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71.
Charles C. Mitchell Gobena Huluka 《Communications in Soil Science and Plant Analysis》2016,47(22):54-63
ABSTRACTPotassium (K) deficiency in crops in southern US Coastal Plain soils has been documented since the l880s. Long-term soil fertility studies such as Alabama’s “Cullars Rotation” experiment (circa 1911) have been conducted with K since 1911. Other Alabama long-term experiments on several Coastal Plain and related Hapludults, Paleudults, and Kandiudults also contain K variable treatments which have been monitored since 1929. Soil test data from these long-term experiments have allowed us to answer some practical questions regarding K dynamics in Coastal Plain soils. Potassium movement through the soil profile is dependent on the soil’s cation exchange capacity (CEC) but relative accumulation is greater in the plow layer regardless of soil CEC. While subsoil K testing may be useful for identifying situations where subsoil K has been depleted, this extra effort and expense is not necessary for most cropping situations. A crop will remove most of its K from the plow layer if it is present in sufficient quantity based on soil test. Crop depletion of plow-layer K to the point where yield may be reduced is gradual and may take 10–15 years or more depending upon soil CEC and initial soil K concentration. Depletion is most rapid in low CEC soils as would be expected. However, soil test K can vary considerably during the course of a crop season with the lowest soil test K concentrations occurring immediately after harvest. 相似文献
72.
Upendra M. Sainju Harry H. Schomberg Bharat P. Singh Wayne F. Whitehead P. Glynn Tillman Sharon L. Lachnicht-Weyers 《Soil & Tillage Research》2007,96(1-2):205-218
Cover crops may influence soil carbon (C) sequestration and microbial biomass and activities by providing additional residue C to soil. We examined the influence of legume [crimson clover (Trifolium incarnatum L.)], nonlegume [rye (Secale cereale L.)], blend [a mixture of legumes containing balansa clover (Trifolium michelianum Savi), hairy vetch (Vicia villosa Roth), and crimson clover], and rye + blend mixture cover crops on soil C fractions at the 0–150 mm depth from 2001 to 2003. Active fractions of soil C included potential C mineralization (PCM) and microbial biomass C (MBC) and slow fraction as soil organic C (SOC). Experiments were conducted in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) under dryland cotton (Gossypium hirsutum L.) in central Georgia and in Tifton loamy sand (fine-loamy, siliceous, thermic, Plinthic Kandiudults) under irrigated cotton in southern Georgia, USA. Both dryland and irrigated cotton were planted in strip tillage system where planting rows were tilled, thereby leaving the areas between rows untilled. Total aboveground cover crop and cotton C in dryland and irrigated conditions were 0.72–2.90 Mg C ha−1 greater in rye + blend than in other cover crops in 2001 but was 1.15–2.24 Mg C ha−1 greater in rye than in blend and rye + blend in 2002. In dryland cotton, PCM at 50–150 mm was greater in June 2001 and 2002 than in January 2003 but MBC at 0–150 mm was greater in January 2003 than in June 2001. In irrigated cotton, SOC at 0–150 mm was greater with rye + blend than with crimson clover and at 0–50 mm was greater in March than in December 2002. The PCM at 0–50 and 0–150 mm was greater with blend and crimson clover than with rye in April 2001 and was greater with crimson clover than with rye and rye + blend in March 2002. The MBC at 0–50 mm was greater with rye than with blend and crimson clover in April 2001 and was greater with rye, blend, and rye + blend than with crimson clover in March 2002. As a result, PCM decreased by 21–24 g CO2–C ha−1 d−1 but MBC increased by 90–224 g CO2–C ha−1 d−1 from June 2001 to January 2003 in dryland cotton. In irrigated cotton, SOC decreased by 0.1–1.1 kg C ha−1 d−1, and PCM decreased by 10 g CO2–C ha−1 d−1 with rye to 79 g CO2–C ha−1 d−1 with blend, but MBC increased by 13 g CO2–C ha−1 d−1 with blend to 120 g CO2–C ha−1 d−1 with crimson clover from April 2001 to December 2002. Soil active C fractions varied between seasons due to differences in temperature, water content, and substrate availability in dryland cotton, regardless of cover crops. In irrigated cotton, increase in crop C input with legume + nonlegume treatment increased soil C storage and microbial biomass but lower C/N ratio of legume cover crops increased C mineralization and microbial activities in the spring. 相似文献
73.
Wareham NJ Jakes RW Rennie KL Schuit J Mitchell J Hennings S Day NE 《Public health nutrition》2003,6(4):407-413
74.
