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Effect of heavy applications of organic residues on the physical properties of paddy soils in China
Soil & Tillage Research, 20 ( 1991 ) 101-108
101
Elsevier Science Publishers B.V., A m s t e r d a m
Effect of heavy applications of organic residues on the physical properties of paddy soils in China A.J. Rixon', Yap Xianliang: and Zhu Hong Xia 2 ~School of Engineering, University College af Southern Queensland, Toowoomba, Qld. 4350 (Ausz calia) "-Institute of Soil Science, Academia Sinica, Nanjing (People's Republic of China) (Accepted for publication 5 March 1990)
ABSTRACT Rixon, A.J., Yao, X . - L and Zhu, H.X., 1991. Effect of h e a w applications of organic residues on the physical properties of paddy soils in China. Soil Tillage Res., 20: 101-108. Applications of ( i ) 22.5 t h a - t of pig dung and ( ii ) 3 t h a - l of dry. rice straw were made on paddy soils ia a field experiment that included an annual rotation of barley, early rice and late rice. Representative undisturbed soil cores and soil samples were collected from the experimental field plots. Physical properties, including soil moisture characteristics, were determined for the soil samples. The various physical properties did not differ significantly, indicating a lack of response to the added organic matter. The absence of improvement in the physical properties of the soil was probably due ~o the action of puddling, which is consistently practised prior to transplanting and the establishment of each rice crop.
INTRODUCTION
Desirable physical properties facilitating the rapid entry, transmission and storage of water in the soil, stability o f aggregates, adequate aeration and related physical properties are correlated positively with high levels o f soil organic matter. This correlation is the principal reason for the practice o f adding organic residues to ameliorate soil. For many centuries, Chinese agriculture, particularly rice production, relied on additions or organic r~;sidues, including straw, pig manure and litter, to maintain soil fertility. Green manure crops also contributed to the maintenance o f soil fertility. The use o f chemical fertilizers by Chinese farmers to supply plant nutrients has increased sig:aificantly during the last 20 years. The convenience of the application o f chemical fertilizer appeals to farmers and there has been a commensurate decline in the application o f organic residues. Furthermore, during the same period, the total area o f ~reen manure in intensive rice-producing regions such as the Taihu region in Jiangsu Province has
102
A,J. RIXON ET AL
declined from 15-20% to < l 0%. Although the addition of nutrients has been m a i n t a i n e d or even increased, the decreased additions of organic residues can result in changed soil physical properties. T h r o u g h o u t China, rice is grown in seedbeds a n d at the age of I m o n t h the rice seedlings are transvlanted into the field. Puddling, which is practised prior to rice transplanting, is virtually s y n o n y m o u s with rice production in China. Puddling invoi,'es the breaking down, usually with ro'ial3, implements, of soil aggregates into ultimate soil parlic!es at or near saturation. The purpos:~'s o f puddling are to make soil soft for transplanting, reduce hydraulic conductivity, reduce deep percolation o f nutrients and control weeds (De Datta. 1981 ). Puddling destroys aggregates and peals, and contributes to a decline in soil structur~ ( S h a r m a and De Datta, 1985 ). Although puddling has traditionally been an i m p o r t a n t activity in rice production, it is unlikely to be of any direct benefit to succeeding dryland crops in the rotation. I m p r o v e m e n t s in the physical characteristics of paddy soils as a r~:sult of additions of organic residues have been recorded (Yap and Yu, 1985a, b) in a glasshouse experiment. Field experiments incorporating heavy additions of organic residues, as well as including the practice of puddling, have been established at W u h u Institute o f Agricultural Sciences centred in a rice-growing region in the Province o f Anwhei. The present publication r~:por:~s the physical properties for surface soils of these experimental plots. MATERIALS AND METHODS
Soil samples were collected in late M a r c h 1987 from a fiela experiment located at Wuhu Institute of Agricultural Science, Anwhei Province, China. At the time of sampling, barley crops were in a vegetative condition. The barley crops are usually harvested in late May and 1987 was a normal year. The field experiment was established in J 983 so that the soil samples were collected after four rotations. Th~ soil was classified as a gleyed paddy soil derived from loe~s. According to the catenary classification o f rice soils used by M o o r m a n and van Breeman ( 1985 ), the soil, was classified as intermediate Type III. T h e soil had 23% clay particles <0.001 m m and 2.71% organic m a t t e r ( % C X 1.724).
