LAUSR

Accurate information on soil inorganic phosphorus (Pi) is crucial for the sustainable development of agriculture in arid regions. An experiment was conducted to investigate the effect of cropping patterns on Pi concentrations in soil aggregates from the 0–10 cm depth in northwest China. The three cropping patterns were as follows: continuous cotton (CC), corn-wheat rotation (CW), and tree-cotton intercropping (TC). The results showed that more than 89% of the soil mass was in the macroaggregates (> 0.25 mm) in all cropping patterns, indicating a good soil structure in the study area. Total Pi and available P concentrations were significantly higher in the < 0.053 mm aggregate size class than in other classes (p < 0.05). As the dominant component, the Ca10-P accounted for 48.0–53.8% of total soil Pi. The Ca10-P concentrations decreased in the order CC > TC > CW. Additionally, the O-P concentrations were enriched in the CC treatment. But, the Ca8-P, Al-P and Fe-P concentrations were significantly greater in CW and TC than in CC. These results suggested that continuous cotton production leads to plant available Pi (Ca8-P, Al-P, and Fe-P) convert into unavailable Pi forms (Ca10-P and O-P). The TC system had the greatest contribution to total P in > 0.25 mm aggregates (p < 0.05), suggesting TC had a greater capacity to supply soil P. TC may be an appropriate farming practice for maximum availability of P in arid farmland ecosystems.