The interaction effect of two sulfonylurea herbicides, bensulfuron methyl (B) and metsulfuron methyl(M), were tested on microbial biomass C, N, N mineralization and C/N ratio in a loamy sand soil. The herbicides we...The interaction effect of two sulfonylurea herbicides, bensulfuron methyl (B) and metsulfuron methyl(M), were tested on microbial biomass C, N, N mineralization and C/N ratio in a loamy sand soil. The herbicides were applied at various levels of: control (B0M0), 0.01 and 0.01 (B1M1), 0.01 and 0.1 (B1M2), and 0.01 and 1.0 (B1M3) μg/g soil. Determinations of soil microbial biomass C, N and N mineralization contents were carried out at 1, 3, 5, 7, 10, 15, 25 and 45 days after herbicides application. The results showed that the soil microbial biomass C (C mic ) and microbial biomass N (N mic ) decreased consistently with the increasing rates of herbicides. The results further indicated that B1M1 and B1M2 caused a significant reduction in C mic and N mic within first 10 and 7 days of incubation, respectively, as compared with the control. These reductions in C mic and N mic were also significant ( P =0.05) with B1M3 application especially within first 15 days of incubation. A significant reduction in N mineralization (N min) was observed with high doses (B1M2, B1M3) of herbicides within first 5 days of incubation, while low rate (B1M1) failed to produce any significant effect. An increase in the soil microbial biomass C:N ratio was also noted.展开更多
Three assays were developed from April 3, 1995 to October 10, 2005. The work with corn was conducted in a greenhouse, using velvet bean (Mucuna aterrima) and sunn hemp (Crotalaria juncea) as green manure with 15N labe...Three assays were developed from April 3, 1995 to October 10, 2005. The work with corn was conducted in a greenhouse, using velvet bean (Mucuna aterrima) and sunn hemp (Crotalaria juncea) as green manure with 15N labeling of either shoots or roots, in two soils with contrasting textural classes. The mineralization of N from legume plants incorporated into the two soils was investigated too. This work included two green manures: velvet bean and sunn hemp, and the common bean (Phaseolus vulgaris) residues. Nitrogen from the velvet bean accounted for a greater proportion of the soil inorganic N;shoots were responsible for most of N accumulated. Common bean residues caused immobilization of inorganic N. The leguminous species added were intensively and promptly mineralized, preserving the soil native nitrogen. One hundred days after emergence of the corn, velvet bean provided higher accumulation of nitrogen in the soil, higher absorption by corn plants and accumulation in the aerial part. The green manure decomposition was more intense in the medium textured soil. In this soil, highest nitrogen losses were also observed. The sugarcane (Saccharum spp.) was cultivated for five years in the field and was harvested three times;15N recovery was evaluated in the first two harvests. The combination of inorganic fertilizer and green manure resulted in higher sugarcane yields than either N source applied separately;however, in the second cutting the yields were higher where sunn hemp was used than in plots with ammonium sulfate. The recovery of N by the first two consecutive harvests accounted for 19% to 21% of the N applied as sunn hemp and 46% to 49% of the N applied as ammonium sulfate. Very little inorganic N was present in the 0-40 cm soil layer with both N sources.展开更多
Soil samples archived over four decades were used in an incubation experiment to measure the effects of reforestation on nitrogen dynamics in old agricultural fields. Samples collected from 0 to 7.5 cm and 35 to 60 cm...Soil samples archived over four decades were used in an incubation experiment to measure the effects of reforestation on nitrogen dynamics in old agricultural fields. Samples collected from 0 to 7.5 cm and 35 to 60 cm depths in Calhoun,South Carolina USA at intervals ranging between five and nine years since 1962 were incubated aerobically at 30 ℃ for 30 days using a system specially designed to maintain constant soil moisture. Mineral N was measured in 2 mol·L -1 KCl extracts. The ratio of mineralized N to total N rapidly decreased in the first two decades of forest development. Within 20 years after planting, plenty of available N had been accumulated in the biomass, which had a significant negative correlation with soil total N ( r - top -0.828～-0.898; r - deep-0.848～-0.989). It indicated that agricultural inputs of N were important to early tree development. Significantly, by age 40, soil mineral N had increased to 50%of that in the beginning of tree planting. The accretion of mineralizable N suggests that forest floor is serving as an increasingly important source for this nutrient. Further, it indicates that forest managers have the opportunity to manipulate a large pool of forest organic matter to sustain soil N supply.展开更多
基金TheNationalKeyBasicResearchDevelopmentandPlanningofChina (No .G19990 1180 9) TheNationalNaturalScienceFoundationofChina (No .
