Effects of companion crops and tillage on soil phosphorus in a Brazilian oxisol: a chemical and 31P NMR spectroscopy study
2021
Eberhardt, Diogo | Marchão, Robélio | Quiquampoix, Hervé | Le Guernevé, Christine | Ramaroson, Volaniaina | Sauvadet, Marie | Muraoka, Takashi | Becquer, Thierry
PURPOSE: Phosphorus (P) is often the main limiting factor for plant growth in highly weathered tropical soils. Phosphate use efficiency and crop yields could be increased in low-input agroecosystems through cropping systems that favor organic matter accumulation or regular additions of composts and manure. Our objective was to determine the amounts and forms of P according to companion crops (Brachiaria ruziziensis–a grass species–or Cajanus cajan–a leguminous species) and tillage systems (conventional or no-tillage). MATERIALS AND METHODS: Soil P pools were determined (Pᵣₑₛᵢₙ, POₗₛₑₙ, PNₐOH₋EDTA, and Pₜₒₜₐₗ) and P species were characterized by ³¹P NMR spectroscopy. RESULTS AND DISCUSSION: The concentrations of available and labile inorganic P (Pᵣₑₛᵢₙ, PiOₗₛₑₙ, and PiNₐOH₋EDTA) were greater in soil samples where companion crops (Brachiaria ruziziensis or Cajanus cajan) and maize were planted on the same row, with a more significant effect with the legume species. According to the ³¹P NMR, it is mostly the proportion and amount of POᵣₜₕₒₚₕₒₛₚₕₐₜₑ that was increased, with a slight increase of the content of PMₒₙₒₑₛₜₑᵣ. Overall, there was a decrease of the proportion of organic P (PoNMR/PNMR) from 32 to 16% when the legume companion crop was associated with maize. CONCLUSIONS: The tillage systems did not lead to any change in the amounts and forms of P. Companion crops are thought to increase available P through mineralization of Po from plant residues and soil organic matter, leading to an increase of fluxes between active P pools.
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