Biochar and compost: Recycling between Chesapeake poultry and corn production while mitigating nutrient leaching losses
Nutrient pollution from intensive food production contributes to many environmental problems, from river and coastal eutrophication to greenhouse gas production. Within the Chesapeake Bay watershed, nutrient pollution from poultry manure is a major concern because of the high density of animals and the value of local aquatic resources. Therefore, we asked whether using composted or biocharred poultry manure as fertilizer on cornfields reduced leaching losses compared to raw poultry manure or urea fertilizer. We worked at two experimental corn farms: State College, PA (high clay soil, 20% clay) and Georgetown, DE (high sand soil, 80-90% sand). At each, we established three 5x10m replicates of five treatments: no fertilizer control, urea, raw poultry manure, composted manure, and manure converted to biochar. We applied each fertilizer at recommended N levels (225kg N ha-1 in DE, 150kg N ha-1in PA). Immediately after plowing, and before fertilization, we installed tension lysimeters to a depth of 70cm in the center of each plot. We collected soil water bi-weekly throughout the growing season and analyzed nitrate, ammonium, and phosphate concentrations to compare N and P concentrations below the rooting zone across treatments.
At both sites, applying poultry manure as biochar or compost reduced deep soil water nutrient concentrations compared with raw manure application. For the high clay soils in PA, dissolved reactive N concentrations (dominanted by NO3- in all cases) below raw manure (19±2.8ppm) were ~2x higher than below biochar (11±1.4ppm) or urea (11±1.1ppm), which were in turn ~2x higher than below composted manure (6±1.0ppm) and the control (5±0.7ppm). The sandy soils in DE had lower N concentrations in deep soil water than the clay rich soils of PA (p<0.001). As in PA, N concentrations in DE were highest below raw manure (3.5±1.3ppm), and lowest below the biochar treatment (1.5±0.3ppm). Phosphate concentrations were slightly (~0.25ppm, p=0.003) higher in DE than PA. In DE, PO43- concentrations were higher below the raw manure-amended fields (1.9±0.1ppm) than below the compost plot (1.3±0.1ppm, p=0.03). Surprisingly, in PA, the concentration of PO43- beneath raw manure (0.8±0.1ppm) was lower (p=0.002) than the other treatments, which were not significantly different from each other (1.2-1.7ppm, p>0.2). Overall, these data suggest that recycling nutrients between Chesapeake poultry and corn production can help mitigate nutrient losses if the manure is biocharred or composted prior to its application.