EFFECT OF THE SYSTEM OF RICE INTENSIFICATION (SRI) ON ...

More documents

Recommendations

Info

e increased during times of flooding and slowly decrease when drained (Mitsuchi, 1974). There will however be a trade-off when considering the possibilities of denitrification and emissions of N2O. Intermittent flooding showed a 17% lower GWP for N2O and CH4 than continuous flooding in China (Yue et al., 2005) and thus the most favorable would seem to go for a fluctuating water table as with SRI. The emissions of N2O are quite large during the dry season – up to three to four times larger than upon the growth season (Dobermann & Fairhurst, 2000) upon aerobic conditions. Denitrification is occurring in situations of lack of oxygen and some bacterial strains will then use nitrate as a source of respiration in stead of oxygen (Patrick & Reddy, 1976). Denitrification can especially occur in wetland soils, poorly drained soils and soils fertilized with nitrate (Borggaard & Elberling, 2003). The theoretical SRI will give fewer rises to denitrification due to the fluctuating water table. The SRI practiced by farmers seems though however to experience some periods with denitrification due to the long drought periods and aerobic conditions. The farmers in Prey Veng do however not possess the means to control water, they are able to drain their fields but not adjust water levels later on. It is therefore very risky if they drain at one point and not are able to adjust water if a prolonged drought is present. Only 3% of the target farmers use less water, and their fields might in theory build up less C than fields that are flooded according to the findings of Mitsuchi (1974) but it is though doubtful if there will be any significant difference between their C levels and the other participating farmers. Especially when considering that one rice season is very short – a few months followed by a fallow period throughout the rest of the year. The farmers who are able to adjust water levels (3%) will though be able to reduce CH4 emissions due to drainage periods resulting in aerobic conditions (Wassmann et al., 2000; Yue et al., 2005; Zou et al., 2005; Li et al., (2009) but will at the same time increase emissions of N2O and CO2 and thereby creating a trade-off. The success of the drainage concepts is though depending on the degree of drainage i.e. complete drainage or as in the SRI theories soil is kept moist/wet to dry depending on the farmer and the area. If the soil is just a little too wet/moist there will still be methane emissions due to anaerobic conditions. The majority of farmers do as mentioned not adjust water levels and their “SRI” fields will emit more CH4 but less N2O and CO2 due to long periods with anaerobic conditions. The question is then which systems are to be preferred considering the present trade-off. Since few farmers use chemical 66
fertilizers which can increase N2O emissions (Nishimura et al., 2004; Mandal et al., 2008), drainage periods will not lead to heavy emissions of N2O. The other important SRI concept is the use of organic amendments (Laulanie, 1993) which will reduce all three GHGs (Yagi & Minami, 1990; Neue, 1993; Nayak et al., 2007) and increase the C content of the soil (Jarecki & Lal, 2003; Ramesh & Chandrasekaran, 2004; Mandal et al., 2008; Rajashekhara Rao & Siddaramappa, 2008). 93% of the farmers follow this SRI concept and their fields will therefore most likely have some influence on GHG emissions and build up of C pools. The fact that farmers remove the rice straw from the fields is removing nutrients, but removal of straw was according to Lou et al. (2007) found to decrease the emissions of CO2 and N2O. This is linked to the higher cellulose content of straw compared to the roots which will result in a slower decomposition of straw than roots (Lou et al., 2007). The degree of GHG emission reductions and C dynamics will very much depend on the applied amount of organic amendments and as discussed above in “compost production” are farmers able to collect quite a lot of natural fertilizers but they are not able to produce larger amounts of compost. Estimates are made on the C pool increase per year based on the organic inputs in table 9 and 10. If farmers in average would grow one ha or more with SRI, apply 3t/ha of compost/GM and have an average yield of 3.5 t rice per ha, a yearly input of C would be 348 kg C per ha per year which corresponds to close to 1% of the soil C pool of 49.5 t/ha. It is estimated that app. 1% of the C soil pool is mineralized per year thus resulting in a steady state where losses matches inputs app. Jarecki & Lal (2003) found similar results from a situation with a rice yield of 3.96 t ha -1 and input of crop residues amounting to 2.67 t ha -1 . They concluded that the soil C pool was enriched with 401 kg C ha -1 annually (Jarecki & Lal, 2003). With the intensions of the ILFARM project to establish 500.000 trees the potential of storing larger amounts of C seems possible. Given the inputs assessed in section 9.5.5, under the nutrient budget, the plantings of e.g. Sesbania on 1 ha would yield 15 t ha -1 of green matter (Singh, 1984). Assuming a C percentage of 42 % (Brady & Weil, 1999a) this would leave the farmers with an additional C input of 6300 kg/ha where however some parts would be lost due to decomposition especially if the Sesbania is added directly and not composted. Conservation tillage or no tillage could increase the C budget in the soil, it is however 67
Page 1 and 2:
EFFECT OF THE SYSTEM OF RICE INTENS
Page 3 and 4:
Abstract The System of Rice Intensi
Page 5 and 6:
Preface This report is part of my M
Page 7 and 8:
Table of contents Preface..........
Page 9 and 10:
1. Introduction Rice (Oryza sativa
Page 11 and 12:
fields will normally result in lowe
Page 13 and 14:
materials. These two chapters lead
Page 15 and 16: the process of puddling - which is
Page 17 and 18: Crop residues The use of rice straw
Page 19 and 20: The degree of GHGs emissions will t
Page 21 and 22: are required (app. 150-200 mm) and
Page 23 and 24: • The use of young seedlings tran
Page 25 and 26: Table 1. The major differences betw
Page 27 and 28: Cambodia during modern times. In 19
Page 29 and 30: Rainfed rice in Cambodia is often g
Page 31 and 32: In general there are three types of
Page 33 and 34: 7. Study and experimental implement
Page 35 and 36: growing rice but the Cambodian rain
Page 37 and 38: Figure 6. Map of the two target com
Page 39 and 40: The following main topics were exam
Page 41 and 42: White & Seng (1997) state that not
Page 43 and 44: conditions signifying little or no
Page 45 and 46: Riel 3000000 2800000 2600000 240000
Page 47 and 48: The involved farmers seem to belong
Page 49 and 50: The farmers’ composts were often
Page 51 and 52: chemical fertilizers. It is part of
Page 53 and 54: 9.5.2 SRI techniques The different
Page 55 and 56: t/ha 5,5 5 4,5 4 3,5 3 2,5 2 1,5 1
Page 57 and 58: the farmers are with SRI. Or farmer
Page 59 and 60: forced to sell labour in order to s
Page 61 and 62: households were in average able to
Page 63 and 64: K, only a minor fraction is availab
Page 65: Table 8. An estimated picture of an
Page 69 and 70: Table 9. An estimated C budget. It
Page 71 and 72: 10. Conclusion The farmers particip
Page 73 and 74: 11. References Anthofer, J. 2004. T
Page 75 and 76: Moldenhauer, K.A.K. & Gibbons, J. 2
Page 77 and 78: Yue, J., Shi, Y., Liang, W., Wu, J.
Page 79 and 80: APPENDIX B. Soil sampling methodolo
Page 81 and 82: Type How much do you apply to your
Page 83 and 84: APPENDIX E. LIVELIHOOD ASSESTS. Per
Page 85 and 86: 3 2 1 Combination of SRI techniques
Page 87: APPENDIX F. Interview with Ma Veasn
show all

EFFECT OF THE SYSTEM OF RICE INTENSIFICATION (SRI) ON ...

Create successful ePaper yourself

Delete template?

Save as template?