Compatible and antagonistic mixtures of diclofop-methyl and flamprop-methyl with herbicides used to control broad-leaved weeds

In glasshouse experiments, the addition of four ‘pyridine herbicides’ (substituted picolinic and pyridyloxyacetic acids) to either diclofop-methyl or flamprop-methyl had little effect on wild oat (Avena fatua) control. This contrasts with the serious antagonisms which occur with 2, 4-D and 2, 3, 6-TBA. With wild and cultivated oat, l'-methylheptyl (4-amino-3, 5-dichloro-6-fluoro-2-pyridyl)oxyacetate (Dowco 433) was completely compatible with diclofop-methyl and flamprop-methyl, and there was evidence that its presence improved the control of wild oats. Picloram, 3, 6-dichloropicolinic acid and triclopyr had only slight effects on phytotoxicity. The control of cleavers (Galium aparine) by picloram, triclopyr and Dowco 433 was not significantly reduced by addition of flamprop-methyl. Preliminary metabolism studies suggest that picloram does not greatly increase the rate of diclofop detoxification as do 2, 4-D and 2, 3, 6-TBA, and the observed compatibility could well be a direct consequence of this. The absence in these greenhouse experiments of serious antagonism between the pyridine herbicides and diclofop-methyl or flamprop-methyl suggests that ‘tank mixes’ of these herbicides could be used for the control of both broad-leaved weeds and wild oats.     

Distribution and thermal stability of physically and chemically protected organic matter fractions in soils across different ecosystems

Accrual of carbon (C) and nitrogen (N) in soil is a significant and realizable management option to mitigate climate change; thus, a clear understanding of the mechanisms controlling the persistence of C and N in soil organic matter (SOM) across different ecosystems has never been more needed. Here, we investigated SOM distribution between physically and chemically stabilized fractions in soils from a variety of ecosystems (i.e., coniferous and broadleaved forest soils, grassland soils, technosols, and agricultural soils). Using elemental and thermal analyses, we examined changes in the quantity and quality of physically fractionated SOM pools characterized by different mechanisms of protection from decomposition. Independently of the ecosystem type, most of the organic C and total N were found in the mineral-associated SOM pool, known to be protected mainly by chemical mechanisms. Indexes of thermal stability and C/N ratio of this heavy SOM fraction were lower (especially in agricultural soils) compared to light SOM fractions found free or occluded in aggregates, and suggested a marked presence of inherently labile compounds. Our results confirm that the association of labile organic molecules with soil minerals is a major stabilization mechanism of SOM, and demonstrate that this is a generalizable finding occurring across different mineral soils and ecosystems.     

The phytotoxicity of mercury vapor

Seed germination and early growth were unexpectedly resistant to Hg-vapor at air saturation levels (14 μg L^?1). Among 15 species and cultivars tested, inhibition of shoot or root growth in excess of 50% was not seen, but occasional stimulation was noted. During extended (70 to 75 days) cultivation at Hg-vapor saturation, inhibitory effects on growth increased with time, and later effects on abscission and necrosis were more severe. Seven days exposures confirmed juvenile resistance at air saturation levels and mature plant sensitivity, expressed by massive abscission at 0.05 μg L^?1. It is suggested that Hg-vapor accelerates senescence-related processes via elevated ethylene production. Evidence suggests that elemental Hg, not ionic Hg, is the active toxicant. An ecophysiological role for Hg-vapor in volcanically active regions is suggested.     

A Cross-sectional Study of Reproductive Performance of Smallholder Dairy Cows in Coastal Tanzania

A retrospective cross-sectional study was conducted on 200 randomly selected smallholder farms from a mixed dairy farming system in Tanga, Tanzania, between January and April 1999. We estimated the frequency and determinants of long calving interval (LCI), retention of fetal membrane (RFM), dystocia, and abortion in smallholder crossbred cattle and explored birth trends. The mean calving interval was 500 days and birth rate was 65 per 100 cow-years. Dystocia was reported to affect 58% of calvings, and 17.2% of animals suffered RFM. Using mixed effect models, the variables associated with LCI, RFM and dystocia were breed, level of exotic blood and condition score. Zebu breeding was associated with LCI (odds ratio (OR) = 2.3, p = 0.041) and Friesian breeding with lower odds for RF (OR = 0.26, p = 0.020). Animals with higher levels of exotic blood had lower odds for evidence of dystocia (OR = 0.45, p =0.021). Evidence of dystocia was significantly associated with poor condition score (P = −1.10, p = 0.001). Our observations suggest that LCIs are common in smallholder dairy farms in this region and a likely source of economic loss. Dystocia, RFM, poor condition score and mineral deficiency were common problems and were possibly linked to LCI.