Crop establishment of legumes in rainfed lowland
rice-based cropping systems
A.A. Rahmianna
a,1, T. Adisarwanto
b, G. Kirchhof
a,2, H.B. So
a,* aSchool of Land and Food Sciences, The University of Queensland, St. Lucia, Brisbane, Qld 4072, AustraliabResearch Institute for Food Legumes and Tuber Crops, Kendalpayak, Malang 65101, Indonesia
Abstract
Poor crop establishment is one of the major limitations to the production of grain legumes after rice (Oryza sativaL.) in rainfed lowland rice-based cropping systems. The success of germination and emergence of mungbean (Vigna radiata(L.) Wilzek), soybean (Glycine max(L.) Merr) and peanut (Arachis hypogaeaL.) planted in zero tilled (ZT), zero tilled combined with mulch application (ZTM) and tilled soils (T) were investigated in a crop establishment trial as a function of sowing delay. Sowing delay was used as a surrogate for soil-water content. This experiment was conducted under a rain-shelter to ensure continuous and progressive drying conditions. A dibbling trial using the same legumes was conducted concurrently and subjected to the prevailing climatic conditions. Germination and emergence success rate of the traditional dibbling method was compared to dibbling incorporating depth control and seed cover. Both experiments were conducted towards the end of the 1994 rainy season in a Vertisol soil at Ngale and an Andosol soil at Jambegede, in East Java, Indonesia where the season gradually changes from wet to dry season. Mungbean emergence was 93±94% at Ngale and soybean emergence was 84±95% at Jambegede, both in the presence and absence of rain. Peanut emergence was low (50±69%) at both sites. In all three species at both sites, the percentage of seeds that failed to germinate was greater than seeds that failed to emerge, indicating that germination rather than emergence was limiting. Seed rot caused by fungal attack and poor imbibition associated with poor seed±soil contact (observed as intact seeds) were the main constraints for the success of germination of mungbean, soybean and peanut. The failure to emerge was mainly caused by seedling rot and the failure of hypocotyl and radicle to penetrate the hard soil, observed as a curling of the hypocotyl. Cultivation at Ngale on a Vertisol resulted in excessively cloddy soil, which in turn resulted in a signi®cant decrease in germination and emergence. The application of straw mulch had little effect on the emergence of legumes on this soil. The use of depth control and application of seed±soil cover did not have a signi®cant effect. Hence the traditional dibbling method where depth of planting ranged from 4 to 7 cm without seed cover was found to be appropriate for planting mungbean and soybean. Germination and emergence of peanut was improved with the application of soil cover and the dibbling stick had a spike added to the tip to assist the root to penetrate the hard compacted soil.
#2000 Elsevier Science B.V. All rights reserved.
Keywords:Germination; Crop establishment; Grain legumes; Rainfed lowland rice; Soil water potential; Dibbling Soil & Tillage Research 56 (2000) 67±82
*Corresponding author. Tel.:61-7-3365-2888; fax:61-7-3365-1188.
E-mail address: [email protected] (H.B. So).
1Present address: Research Institute for Food Legumes and Tuber Crops, Kendalpayak, Malang 65101, Indonesia. 2Present address: NSW Agriculture, PMB 944, Tamworth, NSW 2340, Australia.
1. Introduction
Poor crop establishment is generally accepted as one of the major limitations to the production of grain legumes after rice within a rainfed lowland rice-based cropping system (Greenland, 1985; Carangal, 1986; Fy®eld and Gregory, 1989; Fy®eld et al., 1990). Inferior seed quality, inadequate land preparation, fungal and pest attacks, excessive soil moisture, poor soil drainage, inappropriate method of planting and the massive structure of puddled soils have been listed as factors contributing to poor establishment (Hundal and Tomar, 1985; Sumarno and Adisarwanto, 1992; Cook et al., 1995; Garrity and Liboon, 1995).
Sowing after rice harvest is considered inappropri-ate when there is excessive wetness of the soil leading to possible waterlogging of the seed, particularly where the probability of rain is high during the latter part of the rainy season (Hundal and Tomar, 1985). Although generally accepted, this opinion has not been supported by scienti®c observations. On the other hand, delayed sowing of legumes after rice may encounter dry soils that are compact and hard (Cook et al., 1995; Kirchhof and So, 1995; So and Ringrose-Voase, 2000). Between these two conditions is an ideal window of opportunity, which should result in good crop establishment. The limits of this window of opportunity need to be clearly de®ned.
A practice frequently adopted by farmers is to cultivate the soil to reduce the effect of saturation and to break up the puddled soil. However, cultivation of this wet soil, in particular clay soils, may lead to other problems. The ®rst is excessive cloddiness if cultivation is carried out when the water content is too high, which result in excessive drying and poor seed± soil contact. Increasing turn around time (TAP) between rice harvest and sowing can increase the probability of seedling establishment failure and the likelihood of drought stress during the later growth stages of the legume crop.
An important factor affecting the success rate of crop establishment is the planting technique adopted by the farmer. The two most widely adopted techni-ques in Asian countries are broadcasting and dibbling the seeds either in rows or randomly and the planting technique adopted appears to be location speci®c (Syarifuddin, 1982; Sumarno et al., 1988; Benjasil et al., 1992; Chainuvati, 1992; Gypmantasiri, 1992;
Irawan and Lancon, 1992; Sarobol et al., 1992; Sumarno and Adisarwanto, 1992; Virakul, 1992; Sani-dad, 1996).
