The CarboZALF-D manipulation experiment – experimental design and SOC patterns

Soil erosion is an essential factor for shaping landscapes [1], [2], e.g., for the Uckermark region in the Northern German lowland [3]. Until now, its influence has primarily been examined for differing slope positions or the soil’s function [4], [5]. An erosion-attributed decrease in topsoil depth and nutrient content leads to yield reduction in erosion positions, whereas the aggradation area shows partly positive effects. Erosion is a process with complex factors and can be difficult to predict. It occurs at all scales of the landscape, from the soil aggregate to the landscape scale [6], [7], [8]. In order to examine its influence on the C budget, defined conditions are necessary. One way to achieve those are controlled manipulation experiments at plot or field scale. A number of manipulation experiments had been set up at plot scale in the past. Defined alteration or adjustment of soil properties are a profound tool for experiments [9], [10], [11]. Practical applications in agricultural sciences, in addition to laboratory experiments, demonstrate impact in the field, e.g. fertilization levels for organic mineral fertilizers and their effect on yield and soil functions, initiation of soil compaction for a clarification of soil reloosening processes [12], influence of CO management on yield [13], influence of soil cover on soil loss and runoff [5], 2 and influence of different erosion rates on yield [14], [15]. Field scale manipulation experiments, like relief [16] and summit amelioration [17], aimed to improve site conditions and plant production. Generally, changes in soil properties by soil erosion were examined by means of a comparison before and after a soil erosion event, e.g., using rainfall simulators or laboratory experiments. However, these studies have not been directly related to CO emissions. Körschens et al. [18] 2 pointed out that changes in soil organic matter (SOM) are very slowly and can only be detected and verified after decades by using a mass balance approach. 

In non-redoximorphic soils SOM is related to textural parameters, like clay and fine silt under steady state conditions [19], [20], [21], [22], [23]. However, if textural properties in topsoils are changed by erosion feedbacks to the C cycling, hence SOM, will occur as texture also affects related chemical, physical and biological properties. This has been tested in long-term studies [24], experiments on the influence of topsoil reduction [25], [26], bentonite fertilization [21] and deep ploughing of soils (30 to 60 cm) bringing subsoil material into the Ap horizon [9].

 However, there is no manipulation experiment at field scale, which includes both, erosional and depositional soils representing different landscape scale process domains in terms of C dynamics and C balances. Therefore we established the CarboZALF-D manipulation experiment. The concept, implementation, and preliminary results of which are described below.