Fractionation and mobility of phosphorus in a sandy forest soil amended with biosolids |
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Authors: | Jingjun Su Hailong Wang Mark O Kimberley Katie Beecroft Guna N Magesan Chengxiao Hu |
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Institution: | (1) Ensis, Private Bag 3020, Rotorua, New Zealand;(2) College of Resources and Environment, Huazhong Agricultural University, Wuhan, 430070, China;(3) Glasson Potts Fowler Ltd., PO Box 6062, Rotorua, New Zealand |
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Abstract: | Goal, Scope and Background Biosolids, i.e., treated sewage sludge, are commonly used as a fertilizer and amendment to improve soil productivity. Application
of biosolids to meet the nitrogen (N) requirements of crops can lead to accumulation of phosphorus (P) in soils, which may
result in P loss to water bodies. Since 1996, biosolids have been applied to a Pinus radiata D. Don plantation near Nelson City, New Zealand, in an N-deficient sandy soil. To investigate sustainability of the biosolids
application programme, a long-term research trial was established in 1997, and biosolids were applied every three years, at
three application rates, including control (no biosolids), standard and high treatments, based on total N loading. The objective
of this study was to evaluate the effect of repeated application of biosolids on P mobility in the sandy soil.
Materials and Methods Soil samples were collected in August 2004 from the trial site at depths of 0–10, 10–25, 25–50, 50–75, and 75–100 cm. The
soil samples were analysed for total P (TP), plant-available P (Olsen P and Mehlich 3 P), and various P fractions (water-soluble,
bioavailable, Fe and Al-bound, Ca-bound, and residual) using a sequential P fractionation procedure.
Results and Discussion Soil TP and Olsen P in the high biosolids treatment (equivalent to 600 kg N ha−1 applied every three years) had increased significantly (P<0.05) in both 0–10 cm and 10–25 cm layers. Mehlich 3 P in soil of the high treatment had increased significantly only at
0–10 cm. Olsen P appeared to be more sensitive than Mehlich 3 P as an indicator of P movement in a soil profile. Phosphorus
fractionation revealed that inorganic P (Al/Fe-bound P and Ca-bound P) and residual P were the main P pools in soil, whereas
water-soluble P accounted for approximately 70% of TP in biosolids. Little organic P was found in either the soil or biosolids.
Concentrations of water-soluble P, bioavailable inorganic P (NaHCO3 Pi) and potentially bioavailable inorganic P (NaOH Pi) in both 0–10 and 10–25 cm depths were significantly higher in the
high biosolids treatment than in the control. Mass balance calculation indicated that most P applied with biosolids was retained
by the top soil (0–25 cm). The standard biosolids treatment (equivalent to 300 kg N ha−1 applied every three years) had no significant effect on concentrations of TP, Mehlich 3 P and Olsen P, and P fractions in
soil.
Conclusions The results indicate that the soil had the capacity to retain most biosolids-derived P, and there was a minimal risk of P
losses via leaching in the medium term in the sandy forest soil because of the repeated biosolids application, particularly
at the standard rate.
Recommendations and Perspectives Application to low-fertility forest land can be used as an environmentally friendly option for biosolids management. When
biosolids are applied at a rate to meet the N requirement of the tree crop, it can take a very long time before the forest
soil is saturated with P. However, when a biosolids product contains high concentrations of P and is applied at a high rate,
the forest ecosystem may not have the capacity to retain all P applied with biosolids in the long term.
ESS-Submission Editor: Dr. Jean-Paul Schwitzguébel jean-paul.schwitzguebel@epfl.ch |
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Keywords: | Biosolids land application leaching phosphorus fractionation plantation forest sandy soil |
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