-uous rice-based cropping systems practiced in Asia for several decades has led to declines in productivity and raised concerns about sustainability (Joshi et al.,2007;Guo et al.,2010).Long-term experiments suggest that the productivity of such continuous rice-based cropping systems can be sustained through soil and crop management practices that maintain the resource base (Buresh et al.,2005).The recent adoption of NT is considered bene?cial in rice–wheat cropping system in South Asia (Joshi et al.,2007).There are about 5million ha of NT being practiced in the Indo-Gangetic-Plains in a rice–wheat cropping system,where wheat is the NT crop (Derpsch and Friedrich,2009).
China is one of the major rice production countries in the world (Xiong et al.,2002).In order to feed growing population,China established a nationwide mega-project on the development of super rice based on the ideotype concept in 1996(Cheng et al.,1998).In 1998–2005,34commercially released super hybrid rice varieties were grown on a total area of 13.5million ha and they
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M.Huang et al./Field Crops Research129(2012)28–3829
produced an additional6.7million tonnes of rough rice in China (Cheng et al.,2007).Nevertheless,rice yield depends upon not only the genetic characters but also the agronomic practices(Zou et al.,2003).In China,conventional tillage is the most widely used method for land preparation of paddy?elds,and transplanting is the traditional but still dominant method for rice establishment. The operation of transplanting requires a large amount of man-power(about400man-hour ha?1)and the task is very laborious involving working in a stooping posture and moving in muddy?eld (Thomas,2002).Paradoxically,labor availability is limited in China because an increasing number of young farmers have left for jobs in the cities leaving the older farmers behind(Derpsch and Friedrich, 2009).In recent years,the simple and labor-saving method of direct seeding became increasingly attractive along with the populariza-tion of ef?cient agriculture in China(Wu et al.,2005).
There are many studies regarding the effects of NT on soil prop-erties in rice-based cropping system.Soil compaction is one of the biggest concerns for newcomers to the NT farming community,as well as sometimes to farmers that have been practicing this tech-nology for some time(Derpsch,2003).Previous studies that have compared bulk density of NT and CT in paddy?elds have produced con?icting results because soil bulk density is in?uenced by sev-eral factors such as time since last tillage,residue coverage,soil type and cropping system.In some studies larger bulk densities was found under NT than CT(Zhuang et al.,1999;Li et al.,2001;Iijima et al.,2005),whereas in some studies smaller bulk densities were recorded under NT than CT(Du,1991;Chen et al.,1993;Feng et al., 2006).Ambassa-Kiki et al.(1996)reported that bulk density did not signi?cantly vary between NT and CT under?ooded conditions.Soil acidi?cation is a major problem in soils of intensive Chinese agri-cultural systems(Guo et al.,2010).It is controversial whether NT leads to soil acidi?cation in paddy?elds.Huang(1988)reported that NT could lead to an accelerated soil acidi?cation compared to CT,especially at the0–5cm soil depth.Feng et al.(2006)observed that there was no consistent difference in pH between NT and CT at0–5cm soil depth,while pH was usually higher under NT than CT at5–10cm soil depth.Soil fertility is fundamental in determin-ing the productivity of all farming systems(Watson et al.,2002).It is generally accepted that paddy soils under NT management are rich in organic carbon and nutrients in the surface soil layer(Lal, 1986;Feng et al.,2006;Tang et al.,2007).Soil enzymes are sensitive to variations induced by natural and anthropogenic disturbances (Gupta et al.,1988;Dick,1994).Gao et al.(2004)observed that NT paddy had higher soil enzyme activities at0–20cm soil depth. However,very little information is available on the relationships between soil enzymes and other soil properties in NT paddy soils. More importantly,there is still limited knowledge about the rela-tionships between soil properties and crop yield formation in NT paddy.
Rice yield is the function of biomass production after heading (HD)and translocation of biomass accumulated before HD to grains (Yang et al.,2008).Although both are associated with grain yield, some studies has been suggested that the latter should be empha-sized more than the former(Weng et al.,1982;Miah et al.,1996; Laza et al.,2003),whereas a number of crop physiologists have indi-cated the importance of increased biomass production after HD in rice(Murchie et al.,2002;Takai et al.,2006;Yang et al.,2008).There have been several reports describing NT effects on biomass produc-tion of rice(Liu et al.,2002;Iijima et al.,2005;Xu and Jiang,2007; Dong et al.,2008;Wu et al.,2009).It is showed that NT rice usually produces a lower aboveground biomass before HD but a higher one after HD than CT rice.However,there is still a lack of understanding of the critical physiological processes that elaborate on the differ-ences in aboveground biomass production between NT and CT rice. Moreover,previous studies were usually conducted under trans-planting or seedling throwing conditions,and using ordinary rice cultivars.Limited information is currently available on the effects of NT on biomass production in direct-seeded super hybrid rice.
