Soil nutrients, phosphatase activities and phosphorus species distribution in soils amended sheep manure biochar

Sheep manure-derived biochar (SMB) is applied to enhance soil productivity, but its impacts on soil phosphorus (P) species distribution have not been thoroughly investigated. This research aimed to explore the effects of SMB amended soil on phosphatase activities, nutrients, P species distribution, and the underlying mechanisms in agricultural soil.

The soils (collected from rice and tea cultivation) were incubated for a period of 92 days receiving different rates of biochars 0% (CK), 2% (T₁) and 4% (T₂) respectively. The SMB was manufactured at 500°C, and P species were tested via ³¹P NMR spectroscopy. Acid phosphomonoesterase (ACP) activities, CEC, NH₄⁺–N, pH, NO₃^‾–N, Olsen‒ P and alkaline phosphomonoesterase (ALP) were determined.

The findings suggested that the SMB addition enhanced the pH, NO₃^‾–N, Olsen‒ P, CEC, NH₄⁺–N contents in both paddy and tea soils. Furthermore, compared with CK (control), application of SMB at T₂ reduced the ACP activities by 85.9 and 74.8%, but promoted the ALP activities by 89.1 and 70.6% for paddy and tea soils, respectively. The findings showed that major forms of P were orthophosphate and orthophosphate monoesters.

The SMB application increased soil inorganic P, P availability and ALP activities as a result of increasing of P availability by decomposition of organic P. Our research showed that the SMB application is an alternative nutrient for plants instead of chemical fertilizers. Nevertheless, care should be taken with the long-term SMB application, consequently excessive nutrient utilization has the potential to induce eutrophication in aquatic environments.