Daniel Geisseler

Effects of fertilization and soil management on crop yields and carbon stabilization in soils. A review

The study of sustainable land use is complex and long-term experiments are required for a better understanding of the processes of carbon stabilization. Objectives were (i) to describe for four long-term experiments the effects of fertilization and soil management on crop yields and the dynamics of soil organic carbon (SOC) and total N, and (ii) to discuss the usefulness of models for a better understanding of the underlying processes. Data of soil organic carbon and total N of four long-term experiments in Germany and China which studied the effect of fertilization (Bad Lauchstädt, Darmstadt) and tillage (Göttingen, Quzhou) were evaluated and soil organic carbon fractionation was carried out. The Rothamsted Carbon Model was used for a description and prediction of soil organic carbon dynamics as affected by fertilization and tillage in Bad Lauchstädt and Quzhou. The type of fertilizer added at common rates — either mineral N or farmyard manure — affected the crop yields only slightly, with slightly lower yields after manure application compared with mineral N fertilization. For both fertilization trials, manure applications at common rates had beneficial effects on soil organic carbon stocks in the labile pool (turnover time estimated as <10 years) and to a greater extent in the intermediate pool (turnover time estimated to be in the range of 10 to 100 years). A comparison of the effects of conventional tillage, reduced tillage and no-tillage carried out in Göttingen and Quzhou indicated only small differences in crop yields. Reduced tillage in Göttingen resulted in an increased C storage in the surface soil and C was mainly located in the mineral-associated organic matter fraction and in water-stable macro-aggregates (>0.25 mm). For Quzhou, no-tillage and conventional tillage had similar effects on total C stocks, with a greater spatial variability in soil organic carbon stocks in the no-tillage plots. Modeling required site-specific calibrations for the stock of inert organic matter for each of the sites, indicating that not all carbon stabilization processes are included in the model and that application of a model to a new site may also need site-specific adjustments before it can be used for predictions. After site-specific calibration, however, model predictions for the remaining treatments were generally accurate for the fertilization and tillage trials, which emphasizes the importance of temperature, moisture, soil cover and clay content on the decomposition dynamics of soil organic carbon and the significance of amounts and quality of carbon inputs in the soil for maintaining or increasing soil organic carbon stocks in arable soils.

Short-term dynamics of soil carbon, microbial biomass, and soil enzyme activities as compared to longer-term effects of tillage in irrigated row crops

Biol Fertil Soils (2009) 46:65–72 DOI 10.1007/s00374-009-0400-0 SHORT COMMUNICATION Short-term dynamics of soil carbon, microbial biomass, and soil enzyme activities as compared to longer-term effects of tillage in irrigated row crops Daniel Geisseler & William R. Horwath Received: 6 March 2009 / Revised: 1 May 2009 / Accepted: 5 May 2009 / Published online: 25 August 2009 # The Author(s) 2009. This article is published with open access at Springerlink.com Introduction The effects of disturbance on soil quality are difficult to determine because soil is inherently variable and physical and chemical soil properties change too slowly to reflect recent management history. Microbial and biochemical soil properties have been suggested as early and sensitive indicators of changes in soil quality as they manifest themselves over shorter timescales and are central to the ecological function of a soil (Karlen et al. 1994; Bandick and Dick 1999). Soil enzyme activities in particular are increasingly used as indicators of soil quality because of their relationship to decomposition and nutrient cycling, ease of measurement, and rapid response to changes in soil management (Dick 1994; Dilly et al. 2003). In a long-term study, Kandeler et al. (1999) found that enzyme activities were significantly increased in the top 10 cm of the profile after only 2 years of minimum and reduced tillage compared to conventional tillage. In contrast, significant effects of tillage treatments on microbial biomass, nitrogen (N) mineralization, and potential nitrification were not observed until after 4 years. Soil disturbance, however, is only one of the many factors affecting soil microbial and biochemical properties. Seasonal fluctuations in soil moisture, temperature, and substrate availability can also have large effects on microbial biomass and activity. Franzluebbers et al. (1994) found that soil microbial biomass carbon (C mic ) changed significantly during the cropping season in all crop sequences D. Geisseler (*) : W. R. Horwath Department of Land, Air, and Water Resources, University of California, Davis, PES Building, 1 Shields Ave, Davis, CA 95616, USA e-mail: djgeisseler@ucdavis.edu and tillage regimes under investigation. Bausenwein et al. (2008) also reported significant effects of sampling date on C mic and enzyme activities under minimum tillage. These observations raise the question of whether microbial and biochemical properties are affected by too many factors and fluctuate too much during the course of a season to be sensitive indicators of tillage-induced effects on soil quality. In general, conservation tillage (CT) practices leave a significant amount of plant residue on the soil surface. This results in an increased soil organic matter content in the topsoil, which in turn leads to higher microbial biomass and activity. This increase in organic matter content in the topsoil however is often offset with a decrease in lower soil layers (Dick 1992; Omidi et al. 2008). Franzluebbers (2002) suggested using changes in soil organic C with depth rather than the total amount of soil organic C in the profile as indicators of tillage-induced effects on soil properties. The stratification ratio, calculated by dividing the value for a soil property in the topsoil by its value in the subsoil, could not only be a more sensitive way to measure tillage-induced changes, but it also normalizes for differ- ences in climatic conditions and soil types between study sites. Because surface organic matter is essential to erosion control and water infiltration, the degree of stratification is directly linked to soil quality (Franzluebbers 2002). The objective of this study was to compare short-term dynamics of soil C, microbial biomass, and soil enzyme activities with longer-term effects of tillage in irrigated row crops in order to determine how environmental factors affect the use of these properties as sensitive indicators of tillage-induced changes in soil quality. A field trial was designed to test the following hypotheses: (1) enzyme activities and microbial biomass N (N mic ) respond more rapidly to differences in tillage treatments than total soil C.

C and N dynamics of a range of biogas slurries as a function of application rate and soil texture: a laboratory experiment

Digestates vary in composition and studies regarding their impact on C and N dynamics in soils are scarce. The objective was to analyse the C and N dynamics of digestates originating from various substrates applied to a sandy Cambisol and a silty Anthrosol. In three laboratory experiments (4–6 weeks), the effects of digestate properties, N rate and water content were tested. Averaged over both soils, 21% of the C supplied was emitted as CO2. Potential NH3 emissions during the first week ranged between 6% and 12% of NH4+ present in the digestates. The emission factors in the sandy Cambisol were on average 1.2 and 2 times higher for CO2 and potential NH3, respectively, compared to the silty Anthrosol. Similarly, net nitrogen mineralization in the sandy Cambisol was approximately twice the N mineralized in the silty Anthrosol. Net nitrification was not influenced by soil texture or different digestates, but increased with increasing application rates and had highest values at 75% of water holding capacity. Our results indicate that the type of substrate input for anaerobic digestion influences the properties of the digestate and therefore the dynamics of C and N. However, soil texture can affect these dynamics markedly.

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.