Effects of different organic fertilizers on nitrous oxide and methane emissions from double-cropping rice fields

Rice fields are a major source of greenhouse gases,such as nitrous oxide (N_(2)O) and methane (CH_(4)).Organic fertilizers may potentially replace inorganic fertilizers to meet the nitrogen requirement for rice growth;however,the simultaneous effects of organic fertilizers on N_(2)O and CH_(4)emissions and crop yield in paddy fields remain poorly understood and quantified.In this study,experimental plots were established in conventional double-cropping paddy fields in the Pearl River Delta,China,including an unfertilized control and five fertilizer treatments with fresh organic fertilizer (FOF),successively composted organic fertilizer (SOF),chemically composted organic fertilizer (COF),COF supplemented with inorganic fertilizer (COIF),and chemical fertilizers (CFs)(TFOF,TSOF,TCOF,TCOIF,and TCF,respectively).Paddy field soils behaved simultaneously as an N_(2)O sink (cumulative N_(2)O emission:-196 to-381 g N ha^(-1)) and as a CH_(4)source (cumulative CH_(4)emission:719 to 2 178 kg ha^(-1)).Compared to CFs,the effects of organic fertilizers on N_(2)O emission were not significant.In contrast,total annual CH_(4)emission increased by 157%,132%,125%,and 37%in TFOF,TCOF,TSOF,and TCOIF,respectively,compared to TCF.In TCOIF,rice yield was maintained,while CH_(4)emission was not significantly increased from the paddy fields characterized by a prolonged flood period.An important next step is to extend these field-based measurements to larger rice cultivation areas to quantify the regional and national-scale impacts on greenhouse gas emissions and to help determine the optimum practice for fertilizer use.

Effects of organic fertilizers produced using different techniques on rice grain yield and ammonia volatilization in double-cropping rice fields

Ammonia(NH_(3)) volatilization from rice fields contributes to poor air quality and indicates low nitrogen use efficiency. Although organic fertilizers can meet the nitrogen requirement for rice growth, the simultaneous effects of organic fertilizers on NH_(3) volatilization and rice yield in paddy fields are poorly understood and quantified. To address this gap in our knowledge, experimental field plots were established in a conventional double-cropping paddy field in the Pearl River Delta region, southern China. Five fertilizer treatments were used besides the control with no fertilizer: fresh organic fertilizer, successively composted organic fertilizer, chemically composted organic fertilizer, mixture of chemically composted organic fertilizer with inorganic fertilizer, and chemical fertilizer. Ammonia volatilization was measured using a batch-type airflow enclosure method. No significant differences in grain yield were observed among organic and chemical fertilizer treatments. However, compared with chemical fertilizer, chemically composted organic fertilizer and successively composted organic fertilizer significantly decreased total NH_(3) volatilization by 70% and 68%, respectively. The ammonium-nitrogen concentration in field surface water correlated strongly(P < 0.01) and positively with NH_(3) volatilization across fertilization treatments. Our findings demonstrate that chemically composted organic fertilizer can sustain rice yield while reducing NH_(3) volatilization. An important future step is to promote these field measurements to similar rice cultivation areas to quantify the regional-and national-scale impact on air quality and nitrogen deposition in sensitive areas, and to design and implement better fertilizer management practices.

Genome sequencing and analysis of a granulovirus isolated from the Asiatic rice leafroller, Cnaphalocrocis medinalis

The complete genome of Cnaphalocrocis medinalis granulovirus(CnmeGV) from a serious migratory rice pest, Cnaphalocrocis medinalis(Lepidoptera: Pyralidae), was sequenced using the Roche 454 Genome Sequencer FLX system(GS FLX) with shotgun strategy and assembled by Roche GS De Novo assembler software. Its circular double-stranded genome is 111,246 bp in size with a high A+T content of 64.8% and codes for 118 putative open reading frames(ORFs). It contains 37 conserved baculovirus core ORFs, 13 unique ORFs, 26 ORFs that were found in all Lepidoptera baculoviruses and 42 common ORFs. The analysis of nucleotide sequence repeats revealed that the CnmeGV genome differs from the rest of sequenced GVs by a 23 kb and a 17 kb gene block inversions, and does not contain any typical homologous region(hr) except for a region of non-hr-like sequence. Chitinase and cathepsin genes, which are reported to have major roles in the liquefaction of the hosts, were not found in the CnmeGV genome, which explains why CnmeGV infected insects do not show the phenotype of typical liquefaction. Phylogenetic analysis,based on the 37 core baculovirus genes, indicates that CnmeGV is closely related to Adoxophyes orana granulovirus. The genome analysis would contribute to the functional research of CnmeGV,and would benefit to the utilization of CnmeGV as pest control reagent for rice production.