Management of clay soils for rainfed lowland rice-based
cropping systems: an overview
H.B. So
a,*, A.J. Ringrose-Voase
baSchool of Land and Food Sciences, The University of Queensland, St Lucia, Brisbane, Qld 4072, Australia bCSIRO Land and Water, GPO Box 1666, Canberra, ACT 2601, Australia
Abstract
The problem of concern in this project is that in the dry season following a lowland rice (Oryza sativaL.) crop, yields of post-rice crops are generally low, despite adequate water commonly being available in the soil pro®le to grow a potentially high yielding dry season (DS) crop without irrigation. Maize (Zea maysL.) yields are as low as 1 Mg haÿ1or less, soybean
(Glycine maxL. Merr.) and cowpea (Vigna unguiculataL.) at 0.3 to 0.8 Mg haÿ1
in Indonesia and mungbean (Vigna radiata
(L.) Wilzek) around 0.5 Mg haÿ1in the Philippines. These are all very much below the yield potential of these soils. For
example, mungbean yields of 2.2 Mg haÿ1
have been achieved by IRRI in the Philippines on these soils without irrigation or additional fertilisers. The causes of low yields of DS crops after rice are mainly poor crop establishment and poor root growth due to soil physical constraints. These result from the breakdown of soil structure during wet cultivation (puddling) for rice. Yields are also limited by biological and chemical constraints. As a result of these low yields, farmers are reluctant to invest in post-rice crops. Therefore, land after lowland rice (at least 51 million ha in Asia according to Huke [Huke, R.E., 1982. Rice Area by Type of Culture: South, Southeast, and East Asia. International Rice Research Institute, Los BanÄos, Philippines, 32 pp.]) represents an underutilised resource that can be used to meet the food requirement of the ever increasing population of the developing world. To increase the utilisation of these soils, improved management practices are required to enable dry season crops to use the stored water in the soil pro®le after the rice crop. This paper outlines a project which was established with the general objective of developing soundly based soil management technologies that can overcome soil physical limitations to DS crop production after lowland rice. The speci®c objectives of the program were
1. to test a range of soil management and agronomic practices that have the potential to overcome adverse soil physical conditions for DS crops after rice, across a range of soil and climates;
2. to evaluate these practices by
2.1. measuring the changes in soil physical conditions throughout the complete cropping cycle from rice to DS crops; 2.2. determining the performance of the DS crop (establishment and growth) and its ability to extract soil water. 3. to determine the mechanisms involved in dispersion due to puddling and in ¯occulation and structural development as the
soil dries after draining surface water from rice ®elds.
Relevant outcomes from this project are described in the following papers in this issue.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Soil management; Puddling; Rice; Legumes; Rainfed lowland
*Corresponding author. Tel.:61-7-3365-2888; fax:61-7-3365-1177.
E-mail address: [email protected] (H.B. So).
1. Introduction
To keep pace with rapidly expanding populations, the production of food legumes and other dry season (DS) crops must be increased within the lowland rice growing areas in Indonesia and the Philippines as well as in other countries of southeast Asia. There are 51 million ha of lowland rice in Asia including 8.2 and 3.5 million ha of lowland rice in Indonesia and the Philippines of which 3 and 2 million ha, respectively, are rainfed (Huke, 1982). A feature of lowland rice culture is that the amount of soil water remaining in the dry season after the rice crop is usually adequate for a DS crop. However, when DS crops are grown in these soils, yields are generally low. For example, yields are as low as 1 Mg haÿ1
or less for maize, 0.3± 0.8 Mg haÿ1
for soybeans and cowpeas in Indonesia (Hoque, 1984) and 0.5 Mg haÿ1
for mungbeans is not uncommon in the Philippines. These yields do not provide adequate returns to the farmer, so that lowland rice soils, in particular rainfed lowland rice soils, represent an underutilised resource during the dry season. The potential yield for mungbean in the Philippines is approximately 2.2 Mg haÿ1
(So and Woodhead, 1987). Therefore, increasing yields of DS crops would increase the utilisation of land and residual soil water during the period between rice crops.
