Eco-balance analysis of six agricultural land uses in the Ikushunbetsu watershed

Abstract

This study quantified and evaluated the greenhouse gas emissions of farmland soils at a watershed scale using parameters available at a regional scale. The estimation was based on field monitoring data in the Ikushunbetsu River Watershed, Hokkaido, Japan. Simple regression models were created for carbon dioxide, nitrous oxide and methane emissions associated with six major agricultural land uses, and forest as an alternative land use to farmland. An eco‐balance method involves conducting an analysis on the basis of farmland surplus nitrogen (N) and global warming potential (GWP). Uncertainties associating the estimations were estimated using Mote Carlo simulation. The eco‐balance is the analysis of the relationship between production and environmental load. In this study, production and environmental load were compared by changing each of the land use combinations by 10%. Farmland surplus N was lowest for soybean with 8.2 kg N ha−1 year−1, followed by paddy rice. The highest value was recorded for vegetables with 99.8 kg N ha−1 year−1. The weighted mean of total farmland based on the land use proportion was 44 ± 33.8 kg N ha−1 year−1. The calculated GWP was 7.3 Mg CO2 eq ha−1 year−1 for paddy rice and 0.1 to 6.8 Mg CO2 eq ha−1 year−1 for upland crops. The weighted mean of the total farmland area was 4.0 ± 3.4 Mg CO2 eq ha−1 year−1. The eco‐balance analysis showed that there were 59 combinations out of 8008 combinations able to reduce GWP more than 6%, but less than 7%, than the value in 2005. Among them, in 30 combinations, farmland surplus N became less than the value in 2005; production was reduced compared with the value in 2005 in 27 combinations. Soybean occupied 20–80% in the seven combinations where production was increased compared with 2005, while keeping farmland surplus N below the value in 2005. The estimation of greenhouse gases in this study exhibited high uncertainty because of variability in management and errors in evaluation procedures. Quantification of the data variability is set at maximum, which comprises the measured values in this area. Based on the quantification of the uncertainty, more efficient quantification methods can be established to clarify mitigation potential. This type of quantification and comparison between production and emission enables decision makers to set some threshold values that allow a compromise between production and environmental load.

Changes in fertilizer‐induced direct N2O emissions from paddy fields during rice‐growing season in China between 1950s and 1990s

“…Stehfest & Bouwman (2006) summarized and statistically analyzed 1008 N 2 O emission measurements for agricultural fields, and concluded that agricultural N 2 O emissions were significantly influenced by N application rate, crop type, fertilizer type, soil organic C content, soil pH, and texture. To our knowledge, however, few studies have presented statistical models incorporating the dependence of N 2 O emissions on soil parameters and agricultural practices for rice paddies on country scale, although consideration of these factors could minimize the uncertainty in N 2 O estimates (Stehfest & Bouwman, 2006; Kimura et al , 2007).…”

Aboveground plant biomass, carbon, and nitrogen dynamics before and after burning in a seminatural grassland of Miscanthus sinensis in Kumamoto, Japan

“…Therefore, addition of N due to biological fixation of N 2 by other species, such as L. bicolor and L. cuneata , which are common in M. sinensis grasslands, and wet and dry N deposition possibly contributed to N accumulation in the soil over time. This requires further investigation, but it should be considered that in grassland ecosystems, nearly 20% of the biomass N may come from biological N 2 fixation (Pakrou & Dillon, 2000; Kimura et al , 2007). Also, it has been reported that N 2 ‐fixing clostridia and nondiazotrophic bacteria symbiotically provide N to M. sinensis plants (Ye et al , 2005; Stewart et al , 2009).…”

“…Also, it has been reported that N 2 -fixing clostridia and nondiazotrophic bacteria symbiotically provide N to M. sinensis plants (Ye et al, 2005;Stewart et al, 2009). Moreover, nearly 10 kg N ha À1 yr À1 of N deposition were reported in agricultural fields in Japan (Hayashi et al, 2007;Kimura et al, 2007).…”

Effects of environmental factors on temporal variation in annual carbon dioxide and nitrous oxide emissions from an unfertilized bare field on Gray Lowland soil in Mikasa, Hokkaido, Japan

“…Understanding the factors affecting the decomposition of SOM, quantifying the annual CO 2 emission from bare fields and clarifying the factors affecting temporal variations in annual CO 2 emissions from an unfertilized bare soil are needed to estimate C loss from soil. An understanding of these factors will provide beneficial information for the study of the effect of agricultural activities on C cycle or global warming over the long term for eco‐balance or life cycle analyses (Kimura et al. 2007; Koga et al.…”