Effects of Organic Manure Application with Chemical Fertilizers on Nutrient Absorption and Yield of Rice in Hunan of Southern China

To evaluate the effect of organic manure application with chemical fertilizers on rice yield and soil fertility under long-term double-rice cropping system, a six year field experiment was conducted continually in the paddy soil derived from Quaternary red clay in Hunan Province of southern China. Four different treatments, i.e., no nitrogen with chemical P and K （PK）, swine manure only （M）, N, P and K chemical fertilizers only （NPK）, and half chemical fertilizers combined with half swine manure （NPKM） with four replications were included. Each N, P and K application rate was the same at all the treatments （except the N application rate at PK） and N application rate was 150 kg N ha^-1. All fertilizers were applied to soil tillage layer with once application as baseal fertilizers. The nutrients uptake rate, grain yield, nitrogen use efficiency, and soil organic matter content at each treatment were investigated. The NPKM treatment achieved the highest mean annual yield of 12.2 t ha^-1 （68% higher than that of PK）. Higher dry matter accumulation and nutrients absorption were observed during the middle-late growth period in the NPKM treatment, with higher panicle number per unit and filled-grain number per panicle. Its average nitrogen use efficiency was 36.3% and soil organic matter increased by 18.5% during the experimental period in the NPKM treatment, which were significantly higher than those in the NPK treatment. Organic manure application with chemical fertilizers increased the yield and nitrogen use efficiency of rice, reduced the risk of environmental pollution and improved soil fertility greatly. It could be a good practical technique that protects the environment and raises the rice yield in this region.

Effects of Biochar Particle Size on Methane Emissions from Rice Cultivation

Biochar amendment is generally recognized as an effective mitigation option of methane(CH_(4))emissions from rice cultivation.Although its mitigation mechanisms are not well understood,the potential relevance of surface area and porosity of biochar has been discussed.This study aimed to evaluate the application of different biochar particle sizes on CH_(4) production,oxidation,and emissions from rice cultivation in a clay loam soil,based on the assumption that porosity and surface area of biochar are directly related to its mitigation effects.Rice was grown under greenhouse conditions for two growing seasons,either with 0.5–2 mm(small,SB)or with 2–4 mm(large,LB)biochar.The results show that both sizes of biochar increased soil pH and redox potential(Eh)during rice growth.Soil dissolved organic carbon(DOC),nitrate(NO^(−)_(3)),and sulfate(SO^(2−)_(4))also increased under both biochar amendments,but size effects were not observed.SB and LB suppressed the abundance of CH_(4) producers(methanogens)but stimulated the abundance of CH_(4) consumers(methanotrophs).The increase of soil Eh and electron acceptors(NO^(−)_(3)and SO^(2−)_(4))indicated the increase in soil oxidation capacity is a barrier to CH_(4) production by methanogens in both biochar treatments.Laboratory incubation experiments showed that CH_(4) production activity was significantly(p≤0.05)reduced by 18.5%using SB and by 11.3%using LB compared to the control.In contrast,the stimulation of methanotrophs promoted greater CH_(4) oxidation activity by 15.0%in SB and 18.7%in LB compared to the control.It shows that CH_(4) production was reduced more by larger surface area biochar(SB),while a greater increase in CH_(4) oxidation was found using larger pore volume biochar(LB).The effects on CH_(4) production were more pronounced than those on CH_(4) oxidation,resulting in a greater reduction of cumulative CH_(4) emissions by SB than LB(by 26.6%and 19.9%compared to control,respectively).

施用有机物对水稻田甲烷排放的影响

在水稻整个生育期内,利用密闭箱法测定了日本四个不同地点稻田的甲烷排放量。观察结果表明甲烷通量季节性变化较大。甲烷排放与水稻田土壤氧化还原电位降低密切相关,排水落干和追施化肥能显著降低甲烷排放。甲烷排放量明显与土壤类型有关,泥炭土稻田排放最高(在耕作期内甲烷排放量为44.8克/米~2),其次是潜育化土稻田(为8.0～27.0),浅暗色土稻田,甲烷排放量极低(为0.6～12.6)。以6～9吨/公顷的水稻秸杆施入稻田,甲烷排放量增加了1.8～3.5倍。施用堆肥甲烷排放量有少量增长。每个小区中甲烷的年排放量与淹水前采集的水田土壤易矿化碳(RMC)含量呈正相关,RMC是影响淹水土壤甲烷排放的主要因素之一。

Challenges of reducing excess nitrogen in Japanese agroecosystems

Fertilizer N use in Japan has decreased by about 30% from 1960 to 2000, while keeping a little increase in cereal yields. This has resulted in a significant increase in apparent nitrogen use efficiency, in particular for rice. On the other hand, national N load on the environment associated with the production and consumption of domestic and imported agricultural products has almost tripled during this period, mainly due to the dramatic increase of imports of food and feedstuffs. The environmental problems, including water and air pollution, caused by the excessive loads of N are serious public concerns and there is an urgent need to minimize N losses from agricultural production. In order to meet the necessity for reducing the environmental impacts by excess N, political and technological measures have been taken at regional and country levels. In recent years, the Japanese government has embarked on a series of policies to encourage transition to an environmentally conscious agriculture. Promoting proper material circulation with reducing fertilizer impact and utilizing biomass and livestock wastes is emphasized in these policies. The effectiveness of environmental assessment and planning for reducing regional and national N load has been discussed. Implementation of environmentally friendly technologies and management, both conventional and innovational, have been developed and adopted in Japanese agriculture. The effectiveness of conventional technologies in reducing environmental reactive N has been re-evaluated. Innovative technologies, such as use of controlled availability fertilizers and livestock wastes compost pellets, are being investigated and extended. A comprehensive approach that applies political and technological measures with closer cooperation is necessary to control reactive N in the environment.