Field experiment T h e field experiment was established in 1982, "_~,~included an annual cropping p r o g r a m m e of barley, early rice and late rice. After hurvesting each crop, a stubble of 5 cm remained. Barley was grown from N o v e m b e r to May following a preparation involving m o u l d b o a r d ploughing to a depth of 100-150 mm, then harrowing once or zwice, followed by seed drilling. Surface drainage for each barley crop was
EFFECT OF O R G A N I C RESIDUES ON PADDY SOILS IN C H I N A
]03
provided by 30f;-m_m a;,..k_.,,.ll,.,--adjacent to the plots. This is a c o m m o n practice for barley crops. G r o u n d w a t e r oscillated under the experimental barley plots about a depth of 400 mm. Pre~.aration for early rice included (a) flooding: ( b ) followed soon af~,er by mouldboard ploughing to 120-150-ram depth, (c) puddling and ( d ) finally transplanting !-month-old rice seedlings into moist puddled soil. The rice crop was harvested in late July. The late rice crop was transplanted in late July after harvesting early rice, and harvested in early November. Preparation of the late crop involved flooding, harrowing, no puddling, followed by transplanting of the l-montheld rice seedlings. Each experimental plot was 6 X 11 m and there were three replications. Individual field treatments were as foUows. Plot 1 received only applications of chemical fertilizer, expressed in kg h a - l, as follows: barley 130 ( N ) , 26.2 ( P ) , 66.4 ( K ) ; early rice 130 ( N ) , 21.8 ( P ) , 66.4 ( K ) ; late rice 130 ( N ) , 14.4 ( P ) , 66.4 ( K ) . Plot 2. As for Plc~t i, vi~s 22.5 t pig dung h a - ~ for early rice. Plot 3. As for Plot 1, plus 22.5 t pig dung h a - ~ for barley. Plot 4. As for Plot 1, plus 3 t dry rice straw h a - i for late rice.
Labora for2/determinations Ten replicate undisturbed soil cores of 50 m m depth and 200 ml capacity were collected from 0 - 5 0 - m m depth of each field treatment for the determination of moisture characteristics at 1, 5, 10, 30, 60 and 90 kPa tension. The moisture characteristics of undisturbed soil cores were determined according to tl~,e sandbox method of Stakman et al. ( 1972 ) appropriately modified with mercury columns (Xu, 1985) to extend the capacity to 90 kPa tension. Two undisturbed samples of 1 I capacity were collected to a depth of 100 m m from each field treatment for the determination of modulus of rupture, stability of aggregates and p,~asticity values. The modulus of rupture v~as determined according to the method of Kirkhahn et al. (1959). The plastic limit was determined by the widely used standard method described by Archer and Marks ( 1975 ). The liquid limit was determined according to WaslJff ( 1978 ), with a specialized stainless steel cone having an apex of 30 °, a weight of 76 g and a height of 25 mm. The stainless steel cone with guiding harness and weights was positioned immediately aoove the soil paste and allowed to fall vertically. This process was repeated, after appropriate adjustments to the moisture content, until the cone penetrated precisely to a depth of 10 mm. The shear strength had been calculated as 0.08 kg cm -2 under these conditions at ~;le point ofiiquid limit. The experimental
104
A J . R I X O N ET AL.
sample was immediately weighed and prepared for the determination o f moisture content, which becomes the value for the liquid limit. For the determination of aggregate stability, a representative sample of airdried aggregates weighing 500 g was transfe~ed to the top of a nest o f sieves with each sieve in sequence retaining aggregates > 10, 7, 5, 3, 2, l, 0.5 and 0.25 ram, respectively, according to Servinoff ( 1978 ). Proportional amounts of each aggregate size were weighed to provide two sub-samples weighing 50 g. The stability of sub-sample aggregates > 5, 3, 2, l, 0.5 and 0.25 m m under wet conditions was determined according to Wasliff ( 1 9 7 8 ) . The method included end-over-end shaking, with appropriate pauses, in a litre cylinder. RESULTS
The moisture characteristics for tensions equivalcnt to 1, 5, !0, 30, 60 and 90 kPa of the surface soil from the field experimental plots are represented in Fig. I. Standard errors (not included in Fig. 1 ) for the mean value at each ,:ension for the consistency of treatments remained within the range 2-3.75, and at any given tension there was no significant difference in response to treatment. A single set of values for the stability of aggregates was obtained end is presented below in Table 1. From these values, it can be appreciated that there was no strong trend towards differences in the distribution of aggregates and in the stability of aggregates of soil in response to the treatments. .50
M O I S T U R E R C T E N T I O N DATA RICE ANWHE|
47
-
44
t
PALOY SOILS PRO flNCE, C H I N A
o*)
i-i
TREATMENT I
¢
TREATME~T 3
o
TREATMENT 4
TREATMENf 2
{.u t-r I--o'J
o
41
. . . . .
3E
-
35 -I 0
20
40 TENSION
60
BO
:tOO
(kPa}
Fig. 1. Moisture retention data for rice paddy soils in Anwhei Province, China.