In our current study,we compared soil properties and crop biomass production and related physiological factors between NT and CT wet-seeded?ooded super hybrid rice.Our objectives were (1)to determine the effects of NT on paddy soil properties,(2)to identify the physiological processes contributing to the effects of NT on rice biomass production,and(3)to understand the relation-ships between paddy soil properties and rice biomass production under NT conditions.
2.Materials and methods
2.1.Site and soil
A?xed?eld experiment was conducted at Changsha(28?11 N, 113?04 E and32m altitude),Hunan Province,China in2004–2010. The location is situated in the East-Asian monsoon climatic zone and has a moist sub-tropical monsoon climate.The?eld was cropped with NT oilseed rape before the start of the experiment.The soil of the experimental?eld was clay loam with pH=6.04,organic matter=14.96g kg?1,total N=1.40g kg?1,total P=1.18g kg?1, total K=18.13g kg?1,NaOH hydrolysable N=137.0mg kg?1,Olsen P=38.35mg kg?1,NH4OAc extractable K=113.3mg kg?1.The soil test was based on samples taken from the upper20cm of the soil.
2.2.Plants and treatments
Liangyoupeijiu,an indica–japonica hybrid(Peiai64S×9311) developed by Jiangsu Academy of Agricultural Sciences of China and released in1999,was used in the experiment.This cultivar has been approved as a super hybrid rice cultivar by the Ministry of Agricul-ture of China in2005because of its high yield potential.In each year, Liangyoupeijiu was grown under conventional tillage(CT)and no-tillage(NT)in the single rice-growing season(from May to October), and oilseed rape was grown under NT at2days after harvesting rice. Rice and oilseed rape stubbles were remained in all plots.Plots were arranged in a randomized complete block design with four repli-cations using plot size of30m2.The land preparation of the plots under CT(plowing and two harrowing)was with buffalo;and for the plots under NT,herbicide Gramoxone(paraquat20%)was used (diluted5ml L?1and applied at750L ha?1)7days before sowing. Seeds were?rst sterilized by soaking in0.3%trichloroisocyanuric acid solution for12h,and then washed and soaked in tap water for 24h at room temperature.The soaked seeds were kept between thick layers of cotton cloth and allowed to germinate at room temperature.The pre-germinated seeds were manually broadcast onto the wet soil surface at a seed rate of22.5kg ha?1(about 120seeds m?2)between May11th and June1st.Urea was used as a source of N,single superphosphate of P and potassium chloride of K with rates of150kg N ha?1,90kg P2O5ha?1and180kg K2O ha?1.N was split-applied:90kg ha?1as basal,45kg ha?1at mid-tillering, and15kg ha?1at panicle initiation.P was applied as basal and K was split equally at basal and panicle initiation.In CT plots,the basal fertilizer was broadcast after the?rst harrowing and incorporated with the second harrowing.The regimen for water management was in the sequence of watering to saturation(from seeding to 1.5-leaf stage),?ooding,midseason drainage,re?ooding and moist intermittent irrigation but without water logging.Weeds,insects and diseases were controlled as required to avoid yield loss.How-ever,the yield was detrimentally affected due to lodging caused by a typhoon in the growing season of2005.There was no apparent difference in damage to the NT and CT rice.Hence,the data of2005 were excluded from the analysis.
30M.Huang et al./Field Crops Research129(2012)28–38
2.3.Sampling and measurements
Plants were sampled from a0.48-m2area for each plot at head-ing(HD)and maturity(MA)in2004–2008,2010and at mid-tillering (MT),panicle initiation(PI),HD,20days after heading(DAH)and MA in2009.Plant samples were separated into leaves,stems and panicles at HD and20DAH,and into straw(including rachis)and grains at MA.Each plant organ was oven-dried at70?C to constant weight to determine biomass.In each year,grain yield was deter-mined from a5-m2area in each replication and adjusted to an H2O moisture content of0.14g g?1fresh weight.
