Effect of long-term phosphorus fertilization on soil phosphorus fractions Efecto a largo plazo de la fertilización fosfatada en las fracciones de fósforo del suelo Efeito a longo prazo da aduba o fosfatada nas fra es de fósforo do solo

A limitation to crop production in the southeast of the Buenos Aires province (Argentina) is the low phosphorus (P) availability. P fertilization is required for high yields. The objective of this work was to quantify the forms of soil P as affected by different P fertilization strategies after 8 years under wheat. The combination of high rate (H; 176 kg P ha-1), low rate (L; 88 kg P ha-1), single application (S; at the beginning of the experiment), and fractionated application (F; annual fertilization of 22 and 11 kg P ha-1) were evaluated. Soil total P, total inorganic P, total organic P, organic (Po) and inorganic (Pi) extractable with NaHCO3 and NaOH, were determined, plus available P (P-Bray 1). Fertilization did not change the total P or the total Po (344 and 412 mg P kg-1, respectively). Fertilized treatment, compared with a non-fertilized one, increased the concentration of Pi-NaHCO3 (14.49 and 7.62 mg P kg-1) and Pi-NaOH (47.13 and 28.37 mg P kg-1). The H rate increased the Pi extracted with NaHCO3 (13.16 mg P kg-1) and with NaOH (53.82 mg P kg-1) compared with the L rate (9.82 and 40.43 mg P kg-1, respectively). The FH rate increased the concentration of Pi-NaOH (59.55 mg P kg-1) compared to SH (48.10 mg P kg-1), while the low rate produced no changes in this fraction. In summary, when the amount of P added was fractioned and exceeded the quantity removed by crop, the excess was converted mainly to Pi-NaOH. A positive and significant correlation (r2 = 0.95; P < 0.001) between the sum of Pi-NaHCO3, Pi- NaOH and P-Bray 1 was established. Una de las limitaciones para la producción de cultivos en el sudeste de la provincia de Buenos Aires (Argentina) es la baja disponibilidad de fósforo (P), que es cubierta con la fertilización fosfatada. El objetivo de este trabajo fue cuantificar las formas de P en el suelo después de 8 a os de monocultivo de trigo con diferentes dosis y estrategias de aplicación. Se determinó: P orgánico (Po) e inorgánico (Pi) extractable con NaHCO3 y con NaOH, y P-Bray 1. Se evaluó la combinación de dosis alta (H; 176 kg P ha-1), dosis baja (L; 88 kg P ha-1), aplicación única (S; al inicio del ensayo) y aplicación fraccionada (F; fertilizaciones anuales de 22 y 11 kg P ha-1 durante 8 a os). La fertilización no produjo cambios en el P total ni en el Po total (412 y 344 mg P kg-1, respectivamente), e incrementó el Pi-NaHCO3 (14,49 y 7,62 mg P kg-1) y el Pi-NaOH (47,13 y 28,37 mg P kg-1). La dosis H aumentó el Pi-NaHCO3 (13,16 mg P kg-1) y Pi-NaOH (53,82 mg P kg-1) comparado con la dosis L (9,82 mg P kg-1 y 40,43 mg P kg-1, respec