Cover crop effects on spring soil water content and the implications for cover crop management in south coastal British Columbia
Soil water content in the spring is an important factor in making decisions on cultural operations. A 2-year study was conducted to determine the effects of fall planted cover crops on spring soil water content dynamics and to relate the water content to cover crop management in terms of field trafficability. Each year, cover crops were planted at two planting dates in the fall, late August and late September on a loamy, mixed, mesic Humaquept on the Fraser River delta, south coastal British Columbia. Treatments were bare (control), wheat, rye and spring barley. Soil samples were collected at approximately bi-weekly intervals beginning in early spring to determine soil water content. Plant samples were also obtained late in the spring to determine C:N ratio. Treatments affected soil water content differently at each sampling date. No differences in soil water content at depths 20�40 and 40�60 cm were observed. Critical soil water content value for trafficability was determined to be 0.32 kg kg-1. Cover crops attained critical C:N ratio of 31.7:1 when the soil water was still above the critical value. The results suggest that terminating the cover crop growth in the spring could best be done by either mowing or spraying the cover crops as opposed to incorporation in order to minimize compaction since the critical C:N ratio for net mineralization is achieved when the soil is still too wet.
Plantas de cobertura e qualidade química de Latossolo Amarelo sob plantio direto no cerrado maranhense
Aiming to evaluate the effect of cover plants over soil chemical attributes in the region of Balsas - Maranhao, samples of Oxisol under plant cover of millet [Pennisetum americanum (L.) Leeke], brachiaria (Brachiaria ruziziensis) and native Cerrado (mid-sized), were collected in three depths (0-0.10; 0.10-0.20 and 0.20-0.40 m). Plant cover of millet and brachiaria promoted an increase in soil pH and reductions in amounts of Al3+ and in saturation by Al3+, in relation to the area with native Cerrado. Major amounts of residue were verified on soil surface under native cerrado, due to greater input of plant residue and lower decomposition rate. Amounts of nutrients and levels of organic matter were higher in areas under millet and brachiaria cover, mainly in 0-0.10 e 0.10-0.20 m. depths. Brachiaria and millet cover plants were similar in relation to alterations promoted in chemical attributes of soil.
Intentional poisoning cases of animals with anticholinesterase pesticide-carbofuran in Sri Lanka.
Carbofuran is a broad spectrum insecticide and nematicide which inhibits acetyl cholinesterase. Several intentional poisoning cases of animals and birds including crows, dogs, cow, and elephant, using carbofuran were reported in Sri Lanka. Qualitative analysis of carbofuran in biological specimens was carried out using T.L.C and GC-MS. The quantitative analysis was carried out by HPLC using Zorbax Eclips XDB-C18 (150 x 4.6 mm I.D x 5 microm particle size) column with acetonitrile: water 25:75 v/v mobile phase and UV detection at 210 nm. The liquid-liquid extraction with chloroform was reproducible and sensitive. The procedure was validated in terms of linearity (0.996<r<0.999) for concentrations ranging from 1 to 200 microg/ml, repeatability (RSD 4.4% at 100 microg/ml, n=10) extraction recovery (91.7% at 100 microg/g, 77.3% at 20 microg/g), limit of detection (S/N ratio=3, 0.7 microg/ml) and limit of quantification (S/N ratio=10, 2.4 microg/ml). The method was found satisfactory and successfully applied in fatal cases of animals and birds due to carbofuran poisoning. The fatal carbofuran levels detected were in the range of 42-910 microg/g in crow's gizzard and contents, 50-800 microg/g in dog's stomach contents, 13-20 microg/g in dog's liver, 0.9 microg/g in cow's stomach and contents, 35 microg/g in elephant's stomach and contents.