In2009,plants in a0.48-m2area in each plot were marked to count the tillers(including main stem)and to measure plant height (from the soil surface to leaf tip with the leaves fully expanded) starting at35days after sowing at a3-day interval until the?ag leaf was fully expanded.At MT,PI,HD and20DAH,leaf area was determined by measuring leaf length and maximum leaf width and calculated as:leaf area=leaf length×maximum leaf width×0.75 (Umashankar et al.,2005),and then leaf area index(LAI)was cal-culated.At MT,malondialdehyde content was measured in root by the thiobarbituric acid reaction as described by Heath and Packer (1968).At MT,PI and HD,total chlorophyll content,net photo-synthetic rate and soluble sugar content were measured on the uppermost fully expanded leaves.Total chlorophyll content was measured by extracting with a mixture of ethanol:acetone:distilled water=4.5:4.5:1(v/v/v)for24h(Yang et al.,2007)according to the procedure of Arnon(1949).Net photosynthetic rate was determined with a portable photosynthesis system(LI-6400,Li-Cor,Lincoln,NE,USA)at9:00–10:30A.M.It was measured at a light intensity of1200?mol m?2s?1,a leaf temperature of30?C, a constant CO2concentration of380±5?mol mol?1,and a relative humidity of75±5%in the sample chamber.Soluble sugar content was determined by the anthrone color reaction(Yemm and Willis, 1954)using sucrose as the standard.At HD,20DAH and MA,N, P and K contents were determined in leaves and panicles.N con-tent was determined in an autoanalyzer(Integral Futura,Alliance Instruments,Frépillon,France).P content was determined by the ascorbic acid–molybdate method(Murphy and Riley,1962).K con-tent was determined with a?ame photometer(FP640,Shanghai Precision&Scienti?c Instrument Inc.,Shanghai,China).Net assim-ilation rate(NAR)during HD to20DAH was calculated using the formula as described by Williams(1946).Biomass accumulation after HD(Wr)and translocation of biomass accumulated before HD to the grains(T)were calculated as previously described by Yang et al.(2008).About150representative panicles were marked for each plot at HD,and10of them were sampled at a3-day inter-val from3to36DAH.Spikelets on the top three primary branches (superior grains),spikelets on secondary branches of the bottom three primary branches(inferior grains),and the rest spikelets (medium grains)of the panicles were separated(Tao et al.,2006). These grains were weighed after oven-drying at70?C for48h, and were then counted to calculate grain weight.At5,10,15 and20DAH,soluble protein and malondialdehyde contents were measured in?ag leaves.Soluble protein content was determined with the protein-dye binding method introduced by Braford(1976) using bovine serum albumin as the standard.At booting,roots at 0–5cm,5–10cm and10–20cm soil depths were sampled by using a20cm diameter core.The roots in the core were washed free of soil and oven-dried at70?C to constant weight to determine root biomass.
After harvesting in2009,soil samples were taken from each of the0–5cm,5–10cm and10–20cm soil layers of each plot to determine soil properties.Bulk density was determined by the core method(Blake and Hartge,1986).pH was measured by shak-ing air-dried soil(5g)in distilled water(25ml)for10min and waiting for30min prior to the pH assay with a digital pH meter (PHS-3C,Shanghai Precision&Scienti?c Instrument Inc.,Shanghai, China).Active organic carbon was determined based on the method described by Loginow et al.(1987).Soil sample(1g air-dried soil) was extracted by adding20ml333mmol L?1KMnO4in an orbital shaker at200rpm for1h.The sampled solution was immediately centrifuged at2000×g for5min,and then diluted and measured by spectrophotometer at565nm.The content of active organic carbon was calculated according to the difference of the KMnO4 concentration before and after oxidation.NaOH hydrolysable N was measured by the diffusion method with10ml of1.8mol L?1NaOH, 2%H3BO3and0.01mol L?1H2SO4at40for24h.Double acid P was determined by the method of Sabbe and Breland(1974),where5g soil was shaken with20ml of0.05mol L?1HCl and0.0125mol L?1 H2SO4for5min.NH4OAc extractable K was determined by a?ame photometer(FP640,Shanghai Precision&Scienti?c Instrument Inc., Shanghai,China).Soil enzyme activities were assayed in air-dried samples as described by Guan(1986).Brie?y,invertase activity was determined using sucrose as a substrate and incubation at37?C for 24h,measuring the produced glucose with a colorimetric method, and invertase activity was expressed as mg glucose g?1h?1.Ure-ase activity was determined using urea as substrate,and the soil mixture was incubated at37?C for24h,the produced NH3–N was determined colorimetrically,and urease activity was expressed as ?g NH3–N g?1h?1.Acid phosphatase activity was measured using sodium phenolphthalein phosphate as a substrate,incubation at 37?C for24h,and the liberated phenol was determined by a col-orimetric method,and acid phosphatase activity was expressed as ?g phenol g?1h?1.
2.4.Statistical analysis
Statistix8software package(Analytical software,Tallahassee, Florida,USA)was used for analysis of variance(General AOV/AOCV procedure)and Pearson’s correlation analysis.Means of values were subjected to the least signi?cant difference test(LSD)at the 0.05probability level.