文摘The interaction effect of two sulfonylurea herbicides, bensulfuron methyl (B) and metsulfuron methyl(M), were tested on microbial biomass C, N, N mineralization and C/N ratio in a loamy sand soil. The herbicides were applied at various levels of: control (B0M0), 0.01 and 0.01 (B1M1), 0.01 and 0.1 (B1M2), and 0.01 and 1.0 (B1M3) μg/g soil. Determinations of soil microbial biomass C, N and N mineralization contents were carried out at 1, 3, 5, 7, 10, 15, 25 and 45 days after herbicides application. The results showed that the soil microbial biomass C (C mic ) and microbial biomass N (N mic ) decreased consistently with the increasing rates of herbicides. The results further indicated that B1M1 and B1M2 caused a significant reduction in C mic and N mic within first 10 and 7 days of incubation, respectively, as compared with the control. These reductions in C mic and N mic were also significant ( P =0.05) with B1M3 application especially within first 15 days of incubation. A significant reduction in N mineralization (N min) was observed with high doses (B1M2, B1M3) of herbicides within first 5 days of incubation, while low rate (B1M1) failed to produce any significant effect. An increase in the soil microbial biomass C:N ratio was also noted.
基金To the technical research support of Gilberto Farias,Benedito Mota,and Maria Aparecida C.de GodoyTo FAPESP and CNPq for the grants.Piraíseeds for green manure and cover crops and Fundag for the support.
文摘Three assays were developed from April 3, 1995 to October 10, 2005. The work with corn was conducted in a greenhouse, using velvet bean (Mucuna aterrima) and sunn hemp (Crotalaria juncea) as green manure with 15N labeling of either shoots or roots, in two soils with contrasting textural classes. The mineralization of N from legume plants incorporated into the two soils was investigated too. This work included two green manures: velvet bean and sunn hemp, and the common bean (Phaseolus vulgaris) residues. Nitrogen from the velvet bean accounted for a greater proportion of the soil inorganic N;shoots were responsible for most of N accumulated. Common bean residues caused immobilization of inorganic N. The leguminous species added were intensively and promptly mineralized, preserving the soil native nitrogen. One hundred days after emergence of the corn, velvet bean provided higher accumulation of nitrogen in the soil, higher absorption by corn plants and accumulation in the aerial part. The green manure decomposition was more intense in the medium textured soil. In this soil, highest nitrogen losses were also observed. The sugarcane (Saccharum spp.) was cultivated for five years in the field and was harvested three times;15N recovery was evaluated in the first two harvests. The combination of inorganic fertilizer and green manure resulted in higher sugarcane yields than either N source applied separately;however, in the second cutting the yields were higher where sunn hemp was used than in plots with ammonium sulfate. The recovery of N by the first two consecutive harvests accounted for 19% to 21% of the N applied as sunn hemp and 46% to 49% of the N applied as ammonium sulfate. Very little inorganic N was present in the 0-40 cm soil layer with both N sources.
文摘Soil samples archived over four decades were used in an incubation experiment to measure the effects of reforestation on nitrogen dynamics in old agricultural fields. Samples collected from 0 to 7.5 cm and 35 to 60 cm depths in Calhoun,South Carolina USA at intervals ranging between five and nine years since 1962 were incubated aerobically at 30 ℃ for 30 days using a system specially designed to maintain constant soil moisture. Mineral N was measured in 2 mol·L -1 KCl extracts. The ratio of mineralized N to total N rapidly decreased in the first two decades of forest development. Within 20 years after planting, plenty of available N had been accumulated in the biomass, which had a significant negative correlation with soil total N ( r - top -0.828～-0.898; r - deep-0.848～-0.989). It indicated that agricultural inputs of N were important to early tree development. Significantly, by age 40, soil mineral N had increased to 50%of that in the beginning of tree planting. The accretion of mineralizable N suggests that forest floor is serving as an increasingly important source for this nutrient. Further, it indicates that forest managers have the opportunity to manipulate a large pool of forest organic matter to sustain soil N supply.
