Relay seeding forage species in rice systems in Bhutan

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1 Tropical Grasslands (200) Volume 35, Relay seeding forage species in rice systems in Bhutan W. RODER, P. WANGCHUK 2, S. THSERING 3 AND T. GYELTSEN 4 RNR-Research Center Jakar, 2 RNR-Sub Station Bhur, 3 RNR-Sub Center Tingtingbi, and 4 RNR-Research Center Yusipang, Bhutan Abstract Integrating forage legumes into existing rice production systems in the Himalayas could contribute towards sustaining soil fertility and diversifying production. Technologies need to be refined, especially species selection and establishment, before they can be recommended to farmers. From various studies were carried out across a range of conditions (elevation m) to evaluate effects of species, establishment method and planting date. The species used were: Aeschynomene americana, Astragalus sinicus, Chamaecrista rotundifolia, Crotalaria juncea, Desmodium intortum, Lablab purpureus, Melilotus officinalis, Trifolium alexandrinum, T. incarnatum, T. pratense, T. rueppellianum, Vicia villosa, Vigna parkeri, Lolium multiflorum, Avena sativa and Secale cereale. Broadcast-seeding was tested at 40 days before, 20 days before and after rice harvest. Water management during the rice crop and available moisture after rice harvest are the main factors influencing the feasibility of relay seeding and the potential for fodder production. Except for systems where fields were drained immediately before rice harvest, establishment by relay seeding was possible for all species tested. The most promising legumes were Chamaecrista rotundifolia for elevations below 000 m and Vicia villosa for higher elevations. Earlier planting dates resulted in higher dry matter yields Correspondence: W. Roder, RNR-RC Jakar, Bumthang, Bhutan. wrjakar@druknet.net.bt but had no consistent effect on establishment success. Introduction Nitrogen availability frequently limits rice yields in Himalayan rice systems. Legumes used for green manure and/or fodder may provide opportunities to minimise chemical N-inputs, and increase rice yield and livestock production (Peoples et al. 995). The success of such technologies will depend on the identification of suitable legume species and the availability of appropriate technologies for seed production and establishment. Extensive studies have been carried out in tropical rice production systems on the use of legumes as a source of biologically fixed N (Ladha and Garrity 994; Becker et al. 995). Yet, with the exception of the well documented traditional system using Chinese milkvetch (Astragalus sinicus) (Chen 988) and work carried out in north-eastern Thailand in the 970s (Shelton 980a; 980b), little information is available on the potential of legumes in rice production systems in subtropical environments in general and for fodder legumes in particular. Legume-based pastures are an important component in temperate rice rotation systems in south-eastern Australia (Latimare 994). Activities in subtropical regions are, however, constrained by the limited choice of species available and technologies for their establishment. Cost of establishment, establishment success and early production of seeded fodder species all depend directly on the method of establishment. Suitable establishment methods have been developed for buckwheat and maize systems prevailing in Bhutan (Dukpa et al. 999), but little experience is available for fodder and/or green manure legume establishment in rice systems. Sowing forage species with a companion crop is a widely used practice in temperate as well as tropical conditions (Heath et al. 973; Humphreys

