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 − copper (Cu), iron (Fe) and sulphur (S) − 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 (R²) 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 R² values in the range of 0.63–0.81; an R² 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.

中文翻译：

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用于小农农场快速土壤测试和土壤质量评估的漫反射光谱 (DRS)

快速土壤测试和土壤质量评估对于解决小农农场的土壤退化和低收入问题至关重要。为了测试漫反射光谱 (DRS) 以快速评估土壤化学性质、养分含量和土壤质量指数 (SQI)，我们从印度北方邦邦德尔坎德邦七个地区的 1113 个小农农场采集了表层土壤样本. 遵循最小数据集 (MDS) 方法使用土壤 pH 值、电导率 (EC) 和土壤有机碳 (SOC) 三个化学参数以及 11 种不同的土壤养分来估算 SQI。主成分和相关性分析表明，土壤 pH 值、SOC 含量和三种有效养分 - 铜 (Cu)、铁 (Fe) 和硫 (S) - 可能构成 MDS。估计的 SQI 值与作物产量呈强正相关。化学计量建模的结果表明，DRS 方法可以产生决定系数 (R ² ) 验证数据集中可交换钙 (Ca) 的值范围为 0.79 至 0.94，随后可交换钾 (K) 为 0.67–0.88，SOC 为 0.52–0.86，可用硼 (B) 含量为 0.53–0.81。除一个地区外，DRS 方法可用于估计 SQI 值，R ²值在 0.63–0.81 范围内；一个R ²在合并的数据集中获得了 0.71 的值。我们还估计了三层土壤测试作物反应 (STCR) 评级，以比较 DRS 和湿化学土壤测试方法。在超过 86% 的样本中，这两种方法都获得了类似的 STCR 评级。这两种方法在超过 80% 的样品中产生相似评级的参数是 EC (>98%)、pH 和可交换 Ca (>81%) 和有效 B (>89%)。具有相似的评级，这些结果表明 DRS 方法可以安全地用于农民的田地，取代传统的土壤测试湿法分析方法。