3.Results and discussion
3.1.Effects of NT on soil properties
The difference in bulk density between CT and NT was not signif-icant at0–5cm and10–20cm soil depths,whereas at5–10cm soil depth NT had20%higher bulk density than CT(Fig.1A).This is in agreement with the result of a long-term(12years)experiment in rice–wheat cropping system by Zhuang et al.(1999),who reported that no signi?cant difference was observed in bulk density between CT and NT at0–7cm and14–21cm soil depths,whereas at7–14cm soil depth NT had signi?cantly higher bulk density than CT.On the other hand,pH was a little higher under NT than CT at5–10cm soil depth,whereas pH under NT was almost as high as that under CT at0–5cm and10–20cm soil depths(Fig.1B).It is suggested that NT does not necessarily cause soil acidi?cation in rice paddy. This differs from that reported by Huang(1988),who stated that NT could lead to an accelerated soil acidi?cation compared to CT, especially at the0–5cm soil depth,but is partly consistent with the?ndings in Feng et al.(2006),who observed that there was no consistent difference in pH between NT and CT at0–5cm soil depth,while pH was usually higher under NT than CT at5–10cm soil depth.Furthermore,our results showed that NT effects on pH were similar with those on bulk density(Fig.1A and B).Also,previ-ous studies showed that pH varied synchronously with bulk density in long-term NT system(Jarecki and Lal,2005;Dalal et al.,2011). Therefore,whether NT causes soil acidi?cation may be determined by the effect of NT on bulk density,which differs under different
M.Huang et al./Field Crops Research 129(2012)28–38
31
0.40.81.21.6
B u l k d e n s i t y (g c m -3)
5.0
5.6
6.2
6.8
p H
100
200
300
0-55-1010-20
Soil depth (cm)
A c i d p h o s p h a t a s e (μg p h e n o l g h -1)
0.0
1.0
2.0
3.0
4.0
0-55-1010-20
Soil dep th (cm)
R o o t b i o m a s s (m g c m -3)
Fig.1.Soil properties (A–I)and rice root biomass (J)at 0–5cm,5–10cm and 10–20cm soil depths under conventional tillage (CT)and no-tillage (NT)in 2009.Each column
and vertical bar show mean and SE (n =4).
conditions such as time since last tillage,residue coverage,soil type and cropping system.It is further supported by the result that pH was positively associated with bulk density (Table 1).
In addition,this study observed that contents of active organic carbon,NaOH hydrolysable N and NH 4OAc extractable K were 16%,15%and 13%higher at 0–5cm soil depth but 27%,17%and 7%lower at 5–10cm soil depth under NT than CT,respectively,while at 10–20cm soil depth the differences were relatively small (Fig.1C,D and F).These results are similar to the ?ndings in previous study
(Lal,1986).However,unlike the previous study,our study showed that double acid P content was higher under NT than CT,and the differences were signi?cant at 5–10cm and 10–20cm soil depth (Fig.1E).It has been reported that there is a strong interaction between tillage and soil type on soil P content (Triplett and Dick,2008),indicating that NT effects on soil P content are not always the same with different soil types.In soil,P is relatively immo-bile (Cornish,2009),suggesting that soil compaction may cause an increase in soil P content.This is con?rmed by the result that there
32M.Huang et al./Field Crops Research129(2012)28–38
Table1
Correlation coef?cients of soil properties based on the data obtained from0–5cm,5–10cm and10–20cm soil depth under no-tillage and conventional tillage conditions in 2009(n=6).
Soil property a SP1SP2SP3SP4SP5SP6SP7SP8
SP20.883*
SP3?0.963**?0.895*
SP4?0.916*?0.813*0.984**
SP50.885*0.884*?0.844*?0.771
SP6?0.789?0.6600.900*0.962**?0.611
SP7?0.835*?0.6390.902*0.956**?0.6630.980**
SP8?0.937**?0.818*0.987**0.992**?0.7680.932**0.932**
SP9?0.926**?0.835*0.984**0.993**?0.8090.953**0.956**0.977**
a SP1:bulk density;SP2:pH;SP3:active organic carbon content;SP4:NaOH hydrolysable N content;SP5:double acid P content;SP6:NH4OAc extractable K content;SP7: invertase activity;SP8:urease activity;SP9:acid phosphatase activity.
*Signi?cance at the0.05probability level.
**Signi?cance at the0.01probability level.
Table2
Grain yield and biomass production of rice grown under conventional tillage(CT)and no-tillage(NT)in2004,2006–2010.
