Mirjam M. Pulleman

Management induced organic matter differentiation in grassland and arable soil: a study using pyrolysis techniques

Abstract Differences in agricultural management and land use lead to differences in soil structure, soil organic matter (SOM) dynamics and composition. We investigated the SOM composition at three depth layers in a permanent pasture (PP), an organic arable (OA) and a conventional arable (CA) field within one soil series in marine loam deposits in The Netherlands. Both arable fields were in the grass phase of the rotation. The chemical composition of SOM was determined by a combination of conventional pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and of thermally assisted hydrolysis and methylation (THM) with tetramethylammonium hydroxide (TMAH). In PP, SOM was composed of relatively little decomposed, mainly grass-derived material comprising polysaccharides, lignin, aliphatic compounds (extractable lipids, cutin, suberin) and proteins. With depth, plant-derived constituents decreased, whereas microbial and humified material predominated. Both arable soils contained mainly strongly humified plant material and microbially altered proteineous material that showed heterocyclic N-compounds together with alkylbenzenes and phenols upon pyrolysis. With THM small traces of plant-derived alkanols and cutin/suberin were observed in the arable soils. The upper layers of OA contained little lignin, which can only be derived from the grass vegetation or manure inputs since last ploughing (2 years before) since it was not found in the whole plough layer. Overall SOM composition is therefore hardly affected by organic farming compared to conventional management. The differences in SOM content and composition between the pasture and arable fields can be ascribed to differences in input and depth distribution of fresh organic materials. But a difference in physical protection of easily mineralisable SOM between pasture and arable soils is also likely to contribute.

Soil structure and characteristics of organic matter in two orchards differing in earthworm activity

By consuming plant remains and soil, earthworms incorporate organic matter (OM) into the soil and form biogenic soil structures, which can affect OM dynamics. We carried out a (micro)morphological study of soil structure development and OM distribution in two orchards (45 year) in a Dutch calcareous marine loam: RI − without, and KR + with high earthworm activity, the result of different levels of heavy metal contamination from fungicides. In both soils, sedimentary–stratification was absent to 60 cm depth and equal amounts of biogenic calcite spheroids were counted, suggesting similar earthworm activity in the past. In RI − the current vol.% of worm-worked groundmass in thin sections was 6% in the Ah and 7% in the Bw horizon compared with 51% in the Ah and 16% in the Bw horizon of KR + . Disappearance of earthworms with time in RI − gave rise to a compacted physicogenic soil structure with angular and prismatic aggregates and the absence of earthworm biopores. Due to restricted fragmentation and incorporation of OM fragments in casts, a litter layer formed at the soil surface. OM coatings were present in fissures and root pores of the Ah horizon, indicating the absence of mixing of organic and mineral soil materials. OM fragments were relatively coarse (>50m) and heterogeneously distributed through the Ah groundmass. Stronger decalcification in RI − than in KR + could be ascribed to higher production of organic acids in the litter layer of RI − and the absence of soil homogenisation by earthworms. In KR + earthworm activity was high, which has resulted in a biogenic structure with granular and subangular blocky aggregates and many worm casts and biopores. Particulate OM was relatively fine ( <50m) and encapsulated with clayey material in casts and micro-aggregates. The organic C content was not significantly ( P< 0.05) higher in the Ah horizon of KR + , than in the Ah horizon of RI − (15.7 and 13.7 g kg −1 , respectively). The lower C mineralization rates in KR + below 6 cm depth, however, might be an indication of higher microbial substrate-use efficiency or physical protection of OM against decomposition. The latter explanation would accord with the observed encapsulation of OM in micro-aggregates, and with studies on other management systems that favour biogenic aggregate formation. The quality of the soil macro- and microstructures, degree of soil compaction and decalcification and soil OM dynamics were strongly determined by the occurrence of earthworms in soils.

Features Related to Faunal Activity

Soil fauna plays an important role in transporting and altering various soil components, in particular the decomposition of organic matter and the development of soil structure. Fauna-induced features are found in all types of soils and can be so abundant that they determine the nature and intensity of active physical and chemical processes. However, there is still a lack of knowledge of the impact of soil fauna on soils. Micromorphological techniques provide an excellent tool to understand the role of soil animals and their impact on an array of soil properties. This chapter presents a basic outline of the diversity of faunal features recognized in soil thin sections. The first part deals with the variety of void systems produced by soil fauna, such as channels, chambers and modified voids. The second part presents a review of pedofeatures produced by soil fauna, including different types of excrements, coatings and infillings. Each group of faunal species produces a number of different features related to various factors, such as mobility, food source, life cycle phase, body size, soil composition and moisture status, all commonly with important seasonal variations. One group alone, for example termites, earthworms or molluscs, can produce over 50 different kinds of features, with varying effects on soils. Important applications of micromorphological studies of features related to faunal activity are mainly related to soil formation and humus development, landscape reconstruction, archaeology and faunal impact on soil functions as affected by soil management

Soil Capability: Exploring the Functional Potentials of Soils

Capability, a term that has been well defined in welfare economics, can be applied to soil by defining the intrinsic capacity of a soil to contribute to ecosystem services, including biomass production. Seven soil functions are used to define capabilities, and combining different functions in storylines provides integrated expressions for capability considering the different functions. Applied to biomass production in a sustainable production system, potential production (Yp) is defined as a function of radiation, temperature, CO2 and plant physiology. Yp is independent of soil and provides an absolute point of reference. Yw represents water-limited yield, reflecting actual water regimes and assuming that soil fertility is adequate and pests and diseases don’t occur. Ya represents actual yield. A soil capability index (SCI) is defined as SCI = (Ya/Yw) × 100 for a biomass production storyline for rainfed production systems. Some examples are presented. Using simulation modelling, Yp can be simulated for a given climate and Yw can be simulated for a given soil in a probabilistic manner using weather data for 30 years as a form of quantitative land evaluation. Ya can be measured. Not only capability, as such, is important, however, but also the way in which capability can be realized under practical conditions. Then, a management support system is needed to guide a farmer real time through the growing season, also taking into account long-term effects. Capability is defined for a given type of soil (the genoform), but sometimes management has had significant effects on soil properties, requiring a phenoform approach, as is illustrated.