Diffuse reflectance spectroscopy (DRS) for rapid soil testing and soil quality assessment in smallholder farms

Abstract

Rapid soil testing and soil quality assessment are essential to address soil degradation and low farm incomes in smallholder farms. With the objective of testing diffuse reflectance spectroscopy (DRS) to rapidly assess soil chemical properties, nutrient content and a soil quality index (SQI), samples of surface soil were collected from 1113 smallholder farms in seven districts in Bundelkhand region of Uttar Pradesh, India. A minimum dataset (MDS) approach was followed to estimate SQI using the three chemical parameters of soil pH, electrical conductivity (EC) and soil organic carbon (SOC), and 11 different soil nutrients. Principal component and correlation analyses showed that soil pH, SOC content and three available nutrients À copper (Cu), iron (Fe) and sulphur (S) À may constitute the MDS. Estimated SQI values showed strong positive correlation with crop yields. Results of chemometric modelling showed that the DRS approach could yield the coefficient of determination (R 2 ) values in the validation datasets ranging from 0.79 to 0.94 for exchangeable calcium (Ca) followed by 0.67-0.88 for exchangeable potassium (K), 0.52-0.86 for SOC and 0.53-0.81 for available boron (B) content. Except in one district, the DRS approach could be used to estimate SQI values with R 2 values in the range of 0.63-0.81; an R 2 value of 0.71 was obtained in the pooled dataset. We also estimated the three-tier soil test crop response (STCR) ratings to compare DRS and wet chemistry soil testing approaches. Similar STCR ratings were obtained for both these approaches in more than 86% of the samples. Parameters for which both the methods yielded similar ratings in more than 80% of the samples were EC (>98%), pH and exchangeable Ca (>81%) and available B (>89%). With similar ratings, these results suggest that the DRS approach may safely be used for farmers' fields, replacing the traditional wet analysis approach of soil testing.

Diffuse reflectance spectroscopy for assessing soil quality indicators in cocoa production system validated using multi‐year data

“…Thus, only the well‐correlated variables with the highest factor loading were kept in the MDS (Andrews & Carroll, 2001). Generally, two scoring methods (linear and nonlinear) and three integration methods (additive, weighted additive, and Nemoro) are followed to estimate SQI (Majeed et al., 2023; Nabiollahi et al., 2018).…”

“…However, estimating such a parameter still requires measuring several soil parameters, and conventional soil test methods remain costly and time‐consuming. Diffuse reflectance spectroscopy offers a unique opportunity to estimate such a composite parameter (Askari et al., 2015; Majeed et al., 2023; Paz‐Kagan et al., 2014; Sharififar et al., 2023; Veum et al., 2015) following the spectrotransfer function (STF) approach (Santra et al., 2009) similar to the conventional pedotransfer functions (PTF) used for estimating difficult‐to‐measure soil parameters from easily measurable soil parameters (Bouma, 1989). The STFs are estimated in a rapid and non‐invasive manner through a series of chemometric modelling steps (Ben‐Dor & Banin, 1995; Padarian et al., 2019; Sharififar et al., 2023; van der Meer, 2018).…”

“…Recently, Majeed et al. (2023) showed that the DRS approach may be used to estimate SQIs with reasonable accuracy ( R 2 ~ .7) in smallholder farms while showing strong linkages between SQIs and crop yields. Moreover, the ability to estimate SQIs from hyperspectral data (Majeed & Das, 2024) opens new opportunities to estimate this composite soil parameters from remote sensing data for large geographical areas with high spatial and temporal resolution.…”

Diffusive reflectance spectroscopy for precise analysis of soils: An overview

“…DRS is being compared to standard wet chemistry-based soil testing procedures to determine how well it performs in terms of cost-effectiveness, dependabilityand nutrient recommendations [39,40] . Using DRS data to construct the soil quality indexes [SQI's] is gaining popularity as a comprehensive approach of evaluating soil quality that takes into account a range of soil characteristics to help with soil management decisions [41] . DRS technology is increasingly being employed on smallholder farms, with a focus on fast soil testing and fertilizer recommendations to combat the soil degradation and to increase farm revenue [41] .…”

Soil degradation and mitigation in agricultural lands in the Indian Anthropocene

“…However, Hinz et al (2020) opined that the intensification of agriculture will ultimately play a major role in improving Indian food security and this will change the farm structures as small subsistence farms will be transformed into larger units. To do this sustainably, better land use decisions must be assisted by the implementation of rapid soil testing technologies, such as diffuse reflectance spectroscopy recently successfully applied to test the soil properties and soil quality index (SQI) of >1000 soils in Bundelkhand region in Central India (Majeed et al, 2023). Ultimately, Indian agricultural and environmental policies should consider supporting farmers to implement sustainable intensification measures (location‐specific CA) to minimize biodiversity losses and to increase SOC sequestration.…”