Seed broadcasting is associated with poor spatial distribution, poor seed and soil contact and excessive seed loss due to scavenging by birds and ants (Card-well, 1984; Pratley and Corbin, 1994). Dibbling, on the other hand, is time consuming, labour intensive and requires extra expenses for ash/compost/straw to ensure adequate seed cover (Benjasil et al., 1992; Gypmantasiri, 1992) and a delay in sowing may result in increasing soil strength due to soil drying (Garrity and Liboon, 1995).
Potentially, dibbling should result in better estab-lishment than the broadcast method, as seeds are less exposed and spatial distribution of plants is superior, but the variable success of dibbling by the farmer has been associated with a lack of consistency in the method adopted. An improved dibbling method should therefore increase establishment and crop yield.
Considerable research has been conducted in Indo-nesia to increase dry season grain legume yields (Sumarno, 1991). Most of the work has focused on irrigated crops, with less attention given to crops grown under rainfed conditions after rice.
The objectives of this work is to investigate (1) the effects of cultivation and sowing delay (as a surrogate for soil water status) on the establishment of mung-bean, peanut and soybean in puddled soils after rice, and (2) the factors affecting the success rate of estab-lishment from seeds sown with the traditional dibbling technique.
2. Materials and methods
The study consisted of two experiments: (1) crop establishment under continuous drying conditions and (2) dibbling trial. Both experiments were conducted on a Vertisol at Ngale and an Andosol at Jambegede. Details of these soils and climates are described by Schafer and Kirchhof (2000).
2.1. Crop establishment trial
To prevent interference from rain and to ensure continuous and progressive drying conditions, a
15 m6 m PVC rain-shelter was set up over a selected part of the rice ®elds at Ngale and Jambegede. These ®elds were adjacent to the E2 experiments of ACIAR Project 8938 (So and Ringrose-Voase, 2000) and were drained 1 week before harvest. The rain-shelter was set up immediately prior to harvest, so that soil-water contents at harvest were as close as possible to those expected outside the rain-shelter. Rice harvest occurred on 20 March 1994 at Ngale and on 23 April 1994 at Jambegede.
A split±split plot experiment was set up under the rain-shelter with treatments consisting of three culti-vationsthree periods of sowing delaythree legume speciesthree replicates resulting in a total of 81 plots. Delay of sowing was the main plot treatment with cultivation as subplot and species as sub-subplot. Delay in sowing represented different soil water con-ditions at sowing and were D0(immediately after rice harvest), D1(1 week delay) and D2(2 weeks delay). These were 3, 10 and 17 days after rice harvest at Ngale and 4, 11 and 18 days at Jambegede. Cultivation treatments consisted of zero tillage (ZT), zero tillage
with mulch (5 Mg haÿ1 dry rice straw) (ZTM) and
cultivation by a hand operated hoe to 12.5 cm depth (T). The three legume species used were mungbean cv. Walet, peanut cv. Kelinci and soybean cv. Wilis (all are Indonesian released cultivars).
Each subplot was 1.5 m1.5 m and seeds were
planted with a spatial arrangement of 15 cm15 cm
with two seeds per hole. Planting was conducted using a sharpened dibbling stick, which created a hole 5 cm deep and 4 cm wide in diameter at the top. Seeds were placed in the hole and covered by moist soil to the surface. Drainage ditches were provided around the perimeter of the area to avoid run-off water. Side covers of the shelter were left open, but closed during rainfall events to prevent rain from entering the shel-ter.
The number of seedlings emerged was recorded daily starting at 4 days after sowing (DAS) until 14 DAS. Cumulative germination was recorded daily. At 14 days, the difference between the number of seeds sown and the seedlings that emerged was determined. Seeds that failed to germinate (no radicle growth from the seed or seed is rotting) or the seedlings that failed to emerge (germinated seeds but not emerged) were recovered, counted and the cause of failure examined and recorded.
Measurement of soil physical properties was lim-ited to soil temperature and gravimetric soil-water content. Temperature at the soil surface at 2.5, 5 and 10 cm soil depths were measured using thermo-couples buried at two sites in the ®eld and at corre-sponding depths. During the ®rst 48 h, readings were made every hour to obtain the temperature diurnal cycle as well as the time when the maximum tem-perature occurred for each depth. On the following days, daily recordings were made at these times. Soil-water content was estimated by digging two 20 cm holes using a spade such that one face is nearly perpendicular. A slice of 1±2 cm thickness was taken from this face and water content determined gravime-trically at 1 cm increments for the ®rst 10 cm, and every 2.5 cm increment between 10 and 20 cm depth. At each sampling time the same soil face was cleared by removing a slice of approximately 3±4 cm before a fresh slice is taken and measurements repeated. Soil water potentials were derived using the soil water characteristic curves of undisturbed cores collected from the ®eld and determined in the laboratory using a series of pressure plates. Observa-tion was made at each planting time and on every second day thereafter.
Seed viability (potential for germination) was deter-mined in the laboratory using the standard germina-tion test (Internagermina-tional Seed Testing Associagermina-tion, 1985).
2.2. Dibbling trial
Due to rainfall at Ngale, planting was made 11 days after rice harvest (3 April 1994) when the soil was judged as ready for dibbling, while at Jambegede, it was started sooner at 7 days after rice harvest (1 May 1994).
A split plot design was used to set up the experi-ment. The treatments consisted of six types of dibbling techniquethree species®ve replicates resulting in a total of 90 plots. The six dibbling methods were made up of a combination of depth control, soil cover (in this experiment sand was used in place of soil) and the shape of dibbling hole. These were
1. normal dibbling, with no depth control and no soil cover (farmers practice);
2. normal dibbling, with no depth control, with soil cover;
3. normal dibbling, with depth control, with no soil cover;
4. normal dibbling, with depth control and soil cover;
5. similar to (4) plus spike (to assist roots to penetrate the soil); and
6. narrow slit, with depth control and soil cover; the narrow hole was expected to reduce evaporation and seed drying.
Following farmer's practice, normal dibbling was conducted using a sharpened dibbling stick, similar to that used for the crop establishment trial. A planting depth of 5 cm was used for the depth control treat-ments. In the non-depth control treatment, which represented the farmer's practice, seed placement depths varies from 4 to 7 cm and were mostly greater than 5 cm deep. Moist sand was used as seed cover in treatments 2, 4 and 6. The spike for treatment 5 was made with a wire 2 mm in diameter, and was applied at the centre of the seed hole prior to seed placement. The narrow slit (treatment 6) was produced by a small stick with a width of 1 cm at the top and the seed was planted at 5 cm depth.
The same batch of three legumes species: mung-bean cv. Walet, peanut cv. Kelinci and soybean cv.
Wilis were used in these experiments. Each plot
was 3 m2 m and seeds were planted with a
spatial arrangement of 15 cm15 cm with two seeds
per hole except for the narrow slit with one seed per hole.
Soil temperature was measured at 0, 2.5, 5 and 10 cm depths using thermocouples. Recording of temperature was made daily at the same time when the maximum temperature occurred for each depth, which was obtained from an hourly recording during the ®rst 48 h. Soil-water content was measured in 1 cm increments for the ®rst 10 cm, and every 2.5 cm from 10 to 20 cm using the gravimetric method. Similar times of sampling were used as for the crop establish-ment trial.
Observation of emergence was recorded daily start-ing at 4 DAS until 14 DAS. At 14 days, seeds that failed to germinate or seedlings that failed to emerge were recovered, counted and the causes of failure examined and recorded.
3. Results and discussion
3.1. Crop establishment under drying conditions
Tables 1 and 2 show the data on emergence (the appearance of seedlings at the soil surface), germina-tion (radicle has pierced the seed coat) and emergence failures for Jambegede and Ngale. The latter refers to germinated seeds that failed to emerge (i.e. germina-tion minus emergence). In almost all cases, the failure of seeds to germinate was greater than the failure to emerge. Table 3 shows the range of soil water poten-tials at 0, 4 and 14 DAS for the two sites, which were derived from soil-water contents. In general, the heavy clay soil at Ngale had the lowest soil water potentials than the lighter soils of Jambegede although visually the Ngale soil may appear wetter.
A comparison of the three legume species shows that the emergence of mungbean was very high at
Ngale (92.94.3%), followed by soybean (80.9
14.8%) and peanuts (64.123%). In the wetter soils
at Jambegede, soybean performed best (94.84.9%)
followed by mungbean (70.710.7%) and peanuts
(69.912.5%). These are percentages of viable seeds, which were tested in the laboratory using sandboxes and the results indicated that the potential germination of mungbean was 96%, soybean 81.7% and peanuts 88.7%.
So (1987) pointed out that for germination to be successful, seeds would have to take up water at a suf®ciently rapid rate and reach a critical water con-tent necessary for germination processes to be initiated before other factors (such as fungal or bac-teria infection and soil drying) prevented it from completing the process. On the basis of seed size, critical water contents and the associated rates of germination (Dart et al., 1992), it was expected that establishment would be best and most rapid in mung-bean followed by soymung-bean and peanuts, which was con®rmed at Ngale (Table 1). However, the sequence between mungbean and soybean was reversed in the wetter soil of Jambegede (Table 2) as a result of a high incidence of seed rot in mungbean. The average failure to germinate at Jambegede was 19.4% compared to an average of 5.5% at Ngale. At Jambegede, mungbean is a common crop and a compatible inoculum is likely to be present in suf®ciently large numbers in that soil to infect the seeds. The incidence of germination failure
