Phosphorus Leaching from Soil Profiles in Agricultural and Forest Lands Measured by a Cascade Extraction Method

Abstract

The risk of P leaching from topsoil based on the change‐point estimated via a split‐line model between Olsen P and leachable P extracted by 0.01 M CaCl2 has been reported. However, little information is available for the assessment of P leaching from soil profiles. In this study, samples were collected at three depth profiles (0–20 cm, topsoil; 20–40 cm, subsoil; 40–60 cm, third‐layer soil) at each of 74 sites under agriculture and forest in an agroforestry area. A cascade extraction method was proposed to determine the leachable P in the subsoil, extracted by the topsoil extraction solution; a similar extracted process was followed in the third‐layer soil, and in the topsoil, it was still extracted by 0.01 M CaCl2. A positive linear correlation was found between the subsoil leachable P extracted by the topsoil extraction solution and the accumulated P obtained from the subsoil leached by topsoil leachates, and so on. Therefore, the cascade extraction method for determining leachable P from topsoils and underlying soils could be valuable for predicting the potential of P leaching from soil profiles. Approximately 81, 73, and 73% of the agricultural sampling sites were at or above the change‐points for the soil depths of 0 to 20, 20 to 40, and 40 to 60 cm (30.4, 32.9, and 18.2 mg kg−1 respectively); these values were higher than those for the forest site, implying a high risk of P leaching from agricultural soil profiles in the study area. Core Ideas A cascade extraction method for evaluating P leaching from soil profiles was proposed. The correlation of soil leachable P and accumulated P in soil leachates was confirmed. The risk of P leaching from soil profiles in an agroforestry area was calculated.

A Tool (SPOLERC) to Guide the Evaluation of Phosphorus Leaching for Agricultural Soil by Using Soil Phosphorus Leaching Change Point in the Lake Xingkai Basin, China

“…S3a or S3b, it seems have two different ranges of value distribution, which were similar to some previous graphs presented by Li et al (2015) and Xie et al (2019). Consequently, "Model 1" was selected to calculate the CP value of soil P leaching.…”

“…Similarly, Zhao et al (2007) have founded that the changepoint in 13 types of Chinese agricultural soils were ranged from 30 to 160 mg Olsen-P kg − 1 . The CP value in agricultural soil was slightly higher than that of forest soil, Li et al (2015) and Xie et al (2019) studied that the CP value in agricultural soils were 85 and 30.2 mg kg − 1 , which is higher than that value in forest soils (46 and 20.0 mg kg − 1 , respectively). In addition, there was a special relationship between soil CP value and pH.…”

“…Originally, most studies have concentrated on P losses by soil erosion and surface runoff, as the subsurface P losses were considered negligible. In the last two decades, soil P losses by subsurface pathway, such as P leaching, have been attracting substantial attention, and the subsurface pathways in some events were reported to play a dominated role in P loss from agricultural land to water (Heckrath et al, 1995;Ulen et al, 2007;Li et al, 2015;Jalali and Jalali et al, 2017;Xie et al, 2019). Consequently, it is of great signi cance to conduct soil P leaching loss in farmland soil, which will improve P management in arable soil and water ecosystem.…”

“…Soil P leaching Change point (CP) is estimated by using the split-line model to t the relationship between soil leachable P and soil Olsen-P, and often used to evaluate P leaching risk in topsoil (Heckrath et al, 1995;Zhao et al, 2014;Jalali and Jalali, 2017). Recently, Xie et al (2019) proposed the cascade extraction method and veri ed that the soil leachable P and CP value could use to evaluate P leaching risk in soil pro les. Although the research on soil P leaching risk evaluation has been continuously performing, the calculating process of soil P leaching CP value is not clearly described in the previous literature.…”

“…The CP value often used to evaluate the soil P leaching risk. Generally, when soil Olsen-P was higher than the CP value, signi cant P losses through leaching should occur; otherwise, there was no P leaching risk (Li et al, 2015;Xie et al, 2019). This method is easy to operate, but failed to classi ed the low-risk area and high-risk area, which is not conducive to the hierarchical management of soil P leaching risk areas.…”