Continuous Intercropping Increases the Depletion of Soil Available and Non-Labile Phosphorus

Abstract

Background and aims: This research aimed to evaluate the effects of consecutive intercropping on soil phosphorus (P) partitioning, concentrations, and sensitivity to P fertilizer application, elucidating its impact on soil P bioavailability. Methods: A field experiment investigated soil P fractions and content under continuous wheat and faba bean intercropping. Three P levels (0, 45, and 90 kg P2O5 ha−1 denoted as P0, P1, and P2, respectively) and three planting patterns (monocropped wheat (MW), monocropped faba bean (MF), and wheat and faba bean intercropping (W//F)) were established since 2014. Aboveground P uptake by wheat and faba bean was determined. The soil P fractions and content were analyzed after six-, seven-, and eight-year continuous field experiments. Results: Wheat and faba bean intercropping increased wheat aboveground P uptake by 28.3–42.7% compared to MW under P1 and P2 levels and presented a P uptake advantage (LERPuptake > 1), although W//F had no impact on faba bean P uptake. Consequently, continuous intercropping for 8 years decreased soil available P reserves by 9.0–23.4% in comparison to the weighted average value of MW and MF (It). Faba bean consumed greater non-labile and labile P than wheat with low P input. W//F had nearly no impact on the labile P pool but reduced the non-labile P pool by 5.0–12.1% under all P levels and lowered the moderately labile P pool by 1.7–4.7% at P0 and P1 levels compared to It with consecutive intercropping for 8 years. Consecutive intercropping of wheat and faba bean primarily decreased the proportion of Resin-P in the labile P pool and the proportion of Residual-P in the non-labile P pool. According to the structural equation model, crop P uptake mainly originated from soil available P, which was directly affected by non-labile P (Residual-P and Conc. HCl-P). In addition, intercropping changed the contribution of each P faction to crop P uptake compared to MW and MF, and P uptake in intercropping primarily depended on Conc. HCl- P and Dil. HCl-P. Therefore, consecutive intercropping decreased soil non-labile P and drove soil available P depletion, and intercropping’s increase of P uptake was related to the non-labile P mobilized to moderately labile and labile P. Conclusions: Continuous wheat and faba bean intercropping reduced non-labile P and led to soil available P depletion under low P input. This practice stimulated non-labile P mobilization, enhancing soil P fraction effectiveness and facilitating P uptake in intercropping. Continuous intercropping of wheat and faba bean is as an effective method to maximize the biological availability of soil P and reduce P application rates.