Table 1
Emergence, failure of germination and failure of emergence (%) for mungbean, peanut and soybean at three delays of planting and three types of cultivation planted at Ngalea
Treatments Mungbean Peanut Soybean
Delay Cultivation % Emergence % Germination failure
% Emergence failure
% Emergence % Germination failure
% Emergence failure
% Emergence % Germination failure
% Emergence failure D0 ZT 96.1 (1.6) 2.8 (1.6) 1.1 (1.6) 82.8 (4.1) 3.3 (0) 13.9 (4.2) 94.4 (1.6) 0 (0) 5.6 (1.6)
ZTM 98.9 (1.6) 0 (0) 1.1 (1.6) 71.1 (8.7) 11.1 (5.1) 17.8 (8.2) 96.1 (0.8) 1.7 (2.4) 2.2 (1.6) T 91.1 (5.6) 5.5 (3.4) 3.3 (2.4) 58.3 (13.8) 25.6 (13) 16.1 (0.8) 90.6 (4.8) 3.3 (1.4) 6.1 (4.4) Average (D0) 95.4 2.8 1.8 70.7 13.3 15.9 93.7 1.7 4.6
D1 ZT 93.9 (2.1) 6.1 (2.1) 0 (0) 90.0 (4.9) 4.4 (2.1) 5.6 (4.2) 87.2 (4.4) 8.3 (2.4) 4.5 (2.1)
ZTM 94.5 (2.1) 5.6 (2.1) 0 (0) 87.8 (6.3) 5.4 (4.5) 6.9 (3.5) 80.0 (17.0) 8.9 (6.2) 11.1 (11) T 90.6 (6.3) 8.9 (6.7) 0.6 (0.8) 62.2 (9.1) 27.2 (1.6) 10.6 (7.5) 71.7 (14.3) 20.0 (12) 8.4 (3.6) Average (D1) 93.0 6.9 0.2 80.0 12.3 7.7 79.6 12.4 8.0
D2 ZT 94.4 (0.8) 5.0 (1.4) 0.6 (0.8) 54.5 (10.4) 30.0 (5.9) 15.5 (5.7) 82.8 (8.2) 6.1 (5.1) 11.1 (8.6)
ZTM 93.4 (2.4) 3.3 (1.4) 3.3 (2.7) 61.1 (11.3) 25.6 (11.6) 13.3 (3.6) 81.7 (2.7) 9.4 (4.4) 8.9 (2.8) T 82.8 (4.4) 12.8 (3.9) 4.4 (0.8) 9.4 (5.5) 73.9 (3.9) 16.7 (2.4) 44.4 (12.3) 40.6 (11) 15.0 (2.7) Average (D2) 90.2 7.0 2.8 41.7 43.2 15.2 69.6 18.7 11.7
Mean ZT 94.8 4.6 0.6 75.8 12.5 11.7 88.1 4.8 7.1
Mean ZTM 95.6 2.9 1.5 73.3 14.0 12.7 85.9 6.7 7.4
Mean T 88.2 9.0 2.7 43.3 42.2 14.5 68.9 21.3 9.8
Overall mean (species)
92.9 (4.3) 5.5 (3.5) 1.6 (1.5) 64.1 (23.0) 22.9 (20.7) 12.9 (4.1) 80.9 (14.8) 10.9 (11.8) 8.1 (3.7)
aDelay Ð D
0: immediately; D1: 1 week; D2: 2 weeks after rice harvest; cultivation Ð ZT: zero till; ZTM: zero till mulched; T: tilled with hand hoe. LSD 5%: species: 4.81,
delay of planting: 9.99; type of cultivation: 4.05. Values in brackets are standard errors.
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67±82
Table 2
Emergence, failure of germination and failure of emergence (%) for mungbean, peanut and soybean at three delays of planting and three types of cultivation planted at Jambegedea
Treatments Mungbean Peanut Soybean
Delay Cultivation % Emergence % Germination failure
% Emergence failure
% Emergence % Germination failure
% Emergence failure
% Emergence % Germination failure
% Emergence failure D0 ZT 78.9 (9.6) 16.6 (9.8) 4.4 (3.1) 82.2 (5.7) 7.8 (4.1) 10 (2.7) 94.4 (1.6) 3.3 (2.7) 2.2 (3.1)
ZTM 83.3 (4.7) 11.1 (6.9) 5.6 (4.2) 82.2 (4.2) 11.1 (3.1) 6.7 (4.7) 96.7 (2.7) 3.3 (2.7) 0 (0) T 76.7 (7.2) 16.6 (2.7) 6.6 (7.2) 72.3 (12.8) 15.5 (6.3) 12.2 (6.9) 91.1 (6.9) 4.4 (4.2) 4.4 (3.1) Average (D0) 79.6 14.8 5.5 78.9 11.5 9.6 94.1 3.7 2.2
D1 ZT 64.5 (4.2) 25.5 (1.6) 10.0 (5.4) 61.2 (18.5) 25.5 (13.7) 13.3 (8.2) 96.7 (4.7) 2.2 (3.1) 1.1 (1.6)
ZTM 66.3 (2.3) 32.2 (1.6) 1.1 (1.6) 65.6 (12.5) 26.6 (11.8) 7.8 (1.6) 94.4 (4.2) 1.1 (1.6) 4.4 (4.2) T 80.0 (9.4) 14.4 (6.8) 5.6 (4.2) 66.7 (7.2) 22.2 (6.9) 11.1 (4.1) 91.1 (3.1) 5.6 (3.1) 3.3 (0) Average (D1) 70.3 24.0 5.6 64.5 24.8 10.7 94.1 3.0 2.9
D2 ZT 62.2 (5.7) nab na 60.0 (7.2) na na 97.8 (1.6) na na
ZTM 67.8 (1.6) na na 72.2 (4.2) na na 98.9 (1.6) na na T 56.7 (5.4) na na 66.7 (7.2) na na 92.2 (6.3) na na
Average (D2) 62.2 na na 66.3 na na 96.3 na na
Mean ZT 68.5 21.1 7.2 67.8 16.6 11.7 96.3 2.81 1.7 Mean ZTM 72.5 21.7 3.4 73.3 18.9 7.3 96.7 2.2 2.2
Mean T 71.4 15.5 6.1 68.6 18.9 11.7 91.5 5.0 3.9
Overall mean (species)
70.7 (10.7) 19.4c(9.2) 5.5c(2.7) 69.9 (12.5) 18.1c(11.2) 10.2c(2.3) 94.8 (4.9) 3.3c(3.3) 2.6c(1.6)
aDelay Ð D
0: immediately; D1: 1 week; D2: 2 weeks after rice harvest; cultivation Ð ZT: zero till; ZTM: zero till mulched; T: tilled with hand hoe. LSD 5%: species: 5.01;
delay of planting: 7.49; type of cultivation: 4.35. Values in brackets are standard errors.
bNot available.
cAveraged from two treatments (D 0and D1).
