Evaluation of Soil Quality in a Composite Pecan Orchard Agroforestry System Based on the Smallest Data Set

Abstract

Agroforestry not only takes into account the use of land for forestry and agriculture but can also improve the efficacy of utilized above- and belowground resources, which have always garnered widespread attention. The objective of this study is to evaluate the quality of pecan orchard soil following the implementation of agroforestry. Consequently, 15 indices were selected for a principal component analysis (PCA), which was then combined with the norm value of each index and the correlation coefficients between indices to establish a minimum data set (MDS). A comprehensive index model was used to calculate the soil quality index (SQI) of the total data set (TDS) and MDS (SQI-TDS and SQI-MDS, respectively), and a linear regression of the two was performed. The results revealed that the MDS indices for the evaluation of soil fertility included the pH, electrical conductivity value (EC), bulk density (BD), available potassium (AK), total nitrogen (TN), magnesium (Mg), and the index screening and filtering rates attained 60%. The Soil Quality Index (SQI-MDS) of the four planting patterns, sorted from largest to smallest, were: PPS (0.573) > PPH (0.519) > PPL (0.355) > CK (0.315). BD and AK were the main factors that affected the quality of hickory orchard soils. The agroforestry composite system improved the availability of nutrients and soil quality. Thus, the promotion of understory intercropping and appropriate increases in potassium fertilizers for plantations are recommended.

Long-term intensive management reduced the soil quality of a Carya dabieshanensis forest

“…In deeper soil layers litter and plant residues become scarce and the leaching of inorganic salts gradually decreases; thus, soil nutrients are typically reduced with soil depth 48 . The root systems of herbs and shrubs are primarily distributed through shallow soil, where the interspersion of plant roots is an important factor in improving air permeability 24 . Unlike other indicators, the soil pH increases in deeper soil layers and the degree of acidification is low.…”

“…The evaluation of soil quality is an important aspect of forest management, which can assist managers with the planning of adjustments over time to improve productivity 18 , 24 . In this study a MDS (AN, SMBN, and pH) was established by reducing the dimensionality of the principal components of 20 soil indicators.…”

“…Furthermore, the removal of understory vegetation reduces species richness and cover, aggravates surface soil erosion, and induces the loss of copious salt-based ions (Ca 2+ , Mg 2+ , K + , Na + ), which is another essential factor that cannot be ignored 12,26 . The evaluation of soil quality is an important aspect of forest management, which can assist managers with the planning of adjustments over time to improve productivity 18,24 . In this study a MDS (AN, SMBN, and pH) was established by reducing the dimensionality of the principal components of 20 soil indicators.…”

“…Among them, the BD was found using the ring knife method, whereas a soil pH meter (Mettler Toledo, FE28-Standard, Switzerland) was employed for pH measurements in a soil/water (1:2.5) leachate. The EC value was determined using a conductivity meter (Mettler Toledo, FE38-Standard, Switzerland) at 25 °C using a soil/water (1:5) leachate 24 . The soil TN was measured using an Automatic Kjeldahl nitrogen analyzer (DRICK, DRK-K616K, China).…”

“…As reported in the literature, several representative indicators for the development of a minimum data set (MDS) may be selected primarily through principal component analysis (PCA). The indicator screening and filtration rates can typically reach > 50%, which significantly saves the labor and time required for observations; thus, this lightweight evaluation strategy has been extensively recognized [21][22][23][24] . However, due to the complexity and heterogeneity of soil systems, further investigations are often required to evaluate the soil quality of different regions, various vegetation types, and diverse land management techniques 25,26 .…”