EFFECT OF ORGANIC RESIDUESON '~ADDY SOILS IN CHINA
105
TABLE 1
Stability of aggregates of rice paddy soils from Wuhu, Anwhei, Province, China Size of aggregates
Plot 1
(mm)
%dry
Plot 2 %
% dry
remaining after wetting > 10 7-10 5-7 3-5 2-3 1-2 0.5-1 0.5-0.25 < 0.25
67.5 13.0 5.1 6.3 3,2 1.0 2.0 0.7 1.0
39.3 3.2 1.9 4.7 14.3 11.9 24.8
Plot 3 %
% dry
remaining after wetting 57.7 13.7 6.3 9.5 5.4 1.4 4.1 1.6 2.0
33.2 4.2 3.1 6,5 16.2 11.4 25.6
Plot 4 %
% dry
remaining after wetting 57.7 17.6 6.8 8.0 4.3 1. I 2.7 0.9 1.0
38.0 4.3 3.1 5.6 13.5 11.0 24.6
%
remaining after wetting 55.2 16.9 7.2 8.7 4.6 1.6 3.1 t.2 1.6
37.2 5.0 3.0 4.4 13.4 12.0 25.1
TABLE 2
Physical properties of paddy soils from Wuhu, Anwhei Province, China Plot number
Plastic limit (% water)
Liquid limit (% water)
Plasticity index
1 2 3 4
30.0 30.8 30.0 29.6
41.0 42.0 43.1 42.3
l 1.0 11.2 13. ! 12.7
Ten representative cores were sampled from the undisturbed sample o f soil from each plot for determination o f the modulus o f rupture, expressed in kg c m - 2 . The mean value for each plot, together with the standard errors, were determined and are as follows: Plot 1, 4.65 + 2.48; Plot 2, 4.07 _+2.25; Plot 3, 6.56 _+ 3.30; Plot 4, 3.47 _+ 1.88. There were no significant differences due to treatment for the values o f m o d u l u s o f rupture. In order to gain s o m e further understanding o f the physical properties o f the experimental soil, aggregates > 2 m m and > 10 m m were separately immersed in distilled water and observed at 2 and 20 h according to Loveday ( 1 9 7 4 ) . N o n e o f the aggregates showed any indication o f dispersion or slaking at 2 and 20 h, irrespective o f treatment. The percentage water corresponding to the plastic and the liquid limit, together with values for the plasticity index, are shown in Table 2. It appeared that the treatments had no significant influence on the plastic properties o f the paddy soils.
106
A,J. RIXON ET AL.
DISCUSSION
The values for percentage moisture at each tension did not differ for the four treatments, demonstrating an apparent lack of response to heavy applications of organic matter. Any beneficial effects of soil moisture characteristics cesulting from heavy additions of organic matter were probably removed by the action of puddling. The values for standard error indicate a high degree of variability in the data and this is also probably due to puddliug of the soil. The simple test of immersing aggregates in water indicated that none of the experimental soils showed any tendency to slake or disperse. Dispersion of surface soils indicates crust formation and germination problems. The values for the modulus of rupture can provide an indication of the degree of crust formation and associated germination problems. There was no tendency for crust formation and the results showed that the treatments did not make a significant difference to the modulus of rupture. A decrease in both the stability and the organic matter in soils under annual tillage has been widely observed (Harris et al., 1966; Low, 19"/2), and the maintenance or enhancement of organic matter levels would be expected to maintain or enhance the physical properties of soil (Russell 1973; Marshall and Holmes, 1979). Nevertheless, the results in Tables 1 and 2 showed that the treated soils had plasticity properties and stability of aggregate values similar to the control soil. It is probable that the destructive action of puddling caused this lack of positive response to heavy additions or organic matter. The necessity of puddling for rice production is being questioned (Sharma and De Datta, 1985 ). In order to clarify the effects of puddling which negate the potential benefits resulting from heavy additions of organic residues, additional field experiments are planned for the rice-growing regions of China. In rice-producing countries other than China, the need for and benefits from puddling in land preparation andtillage practice for rice production are being investigated. Zero and minimum t[~iage have produced grain yields of transplanted rice similar to those produced from puddling (Croon, 1978; De Datta et al., 1979). Seedlings roots are damaged during transplanting to submerged non-puddled soils with significant soil strength. Subsequent seedling growth is slower and crop stand poorer when compared with puddled soils. Direct seeding may be a substitute for transplanting in such soils. Much research, mainly by the International Rice Research Institute, is involved with the development of appropriate machinery and agronomic practices aimed at alternatives to or avoidance of puddling in rice production. The practice of applying heavy additions of organic residue to rice-growing soils in China is declining. Nevertheless, there is a probable need to study long-term comparisons of minimum ti~iagc and puddling with and without heavy additions of organic residues in terms of the modification of soil physical pioperties and productiott of lowland rice in China.