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due to seed rot was 10.9% for soybean at Ngale compared to 3.3% at Jambegede, most probably asso-ciated with the cropping history of the region and the presence of compatible inoculum. Soybean is the common legume crop after rice at Ngale.
Cultivation of the Vertisol 1 week after rice harvest resulted in a very cloody seedbed which contributed to the failure of germination as a result of poor seed±soil contact and reduced imbibition. This is observed as intact seeds. The high incidence of germination failure in peanuts was not associated with fungal infection, but rather with poor seed±soil contact as a signi®cant proportion of seeds remained intact (18.1% at Jam-begede and 22.9% at Ngale). In addition, a signi®cant proportion of germinated peanut seeds failed to emerge (10±13%), probably as a consequence of the high soil strength at the time of emergence. Even though germination of the three legumes was rapid, peanut emergence was considerably slower than the other legumes (the emergence for mungbean and soybean started at 3±4 DAS compared to 6±7 DAS for peanut).
In the absence of rain, an increasing period of delay in sowing legumes after rice harvest generally reduced the emergence and establishment of legumes at both Jambegede and Ngale except for mungbean at Ngale and soybean at Jambegede. Increasing the period of sowing delay lead to low water potentials (Table 3). Therefore, the rate of water uptake by the seed and hence rate of germination was reduced and the
oppor-tunity for fungal infection was increased. This is consistent with the ®nding of Bewley and Black (1985), who reported that germination is not affected by soil water potential until it reaches fairly low values provided biotic factors are controlled. Therefore, if fungal infection is not likely to occur, 1 or 2 weeks sowing delay should not affect germination signi®-cantly, which is the case with mungbean at Ngale and soybean at Jambegede. Thus, it appeared that under the condition of this experiment, the reduction in establishment with a delay in sowing was strongly associated with increased opportunity for fungal infec-tion due to the reduced rate of germinainfec-tion. Therefore in such cases, the use of appropriate fungicides for seed treatment may alleviate some or all of the pro-blems.
It should be noted that this experiment was carried out in East Java where the transition from the rainy season to the dry season is gradual and drying con-ditions during the experiment was relatively mild. Hence soil strength did not appear to be limiting. The effect of increasing sowing delay on seed germi-nation and emergence will most likely be greater if the rate of soil drying is increased and soil strength becomes an important limiting factor, e.g. in drier areas with an abrupt end to the rainy season.
The effect of cultivation and mulch on legume establishment were not consistent between the two sites. Cultivation of the top 12.5 cm (treatment T) resulted in greater rate of soil drying (Fig. 1) and
Table 3
The range of soil water potentials (MPa) at 5 cm depth in the various combination of sowing delay and type of cultivation at Jambegede and Ngale for the period of 0±4 days and 14 days after sowing (DAS)
Treatments Water potential (MPa) after sowing
Sowing delay Type of cultivation Jambegede Ngale
0 DAS 4 DAS 14 DAS 1 DAS 4 DAS 14 DAS D0 ZT 0 ÿ0.004 ÿ0.025 ÿ0.018 ÿ0.022 ÿ0.056
ZTM 0 0 ÿ0.036 ÿ0.05 ÿ0.045 ÿ0.079 T 0 ÿ0.016 ÿ0.56 ÿ0.036 ÿ0.028 ÿ0.112 D1 ZT ÿ0.02 ÿ0.035 ÿ0.036 ÿ0.045 ÿ0.04 ÿ0.071
ZTM ÿ0.016 ÿ0.014 ÿ0.036 ÿ0.045 ÿ0.063 ÿ0.20 T ÿ0.11 ÿ0.18 ÿ0.71 ÿ0.071 ÿ0.159 ÿ0.20 D2 ZT ÿ0.025 ÿ0.045 ÿ0.14 ÿ0.056 ÿ0.063 ÿ0.28
ZTM ÿ0.036 ÿ0.04 ÿ0.089 ÿ0.079 ÿ0.079 ÿ0.28 T ÿ0.56 ÿ0.79 ÿ6.31 ÿ0.112 ÿ0.282 ÿ1.12
Fig. 1. Soil-water content (g/g) at various times after harvest in the top of 12 cm soil depth in zero tillage (&), zero tillage and mulch (5) and tilled (*) in the Andosol soils at Jambegede and Vertisol soils at Ngale. The solid lines indicate the value of LSD with 95% level of con®dence.
signi®cantly lower soil potentials (Table 3). This effect was greater in the lighter textured Andosol at Jambe-gede (Table 3). This soil with a plant available water capacity (PAWC) of 0.14 m3/m3, was higher in water potentials than the Vertisol at Ngale immediately after rice harvest, but after 17 days its water potential was less than the Vertisol, which can hold a greater amount of water (PAWC of 0.32 m3/m3).
The use of 5 Mg haÿ1of rice straw as soil mulch was intended to reduce water loss from surface eva-poration, however, the data show that the effect on soil-water content in the seed placement zone was insigni®cant (Fig. 1 and Table 3) and very little effect on seedling emergence.
