Influence of soil test phosphorus level and leaching volume on phosphorus leaching

Authors: LEVERICH, LEANNA - University Of Minnesota; KAISER, DANIEL - University Of Minnesota; Feyereisen, Gary

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2022
Publication Date: 6/25/2022
Citation: Leverich, L.M., Kaiser, D.E., Feyereisen, G.W. 2022. Influence of soil test phosphorus level and leaching volume on phosphorus leaching. Soil Science Society of America Journal. 86(5):1280–1295. https://doi.org/10.1002/saj2.20452.
DOI: https://doi.org/10.1002/saj2.20452

Interpretive Summary: Loss of phosphorus (P), an essential nutrient in agricultural production, contributes to algal blooms and eutrophication of freshwater bodies. Much focus is given to P loss via surface runoff, with less consideration to P leaching losses. This research was conducted to evaluate water soluble P leaching losses from topsoils across a range of Minnesota soil types and low, medium, high, and very high background soil test P concentrations. Leached P concentrations were the same across sites and soil test P values, although the loamy sand leached less P per mass of soil. There was a general trend of greater leaching losses with increase in soil test P value. Averaged across sites, only the very high soil test P soils leached statistically more P. Soils from three of the sites and two soil test P concentrations were subjected to additional leaching. There were no differences in P leachate concentrations with increased leaching volumes, indicating a similar P release rate from the various soils. Computer model predictions of leaching P concentrations using two common soil input parameters were promising. The findings support the idea that soil P leaching concentrations can be predicted, and by including estimated leaching from precipitation inputs, P leaching loads also can be predicted. The findings of this research are pertinent to researchers, agency and extension personnel, policy makers, industry personnel, and practitioners who want to better understand and reduce phosphorus leaching loads from agriculture.

Technical Abstract: Phosphorus (P) is an essential nutrient in agricultural production, yet its losses contribute to eutrophication in freshwater systems. To mitigate this, there is increasing interest in quantifying soluble P leaching losses and including them in P indices. The objectives of this research were to 1) evaluate water soluble P leaching loss from topsoils (0-15 cm) across a range of initial soil test P (STP) levels; 2) determine the effects of soil type, physiochemical soil properties, and leaching volume on P leaching loss; and 3) determine the predictability of P leaching losses from soil tests. Intact soil cores (3.81 cm in diameter, 0-15 cm deep) were collected from six agricultural fields in Minnesota and leached with deionized water offsite. Additional columns were collected to identify the influence of three leaching volumes on P leaching losses. Phosphorus leaching loss was impacted by soil type, initial STP level, and the volume of the leaching event. Leachate P concentration increased with increasing STP level and remained consistent among leaching volumes. Concentrations were not diluted with increased leaching volumes. Consequently, leaching volume was the primary driver of total P load. Several linear and machine learning models were employed to predict P leachate concentration. Phosphorus concentration was best predicted using a Ridge Regression model using two soil tests: the degree of phosphorus sorption (DPSOP) and water extractable P (WEP) (R2 = 0.58, RMSE = 0.06). The model prediction of P leaching loss is promising, although further research on subsoil interactions is needed.