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1 àößåàìàßåéàçà ãöß ÎñàæÓò, ÅßÍèÍËê 5 ÀàÌÅëÀÅàÀàÌÎïÀâÁ àæýñãöß ÚàÀâÈìÜÇ åìâãìñüìæáýüí ÞÌÅ Ì ÔïñãÁ à Øð ÃÑßÍàà ãüììéâàòâèéõîç 1, ÒêÕéÍâÎòÇàÕèÃâÀê 1 ãöß ÍîÌÅßæÚ ÅîÖéÖèÈ 1 ÍíÈÂèÈØÇçðû ÀàÌâÝèÈæÝñÎïÀÑìÈåÌѺÌËêñÎñàâÖíñàÜñÜÌ ãóñìíèìøàùëñãëêñâýèèåøò èèåßñìèâàêèøðàç ãöß ÁßØÇàÇÉí æ ÆëñÃâÝèÈåØòÅßÓèÈÉßÑàÍÀàÌÏßÖéÈÉ à, ÑòÜÓÀèÌÌ ÌæÖÇßÀàÌâÅèÇ ØÇòàÀçÊêñƒÀèÌÆëñÃâÎèÌâÃìñÜÌæÁÜèÌÙëñà ËêñâÝèÈåØòâÀêÈÓêÀàÌÅïÌâÅèÇÈéÌÄàÀÀàÌâÆàßâÄìñÜÌæÈò ÃñàÇ. ÀàÌÎïÀÚàÀâÈìÜÇ (Coix Lacryma-Jobi L.) ÁÜÃÆà ÀßÅéÀÜÌâÁÈÑàÀâÙìÜÁÜà Öà Ì Ì ãóñìëàãâöìüàùëñãëêñæñ Ç åøòààìâ ÍÂîÓ èèåßñìè æèòèêàñ àààìîïàâá àæýñ. ÔïñÅßÊàÌê ÌÂò àëíèöüãèéìøò ÇÎàÚçò æèòóêààìåíóëþíãîãîïàâá àæýñãííæà ÀßÅéÀÜÌ (4) ÀèÍãÎÃÎïÀÚàÀâÈìÜÇ (5). ÏíÌÁÜÃÀàÌ ÌÂò àëíèöüãñíí ñà: ÏíÌÏßÖéÈ ÚàÀâÈìÜÇæÈò 1.4 äéì/âýèàéà, Åñ ÌÏíÌÏßÖéÈâÁ àæýñãóñì 0.8 äéì/âýèàéà,ìÿ ÙèÀãØòÃÁÜÃÉ ÌÚàÀâÈìÜÇåÌâ ÖàâÀèÍÀñÞ æèò 6 É/ÝÉ, ÀíÃÀèÌÁòàÓÌŸÙèÀâÒìÜÃâÁ àæèñãæèò 1.7 É/ÝÉ. åìæñ ÃÖßÈïÀàÌÏßÖéÈåÌѺÌËêñÎïÀâÁ àæýñ Æà æýñæèòâåèçøçòà 4.3  Ã, ÆèñÃÌŸÙèÀØÇàò ãøòãëêñâåèçüüàæèò 158 ÀÕàÓ/Ó 2 ãöß ÓêÀàÌâÅèÇØÇòàæÝñÚàÀâÈìÜÇ 3.9  à ÅßâÖèñÇÌŸÙèÀ ØÇòàãØòÃæÈò 57 ÀÕàÓ/Ó 2. ÅçàÖèÍѺÌËêñ ËêñÎïÀÚàÀâÈìÜÇÅßãÈÃåØòâØèÌ ñà: åìæñ ÃæÖÇßâ Öà 3 âèìüì ÀàÌÎïÀÚàÀâÈìÜÇÅàÓàÈÂîÓØÇòà ãöß ÜßÌîÖèÀÈéÌæÈòâÊéà 90% âóìñüåíóëþíååñ ÀèÍÀàÌÎïÀâÁ àæýñëêñâ ÓÂîÓØÇòàæÈòÑÞà 70% åìæñ ÃæÖÇßâ Öà 1 âèìüì, âåèñìèãøòãäàà ÚàÀâÈìÜÇæÈòÎßÓàÌ 4-5 É/ÝÉ Åñ ÌâÒìÜÃãØòÃæÈòÑÞÃãÉñ 1 É/ÝÉ. ÀàÌÎïÀÚàÀâÈìÜÇãÓñÌ æèòåæòãýããàìùòüçñþããéñ 168 èìãàì âóìñüåíóëþíååñâá àæýñ ËêñåÆòãÝÃÃàÌâÊéà 228 èìãàì ãöß ÀàÌâÝèÈæÝñÇèÃæÈòÇëÈâ ÖàæÎâÊéà 9 âèìüìãéñààìîïàúààâèìüçãóñì 7 âèìüì, ÇéñÃæÎÀñ àì ÌÉ ÌÚàÀâÈìÜÇÅàÓàÈÎíÀÂîÓÈéÌæÈòÈê ÓêËñàÜñÞÃÆñ ÇÖíÈ ÎßÖéÓàÌÀàÌ ÅïÌâÅèÇ ÈéÌæÈòÈêÀñ àààìîïàâá àæýñ. 1 äâãààìâîòóâüãèéìâæàßâäìñüì, ÅïÌÅçàØð È ãöß ãíñãâáèèéìàßåéàçà ÀçÖßÀíÈ - ËèÌ à

