摘要:

Soil collected from an induced tillage pan in the A2 horizon of a Norfolk sandy loam soil was fractionated into sand, silt, and clay separates and reconstituted, yielding four soil textures, each having approximately 5% clay, but with sand percentages ranging from 66.6 to 82.2%. Twelve soil cores for each texture were packed to bulk densities of 1.79 ± 0.03 g/cm3. Cone index (CI), the soil water characteristic, pore-size distribution, and saturated hydraulic conductivity (K) were measured for the induced pan and the reconstituted soil cores.The cone indices for the undisturbed cores of induced pan were significantly greater than for the reconstituted soil for the same texture. Saturated hydraulic conductivity of the undisturbed pan was only slightly greater than for the disturbed pan material having the same texture. For the reconstituted soils, saturated hydraulic conductivity increased, and the volume of water-filled pores at soil water pressures less than —80 mb decreased as the percentage of sand increased. The cone index for each texture increased monotonically with decreasing soil water pressure, but no simple relationship between CI and texture was found. Regression equations relating CI to water content, percentage of sand, and the volume of pores greater than 150 μm in diameter were developed, were significant at the 0.0001 probability level, and explained 67 to 72% of the observed variability.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

The use of a single extraction with dilute unbuffered silver-thiourea (AgTU) solution (0.01MAg+) for measuring exchangeable cations and the cation exchange capacity (CEC) of soils was compared with the conventional effective CEC method, which usedNNH4OAc displacement for exchangeable “bases” (Ca, Mg, K, Na) andNKCI extraction for exchange acidity (Al + H). Fifty-seven selected surface and lower B horizon samples of Alfisols, Ultisols, and Oxisols with low-activity clays derived from a wide range of parent materials were used.The two extraction methods gave essentially the same CEC values for all soils studied (R2= 0.92). Good agreements were also obtained between the dilute AgTU-extractable bases (Ca, Mg, K, Na) andNNH4OAc-extractable bases. The dilute AgTU extraction gave slightly larger values of exchange acidity (Al + H) than theNKCl extraction for most soils.The single-extraction method using unbuffered Ag-thiourea is suitable for rapid, routine measurements of effective CEC and exchangeable cations for soils dominating in variable-charge colloids.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Maize (Zea maysL.) was grown in greenhouse soil pot cultures to evaluate the effect of cattle feedlot manure and NPK fertilizer on the improvement of the yield capacity of the Iwo subsoil in Western Nigeria. Manure was applied at 0, 3, and 6 percent rates, and fertilization levels were zero and complete, complete fertilization consisting of 100 micrograms of nitrogen, 40 micrograms of phosphorus, and 100 micrograms of potassium per gram of soil. Subsoil treatments were evaluated against corresponding topsoil that was under 25-year bush fallow.A combination of NPK fertilization and manure applied at the rate of 6 percent (of dry soil) produced dry matter yields on the subsoil equivalent to those on the topsoil. The effect of adding manure alone on yield from the topsoil was comparable to that resulting from fertilization. Root growth generally reflected a large complementary effect of manure and fertilization.Recovery of nutrient elements, expressed as a percentage of applied nitrogen, phosphorus, and potassium, was explained in terms of their uptake by plants. Manure addition resulted in substantially high phosphorus uptake, and potassium concentrations in roots and shoots were consistently high and not as limiting as nitrogen and phosphorus in the subsoil.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

