Effects of soil pH and texture on soil carbon and nitrogen in soil profiles under different land uses in Mun River Basin, Northeast Thailand

Abstract

Soil carbon and nitrogen are essential factors for agricultural production and climate changes. A total of 106 soil samples from three agricultural lands (including two rice fields and one sugarcane field) and four non-agricultural lands (including two forest lands, one wasteland and one built-up land) in the Mun River Basin were collected to determine soil carbon, nitrogen, soil pH, soil particle sizes and explore the influence of pH and soil texture on soil C and N. The results show that total organic carbon (TOC) and nitrogen (TON) contents in topsoil (TOC: 2.78 ~ 18.83 g kg−1; TON: 0.48 ~ 2.05 g kg−1) are much higher than those in deep soil (TOC: 0.35 ~ 6.08 g kg−1; TON: <0.99 g kg−1). In topsoil, their contents of forest lands and croplands (TOC: average 15.37 g kg−1; TON: average 1.29 g kg−1) are higher than those of other land uses (TOC: average 5.28 g kg−1; TON: average 0.38 g kg−1). The pH values range from 4.2 to 6.1 in topsoil, and with increase in soil depth, they tend to increase and then decrease. Soil carbon, nitrogen and the C/N (TC/TN ratio) are negatively correlated with soil pH, demonstrating that relatively low pH benefits the accumulation of organic matter. Most soil samples are considered as sandy loam and silt loam from the percentages of clay, silt and sand. For soil profiles below 50 cm, the TOC and TON average contents of soil samples which contain more clay and silt are higher than those of other soil samples.

Vertical Distribution and Controlling Factors Exploration of Sc, V, Co, Ni, Mo and Ba in Six Soil Profiles of The Mun River Basin, Northeast Thailand

“…In this case, Mo is more available and mobile under higher pH conditions which corresponds to the negative relationship between Mo and soil pH. The soil pH values of these samples are in the range of 5.6-7.2 for most samples (around 75%) [47]. The heavy metal Ni is reported to be most sensitive to soil pH when the soil pH ranges from 5.0-5.5 [48], so the weak relationship between Ni and soil pH may result from the ranges of soil pH values.…”

“…Finer soil particles are reported to have a stronger ability to absorb and fix heavy metals on their surface because of their bigger surface area and various functional groups [1,[50][51][52]. Moreover, clay is also found to stabilize soil organic matter that would also fix heavy metals [13,47].…”

Effects of Soil Properties on K Factor in the Granite and Limestone Regions of China

“…Soil particle distribution in the JRC and CC fluctuated within a narrow range without obviously increasing or decreasing trend with increasing depth [30,37]. Although the soils in both the JRC and CC were classified into silt loam based on soil texture classes defined by the USDA [36], the soils in the JRC were coarser textured than those in the CC. Soil pH in the soils of the JRC ranged from 4.0 to 4.9, while it was 6.5-7.7 in the soils of the CC (Figure 2d).…”

“…Soil samples were passed through 10 mesh (2 mm) sifter after air-drying at room temperature and removing big roots and stones. Soil pH (soil:water of 1:2.5) was determined using a pH meter with a precision of ±0.05 [36]. Soil particle size distribution was measured by the laser particle size analyzer (Mastersizer 2000, Malvern, England) with a precision of ±1% [37].…”

“…Public Health 2020, 17, x 6 of Soil properties, including (a) clay percent, (b) silt percent, (c) sand percent, (d) soil pH, (e) SOC content, and (f) SON content, in the soils of the JRC and CC. The data of the JRC and CC are cited from[30][31][32][33][34][35][36][37]. SOC, soil organic carbon; SON, soil organic nitrogen.…”