Abstract
Phosphate mineral fertilisers are manufactured from non-renewable resources. Soil fertilisation with composts is considered a good source of reuse nutrients such as phosphorus (P). The aim of this work was to evaluate the effect of compost fertilisation on soil P sorption and consequently on P availability. It was done an incubation experiment followed by a sorption experiment in a low-P acid soil fertilised with compost (CP) or single superphosphate (SSP). The P application rates were: 0, 6.5, 13, 26 and 52 (kg•P•ha−1). In CP treatments, the rates 26 and 52 kg•P•ha−1 were achieved by adding SSP to CP since it was not allowed to incorporate into soil more than 170 kg•N•ha−1 from organic amendments. Although SSP has a higher proportion of easily available P than CP (86% vs 50%), the results showed that after 140 days of soil incubation, the available P was higher in CP treatments compared with SSP at the same rate of P application. The sorption experiment showed that after incubation of the fertilised soils, the P sorption maximum had lower values in treatments with CP in combination with SSP compared with only SSP fertilisation and the bonding energy had a deeper decrease in the same treatments. Also, the Standard Phosphate Requirement decreased in the CP in combination with SSP treatments. The reduction of soil P sorption capacity after compost addition to soil highlights the need of reducing P fertilisation rates to achieve similar levels of available P compared with only SSP fertilisation.
Highlights
The phosphorus (P) availability depends on the P sorption/desorption processes between the solid and the liquid phases of the soil
SSP has a higher proportion of available P than CP (86% vs 50%), the results showed that after 140 days of soil incubation, the available P was higher in CP treatments compared with SSP at the same rate of P application
The main processes to explain this conclusion include: 1) Competitive sorption between humic and fluvic acids [10] [11] [12] or low molecular weight aliphatic acids (LOA) and P for soil sorption sites resulting in increased P concentration in the soil solution [13] [14] [15]; 2) Metal complexation with Organic (DM) Matter (OM) compounds (LOA) or dissolution reactions affecting mainly Fe an Al oxides decreasing P sorption sites [14] [16] and 3) Sorption of OM compounds that could increase the negative charge on the soil surface, or decrease the point of zero charge (PCZ) increasing the resistance to P sorption
Summary
The phosphorus (P) availability depends on the P sorption/desorption processes between the solid and the liquid phases of the soil. The main processes to explain this conclusion include: 1) Competitive sorption between humic and fluvic acids [10] [11] [12] or low molecular weight aliphatic acids (LOA) and P for soil sorption sites resulting in increased P concentration in the soil solution [13] [14] [15]; 2) Metal complexation with OM compounds (LOA) or dissolution reactions affecting mainly Fe an Al oxides decreasing P sorption sites [14] [16] and 3) Sorption of OM compounds that could increase the negative charge on the soil surface, or decrease the point of zero charge (PCZ) increasing the resistance to P sorption Unlike these effects, OM added to soil could increase the formation of metal bridges leading to increased P sorption sites [17] or in turn the P content of the added OM could be a source of available P to soil solution [18] [19].
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