Suwei Xu, Yuhei Nakayama, Maia G. Rothman, Andrew J. Margenot
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引用次数: 0
Abstract
Agricultural management practices can profoundly influence soil phosphorus (P), with effects accumulating over time. To test the overarching hypothesis that soil P pools estimated by sequential fractionation would be altered by long-term agricultural practices, we used an experiment established in 1876 in the north-central US to quantify 145-year impacts of crop rotation (continuous maize [Zea mays L.], maize-soybean [Glycine max L. Merr.] and maize-oat [Avena sativa L.]-alfalfa [Medicago sativa L.]) and 117-year impacts of fertilization (unfertilized and fertilized) with rock phosphate, manure or synthetic fertilizer on soil P fractions at 15 cm intervals across 0–90 cm depth. Fertilization impacts on soil P were mostly limited to the surface (0–30 cm) depth, but extended to 90 cm depth under diverse rotations. Under fertilization, soil total P concentration increased by 51% at 0-30 cm while concomitantly decreasing by 30% at 60–90 cm compared to no fertilization, indicating that vertically stratified surface soil P accumulation and subsoil P depletion can co-occur even under positive P balances. Positive P balances (1222–1494 kg/ha) induced by fertilization enriched inorganic P (Pi) (+39% to 358%) and labile organic P (Po) fractions (+11%) while depleting non-labile Po fractions (−31%), with depletion increasing with the degree of crop diversification. Fertilization had minor impacts on P fractions beyond 30 cm depth, except for acid extractable Pi (HCl-Pi) depletion under continuous maize and maize-soybean rotations (−16% to −78%) and accumulation under maize-oat-alfalfa rotation (+41% to +84%) at 60–90 cm. In contrast, without fertilization, diversifying maize rotations with oat and alfalfa decreased HCl-Pi and residual P (−21% to −57%) but increased non-labile Po fractions (+54%), suggesting potential mining of non-labile Pi pools by deep-rooted legumes under nutrient limitation. The 1–2 orders of magnitude greater changes in stocks of P fractions than stocks of total P emphasize the importance of distinguishing P pools even with operational fractionation to fully capture changes in P cycling beyond total P stocks. Our study revealed that a positive P balance under 117 years of fertilization (i) enriched Pi and labile Po pools but (ii) depleted non-labile Po pools, (iii) largely at 0–30 cm, and (iv) non-labile Po depletion increased with crop diversification under 145-year rotation treatments.
期刊介绍:
The EJSS is an international journal that publishes outstanding papers in soil science that advance the theoretical and mechanistic understanding of physical, chemical and biological processes and their interactions in soils acting from molecular to continental scales in natural and managed environments.