Leaching of basic cations by winter rainfall and irrigation water and the increasing use of NH+4‐fertilizers have resulted in wide‐spread soil acidity in western Oregon. While applications of liming materials are often made in this region, the rates at which limed soils reacidify are generally not known. The objectives of this study were to: (i) quantify long‐term acidification rates of two lime‐amended soils in western Oregon, and (ii) identify soil‐plant processes which may control acidification rates. Lime applications ranging from 0 to 14 650 kg ha−1 were made on a Nekia sicl (Xeric Haplohumults, initial pH 5.0) and from 0 to 11 200 kg ha−1 on a Woodburn sil (Aquultic Argixerolls, pH 5.3) in the Willamette Valley of western Oregon in 1971 to 72. Monitoring of soil pH and levels of extractable basic cations applied in the liming materials for 11 to 12 yr permitted estimation of the rate of acidification of soils receiving different amounts of lime. Whether estimated by declines in pH or extractable basic cations, soil acidification rates increased with increasing quantities of lime initially applied. Acidification rates of unlimed Nekia soil were 0.025 pH units yr−1 and 0.17 cmol(+) Ca2+ + Mg2+ kg−1yr−1 while the unlimed Woodburn soil showed no net acidification. Maximum rates of acidification of 0.09 pH units yr−1 and 0.62 cmol(+) extractable Ca2+ + Mg2+ kg−1yr−1 on the Nekia soil and 0.08 pH units yr−1 and 0.36 cmol(+) extractable Ca2+ kg−1yr−1 on the Woodburn soil were measured on plots receiving the highest amounts of lime. Faster reacidification of soils amended with higher lime rates is explained by the pH dependence of acidifying processes such as nitrification, CO2 release via plant and microbial respiration, mineralization of organic matter and dissociation of organic acids in soil solution. Ca2+ release from mineral weathering appeared to have an important effect on soil pH and extractable Ca2+, particularly in the absence of large inputs of acidifying materials such as NH+4‐fertilizers. Accurate prediction of soil acidfication rates will require additional information concerning the pH dependence of soil acidifying processes, the quantity and composition of seasonal through drainage, and the rates of mineral weathering in soils.
Using a lime requirement (LR) test not calibrated under field conditions or on soils which differ greatly from those used to calibrate the procedure may lead to erroneous results. The objectives of this research were, (i) to compare under field conditions the accuracy of four methods of interpreting the SMP LR test, and (ii) to quantify the random, constant, and proportional error associated with each method. Lime applications ranging from 0 to 14.6 Mg ha−1 were made to field plots on two acid soils in northwest Oregon. Surface soil samples taken prior to liming were analyzed according to four methods of interpreting the SMP lime requirement test, namely the original SMP single buffer (SB), McLean's double buffer (DB) and two modified SMP procedures currently used in Oregon and Washington (Modified SB and Modified SB + initial pH, respectively). Statistical models from these four methods were algebraically solved to permit calculation of predicted pH values due to lime amendment which were compared to soil pH measured one and two years after liming. The proportional errors associated with the Original SB, DB, Modified SB and Modified SB + initial pH procedures were 1.2, 1.3, 0.19, and 0.06, respectively. The magnitudes of the constant and random errors associated with these same four methods were 7.8, 8.6, 0.64, and 0.26 pH units; and 0.83; 0.77, 0.19, and 0.25 pH units, respectively. All methods not calibrated under field conditions under‐predicted soil pH values resulting from applications of lime by an average of 0.5 to 0.7 pH units. These results emphasize the importance of employing field conditions and soils from similar geographical areas when calibrating LR tests.
In an irrigated pasture experiment on Vancouver Island, on a soil deficient in available nitrogen and potassium but apparently containing sufficient available phosphorus, calcium and magnesium for adequate plant growth, an irrigated Ladino clover-grass mixture greatly outproduced a grass mixture on a forage, protein and mineral nutrient yield basis. In order to attain even a moderate yield with a grass mixture, heavy fertilization with nitrogen and potassium was necessary. Nitrogen fertilization was not essential to high yields with the Ladino clover-grass mixture. Nitrogen fertilization tended to decrease the per cent Ladino clover and the protein and calcium content in the clover-grass forage and increased the protein content of the grass herbage. The calcium content of the grass herbage was decreased by nitrogen fertilization. The phosphorus and magnesium contents of the clover-grass and grass herbage were not appreciably altered by nitrogen fertilization. Decreasing the time interval between nitrogen applications resulted in a more even production of dry matter over the growing season but did not increase the total seasonal yield. Potassium fertilization increased the yield of both mixtures and increased the per cent clover in the grass-clover sward. Multi-annual potassium applications were required for the elimination of plant potassium deficiency symptoms and the applied potassium was quickly absorbed by the plants. Grass herbage contained more potassium, slightly more phosphorus and less calcium, magnesium and nitrogen than grass-clover herbage.
Surface soil from five diverse soil series was used to investigate the influence of soil properties and constituents on the mobility of boron (B) in a greenhouse study. Using pots 16.5 by 18.5 cm in diameter, from 13 to 61% of a 2.0 mg/kg liquid application of B was recovered in 25 cm of leachate. Recovery of B decreased with increased soil organic matter, clay, and free Fe and Al oxide content, but statistical separation of the effects of individual components was complicated by intercorrelations among these soil properties. No effect of soil pH on B mobility over a range of 5.4 to 7.5 was observed.Following leaching, the soils were cropped with New Zealand white clover (Trifolium repens L.). Yield differences were not correlated with hot water‐extractable B levels ranging from 0.47 to 2.34 µg/g or with B applied at planting. Plant B concentrations were high, ranging from 60 to 150 µg/g. As the range in hot water‐soluble B values encompassed current concepts of deficiency levels in western Oregon soils, the merits of investigating soil‐B critical levels under greenhouse conditions are questioned.A balance sheet approach indicated that soils have reserves of leachable and plant‐available B not detected in the conventional hot water extraction. The boron‐supplying power of these soils varied both within and among soil series and depended on soil properties and the amount of B in the soil system.
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