ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02284.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA two‐domain model of water movement, storage and drainage in a cracked clay soil has been applied and tested in the field by irrigating an instrumented lysimeter constructed around a 2.0 m length of mole drain. Measurements of drain outflow rates and of increases in soil water content were compared with model predictions. The model predicted satisfactorily the peak drain outflow rate and subsequent drain recession although there was a tendency for the model to underestimate the time to the start of drainage. Good agreement with the measured recharge profile was generally foun

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02285.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYAt Onne in South‐east Nigeria, drainage water was collected from four monolith lysimeters and analysed for nitrate. The lysimeters contained an acid sandy loam. At the start of the first rainy season two lysimeters received urea labelled with15NO3–and two received no nitrogen fertilizer; all four were uncropped in the first year.The peak concentrations of15NO3–and of unlabelled (soil) NO3–were found after 2.5 pore volumes of water had passed through the lysimeters. Using the same soil in the laboratory after fine sieving, the peak concentration of tritiated water was found at 1 pore volume whereas nitrate leaching was retarded. The pattern of nitrate leaching was well described by miscible and immiscible models which included an adsorption coefficient for nitrate. Over the 2 years 81.4% of the15N added at the start of the first rainy season was recovered in the drainag

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02286.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA combination of mathematical analysis and computer simulation, using parameters readily measured in a nitrogen‐15 field experiment, is employed to determine rates of mineralization, immobilization and nitrification under a growing crop. The procedure also yields the proportion of crop nitrogen uptake occurring as ammonium and nitrate.When applied to ‐results from grass lysimeters receiving 250 or 900 kg N ha–1a–1as ammonium nitrate, the analysis suggested that at 250 kgN ha–1a–164–66% of crop nitrogen uptake was as ammonium; at 900 kg N ha–1a–1the figure was 43–49%. Nitrification at 250kgNha–1was only 13–19kgN ha–1over 160d while at 900 kg N ha–1between 191 and 232 kg N ha–1were nitrified.The results suggested that the apparent inhibition of nitrification in grassland soils may simply reflect poor substrate competition by nitrifying bacteria. Finally, there was a suggestion that mineralization/immobilization was lowe

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02287.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYEmissions of nitrous oxide (N2O) and nitrogen gas (N2) from denitrification were measured using the acetylene inhibition method on drained and undrained clay soil during November 1980‐June 1981. Drainage limited denitrification to about 65% of losses from undrained soil. Emissions from the undrained soil were in the range 1 to 12 g N ha–1h–1while those from the drained soil ranged from 0.5 to 6 g N ha–1h–1giving estimated total losses (N2O + N2) of 14 and 9 kgN ha–1.Drainage also changed the fraction of nitrous oxide in the total denitrification product. During December, emissions from the drained soil (1.8±0.6 gN ha–1h–1) were composed entirely of nitrous oxide, but losses from the undrained soil (2.7 ± 1.1 g N ha–1h–1) were almost entirely in the form of nitrogen gas (the fraction of N2O in the total loss was 0.02). In February denitrification declined in colder conditions and the emission of nitrous oxide from drained soil declined relative to nitrogen gas so that the fraction of N2O was 0.03 on both drainage treatments. The delayed onset of N2O reduction in the drained soil was related to oxygen and nitrate concentrations. Fertilizer applications in the spring gave rise to maximum rates of emission (5–12g N ha–1h–1) with the balance shifting towards nitrous oxide production, so that the fraction of N2O w

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02288.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYIn a field experiment with soil compaction by tractor traffic on a loam soil, the denitrification rate (using the C2H2inhibition method), the soil structure, and the wheat yield were investigated. Tractor traffic on wet soil (>– 50 mbar matric potential) reduced the pore volume, doubled the percentage of large aggregates (>20 mm), reduced the wheat yield by about 25%, and increased the N‐loss through denitrification by a factor of 3–4. Neither of these parameters were affected by tractor traffic at low soil moisture content. The weight of the tractor (1800 kgvs4800 kg) did not significantly alter the effect of compaction on the measured parameters. There was a factor of 2–6 between the measured denitrification rate in compacted and that in uncompacted soil, and this factor showed little dependence on the average activity level on each date of measurement. Accumulated values for the measured denitrification during 75 days (May 23‐August 9) were 3–5 kg N ha–1in uncompacted soil and 15–20 kg N ha–1in soil which was compacted

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02289.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY