Dairy Manure Influences on Phosphorus Retention Capacity of Spodosols
- V. D. Nair *,
- D. A. Graetz and
- K. R. Reddy
Land areas used for dairy farming can result in accumulation of manure on soils that could produce nutrient-rich surface and subsurface runoff and cause accelerated lake eutrophication. This research was conducted on Spodosols that were differentially impacted by manure; the study included sites with different levels of total P (TP), from 2300 mg kg−1 in the soil highly impacted by intensive dairy farming to 18 mg kg−1 in an unimpacted area. The P retention characteristics of these soils were determined by using both single-point (1000 mg P kg−1 or 100 mg P L1) and traditional Langmuir isotherms. Phosphorus sorption values using a single high P solution had approximately a 1:1 relationship with values obtained for the maximum retention capacity, Smax, obtained from Langmuir isotherms (r2 = 0.98). The surface A and E horizons of manure-impacted soils had essentially no sorbing capacity while the Bh (spodic) and Bw horizons had mean Smax values 430 and 385 mg kg−1, respectively. The P sorbing capacity of the Bh and Bw horizons were attributed to high Al concentrations in these horizons. Higher P concentrations in the surface A horizon resulted in greater P concentrations in solutions equilibrated with the Bh- and Bw- horizon materials, which suggests a potential for vertical P movement through the soil profile. The spodic horizon of the less-impacted soils may not have been exposed to sufficiently high solution P concentrations to accumulate significant P in the soluble fraction.
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