Despite the lower yields of DS crops compared to rice, Table 1 shows that the lower costs and higher prices of some DS crops, in particular mungbean, can result in greater net returns from these crops than from the rice crop if moderate yields can be obtained (Maranan, 1986, 1987). Considerable bene®ts could be expected from growing DS crops, including increased farmer income and nutrition and a reduction
in imports of food legumes. In 1987, imports of maize and soybean cost Indonesia about $25 million and $63 million, respectively and the Philippines about $7 million and $2.5 million. Peanut (Arachis hypogaea L.) imports cost $22 million and $7.5 million to Indonesia and the Philippines, respectively. In addi-tion, the introduction of food legumes into the rice rotation could result in substantial savings in nitro-genous fertilisers. These bene®ts would also be applic-able to lowland rice areas in other southeast Asian countries.
Both the Indonesian and Philippine governments place high priority on raising yields of DS crops, particularly legume crops, as a means of increasing farmers' income as well as nutrition. The Indonesian government expressed this through its Five Year Plans (PELITAs), of which the Sixth Plan is current. The Philippine Council for Agriculture, Forestry and Nat-ural Resources Research and Development (PCARRD) has a Mungbean Development Action Plan to co-ordinate efforts to increase production of mungbeans.
The causes of low yields of DS crops after rice are often poor crop establishment and inferior root growth due to adverse physical conditions of the soil which, in turn, are caused by the wet cultivation (puddling) undertaken for paddy rice (Pasaribu and McIntosh, 1985; So and Woodhead, 1987; Adisarwanto et al., 1989). Yields are also limited by nutritional and biological constraints.
Project 8938 was funded by the Australian Centre for International Agricultural Research (ACIAR) titled `The Management of Clay Soils for Lowland Rice-based Cropping Systems' aimed to investigate the factors that affect the success or failure of DS crops grown after rice and to make a contribution towards
Table 1
National average yield, actual price, relative pro®tability and the ratio of returns/costs for several crops in the Philippines, 1985a
Crops Yield Price Total return Cost of production Net return Net return/cost
(Mg haÿ1) (Pesos/kg) (Pesos/ha) (Pesos/ha) (Pesos/ha) (%)
Rice 2.40 3.24 7776 5370 2406 44.8
Maize 1.04 2.80 2912 2078 834 40.1
Soybean 0.99 7.30 7227 3697 3530 95.5
Mungbean 0.69 15.40 10626 3780 6846 181.1
Peanut 0.85 10.10 8585 6959 1626 23.4
the development of stable cropping systems that incorporate DS crops within rainfed, lowland rice-based cropping systems. It was a synthesis of two proposals, one from the University of Queensland and another from CSIRO and the Philippine Bureau of Soil and Water Management(BSWM) and involved the University of Brawijaya, Indonesia and two Indone-sian Institutes for Food Crops. The factors investigated are tillage during the preparation for the rice and DS crop phases, soil amendments, time of sowing the DS crop, surface drainage and fertilisers.
This paper outlines the background to the project, a review of the relevant literature and a description of the experimental design and set-up of the project.
2. Background to the project
Rice in southeast Asian countries is mostly grown under lowland conditions with 1±3 crops a year depending on the availability of irrigation water and the use of modern, short season varieties. After long-term submergence for lowland rice, soil water is suf®cient to grow a DS crop with reasonable yield potential. However, under current management prac-tices the yields of DS crops (see above) are generally well below the yield potential (Pasaribu and McIntosh, 1985; Adisarwanto et al., 1989). The area of lowland rice is approximately 51 million ha in Asia (Huke, 1982). The untapped potential for food production from DS crops is a large, underutilised resource. Furthermore, in Africa there are approximately 100 million ha of land that could potentially be adapted to rainfed lowland rice with appropriate soil physical management (Woodhead, 1990).
The realisation that multiple cropping programs are essential to raise production from rice based systems lead to the formation of the Asian Cropping Systems Network. This network coordinates efforts by the International Rice Research Institute (IRRI) and the various national programs to jointly develop appro-priate rice-based cropping systems in major rice grow-ing environments. (Hoque, 1984). As soil factors are known to limit yield of DS crops, appropriate soil management is an essential part of improved cropping systems. For these systems to be developed, the dynamics of soil-crop interactions in DS paddy soils must be better understood.
2.1. The importance of legumes in rice-based cropping systems
Indonesia has been self-suf®cient in rice since 1985 through the success of the government coordinated BIMAS (mass guidance) and INMAS (mass intensi-®cation) programs during past Five Year Plans or PELITAs. From 1984, PELITA IV gave special atten-tion to the ®rst DS crop (®rst secondary crop within a lowland rice±DS crop±DS crop cropping system), with particular emphasis on legumes (Nanseki et al., 1989). These crops were targeted for increased pro-duction with the aim of improving farmers' income and nutritional status (Vademecum BIMAS, 1987). The target, in irrigated lowland areas, is to replace the third rice crop with a DS crop and, in rainfed lowland areas, is to grow a DS crop before or after the rice crop. Based on the rate of consumption and imports, the major DS crops in Indonesia are, in decreasing order, maize, soybeans, peanuts and mungbeans (FAO, 1984). The success of the BIMAS and INMAS programs is partly due to the setting of realistic production targets, which are negotiated for each province, county and village which elected to join the program. These production targets, when agreed to by the parties concerned, become contracts that must be adhered to (Agricultural Intensi®cation Program, 1988±1989) and involve a minimum mandatory set of technology packages (recipes) that must be carried out. If the recipe is adhered to, a minimum and achievable improved yield level is guaranteed. However, these technology packages do not include soil physical management recommendations due to a lack of knowledge in this area. Where adequate irrigation water is available, improved technology for soybean has recently been launched through the government extension program `Supra-insus' (special program for intensi®cation) with the aim of raising soybean yield from 1 to 1.5 Mg haÿ1
(Sumarno, 1990). As yet, satisfactory packages have not been developed for DS crops after rice.
1990). Faster growing varieties are particularly suita-ble for growing after rice, when the legume is largely dependent on stored soil water. Mungbean is the major legume crop in the Philippines partly because, with a protein content of 20±25%, it is a popular and inex-pensive source of protein, often being referred to as `the poor man's meat' (Cabahug, 1990). Its price is relatively high and stable and farmer consumption tends to compensate for any over-production, because unlike soybean, it does not require processing. In addition, Table 1 shows that it can be more pro®table than other legumes or rice, if moderate yields can be obtained.
Modest increases in mungbean yield in a rice-legume rotation can result in net returns from mung-bean being greater than that from the rice component (Lavapiez et al., 1977; Maranan, 1986, 1987). The pro®tability of mungbean in Indonesia is also cited as a major incentive towards their use after rice. How-ever, under current management practices yields of DS crops are poor and result in a reluctance to invest management and resources in DS crops so that much land is underutilised after lowland rice (Varade, 1990). In addition, there is a social preference for rice. Therefore, the introduction of management systems that can stabilise yields of DS crops, particularly legumes, after rice will have considerable socio-eco-nomic bene®ts.
2.2. Physical limitations of puddled soil
The physical limitations imposed by puddled soil have been recognised as the major cause of poor establishment and yield of post-rice crops in Asia, including soybeans in east Java (Adisarwanto et al., 1989) and mungbeans in the Philippines and other Asian countries (IRRI, 1984; So and Woodhead, 1987; Mahata et al., 1990; Varade, 1990). Puddling is asso-ciated with the breakdown of soil aggregates during wet cultivation (Sharma and De Datta, 1985; Adachi, 1990) and results in a massive structure after rice. After drainage of the surface water prior to rice harvest, the water content of the surface soil decreases which is accompanied by a rapid increase in redox potential (IRRI, 1987; Maghari, 1990) and soil strength (IRRI, 1985, 1986, 1987, 1988). Puddling also creates a compacted layer below the puddled layer, which increases in strength during drying (IRRI,
1986). The effect of seasonal conditions and soil type on the germination, establishment and root growth of DS crops after rice is determined by the interactions between the rates of change of redox potential, soil strength and available water as the soil dries. To devise ways of overcoming these limitations, it is important to quantify the nature of these interactions through a program of detailed monitoring of the soil physical conditions.
3. Factors affecting the establishment and growth of DS crops after lowland rice
3.1. Effect of delay between ®eld drainage and sowing on germination and establishment of post-rice DS crops
Successful crop establishment is essential for high yields, for example, yield of DS mungbean was lin-early related to plant population density up to 0.55±0.6 million plants/ha (So and Woodhead, 1987; IRRI, 1988). A key factor determining the success of crop establishment is the rate of germination. Rapid ger-mination, which depends largely on soil water content and seed-soil contact, is essential to minimise risks from adverse factors (So and Woodhead, 1987).
The delay between ®eld drainage and sowing has a major in¯uence on crop establishment because it affects soil water content and hence germination and emergence. Although mungbeans under con-trolled conditions can germinate at soil water poten-tials as low asÿ2.2 MPa (below wilting point), poor seed-soil contact under ®eld conditions reduces ger-mination rates at low potentials and radicle elongation rate is reduced at potentials belowÿ0.2 MPa (Fy®eld, 1987; IRRI, 1988). Emergence is slower and falls below 50% when water potential is reduced below ÿ0.1 MPa (IRRI, 1986).
low water potentials and increased seedbed and sub-soil strength. On the other hand, growth and yield can also be reduced after sowing at delays of 0±3 DAD apparently due to low redox potentials and poor aeration (IRRI, 1987). It is not clear how these periods would vary with soil types.
Since rice is generally harvested 7±10 DAD, it is important that sowing of DS crops be carried out as soon as possible after harvest. However, in regions where the probability of rainfall after rice harvest is high, farmers tend to avoid waterlogging by either postponing sowing or by providing surface drainage. Relay cropping, where legumes are sown soon after draining and before rice is harvested, has been tried as a means of reducing the sowing delay. However, this method tends to reduce establishment and yield, as well as increase problems of weeds and ratooning of rice (IRRI, 1987, 1989).
3.2. The effect of soil amendments
3.2.1. Surface mulch
The use of surface organic mulch reduces the rate of water loss from the soil. Mulching with rice straw at 8 Mg haÿ1
over the mungbean rows has been shown to improve emergence by 17% when sown 17 days after draining (IRRI, 1988). In the drier regions of the Philippines a mulch rate of 1.6 Mg haÿ1
increased yield by 26% (IRRI, 1989). Similarly, in east Java a surface mulch of 5 Mg haÿ1
rice straw increase yield by 30% (Adisarwanto, 1985).
Incorporation of organic matter may improve soil in the long term, but 4 years of organic matter incorpora-tion caused only marginal improvement in topsoil porosity and in®ltration rate and had no signi®cant effect on the crop (T. Woodhead, personal commu-nication). This, however, might help to offset further deterioration in soil structure under intensive rice-based cropping systems (Cass et al., 1994).
3.2.2. Chemical amendments
Calcium amendments, such as gypsum and lime, have been used successfully to overcome soil physical problems associated with dispersion of Vertisols (So and McKenzie, 1984; McKenzie and So, 1989a,b) and could in¯uence physical properties of clay soils after drainage. Amendments have also been used in rice bays in New South Wales, Australia to clear cloudy
water by suppressing dispersion (Bacon, 1979). It is possible that calcium amendments may improve struc-tural development and water relations in drying puddled soils and may assist establishment of DS legumes. Gypsum applied to a silty clay loam rice soil 10 days before draining (20 days before harvest) resulted in higher seed zone water content over the 30 days after harvest and increased wheat seedling emer-gence when moisture conditions were sub-optimal (Zhang, 1990).
The uncertainties surrounding the use of organic mulch and gypsum or lime as part of soil management practices and their effect on DS crops after rice warrants further investigation.
3.3. The effects of tillage
3.3.1. The effect of tillage for the DS crop
The structure of the puddled layer becomes massive as the soil dries. Puddling also results in the formation of compacted soil layers below the puddled zone, on which soil strength increases rapidly as the soil dries and limits the depth of root exploitation (IRRI, 1986). The depth of exploitable soil determines the yield of the crop. For example, mungbean yield has been shown to be correlated with the depth at which penet-rometer resistance increases sharply (IRRI, 1985, 1986). The growth of DS peanuts can also be adversely affected by the compacted layer and can be signi®cantly improved by breaking that layer (G. Wright, ACIAR project 8834, personal communica-tion).
because water becomes more limiting and can be lost faster from tilled soil (IRRI, 1987, 1989; Cook, 1989; Cook et al., 1995).
The disappointing responses to tillage found in many experiments may also be because tillage is not adequately loosening the soil. Results show that manual loosening of the soil to 1 m using a spade consistently improved mungbean yield more than tillage (IRRI, 1987, 1988). The residual effects of DS deep tillage on increased percolation from the subsequent rice crop have not been widely investi-gated, but appear insigni®cant (IRRI, 1984) because deep cracks developed irrespective of whether tillage was used or not.
Deep strip tillage, a new technology developed at IRRI which breaks the compacted layer directly below the crop rows, can signi®cantly improve soil physical conditions and root growth of mungbeans (IRRI, 1984, 1985, 1986, 1987; So and Woodhead, 1987; Woodhead, 1990). However, deep tillage has a high draft requirement which can be met by hand operated two-wheel tractors. It requires four-wheel drive trac-tors or cable winch systems which are generally not available in southeast Asia (IRRI, 1985, 1986). In addition, four-wheel tractors can result in greater compaction. Therefore, this solution does not seem to be a practical option for the near future.
3.3.2. Effects of puddling intensity on subsequent DS crops
Wet cultivation or puddling is synonymous with rice culture in Asia and is used to assist in transplanting of rice seedlings; to reduce water and nutrient losses and to control weeds (Sharma and De Datta, 1985). Pud-dling breaks down and disperses soil aggregates into individual component particles. The degree of disper-sion for a given puddling effort is dependent on the structural stability of the soil and is likely to affect the regeneration of soil structure after rice, which, in turn, will affect the DS crop. The effects of degree of puddling prior to the rice phase on structure regenera-tion and growth of a DS crop after rice is related to soil type. For example, increasing intensity of puddling resulted in increased maize yields on a Vertisol but decreased yields in hardsetting, lighter textured Rego-sols (Trenggono and Willatt, 1988). Similarly, inten-sive puddling increased DS mungbean yield on a clay loam but decreased it on a sandy loam (IRRI, 1988).
These differences were attributed to clay content and mineralogy. The concept of partially controlling soil structure regeneration after rice through the puddling treatment prior to the rice phase should be investigated further by determining which soil types are respon-sive.
3.4. Seeding techniques
The most commonly used technique for DS legumes after rice is manual dibbling. However, Cook et al. (1995) found that dibbling gives variable results, especially when the soil is wet in the few days after rice harvest. An inexpensive alternative is manual furrow seeding, which also gave variable results, but was better in wet soils. Neither method was reliable at lower water contents. They also found that an inverted T seeder (Choudhary, 1985) pulled by a hand tractor gave better performance in tilled soils except when very wet or dry.
3.5. Crop/cultivar selection for improved root performance
A factor in¯uencing the penetration of compacted subsoils is the pressure that the root system can exert. Different plants vary in their ability to penetrate compaction layers. For example, bahia-grass ( Paspa-lum notatum Flugge) penetrated compacted subsoils better than cotton, which has a taproot, with the result that cotton grown after bahia-grass yielded better and extracted more water than cotton after cotton (Elkin et al., 1977). Similarly, maize after pigeonpea ( Caja-nus cajanL.) grew better and yielded more than maize after maize partly because of the superior penetration by pigeonpea roots (Hulugalle and Lal, 1986).
crops suitable as DS crops after lowland rice and possibly in breeding suitable cultivars for that purpose.
3.6. Soil chemical and biological limitations
Crops grown in lowland soils after rice may suffer from de®ciencies of plant nutrients and from a lack of suitable micro-organisms such as rhizobia or VA mycorrhiza, which may not survive prolonged water-logged conditions. The availability of residual nutri-ents from the rice phase is dependent on cultural practices and soil type. In 1984, IRRI achieved mung-bean yields of 2.1 Mg haÿ1
after rice without fertiliser, inoculum or irrigation and with only 35 mm of DS rain (IRRI, 1985). However, during a visit to east and central Java, we saw signi®cant responses of mung-bean and peanuts after rice to various combinations of fertilisers and inoculum. The interaction of phos-phorus and zinc has been observed to in¯uence plant growth in student projects with Vertisols in Indonesia (S. Setijono, personal communication). Zinc, copper and boron de®ciencies have been reported for IR 64 rice in some areas of east Java and zinc and copper applications have increased lowland rice yields (Suyono, 1990). Therefore, it is possible that these elements could be de®cient for DS crops as well and should be evaluated.
