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Acidity distribution within any given soil profile is dependent on mineralogical make-up of the parent material as well as environmental conditions prevalent during the weathering history of the soil. An experiment was designed to study the distribution pattern of exchange acidity, exchangeable aluminum, exchangeable manganese and pH of six acid soils of Western Oregon. 1N KCl extracts of four depths of each soil were obtained and the levels of the parameters mentioned above were measured. It was found that various soil series had different acidity distribution patterns within their profiles. Also, a highly significant linear correlation was observed between exchange acidity and exchangeable aluminum of each soil. Liming acid soils raises pH of the soil extract and improves its fertility status. The rise in pH is due to neutralization of acid groups or acid-producing species present in various forms and on various sites in the soil system. One group of these acid producing species is the exchangeable form of various hydrolyzable cations, especially Al3, H3O+, Mn+2, also perhaps Fe+3, and others. These cations are extracted with solutions of 1N neutral salts such as KC1 and are neutralized by hydroxyls of the applied lime. A second experiment was designed to study the effect of liming, using an incubation procedure, on exchange acidity, exchangeable aluminum, exchangeable manganese and pH of these soils. It was observed that additions of increments of Ca(OH)2 to soil resulted in progressive increase in pH of the soil extract and the relationship between pH and amounts of lime applied was curvilinear with the titration curves approximating linear patterns. As lime rates increase, there was a drop in both Al+3 and exchange acidity content of the soil extract as well as the amount of Mn+2 extracted. For all these three parameters the initial drop was much sharper than the subsequent reductions occurring due to further additions of lime. Point of zero acidity or zero exchangeable aluminum did not necessarily coincide with pH of neutrality. Applications of lime to acid soils improves their crop raising ability, especially with regard to legumes. A third experiment was set up to study the response pattern of alfalfa (Medicago sativa L. var. Du Puits) to lime and phosphorous applications and the effect of such applications on aluminum, manganese, phosphorous, and calcium concentrations of plant tops. Significant yield responses were obtained in some cases but not in others. Phosphorous concentration of the tops was not significantly affected, but aluminum, manganese, and calcium concentrations were affected to varying degrees.
Two soils representative of the coast and three representing the Willamette Valley have been studied for their general chemical characteristics. Exchange capacity and exchangeable cations were determined by the ammonium acetate and the BaCl2-triethanolamine buffer methods. Exchange capacity was also obtained from conductimetric titrations which were run on each soil before and after destroying the organic matter. Potentiometric titrations were run before and after leaching each soil with HCl. Lime requirement was determined by Woodruff's method and also obtained from the pH-lime curves. The two coastal soils, Astoria and Clatsop, have lower pH and base saturation and higher organic matter content and exchange capacity than the Melbourne, Olympic, and Willamette soils from the valley. The Melbourne soil had the highest base saturation percentage and Astoria had the lowest. The amount of exchangeable aluminum was also higher in the coastal soils. The amount of exchange capacity contributed to the organic fraction was 65 per cent in the Olympic and Willamette soils and 50 per cent in the other three. The value for exchange capacity by the different methods was in good agreement in the three valley soils before and after the organic matter was destroyed. In the coastal soils there was no agreement between methods in any case. This would indicate that in the latter two soils, type of clay mineral present may be more of an influence than in the former soils. The potentiometric titration curves showed that the two coastal soils were well buffered and the valley soils were only slightly buffered. After the soils were leached with HCl the Melbourne soil was the only one which indicated a strong acid property. The exchange properties of the soils as affected by additions of lime were studied by incubating the soils for four weeks with added increments of lime. With each added increment of lime the pH increased and exchangeable acidity decreased in each soil. The amount of lime to bring the soils to any given degree of base saturation appeared to be proportional to the magnitude of the exchange capacity and inversely proportional to the degree of base saturation. At any given pH value there was a considerable difference in the degree of base saturation for these soils. This might well be a reflection of the type of minerals present in the different soils. More lime was required to bring the two coastal soils up to pH 6.5 as indicated by the pH-lime relationship curve than that estimated by the Woodruff method. Consistent results were observed in the three valley soils. This suggests that the buffer solution at pH 7 as recommended by Woodruff was not strong enough to neutralize the acidity in the coastal soils. There was good agreement between the two methods in the determination of the exchangeable bases. The BaCl2-buffer method gave much higher values of exchangeable acidity than did the ammonium acetate method. These values, when converted to tons of calcium carbonate, agree fairly closely with the amount of lime required to bring the soils to pH 7 when added directly to the soil. When lime was added above the saturation point the amount of exchangeable calcium as determined by the ammonium acetate method increased but remained relatively constant for the BaCl2-buffer method. The various analysis seem to indicate that the Astoria and Clatsop soils contain predominantly 2:1 type clay minerals while the Olympic and Willamette soils contain predominantly the 1:1 type. The Melbourne soil exhibits properties more closely associated with the coastal soils.
