Soil pH is seldom uniform with depth, rather it is stratified in layers. The soil surface (0–0.02 m) commonly exhibits relatively high pH and overlies a layer of acidic soil of 0.05–0.15 m deep, termed an acidic subsurface layer. Commercial and research sampling methods that rely on depth increments of 0.1 m either fail to detect or under report the presence or magnitude of pH stratification. The occurrence of pH stratification and the presence of acidic subsurface layers may cause the extent of acidity in NSW agricultural land to be underestimated. Though the cause of pH stratification in agricultural systems is well understood, the effect on agricultural production is poorly quantified due in part to inadequate sampling depth intervals resulting in poor identification of acidic subsurface layers. Although liming remains the best method to manage acidic soil, current practices of low pH targets (pHCa 5), inadequate application rates and no or ineffective incorporation have resulted in the continued formation of acidic subsurface layers. Regular monitoring in smaller depth increments (0.05 m), higher pH targets (pHCa > 5.5) and calculation of lime rate requirements that account for application method are required to slow or halt soil degradation by subsurface acidification. If higher pH is not maintained in the topsoil, the acidification of subsurface soils will extend further into the profile and require more expensive operations that mechanically place amendments deep in the soil. Although the use of organic amendments has shown promise to enhance soil acidity amelioration with depth, the longevity of their effect is questionable. Consequently, proactive, preventative management of topsoil pH with lime addition remains the most cost-effective solution for growers.

中文翻译：

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澳大利亚新南威尔士州南部地下酸度的范围、意义和改善

土壤 pH 值很少随深度一致，而是分层分层。土壤表面（0-0.02 m）通常表现出相对较高的 pH 值，覆盖在 0.05-0.15 m 深的酸性土壤层上，称为酸性地下层。依赖于 0.1 m 深度增量的商业和研究采样方法要么无法检测到，要么未报告 pH 分层的存在或程度。pH 分层的发生和酸性地下层的存在可能导致新南威尔士州农业用地的酸性程度被低估。尽管农业系统中 pH 分层的原因已广为人知，但其对农业生产的影响却很难量化，部分原因是采样深度间隔不足导致酸性地下层识别不佳。尽管石灰仍然是管理酸性土壤的最佳方法，但目前低 pH 目标 (pHCa 5) 的做法、施用率不足以及没有掺入或掺入无效导致酸性地下层的持续形成。需要以较小的深度增量 (0.05 m)、更高的 pH 目标 (pHCa > 5.5) 进行定期监测，并计算考虑应用方法的石灰率要求，以减缓或阻止地下​​酸化造成的土壤退化。如果表土中没有保持较高的 pH 值，地下土壤的酸化将进一步延伸到剖面中，并且需要更昂贵的操作，以机械方式将改良剂放入土壤深处。尽管有机改良剂的使用已显示出随着深度增强土壤酸度改善的前景，但其效果的持久性值得怀疑。