Cultivation tended to produce a cloddy surface soil that increased the rate of soil drying, and result in reduced germination and emergence, particularly on the Vertisol at Ngale. The high rate of failure to germinate in this soil under the tillage (T) treatment (Table 1) is largely attributed to poor seed±soil con-tact. The cloddy nature may also allow deeper pene-tration of light and the premature breaking of the hypocotyl before emergence is completed. Cultivation had very little effect on the germination or emergence of any of the legumes in the Andosol at Jambegede despite the drier conditions (Table 3), probably because this soil displayed a ®ner surface tilth and hence better seed±soil contact.
3.2. Crop establishment in the dibbling trial
Data on emergence, germination and emergence failure for mungbean, soybean and peanut planted at Ngale and Jambegede are presented in Tables 4 and 5. The percentage of peanut and soybean seeds that emerged was clearly smaller than the percentage of seeds that germinated. Hence it appeared that the main limitation to establishment of peanut and soy-bean was the strength of the dry surface soil or sand. The number of mungbean seedlings that failed to emerge was low, whereas the number that failed to germinate was high for all dibbling types at Jambe-gede. Table 6 shows the range of soil water potentials at 0, 4 and 14 days after sowing for the two sites. The soil water potentials in the Andosol at sowing were slightly higher compared to the Vertisol at Ngale, although there was more rain at Ngale (76 mm) than Jambegede (49 mm) during the ®rst 14 days.
Soil-water contents did not appear to be limiting seedling establishment.
In the dibbling trial, the relative performance of the three species in the presence of rainfall (dibbling trial) was similar to that in the absence of rainfall
(rain-shelter). Mungbean performed best (943.8%),
fol-lowed by peanut (69.113.4%) and soybean
(52.518.2%) at Ngale. At higher water potentials
at Jambegede, soybean performed best (84.215.2%),
followed by mungbean (72.47.9%) and peanut
(50.513.3%). Compared to the emergence at Ngale,
mungbean emergence at Jambegede was lower by 21.6%. For soybean, however, there was a signi®cant increase (32%). It showed that germination and emer-gence of mungbean are susceptible to wet conditions while soybean was better able to cope with wet conditions.
Low emergence of mungbean at Jambegede was associated with high germination failure caused by a high incidence of seed rot (average 20.3%). The combination of wet soil and warm conditions (soil
temperature at 5 cm depth averaged 318C at
Jambe-gede and 338C at Ngale) promoted fungal growth. The low emergence of soybean at Ngale was mainly caused by the high number of seedlings (average 35.2%) unable to emerge (curling growth). This was caused by the failure of radicle to penetrate the hard soil.
Peanut performed better at Ngale than Jambegede. There was higher germination failure on the wetter soil at Jambegede. Seed rot and incomplete imbibition were observed as the main causes for this failure. At both sites, low emergence was caused by the failure of the hypocotyl to emerge through the soil surface, with an average of 27.6% at Ngale and 34.5% at Jambegede.
Table 4
Emergence, failure of germination and failure of emergence (%) for mungbean, peanut and soybean in the six dibbling techniques planted at Ngalea
Dibbling technique
Mungbean Peanut Soybean
% Emergence % Germination failure
% Emergence failure
% Emergence % Germination failure
% Emergence failure
% Emergence % Germination failure
% Emergence failure T1 95.4 (2.1) 1.1 (0.4) 3.5 (2.1) 55.4 (13.8) 5.2 (4.7) 39.4 (7.5) 65.0 (4.6) 6.7 (0.8) 28.3 (5.4)
T2 95.4 (1.4) 4.6 (1.3) 0 (0) 77.8 (5.0) 1.2 (1.9) 21.0 (4.7) 62.6 (9.0) 8.2 (4.0) 29.2 (4.0)
T3 95.2 (4.6) 4.8 (1.7) 0 (0) 52.2 (6.5) 5.9 (2.0) 41.9 (2.1) 56.8 (15.8) 7.3 (1.6) 35.9 (16.2)
T4 93.4 (4.6) 6.6 (4.0) 0 (0) 78.2 (2.4) 0.5 (0.4) 21.3 (3.2) 58.6 (12.4) 13.0 (1.1) 28.4 (14.9)
T5 96.6 (1.0) 3.4 (1.0) 0 (0) 74.4 (5.1) 0.7 (0.7) 24.9 (1.7) 52.2 (5.0) 12.4 (4.6) 35.4 (4.8)
T6 88.2 (3.1) 3.0 (2.6) 8.8 (1.9) 76.6 (8.6) 6.5 (5.9) 16.9 (7.4) 19.8 (6.9) 26.3 (8.6) 53.9 (8.1)
Average 94.0 (3.8) 3.9 (2.6) 2.0 (3.5) 69.1 (13.4) 3.3 (4.0) 27.6 (10.7) 52.5 (18.2) 12.3 (7.9) 35.2 (13.0)
aDibbling technique Ð T
1: farmers practise; T2: soil cover; T3: depth control; T4: soil cover and depth control; T5: as T4plus spike; T6: narrow slit. LSD 5%: species: 6.69;
dibbling technique: 11.29. Values in brackets are standard errors.
