Evaluation of Greenhouse Gas Emission Reduction Effect in No-Tillage Rice Transplanting System by LCA

Transcription

1 Evaluation of Greenhouse Gas Emission Reduction Effect in No-Tillage Rice Transplanting System by LCA Abstract For rice production, as compared with the puddling transplanting system, the no-tillage transplanting system has approximately 1,800kgha-1 carbon dioxide (CO2) equivalent of greenhouse gas reduction effect mainly due to methane (CH4) emission reduction. On the other hand, tillage, specialized transplanter, pesticide and other practices will have small reduction effects. The impact of the non-puddling transplanting system on global warming is almost identical to that of the puddling system. Research Institute: Hisatomo Harada, Hitomi Kobayashi, Hayato Shindo, Akita Prefectural Experimental Station Background and Purposes It is expected that the no-tillage transplanting system of rice has multi-dimensional effects not only on water quality protection through avoiding drainage of muddy water during puddling but also saving in fuel through the skipping of tillage, atmosphere protection through reduction of CH4 emission, and conservation of aquatic plants/animals. On the other hand, the preparation of a specialized transplanter with minimum tillage function and application of non-selective herbicides for this system will increase greenhouse gases. Therefore, the Life Cycle Assessment (LCA) is applied to evaluate these two technologies. Achievements and Features 1. To compare effects on global warming, large-scale paddy fields with fine sandy gley soil are assumed as a precondition (Table 1). The effect of the difference in tillage system on brown rice and straw yield were small. 2. As compared with the puddling system, the no-tillage transplanting system requires non-selective herbicides but does require neither tillage nor puddling. And, non-puddling transplanting requires clod breaking after tillage (Figure 1). 3. The soil condition under the no-tillage transplanting system became oxidative and emitted approximately 60% of CH4 emitted by the puddling system (Figure 2). Emission of CH4 and soil oxidation-reduction potential (Eh) by the non-puddling

2 transplanting were the same as those by the puddling system. 4. The no-tillage transplanting system had effects to save fuel energy by omitting tillage and puddling and to overcome energy consumption by the heavier non-tillage transplanter and application of non-selective herbicides. Therefore, it reduced CO2 emission by 30 kg/ha as compared with the puddling transplanting system (Table 2). 5. In the greenhouse gas emission/absorption balance,the tillage system affected CH4 emission to the largest extent (Table 2), while it affected nitrous oxide (N2O) emission by less 10% of CH4 equivalent and did not affect CO2 emission (soil respiration) from soil. 6. In considering the effects by the tillage system on global warming, if combined with working practices, materials, and greenhouse gas emission, the no-tillage transplanting system has approximately 1,800kgha-1 CO2 equivalent of greenhouse gas reduction effect mainly due to methane emission (Table 2). The impact of the non-puddling transplanting system on global warming is almost identical to that of the puddling system. Applications and Notes 1. Compared to the pudding system, it was reported that CH4 emission was increased when the no-tillage system was continued for 7 to 8 years. And, the present long-term study did not concern other problems such as weed control and uneven subsidence of paddy fields. 2. When the iron content was high under high iron soil conditions, it was reported that CH4 emission of the puddling system was reduced and became smaller than that of the no-tillage system, however, CH4 emission at the present study was the average value in typical paddy soils in Japan, and active bivalent iron content immediately after the mid-season drainage was lower than that when the methane emission was suppressed. 3. LCA assesses environmental impacts of the raw materials of a product from extraction, manufacturing, utilization, and disposal through a life span. The present study reviewed the differences of working practices, materials, and greenhouse gas emission from paddy fields only.

3 Table 1. Conditions for comparison of global warming impacts in different rice transplanting Object Difference of global warming impact in no-tillage, no-puddling and puddling by converting CO2. Management and soil Large scale farm management with area 15ha, 10ha for rice paddy field Fine sandy gley soil, no long-term no-tillage condition required Transplanting, yield Akitakomati with application of coated fertilizer (50kgN ha -1 ) in nursery box Yield of no-tillage system is 101% of pudding system yield (5470kg ha -1 from 2002 to 2005) Straw yield of no-tillage system is 97% of puddling system (7110kg ha -1 ), straw length is slightly shorter. Yield of no-pudding system is 98% of puddling system, and straw production (101%) is the same as puddling system. Assessment unit Difference of CO2 emission for each ha CO2 emission from machinery operation and materials Life of Rice transplanter and other farm machinery is 5 years. Database (National Agricultural Research Center, 2004) used for assessment of environment impact based on agricultural operations LCA database (Architectural Institute of Japan, based on industry-related data in 2003 and 2005), which is considered as a fixed capital. Fuel primary unit Enforcement Ordinance of Law based on Promotion of Global Warming Countermeasures (Ministry of Environment, revised version) Global warming factor To convert to equivalent CO2, CH4 is multiplied by 23, and N2O is multiplied by 296 (Third Assessment Report 2001). Transplanting history in field Puddling (2000) -> puddling (2001) -> no-puddling -> no-tillage (2003) -> puddling, no-puddling, no-tillage (2004, 2005) No direct investigated objects were selected for impact on soil carbon content.

4 Figure 1. Difference in Rice Field Chores in Puddling Transplanting, Non-Puddling Transplanting, and No-Tillage Transplanting System Figure 2. Impacts on CH4 and N2O flux, soil Oxidation-Reduction Potential (Eh), and soil respiration due to different tillage systems (2005) Note: CH4 and N2O were measured by method of chamber and gas chromatography. Soil respiration was measured by method of chamber and absorption titration)

5 Table 2. Comparison of impact on global warming based on different rice transplanting system by converting equivalent CO2 emission (kg CO2 ha -1 ) Pudding No-tillage No-pudding Operation Herbicide application before tillage 9.1 Tillage and clod breaking (rotary) Clod breaking (puddling rotary) 30.6 Puddling (puddling rotary, 2.5 times) line high speed rice transplanter Material Herbicide (7.5kg) 47.7 Weight increase by rice transplanter Total of operation and material Difference with tillage Greenhouse gas emission from paddy field CH4 emission (average of 2004 and 2005 ) N2O emission (from April 26, 2005 to November 21, 2005 except flooding period from May 11 to June 29) Total of greenhouse gas emission Difference with tillage Total of 1 and , : there are significant differences between processes based on two-factor ANOVA method ( p<0.05, p<0.1). Adjustment: soil respiration in 2005 (include root respiration, Figure 2) is (puddling), (no-tillage), and (no-puddling) kg ha -1. There is no recognized difference between transplanting system for CO2 emission from soil. At the same time, the straw inputs (converted to CO2) are (puddling), 9882 (no-tillage) and (no-tillage) kg ha -1.