Organic and inorganic P forms in soil as affected by cover crops and nitrogen fertilization

The objective of this work was to evaluate the effects on organic and inorganic forms of soil phosphorus of the cultivation of cover crops and the use of nitrogen levels in soil under notillage system. The experiment was carried out in a randomized complete block design, in split plot, on a Rhodic Hapludox. The main treatments were cover crops: four legumes, one grass, and fallow (spontaneous vegetation); the secondary treatments were N fertilization in top-dressing (0 and 120 kg ha(-1)) applied on corn. Soil samples were collected 12 years after the beginning of the experiment, and organic and inorganic P forms were measured in them. The P forms were extracted with: resin; solutions of NaHCO3, NaOH, and HCl; and a mixture of H2SO4+ H2O2+ HF. The obtained forms were classified as labile P (resin-P + NaHCO3-P), moderately labile P (NaOH-P) and non-labile P. The cultivation of sunn hemp, lablab, and velvet bean in corn pre-cropping increases the moderately labile organic P (Po-NaOH I) in the topsoil in comparison with the fallow area. Nitrogen fertilization favors organic P mineralization in soil and redistributes forms of inorganic and organic P between the labile and moderately labile compartments, without impacting available P.