3.7. Summary
In summary, it is clear that the limitations to DS crop growth and yield after lowland rice soils are complex and still not clearly understood. The need for solutions to the problems of clay soils after low-land rice received strong endorsement from the 1989 Asian Rice Farming Systems Network workshop in Bogor which recommended that work on this topic should be initiated simultaneously in a number of Asian countries.
4. The project `Management of clay soils for lowland rice-based cropping systems'
4.1. General objectives
The overall objective of this project was to con-tribute towards the development of soundly based soil
management technologies that can overcome soil physical limitations to DS crop production after low-land rice.
4.2. The speci®c objectives of the project
1. To test soil management and agronomic practices across a range of soils and climates, that have the potential to overcome adverse soil physical conditions for DS crops after rice, including amendments (calcium or organic matter mulch), tillage technologies and length of delay periods in sowing of the DS crop after rice harvest.
2. To evaluate these practices by
2.1. measuring the changes in soil physical conditions throughout the complete cropping cycle from rice to DS crop.
2.2. determining the performance of the DS crop (establishment and growth) and its ability to extract soil water.
3. To determine the mechanisms involved in soil dis-persion due to puddling and the factors controlling ¯occulation and structural reformation as the soil dries after draining of surface water from rice ®elds.
4.3. The contrasting requirements of rice and DS crops
The project dealt with components of a cropping system that have vastly different soil structural require-ments. The rice phase requires a puddled soil with the structure largely broken down, whereas the DS crop requires a soil with good structure to express reasonable productivity. We recognised that as a result of ameli-orative treatments of the soil for the DS crop, detrimental as well as bene®cial effects to the subsequent rice crop may follow, e.g. paddy ®elds may become more per-meable and leaky; residual N from legumes may be bene®cial for rice. Therefore, it was important that, where possible, the changes in physical properties were monitored throughout the complete cropping cycle.
4.4. Selection of ®eld experimental sites
(mungbean) and common methodologies covering a range of sites with different soils and climates. Treat-ments and species which are speci®c to particular areas or soils are included at relevant sites.
Table 2 shows the textures of the sites in Indonesia at Ngale (deep Vertisol) and Jambegede (silty clay loam) in east Java, where soybean and peanuts are included alongside mungbean; and a site near Maros in south Sulawesi (silty clay). The sites in the Phi-lippines are the research station at San Ildefonso, Bulacan (Vertisol) and a farmer's ®eld near Manaoag, Pangasinan (silty clay). The sites cover a wide range of clay contents and clay mineralogies (Ringrose-Voase et al., 1995). The Ngale site has the greatest clay content with 740 g kgÿ1
total clay and 73% (on whole soil basis) swelling clay (smectite and vermiculite), giving it the greatest shrink/swell potential (0.19 linear shrinkage). The site at San Ildefonso has 410 g kgÿ1
total clay and 26% swelling clay and intermediate shrink/swell poten-tial (0.07 linear shrinkage). It also has a signi®cant sand content of 330 g kgÿ1
. The Maros and Manaoag sites have similar particle size distributions with 460 g kgÿ1 and 520 g kgÿ1
total clay, respectively. However, they have different mineralogies with 9% and 33% swelling clays, respectively, giving them different shrink/swell potentials (0.05 and 0.10 linear shrinkage, respectively). Detailed descriptions of these soil and climates are given by Schafer and Kirchhof (2000).
5. Experimental methodology
5.1. Field experiments in Indonesia and the Philippines
At each site in Indonesia and the Philippines, three ®eld experiments were conducted to investigate the effect of potentially useful management practices on
soil conditions and the resulting growth of DS crops. Since a complete factorial experiment involving all the factors of interest will result in a very large exper-iment which will be dif®cult to manage, treatments were selected that are relevant to the farmers interest and incorporated into three ®eld experiments that are of manageble size. Experiments were also designed to suit the local expertise and available facilities.
The ®rst two experiments were intended to reduce the need for large numbers of treatment combinations by separating treatments applied during the rice phase (E1) and treatments applied during the legume phase (E2). A third experiment (E3) measured the dynamics of changes in soil properties in the period immediately following ®eld drainage for rice harvest at four of the ®ve sites. The information gained from the latter will help extrapolate the results from the ®rst two experi-ments to other soils and climates.