EFFECT OF ORGANIC RESIDUES ON PADDY SOILS IN CHINA
107
CONCLUSIONS T h e effects o f h e a v y a p p l i c a t i o n s o f o r g a n i c r e s i d u e s o n t h e p h y s i c a l p r o p e r t i e s o f p a d d y soils i n C h i n a w e r e s t u d i e d . P h y s i c a l m e a s u r e m e n t s i n c l u d e d : (i) moisture characteristics over the 1-90-kPa tension range; (ii) stability of aggregates; (iii) modules of rupture; (iv) plasticity properties. There was no p o s i t i v e r e s p o n s e in a n y o f t h e m e a s u r e d p h y s i c a l p r o p e r t i e s r e s u l t i n g f r o m t h e h e a v y a d d i t i o n s o f o r g a n i c r e s i d u e s , a n d t h i s is c o ~ c l u d e d t o b e d u e t o t h e d e s t r u c t i v e a c t i o n o f soil p u d d l i n g . ACKNOWLEDGEMENTS The senior author wishes to thank the Darling Downs Institute of Adv a n c e d E d u c a t i o n , now- c a l l e d U n i v e r s i t y C o l l e g e o f S o u t h e r n Q u e e n s l a n d , f o r f i n a n c i a l s u p p o ~ !Dr t h e P r o f e s s i o n a l E x p e r i e n c e P r o ~ a m i n C h i n a , T h e author expresses appreciation to Mr. John Ruffini and Mr. Ampon Chumpia o f t h e S c h o o l o f E n g i n e e r i n g f o r t h e p r o d u c t i o n o f Fig. i.
REFERENCES Archer, J.R. and Marks, M.J., mid-! 970s. Techniques for measuring soil physical parameters. Advis. Pap. No. 18. Ministry of Agriculture, Fisheries and Food, U.K. Croon, F.W., 1978. Zero tillage for rice on vertisols. World Crops Livest, 30:12-13. De Datta, S.K., 1981. Principles and Practices of Rice Production. Wiley, New York, 618 pp. De Datta, S.K., BoRon, F.R. and Win, W.L., 1979. Prospects of using zero and minimum tillage in tropical low-land rice. Weed Res., 19:9-15. Harris, R.F., Chesters, G. and Allen, D.N., 1966. Dynamics of soil aggregation. Adv. Agron., 18: 107-169. Kirkham, D., de Boodt, M.F. and de Leenheer, L., 1959. Modulus of rupture determination on undisturbed soil core samples. Soil Sci., i 8: 141-144. Loveday, J., 1974. Methods for analysis of irrigated soils. Tech. Commun. No. 54, Commonwealth Bureau of Soils, Commonwealth Agricultural Bureau, U.K., 208 pp. Low, A.J., 1972. The effect of cultivation on the structure and other physical characteristics of grassland and arable soils. J. Soil Sci., 23: 363-380. Marshall, T.J. and Holmes, J.W., 1981. Soil Physics. Cambridge University Press, Cambridge, 345 pp. Moorman, F.R. and van Breeman, N., 1978. Rice: Soil, Water and Land. International Rice Research Institute, Los Bafios, Philippines. Russell, E.W., 1973. Soil Conditions and Plant Growth. 10th Edn. Longman, London, 849 pp. Servinoff, N.E., 1978. Measurement of macroaggregate stability. In: Methods of Measuring Physical Properties of Soils. Department of Soil Physics, Institute of Soil Science, Academia Sinica, Nanjing, China. Science Press, Beijing. Sharma, P.K. and De Datta, S.K., 1985. Effects of puddling on soil physical properties and processes. In: Soil Physics and Rice. International Rice Research Institute, Los Bafios, Philippines, pp. 217-234.
108
A.J. RIXON ET AL.
Stakman, W.P., Valk, G.A. and van der Harst, G.G., | 969. Determination o f soil moisture retention curves I sand box apparatus. Range PFO to 2.7. Institute for Land and Water Management Research, P.O. Box 35, Wageningen, Netherlands. Wasliff, A.M., i 978. Determination o f liquid limit. In: Methods of Measuring Physical Propertie~ o f Soils. Department o f Soil Physics, Institute of Soil Science, Academia Sinica. Na~jing, China. Science Press, Beijing. Xu. F.A., 1985. The explanation o f the tension plate made of quartz and kaolin. Chin. J. Soil Sci., (in Chinese). Yao, X . - L and Yu, D.-F., 1985a. On the soil structure under inlensive farming systems. (i) Effects o f organic materials and methods of their application on soil structure. (ii) Effect of flooding duration and puddling and soil structure. Acta Pedol. Sin., 17:102-118. Yao, X.-L. and Yu, D.-F., 1985b. Current Progress in Soil Rese~_rch in Pcc~Ic's Republic of China ( 1986 ), Soil Science Society o f China, pp. 26-33.
