Soil assessment – nutrient availability in effective root space, evaluated nationwide

The so-called S-value is a characteristic value for evaluating the soil as a component of nutrient retention and is evaluated by nutrient availability. The S-value is the amount of nutrients (cations, not e.g. nitrate) that a soil can interchangeably bind or absorb to clay, humus particles, oxides and hydroxides (cation exchange capacity). The S-value is therefore well suited to describe the nutrient availability. Similar to the field capacity in the effective root space (FKwe), high levels of clay, humus, as well as a large effective root space require a high S-value and vice versa. The pH value also has a great influence on the S-value. The pH may fluctuate in a wide range depending on the use. The higher the S-value, the more nutrients the soil can bind to exchangers. Nutrient inputs via air or fertilisation are thus protected against discharge with the leachate water. At the same time, this ensures a more uniform supply of nutrients to the plants. The S-value evaluates a natural soil function in accordance with § 2(2) of the BBodSchG, namely in accordance with point 1.b) as part of the natural balance, in particular with its water and nutrient cycles. The criterion chosen for this purpose is the nutrient availability with the characteristic value S-value. The maps are available for the following scale levels: — 1: 1,000 – 10.000 for high-resolution or parcel-sharp planning, – 1: 10.001 – 35.000 for municipal level planning, – 1: 35.001 – 100.000 for planning in larger regions, – 1: 100.001 – 350.000 for nationally differentiated planning, – 1: 350.001 – 1000.000 for nationwide to nationwide planning. In this presentation, the S-value is classified uniformly across the country. Under the title “Soil assessment – nutrient availability in effective root space (SWE), assessed regionally”, there is still a natural space-related classification of the S-value, which represents the S-value more regionally differentiated.所谓S值是用于评估土壤养分保持能力的特征参数，其评价依据为养分有效性。S值指土壤可与黏土、腐殖质颗粒、氧化物及氢氧化物进行可逆结合或吸附的养分（阳离子类，而非硝酸盐等）的总量，即阳离子交换量（cation exchange capacity）。因此S值非常适合用于表征土壤养分有效性。与有效根域的田间持水量（field capacity, FKwe）类似，土壤中黏土、腐殖质含量越高，有效根域范围越大，则所需S值也越高，反之亦然。pH值同样对S值存在显著影响。pH值会因土地利用方式的不同而在较大范围内波动。S值越高，土壤可与交换位点结合的养分量就越多。通过大气沉降或施肥输入的养分因此可避免随渗滤液流失；同时，这也保障了植物能够获得更为均匀的养分供应。 依据《联邦土壤保护法》（BBodSchG）第2条第2款，S值用于评估土壤的自然功能，具体而言即依据第1.b)项，作为自然平衡（尤其是其水分与养分循环）的组成部分开展评估。本次选取的评价标准为以S值作为特征参数的养分有效性。 该数据集提供以下比例尺档位的地图： ——1:1000~1:10000，适用于高分辨率或地块级精细规划； ——1:10001~1:35000，适用于市级层面规划； ——1:35001~1:100000，适用于更大区域的规划； ——1:100001~1:350000，适用于全国差异化规划； ——1:350001~1:1000000，适用于全国范围及跨区域规划。 在本次展示中，S值采用全国统一分级标准。而在题为"土壤评价——有效根域养分有效性（SWE）区域评估"的内容中，仍存在基于自然空间的S值分级方式，该分级方式能够更具区域差异性地体现S值水平。