Establishing environmental soil phosphorus thresholds to decrease the risk of losses to water in soils from Rio Grande do Sul, Brazil

Abstract

The overloading of soil with manure or mineral fertilizers enhances phosphorus (P) availability, promoting its loss to water bodies and increasing the risk of eutrophication. In this sense, the establishment of an environmental P threshold is a simple and useful tool to classify soils regards its risk of P losses. Here we propose a P-threshold for soils from the state of Rio Grande do Sul (RS) in Brazil, with the soil clay content as the principal variable of the model. Samples from 20 representative soils of Rio Grande do Sul State were collected in the 0.00-0.10 and 0.10-0.20 m layers. Samples were physically and chemically characterized and incubated with P rates varying from 0 to 100 % of its maximum adsorption capacity. After 20 days of incubation, the P availability was determined in water and Mehlich-1 extractant. We assessed trough segmented linear functions the value of P-Mehlich in which the levels of P water enhance abruptly (i.e., breaking point) to determine the P limit for each soil. Subsequently, the P limit values were linked to the clay content in the sample, adopting the linear equation arising from it as the P-threshold. Adding a safety margin of 20 % to the P-threshold equation, we propose a simplified one "P-threshold = 20 + clay". Based on the current critical level of P adopted by the regional recommendation in RG, the equation proposed does not limit the production of the most crop species.

Slope and pig slurry rate may increase the transfer of chemical elements by surface water runoff

“…As soils with lower clay content have higher infiltration rates and vertical distribution of nutrients, they are more susceptible to cause subsurface water contamination through leaching losses (Gatiboni et al, 2015(Gatiboni et al, , 2020. Complementary conservation practices such as terraces, crop residue management and maintenance, buffer strips, and contour crops are necessary strategies to prevent/reduce runoff and potentially cause environmental pollution (Sharpley, 2016;Zanon et al, 2020).…”

“…The potentially toxic heavy metals in water, sediments, and soils should be regularly assessed and monitored (Ali et al, 2019). Monitoring critical transfer levels for P (Gatiboni et al, 2015(Gatiboni et al, , 2020Sharpley et al, 2012) and Cu and Zn (Morais et al, 2021) are tools that control the levels of these elements in the soil. Although transfer limits are proposed according to soil use or properties there are many limits from one country to another, even when there is identical use or soils with the same characteristics (Antoniadis et al, 2019;Islam et al, 2020).…”