2 236 W. Roder, P. Wangchuk, S. Thsering and T. Gyeltsen 978). This method has several advantages, including: greater farmer acceptability, income from the companion crop, weed suppression, protection against adverse conditions, and an increase in forage quality and quantity after crop harvest (Thomas and Bennett 975; Humphreys 978). However, there is little published information on the use of this method in lowland rice. Various investigations have been published on studies carried out in upland rice systems (Shelton and Humphreys 972; Roder and Maniphone 995). Research on establishment methods for pre-rice green manure legume species was reviewed by Pradhan and Garrity (994). With the objective to develop rice-fodder systems that enhance soil fertility and/or increase winter fodder production, investigations during evaluated: ) the feasibility of relay seeding selected fodder species in rice; and 2) the effect of planting date. Materials and methods On-station and on-farm studies were carried out across a range of conditions at locations ranging from m elevation (Table ). All sites experience a typical monsoon climate with rainfall peaks during July and August and extended dry periods from October April (Table 2). Rice planting and weeding were carried out as per customary practices. Fodder species were broadcast-seeded at dates and rates indicated, and no attempt was made to cover the seeds in any of the experiments. Trifolium and Melilotus spp. were inoculated with appropriate inoculants prior to seeding. Earlier investigations have shown that inoculation was not required for the other species used (Roder et al. 998). Table. Locations and their characteristics. Location Elevation (m) Soil Water management Bhur station 300 Sandy Drained 50 d before harvest Goling 800 Loam Drained 20 d before harvest Mebari 820 Sandy Drained at grainfilling stage Paro 2500 Sandy loam Drained 7 0 d before harvest Although the studies were conducted over a period of 3 years, experiments of the same design were not repeated. Experimental designs were modified based on the results from the previous year and the requirements of a particular environment. Table 2. Rainfall measured at Bhur station. Month Mean for (mm) Oct Nov Dec Jan 3 < 5 9 Feb 7 4 < 23 Total On-station studies (Bhur) The Bhur station is representative of conditions in the plain areas along the border of Bhutan. Soils are characterised by high sand content, low buffering capacity and low organic matter. From , 3 different studies were conducted (Table 3). Table 3. Details of individual studies. Location Season Design Replicates Plot size (m 2 ) S = species, PD = planting date. Factors tested Bhur RCBD 3 4 S Bhur Split-plot 3 6 S, PD Bhur Split-plot 3 8 S, PD Goling RCBD 3 6 S Mebari RCBD 3 8 S Bhur : Rice seedlings were transplanted in July at a spacing of 5 40 cm. The legumes African clover (Trifolium rueppellianum), crimson clover (T. incarnatum), red clover (T. pratense), berseem (T. alexandrinum), hairy vetch (Vicia villosa), sweet clover (Melilotus officinalis), lablab (Lablab purpureus), jointvetch (Aeschynomene americana), cassia (Chamaecrista rotundifolia) and Vigna parkeri were broadcast-seeded on November 9, 996, at the rate of 20, 30, 30, 30, 60, 30, 80, 30, 30 and 30 kg/ha, respectively. Legume plants present were counted in 4 randomly placed quadrats of 0.25 m 2 per plot on December 8, immediately after rice harvest. Ground cover of sown species was rated again in February 997 using a scale of 6 ( = legume absent; 2 = cover <5 %; 3 = cover 5 0%; 4 = cover 20%; 5 = cover 2 40%; 6 = cover

3 Relay seeding forages in rice systems 237 >40%). Fresh biomass was measured from 2 randomly placed quadrats of m 2 per plot for jointvetch and cassia on July 4, 997, before field preparation for rice cultivation. Bhur 2 and 3: and Rice seedlings of the traditional variety Bhoke were transplanted in July 997 and 998 at a spacing of cm. Seeding rates used were 20, 20, 30, 20, 60, 80, 20, 20 and 80 kg/ha for Aeschynomene americana, berseem, Crotalaria juncea, sweet clover, hairy vetch, lablab, greenleaf desmodium (Desmodium intortum), cassia and oats (Avena sativa), respectively. The first 4 species were included in only and oats was used only in All species were broadcast-seeded at: ) 40 days before rice harvest (November 7, 997); 2) 20 days before rice harvest (November 27, 997 and November 4, 998); and 3) after rice harvest (December 22, 997 and November 28, 998). Legume density and cover were recorded from 4 frames of 0.6m 2 placed randomly in each plot at 30 and 60 days after rice harvest. All plots were irrigated on January 6, February 9 and March 9, 998, and January, February 5 and April 26, 999. Fresh biomass yield was measured from the whole plots on May 3, 998 and May 25, 999 before field preparation for rice cultivation. On-farm studies Goling (Zhemgang): Rice seedlings were transplanted by the farmer following the traditional method. Planting density was approximately hills/m 2. Seed of berseem, crimson clover, hairy vetch, sweet clover, Chinese milkvetch and Italian rye grass (Lolium multiflorum) was broadcast-seeded in October, at rates of 25, 25, 80, 25, 5 and 20 kg/ha approximately 40 days before rice harvest. At the time of seeding, water depth was approximately 0 cm. Germination was rated 0 days after rice harvest. No further observations were possible due to free grazing by cattle. Mebari (Chhukha): Rice was planted on June 25. Seed of berseem, crimson clover, hairy vetch, sweet clover, Chinese milkvetch, Italian rye grass, oats and rye (Secale cereale) was broadcast-seeded at rates of 25, 25, 80, 25, 5, 20, 80 and 88 kg/ha approximately 30 days before rice harvest (October, 997). At the time of rice harvest, 300 kg/ha single superphosphate and 30 kg/ha urea were applied. The trial was irrigated at intervals of days. Fresh yield was measured from whole plots on April 24 and May 6. No statistical analysis was made because data were missing from many plots. Paro: The experiment had to be terminated because the water was drained only 7 0 days before rice harvest. Results Rainfall during October February was close to average for , but below average for and substantially below average for (Table 2). Soil moisture may have been a major limiting factor for legume survival and biomass production. The effects of uncharacteristically low rainfall for were, however, minimised by providing irrigation during the onstation studies. On-station studies Bhur : Soil moisture was low after the seed was broadcast. Observations 30 days after broadcasting seed showed that plant densities were satisfactory for African clover, crimson clover, hairy vetch and sweet clover (Table 4). Due to moisture stress, most germinated plants disappeared during December and January, and on February 25, only cassia showed an appreciable contribution to the ground cover. A few plants of African clover, hairy vetch, lablab and Vigna parkeri were present but their contribution to the biomass cover was negligible. All other species had disappeared. Table 4. Density and cover of legume species planted in a rice crop (Bhur station, ). Species Density (Dec 8) (plants/m 2 ) Cover (Feb 25) African clover 25.7 Crimson clover 3 Red clover 0 Berseem 4 Hairy vetch Sweet clover 28 Lablab 3 2 Jointvetch 7 Cassia 4 4 Vigna parkeri 7.7 CV % LSD (P < 0.05) Rating scale of 6 ( = legume absent; 2 = cover <5 %;

