Rolf Rauber

Long-term impacts of different tillage intensities on the C and N dynamics of a Haplic Luvisol

The objectives of the study were to quantify the effects of 40 years of conventional tillage (CT) and reduced tillage (RT, maximum tillage depth of 8 cm) on C and N dynamics in the surface (0–5 cm) and subsurface (5–25, 25–40 cm) soils of a silty Luvisol in a long-term trial at Garte Süd, Germany (temperate climate). Stocks of C and N and contents of microbial biomass C and N were significantly higher in the surface soil of the RT treatment than in the CT treatment. However, over the entire profile (0–40 cm), C and N stocks did not differ significantly. Cumulative net N mineralization (determined in a laboratory incubation at 13.7°C and 60% water holding capacity) was significantly higher in the surface soil of RT (58.6 mg kg−1) than that of CT (26.7 mg kg−1), whereas in the subsurface soil depths, cumulative N mineralization was higher in the CT treatment. By contrast, gross N mineralization rates did not generally differ significantly between the treatments. Overall, different tillage intensities affected C and N dynamics only slightly in the entire profile because increases in C and N stocks and N mineralization rates in the surface soil of RT were counterbalanced at greater depths.

Root discrimination of closely related crop and weed species using FT MIR-ATR spectroscopy

Root discrimination of species is a pre-condition for studying belowground competition processes between crop and weed species. In this experiment, we tested Fourier transform mid-infrared (FT MIR)-attenuated total reflection (ATR) spectroscopy to discriminate roots of closely related crop and weed species grown in the greenhouse: maize/barnyard grass, barley/wild oat, wheat/blackgrass (Poaceae), and sugar beet/common lambsquarters (Chenopodiaceae). Fresh (moist) and dried root segments as well as ground roots were analyzed by FT MIR-ATR spectroscopy. Root absorption spectra showed species specific peak distribution and peak height. A clear separation according to species was not possible with fresh root segments. Dried root segments (including root basis, middle section, and root tip) of maize/barnyard grass and sugar beet/common lambsquarters formed completely separated species clusters. Wheat and blackgrass separated in species specific clusters when root tips were removed from cluster analysis. A clear separation of dried root segments according to species was not possible in the case of barley and wild oat. Cluster analyses of ground roots revealed a 100% separation of all tested crop and weed species combinations. Spectra grouped in Poaceae and Chenopodiaceae clusters. Within the Poaceae cluster, C3 and C4 species differed significantly in heterogeneity. Thus, root spectra reflected the degree of kinship. To quantify species proportion in root mixtures, a two- and a three-species model for species quantification in root mixtures of maize, barnyard grass, and wild oat was calculated. The models showed low standard errors of prediction (RMSEP) and high residual predictive deviation values in an external test set validation. Hence, FT MIR-ATR spectroscopy seems to be a promising tool for root research even between closely related plant species.

Root Differentiation of Agricultural Plant Cultivars and Proveniences Using FTIR Spectroscopy

The differentiation of roots of agricultural species is desired for a deeper understanding of the belowground root interaction which helps to understand the complex interaction in intercropping and crop-weed systems. The roots can be reliably differentiated via Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR). In two replicated greenhouse experiments, six pea cultivars, five oat cultivars as well as seven maize cultivars and five barnyard grass proveniences (n = 10 plants/cultivar or provenience) were grown under controlled conditions. One root of each plant was harvested and five different root segments of each root were separated, dried and measured with FTIR-ATR spectroscopy. The results showed that, firstly, the root spectra of single pea and single oat cultivars as well as single maize and single barnyard grass cultivars/proveniences separated species-specific in cluster analyses. In the majority of cases the species separation was correct, but in a few cases, the spectra of the root tips had to be omitted to ensure the precise separation between the species. Therefore, species differentiation is possible regardless of the cultivar or provenience. Consequently, all tested cultivars of pea and oat spectra were analyzed together and separated within a cluster analysis according to their affiliated species. The same result was found in a cluster analysis with maize and barnyard grass spectra. Secondly, a cluster analysis with all species (pea, oat, maize and barnyard grass) was performed. The species split up species-specific and formed a dicotyledonous pea cluster and a monocotyledonous cluster subdivided in oat, maize and barnyard grass subclusters. Thirdly, cultivar or provenience differentiations within one species were possible in one of the two replicated experiments. But these separations were less resilient.