Year Grain yield(t ha?1)Aboveground biomass accumulation(g m?2)
Before heading After heading Total
CT
200410.1413254561781 200610.4511198701989 200710.6117973682165 20089.56111111822293 20099.4012244181642 20109.6612384811719 Mean9.9713026301932 SE a0.33724591
NT
20049.3511427551897 200611.1292611212047 200710.8015846672251 200810.28112211042226 20099.508936811574 20108.8210866141700 Mean9.9811268231949 SE0.3849106142 Analysis of variance
Tillage NS****NS Year******** Tillage×Year NS**NS NS
NS denotes non-signi?cance at the0.05.
a Average SE of the six years.
**Signi?cance at the0.01probability level.
was a signi?cant positive relationship between bulk density and double acid P content(Table1).Moreover,this study showed that roots at5–10cm soil depth were30%less under NT than CT(Fig.1J), which would further lead to less P uptake by NT rice from this soil depth.Taken together,we concluded that the combined action of relatively immobile characteristic of soil P and NT effects on bulk density and root distribution were responsible for the higher dou-ble acid P content under NT at5–10and10–20cm soil depths.
Similar to the effects of NT on contents of active organic carbon, NaOH hydrolysable N and NH4OAc extractable K(Fig.1C,D and F), activities of invertase,urease and acid phosphatase were10%,25% and12%higher at0–5cm soil depth but30%,28%and33%lower at 5–10cm soil depth under NT than CT,respectively,while the differ-ences were relatively small at10–20cm soil depth(Fig.1G–I).These results indicate that activities of invertase,urease and acid phos-phatase are sensitive to the changes of active organic carbon,NaOH hydrolysable N and NH4OAc extractable K in paddy soil.It is further supported by the results that activities of invertase,urease and acid phosphatase were strongly positively related to contents of active organic carbon,NaOH hydrolysable N and NH4OAc extractable K (Table1).This?nding is in agreement with previous studies(Dick, 1984;Deng and Tabatabai,1997;Franzluebbers,2002;Shi et al., 2008).However,unlike the study of Shi et al.(2008),no signi?cant positive relationship between acid phosphatase activity and dou-ble acid P content was observed in the present study(Table1).It is suggested that acid phosphatase activity is not necessarily sensitive to the change of double acid P in paddy soil.Acid phosphatase is a phosphoric monoester hydrolase that acts on ester bonds(Deng and Tabatabai,1997),and it has been reported that its activity is negatively related to pH(Iyyemperumal and Shi,2008).In this study,we also observed a similar relationship between the two soil properties(Table1).Moreover,as mentioned above,pH was increased with increasing bulk density.As a consequence of these two aspects,a signi?cantly negative correlation was found between acid phosphatase activity and bulk density(Table1).On the con-trary,as outlined above,soil compaction could cause an increase in soil P content.Therefore,in the present study,the insensitive of acid phosphatase activity to the change of double acid P in paddy soil was attributed to the contrast responses of acid phosphatase activity and double acid P content to bulk density.
3.2.Effects of NT on crop properties
There was no signi?cant difference in grain yield and total aboveground biomass between CT and NT(Table2).However,
M.Huang et al./Field Crops Research 129(2012)28–38
33
250500
750
SO-MT
MT-PI P I-HD HD -20 DAH 20 DAH-MA
Grow th period
A b o v e g r o u n d b i o m a s s a c c u m u l a t i o n
(g m -2)
Fig.2.Aboveground biomass accumulation from sowing (SO)to mid-tillering (MT),from MT to panicle initiation (PI),from PI to heading (HD),from HD to 20days after
heading (DAH)and from 20DAH to maturity (MA)of rice grown under conventional tillage (CT)and no-tillage (NT)in 2009.Each column and vertical bar show mean and SE (n =4).
tillage had signi?cant effects on aboveground biomass accumu-lation both before and after HD.Mean aboveground biomass accumulation across six years was 14%less before HD but 31%more after HD under NT than CT.This is consistent with pre-vious studies conducted under transplanting (Dong et al.,2008)and seedling throwing (Liu et al.,2002;Xu and Jiang,2007)con-ditions.The differences in grain yield and aboveground biomass accumulation were signi?cance among years (Table 2).In 2006,NT produced a maximum grain yield of 11.12t ha ?1,with aboveground biomass accumulation of 926and 1121g m ?2before and after HD,respectively.The interactive effect between tillage and year was signi?cant only on aboveground biomass accumulation before HD.
