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Until recently, occurrence of milk fever (MF) has been attributed to prepartum calcium intake. However, researchers in Iowa have concluded that high prepartum dietary potassium (K) is the major cause of MF. Potassium concentrations have been increasing on manure fertilized soils over the last 20 years. Grasses grown on these fields mirror the increase in available soil K. When high K forages are fed to dry cows, it has been associated with increased MF in some, but not all cases. Our objective was to identify factors that differed between low and high occurrence of disorders when high K forages were fed. For 1 yr, monthly interviews were conducted on 10 dairies in Western Oregon. Close-up rations, dystocia rating, crowding, and cow comfort data were collected. Cows were diagnosed healthy or having one or more of the following metabolic diseases: MF, retained fetal membranes (RFM), and left displacement of the abomasum (LDA). Feedstuffs were collected each month and analyzed for dry matter, crude protein (CP), acid detergent fiber (ADF), and macrominerals. Of the multiparous cows (n=3,587) included, incidences of MF, RFM and LDA were 3.6, 11.3, and 1.5%, respectively. Increasing MF occurrence was associated with uncomfortable conditions, dystocia, increasing prepartum dietary Na and ADF, and increasing Ca to P ratios; there was also a dietary K by Mg concentration interaction. Increased dietary concentrations of Mg can prevent MF if dietary K is <2.6%. In addition, dietary conditions of K >2.6% and Mg >0.4% increase the occurrence of MF. Inversely, high concentrations of K can prevent MF in a Mg deficient diet. Dietary factors associated with an increase in the occurrence of RFM are increased dietary concentrations of Ca, S, CP, use of anionic salts, and the K forage source. Factors associated with an increase in hypocalcemia in the postpartum cow are crowding, uncomfortable housing, and a dietary K by Mg concentration interaction. In conclusion, improved cow comfort, and the addition of Mg to high K forage diets could decrease the risk of the cow exhibiting MF, RFM, and hypocalcemia. / Graduation date: 1999

M.S.

Three crops of corn (<i>Zea mays</i> L.) were grown on four Coastal Plain soils in a greenhouse study to determine the effects of increasing rates of Kon corn growth, elemental composition of corn tissue and soil nutrient levels. Plant height and production of dry matter were measured to determine the effect of K application on corn yield. Plant tissue concentrations of Ca, Mg and K were determined, as were NH₄OAc extractable soil Ca, Mg and K. Potassium, as KCl, was applied at rates of 0, 100, 200, 300 and 400 ppm K to the first corn crop. Potassium application of 100 ppm increased corn yield on the Kenansville and Uchee soils, but no further increase or decrease in yield occurred at higher K rates. Increasing K rates caused an increase in plant tissue Kand a simultaneous decrease in plant tissue Mg. Plant tissue Ca was also reduced in plants grown on the Kenansville and Uchee soils. Magnesium deficiency symptoms were observed on corn plants grown at K rates greater than 100 ppm Kon the Goldsboro, Kenansville, and Uchee soils. Magnesium deficiency was confirmed by plant tissue analysis which revealed plant Mg levels as low as 0.07% on the Goldsboro soil. A second corn crop was grown in the previously amended soil. Results were similar to the first crop with yield increasing with the application of 200 ppm K on the Kenansville and Uchee soils. Yields did not significantly increase or decrease at higher K rates. Plant tissue K increased with increasing K rates with a simultaneous decrease in plant tissue Mg in plants grown on three of the four soils. Potassium, as K₂SO₄•2MgSO₄, was applied to a third corn crop at the same K rates as the first crop (ie. 0, 100, 200, 300, and 400 ppm K). Application of K₂SO₄•2MgSO₄ also supplied Mg at rates of 0, 60, 120, 180 and 240 ppm Mg. Plant yield increased at the 100 ppm K application rate on the Kenansville and Uchee soils, but decreased at rates of 300 ppm Kor greater on the Kenansville and at rates of 200 ppm Kor greater on the Uchee soil. Plant tissue K increased in plants grown on all soils, and Mg increased in plants grown on three of the four soils. However, Ca levels in plant tissue were reduced with increasing Kand Mg application in plants grown on all soils. Reduction in yield on the Kenansville and Uchee soils coincided with Ca levels of 0.3% or less. These Ca levels are considered to be insufficient for proper plant growth and decreases in plant yield were attributed to Ca deficiency. Excessive rates of K as K₂SO₄•2MgSO₄ (300 and 400 ppm K) were necessary to induce Ca deficiency. / M. S.

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The role of manure applications on soil nutrient dynamics in years after manure applications cease has not been extensively studied. An investigation of two long-term manure trials in the Battersea Drain watershed in southern Alberta was undertaken in 2004 to determine changes in soil nutrient status three years after the initial study was completed. The investigation of the nutrient status of an intensive livestock operation was another component of the study. There was a significant decrease in levels of soil nitrogen, phosphorus and potassium in the plots that received manure application rates over 60 Mg ha-1. The nutrient status of the farm showed a net export of nitrogen and an accumulation of phosphorus and potassium in the soil. Recommendations for alternate methods for handling manure were presented. / x, 120 leaves : ill (some col.), col. maps ; 29 cm