Abstract
The effects of conversion from staple rice to forage rice on carbon and greenhouse gas (GHG) balances in a paddy field were evaluated. A staple rice plot without the application of livestock manure compost (LMC, S − M plot) and forage rice plots with and without the application of LMC, derived mainly from cattle (2 kg−FW m−2, F + M and F − M plots, respectively), were established. CH4 and N2O fluxes and CO2 flux from a bare soil plot for organic matter decomposition (OMD) were measured. The carbon budget was calculated by subtracting the OMD, CH4 emission, and harvested grain and straw (forage rice only) from the net primary production and LMC. The net GHG balance was calculated by integrating them as CO2 equivalents. There were no significant differences in GHG flux among the plots. Compared to the carbon loss in the S − M plot, the loss increased by harvesting straw and was mitigated by LMC application. The net GHG emission in the F + M plot was significantly lower than that in other plots (1.78 and 2.63−2.77 kg CO2-eq m−2 year−1, respectively). There is a possibility that GHG emissions could be suppressed by forage rice cultivation with the application of LMC.
Highlights
The Japanese self-sufficiency rate of feed is 27% [1], and livestock production in Japan is highly dependent on imported feed which has an unstable price
There is a possibility that greenhouse gas (GHG) emissions could be suppressed by forage rice cultivation with the application of LMC
There were no significant differences in soil temperature among the plots
Summary
The Japanese self-sufficiency rate of feed is 27% (total digestible nutrients base, average from 2013−2016) [1], and livestock production in Japan is highly dependent on imported feed which has an unstable price. In Japanese paddy fields, conversion from the cultivation of staple rice (Oryza sativa L.) to other crops (adjustment of rice production) has been conducted over 40 years to suppress the over-production of rice. The production of forage crops, such as grass and maize, in uplands converted from paddy fields has been recommended to improve the feed self-sufficiency rate. Forage crop production in converted paddy fields with poor drainage is generally low and it tends to be unstable, and the improvement of drainage through the construction of open ditches and underdrains is necessary. Forage rice consists of “whole-crop silage (WCS)”, which utilizes panicles, leaves, and stems, and “rice for feed”, which utilizes rice grains or brown rice only
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