Ai Leon

Factors controlling organic amendment application rate and long-term change in application rate in Japanese paddy field using longitudinal questionnaire survey dataset (the Basic Soil Environment Monitoring Project, Stationary Monitoring, 1979–1998)

Using data from a longitudinal survey (the Basic Soil Environment Monitoring Project, Stationary Monitoring, 1979–1998, launched by the Ministry of Agriculture, Forestry and Fisheries of Japan), it was found that livestock possession, soil type, utilization form of paddy fields and full-/part-time status of farmers were important factors controlling application rates of organic amendments (OA) in Japanese paddy fields. When data points were categorized in terms of these four factors, application rate of livestock waste compost (LWC) on the basis of fresh weight (FW) varied remarkably. Application rates of LWC decreased during the survey period, whereas rice straw residue (RSR) application rates increased. The smallest LWC application rate (average 0.3 ± 0.2 Mg FW ha−1 for the period between 1994 and 1998) was found among rice (Oryza sativa L.) single-cropping, poorly drained lowland paddy soils (PDLPS) including Histosols, with full-time farmers possessing no livestock. Even among rice single-cropping, the application rate was clearly larger (average 10.6 ± 0.5 Mg FW ha−1 for the period between 1979 and 1983) for non-poorly drained lowland paddy soils (non-PDLPS), with full-time farmers possessing livestock. Much greater than this was the LWC application rate for converted paddy fields (average 29.9 ± 4.3 Mg FW ha−1 for the period between 1989–1993), non-PDLPS, with full-time farmers possessing livestock. Accordingly, this study emphasizes the importance of categorizing data points at least in terms of soil type, utilization form of paddy fields, livestock possession and part- or full-time farming status when constructing an inventory, exploring changes in OA application rate, and making policy.

Estimation of total CH4 emission from Japanese rice paddies using a new estimation method based on the DNDC-Rice simulation model ☆

Methane (CH4) is a greenhouse gas, and paddy fields are one of its main anthropogenic sources. In Japan, country-specific emission factors (EFs) have been applied since 2003 to estimate national-scale CH4 emission from paddy field. However, these EFs did not consider the effects of factors that influence CH4 emission (e.g., amount of organic C inputs, field drainage rate, climate) and can therefore produce estimates with high uncertainty. To improve the reliability of national-scale estimates, we revised the EFs based on simulations by the DeNitrification-DeComposition-Rice (DNDC-Rice) model in a previous study. Here, we estimated total CH4 emission from paddy fields in Japan from 1990 to 2010 using these revised EFs and databases on independent variables that influence emission (organic C application rate, paddy area, proportions of paddy area for each drainage rate class and water management regime). CH4 emission ranged from 323 to 455ktCyr-1 (1.1 to 2.2 times the range of 206 to 285ktCyr-1 calculated using previous EFs). Although our method may have overestimated CH4 emissions, most of the abovementioned differences were presumably caused by underestimation by the previous method due to a lack of emission data from slow-drainage fields, lower organic C inputs than recent levels, neglect of regional climatic differences, and underestimation of the area of continuously flooded paddies. Our estimate (406ktC in 2000) was higher than that by the IPCC Tier 1 method (305ktC in 2000), presumably because regional variations in CH4 emission rates are not accounted for by the Tier 1 method.

Assessment of new functional units for agrivoltaic systems

In agrivoltaic systems, photovoltaic (PV) modules are ground-mounted between crops replacing a part of greenhouse or are set below or above the cover film of greenhouse; these can provide solutions with respect to land competition and climate change mitigation. These systems have certain additional functions, namely, sunlight sharing, land sharing and power generation, as compared to the conventional agricultural production systems. These new functions are not adequately performed by traditionally used functional units (FUs), such as the mass- or the area-based FU, in agricultural life cycle assessment (LCA). Therefore, this study proposed new FUs for agrivoltaic systems, namely the modified area-based FU and the monetary-based FU. The modified area-based FU was derived by adding area covered by PV modules to the cultivated area addressing the function of land sharing. The monetary-based FU was derived by adding the prices of crops and electricity addressing the function of the system as a producer of differently valued market goods. The traditional area-based FU is based on the function of solar sharing because crop cultivation and power generation share the same sunlight falling on the same land. These new and traditional FUs were applied to a tomato greenhouse, with and without organic photovoltaics, as a case study of Japan. A combination of traditional and new FUs helps to maintain focus on crop production as the primary function of agricultural land and to better understand the environmental impacts of agrivoltaic systems. Finally, as the sharing of sunlight and land happen simultaneously, a method that addresses both these functions while reporting LCA results was considered.

Livestock Waste, Potential Manure Production and Its Use in Japan in 1980 and 2010

ABSTRACT The aim of this work is to quantify life cycle of nutrient elements for soil and crops, namely nitrogen (N), phosphorus (P), potassium (K), and carbon (C), from feed of livestock to potential of manure production via livestock waste, a potentially sustainable application of manure for farmland soils in Japan in 1980 and 2010. We also estimated real application to farmland from a questionnaire by setting several hypotheses to collect real proportion of farm households, because the questionnaire was intended for full-time farms, the proportion of which is minor within all farms. The questionnaire survey was conducted five times, from 1979 to 2003 for 5-year intervals, and one time from 2008 to 2013. These data were set for the years 1980 and 2010. As a result, the livestock feed became lower in P and K input, livestock got better nutrient use efficiency for livestock products, and waste production was reduced in 2010 than 1980. Potential of manure production was decreased in 2010 from what it was in 1980; however, estimated application of manure was also reduced from full to half of potential of manure production. Application level of manure in 1980 was higher than the amount that farmland received sustainably. This might be allowed for enhancing soil fertility; as such activity was also needed at that time. On the other hand, in 2010, application of manure was estimated to be less than half of that in 1980 and had not reached sustainable application level. From 1980 to 2010, manure application had been decreased, even though trends of manure application for crops per area were different in each crop. Although lack or surplus of manure might not always explain trend of soil fertility, we need continues survey of soil fertilities to check and monitor to grasp the trend of soil fertility indicated by total C and N, available N, P, and K, as well as estimate application of manure to farmland.