4 238 W. Roder, P. Wangchuk, S. Thsering and T. Gyeltsen 3 = cover 5 0%; 4 = cover 20%; 5 = cover 2 40%; 6 = cover >40%). Cassia continued to perform well throughout the dry season. Jointvetch seed germinated when moisture conditions improved in April. Both cassia and jointvetch produced appreciable quantities of biomass. Fresh biomass quantities measured at the time of field preparation for rice planting in July were 4, 6, 4.4 and 4.6 t/ha for jointvetch, cassia, weed in the jointvetch plot and weed in the cassia plot, respectively. Bhur 2 and 3: and Germination for all species was good in both years, except for Crotalaria juncea in and desmodium in (Table 5). Crotalaria juncea is apparently not suited to the existing conditions. The lack of germination of desmodium in could not be explained. Planting date effects were not consistent. High plant densities observed when planting after rice harvest in were due to the high densities for berseem and sweet clover (Figure ). These two species were not included in the study. The higher plant densities observed for the later planting dates (for ) did not result in a higher yield. Earlier planting dates resulted in more vigorous plants with better dry matter production. The planting date species interaction was highly significant in These interactions did, however, not affect the conclusions drawn from the means shown in Table 5 or reveal any particular trend and are therefore shown only for observations taken 60 days after rice harvest (Figure ). Hairy vetch was the most vigorously growing species during December January, but its yield was only moderate in both years. It was expected that the subtropical species, Crotalaria juncea, lablab, greenleaf desmodium, Aeschynomene americana and cassia, would become more productive with increasing temperatures in March April, but their production too was moderate, except for greenleaf desmodium in and cassia in Berseem Desmodium Hairy vetch Sweet clover Jointvetch Cassia Density (plants/m 2 ) Figure. Effect of planting date of legumes ( 40 d before harvest; 20 d before harvest; after harvest) on plant density 60 d after rice harvest (997 98) at Bhur Station.

5 Relay seeding forages in rice systems 239 Table 5. Effect of planting date and species on plant density and yield (Bhur station). Treatments Plant density (plants/m 2 ) Yield (g/m 2 ) Days after rice harvest, when observation was taken. 2 Treatment or species not included. 30 d 60 d 30 d 60 d Planting dates 40 d before harvest d before harvest After rice harvest Legume species Aeschynomene americana Berseem Crotalaria juncea Sweet clover Cassia (C. rotundifolia) Greenleaf desmodium Hairy vetch Lablab Oats Anova summary (PR>F) Planting date (A) <0.0 < Legume species (B) <0.0 <0.0 <0.0 <0.0 <0.0 <0.0 A B <0.0 <0.0 NS NS NS 0.06 LSD A (P < 0.05) LSD B (P < 0.05) On-farm studies Goling (Zhemgang): Germination was poor except for Chinese milkvetch (Table 6). The poor results were attributed to high levels of standing water for about 5 20 days after broadcasting the seed. Chinese milkvetch has probably the highest tolerance to such water conditions and had the best germination. A study with the same species should be repeated with delayed planting dates. Table 6. Observations for on-farm studies. Species Goling Germination (%) Mebari Green yield (t/ha) Berseem 4.3. Crimson clover Hairy vetch Sweet clover.3 0 Chinese milkvetch Italian rye grass Oats n.i. 2.7 Rye n.i. 2.0 LSD (0.05) CV (%) 37.4 Species was not included at this site. 2 Statistical analysis not possible due to large number of missing plots. Mebari (Chhukha): Good germination was observed for all species, but Chinese milkvetch and sweet clover remained weak and disappeared after a few weeks. Their poor performance may be attributed to the lack of nodulation. No observations on yield were made for these two treatments. Discussion These studies show that relay seeding in rice is possible, but its success or failure will be influenced by many factors including: soil, climate, pests, diseases, weed control, weed competition, planting date, rice variety, rice cover, rice vigour, legume seed quality and legume shade tolerance. Two of the most important factors, which are inter-related, are planting date and water management. Changes in the treatment designs between years and high variation in the yield of individual species do, however, not allow us to make strong conclusions on the species suitability and the choice of planting date. Planting date and water management Unlike relay seeding in other crops, there are limited opportunities for manipulation of planting date in rice systems. The choice of planting date is largely dictated by the water management applied. It is important to broadcast

