Abstract
Although composted liquid pig manure is increasingly being applied to agricultural soils, little is known about its impacts on N dynamics (mineralization, denitrification, immobilization, and plant uptake) in the crop root zone compared to liquid pig manure (LPM) or other types of composts. A greenhouse pot experiment was conducted to determine N mineralization and plant uptake in a ryegrass-cropped clay loam soil that had been amended with either LPM, LPM + wheat straw compost (PMS), or yard waste compost (YWC). Over a 20-wk growth period, plant biomass was increased relative to the control by 164% for LPM, 64.3% for YWC, and 39.6% for PMS. However, the recovery of amendment N in the ryegrass was low and variable at 3.3% for PMS (12.7 mg N kg-1), 3.7% for YWC (21.5 mg N kg-1), and 15.3% for LPM (90.9 mg N kg-1). Although gains and losses of mineral N occurred primarily within the first 8 wk, assimilation of amendment N by the ryegrass appeared to continue throughout the entire growth period. High amounts of inorganic N present in the LP M treatment led to the greatest loss of N, as N2O, through denitrification and nitrification (39.1 mg N kg-1). This was 35 times greater than the YWC treatment (1.1 mg N kg-1), over 50 times greater than the N2O loss from the PMS treatment (0.7 mg N kg-1) and over 76 times greater than the N2O loss from the control (0.5 mg N kg-1). There was a net gain in mineral and plant assimilated N from mineralization with the control (6.4 mg N kg-1) and YWC treatments (8.8 mg N kg-1) over 20 wk. However, there was a small decrease in mineral and plant assimilated N with the PMS treatment (4.3 mg N kg-1) and a large decrease with the LPM treatment (90.1 mg N kg-1). From an environmental perspective, the large amount of N2O generated by the LPM treatment compromises the usefulness of LPM as a source of crop-available N. Key words: Compost, pig manure, ryegrass, swine, hog, nitrogen mineralization
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