Nobuhito Ohte Myron J. Mitchell Hideaki Shibata Naoko Tokuchi Hiroto Toda Goro Iwatsubo 《Water, air, and soil pollution》2001,130(1-4):649-654
To analyze the differences in the status and processes of nitrogen saturation in Japan and northeastern United States, we examined the hydrobiogeochemistry of nitrogen of forested watersheds in these regions. Two distinct differences were found between watersheds in Japan compared with those in US. 1) In Japanese watersheds, marked decreases of NO3 ? concentration in surface waters during the summer growing season were not found and NO3 ? concentrations sometimes increased especially in the summer at nitrogen saturated sites. This contrast with watersheds in US where decreases in NO3 ? concentration during the summer are commonly observed except those watersheds in advanced stages of nitrogen saturation. These differences in NO3 ? concentration relationships can be attributed to climatic differences, with Japan having high precipitation and high discharge during the summer, while in many regions of North America lowest discharges are found in the summer. The climatic regime in Japan leads to high rates of mineralization and the rapid transport of NO3 ? to streams in summer. 2) Japanese watersheds, even those with high NO3 ? concentrations in surface waters, show little evidence of acidification. This is in contrast to sites in US where increased NO3 ? concentrations, especially during episodic events, result in surface water acidification. 相似文献
75.
76.
F E McDonough F H Steinke G Sarwar B O Eggum R Bressani P J Huth W E Barbeau G V Mitchell J G Phillips 《Journal of the Association of Official Analytical Chemists》1990,73(5):801-805
Eight laboratories participated in a collaborative study to estimate precision of a standardized rat assay for determining true protein digestibility in selected animal, fish, and cereal products. Each of 7 test protein sources (casein, tuna fish, macaroni/cheese, pea protein concentrate, rolled oats, pinto beans, and nonfat dried milk) was fed as the sole source of protein at a 10% protein level in mixed diets. Each diet was fed to 2 replicate groups of 4 rats each for a 4-day acclimation period and a 5-day balance period. Mean digestibilities ranged from 98.6% for casein to 72.6% for pinto beans. Repeatability standard deviations ranged from 0.5 to 2.0%; the mean relative standard deviation for repeatability was 0.9% (range 0.5-2.8%). Reproducibility standard deviations ranged from 1.2 to 3.2%, and the mean relative standard deviation for reproducibility was 2.4% (range 1.3-4.4%). The method has been approved interim official first action for determining true protein digestibility in foods and ingredients. 相似文献
77.
Campbell John L. Hornbeck James W. Mitchell Myron J. Adams Mary Beth Castro Mark S. Driscoll Charles T. Kahl Jeffrey S. Kochenderfer James N. Likens Gene E. Lynch James A. Murdoch Peter S. Nelson Sarah J. Shanley James B. 《Water, air, and soil pollution》2004,151(1-4):373-396
Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watersheds at 15 locations in the northeasternUnited States. The study watersheds are completely forested, free of recent physical disturbances, and span a geographical region bounded by West Virginia on the south and west, and Maine on the north and east. Total N budgets are not presented; however, fluxes of inorganic N in precipitation and streamwater dominate inputs and outputs of N at these watersheds. The range in inputs of DIN in wet-only precipitation from nearby National Atmospheric Deposition Program (NADP) sites was 2.7 to 8.1 kg N ha-1 yr-1 (mean = 6.4 kg N ha-1 yr-1; median = 7.0 kg N ha-1 yr-1). Outputs of DIN in streamwater ranged from 0.1 to 5.7 kg N ha-1 yr-1 (mean = 2.0 kg N ha-1 yr-1; median = 1.7 kg N ha-1 yr-1). Precipitation inputs of DIN exceeded outputs in streamwater at all watersheds, with net retention of DIN ranging from 1.2 to 7.3 kg N ha-1 yr-1 (mean = 4.4 kg N ha-1 yr-1; median = 4.6 kg N ha-1 yr-1). Outputs of DIN in streamwater were predominantly NO3-N (mean = 89%; median = 94%). Wet deposition of DIN was not significantly related to DIN outputs in streamwater for these watersheds. Watershed characteristics such as hydrology, vegetation type, and land-use history affect DIN losses and may mask any relationship between inputs and outputs. Consequently, these factors need to be included in the development of indices and simulation models for predicting 'nitrogen saturation' and other ecological processes. 相似文献
78.
The severely depleted bowhead whale Balaena mysticetus has failed to recover from overexploitation during the 18th and 19th centuries in the Eastern Arctic. Although commercial whaling for bowheads ended in this region about 1915, bowhead whaling by native people has continued until recently in parts of the Eastern Arctic. Low-level but persistent hunting by Inuit (Eskimos) may have inhibited bowhead population increase. Two natural mortality factors can be documented—ice entrapment and predation by killer whales Orcinus orca. There is little direct evidence of ice-related mortality but a strong circumstantial argument that ice conditions affect survival. Killer whales are known to prey on most species of large whales, and we believe bowhead whales and right whales Eubalaena glacialis are especially vulnerable. The bowhead's apparent failure to recover in the Eastern Arctic may be due to a combination of continued low-level hunting, habitat instability, and predation. Complete protection from all forms of hunting is necessary to ensure the bowhead's survival. Environmental disturbances due to industrial development in the Arctic may have direct and indirect impact on bowhead habitat and behaviour, creating an urgent need for further study. 相似文献
79.
80.