@article{HorfBoeneckeGebbersetal.2023, author = {Horf, Michael and B{\"o}necke, Eric and Gebbers, Robin and Kling, Charlotte and Kramer, Eckart and R{\"u}hlmann, J{\"o}rg and Schr{\"o}ter, Ingmar and Schwanghart, Wolfgang and Vogel, Sebastian}, title = {Utility of visible and near-infrared spectroscopy to predict base neutralizing capacity and lime requirement of quaternary soils}, series = {Precision Agriculture}, volume = {24}, journal = {Precision Agriculture}, publisher = {Springer Nature}, issn = {1385-2256}, doi = {10.1007/s11119-022-09945-9}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-4916}, pages = {288 -- 309}, year = {2023}, abstract = {Detailed knowledge of a soil's lime requirement (LR) is a prerequisite for a demand-based lime fertilization to achieve the optimum soil pH and thus sustainably increasing soil fertility and crop yields. LR can be directly determined by the base neutralizing capacity (BNC) obtained by soil-base titration. For a site-specific soil acidity management, detailed information on the within-field variation of BNC is required. However, soil-base titrations for BNC determination are too laborious to be extensively applied in routine soil testing. In contrast, visible and near-infrared spectroscopy (visNIRS) is a time and cost-effective alternative that can analyze several soil characteristics within a single spectrum. VisNIRS was tested in the laboratory on 170 air-dried and sieved soil samples of nine agricultural fields of a quaternary landscape in North-east Germany predicting the soil's BNC and the corresponding lime requirement (LRBNC) at a target pH of 6.5. Seven spectral pre-processing methods were tested including a new technique based on normalized differences (ND). Furthermore, six multivariate regression methods were conducted including a new method combining a forward stagewise subset selection algorithm with PLSR (FS-PLSR). The models were validated using an independent sample set. The best regression model for most target variables was FS-PLSR combined with the second Savitzky-Golay derivation as pre-processing method achieving R2s from 0.68 to 0.82. Finally, the performance of the direct prediction of LRBNC (R2 = 0.68) was compared with an indirect prediction that was calculated by the predicted BNC parameters. This resulted in slightly higher correlation coefficients for the indirect method with R2 = 0.75.}, language = {en} } @article{HorfBoeneckeGebbersetal., author = {Horf, Michael and B{\"o}necke, Eric and Gebbers, Robin and Kling, Charlotte and Kramer, Eckart and R{\"u}hlmann, J{\"o}rg and Schr{\"o}ter, Ingmar and Schwanghart, Wolfgang and Vogel, Sebastian}, title = {Utility of visible and near-infrared spectroscopy to predict base neutralizing capacity and lime requirement of quaternary soils}, series = {Precision Agriculture}, volume = {24}, journal = {Precision Agriculture}, number = {1}, publisher = {Springer US}, issn = {1385-2256}, doi = {10.1007/s11119-022-09945-9}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-9257}, pages = {288 -- 309}, abstract = {AbstractDetailed knowledge of a soil's lime requirement (LR) is a prerequisite for a demand-based lime fertilization to achieve the optimum soil pH and thus sustainably increasing soil fertility and crop yields. LR can be directly determined by the base neutralizing capacity (BNC) obtained by soil-base titration. For a site-specific soil acidity management, detailed information on the within-field variation of BNC is required. However, soil-base titrations for BNC determination are too laborious to be extensively applied in routine soil testing. In contrast, visible and near-infrared spectroscopy (visNIRS) is a time and cost-effective alternative that can analyze several soil characteristics within a single spectrum. VisNIRS was tested in the laboratory on 170 air-dried and sieved soil samples of nine agricultural fields of a quaternary landscape in North-east Germany predicting the soil's BNC and the corresponding lime requirement (LRBNC) at a target pH of 6.5. Seven spectral pre-processing methods were tested including a new technique based on normalized differences (ND). Furthermore, six multivariate regression methods were conducted including a new method combining a forward stagewise subset selection algorithm with PLSR (FS-PLSR). The models were validated using an independent sample set. The best regression model for most target variables was FS-PLSR combined with the second Savitzky-Golay derivation as pre-processing method achieving R2s from 0.68 to 0.82. Finally, the performance of the direct prediction of LRBNC (R2 = 0.68) was compared with an indirect prediction that was calculated by the predicted BNC parameters. This resulted in slightly higher correlation coefficients for the indirect method with R2 = 0.75.}, subject = {-}, language = {en} } @article{VogelEmmerichSchroeteretal., author = {Vogel, Sebastian and Emmerich, Katja and Schr{\"o}ter, Ingmar and B{\"o}necke, Eric and Schwanghart, Wolfgang and R{\"u}hlmann, J{\"o}rg and Kramer, Eckart and Gebbers, Robin}, title = {The effect of soil moisture content and soil texture on fast in situ pH measurements with two types of robust ion-selective electrodes}, series = {SOIL}, volume = {10}, journal = {SOIL}, number = {1}, publisher = {Copernicus Publications}, address = {G{\"o}ttingen, Germany}, issn = {2199-398X}, doi = {10.5194/soil-10-321-2024}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-9377}, pages = {321 -- 333}, abstract = {Abstract In situ soil pH measurements with ion-selective electrodes (ISEs) are receiving increasing attention in soil mapping for precision agriculture as they can avoid time-consuming sampling and off-site laboratory work. However, unlike the standard laboratory protocol, in situ pH measurements are carried out at lower and varying soil moisture contents (SMCs), which can have a pronounced effect on the sensor readings. In addition, as the contact with the soil during in situ measurements should be relatively short, effects of soil texture could be expected because texture controls the migration of protons to the electrode interface. This may be exacerbated by the fact that the electrodes used for in situ measurements are made of less sensitive but more robust materials as compared to the standard glass electrode. Therefore, the aim of the present study was to investigate the effect of soil moisture and soil texture on pH measurements using robust antimony and epoxy-body ISEs pressed directly into the soil for 30 s. The SMC was gradually increased from dry conditions to field capacity. A wide range of soil texture classes were included, with sand, silt, and clay contents ranging from 16 \% to 91 \%, 5 \% to 44 \%, and 4 \% to 65 \%, respectively. An exponential model was fitted to the data to quantify the relationship between SMC and pH. The results show that an increase in SMC causes a maximum increase in pH of approximately 1.5 pH units, regardless of the type of pH ISE used. Furthermore, for sandy soil textures, a rather linear relationship between pH and SMC was observed, whereas, with decreasing mean particle diameter (MPD), the model had a pronounced exponential shape, i.e., a greater pH increase at low SMC and a plateau effect at high SMC. With increasing SMC, the pH values asymptotically approached the standard pH measured with a glass electrode in 0.01 M CaCl 2(soil : solution ratio of 1:2.5). Thus, at high SMC, subsequent calibration of the sensor pH values to the standard pH value is negligible, which may be relevant for using the sensor pH data for lime requirement estimates. The pH measurement error decreases exponentially with increasing soil moisture and increases with decreasing MPD. Using a knee point detection, reliable pH values were obtained for SMC  > 11 \%, irrespective of the pH ISE used. An analysis of the regression coefficients of the fitted exponential model showed that the maximum pH increase also depends on soil texture; i.e., the influence of soil moisture variation on the pH value increases with decreasing MPD. Moreover, the concavity of the exponential curve increases with decreasing MPD.}, subject = {-}, language = {en} }