Abstract
Although the spatial mapping and fertility assessment of soil chemical properties (SCPs) are well studied in the Loess Plateau region of China at farmland scale, little is known about spatial mapping the SCPs and their fertility and their influence factors at urban forest scale. The objectives of this study were to (1) compare the performance of two spatial interpolation methods, Ordinary kriging (OK) and regression kriging (RK), and (2) explain the relationships of the vegetation, terrain, and soil layer depth between the eight SCPs and their fertility, and (3) find the limiting factors of soil comprehensive fertility in this study area? The Yan’an urban forest was taken as study case, used hybrid spatial interpolation methods based on OK and RK to mapping eight SCPs and the soil fertility in each soil layer (0–20 cm, 20–40 cm, and 40–60 cm) for 285 soil samples. The results indicated that RK outperformed OK for total nitrogen (TN), available potassium (AK), organic matter (OM) in 0–60 cm profile and available phosphorus (AP) in the 0–20 cm and 40–60 cm soil layers because RK considered the impact of terrain. The terrain factors, comprising the relative terrain position, slope, aspect, and relative elevation significantly affected the SCPs and spatial heterogeneity of fertility, where the vegetation cover types determined the average SCPs to some extent. On average, the six SCPs (except total potassium and AP) and the fertility decreased as the soil layer depth increased. Ten vegetation cover types comprising broadleaved mixed natural forest (BM), cultivated land (CL), economic forest (EF), grassland (GL), Platycladus orientalis natural forest (PON), Platycladus orientalis plantation (POP), Pinus tabuliformis plantation (PT), Quercus wutaishanica natural forest (QW), Robinia pseudoacacia plantation (RP), and Shrubwood (SW) were associated with significant differences in TN, OM, AN, AP, and AK, across the three soil layers. QW, PON, and BM also had higher content of TN, OM, AN, and AK contents than the other vegetation cover types. There were small differences in TK, AK, and pH among the 10 vegetation cover types. We concluded that AN, TN, and OM are the limiting factors of soil comprehensive fertility in this region. These results improve understanding of the spatial mapping, influence and limiting factors of SCPs and their fertility at urban forest scales.
Highlights
Soil plays an essential role in the biosphere by governing plant productivity, organic matter (OM) degradation, and nutrient cycles [1]
Which have effectively controlled the disturbance to Yan’an urban forest, especially the soils. (d) This area has a typical semiarid continental climate with average annual rainfall of approximately 470 mm, over 65% occurs during June and September. (e) The northern region mainly consists of Robinia pseudoacacia plantation and Platycladus orientalis plantation, and a few of economic forests, i.e., apple (Malus pumila), walnut (Juglans regia), etc
We found that the total nitrogen (TN), total potassium (TP), available nitrogen (AN), available phosphorus (AP), AK, and OM contents were highly variable in the 0–60 cm soil layers (CV 20%) due to complex topographical changes over a short scale in the study area, even within same land use type (S3 Fig)
Summary
Soil plays an essential role in the biosphere by governing plant productivity, organic matter (OM) degradation, and nutrient cycles [1]. Many studies have shown that a geostatistical approach based on the integration of terrain factors is an effective tool for accurately predicting the spatial distribution of soil chemical properties [3,15,21,25,26,27,28,29]. Differences in the distribution and supply of soil chemical properties could alter the composition and diversity of forest ecosystems by interacting with the patterns of variability in the plant and heterotrophic organisms These activities may continue to influence the distributions of soil nutrients by altering their spatial heterogeneity in ecologically sensitive regions, such as, the Loess Plateau in China (LPC)
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