Denaturing gradient gel electrophoresis (DGGE) of amplified fragments of genes coding for 16S rRNA was used to study the development of bacterial communities during decomposition of crop residues in agricultural soils. Ten strains were tested, and eight of these strains produced a single band. Furthermore, a mixture of strains yielded distinguishable bands. Thus, DGGE DNA band patterns were used to estimate bacterial diversity. A field experiment performed with litter in nylon bags was used to evaluate the bacterial diversity during the decomposition of readily degradable rye and more refractory wheat material in comparable luvisols and cambisols in northern, central, and southern Germany. The amount of bacterial DNA in the fresh litter was small. The DNA content increased rapidly after the litter was added to the soil, particularly in the rapidly decomposing rye material. Concurrently, diversity indices, such as the Shannon-Weaver index, evenness, and equitability, which were calculated from the number and relative abundance (intensity) of the bacterial DNA bands amplified from genes coding for 16S rRNA, increased during the course of decomposition. This general trend was not significant for evenness and equitability at any time. The indices were higher for the more degradation-resistant wheat straw than for the more easily decomposed rye grass. Thus, the DNA band patterns indicated that there was increasing bacterial diversity as decomposition proceeded and substrate quality decreased. The bacterial diversity differed for the sites in northern, central, and southern Germany, where the same litter material was buried in the soil. This shows that in addition to litter type climate, vegetation, and indigenous microbes in the surrounding soil affected the development of the bacterial communities in the litter.

To simulate growth conditions experienced by microbiota at O 2-limited interfaces of organic matter in compost, an experimental system capable of maintaining dual limitations of oxygen and carbon for extended periods, i.e., a pO 2-auxostat, has been used. 15 N tracer studies on thermophilic (53؇C) decomposition processes occurring in manure-straw aggregates showed the emission of dinitrogen gas from the reactor as a result of simultaneous nitrification and denitrification at low pO 2 values (0.1 to 2.0%, vol/vol). The N loss was confirmed by nitrogen budget studies of the system. Depending on the imposed pO 2 , 0.6 to 1.4 mmol of N/day (i.e., 20 to 40% of input N) was emitted as N 2. When the pO 2 was raised, the rates of both nitrification and denitrification increased instantaneously, indicating that ammonia oxidation was limited by oxygen. In auxostats permanently running at pO 2 > 2% (vol/vol), the free ammonium pool was almost completely oxidized and was converted to nitrite plus nitrate and N 2 gas. Labelling of the auxostat with [ 13 C]carbonate was conducted to reveal whether nitrification was of autotrophic or heterotrophic origin. Incorporation of 13 CO 2 into population-specific cellular compounds was evaluated by profiling the saponifiable phospholipid fatty acids (FAs) by using capillary gas chromatography and subsequently analyzing the 13 C/ 12 C ratios of the individual FAs, after their combustion to CO 2 , by isotope ratio mass spectrometry. Apart from the observed label incorporation into FAs originating from a microflora belonging to the genus Methylococcus (type X group), supporting nitrification of a methylotrophic nature, this analysis also corroborated the absence of truly autotrophic nitrifying populations. Nevertheless, the extent to which ammonia oxidation continued to exist in this thermophilic community suggested that a major energy gain could be associated with it.

1. Forty-nine clones and 25 families of white clover were tested in monoculture and in association with grass. The monoculture was mown only. The mixed cultivation was subdivided in a grazed part and a mown part. 2. Comparison of the families at the end of the second year after sowing showed rather low correlations for the characteristics area and density in monoculture and area in mixture. For height and type in monoculture and area in a mixture with grass correlations were even lower. The finer-leaved types of monoculture often performed better under mixture/grazing, but did not belong to the best. Under this kind of utilization the coarse Ladino types were frequently worse. They indeed often ranked among the worst. There was a very close relation between density and area in pasture. The correlation of area in mixture/mowing for the families of clover with area in monoculture was lower than the correlation between the same characteristic in mixture/grazing and monoculture. For the clones the correlation coefficients were lower than for the families. Among the characteristics themselves differences in correlations were found similar to those of the families. 3. For the best families in monoculture the correlation with growth in mixture is often higher than for the average of the other families. 4. In the second year after sowing the correlation between spread of clover in mixture/mowing and in mixture/grazing was very low. 5. Mass per area and density under monoculture in the year of sowing appeared to be moderately correlated with area under mixture/grazing in the second year after sowing as far as the families are concerned. For the best objects the correlation was higher. In a similar comparison area appeared to have much less significance than density. 6. Under grazing conditions the mother clones of the two best families showed the greatest number of surviving plants, indicating thus a clear inheritance of the competitive ability. 7. If breeding clover for cultivation with grass is intended, one must include clover/ grass mixture in the selection scheme. Mixture/mowing and mixture/grazing require a rather great number of replications. Another disadvantage of testing under grazing is the need for cattle. On the other hand testing with a clover/grass association does not require so much weed control, which is a great advantage, ince weed control in a monoculture demands expensive labour.

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Seedlings of allopolyploidfamilies from Lolium multiflorum x Festuca arundinacea were compared with varieties of the two parental species. They were investigated at different stages in a heated and an unheated greenhouse and in the field. Early seedling growth in the hybrid families in most cases, proved to be significantly better than in the two Festuca arundinacea standard varieties.One family of the hybrids performed well for height and yield under all conditions.The data indicate good possibilities for selection.