In each growth period before HD,aboveground biomass accu-mulation was less under NT than CT (Fig.2).Previous studies have demonstrated that rice plant accumulation before HD is correlated with number of tillers and plant height (Samonte et al.,2006;Ao et al.,2010).In the present study,tillers per m 2were obviously less under NT than CT (Fig.3A),whereas the difference in plant height was relatively small (Fig.3B).This result suggests that num-ber of tillers is a critical factor that determines the difference in aboveground biomass accumulation before HD between NT and CT.It has been reported that energy supply regulates tillering of plant (Mitchell,1953)and that tiller appearance depends on car-bon supply (Gautier et al.,1999).Consistently,in this study,LAI was lower under NT than CT by 26%,34%and 34%at MT,PI and HD,respectively (Fig.4A).Meanwhile,total chlorophyll content,net photosynthetic rate and soluble sugar content in the uppermost fully expanded leaf were lower under NT than CT,especially at MT (Table 3).There has been growing evidence that shoot photosynthe-sis can be in?uenced by changes in the root environment (Ahmed et al.,2006).Usually the structure and composition of root cell membranes are employed as indices of the changes in the root envi-ronment (Svenningsson and Liljenberg,1986).Malondialdehyde is one of the major products of membrane lipid peroxidation,which expresses cell membrane plasmalemma peroxide degree and plant reaction to the adverse conditions (Xu et al.,2011).In this study,malondialdehyde content in roots was 13%higher under NT than CT at MT (Fig.4B).These results indicate that the less number of tillers in NT rice is attributed to a lower capacity of photosynthetic carbon metabolism caused by an adverse root environment at MT.Aboveground biomass accumulation was 2.4times more under NT than CT during HD to 20DAH,whereas the difference was not signi?cant during 20DAH to MA (Fig.2).It is suggested that
Table 3
Physiological properties in the uppermost fully expanded leaf at mid-tillering (MT),panicle initiation (PI)and heading (HD)of rice grown under conventional tillage (CT)and no-tillage (NT)in 2009.
Physiological property
CT
NT
Total chlorophyll content (mg g ?1FW)
MT
2.83±0.02a 2.46±0.06b
PI
2.59±0.03a 2.33±0.15b HD
3.61±0.03a
3.52±0.03a
Net photosynthetic rate (?mol CO 2m ?2s ?1)MT 23.4±0.5a 20.2±0.6b PI 16.8±0.9a 15.3±0.6a HD 27.1±1.4a
24.0±1.9a
Soluble sugar content (mg g ?1FW)
MT
15.5±0.3a 13.6±0.2b PI
19.1±0.6a 17.5±0.3a HD
20.1±0.2a
18.8±0.6a
Data are mean ±SE (n =4),means of tillage methods for each parameter with the same letters are not signi?cantly different according to LSD at P =0.05.
the initial 20days after HD was the key period for the more aboveground biomass production after HD under NT.During the period,decreases in stem and leaf biomass were lower under NT (57.6and 30.6g m ?2,respectively)than CT (225.2and 123.8g m ?2,respectively)(Fig.5A and B),while panicle biomass under NT was increased as much as that under CT (Fig.5C).That was to say,panicle biomass was not necessarily reduced when decrease in transloca-tion of biomass accumulated before HD to panicles was observed,as it could be compensated for by more aboveground biomass produc-tion after HD.It is further supported by the results that NT had 63%higher Wr but 72%lower T than CT (Fig.6),and inferior,medium and superior grain weights under NT were almost the same as those under CT in different DAH (Fig.7A–C).
Similar to the more aboveground biomass accumulation dur-ing HD to 20DAH under NT,NAR was 3.4times higher during this period under NT than CT (Fig.8).Previous studies concluded that there must be an optimum LAI for plant growth (Harper,1963;Ludwig et al.,1965).Beyond the point of optimum LAI,NAR of the canopy would be reduced (Evans,1978;Joggi et al.,2006).Therefore,in the present study,LAI under NT was smaller (Fig.4A)but more appropriate than that under CT during HD to 20DAH.It has been reported that direct-seeded rice usually produces a high population density (Cho et al.,2001),suggesting that an exces-sive LAI should be avoided in direct-seeded rice production.Ao
34
M.Huang et al./Field Crops Research 129(2012)28–38
100
300500700900
30
507090
Days after sowing
T i l l e r s p e r m 2
20
40
60
80
100
30507090
Days after sowing
P l a n t h e i g h t (c m )
Fig.3.Tillers per m 2(A)and plant height (B)in different days after sowing of rice grown under conventional tillage (CT)and no-tillage (NT)in 2009.Each data point and
vertical bar show mean and SE (n =4).
0.0
3.06.0
9.0
MT
PI HD 20 DAH
Growth stag e
L e a f a r e a i n d e x
1.0
3.0
5.0
7.0
MT
P I HD
Growth stage
M a l o n d i a l d e h y d e (μm o l g -1 F W )
Fig.4.Leaf area index (A)and malondialdehyde content in root (B)at mid-tillering (MT),panicle initiation (PI),heading (HD)and 20days after heading (DAH)of rice grown
under conventional tillage (CT)and no-tillage (NT)in 2009.Each data point/column and vertical bar show mean and SE (n =
4).
