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Soil quality degradation associated with resources scarcity is the major concern for the sustainability of conventional rice-wheat system in South Asia. Replacement of conventional management practices with conservation agriculture (CA) is required to improve soil quality. A field experiment was conducted to assess the effect of CA on soil physical (bulk density, penetration resistance, infiltration) and chemical (N, P, K, S, micronutrients) properties after 4 years in North-West India. There were four scenarios (Sc) namely conventional rice-wheat cropping system (Sc1); partial CA-based rice-wheat-mungbean system (RWMS) (Sc2); CA-based RWMS (Sc3); and CA-based maize-wheat-mungbean (Sc4) system. Sc2 (1.52 Mg m−3) showed significantly lower soil bulk density (BD). In Sc3 and Sc4, soil penetration resistance (SPR) was reduced and infiltration was improved compared to Sc1. Soil organic C was significantly higher in Sc4 than Sc1. Available N was 33% and 68% higher at 0–15 cm depth in Sc3 and Sc4, respectively, than Sc1. DTPA extractable Zn and Mn were significantly higher under Sc3 and Sc4 compared to Sc1. Omission study showed 30% saving in N and 50% in K in wheat after four years. Therefore, CA improved soil properties and nutrient availability and have potential to reduce external fertilizer inputs in long run.

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Rhodobacter sphaeroides is a gram-negative purple nonsulfur bacterium belonging to the alpha-3 subdivision of the Proteobacteria (49). This organism is capable of a wide range of metabolic lifestyles, exhibiting growth chemoautotrophically, photoautotrophically, photoheterotrophically, chemoheterotrophically, and diazotrophically (reviewed in reference 24). The ability of purple nonsulfur bacteria, as well as other bacterial species, to utilize dimethyl sulfoxide (DMSO) and trimethylamine N-oxide (TMAO) as terminal electron acceptors in the absence of oxygen for chemoheterotrophic growth has been well documented (12,23,52). Both DMSO and TMAO are commonly occurring compounds in nature and play roles in sulfur and nitrogen cycling (1).Under anoxic conditions in the presence of DMSO or TMAO and in the absence of light, R. sphaeroides can grow via a periplasmic DMSO reductase (DMSOR), which serves as the terminal electron acceptor in a cascade in which electrons are transferred from quinol to DMSO or TMAO (24). This process does not require the cytochrome bc 1 complex, and electrons are transferred from quinol to DMSOR via a membranebound b-type cytochrome and a periplasmic c-type cytochrome (25). DMSOR from both R. sphaeroides and the closely related bacterium R. capsulatus have been crystallized and shown to contain the molybdopterin cofactor (Moco) as the sole prosthetic group (for a review, see reference 21).Studies on the genetics of DMSO reduction in both R. sphaeroides and R. capsulatus have been limited mainly to several reports which describe the sequence of the gene encoding DMSOR (2, 22, 37, 51). The dmsA or dorA gene product has extensive homology to other molybdoenzymes such as biotin sulfoxide reductase and TMAO reductase (50). Recently, the sequences of two genes upstream of the dmsA gene of R. sphaeroides f. sp. denitrificans were reported (45). The dmsC and dmsB gene products were shown to be homologous to the torC and torD gene products, which encode a c-type cytochrome and a membrane protein, respectively, and it was suggested that the dmsCBA genes form a transcriptional unit, similar to the torCDA genes in E. coli (27). Studies from our laboratory revealed that R. sphaeroides 2.4.1 T possesses two different circular chromosomes, of ϳ3.0 Mbp (CI) and ϳ0.9 Mbp (CII) (42,43). A number of genes have been shown to be duplicated between CI and CII (5). In contrast, we have previously shown by Tn5 mutagenesis that some pathways, e.g., p-aminobenzoic acid, uracil, histidine, and thymine biosynthesis, are partitioned rather than duplicated between CI and CII (4). These results suggested that CII is an essential genomic element, having unique as well as shared and duplicated functions.Recently, we used a low-redundancy sequencing strategy for analysis of the genetic content of CII (5). We analyzed ϳ300 kb of unique DNA which identified approximately 200 putative open reading frames (ORFs) representing a wide variety of functions, e.g., amino acid biosynthesis, nutrient transporters, redox-active systems, ...

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Agricultural practices are believed to be the major anthropogenic source of enhanced nitrous oxide (N 2 O) gas emissions in New Zealand. Studies conducted in New Zealand generally suggest low N 2 O emission from pasture; however, there is little information for arable farming systems. This paper evaluates tillage and land use effects on N 2 O emissions using a closed chamber technique at an Ohakea silt loam (Gleyic luvisol) where winter oats (Avena sativa L.)/fodder maize (Zea mays L.) was double-cropped for 5 years. The tillage types included conventional tillage (CT) and no-tillage (NT) systems, and a permanent pasture (PP) was used as a control.Spatial variability in all treatments showed large inherent variations in N 2 O fluxes (a mean CV = 119%), which reflected natural soil heterogeneity, and perhaps the measurement technique used rather than the real differences due to the tillage and cropping systems evaluated. On an annualised basis, N 2 O emissions measured from December 1998 to September 1999 from the PP (1.66 kg N 2 O-N/ha per year or 19 g N 2 O-N/(m 2 h)) were significantly lower than the CT and NT fields averaging at 9.20 (or 105) and 12.0 (or 137) kg N 2 O-N/ha per year (or g N 2 O-N/(m 2 h)), respectively. However, there were no differences in N 2 O emission rates between the CT and NT treatments. Seedbed preparation using a power harrow which followed within a few days of first ploughing the CT field reduced N 2 O emissions by 65% within the first hour after power harrowing. However, N 2 O emission rates returned to the pre-power harrowing levels at the next sampling period, which was 1 month later.There was a strong relationship between log-transformed data of soil water content (SWC) and N 2 O emissions in all treatments with r = 0.73, 0.75 and 0.86 for the PP, CT and NT treatments, respectively. Seasonal variations in N 2 O emission from the PP were in the order of winter = autumn > summer. Although fluxes in the CT were higher in winter than in the autumn season, there were no differences between the summer and autumn data. The seasonal variations in N 2 O emission in the NT treatment were in the order of winter > autumn = summer.

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