Decomposition of Bt and non-Bt corn hybrid residues in the field. Nutrient Cycling in Agroecosystems

Results of a previous laboratory study indicated that six transgenic crops expressing the Cry1Ab insecticidal protein from Bacillus thuringiensis (Bt) decomposed at a slower rate than their respective non-Bt isolines. Consequently, litter decomposition rates, nitrogen cycling, and carbon pools may change in agricultural systems as the result of the widespread use of Bt crops. In this study, we assessed the decomposition rates and chemical composition of commonly grown hybrids of Bt and non-Bt isolines of corn (Zea mays L.) in the field. Leaves, stalks, and cobs from two Bt corn hybrids (Pioneer 34N44 Bt and NC+ 4990 Bt) and their non-Bt isolines (Pioneer 34N43 and NC+ 4880) were analyzed for biomass fractions (soluble, hemicellulose, cellulose, and lignin) and total C and N content. Litterbags containing these residues were buried at a depth of 10 cm in a Holdrege silt loam (fine-silty, mixed, mesic Typic Argiustolls) soil and recovered 5, 11, 17, and 23 months after placement in the field. There were no differences in the rates of decomposition and mass of C remaining over time between the Bt and non-Bt corn residues. Plant parts differed in decomposition rates where leaves > stalks > cobs. There were differences in total C, total N, biomass fractions, and C:N ratios between initial Bt and non-Bt corn residues, and between companies (NC+ and Pioneer), however, these differences did not result in differences in their rates of decomposition or mass of C remaining over time. For each plant part, there were no differences in lignin content between the Bt and non-Bt residues. These data suggest that the Bt and non-Bt corn hybrids used in this study should not cause differences in carbon sequestration when their residues decompose under similar environmental conditions

Decomposition of Bt and non-Bt corn hybrid residues in the field. Nutrient Cycling in Agroecosystems

Results of a previous laboratory study indicated that six transgenic crops expressing the Cry1Ab insecticidal protein from Bacillus thuringiensis (Bt) decomposed at a slower rate than their respective non-Bt isolines. Consequently, litter decomposition rates, nitrogen cycling, and carbon pools may change in agricultural systems as the result of the widespread use of Bt crops. In this study, we assessed the decomposition rates and chemical composition of commonly grown hybrids of Bt and non-Bt isolines of corn (Zea mays L.) in the field. Leaves, stalks, and cobs from two Bt corn hybrids (Pioneer 34N44 Bt and NC+ 4990 Bt) and their non-Bt isolines (Pioneer 34N43 and NC+ 4880) were analyzed for biomass fractions (soluble, hemicellulose, cellulose, and lignin) and total C and N content. Litterbags containing these residues were buried at a depth of 10 cm in a Holdrege silt loam (fine-silty, mixed, mesic Typic Argiustolls) soil and recovered 5, 11, 17, and 23 months after placement in the field. There were no differences in the rates of decomposition and mass of C remaining over time between the Bt and non-Bt corn residues. Plant parts differed in decomposition rates where leaves > stalks > cobs. There were differences in total C, total N, biomass fractions, and C:N ratios between initial Bt and non-Bt corn residues, and between companies (NC+ and Pioneer), however, these differences did not result in differences in their rates of decomposition or mass of C remaining over time. For each plant part, there were no differences in lignin content between the Bt and non-Bt residues. These data suggest that the Bt and non-Bt corn hybrids used in this study should not cause differences in carbon sequestration when their residues decompose under similar environmental conditions

Seeding uniformity for vacuum precision seeders Uniformidade de semeaduras para semeadeiras de precisão a vácuo

The performance of three vacuum precision seeders was investigated in a field study. Seeding uniformity was determined in three different within-row distances: 14, 18 and 21 cm. The seeders were operated at 1.8, 3.6, 5.4 and 7.2 km h-1. Successive seed spacing along of 3 m of row was measured in three replications on each row. For evaluating the seeding uniformity of seeders, seed spacings were analyzed using the methods (MISS, MULT, QFI and PREC). There were no differences between seeders. For P < 0.01, operating speed affected MISS and QFI values, and the within-row seed spacing affected MULT and PREC values. The best operating speed was 1.8 km h-1 because of the highest QFI value (88.5%). There was no difference between 1.8 and 3.6 km h-1. The speeds, 1.8 and 3.6 km h-1, were different from 5.4 and 7.2 km h-1. The best within-row distance was 18 cm because the QFI value was higher than those of 14 and 20 cm, 86.9%, 82.0% and 81.8%, respectively. The best PREC value was obtained for 21 cm within-row distance (17.4%). PREC values were acceptable for precision seeding in all trials.<br>O comportamento de três semeadeiras de precisão a vácuo foi investigado em um estudo de campo. A uniformidade de semeadura foi determinada para três distâncias de entrelinha: 14, 18 e 21 cm. As semeadeiras operaram nas velocidades de 1,8; 3,6; 5,4 e 7,2 km h-1. O espaçamento entre sementes sucessivas foi feito ao longo de 3 m de linha, com três repetições em cada linha. Para avaliar a uniformidade, os espaçamentos entre sementes foram analisados usando os métodos (MISS, MULT, QFI e PREC) e nos resultados não foi achada diferença entre semeadeiras. Para P < 0,001 a velocidade de operação afetou MISS e QFI e o espaçamento entre linhas afetou MULT e PREC. A melhor velocidade de operação foi de 1,8 km h-1 devido ao seu mais alto valor de QFI (88,5%). Não houve diferença entre as velocidades de 1,8 e 3,6 km h-1, mas elas foram diferentes das velocidades 5,4 e 7,2 km h-1. A melhor distância entre linhas foi de 18 cm, pois seu QFI foi maior em relação à 14 e 20 cm, 86,9%, 82,0% e 81,8%, respectivamente. O melhor PREC foi obtido para 21 cm de entrelinha (17,4) e os valores de PREC foram aceitáveis para todos experimentos

Multiplicative random regression model for heterogeneous variance adjustment in genetic evaluation for milk yield in Simmental

v2008okBEL/BG