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Nitrogen Budget and Soil N Dynamics after Multiple Applications of Unlabeled or ¹⁵Nitrogen-Enriched Dairy Manure

^a Dep. of Soil Science, Univ. of Wisconsin, 1525 Observatory Dr., Madison, WI 53706
^b USDA-ARS Dairy Forage Research Ctr., 1925 Linden Dr. West, Madison, WI 53706

View larger version (18K): [in a new window]   Fig. 1. Actual and fitted total soil N levels to a depth of 90 cm as affected by repeated manure or fertilizer applications in south-central Wisconsin, 1998–2000. Fertilizer rates were 90 and 179 kg N ha-1 yr-1 for the low and high levels, respectively. 3-yr average manure rates were 236 and 459 kg total N ha-1 yr-1 for the low and high levels, respectively. Regression equations: Fertilizer high, y = 12.88 + 0.4004x, R2 = 0.743, P = 0.027; Fertilizer low, y = 12.76 + 0.3775x, R2 = 0.637, P = 0.057; Manure high, y = 14.48 - 1.241x + 0.2595x2, R2 = 0.912, P = 0.026; Manure low, y = 14.83 - 2.115x + 0.3579x2, R2 = 0.906, P = 0.029; Control, y = 13.53.

View larger version (16K): [in a new window]   Fig. 2. Soil NO3–N increase due to manure application frequencies as estimated by 15N measurements in south-central Wisconsin, 2000. Numbers above each bar represent the percentage of recovered 15NO3–N present in the top 30 cm only. For NO3–N increase in the 0- to 90-cm depth, bars with the same letter are not significantly different at the 0.05 level.

View larger version (19K): [in a new window]   Fig. 3. Total soil N increase due to manure application frequencies as estimated by 15N measurements in south-central Wisconsin, 2000. Numbers above each bar represent the percentage of recovered total soil 15N present in the top 30 cm of soil only. For total N increase in the 0- to 90-cm depth, bars with the same letter are not significantly different at the 0.05 level.