In a field study utilizing15N on Manotick sand, leaching, denitrification, clay fixation of NH4+, mineralization, and immobilization all played a significant role in the transport and transformation of fertilizer NH4+. Fertilizer NH4+applied 24 June was distributed throughout the 75-cm profile by 29 July. The relatively small amount (0.5% of the total15N recovered) found in the deepest sample (60 to 75 cm) suggested that a larger portion of the 27% unrecovered15N was denitrified rather than leached. Denitrification, then, was assumed to be more prevalent early, rather than late, in the season. On 4 October, a much larger proportion of the15N was found deep in the profile, showing that leaching losses after 29 July became more important. Four percent of the fertilizer15NH4+-N was immediately clay-fixed. By 29 July, 9% of the initially fixed15NH4+-N was released, but by 4 October, 77% of the initially fixed15NH4+-N was released. The total amount of immobilized15N was similar on both 29 July and 4 October samplings. The relatively constant amount of organic15N during the field season showed that immobilization was more active between 24 June and 29 July than between 29 July and 4 October. Immobilized15N accounted for 19 to 20% of the applied fertilizer15N. The dynamics of N transformations were compared with a previously studied adjacent clay loam soil.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Three acid, surface-mined soils and an adjacent undisturbed soil were evaluated for nitrification potentials and nonexchangeable NH4+-N retention to better understand N mechanisms and improve the reclamation efficiency of these soils. The mined soils nitrified a maximum of only 7% of an added 100 ppm NH4+-N, although the undisturbed soil nitrified 93% of the applied N.Total N digestion showed one mined soil to have a nonexchangeable NH4+-N retention capacity of 6.2 meq/100g. Organically retained NH4+-N accounted for 73% of the total retention.Another procedure utilizing differences in exchangeable NH4+-N between moist and dried samples as estimates of nonexchangeable NH4+-N retention, showed retentive capacities of the mined soils ranging from 4.1 to 7.8 meq NH4+-N/100g. Lignite exhibited a retentive capacity of 46.0 meq NH4+-N/100g. Nonexchangeable retention was significantly correlated with the residual lignite content of the soil.Low nitrification potentials and large nonexchangeable NH4+-N retention capacities suggested that applied NH4+-N fertilizers might be inefficient in the mined soils.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Thirty-one surface soil samples from nine years of rate and ratio rice fertilization experiments at different locations in Louisiana were analyzed for their available-nitrogen content, using six chemical and two biological extraction methods. The relationship between the available soil nitrogen and rough rice yields was then investigated.Total soil nitrogen varied widely, ranging from 540 to 5460 parts per million. The average percentage recovery of total soil nitrogen (representing the available soil nitrogen), as determined by the various methods used, also ranged widely, from as high as 16.74 percent, by the hot alkaline permanganate method, to the lowest value of 1.08 percent, by boiling soils in 0.01MCaCl2solution. Good correlation coefficients were obtained, especially among the anaerobic incubation and each of the other extraction methods used. The acid hydrolysis method correlated the least with the other extraction methods. Highly significant correlation coefficients were obtained between the rough rice yields from the untreated plots (plots that received no nitrogen) and the available soil nitrogen determined by all the extraction methods. The best correlation was obtained with the anaerobic incubation method (r= 0.622). The rough rice yield in plots receiving 56 or more kilograms of nitrogen per hectare did not exhibit a significant relationship with the available soil nitrogen. Relationships between the rough rice yields at zero and 28 kg/ha N and the available soil nitrogen, as determined by the anaerobic incubation method, were better described by curvilinear models than by linear ones. The relationship was also established between yield increase from application of 112 kg/ha N (the level of nitrogen generally considered near optimum for rice in Louisiana) and available soil nitrogen determined by the anaerobic incubation method. With some reasonable degree of accuracy, yield increase could be predicted from the graph signifying this relationship.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Variable selenium (Se) concentration effects in sand culture and sandy soils were studied on raya (Brassica junceaCoss.), an oil crop, in the greenhouse. The sand cultures were supplied with Se at rates of 0, 0.5, 1, 2, 4, 8, 16, and 32 parts per million (ppm), whereas the sandy soil was treated with 0, 0.1, 0.5, 1, 2, 4, 8, and 16 ppm Se as sodium selenite (Na2SO3·5H2O). Sulfur (S) was supplied at rates of 0, 50, and 100 ppm in both cases. When S was not applied in the sand cultures, 1 ppm and higher Se decreased root and shoot weight significantly. Four parts per million and higher concentrations of Se induced white chlorosis in younger leaves of raya. In sandy soil, yield reduction started with 2 ppm and higher Se doses, but there was no chlorosis in the leaves. When S was applied at the rate of 50 and 100 ppm in both cases, the dry weights of roots and shoots increased significantly. In the presence of 100 ppm S, shoot dry matter was higher than the control for 1, 2, 4, and 8 ppm Se application, and significant reduction in dry matter yield was observed with 16 and 32 ppm Se. In the absence of added S, Se tended to accumulate in the plant roots, but with the addition of S, more Se was translocated to the shoots.The plant nitrogen, sulfur, methionine, cystine, and cysteine concentration decreased with increased Se concentration in the growth medium. Supplying S at 50 and 100 ppm decreased Se and increased all other measured chemical concentrations in raya plants. Selenium and S were antagonistically related.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Computer models are often used to simulate solute transport through soil profiles. This paper compares the results obtained with two such models. The first model is rather complex and requires a complete description of the soil hydrological properties. The second model is much simpler and uses an average percolation rate as input. Solute transport was compared with and without adsorption and with and without root water uptake. The results show that the relative solute concentration at a given soil depth, as a function of cumulative drainage of an intermittently irrigated soil, is a smooth curve, which can also be simulated with the simple model. Such models are apparently appropriate for predicting solute transport through field soils with their inherent spatial variability in physical and chemical properties.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Storing topsoil for 3 years was shown to reduce substantially the levels of viable inocula relative to levels in adjacent, undisturbed prairie soils. The detrimental effect of storage on VA mycorrhiza is associated with the loss of viability of mycorrhizal fragments occurring in the stored soil. Data are also presented supporting an interaction between infected root segments and roots of uninfected plants as a major means of spreading mycorrhiza in these soils.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Algorithms are presented for computer acquisition of data from an autoanalysis system. These algorithms are implemented using an HP9825 computer-data-acquisition system and a Technicon Auto-Analyzer. In addition to providing accurate digital records, the algorithm has saved approximately 25 percent of the time required to record and enter the data into a computer for further statistical and data analyses.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID