Stefan Pätzold

Soil heterogeneity at the field scale: a challenge for precision crop protection

Crop protection seldom takes into account soil heterogeneity at the field scale. Yet, variable site characteristics affect the incidence of pests as well as the efficacy and fate of pesticides in soil. This article reviews crucial starting points for incorporating soil information into precision crop protection (PCP). At present, the lack of adequate field maps is a major drawback. Conventional soil analyses are too expensive to capture soil heterogeneity at the field scale with the required spatial resolution. Therefore, we discuss alternative procedures exemplified by our own results concerning (i) minimally and non-invasive sensor techniques for the estimation of soil properties, (ii) the evidence of soil heterogeneity with respect to PCP, and (iii) current possibilities for incorporation of high resolution soil information into crop protection decisions. Soil organic carbon (SOC) and soil texture are extremely interesting for PCP. Their determination with minimally invasive techniques requires the sampling of soils, because the sensors must be used in the laboratory. However, this technique delivers precise information at low cost. We accurately determined SOC in the near-infrared. In the mid-infrared, texture and lime content were also exactly quantified. Non-invasive sensors require less effort. The airborne HyMap sensor was suitable for the detection of variability in SOC at high resolution, thus promising further progress regarding SOC data acquisition from bare soil. The apparent electrical conductivity as measured by an EM38 sensor was shown to be a suitable proxy for soil texture and layering. A survey of arable fields near Bonn (Germany) revealed widespread within-field heterogeneity of texture-related ECa, SOC and other characteristics. Maps of herbicide sorption and application rate were derived from sensor data, showing that optimal herbicide dosage is strongly governed by soil variability. A phytoassay with isoproturon confirmed the reliability of spatially varied herbicide application rates. Mapping areas with an enhanced leaching risk within fields allows them to be kept free of pesticides with related regulatory restrictions. We conclude that the use of information on soil heterogeneity within the concept of PCP is beneficial, both economically and ecologically.

Adsorption von Pflanzenschutzmitteln und DOC an Saugkerzen aus Glas und Keramik

Bei der Gewinnung von Bodenlosung mittels Saugkerzen konnen die Konzentrationen geloster Stoffe in Abhangigkeit vom Kerzenmaterial durch Ad- und Desorptionsprozesse stark verandert werden. Zum Vergleich der bislang uberwiegend ublichen Keramik-Saugkerzen mit neuartigen Saugkerzen aus Borosilikatglas wurden wassrige Losungen von Pflanzenschutzmitteln (PSM) und DOC durch diese Kerzentypen geleitet. Dabei zeigte sich, dass die Adsorption der PSM Pendimethalin, Terbuthylazin, Metolachlor und Chlortoluron (Konzentrationen: 2, 20 und 200 μg 1−1) an Saugkerzen aus Borosilikatglas z. T. erheblich geringer war als an Saugkerzen aus Keramik. Wahrend bei der Perkolation durch die Keramik-Saugkerzen im Mittel 10% (1,1—31%) der Wirkstoffe adsorbiert wurden, betrugen die Verluste bei den Glas-Saugkerzen im Mittel nur 3,1% (0—11%). Die Unterschiede zwischen den beiden Saugkerzentypen nahmen mit steigender Hydrophobie der PSM-Wirkstoffe und sinkender Losungskonzentration deutlich zu. So wurden bei einer Losungskonzentration von 2 μg 1−1 in den Keramik-Saugkerzen 31% des gelosten Pendimethalins adsorbiert, wahrend die Verluste in den Glas-Saugkerzen mit 7,7% deutlich geringer waren. Entsprechende Adsorptionstests mit bodeneigenem gelostem organischem Kohlenstoff (DOC) fuhrten zu ahnlichen Ergebnissen. Vom DOC verschiedener Bodenextrakte wurden in den Glas-Saugkerzen durchschnittlich 2,4% adsorbiert, wahrend die Keramik-Saugkerzen bis zu 50% der gelosten organischen Substanz retardierten. Da bodeneigene geloste organische Substanzen bedeutende Sorbenten und Carrier fur Pflanzenschutzmittel darstellen, wird durch die weitgehende Neutralitat des Glas-Materials gegenuber PSM und DOC die Eignung dieses Werkstoffs fur die Gewinnung von Saugkerzen-Losungen in Pflanzenschutzmittel-Studien nachdrucklich unterstrichen.

Organic fertilization and sufficient nutrient status in prehistoric agriculture?--Indications from multi-proxy analyses of archaeological topsoil relicts.

Neolithic and Bronze Age topsoil relicts revealed enhanced extractable phosphorus (P) and plant available inorganic P fractions, thus raising the question whether there was targeted soil amelioration in prehistoric times. This study aimed (i) at assessing the overall nutrient status and the soil organic matter content of these arable topsoil relicts, and (ii) at tracing ancient soil fertilizing practices by respective stable isotope and biomarker analyses. Prehistoric arable topsoils were preserved in archaeological pit fillings, whereas adjacent subsoils served as controls. One Early Weichselian humic zone represented the soil status before the introduction of agriculture. Recent topsoils served as an additional reference. The applied multi-proxy approach comprised total P and micronutrient contents, stable N isotope ratios, amino acid, steroid, and black carbon analyses as well as soil color measurements. Total contents of P and selected micronutrients (I, Cu, Mn, Mo, Se, Zn) of the arable soil relicts were above the limits for which nutrient deficiencies could be assumed. All pit fillings exhibited elevated δ15N values close to those of recent topsoils (δ15N>6 to 7‰), giving first hints for prehistoric organic N-input. Ancient legume cultivation as a potential source for N input could not be verified by means of amino acid analysis. In contrast, bile acids as markers for faecal input exhibited larger concentrations in the pit fillings compared with the reference and control soils indicating faeces (i.e. manure) input to Neolithic arable topsoils. Also black carbon contents were elevated, amounting up to 38% of soil organic carbon, therewith explaining the dark soil color in the pit fillings and pointing to inputs of burned biomass. The combination of different geochemical analyses revealed a sufficient nutrient status of prehistoric arable soils, as well as signs of amelioration (inputs of organic material like charcoal and faeces-containing manure).