101
Elsevier Science Publishers B.V., A m s t e r d a m
Effect of heavy applications of organic residues on the physical properties of paddy soils in China A.J. Rixon', Yap Xianliang: and Zhu Hong Xia 2 ~School of Engineering, University College af Southern Queensland, Toowoomba, Qld. 4350 (Ausz calia) "-Institute of Soil Science, Academia Sinica, Nanjing (People's Republic of China) (Accepted for publication 5 March 1990)
ABSTRACT Rixon, A.J., Yao, X . - L and Zhu, H.X., 1991. Effect of h e a w applications of organic residues on the physical properties of paddy soils in China. Soil Tillage Res., 20: 101-108. Applications of ( i ) 22.5 t h a - t of pig dung and ( ii ) 3 t h a - l of dry. rice straw were made on paddy soils ia a field experiment that included an annual rotation of barley, early rice and late rice. Representative undisturbed soil cores and soil samples were collected from the experimental field plots. Physical properties, including soil moisture characteristics, were determined for the soil samples. The various physical properties did not differ significantly, indicating a lack of response to the added organic matter. The absence of improvement in the physical properties of the soil was probably due ~o the action of puddling, which is consistently practised prior to transplanting and the establishment of each rice crop.
INTRODUCTION
Desirable physical properties facilitating the rapid entry, transmission and storage of water in the soil, stability o f aggregates, adequate aeration and related physical properties are correlated positively with high levels o f soil organic matter. This correlation is the principal reason for the practice o f adding organic residues to ameliorate soil. For many centuries, Chinese agriculture, particularly rice production, relied on additions or organic r~;sidues, including straw, pig manure and litter, to maintain soil fertility. Green manure crops also contributed to the maintenance o f soil fertility. The use o f chemical fertilizers by Chinese farmers to supply plant nutrients has increased sig:aificantly during the last 20 years. The convenience of the application o f chemical fertilizer appeals to farmers and there has been a commensurate decline in the application o f organic residues. Furthermore, during the same period, the total area o f ~reen manure in intensive rice-producing regions such as the Taihu region in Jiangsu Province has
102
A,J. RIXON ET AL
declined from 15-20% to < l 0%. Although the addition of nutrients has been m a i n t a i n e d or even increased, the decreased additions of organic residues can result in changed soil physical properties. T h r o u g h o u t China, rice is grown in seedbeds a n d at the age of I m o n t h the rice seedlings are transvlanted into the field. Puddling, which is practised prior to rice transplanting, is virtually s y n o n y m o u s with rice production in China. Puddling invoi,'es the breaking down, usually with ro'ial3, implements, of soil aggregates into ultimate soil parlic!es at or near saturation. The purpos:~'s o f puddling are to make soil soft for transplanting, reduce hydraulic conductivity, reduce deep percolation o f nutrients and control weeds (De Datta. 1981 ). Puddling destroys aggregates and peals, and contributes to a decline in soil structur~ ( S h a r m a and De Datta, 1985 ). Although puddling has traditionally been an i m p o r t a n t activity in rice production, it is unlikely to be of any direct benefit to succeeding dryland crops in the rotation. I m p r o v e m e n t s in the physical characteristics of paddy soils as a r~:sult of additions of organic residues have been recorded (Yap and Yu, 1985a, b) in a glasshouse experiment. Field experiments incorporating heavy additions of organic residues, as well as including the practice of puddling, have been established at W u h u Institute o f Agricultural Sciences centred in a rice-growing region in the Province o f Anwhei. The present publication r~:por:~s the physical properties for surface soils of these experimental plots. MATERIALS AND METHODS
Soil samples were collected in late M a r c h 1987 from a fiela experiment located at Wuhu Institute of Agricultural Science, Anwhei Province, China. At the time of sampling, barley crops were in a vegetative condition. The barley crops are usually harvested in late May and 1987 was a normal year. The field experiment was established in J 983 so that the soil samples were collected after four rotations. Th~ soil was classified as a gleyed paddy soil derived from loe~s. According to the catenary classification o f rice soils used by M o o r m a n and van Breeman ( 1985 ), the soil, was classified as intermediate Type III. T h e soil had 23% clay particles <0.001 m m and 2.71% organic m a t t e r ( % C X 1.724).
