Changes in soil phosphorus fractions following sole cropped and intercropped maize and faba bean grown on calcareous soil

Abstract

This study aimed to investigate the effects of coexistence with faba bean, a phosphorus (P)-efficient crop, on soil-accumulated P use by a maize/faba bean intercropping system on dynamic changes in soil P pool. Maize and faba bean were grown in P-accumulated soil as either sole cropping or intercropping. After one year (Stage I) or four years (Stage II) of no P application, soil samples were collected respectively and analyzed for soil P pools using sequential fractionation. Aboveground biomass and P content were annually measured from 2013 to 2016 to assess the annual P balance. The intercropped maize/faba bean system showed a P-uptake advantage, with a Land Equivalent Ratio (LER) ranging from 1.2 to 1.5. The average shoot P content over the four years in intercropped maize and faba bean was significantly greater than that of the corresponding sole crops by 29% and 30%, respectively. Over the three-year P depletion period, the three cropping systems primarily depleted the 1 M HCl-Pi fraction, followed by sole maize, which depleted the NaOH-Pi and concentrated HCl-Po fractions. Sole faba bean depleted the alkali-soluble Po fraction (extracted by NaHCO3 and NaOH), and the intercropped maize/faba bean system depleted the conc. HCl-Po fraction, which was similar to the effect of sole maize. Both sole crops and intercrops mainly depleted 1 M HCl-Pi, but differed in Po depletion. Sole maize and maize/faba bean intercropping depleted the sparingly labile Po fraction, while sole faba bean depleted the labile and moderately labile Po fractions.