76
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Table 5
Emergence, failure of germination and failure of emergence (%) for mungbean, peanut and soybean in the six dibbling techniques planted at Jambegedea
Dibbling technique
Mungbean Peanut Soybean
% Emergence % Germination failure
% Emergence failure
% Emergence % Germination failure
% Emergence failure
% Emergence % Germination failure
% Emergence failure T1 71.2 (8.5) 22.4 (5.6) 6.4 (2.8) 44.2 (7.3) 19.7 (8.0) 35.4 (9.1) 92.6 (3.8) 3.3 (2.6) 4.1 (2.8)
T2 72.8 (7.9) 20.4 (5.4) 6.8 (3.6) 46.6 (9.7) 10.0 (2.8) 43.4 (13.2) 95.8 (2.7) 1.1 (1.1) 3.1 (1.8)
T3 69.2 (12.4) 25.7 (10.8) 5.1 (1.0) 41.2 (14.5) 28.7 (9.2) 34.1 (16.1) 84.6 (5.4) 5.7 (2.6) 9.7 (5.6)
T4 74.8 (5.2) 18.0 (4.2) 7.2 (3.8) 45.8 (9.5) 8.5 (3.2) 43.1 (9.9) 91.2 (3.3) 4.4 (2.1) 4.4 (1.6)
T5 75.2 (4.5) 16.9 (4.4) 7.9 (2.1) 60.8 (7.5) 14.9 (5.9) 24.3 (3.1) 87.8 (4.3) 2.4 (1.8) 9.8 (3.4)
T6 71.0 (3.6) 18.2 (3.7) 10.8 (2.8) 64.6 (9.5) 10.5 (3.4) 26.9 (12.9) 53.2 (8.5) 5.7 (3.4) 41.1 (9.3)
Average 72.4 (7.9) 20.3 (6.4) 7.3 (3.1) 50.5 (13.3) 15.4 (9.0) 34.5 (12.8) 84.2 (15.2) 3.8 (2.8) 12.0 (14.2)
aDibbling technique Ð T
1: farmers practise; T2: soil cover; T3: depth control; T4: soil cover and depth control; T5: as T4plus spike; T6: narrow slit. LSD 5%: species: 7.65;
dibbling technique: 10.22. Values in brackets are standard errors.
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67±82
causes of the low soybean emergence at Ngale were high germination failure caused by seed rot (26.3%), and high emergence failure at both sides caused by seedling rot and the failure of the seedlings to emerge through the soil above the seed (Tables 4 and 5).
The response of peanut emergence to dibbling techniques was different from soybean (Tables 4 and 5). Soil cover signi®cantly increased the emer-gence (24.2% on average) at Ngale. High evaporation from the large exposed surface of the seed reduced the rate of imbibition resulting in failure of seeds to germinate. At Jambegede, the size of the seed hole played an important role in governing the success of
emergence. Narrow seed holes (T6) signi®cantly
increased emergence (approximately 20%) compared with normal/larger holes, probably associated with better soil±seed contact.
4. General discussion
The aim of the trial under the rain-shelter was to determine the effects and interactions of sowing time and cultivation on germination and emergence of legumes. Controlled dibbling was used in this experi-ment similar to treatexperi-ment T4in the dibbling trial. The dibbling trial was intended to examine the effects of depth of sowing and soil cover on the success of germination and emergence of legumes, subject to the normal vagaries of the prevailing climatic condi-tions, in particular rainfall. During the experiment, 49 and 76 mm of rain fell during the trial at Jambegede and Ngale, respectively. Sowing in the latter
experi-ment was conducted with a delay time similar to D1in the ®rst experiment.
The result in Tables 1, 2, 4 and 5 showed germina-tion and emergence of the three legumes were con-sistent across the two trials. Rain did not affect the results in these experiments. For all three legumes and on both soils, highest germination and emergence were obtained when sowing delay was smallest (3± 4 days) and longer delays will tend to reduce germina-tion and emergence. These observagermina-tions dispel the general belief that sowing legumes too early after rice harvest will result in crop establishment failures due to waterlogging, particularly when sowing is followed by rain. However, it is possible that a prolonged period rain or an excessively heavy rainfall immediately fol-lowing sowing may result water logging of the seeds and subsequent germination failure. This happened repeatedly at San Ildefonso where typhoons occur reg-ularly and the trials were resown after each typhoon.
4.1. The response of seeds to environmental factors in the laboratory
If the data reported in this paper is to be extra-polated to other soil and climatic conditions, a gen-eralised model of crop establishment needs to be developed from these data. Assuming an absence of biotic constraints and no limitation in seed, soil con-tact, the response of seeds to water potentials and temperature can be measured in the laboratory, which can be used as the basis for the development of such a model. The relationship between these two factors and germination of the three Indonesian legume cultivars
Table 6
The range of soil water potentials (MPa) at 5 cm depth in the various dibbling types at Jambegede and Ngale for the period of 0±4 days and 14 days after sowing (DAS)
Treatments Water potential (MPa) after sowing
Jambegede Ngale
0 DAS 4 DAS 14 DAS 0 DAS 4 DAS 14 DAS T1 ÿ0.011 ÿ0.025 ÿ0.028 ÿ0.04 ÿ0.036 ÿ0.056
T2 ÿ0.001 ÿ0.019 ÿ0.035 ÿ0.036 ÿ0.04 ÿ0.056
T3 ÿ0.005 ÿ0.016 ÿ0.025 ÿ0.026 ÿ0.036 ÿ0.056
T4 ÿ0.011 ÿ0.028 ÿ0.025 ÿ0.036 ÿ0.036 ÿ0.063
T5 0 ÿ0.013 ÿ0.011 ÿ0.036 ÿ0.028 ÿ0.045
T6 0 ÿ0.019 ÿ0.026 ÿ0.028 ÿ0.036 ÿ0.056
(Y), can be expressed by the following regression
where pF is the logarithm of the positive value of soil water potential in cm, andTis temperature in8C. A similar relationship was also obtained with Australian cultivars (Rahmianna, 1993).