200
400
600
800
HD 20 DAH
B i o m a s s (g m -2)
HD 20
DAH
Growth stage
HD 20 DAH
Fig.5.Stem (A),leaf (B)and panicle (C)biomass at heading (HD)and 20days after heading (DAH)of rice grown under conventional tillage (CT)and no-tillage (NT)in 2009.
Each data point and vertical bar show mean and SE (n =4).
M.Huang et al./Field Crops Research 129(2012)28–38
35
200
400
600
800Wr
T
B i o m a s s (g m -2)
Fig.6.Biomass accumulation after heading (Wr)and translocation of biomass accu-mulated before heading to the grains (T)of rice grown under conventional tillage (CT)and no-tillage (NT)in 2009.Each data point and vertical bar show mean and SE (n =4).
et al.(2010)stated that reducing unproductive tillers by removal of tillers manually or physical restriction could lead to a decrease in LAI.Consistently,the result of this study showed NT rice had both less unproductive tillers and lower LAI than CT rice (Figs.3A and 4A ).It is generally accepted that unproductive tillers compete for light and nutrients with productive tillers.Jiang et al.(1994)reported that reducing unproductive tillers at the middle growth stage improved canopy structure and photosynthetic ef?ciency at the late growth stage.However,our study showed that there was little difference in net photosynthetic rate between NT and CT rice at HD (Table 3).It is well known that NAR is a hybrid concept,involving photosynthesis by leaves and respiration of leaf,stem and root (Loach,1967).Previous studies investigating the interactions of LAI with respiration and photosynthesis assumed that respira-tion was linearly related to LAI while photosynthesis increased asymptotically (Harper,1963;Ludwig et al.,1965).Therefore,in the present study,the difference in NAR between CT and NT rice might be due to the difference in respiration rather than photo-synthesis.In addition,it has been reported in other crops that NAR decreases with reduced photosynthetic ef?ciency of older leaves (Yasari and Patwardhan,2006;Baligar et al.,2008).In this study,we only measured the net photosynthetic rate on the uppermost fully expanded leaves at HD.This suggests that the validity of
estimating
0.0
2.0
4.0
6.0
CT NT
Till age
N A R (g m -2 d -1)
https://www.doczj.com/doc/3b10696104.html, assimilation rate (NAR)during heading to 20days after heading of rice
grown under conventional tillage (CT)and no-tillage (NT)in 2009.Each column and vertical bar show mean and SE (n =4).
the photosynthetic production of the whole plant from short-term measurements on single leaves is doubtful.On the other hand,high population density can cause increases in mutual shading of plants (Monneveux et al.,2008)and a consequent acceleration in leaf senescence (Baylis and Dicks,1983).Remobilization of min-eral nutrients from leaves to reproductive structures is a possible regulatory factor in leaf senescence (Crafts-Brandner,1992).In the present study,during HD to 20DAH,decreases in N,P and K accu-mulation in leaves were 53%,61%and 51%,respectively lower under NT than CT,while NT had a 18%higher increase in N accumulation,a 31%higher increase in K accumulation and an equal increase in P accumulation in panicles than CT (Fig.9A–C).It is suggested that leaf senescence under NT was not as great as that under CT during HD to 20DAH.Membrane damage through lipid peroxidation is reported to play a major role in the process of leaf senescence (Kahn et al.,1996).In this study,malondialdehyde content in ?ag leaves was 19%,7%,7%and 27%lower under NT than CT at 5,10,15and 20DAH,respectively (Fig.10A).Huang et al.(2004)observed that malondialdehyde accumulation could lead to a lessening of soluble protein in rice leaves.Similarly,in the present study,soluble protein content in ?ag leaves was 9%,14%,6%and 12%higher under NT than CT at 5,10,15and 20DAH,respectively (Fig.10B).It is well known
05
10
15
20
25
10203040
G r a i n w e i g h t (m g )
010203040
DAH
010203040
Fig.7.Inferior (A),medium (B)and superior (C)grain weights in different days after heading (DAH)of rice grown under conventional tillage (CT)and no-tillage (NT)in 2009.Each data point and vertical bar show mean and SE (n =4).
36
M.Huang et al./Field Crops Research 129(2012)28–38
-6. 0
-3.
00.0
3.06.09.0
N a c c u m u l a t i o n (g m -2)
-1. 0
0.0
1.0
2.0
3.0
P a c c u m u l a t i o n (g m -2)
-3. 0
-2.
