Traditionally, soil-testing laboratories have used a variety of methods to determine soil organic matter, yet they lack a practical method to predict potential N mineralization/immobilization from soil organic matter....Traditionally, soil-testing laboratories have used a variety of methods to determine soil organic matter, yet they lack a practical method to predict potential N mineralization/immobilization from soil organic matter. Soils with high micro-bial activity may experience N immobilization (or reduced net N mineralization), and this issue remains unresolved in how to predict these conditions of net mineralization or net immobilization. Prediction may become possible with the use of a more sensitive method to determine soil C:N ratios stemming from the water-extractable C and N pools that can be readily adapted by both commercial and university soil testing labs. Soil microbial activity is highly related to soil organic C and N, as well as to water-extractable organic C (WEOC) and water-extractable organic N (WEON). The relationship between soil respiration and WEOC and WEON is stronger than between respiration and soil organic C (SOC) and total organic N (TON). We explored the relationship between soil organic C:N and water-extractable organic C:N, as well as their relationship to soil microbial activity as measured by the flush of CO2 following rewetting of dried soil. In 50 different soils, the relationship between soil microbial activity and water-extractable organic C:N was much stronger than for soil organic C: N. We concluded that the water-extractable organic C:N was a more sensitive measurement of the soil substrate which drives soil microbial activity. We also suggest that a water-extractable organic C:N level > 20 be used as a practical threshold to separate those soils that may have immobilized N with high microbial activity.展开更多
Phosphorus-containing amendments can reduce the mobility of Pb in soil. Hydroxyapatite (HAP) is one of the most commonly used phosphorus-containing amendments. With the development of nanotechnology, nano-hydroxyapati...Phosphorus-containing amendments can reduce the mobility of Pb in soil. Hydroxyapatite (HAP) is one of the most commonly used phosphorus-containing amendments. With the development of nanotechnology, nano-hydroxyapatie (n-HAP) was gradually applied to remediate soil polluted by heavy metals. Considering the concentrations of HAP/n-HAP were not more than 5% in most studies, soil polluted by Pb was artificially prepared and three different concentrations of n-HAP: 5%, 7% and 10% by weight, were added into the Pb-polluted soil separately. The mixtures of soil and n-HAP were incubated for 180 d and sampled regularly. The bioaccessibility of Pb in soil was determined using simulated gastric juices of two in-vitro digestion tests: USPM (United States Pharmacopeia Methodology) and PBET (Physiologically-Based Extraction Test). The results showed that the immobilizing efficiency of 5% n-HAP to Pb in soil was the highest in PBET. The extractable Pb from soil by USPM was not affected by concentration of n-HAP. So, the least concentration of n-HAP, i.e. 5% n-HAP treatment, was the most cost-effective in USPM. Soil pH increased with concentration of n-HAP. However concentration of n-HAP had little effects on content of soil OM. According to regression analysis, more than 50% differences of the extractable Pb from soil by PBET can be explained by soil pH, while soil pH, organic matter content and incubation time together explained nearly 85% differences of extractable Pb from soil by USPM.展开更多
Adjusting the N fertilization to soil potentially mineralizable N in Histosols is required to secure high vegetable yields while mitigating nitrate contamination of surface waters. However, there is still no soil test...Adjusting the N fertilization to soil potentially mineralizable N in Histosols is required to secure high vegetable yields while mitigating nitrate contamination of surface waters. However, there is still no soil test N (STN) relating the response of Histosol-grown onion (Allium cepa L.) to added N. Compositional data analysis can integrate soil C and N composition into a STN index computed as Mahalanobis distance (M<sup>2</sup>) across isometric log ratios (ilr) of diagnosed and reference soil C and N compositions. Our objective was to calibrate onion response to added N against a compositional STN index for Histosols. Reference compositions were computed from high N-mineralizing Histosols reported in the literature. Soil analyses were total C and N, and a residual soil mass (F<sub>v</sub>) was computed as 100%-%C-%N to close the compositional vector to 100%. The C, N, and F<sub>v</sub> proportions were synthesized into two ilrs. We conducted thirteen onion N fertilization trials in Histosols of south-western Quebec showing contrasting C, N, and F<sub>v</sub> proportions. Each crop received four N rates broadcast before seeding or split-applied. We derived two STN classes separating weakly to highly responsive crops about the M<sup>2</sup> value of 5.5. Onion crops grown on soils showing M<sup>2</sup> values >5.5 required more N and yielded less in control treatments compared with soils showing M<sup>2</sup> values 5.5) soils responded significantly (P < 0.10) to 60 and 180 kg N ha<sup>-1</sup>, respectively. Using literature data and the results of this study, we elaborated a provisory N requirement model for Histosol-grown onions in Quebec.展开更多
