. 1999. Tillage effects on the dynamics of total and corn-residue-derived soil organic matter in two southern Ontario soils. Can. J. Soil Sci. 79: 473-480. Agricultural management practices affect the dynamics of soil organic matter (SOM) by influencing the amount of plant residues returned to the soil and rate of residue and SOM decomposition. Total organic C and δ 13 C of soil were measured in two field experiments involving corn cropping to determine the effect of tillage practices on SOM dynamics. Minimum tillage (MT) and no tillage (NT) had no significant impact on the soil C compared with conventional tillage (CT) in the 0-to 50-cm soil depth sampled at both sites. Continuous corn under MT and CT for 29 yr in a silt loam soil sequestered 61-65 g m -2 yr -1 of corn-derived C (C 4 -C), and it accounted for 25-26% of the total C in the 0-to 50-cm depth. In a sandy loam soil cropped to corn for 6 yr, SOM contained 10 and 8.4% C 4 -C under CT and NT, respectively. Reduced tillage practices altered the distribution of C 4 -C in soil, causing the surface (0-5 cm) soil of reduced tillage (MT and NT) plots to have higher amounts of C 4 -C compared to CT. Tillage practices did not affect the turnover of C 3 -C in soil.Key words: Soil organic matter, 13 C natural abundance, tillage practices Wanniarachchi, S. D., Voroney, R. P., Vyn, T. J., Beyaert, R. P. et MacKenzie, A. F. 1999. Effets du travail du sol sur la ciné-tique de la matière organique totale et de la fraction dérivée des restes de culture du maïs dans deux sols du sud de l'Ontario. Can. J. Soil Sci. 79: 473-480. Les pratiques agronomiques se répercutent sur la cinétique de la matière organique du sol (MOS) en jouant sur la quantité de restes de culture restitués au sol ainsi que sur le taux de décomposition de ces résidus et de la MOS. Nous avons mesuré le C organique total et le δ 13 C du sol dans deux expériences au champ sous culture de maïs, pour établir l'effet des pratiques de travail du sol sur la cinétique de la MOS. Le travail minimum (TM) et le semis direct (SD) ne donnaient lieu à aucun effet significatif par comparaison avec le travail classique (TC), sur le C du sol mesuré à partir d'échantillons de sol prélevés aux deux emplacements, dans la tranche de 0 à 50 cm de profondeur. Le maïs cultivé en continu en régimesTM et SD pendant 29 ans dans le loam limoneux (Elora) retenait 61-65 g m -2 an -1 de carbone (type C 4 ) et il comptait pour 25-26 % du carbone total récupéré dans la tranche de 0 à 50 cm. Dans le loam sableux (Delhi) cultivé en maïs depuis 6 ans, la MOS contenait, respectivement, 10 et 8,4 % C de type C 4 en régimes TC et SD. Les régimes de travail réduit (TM et SD) modifiaient la réparti-tion de C de type C 4 dans le sol, les 5 cm supérieurs des sols ainsi conduits produisant une plus forte proportion de C de type C 4 par rapport au carbone total que les sols conduits en TC. Les pratiques de travail du sol n'ont pas eu d'effet sur le renouvellement du C de type C 3 dans le sol.

The availability of paddy husk (PH) as a litter material for poultry production is decreasing. The objective of the present study was to determine the suitability of refused tea (RT), a waste generated during the processing of green leaves into black tea, as alternative litter material. Three experiments using completely randomized design were conducted for PH and RT each alone or as mixtures to determine the effects of the type of litter material on growth performance, behaviour of broilers, litter characteristics, and litter ammonia emission. In experiment one, 300 male broilers (Cobb-500) chicks were raised from day 5 to 21 on ten-floor pens (1.5m 2 ), each provided with either PH or RT as the litter material. Five and three PH and RT mixtures (v/v) were used in experiment two and three, respectively to raise broilers (n=300 in each experiment) from day 21 to 42. The type of litter material had no significant effect (P>0.05) on growth performances, hock burn damage score, bird's cleanliness score and dressing percentage. Compared to PH, RT litter reported a significantly (P<0.05) higher bulk density, N content and caked surface area and tend to have a higher moisture level (p<0.10). Compared to PH alone, RT alone or 1:1 PH:RT litter reduced the emission of ammonia by 53.6 and 34%, respectively. Percentage time spent on foraging was significantly (P<0.05) higher on PH than on RT. The time spent on and the frequency of inter-bird interactions were significantly (P<0.05) higher among the birds raised on RT, compared to those kept on PH. The study concluded that RT can be used as an alternative litter material for broilers. Other advantages of RT litter were the lower ammonia emission and higher litter N contents. Higher litter moisture content and incidence of caking were the disadvantages of RT as litter material.