2 The Lao Journal of Agriculture and Forestry, No. 5 Upland Rice and Jobs Tear Cultivation in Slash and Burn Systems under very Short Fallow Periods in Luang Prabang Province A. de Rouw 1, P. Baranger 1 and B. Soulidad 1 Abstract Weed infestation and low yields are problems resulting from very short fallow periods. In addition, frequent weeding favours soil losses by erosion. Farmers in northern Laos start cultivating Jobs tears, ( Coix lacryma-jobi L. ) as an alternative for the very weed sensitive upland rice. In the Hoqay Pano study site, farmers fields of upland rice (4) and Jobs tears (5) were compared. Grain yield of Jobs tears averaged 1.4 t ha -1 and rice 0,8 t ha -1, total bomass at harvest was 6 t ha -1 dry weight for Jobs taers against only 1.7 t ha -1 in rice. Farmers cleared the rice fields 4.3 times during the season, removing a total of 158 g m -2 dry weight of weeds; this was 3.9 times and 57 g m -2 dry weight in Jobs tear fields. Jobs tear fields ensured good soil cover by crop and weeds, 90% cover during 3 months, compared to upland rice fields, 70% cover during 1 month. Crop residues from Jobs tears amount 4-5 t ha -1 dry weight against only 1 t ha -1 from rice. Not only labour requirements were less in Jobs tears, 168 days, compared to rice 228 days; the work could be stretched over 9 months instead of 7. Superior soil cover and less tillage in Jobs tear cultivation are liable to induce less erosion than upland rice cultivation. 1 Management of Soil Erosion Consortium ( MSEC ), Soil Survey and Land Classification Center (SSLCC). 2 July - December 2002