5.1.1. Experiment E1
The objective was to investigate the effects of degree of puddling on soil physical conditions for the subsequent DS crop. Previous work has indicated that increased puddling may increase yields of the following DS crop on heavy clay soils but decrease yield on lighter textured soils (Trenggono and Willatt, 1988). If this is correct, puddling intensity can be used as an inexpensive and readily adoptable practice on suitable soils. The puddling intensity treatments imposed during soil preparation for the rice crop were
1. dry cultivation prior to submergence,
2. one wet ploughing and harrowing using draught animal power,
3. two wet ploughings and harrowings using draught animal power,
4. two wet cultivations with mechanised rototiller or hydrotiller.
Table 2
Description of the selected ®eld sites in Indonesia and the Philippines with the main relevant soil characteristics
Country Site Soil texture Clay (g kgÿ1) Swelling clay (%) Linear shrinkage
Indonesia Ngale, East Java Heavy clay 740 g kgÿ1 73 0.19
Jambegede, East Java Silty clay loam 450 g kgÿ1 15 n.a.a
Maros, Sulawesi Silty clay loam 460 g kgÿ1 9 0.05
Philippines San ildefonso, Bulacan Heavy clay 410 g kgÿ1 26 0.07
Manaoag, Pangasinan Silty clay 520 g kgÿ1 33 0.10
The treatments were combined with two tillage and sowing treatments (zero-till and dibbled, ZTD versus ploughing, broadcasting and harrowing Ð PBH) for the DS crops in the Philippines and two drainage treatments (without and with surface drainage) in Indonesia. PBH is the common farmer practice in the Philippines, and ZTD with surface drainage are common on heavy clay soils in Indonesia. In this project, ZTD without surface drainage was the com-mon treatment between the two countries. In both countries, the most common farmer practice of soil preparation for rice is two wet ploughings and harrow-ings using draught animals.
Treatments were replicated four times in a split-plot design, with puddling intensity as the main plots and tillage or drainage treatments as sub-plots. The experi-ment was carried out at each site over a period of 3 years, i.e. three rice-DS crop cycles.
5.1.2. Experiments E2
This experiment investigated the effects of DS crop management practices on soil properties and crop performance. To allow comparisons with experiment E1, soil preparation for the rice phase was done using two wet ploughings and harrowings (equivalent to treatment 2 in E1).
Treatments included combinations of amendments (none, A0; gypsum, AG; and organic matter mulch, AOM); cultivation (zero-till, C0 and rotovator, C1) and sowing delay after rice harvest (no delay, D0; one week delay, D1 and two weeks delay, D2) as follows:
T1 C0 A0 D1 No fertiliser (farmers' practice in Indonesia) T2 C0 A0 D1 Adequate fertilisers T3 C0 AG D1 Adequate fertilisers T4 C0 AOM D1 Adequate fertilisers T5 C0 A0 D0 Adequate fertilisers T6 C0 A0 D2 Adequate fertilisers T7 C1 A0 D1 Adequate fertilisers T8 C1 A0 D2 Adequate fertilisers T9 PBH A0 D1 No fertiliser (farmers'
practice in the Philippines)
The DS crop was sown by dibbling for all treat-ments except T9. Treattreat-ments were replicated four times in a randomised block design and the
experi-ment was conducted at each site over a period of three consecutive crop cycles.
Please note that
1. treatments T1 to T8 were used on all sites and treatment T9 only in the Philippines,
2. treatments T1 and T2 provide a measure of the nutritional limitations of the soil,
3. treatments T2 to T4 provide a measure of the effects of gypsum and organic mulch,
4. treatments T2 and T5 to T8 provide a measure of the effects of cultivation and sowing delay and their possible interactions.
It should be stressed that all treatments selected had already been shown as potentially useful for DS crops after rice in past trials, on speci®c soils and under a narrow range of climatic conditions. This project compared these potentially useful treatments on a wider range of soils and climatic conditions and attempts to quantify the agronomically relevant changes in the soil conditions resulting from these treatments, to enable extrapolation to other sets of environments.
5.1.3. Experiment E3
A third short-term ®eld experiment was conducted at one or two sites each season. This experiment monitors changes in soil mechanical and hydrological properties and soil structure with time as the soil dries after draining surface water prior to rice harvest. The information obtained for each soil will provide func-tional relationships required to interpret the conditions encountered at planting and during early seedling growth in the ®rst two experiments which involve only three sowing delays. These experiments were expected to last 2±4 weeks each.
This experiment was carried out on soils with standard puddling treatments (two ploughings and two harrowings). The following properties were mea-sured at pre-determined intervals: soil water content, soil strength (shear and penetrometer resistance), macropore structure development (using crack mea-surements and resin impregnated samples).
5.1.4. Selection of dry season crop species
legume in Indonesia. A second crop of soybean was included in east Java with soybean on the Vertisol (Ngale) and peanuts on the lighter textured soil (Jam-begede). Thus the crop rotations are as follows:
Ngale Rice±mungbean/soybean±
mungbean/soybean
Jambegede Rice±mungbean/peanut±
mungbean/peanut Maros, San
Ildefonso, Manaoag
Rice±mungbean
5.1.5. Measurements
This paper provides an overview of the measure-ments undertaken in this project. However, detailed descriptions of the methodologies will be found in the relevant sections of this special issue.
5.1.5.1. Initial characterisation of the site. The uniformity of each site was investigated using a 20± 25 m grid system. Morphological descriptions were made to determine any gradation in soil characteristics and to avoid any unrepresentative areas. Composite samples from sections of the field at different depths were analysed to provide a baseline data-set prior to imposition of treatments. These were
soil texture, bulk density, cation exchange capacity, cations, pH, electrical conductivity, soil organic carbon,
soil water characteristics,
plastic and liquid limits,
soil structural stability (wet sieving and dispersi-bility).
5.1.5.2. Measurements during the rice phase. The following were measured for some sites at the start, middle and end of the rice phase:
sinkage capacity,
infiltration rates,
dispersibilty of the soil,
yield of rice on all sites.
5.1.5.3. Measurements during the dry season crop phase. Soil measurements were made at the same time as plant measurements at the appropriate phenological
phases of the crop: emergence, vegetative, flowering, pod formation and maturity. Measurements included
soil physical measurements;
soil bulk density profiles,
soil strength profiles Ð penetrometers,
soil water content profiles and water use by the crop,
root distribution/root length densities (at flower-ing only),
plant measurements;
emergence as a measure of establishment,
plant density at harvest as a measure of survival,
plant biomass and its components,
yield and yield components,
climatic measurements(local weather station data);
rainfall,
evaporation (E pan),
temperature,
radiation.
5.1.6. Simulation of soil puddling and drying in the laboratory
Laboratory experiments were conducted at the Uni-versity of Queensland to measure the degree of dis-persion after the soil is subjected to a range of standard puddling treatments similar to those in the ®eld experiments (Kirchhof et al., 2000b). Degree of dis-persion was adopted as a measure of the degree of puddling and the decrease in structural stability. Since one major objective of puddling is to reduce percola-tion rate, soil hydraulic conductivities were measured for each puddling treatment and related to the degree of dispersion. The effects of repeated wetting and drying on soil structural development were also inves-tigated. Soil changes occurring during the rice-DS crop sequence were observed and quanti®ed in large lysimeters (approximately 1.2 m1 m1 m) in which rice was grown under puddled conditions followed by a DS crop. Soils used covered a similar range of textures to those used in the ®eld experiments. Details are described by Kirchhof and So (1994, 1996).
6. Summary
project in Indonesia and the Philippines. Details of the soils and climate of the ®ve experimental sites are described by Schafer and Kirchhof (2000). The results and implications of the E1 experiments are described by Kirchhof et al. (2000a,b) and those for the E2 experiments by Kirchhof et al. (2000a). Results on the changes in soil physical properties in experiment E3 is discussed by Ringrose-Voase et al. (2000) and crop establishment aspects are discussed by Rahmianna et al. (2000). The paper by Cabangon and Tuong (2000) was not part of the collaborative project, but is relevant as it deals with the in¯uence of cracks on soil preparation for rice and how shallow tillage can result in early sowing of rainfed lowland rice, an important factor during low rainfall seasons.
Acknowledgements
The project was funded by the Australian Center for International Agricultural Research and their contri-bution and support is gratefully acknowledged.
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