Predicting soil test phosphorus decrease in non‐P‐fertilized conditions

Abstract

Monitoring the availability of phosphorus (P) in soil under continuous cropping facilitates finding deficiency in crops and contributes to improving crop growth and nutrient management models. Soil P availability for crops is usually estimated by soil test P (STP), such as Bray‐1. This is widely used in the Americas. The relationship between the decrease of STP Bray‐1 and cumulative removal of P was evaluated in non‐P‐fertilized areas in long‐term studies. This removal was the sum of annual P removal over the study period as P exported in grains/crop outside the soil. The objectives were to: (a) quantify changes in STP as a function of cumulative P removal, (b) assess the relationship between relative decrease rate of STP and soil variables as well as annual removal of P by crops, and (c) develop a model to predict decrease of STP Bray‐1. Exponential decay functions were used to describe annual cumulative removal of P and STP from soil over time for 12 long‐term studies where no addition of P fertilizer was carried out. Changes in the relative rate of decrease of STP, relative to the initial STP Bray‐1 value at the onset of the experiment, were predicted by the ratio of soil organic matter to clay and silt and the average annual P removal by exponential decay (R2adj = 0.64; RMSE = 3.2 mg kg−1). We propose this predictive model as suitable to provide estimates of the relative decrease rate of STP by Bray‐1 and thereby improve management of P for optimizing crop yield. Highlights STP Bray‐1 decrease and cumulative P removal were related by exponential decay functions. Relative decrease rate of STP Bray‐1 was related to SOM/(clay+silt) ratio and annual P removal. A predictive model of the relative decrease rate of STP Bray‐1 was fitted and validate. Our model is a useful tool to help predict soil P availability and nutrient management.

Changes in Soil Phosphorus Pools in Long-Term Wheat-Based Rotations in Saskatchewan, Canada With and Without Phosphorus Fertilization

“…These results indicate that stopping P fertilization reduced soil TP and Olsen P compared to treatments with continued P fertilization, which is consistent with the results for P fertilizer cessation studies from other regions, including Denmark (Rubaek et al, 2013), Ireland (Cade-Menun et al, 2017, Germany (Medinski et al, 2018), Canada (Liu et al, 2019), and with a global data set (Appelhans et al, 2020). Drawdown was greater in FWW and CW treatments fertilized with N (+N-P) than without N (-N-P), where greater crop growth would have increased P uptake.…”

“…This requires data from fertilizer cessation studies from different crops grown in a wide range of conditions, including: the time required to draw down soil test P concentrations; changes in soil P pools beyond soil test P, such as total P and organic P; and the effects of different management practices on the rate of P drawdown. Longterm studies are an essential source for this information, particularly with respect to the time frame needed to reduce soil P concentrations, which will vary with factors including soil type and texture, initial soil P concentrations, and other influences on crop health (Rubaek et al, 2013;Cade-Menun et al, 2017;Liu et al, 2019;Appelhans et al, 2020).…”

Dynamic Changes in Soil Phosphorus Accumulation and Bioavailability in Phosphorus-Contaminated Protected Fields

“…The linear platform function method, the exponential decay function method, and the Mitscherlich function method are currently the three mainstream methods for building models [39]. Previous research has shown that using Bray-1 to fit the annual decline rate model of soil test P (STP) with an exponential decay function in areas without phosphate fertilizers is feasible [40]. The relative decay rate k = −0.023 and the constant a = 60.344 are both directly related to the initial Bray-P content in the model y = 60.344(1 − e −0.023x ) predicting the effects of soil available phosphorus on the fresh weight of spinach [41].…”