Biology and Fertility of Soils

Winter wheat was grown over 2 years (1995, 1996) in an organic and integrated cropping system on sandy and loamy soils. Root growth was measured on five to six occasions each year with an auger sampling procedure and the ingrowth core method. The first resulted in an estimate of net root development, while the latter revealed gross root growth (GG) or root production. Total root production was about 80–150 km m–2 (0- to 30-cm soil layer) between April and July and exceeded the net size of the root system at harvest by a factor of between 2 and 4. The C input into the soil could be estimated as 1.4–2.6 t ha–1 by this root production. The cropping systems had nearly no influence on root production. The largest differences occurred between the years. The net root length tended to be lower on sandy soils compared to the loam, but total root production was higher. Root mortality, which is the difference between GG and net root growth, was also higher on sandy soils. The turnover index, which is the mean of the relative root production rates and relative root mortality rates, was positively related to the soil sand content in both years.

Examples of the practical use of microarthropod life-history tactics in nature management and ecotoxicology were selected. A key to the tactics was developed to facilitate the use of the life-history tactics. Examples of the microarthropod distribution over these tacties were selected from a forest, a grassland, and a salt marsh. The process of decomposition of grass leaves in litterbags was described using life-history tactic diagrams. The effects of various disturbances were described in terms of shifts in the distribution of life-history tactics of species. Irregular unpredictable disturbances lead to an increased representation of phoresy tactics. Regular disturbances lead to an increased representation of synchronization tactics. Permanent and persistent pollution, finally, leads to an increased representation of tactics with thelytokous reproduction. The consequences of the latter for ecotoxicology were examined. It was concluded that microarthropod life-history tactics meet the criteria described, permitting comparisons between effects of management measures and pollution in different biotopes and countries.

An acid forest soil from beech forest gaps, which were either limed or unlimed, and the undisturbed forest was investigated for the type of nitrifying populations and the process of N2O evolution. To see whether nitrifiers were of heterotrophic or autotrophic origin, the nitrification inhibitors nitrapyrin and sodium chlorate were applied to disturbed soil samples which underwent laboratory incubations. Nitrapyrin inhibits autotrophic nitrification. In different studies, sodium chlorate has been identified as an inhibitor either of autotrophic or of heterotrophic nitrification. In the samples investigated only nitrapyrin inhibited the autotrophic nitrification occurring in the limed soil. Sodium chlorate effectively inhibited heterotrophic nitrification. In the limed forest floor samples, where most autotrophic nitrification occured, sodium chlorate showed no inhibitory effect. In another laboratory incubation experiment, N2O evolution from undisturbed soil columns, to which the above inhibitors were applied, was investigated. In those samples, in which nitrification had been reduced, neither inhibitor significantly reduced N2O evolution. Thus it was concluded that the contribution of nitrification to N2O losses is negligible, and that N2O evolution arises from the activity of denitrifying organisms. Microbial biomass and respiration measurements showed that the inhibitors did not affect microflora negatively.

 Earthworms may alter the physical, chemical, and biological properties of a forest soil ecosystem. Any physical manipulation of the soil ecosystem may, in turn, affect the activities and ecology of earthworms. The effects of removing organic matter (logs and forest litter) and severely compacting the soil on native earthworm species were measured in a central USA hardwood region (oak-hickory) forest in the Missouri Ozarks (USA). Soils in this region are characterized by a cherty residuum that is primarily of the Clarksville series (Loamy-skeletal, mixed, mesic Typic Paledults). Earthworms were collected from 0–15 cm depth each spring and fall for 2 years by handsorting, and densities were determined on a per meter square basis. Two native earthworm species, Diplocardia ornata and Diplocardia smithii, were dominant on this site. Organic matter removal decreased the average individual biomass of both species. However, both species responded differently to soil compaction. Soil compaction affected D. ornata adversely and D. smithii favorably. This suggested that the degree of soil compaction was not as restrictive with respect to D. smithii (2 mm diameter) as to D. ornata (5 mm diameter). Moreover, the apparently improved soil environmental conditions resulting from the remaining organic matter in compacted soil enhanced the population and growth of D. smithii. Sampling position on the landscape affected D. ornata but not D. smithii. Soil microbial biomass C and soil microbial biomass N were decreased under soil compaction when the organic matter was removed. Other factors influencing the ecology and activity of these two species will require further study.

Soil was amended with a variety of carbon sources, including four soluble compounds (glucose, sucrose, glycerol and mannitol) and two plant residues (straw and alfalfa).. Potential denitrification rates, measured both as N2O accumulation and NO3 − disappearance, were compared, and the predicted values of available C, measured as CO2 production and water-extractable C, were assessed. The two measures of denitrification agreed well although N2O accumulation was, found to be most sensitive. Soil treated with the four soluble C compounds resulted in the same rate of denitrification although glycerol was not as rapidly oxidized. Alfalfa-amended soil produced a significantly higher rate of denitrification than the same amount of added straw. CO2 evolution was found to be a good predictor of denitrification over the first 2 days of sampling, but neither measure of available substrate C correlated well with denitrification rate beyond 4 days, when NO3 − was depleted in most treatments. The data with alfalfa-amended soil suggested that denitrifiers used water-extractable C. materials produced by other organisms under anaerobic conditions.