Wanniarachchi, S. D. and Voroney, R. P. 1997. Phytotoxicity of canola residues: Release of water-soluble phytotoxins. Can. J. Soil Sci. 77: 535-541. Phytotoxicity of root, stem and leaf residues of canola (Brassica napus L.) was studied in a laboratory incubation for 8 wk. Bioassays were conducted with corn (Zea mays L.), barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) seeds to determine the relative toxicity of residue extracts. The release of volatile fatty acids (VFAs) and phenolic compounds (PCs) during incubation was studied to assess the role of these compounds in phytotoxicity. Canola residue extracts significantly inhibited (P ≤ 0.01) seedling growth (coleoptile and radicle lengths) of all crop species tested, with leaf and root residues causing the greatest and least toxicity, respectively. Incubation temperature had no impact on the toxicity of extracts. All residue extracts had VFAs prior to and during the incubation, with leaf residues producing relatively high levels of VFAs. The release of VFAs declined drastically during the incubation period. The release of PCs, measured as total phenolic compounds in extracts, was highest in leaf residues and remained higher than those of root or stem residues. Toxicity of residue extracts was not related to the amounts of VFAs and PCs found. However, toxicity appeared to be most related to the presence of total phenolic compounds in residue extracts.Key words: Phytotoxicity, canola residues, volatile fatty acids, phenolic compounds, residue decomposition Wanniarachchi, S. D. et Voroney, R. P. 1997. Phytotoxicité des restes de culture du colza canola : relargage de phytotoxines hydrosolubles. Can. J. Soil Sci. 77: 535-541. Nous avons étudié pendant 8 semaines en laboratoire d'incubation la phytotoxicité relative des restes de racines, de tiges et de feuilles laissés par une culture de colza canola. Des tests biologiques étaient conduits sur des graines de maïs (Zea mays L.), d'orge (Hordeum vulgare L.) et de blé (Triticum aestivum L.) pour déterminer la toxicité relative des extraits des résidus. On cherchait également à établir le rôle des acides gras volatils (AGV) et des composés phéno-liques (Cp) dégagés au cours de l'incubation, dans les phénomènes de phytotoxicité. Tous les extraits inhibaient significativement (P ≤ 0,01) la croissance au départ, longueur du coléoptile et de la radicules, chez les 3 espèces de céréale, les restes de feuilles et de racines manifestant, respectivement, la plus forte et la plus faible toxicité. La température d'incubation n'avait pas d'effet sur la toxicité des extraits. Tous les extraits produisaient des AGV avant et "pendant" l'incubation. Le dégagement d'AGV diminuait considérablement tout au long de l'incubation. Ce sont les extraits de restes foliaires qui généraient le plus de composés phéno-liques (mesurés en composés phénoliques totaux). La toxicité des extraits était sans rapport avec les quantités observées pour l'un ou l'autre des divers AGV et Cp. Elle manifestait, toutefois, une relation particulière...

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The effect of different combinations of vermicompost and coir dust on microbial respiration and nitrogen mineralization in soil was studied under laboratory conditions. Treatment with 75% vermicompost and 25% coir dust (T2) demonstrated the highest carbon mineralization and NH+4-N contents followed by treatment T1 (100% vermicompost) and T3 (50% vermicompost and 50% coir dust). Despite the varied NO3-N contents at the initial stages of incubation, the NO3-N content steadily increased for all the treatments at day 49 onwards. The highest NO3-N content was observed in T1 followed by that in T2 and T3. Such studies need be conducted under field conditions to reach a definite conclusion. Key Words: Vermicompost; coir dust; mineralization. DOI: 10.3329/bjar.v34i4.5830Bangladesh J. Agril. Res. 34(4) : 537-543, December 2009