3 àößåàìàßåéàçà ãöß ÎñàæÓò, ÅßÍèÍËê 5 Introduction The rotational shifting cultivation in the mountainous land of Northern Laos is responding to population pressure by intensification of land use. Paddies for wet rice were developed where possible and the rotational cycle has been shortened locally to an unsustaianble 3-5 years. Excessive weed growth is the actual major constrain in upland rice production, particulary where only hand tools are used ( Roder 2001 ). Not only labour inputs are enormous, frequent hoeing accentuates the problem of erosion. Soil losses will be a chief problem in futere land use so minimising soil movement down the slope is the basic requirement for sustainable agriculture in mountains. Farmers in the region resort to an alternative cereal, Jobs tears ( Coix lacryma-jobi L. ), possibly because it requ- ires little care. Since 1999, farmers in the study area grow Jobs tears as a cash crop along with the subsistence crop upland rice. This study compares the two cereals with emphasis on : 1\ productivity grain yield, yield components and biomass, 2\ labour, 3\ seasonal soil cover by crops and weeds. Our first hypothesis is that the cultivation of Jobs tears requires less weeding because the crop it self is weed tolerant compared to upland rice; secondly, that Jobs tears cultivation guarantees better seasonal soil cover. Less weeding and more soil cover in Jobs tears would result in a superior protection against erosion compared to upland rice cultivation. The study is part of regional MSEC programme ( Managing Soil Erosion Consortium ) which started in 1998 in Laos in the Houay Pano catchment ( 102 o to 102 o E longitude and 19 o 51 0 to 19 o N latitude ). Soil and water studies are carried out along with vegetation and agronomic studies. This study is part of a compare- hensive agronomic study investigating systems that evolve from short fallow periods (4-6 years) to very short fallow periods (1-3 years) The present study was carried out by two students, one from the agronomy Faculty of Nabong, Laos, the other from the National Institute of Agronomy in Paris. Materials and Methods Study site The Houay Pano catchment, comprising 67 ha, is situated near the village Lak Sip, 10 km from Luang Prabang along the national road No. 13. About 75% of the land is involved in slash and burn cycles. In 1998, 22% of the catchment was planted with cereals, this was 52% in 1999, 14% in 2000 and only 9% in 2001 (MSEC 2001). Altitudes range from 425 to 718 m above sea level and slope in fields varies from 20 to over 100%. Long term annual rainfall recorded in the Luang Prabang meteorological station averages 1403 mm, more than 90% falling in the rainy season May-October. According to the US Taxonomy soil are classifies as Entisols (20%), Ultisols (30%) and Alfisols (50%). The inhabitants of the Lak Sip village are Kmhmu. ÀçÖßÀíÈ - ËèÌ à

4 The Lao Journal of Agriculture and Forestry, No. 5 Measrements Field observation were carried out in permanent plots in farmers fields in order to follow weed development and crop performance over the cultivation period. Plots were established in 9 of 10 upland fields cultivation in 2001 in the catchment : 4 fields with upland rice and 5 fields with Jobs tears. Blocks of three plots ( 3 x 3 m each ) were laid out midslope. Treatments were : (1) weeding with a hoe, implying shallow tillage of the soil; (2) weeding with a machete, implying no disturbance of the soil; (3) no tillage during the second half of the growing cycle, i.e. after 15 th July. The Kmhmu farmers in the catchment commonly use both weeding tools. Hoeing the soil does eliminate the roots of most weeds but the subsequent disturbance of the topsoil would trigger germination of others. Weeding with a machete only destroys the weeds above the soil surface. The no weeding treatment served as a check on the effectiveness of full-grown rice or Jobs tears to suppress weeds. At weekly intervals, height and cover of crop and weeds were recorded in each plot. Plots were weeded at the same time as the farmer weeded the field. The aboveground weed biomass was sampled from 1 m 2 and dried for dry weight determination. In each plot, at harvest, number of hills, number of panicles, panicle weight, and total biomass fresh weight was determined in the field. Samples of leaves and stems were taken for dry weight determination. Grain yield was determined from grains that were air-dried following local practice. Single seed weight was determined by taking 5 samples of 200 grains at random from the grain harvest. In addition, labour input for all major farm operations for each field was determined. The cultivation history over the last 10 years for each field was recorded from interviews with the farmer. Reslts Productivity Grain yield of Jobs tears averaged 1.4 t ha -1 ; this was almost twice as high as the yield of upland rice, 0.8 t ha -1 ( Table 1 ). Another prominent difference between the two cereals was the quantity of crop biomass produced. Jobs tears provided 5 times as much dry matter compared to upland rice. Several factors contribute to this. (i) The high statue of the Jobs tears. At harvest the height of Jobs tear averaged 2 m against 1.1 m in rice. (ii) The longer growing season of Jobs tears. Jobs tears occupied the field 7-8 months compared to 5-6 months of the local rice varieties. (iii) The low Harvest Index of Jobs tears. In Jobs tears, 78% of aboveground biomass is spend on stems and leaves and only 22% of total production is put into grain yield. In contrast with this, the upland rice varieties were efficient producers of grain because 47% of total aboveground biomass contributed to grain yield. (iv) The habit of trashing the Jobs tears panicles on the spot thus exporting only the grain from the field. The combined effect of these four points resulted in a far superior amount of crop residues after Jobs tear cultivation compared to upland rice. Two months after the harvest, 4 July - December 2002