0-1. 0
0.01.02.03.0K a c c u m u l a t i o n (g m -2)
Lea ves
Panicles
Fig.9.N (A),P (B)and K (C)accumulation in leaves and panicles during heading to
20days after heading of rice grown under conventional tillage (CT)and no-tillage (NT)in 2009.Each column and vertical bar show mean and SE (n =4).
that a considerable proportion of the soluble protein is Rubisco (EC 4.1.1.39)(Stitt and Schulze,1994;Sarker et al.,2002),which is the most important enzyme involved in the CO 2?xation and its con-tent is thought to be a rate-limiting factor for the light-saturated rate of the photosynthesis at atmospheric CO 2pressure (Makino et al.,1985).Many studies have demonstrated that the decrease in soluble protein content is always accompanied by a reduced pho-tosynthesis in rice (Weng and Chen,1987;Sarker et al.,2002;Chen et al.,2005).Therefore,leaf senescence was another critical fac-tor that explains the higher NAR under NT during HD to 20DAH.However,leaf senescence is not only a degenerative process,but it also may allow acclimation to the growth conditions to maintain the overall carbon balance of a plant (Crafts-Brandner,1992).This might be why aboveground biomass accumulation under NT was as much as that under CT during 20DAH to MA (Fig.2).
0.0
2.0
4.0
6.0
8.0
10. 0
M a l o n d i a l d e h y d e (μm o l g -1 F W )
10
20
30
5101520
DAH
S o l u b l e p r o t e i n (m g g -1 F W )
Fig.10.Soluble protein (A)and malondialdehyde (B)contents in ?ag leaves at 5,10,15and 20days after heading (DAH)of rice grown under conventional tillage (CT)and no-tillage (NT)in 2009.Each column and vertical bar show mean and SE (n =4).
3.3.Relationships between soil and crop properties under NT conditions
Previous studies reported that NT crop production could lead to excessive soil compaction,resulting in adverse conditions for crop growth (Hammel,1989;Mahboubi et al.,1993).Consistently,in the present study,NT caused signi?cant soil compaction at 5–10cm soil depth,and it was observed that NT rice roots were subject to an adverse environment at early growth stage,which resulted in a lower capacity of photosynthetic carbon metabolism and consequent reductions in number of tillers and aboveground biomass accumulation before HD.Similarly,some researchers con-cluded that high mechanical impedance and poor aeration reduced root growth of wheat and caused a consequent reduction in early growth in conservation tillage systems (Cornish and Lymbery,1987;Kirkegaard et al.,1994,1995).Larney and Kladivko (1989)and Oussible et al.(1992)reported that root growth could be affected by high soil mechanical resistance restricting water and nutrient supply.This is obviously not the case with the wet-seeded ?ooded rice in this study.Recently,there is growing evidence that biological changes in the soil,often associated with accumula-tion of Pseudomonas spp.in the rhizosphere,are responsible for reduced root growth of upland crops under soil compaction condi-tions (Watt et al.,2003,2006a,b ),highlighting the need for greater fundamental understanding of the effects of NT or associated soil compaction on soil biological properties under ?ooded conditions.Unlike in the previous studies,there were no reductions observed in total aboveground biomass and grain yield in NT rice,since the negative effects of NT on aboveground biomass produc-tion before HD were compensated for by its positive effects on
M.Huang et al./Field Crops Research 129(2012)28–38
37
5
10
15
20
SO-HD
HD-MA
Growth pe riod
N u p t a k e (g m -2)
Fig.11.N uptake in aboveground biomass from sowing (SO)to heading (HD)and
from HD to maturity (MA)of rice grown under conventional tillage (CT)and no-tillage (NT)in 2009.Each column and vertical bar show mean and SE (n =4).
aboveground biomass accumulation after HD.On one hand,the reduction in growth before HD of NT rice made its population den-sity lower but more suitable during HD to 20DAH,which resulted in a more appropriate LAI,a lower leaf senescence and consequent increases in NAR and aboveground biomass accumulation after HD.On the other hand,nutrient contents in the surface soil layer were higher under NT than CT,and about 80%of roots were distributed in this soil layer for both NT and CT rice (Fig.1J).More interestingly,our study showed that N uptake in aboveground biomass was 27%less before HD but 73%more after HD under NT than CT (Fig.11),indicating that N uptake was delayed in NT rice.It is considered that leaf senescence is a common response to inadequate nutri-ent supply (Chapin,1980).Therefore,we deduced that the delayed N uptake was another critical factor in determining the low leaf senescence in NT rice.The results of this study suggest that the neg-ative effects of NT or associated soil compaction on crop growth at early stage do not necessarily become concerns in NT wet-seeded ?ooded rice production.
Acknowledgements
This study was a part of the PhD thesis research of the senior author.The ?nancial support was provided by the International Rice Research Institute,the German Federal Ministry of Economic Cooperation and Development,the Ministry of Agriculture of China,and the China National Rice Research Institute.
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