Refining phosphorus fertilizer recommendations based on buffering capacity of soils from southern Brazil

Abstract

The phosphorus (P) rates recommended for corrective fertilization-P of soils from southern Brazil may be insufficient to reach the critical level for optimal plant growth. This study aimed to quantify the fertilizer-P rates for total correction fertilization with varying soil buffering capacity in the states of Rio Grande do Sul (RS) and Santa Catarina (SC). Soil samples from 0.00-0.10 and 0.10-0.20 m layers were collected from 41 locations distributed in both states. Twelve P rates were applied to each soil, varying between 0 and 100 % of the maximum adsorption capacity (P-max), and incubated for 20 days. After incubation, the extractable P was determined by Mehlich-1. Based on the relationship between applied rates and extracted P, the P buffer capacity (trP_M1) of the soils was quantified, relating it to soil properties. The trP_M1 values, that is, amounts of P 2 O 5 required to increase 1 mg dm -3 of P extracted by Mehlich-1, varied between 2.4 and 34.5 kg ha -1 of P 2 O 5 . A multiple explanatory equation for the variable P was generated, in which only P-max, clay content, and initial P availability have a significant effect. The P buffer capacity was significantly higher in the soils with the highest clay content, and there was a reduction in trP_M1 for soils with higher initial P availability. Considering 270 soil samples with low P, the P rate to reach the sufficient levels may be 2-folds higher than the values currently indicated for the RS and SC states, especially for soils with more than 40 % of clay. Phosphorus rates for corrective fertilization must be based on the soil clay content and in P initial availability. The fertilizer-P in clayey soils must be increased.

Potassium buffering capacity and corrective potassium fertilizer recommendations in soils from Southern Brazil

“…The soil samples were oven-dried at 60 °C for 72 hours, ground, and sieved in a 2 mm aperture sieve. Soil acidity was accessed, and when necessary, the soil pH was raised to 6.0, through incubation with dolomitic limestone with 90 % of PRNT, as described by Mumbach et al (2021). Then, the soils were chemically characterized (Table 1), according to Sparks et al (1996), and the clay content was determined by the pipette method (Teixeira et al, 2017).…”