Agricultural nitrogen and phosphorus balances of Korea and Japan: Highest nutrient surplus among OECD member countries.

Excessive nutrient balance is a very crucial issue for environmental hazards. The constant addition of high-amounts of nutrient sources in agricultural production generates negative environmental conditions in Korea and Japan yet to be resolved. Therefore, it is obligatory to comprehend the nutrient (nitrogen (N) and phosphorus (P)) balance that is assessed by the difference between nutrient input and output in the soil surface in Korea and Japan. Among 34 Economic Co-operation and Development (OECD) countries, Korea and Japan had the highest N and P balances and thus both countries are primarily responsible for severe environmental pollution via nutrient release. The cultivable land area in both countries has constantly decreased during 1990-2017 at approximately 20 and 15% in Korea and Japan, respectively. Even N and P use efficiency sharply decreased with increasing N and P balance in both targeted countries. Japanese P balance, Korean N and P balances were decreased after the mid-1990s whereas, Japanese N balance almost unchanged for the last 28 years. Unlike chemical fertilizer input, Korean manure input level significantly increased from 78 kg N ha-1 in 1990 to 157 kg N ha-1 in 2017. Japanese manure input level was higher than that of chemical fertilizer without any big change for the last 28 years. The lion share of high N and P balance in both countries could generate from manure inputs, therefore, the number of livestock and their produced debris need to be used with more cautious for the reduction of national N and P surpluses at a benchmark level. These findings ensure to make a more environment friendly policy that can further reduce nutrient balance as well as improve soil health.

Eco-friendly yield-scaled global warming potential assists to determine the right rate of nitrogen in rice system: A systematic literature review.

Rice paddies are one of the largest greenhouse gases (GHGs) facilitators that are predominantly regulated by nitrogen (N) fertilization. Optimization of N uses based on the yield has been tried a long since, however, the improvement of the state-of-the-art technologies and the stiffness of global warming need to readjust N rate. Albeit, few individual studies started to, herein attempted as a systematic review to generalize the optimal N rate that minimizes global warming potential (GWP) concurrently provides sufficient yield in the rice system. To satisfy mounted food demand with inadequate land & less environmental impact, GHGs emissions are increasingly evaluated as yield-scaled basis. This systematic review (20 published studies consisting of 21 study sites and 190 observations) aimed to test the hypothesis that the lowest yield-scaled GWP would provide the minimum GWP of CH4 and N2O emissions from rice system at near optimal yields. Results revealed that there was a strong polynomial quadratic relationship between CH4 emissions and N rate and strong positive correlation between N2O emissions and N rate. Compared to control the low N dose emitted less (23%) CH4 whereas high N dose emitted higher (63%) CH4 emission. The highest N2O emission observed at moderated N level. In total GWP, about 96% and 4%, GHG was emitted as CH4 and N2O, respectively. The mean GWP of CH4 and N2O emissions from rice was 5758 kg CO2 eq ha-1. The least yield-scaled GWP (0.7565 (kg CO2 eq. ha-1)) was recorded at 190 kg N ha-1 that provided the near utmost yield. This dose could be a suitable dose in midseason drainage managed rice systems especially in tropical and subtropical climatic conditions. This yield-scaled GWP supports the concept of win-win for food security and environmental aspects through balancing between viable rice productivity and maintaining convincing greenhouse gases.