Total P (TP), total participate P (PP), total dissolved P (TDP), molybdatereactive P (MRP) and dissolved organic P (DOP) were determined in waters from pipe-drains (at 65-cmdepth) from the Broadbalk Experiment at Roth...Total P (TP), total participate P (PP), total dissolved P (TDP), molybdatereactive P (MRP) and dissolved organic P (DOP) were determined in waters from pipe-drains (at 65-cmdepth) from the Broadbalk Experiment at Rothamsted Research, UK. Average TPand PP exceeded 1 mgL^(-1) in about half of the 12 plots receiving superphosphate for the 5 measurements taken betweenDecember 2000 and April 2001. Ranging between 33.8% and 87.3% of TP, PP was the largest P fractionin drainage waters, with DOP, ranging from 0.5% to 26.2% of TP, being the smallest fraction Meanproportions of PP, MRP and DOP in TP in drainage waters were 63.4%, 32.5% and 4.1%, respectively.These findings support previous findings that P losses from soil to drainage waters were muchlargerthan previously thought, and could therefore make a significant contribution to eutrophication.展开更多
Osmotic potential （OP） of soil solution may be a more appropriate parameter than electrical conductivity （EC） to evaluate the effect of salts on plant growth and soil biomass. However, this has not been examined i...Osmotic potential （OP） of soil solution may be a more appropriate parameter than electrical conductivity （EC） to evaluate the effect of salts on plant growth and soil biomass. However, this has not been examined in detail with respect to microbial activity and dissolved organic matter in soils with different texture. This study evaluated the effect of salinity and sodicity on respiration and dissolved organic matter dynamics in salt-affected soils with different texture. Four non-saline and non-sodic soils differing in texture （S-4, S-13, S-24 and S-40 with 4%, 13%, 24~ and 40~~ clay, respectively） were leached using combinations of 1 mol L-1 NaC1 and 1 mol L-1 CaC12 stock solutions, resulting in EC （1：5 soil：water ratio） between 0.4 and 5.0 dS m-1 with two levels of sodicity （sodium absorption ratio （SAR） 〈 3 （non-sodic） and 20 （sodic）, 1：5 soil：water ratio）. Adjusting the water content to levels optimal for microbial activity~ which differed among the soils, resulted in four ranges of OP in all the soils： from -0.06 to -0.24 （controls, without salt added）, -0.55 to -0.92, -1.25 to -1.62 and -2.77 to -3.00 Mpa. Finely ground mature wheat straw （20 g kg-1） was added to stimulate microbial activity. At a given EC, cumulative soil respiration was lower in the lighter-textured soils （S-4 and S-13） than in the heavier-textured soils （S-24 and S-40）. Cumulative soil respiration decreased with decreasing OP to a similar extent in all the soils, with a greater decrease on Day 40 than on Day 10. Cumulative soil respiration was greater at SAR ---- 20 than at SAR 〈 3 only at the OP levels between -0.62 and -1.62 MPa on Day 40. In all the soils and at both sampling times, concentrations of dissolved organic C and N were higher at the lowest OP levels （from -2.74 to -3.0 MPa） than in the controls （from -0.06 to -0.24 MPa）. Thus, OP is a better parameter than EC to evaluate the effect of salinity on dissolved organic matter and microbial activity in different textured soils.展开更多
基金Project supported by the Rothamsted International, UK the Scientific Research Foundation for Returned Overseas Chinese Scholars, the State Education Ministry of China and the Natural Science Foundation of Shaanxi Province, China (No. 2002D09).
文摘Total P (TP), total participate P (PP), total dissolved P (TDP), molybdatereactive P (MRP) and dissolved organic P (DOP) were determined in waters from pipe-drains (at 65-cmdepth) from the Broadbalk Experiment at Rothamsted Research, UK. Average TPand PP exceeded 1 mgL^(-1) in about half of the 12 plots receiving superphosphate for the 5 measurements taken betweenDecember 2000 and April 2001. Ranging between 33.8% and 87.3% of TP, PP was the largest P fractionin drainage waters, with DOP, ranging from 0.5% to 26.2% of TP, being the smallest fraction Meanproportions of PP, MRP and DOP in TP in drainage waters were 63.4%, 32.5% and 4.1%, respectively.These findings support previous findings that P losses from soil to drainage waters were muchlargerthan previously thought, and could therefore make a significant contribution to eutrophication.
文摘Osmotic potential （OP） of soil solution may be a more appropriate parameter than electrical conductivity （EC） to evaluate the effect of salts on plant growth and soil biomass. However, this has not been examined in detail with respect to microbial activity and dissolved organic matter in soils with different texture. This study evaluated the effect of salinity and sodicity on respiration and dissolved organic matter dynamics in salt-affected soils with different texture. Four non-saline and non-sodic soils differing in texture （S-4, S-13, S-24 and S-40 with 4%, 13%, 24~ and 40~~ clay, respectively） were leached using combinations of 1 mol L-1 NaC1 and 1 mol L-1 CaC12 stock solutions, resulting in EC （1：5 soil：water ratio） between 0.4 and 5.0 dS m-1 with two levels of sodicity （sodium absorption ratio （SAR） 〈 3 （non-sodic） and 20 （sodic）, 1：5 soil：water ratio）. Adjusting the water content to levels optimal for microbial activity~ which differed among the soils, resulted in four ranges of OP in all the soils： from -0.06 to -0.24 （controls, without salt added）, -0.55 to -0.92, -1.25 to -1.62 and -2.77 to -3.00 Mpa. Finely ground mature wheat straw （20 g kg-1） was added to stimulate microbial activity. At a given EC, cumulative soil respiration was lower in the lighter-textured soils （S-4 and S-13） than in the heavier-textured soils （S-24 and S-40）. Cumulative soil respiration decreased with decreasing OP to a similar extent in all the soils, with a greater decrease on Day 40 than on Day 10. Cumulative soil respiration was greater at SAR ---- 20 than at SAR 〈 3 only at the OP levels between -0.62 and -1.62 MPa on Day 40. In all the soils and at both sampling times, concentrations of dissolved organic C and N were higher at the lowest OP levels （from -2.74 to -3.0 MPa） than in the controls （from -0.06 to -0.24 MPa）. Thus, OP is a better parameter than EC to evaluate the effect of salinity on dissolved organic matter and microbial activity in different textured soils.