5 àößåàìàßåéàçà ãöß ÎñàæÓò, ÅßÍèÍËê 5 Table 1 : Yield and yield components of upland rice and Jobs tears in relation with three weeding treatments, Houay Pano, Luang Prabang Province, 2001 stems and leaves of Jobs tears covered the soil for over 20% whereas soil cover of rice residues was down below 10%. For both cerals, high yields are associated with high panicle number and low yields with a low panicle number (Table 1). Because the number of paincles is fixed in the first half of the growing cycle, good crop condition in this period is determinant for high yield. No weeding in the second half of the growing cycle slightly reduced grain yield in upland rice (-9%), by decreasing grain number and grain weight. On the other hand, suppressing the last weeding round in Jobs tears had servere consquences for grain yield (-43%). Grain number was effected but also panicle number because late tillers on the main stem were suppressed by weed growth. Hoe weeding and machete weeding had reverse effects in rice and Jobs tears but this is difficult to explain. The great variance at the plot level in combination with the small number of fields precluded a statistical analysis. Labour Table 2 shows the number of working days per hectare needed to accomplish the different task in upland rice and in Jobs tear cultivation. Both crops are sown with similar planting sticks, but planting upland rice requires much more work. This is due to differences in densities: Jobs tears hills are cm against cm in upland rice. ÀçÖßÀíÈ - ËèÌ à

6 The Lao Journal of Agriculture and Forestry, No. 5 Weeding operations during the first half of the growing cycle in Jobs tears took more time because its growing season is longer and because wide spacing of hills allowed undisturbed weed growth between hills. Conversely, weeding time during the second half of the growing cycle was less in Jobs tears because the crop grows tall and dense and thus suppresses weeds. However, the 22 days spent on weeding during this period (Table 2) are vital for grain yield because not performing this labour reduces grain yield by 43% (Table 1). Total labour requirements in Jobs tears cultivation were less, 168 days, compared to upland rice, 228 days. In addition, the work is spread over a longer period (Table 2). Weed biomass and grain yield During each weeding round, biomass samples were taken from 1 m 2. Cumulative biomass per plot was compared with gain yield adding the number of weeding rounds in the plot (Figure 1). The straight line Figure 1 shows grain yield limited by weed biomass. Plots close to this line had weed competition as a main constrain, plots far below this line suffered from other problems too, mainly rats and poor soil. In most cases the number of weeding rounds (2, 3, 4) had no relation with yield because farmers strated weeding in responds to a similar level of weed infestation. Plots with five weeding rounds all had low yields. This denotes a level of weed infestation beyond the control of farmers. During the 2001 rainy season, farmers cleared the soil of vegetation 4.3 time in the rice fields, and 3.9 times in Jobs tears. During these weeding operations 57 g m -2 dry weight biomass was removed in Jobs tears, against 158g m -2 in upland rice. This demonstrates that upland rice competes poorly with weeds compared to jobs; tears. Cover by crops and weeds Seasonal plant cover followed different Table 2 : Labour needed for the cultivation of upland rice and Jobs tears with month of execution, Houay Pano, July - December 2002

7 àößåàìàßåéàçà ãöß ÎñàæÓò, ÅßÍèÍËê 5 Figure 1. Grain yield and weed biomass in farmersmfields with number of weeding rounds, season 2001, Houay Pano patterns in Jobs tears and upland rice (Figure 2a and 2b). the period of good soil cover extended over 3 months in Jobs tears but was limited to 1 month in rice. Besides, maximum cover was 70% in rice and over 90% in Jobs tears. A third difference between the crops was early season weed cover. Planting of Jobs tears only requires the clearing of a circle of about 30 cm diameter around the hill. Removal of weeds between the widely spaced hills can be postponed for about a month upon planting. Undisturbed weeds growth between hills allowed high levles of soil cover, up to 60% during the first months of the rainy season (Figure 2b). In contrast with Jobs tears, successful hill planting of upland rice is only possible after complete clearing of the field because plant density is high. As a result early season soil cover in rice is poor (Figure 2a). Discussion and Conclusion The slash and burn cropping systems in the Luang Prabang province have evolved in recent years from short fallow periods 7-5 years, studies by Roder (2001) to locally very short periods of 3-2 years. An example of the latter is the Houay Pano catchment (MSEC 2000). The very short fallow periods do not constitute a weed break because the natural fallow vegetation no longer eliminates arable weed by shading. Secondly, the biomass produced by the natural fallow after 2 years of growth amounts only 1-3 t ha -1 dry weight (Jullien 2002). Burning this material produces a heat that is insufficient to kill superficial weed seed throughout the field. Weed free areas in fields are limited to places where ÀçÖßÀíÈ - ËèÌ à

