Abstract
Minable rock phosphate is a finite resource. Replacing mineral phosphorus (P) fertilizer with P-rich secondary resources is one way to manage P more efficiently, but the importance of physicochemical and microbial soil processes induced by secondary resources for plant P uptake is still poorly understood. Using radioactive-labeling techniques, the fertilization effects of dairy manure, fish sludge, meat bone meal, and wood ash were studied as P uptake by barley after 44 days and compared with those of water-soluble mineral P (MinP) and an unfertilized control (NoP) in a pot experiment with an agricultural soil containing little available P at two soil pH levels, approximately pH 5.3 (unlimed soil) and pH 6.2 (limed soil). In a parallel incubation experiment, the effects of the secondary resources on physicochemical and microbial soil processes were studied. The results showed that the relative agronomic efficiency compared with MinP decreased in the order: manure ≥fish sludge ≥wood ash ≥meat bone meal. The solubility of inorganic P in secondary resources was the main driver for P uptake by barley (Hordeum vulgare). The effects of secondary resources on physicochemical and microbial soil processes were of little overall importance. Application of organic carbon with manure resulted in microbial P immobilization and decreased uptake by barley of P derived from the soil. On both soils, P uptake by barley was best explained by a positive linear relationship with the H2O + NaHCO3-soluble inorganic P fraction in fertilizers or by a linear negative relationship with the HCl-soluble inorganic P fraction in fertilizers.
Highlights
Minable rock phosphate is a finite resource
All secondary resources resulted in high P concentration as mineral P (MinP) on both soils except manure, which resulted in significantly lower P concentration than MinP on the limed soil
None of the secondary resources increased dry matter (DM) compared with no P fertilizer (NoP) on either soil, while MinP significantly increased DM compared with NoP on both soils
Summary
Minable rock phosphate is a finite resource. Industrialized agroecosystems are today far from managing phosphorus (P) efficiently and Europe’s food production is largely dependent on imports of mined rock phosphate [1]. The greatest reductions in P imports could be achieved by replacing mineral fertilizer with recycled P from secondary resources [2]. Drivers of Secondary P Recycling accumulated P content in secondary resources is often of the same order of magnitude as that in mineral fertilizer, as shown for Europe [3]. In Norway, the total amount of P in secondary resources (27,700 Mg P year−1) greatly exceeds the amount of P applied to soil with mineral fertilizer (8400 Mg P year−1) and the amount of P removed by crops (11,000 Mg P year−1) [4]. A residue from bioenergy plants and industrial timber production, contains considerable amounts of secondary P (800 Mg P year−1) [5]
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