6 240 W. Roder, P. Wangchuk, S. Thsering and T. Gyeltsen the seed when moisture levels are optimal after draining the standing water. Relay seeding is not successful in fields with standing water and will not be possible in systems where the water is drained immediately before rice harvest. In some situations, a change in water management may be possible to allow for relay seeding before harvest. Competition between the seed species and the rice crop is not a concern. Earlier planting dates resulted in higher dry matter yields of the seeded species, but had no consistent effect on establishment success. Species All fodder/green manure species used in our studies are suitable for establishment in rice, provided the water level allows for their germination/survival. Of the species tested, cassia for lower elevations (<000 m), and hairy vetch for elevations above 000 m, were the most promising. Seed production for both species is relatively easy. It is, however, important to realise that the study was designed to evaluate establishment methods for a range of potential species but not to select species suitable for a particular environment. The main challenge will be to find an appropriate species for a particular farming system and location. In our investigations, we used mainly annuals or short-lived perennials on the assumption that the species have to be grown during the current fallow period of 4 6 months. For this reason, species like Stylosanthes guianensis were not included. As for temperate rice-pasture rotation systems used in south-eastern Australia (Latimare 994), there may be situations where fodder could be produced for longer periods, alternating with a rice crop every 2 4 years. In such systems, species with slow initial growth and/or higher seed cost could also be considered. On-farm studies at lower elevations should therefore include cassia and Stylosanthes guianensis. Future research requirements Relay seeding may offer advantages in some situations but further investigations are necessary. Legume establishment in rice systems needs additional research, with the identification of suitable species for particular locations and cropping systems being the main challenge. Additional studies are also needed to: quantify potential biomass production and effects on N-pools and rice yields; evaluate moisture and location interactions; and document economic aspects. References BECKER, M., LADHA, J.K. and ALI, M. (995) Green manure technology: Potential, usage and limitations. A case study for lowland rice. Plant and Soil, 74, CHEN, L. (988) Green manure cultivation and use for rice in China. In: Ladha, J.K. and Garrity, D.P. (eds) Green manure production systems for Asian ricelands. Selected papers from the International Rice Research Conference. pp (IRRI: Manila, Philippines). DUKPA, T., TSHERING, S., WANGCHUK, P. and RODER, W. (999) Forage legume establishment by relay seeding in wheat, maize or rice. Journal of Renewable Natural Resources Bhutan,, HEATH, M.E., METCALFE, D.S. and BARNES, R.F. (973) Forages. 3rd Edn. (Iowa State University Press: Ames). HUMPHREYS, L.R. (978) Tropical Pastures and Fodder Crops. (Longman Group Limited: London). LADHA, J.K. and GARRITY, D.P. (eds) (994) Green manure production systems for Asian ricelands. Selected papers from the International Rice Research Conference. (IRRI: Manila, Philippines). LATIMARE, M.E. (994) Pastures in temperate rice rotations of south-eastern Australia. Australian Journal of Experimental Agriculture, 34, PEOPLES, M.B., HERRIDGE, D.F. and LADHA, J.K. (995) Biological nitrogen fixation: An efficient source of nitrogen for sustainable agriculture production? Plant and Soil, 74, PRADHAN, P. and GARRITY, D.P. (994) Establishment practices for prerice green manure. In: Ladha, J.K. and Garrity, D.P. (eds) Green manure production systems for Asian ricelands. Selected papers from the International Rice Research Conference. pp (IRRI: Manila, Philippines). RODER, W. and MANIPHONE, S. (995) Forage legume establishment in rice slash-and-burn systems. Tropical Grasslands, 29, RODER, W., WANGDI, K., GYAMTSHO, P. and DORJI, K. (998) Feed and fodder research and development in Bhutan. RNR- RC Jakar, Special Publication No. RNR-RC Jakar, Bumthang. SHELTON, H.M. (980a) Dry-season legume forages to follow paddy rice in N.E. Thailand. I. Species evaluation and effectiveness of native rhizobium for nitrogen fixation. Experimental Agriculture, 6, SHELTON, H.M. (980b) Dry-season legume forages to follow paddy rice in N.E. Thailand. II. Soil fertility and planting methods. Experimental Agriculture, 6, SHELTON, H.M. and HUMPHREYS, L.R. (972) Pasture establishment in upland rice crop at Na Pheng, Central Laos. Tropical Grasslands, 4, THOMAS, D. and BENNETT, A.J. (975) Establishing a mixed pasture under maize in Malawi. I. Time of sowing. Experimental Agriculture,, (Received for publication November 5, 2000; accepted July 4, 200)

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