Field experiment T h e field experiment was established in 1982, "_~,~included an annual cropping p r o g r a m m e of barley, early rice and late rice. After hurvesting each crop, a stubble of 5 cm remained. Barley was grown from N o v e m b e r to May following a preparation involving m o u l d b o a r d ploughing to a depth of 100-150 mm, then harrowing once or zwice, followed by seed drilling. Surface drainage for each barley crop was
EFFECT OF O R G A N I C RESIDUES ON PADDY SOILS IN C H I N A
]03
provided by 30f;-m_m a;,..k_.,,.ll,.,--adjacent to the plots. This is a c o m m o n practice for barley crops. G r o u n d w a t e r oscillated under the experimental barley plots about a depth of 400 mm. Pre~.aration for early rice included (a) flooding: ( b ) followed soon af~,er by mouldboard ploughing to 120-150-ram depth, (c) puddling and ( d ) finally transplanting !-month-old rice seedlings into moist puddled soil. The rice crop was harvested in late July. The late rice crop was transplanted in late July after harvesting early rice, and harvested in early November. Preparation of the late crop involved flooding, harrowing, no puddling, followed by transplanting of the l-montheld rice seedlings. Each experimental plot was 6 X 11 m and there were three replications. Individual field treatments were as foUows. Plot 1 received only applications of chemical fertilizer, expressed in kg h a - l, as follows: barley 130 ( N ) , 26.2 ( P ) , 66.4 ( K ) ; early rice 130 ( N ) , 21.8 ( P ) , 66.4 ( K ) ; late rice 130 ( N ) , 14.4 ( P ) , 66.4 ( K ) . Plot 2. As for Plc~t i, vi~s 22.5 t pig dung h a - ~ for early rice. Plot 3. As for Plot 1, plus 22.5 t pig dung h a - ~ for barley. Plot 4. As for Plot 1, plus 3 t dry rice straw h a - i for late rice.
Labora for2/determinations Ten replicate undisturbed soil cores of 50 m m depth and 200 ml capacity were collected from 0 - 5 0 - m m depth of each field treatment for the determination of moisture characteristics at 1, 5, 10, 30, 60 and 90 kPa tension. The moisture characteristics of undisturbed soil cores were determined according to tl~,e sandbox method of Stakman et al. ( 1972 ) appropriately modified with mercury columns (Xu, 1985) to extend the capacity to 90 kPa tension. Two undisturbed samples of 1 I capacity were collected to a depth of 100 m m from each field treatment for the determination of modulus of rupture, stability of aggregates and p,~asticity values. The modulus of rupture v~as determined according to the method of Kirkhahn et al. (1959). The plastic limit was determined by the widely used standard method described by Archer and Marks ( 1975 ). The liquid limit was determined according to WaslJff ( 1978 ), with a specialized stainless steel cone having an apex of 30 °, a weight of 76 g and a height of 25 mm. The stainless steel cone with guiding harness and weights was positioned immediately aoove the soil paste and allowed to fall vertically. This process was repeated, after appropriate adjustments to the moisture content, until the cone penetrated precisely to a depth of 10 mm. The shear strength had been calculated as 0.08 kg cm -2 under these conditions at ~;le point ofiiquid limit. The experimental
104
A J . R I X O N ET AL.
sample was immediately weighed and prepared for the determination o f moisture content, which becomes the value for the liquid limit. For the determination of aggregate stability, a representative sample of airdried aggregates weighing 500 g was transfe~ed to the top of a nest o f sieves with each sieve in sequence retaining aggregates > 10, 7, 5, 3, 2, l, 0.5 and 0.25 ram, respectively, according to Servinoff ( 1978 ). Proportional amounts of each aggregate size were weighed to provide two sub-samples weighing 50 g. The stability of sub-sample aggregates > 5, 3, 2, l, 0.5 and 0.25 m m under wet conditions was determined according to Wasliff ( 1 9 7 8 ) . The method included end-over-end shaking, with appropriate pauses, in a litre cylinder. RESULTS
The moisture characteristics for tensions equivalcnt to 1, 5, !0, 30, 60 and 90 kPa of the surface soil from the field experimental plots are represented in Fig. I. Standard errors (not included in Fig. 1 ) for the mean value at each ,:ension for the consistency of treatments remained within the range 2-3.75, and at any given tension there was no significant difference in response to treatment. A single set of values for the stability of aggregates was obtained end is presented below in Table 1. From these values, it can be appreciated that there was no strong trend towards differences in the distribution of aggregates and in the stability of aggregates of soil in response to the treatments. .50
M O I S T U R E R C T E N T I O N DATA RICE ANWHE|
47
-
44
t
PALOY SOILS PRO flNCE, C H I N A
o*)
i-i
TREATMENT I
¢
TREATME~T 3
o
TREATMENT 4
TREATMENf 2
{.u t-r I--o'J
o
41
. . . . .
3E
-
35 -I 0
20
40 TENSION
60
BO
:tOO
(kPa}
Fig. 1. Moisture retention data for rice paddy soils in Anwhei Province, China.