There are two major problems associated with soil acidity and lime response investigations: A. Determining how much lime (100% "available" CaCO3 equivalent) is required to raise a soil pH (or degree of acidity) from its existing level to a specified level - presumably where need for lime is eliminated. B. Determining responses of different crops on different soils to lime; and defining some chemical measurement of the soil that will predict the response of a specified crop. Investigations in this study were limited to the first problem. Liming characteristics of 45 acid Willamette Valley soils, representing the major agricultural soil associations, were determined by incubating the soils with increments of CaCO3. The lime required to bring the soils to the specified pH levels of 6.8, 6.4 and 6.0 varied widely within the respective pH levels. Relationships between soils, however, as determined by the value of the incubation curve slope (meq. of CaCO3 /100g of soil required to raise soil pH by one unit), were improved by grouping into related soils. Laboratory measurements of other soil chemistry parameters were compared with changes in pH to determine if a satisfactory quick laboratory procedure could be developed to measure the incubation lime requirement of soils with different chemical characteristics. Measurements of soil pH were made by three different methods: (1) in the supernatant of a 1:2 soil to water suspension; (2) in the sedimented paste of the 1:2 soil to water suspension; and (3) in the supernatant of a 1:2 soil to 1 N KCl suspension. Lime requirement with a buffered solution was measured in limed and unlimed soils by use of the SMP (Shoemaker, McLean, and Pratt) buffer method. Soil samples treated with increments of lime were analyzed for extractable Al and exchange acidity by titration and the unincubated soils were analyzed for exchange acidity determined by subtracting exchangeable bases from CEC measured at pH 7. 0 and pH 6. 0. Results of the correlation analyses showed that the SMP buffer method should prove useful for predicting the incubation lime requirement. Correlation coefficients for these two values were .89, .90 and 86, respectively, to reach pH levels of 6.8, 6.4 and 6.0. Soil pH measurements, extractable Al, and exchange acidity determinations did not provide as good a basis for determining incubation lime requirements, Regression equations were calculated for the SMP buffer/incubation lime requirement relationships. The purpose of this study was to identify the changes in soil chemical measurements that take place with application of lime. No attempt was made to determine whether a crop might respond to an application of lime on an acid soil. The assumption was made that yield could be related to specific pH or soil acidity levels that could be measured in the laboratory. Therefore, the problem was approached by studying procedures that might determine the application of lime required to reach a specified pH or soil acidity measurement. It anticipated that field trials for evaluating lime response will be carried out in the future to evaluate the usefulness of the SMP buffer method which showed promise in this regard.
Extractable forms of Al and Fe were studied in five soils from the Coast Range, and in two soils from the Willamette Valley in Oregon. Exchangeable Al was determined in a way which permitted a comparison of three different methods for its determination. Values for exchangeable Al obtained by the method of lirrited leaching by Lin and Coleman (1960) agreed closely with those obtained by the method of Skeen and Sumner (1965) which consists of successive extractions and extrapolation to obtain the exchangeable Al content. Values for exchangeable Al measured by the method of exhaustive leaching proposed by Dewan and Rich (1970) exceeded the Coleman values in different amounts depending on the amount of exchangeable Al present, and on the final slope of the extraction curves. Steep slopes were found in coastal soils containing amorphous aluminosilicates, indicating that these soils have a strong supplying power for exchangeable Al, From the shape of the Al extraction curves it was concluded that two different forms of Al were extracted by the method of successive extractions, namely, a readily exchangeable form, and a form that is slowly released and which presumably results from mineral solution of amorphous oxides or from Al-organic complexes. In soils with a high base saturation good agreement between both the Coleman and the Rich values for exchangeable cations with the neutral salt CEC was observed. In soils in which Al is the dominant cation of the exchange complex, the neutral salt CEC was from 2 to 3 meq lower than the Coleman value for exchangeable cations. These differences were attributed to errors in the CEC determination due to hydrolysis. The Rich values for exchangeable cations exceeded the neutral salt CEC by amounts as high as 10 meq/100g. It was therefore concluded that Rich's method to determine exchangeable Al furnishes values that are not compatible with other standard methods. The ratios of humic to fulvic acid extracted by pyrophosphate were higher in grassland soils than in forest soils. The total amounts of Al and Fe correlate fairly well with the organic carbon extracted by pyrophosphate. The contents of Al and Fe were much higher in fulvic acid than in humic acid, but this was ascribed to the formation of soluble complexes of previously organically bound Al and Fe with pyrophosphate appearing in the fulvic fraction. It was concluded that pyrophosphate extractable Al and Fe represent a rough estimate of the amounts of Al and Fe involved in cation bridges. The ratio of Al or Fe to organic carbon extracted by pyrophosphate increased with depth. This could be due either to a change in organic matter composition, or a result of increased dissolution of inorganic amorphous oxides in lower horizons. In the top horizons of soils high in organic matter the absolute amounts of pyrophosphate extractable Al and Fe were much higher than in soils low in organic matter. However, the metal to organic carbon ratios in the top horizons were fairly similar. This suggests that the proportions of organic matter bonded to inorganic surfaces by cation bridges have similar contents of polyvalent cations. It was therefore concluded that differences in organic matter accumulations should be explained in terms of the kinds and amounts of inorganic surfaces available for organic matter adsorption in a soil. In previous work, the coastal soils with high organic matter accumulations have been shown to contain amorphous alumino-silicates. These minerals are unique in that they combine negative charges and an aluminous surface with a high specific surface area. Thus, they favor the formation of all the known types of organo-mineral bonds, except anion exchange. The oxalate and dithionite extractions did not yield much information, and were difficult to interpret due to uncertainties regarding their presumed specificity for pedogenetic oxides. However, dithionite in conjunction with pyrophosphate appears to be useful for the chemical identification of spodic horizons. The classification of the Knappa and the Nehalern profiles did not correspond to the official series classification. The Knappa profile was classified as a Typic Dystrandept instead of a Pachic Haplumbrept. The Nehalern profile was found to be a member of the Fluventic. Hapludoll instead of the Fluventic Haplumbrept subgroup.
The burgeoning demand on the world food supply, coupled with concern over the use of chemical fertilizers, has led to an accelerated interest in the practice of precision agriculture. This practice involves the careful control and monitoring of plant nutrition to maximize the rate of growth and yield of crops, as well as their nutritional value.