Soil temperatures in the seed placement zone during the ®eld experiment were relatively constant at around 28±338C for the top 20 cm. In Fig. 2, the laboratory-derived functions were plotted for the temperatures 28 and 338C representing predicted germination rates in response to temperature and water potential of the soil immediately around the seed. Where predicted germi-nation was greater than 100% as a result of the quadratic nature of the equations, germination was assumed as 100%. The symbols in Fig. 2 represent germination data collected in the ®eld. These were plotted against the water potential derived from water contents measured at seed placement depth. The agreement between measured and predicted germina-tion is good, with some excepgermina-tions, e.g. at the lower pF values (i.e. higher soil water potentials). Mungbean germination in both the establishment and dibbling trials at Jambegede (open symbols) between pF 0 and 2.3 were signi®cantly lower than predicted. This reduction was mainly caused by the high incidence of seed rot. As mungbean is a common legume crop grown after rice in the region and at the experimental site, it is reasonable to assume that suf®cient inocu-lums are present in the soil that can infect mungbean seeds. Intact seeds that failed to adequately imbibe, also contributed to the failure of germination,
parti-cularly when mungbean was planted with no seed cover (T1and T3) or when planted late (D1) and in the absence of rain. Predicted mungbean germination for all treatments at Ngale agrees well with the measured germination since the incidence of seed rot was very low. In contrast, predicted soybean germination at Jam-begede agrees well with measured germination, but on the Vertisol at Ngale, lower germination was caused by seed rot when soybean was planted later than 1 week after rice harvest. Soybean is the preferred legume after rice in this region with probably a high population of inoculum compatible with soybean. Late planting in tilled soils at Ngale resulted in a high proportion of intact seeds associated with imbibition from poor seed±soil contact. Compared to the normal cone-shaped dibbling hole, soybean sown in narrow
holes (T6) showed reduced germination and a high
incidence of seed rot, presumably associated with higher humidity from this treatment.
Peanut germination in both trials at Jambegede and Ngale were lower than the predicted germination associated with a large incidence of either germination failure or failure of seedlings to emerge. The latter appears to be due to an inability of seedling roots to establish into the hard soil that showed as root curling around the seed. Germination is slower in peanut than mungbean or soybean. Tillage of the Vertisol at Ngale created a rough seedbed and hence gave poor seed± soil contact that increased germination failure in the establishment trial (22.9%). However, 76 mm of rain reduced germination failure signi®cantly in the dib-bling trial (3.3%). Germination was high when peanut was planted in zero tilled and wet soil (D0and D1) at Ngale. In the lighter soil at Jambegede, germination failure was generally associated with high numbers of intact seed. Poor seed and soil contact was also a problem when peanut was planted without any seed cover (T1and T3) in the dibbling trial and 46 mm of rain at 10 days after planting appears to be too late to affect germination and establishment of peanuts in this soil. Poor seed±soil contact is probably a result of the large seed size.
the range of pF 0±2.8 when predicted germination should be around 100%. Therefore, planting legumes up to 7 cm under the conditions at Jambegede and Ngale should not be limiting. Observed reductions in actual germination of all species may be associated with reduced seed±soil contact, high soil strength,
biological constraint (fungal or bacterial infections) and seed vigour. These reductions can be incorporated into a simple model where they may be expressed as a ratio relative to germination with no constraints. Further work is required to quantify the effect of such constraints.
Fig. 2. Relationship between germination and water potential for three different legumes from the establishment (ET) and dibbling trials (DT) at Jambegede (open symbols) and Ngale (closed symbols). Observed germination were derived as the sum of % emergence and % failure to emerge in Tables 1, 2, 4 and 5.
5. Conclusions
In conclusion, this work has shown that:
Generally the effect of mulch on legume
germina-tion and establishment in the humid region of East Java is negligible.
Tillage of the surface soil has no effect on germina-tion and emergence of legumes in the Andosol at Jambegede, but in the Vertisol at Ngale tillage reduced germination and emergence, most prob-ably associated with the cloddy nature of the soil after tillage.
Sowing legumes immediately after lowland rice
harvest did not result in waterlogging of the seeds, even when it is followed by rainfall. On the contrary it gave the best rate of germination and establishment. Increasing the delay period between rice harvest and sowing results in drying of the soil, particularly after tillage. By itself, the degree of drying does not affect germination signi-ficantly but increased the susceptibility of the seed to fungal infection resulting in reduced total germination.
Germination of mungbean at Jambegede and
soy-bean at Ngale were reduced mainly by seed rot, most probably associated with the presence of compatible inoculum population associated with its previous cropping history. Germination of pea-nut was limited at both sites largely due to poor seed±soil contact and an inability of the root to penetrate the soil.
The farmer's practice of dibbling without depth
control (range 4±7 cm) and no seed cover are adequate for mungbean and soybean after lowland rice in East Java, however, peanut would benefit from improved dibbling technique such as the use of cover and a spike to assist the root in penetrating the puddled soil.
Acknowledgements
The senior author was funded by the Australian Agency for International Development (AusAID) postgraduate award and the research was funded by the Australian Centre for International Agricultural Research (ACIAR).
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