EFFECT OF ORGANIC RESIDUESON '~ADDY SOILS IN CHINA
105
TABLE 1
Stability of aggregates of rice paddy soils from Wuhu, Anwhei, Province, China Size of aggregates
Plot 1
(mm)
%dry
Plot 2 %
% dry
remaining after wetting > 10 7-10 5-7 3-5 2-3 1-2 0.5-1 0.5-0.25 < 0.25
67.5 13.0 5.1 6.3 3,2 1.0 2.0 0.7 1.0
39.3 3.2 1.9 4.7 14.3 11.9 24.8
Plot 3 %
% dry
remaining after wetting 57.7 13.7 6.3 9.5 5.4 1.4 4.1 1.6 2.0
33.2 4.2 3.1 6,5 16.2 11.4 25.6
Plot 4 %
% dry
remaining after wetting 57.7 17.6 6.8 8.0 4.3 1. I 2.7 0.9 1.0
38.0 4.3 3.1 5.6 13.5 11.0 24.6
%
remaining after wetting 55.2 16.9 7.2 8.7 4.6 1.6 3.1 t.2 1.6
37.2 5.0 3.0 4.4 13.4 12.0 25.1
TABLE 2
Physical properties of paddy soils from Wuhu, Anwhei Province, China Plot number
Plastic limit (% water)
Liquid limit (% water)
Plasticity index
1 2 3 4
30.0 30.8 30.0 29.6
41.0 42.0 43.1 42.3
l 1.0 11.2 13. ! 12.7
Ten representative cores were sampled from the undisturbed sample o f soil from each plot for determination o f the modulus o f rupture, expressed in kg c m - 2 . The mean value for each plot, together with the standard errors, were determined and are as follows: Plot 1, 4.65 + 2.48; Plot 2, 4.07 _+2.25; Plot 3, 6.56 _+ 3.30; Plot 4, 3.47 _+ 1.88. There were no significant differences due to treatment for the values o f m o d u l u s o f rupture. In order to gain s o m e further understanding o f the physical properties o f the experimental soil, aggregates > 2 m m and > 10 m m were separately immersed in distilled water and observed at 2 and 20 h according to Loveday ( 1 9 7 4 ) . N o n e o f the aggregates showed any indication o f dispersion or slaking at 2 and 20 h, irrespective o f treatment. The percentage water corresponding to the plastic and the liquid limit, together with values for the plasticity index, are shown in Table 2. It appeared that the treatments had no significant influence on the plastic properties o f the paddy soils.
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DISCUSSION
The values for percentage moisture at each tension did not differ for the four treatments, demonstrating an apparent lack of response to heavy applications of organic matter. Any beneficial effects of soil moisture characteristics cesulting from heavy additions of organic matter were probably removed by the action of puddling. The values for standard error indicate a high degree of variability in the data and this is also probably due to puddliug of the soil. The simple test of immersing aggregates in water indicated that none of the experimental soils showed any tendency to slake or disperse. Dispersion of surface soils indicates crust formation and germination problems. The values for the modulus of rupture can provide an indication of the degree of crust formation and associated germination problems. There was no tendency for crust formation and the results showed that the treatments did not make a significant difference to the modulus of rupture. A decrease in both the stability and the organic matter in soils under annual tillage has been widely observed (Harris et al., 1966; Low, 19"/2), and the maintenance or enhancement of organic matter levels would be expected to maintain or enhance the physical properties of soil (Russell 1973; Marshall and Holmes, 1979). Nevertheless, the results in Tables 1 and 2 showed that the treated soils had plasticity properties and stability of aggregate values similar to the control soil. It is probable that the destructive action of puddling caused this lack of positive response to heavy additions or organic matter. The necessity of puddling for rice production is being questioned (Sharma and De Datta, 1985 ). In order to clarify the effects of puddling which negate the potential benefits resulting from heavy additions of organic residues, additional field experiments are planned for the rice-growing regions of China. In rice-producing countries other than China, the need for and benefits from puddling in land preparation andtillage practice for rice production are being investigated. Zero and minimum t[~iage have produced grain yields of transplanted rice similar to those produced from puddling (Croon, 1978; De Datta et al., 1979). Seedlings roots are damaged during transplanting to submerged non-puddled soils with significant soil strength. Subsequent seedling growth is slower and crop stand poorer when compared with puddled soils. Direct seeding may be a substitute for transplanting in such soils. Much research, mainly by the International Rice Research Institute, is involved with the development of appropriate machinery and agronomic practices aimed at alternatives to or avoidance of puddling in rice production. The practice of applying heavy additions of organic residue to rice-growing soils in China is declining. Nevertheless, there is a probable need to study long-term comparisons of minimum ti~iagc and puddling with and without heavy additions of organic residues in terms of the modification of soil physical pioperties and productiott of lowland rice in China.
EFFECT OF ORGANIC RESIDUES ON PADDY SOILS IN CHINA
107
CONCLUSIONS T h e effects o f h e a v y a p p l i c a t i o n s o f o r g a n i c r e s i d u e s o n t h e p h y s i c a l p r o p e r t i e s o f p a d d y soils i n C h i n a w e r e s t u d i e d . P h y s i c a l m e a s u r e m e n t s i n c l u d e d : (i) moisture characteristics over the 1-90-kPa tension range; (ii) stability of aggregates; (iii) modules of rupture; (iv) plasticity properties. There was no p o s i t i v e r e s p o n s e in a n y o f t h e m e a s u r e d p h y s i c a l p r o p e r t i e s r e s u l t i n g f r o m t h e h e a v y a d d i t i o n s o f o r g a n i c r e s i d u e s , a n d t h i s is c o ~ c l u d e d t o b e d u e t o t h e d e s t r u c t i v e a c t i o n o f soil p u d d l i n g . ACKNOWLEDGEMENTS The senior author wishes to thank the Darling Downs Institute of Adv a n c e d E d u c a t i o n , now- c a l l e d U n i v e r s i t y C o l l e g e o f S o u t h e r n Q u e e n s l a n d , f o r f i n a n c i a l s u p p o ~ !Dr t h e P r o f e s s i o n a l E x p e r i e n c e P r o ~ a m i n C h i n a , T h e author expresses appreciation to Mr. John Ruffini and Mr. Ampon Chumpia o f t h e S c h o o l o f E n g i n e e r i n g f o r t h e p r o d u c t i o n o f Fig. i.
REFERENCES Archer, J.R. and Marks, M.J., mid-! 970s. Techniques for measuring soil physical parameters. Advis. Pap. No. 18. Ministry of Agriculture, Fisheries and Food, U.K. Croon, F.W., 1978. Zero tillage for rice on vertisols. World Crops Livest, 30:12-13. De Datta, S.K., 1981. Principles and Practices of Rice Production. Wiley, New York, 618 pp. De Datta, S.K., BoRon, F.R. and Win, W.L., 1979. Prospects of using zero and minimum tillage in tropical low-land rice. Weed Res., 19:9-15. Harris, R.F., Chesters, G. and Allen, D.N., 1966. Dynamics of soil aggregation. Adv. Agron., 18: 107-169. Kirkham, D., de Boodt, M.F. and de Leenheer, L., 1959. Modulus of rupture determination on undisturbed soil core samples. Soil Sci., i 8: 141-144. Loveday, J., 1974. Methods for analysis of irrigated soils. Tech. Commun. No. 54, Commonwealth Bureau of Soils, Commonwealth Agricultural Bureau, U.K., 208 pp. Low, A.J., 1972. The effect of cultivation on the structure and other physical characteristics of grassland and arable soils. J. Soil Sci., 23: 363-380. Marshall, T.J. and Holmes, J.W., 1981. Soil Physics. Cambridge University Press, Cambridge, 345 pp. Moorman, F.R. and van Breeman, N., 1978. Rice: Soil, Water and Land. International Rice Research Institute, Los Bafios, Philippines. Russell, E.W., 1973. Soil Conditions and Plant Growth. 10th Edn. Longman, London, 849 pp. Servinoff, N.E., 1978. Measurement of macroaggregate stability. In: Methods of Measuring Physical Properties of Soils. Department of Soil Physics, Institute of Soil Science, Academia Sinica, Nanjing, China. Science Press, Beijing. Sharma, P.K. and De Datta, S.K., 1985. Effects of puddling on soil physical properties and processes. In: Soil Physics and Rice. International Rice Research Institute, Los Bafios, Philippines, pp. 217-234.
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Stakman, W.P., Valk, G.A. and van der Harst, G.G., | 969. Determination o f soil moisture retention curves I sand box apparatus. Range PFO to 2.7. Institute for Land and Water Management Research, P.O. Box 35, Wageningen, Netherlands. Wasliff, A.M., i 978. Determination o f liquid limit. In: Methods of Measuring Physical Propertie~ o f Soils. Department o f Soil Physics, Institute of Soil Science, Academia Sinica. Na~jing, China. Science Press, Beijing. Xu. F.A., 1985. The explanation o f the tension plate made of quartz and kaolin. Chin. J. Soil Sci., (in Chinese). Yao, X . - L and Yu, D.-F., 1985a. On the soil structure under inlensive farming systems. (i) Effects o f organic materials and methods of their application on soil structure. (ii) Effect of flooding duration and puddling and soil structure. Acta Pedol. Sin., 17:102-118. Yao, X.-L. and Yu, D.-F., 1985b. Current Progress in Soil Rese~_rch in Pcc~Ic's Republic of China ( 1986 ), Soil Science Society o f China, pp. 26-33.