The effect of repeated liquid swine manure applications on soil nutrient supply rates and growth of different hybrid poplar clones
Intensive hog operations generate large amounts of manure that must be dealt with in an environmentally responsible and economically practical manner. Repeated applications of liquid swine manure within nearby hybrid poplar plantations recently has been proposed as an effective alternative manure management practice, given that these fast-growing tree species have high soil moisture and nutrient demands and, therefore, represent a tremendous sink for the applied effluent. The objectives of this two-year study were to: i) evaluate the effect of repeated broadcast applications of liquid swine manure on soil nutrient supply rates and growth of five hybrid poplar clones (CanAm, Hill, Katepwa, Walker, and WT-66V) and, ii) assess the relationship between growing season soil nutrient supply rates, measured using in situ burials of ion-exchange membrane (Plant Root Simulator™-probes), and growth of different hybrid poplar clones. There was a limited effect of applied hog effluent on soil nutrient supply rates after the first year and hybrid poplar growth after two years, which is surprising considering the application rate was three times larger than the agronomic rate typically applied. The limited measureable difference following manure addition may be attributable to a number of factors, including: substantial volatilization, microbial immobilization, increased leaching and denitrification losses, timing of manure application being out of sync with temporal nature of nutrient uptake by the trees, and a delayed growth response as absorbed nutrients are retranslocated within the trees. Determining the effects of repeated applications of hog effluent on soil nutrient supply rates and subsequent tree growth should help to support effective management strategies, in terms of developing practical effluent management practices required to mitigate any adverse environmental effects, but also increasing plantation productivity and the concomitant non-wood product benefit of increasing biodiversity within the agricultural landscape.
Plant Root Simulator™-probes
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