文摘Traditionally, soil-testing laboratories have used a variety of methods to determine soil organic matter, yet they lack a practical method to predict potential N mineralization/immobilization from soil organic matter. Soils with high micro-bial activity may experience N immobilization (or reduced net N mineralization), and this issue remains unresolved in how to predict these conditions of net mineralization or net immobilization. Prediction may become possible with the use of a more sensitive method to determine soil C:N ratios stemming from the water-extractable C and N pools that can be readily adapted by both commercial and university soil testing labs. Soil microbial activity is highly related to soil organic C and N, as well as to water-extractable organic C (WEOC) and water-extractable organic N (WEON). The relationship between soil respiration and WEOC and WEON is stronger than between respiration and soil organic C (SOC) and total organic N (TON). We explored the relationship between soil organic C:N and water-extractable organic C:N, as well as their relationship to soil microbial activity as measured by the flush of CO2 following rewetting of dried soil. In 50 different soils, the relationship between soil microbial activity and water-extractable organic C:N was much stronger than for soil organic C: N. We concluded that the water-extractable organic C:N was a more sensitive measurement of the soil substrate which drives soil microbial activity. We also suggest that a water-extractable organic C:N level > 20 be used as a practical threshold to separate those soils that may have immobilized N with high microbial activity.
文摘Phosphorus-containing amendments can reduce the mobility of Pb in soil. Hydroxyapatite (HAP) is one of the most commonly used phosphorus-containing amendments. With the development of nanotechnology, nano-hydroxyapatie (n-HAP) was gradually applied to remediate soil polluted by heavy metals. Considering the concentrations of HAP/n-HAP were not more than 5% in most studies, soil polluted by Pb was artificially prepared and three different concentrations of n-HAP: 5%, 7% and 10% by weight, were added into the Pb-polluted soil separately. The mixtures of soil and n-HAP were incubated for 180 d and sampled regularly. The bioaccessibility of Pb in soil was determined using simulated gastric juices of two in-vitro digestion tests: USPM (United States Pharmacopeia Methodology) and PBET (Physiologically-Based Extraction Test). The results showed that the immobilizing efficiency of 5% n-HAP to Pb in soil was the highest in PBET. The extractable Pb from soil by USPM was not affected by concentration of n-HAP. So, the least concentration of n-HAP, i.e. 5% n-HAP treatment, was the most cost-effective in USPM. Soil pH increased with concentration of n-HAP. However concentration of n-HAP had little effects on content of soil OM. According to regression analysis, more than 50% differences of the extractable Pb from soil by PBET can be explained by soil pH, while soil pH, organic matter content and incubation time together explained nearly 85% differences of extractable Pb from soil by USPM.
文摘Adjusting the N fertilization to soil potentially mineralizable N in Histosols is required to secure high vegetable yields while mitigating nitrate contamination of surface waters. However, there is still no soil test N (STN) relating the response of Histosol-grown onion (Allium cepa L.) to added N. Compositional data analysis can integrate soil C and N composition into a STN index computed as Mahalanobis distance (M<sup>2</sup>) across isometric log ratios (ilr) of diagnosed and reference soil C and N compositions. Our objective was to calibrate onion response to added N against a compositional STN index for Histosols. Reference compositions were computed from high N-mineralizing Histosols reported in the literature. Soil analyses were total C and N, and a residual soil mass (F<sub>v</sub>) was computed as 100%-%C-%N to close the compositional vector to 100%. The C, N, and F<sub>v</sub> proportions were synthesized into two ilrs. We conducted thirteen onion N fertilization trials in Histosols of south-western Quebec showing contrasting C, N, and F<sub>v</sub> proportions. Each crop received four N rates broadcast before seeding or split-applied. We derived two STN classes separating weakly to highly responsive crops about the M<sup>2</sup> value of 5.5. Onion crops grown on soils showing M<sup>2</sup> values >5.5 required more N and yielded less in control treatments compared with soils showing M<sup>2</sup> values 5.5) soils responded significantly (P < 0.10) to 60 and 180 kg N ha<sup>-1</sup>, respectively. Using literature data and the results of this study, we elaborated a provisory N requirement model for Histosol-grown onions in Quebec.