8 The Lao Journal of Agriculture and Forestry, No. 5 Figure 2a. Cover by upland rice and weed during the season 2001, Houay Pano. Vertical bars are 1 S.D. Figure 2b. Cover by Jobs tears and weed during the season 2001, Houay Pano. Vertical bars are 1 S.D. 8 July - December 2002

9 àößåàìàßåéàçà ãöß ÎñàæÓò, ÅßÍèÍËê 5 wood had been piled and burned. Excessive weed growth after the burn and the necessity of cleaning the field a second time before planting is a driect result of the very short fallow periods (de Rouw 1995). The 2001 season was marked by the early onset of the rainy season but only those farmers cultivating Jobs tears could benefit from this. Jobs tear was planted one month and a half ahead of the rice crop because the crop does not need thorough weeding prior the planting. Though early planting is generally associated with high yields rice farmers could not benefit from the early rains because the upland rice requires complete weeding prior to planting. It rice farmers were to use herbicides, the best period of application would be prior to planting. In suppressing the pre-plant weeding, rice farmers can make a better use of the available rain.this was also suggested in Roder et al. (1995). Hand weeding is still the only effective method to control weeds in slash and burn systems on steep slopes, making weed control by far the most labour consuming task in upland rice production. In 2001, clearing and weeding operations accounted for 140 days or 61% of total crop labour input in upland rice. These values are comparable with Roder et al.(1997) who recorded in the region an average of 146 days per ha in upland rice accounting for % of total labour requirements. Comparing Jobs tear fields with upland rice, we summarise that farmers in Houay Pano carried out less weeding rounds in Jobs tears than in rice; secondly, that the amount of weed biomass removed is three times less in Jobs tears compared to rice. Thirdly, good soil cover by both crop and weeds is assured in Jobs tears during most of the rainy season against poor soil cover during a much shorter period of the rainy season in upland rice. Finally, after the harvest,a heavy mulch cover of 4-5 t / ha of crop residues occupies Jobs tears field compared to only 1 t / ha of crop residues in rice. With respect to erosion we conclude that frequent weeding and abundance of weeds are liable of increasing soil losses by tillage erosion in upland rice, and less in Jobs tears. References Jullien, F Impact de la baisse du temps de jachere sur 1 agriculture de 1 ethnie Khamou au nord Laos. Memoire de fin d etudes, ISTOM Ecole d Agro-economic international, Cergy - Pontoise, France, 96 p. MSEC Management of Soil Erosion Consortium. An innovative approach to sustainable land management in Laos. Technical report Oct Oct National Agriculture and Forestry Research Institute, Ministry of Agriculture and Forestry, Vientiane, Lao PDR., 60 p. MSEC Management of Soil Erosion Consortium. Annual progress report October October National Agriculture and Forestry ÀçÖßÀíÈ - ËèÌ à

10 The Lao Journal of Agriculture and Forestry, No. 5 Ressarch Institute, Ministry of Agriculture and Forestry, Vientiane Lao PDR., 43 p. Roder, W., Phengchanh, S., Maniphone, S., Songnhikongsuathor, K., Keoboulapha, B Weed management strategies aimed at reducing labour for upland rice productin. In: Fragile lives in fragile ecosystems. Proceedings of the International Rice Research Conf. IRRI, Los Banos, Laguna, p Roder, W., Phengchanh, S. Keoboulapha, B Weeds in slash-and-burn rice fields in Northern Laos. Weed Research, 37 : Roder, W Slash and burn rice systems in the hills of Northern Lao PDR. Description, challenges, and opportunities. Los Banos, Philippines, International Rice Research Institute. 201 p. Rouw, de A The fallow period as a weed break in shfting cultivation (tropical wet forests). Agriculture, Ecosystems & Environment, 54 : July - December 2002