Effect of different soil cultivation systems, including no-tillage, on electro-ultrafiltration extractable organic nitrogen
The effect of different long-term soil-cultivation systems (ploughing, two types of cultivator, notillage) on organic N, extracted with the electroultrafiltration (EUF) technique, was studied in two arable soils, a Luvic Phaeozem derived from loess and a Eutric Cambisol. A modified EUF extraction procedure (the 80°C fraction extended from 5 to 90 min) was used to investigate the release of organic N from the ploughing and no-tillage treatment, and the content of hydrolysable N was measured in the combined filtrates. No-tillage and the two non-turning cultivation systems led to an accumulation of EUF organic N in the 0- to 10-cm depth compared to the ploughing treatment. In the lower horizon (15–25 cm) the reverse pattern was found in the loamy soil, with higher concentrations after ploughing than after reduced tillage. However, in the sandy soil all four cultivation treatments showed similar values in the 15- to 25-cm depth. During the time of investigation (May 1987 to February 1989) an EUF organic N accumulation occurred, which was about twice as high in the loamy as in the sandy soil. Therefore we conclude that in the sandy soil the mineralization of organic N was faster, and that reduced tillage retarded its degradation. In the total 0- to 25-cm depth, this delay was not observed in the loamy soil. The N release rates were much lower in the sandy than in the loamy soil and they were higher for the notillage than for the ploughing treatment. Only 30–40% of the total organic N desorbed was hydrolysable and the amino acid composition indicates that part of it originated from microbial Cells. The overall evaluation showed clearly that EUF-extractable organic N is a sitespecific factor.
The Role of Traces of Molybdenum in the Physiology and Agrobiology of Azotobacter1
A study has been made of the interrelationships existing between the influences of molybdenum, vanadium, natural soil humate, and synthetic sugar humates upon the growth of strains of Azotobacter cultivated in free nitrogen and in a variety of fixed nitrogen compounds at different temperatures over the physiological range 20° 40°C. A. chroococcum Strain B8, obtained from a garden soil in Moscow, U.S.S.R., gave more response to addition of molybdenum, and fixed nitrogen faster under optimum conditions, . than did A_. vinelandii, as indicated in the following table giving the growth velocities (0.69/ generation times) in different forms of nitrogen, at about optimum temperature (S3 36°). It is evident that, contrary to a long-established opinion, it is quite possible for Azotobacter to grow faster in nitrogen gas as a source of nitrogen than in probably most fixed nitrogen compounds except ammonia and possibly urea, providing adequate Mo is present. When Mo is partially deficient, as indicated in the table, many fixed nitrogen compounds may be superior sources of nitrogen for nutrition. According to our recent results, Mo has no influence on the growth of Azotobacter in fixed nitrogen, providing N2 gas is not present, as was the case in the experiments reported in Table I. These findings have an obvious bearing on the question of nitrogen fixation by Azotobacter in soils, especially in relation to their molybdenum content. Van Niel has shown that molybdenum can be sufficiently deficient in soils to prevent the growth of Azotobacter under conditions otherwise entirely favorable for its multiplication. As is evident from Table II, the concentrations of Mo in such soils are of the same order as those we have found to be limiting in solution cultures, due allowance being made for the heterogeneous nature of the soil.
D'une application pratique des indices bio-météorologiques
Abstract The purpose of the author is to determine statistically in what part of Switzerland maize could be cultivated with certain chance of rentability. The author gives first the method he used for determining the biometeorological index of four species of maize which were selected by the Swiss agronomical research stations. He has considered two possibilities for the growing period: ( a ) raising-ripening (l'approche globale); ( b ) raising-flowering, flowering-ripening (l'approche fractionee). From the biometeorological index, he calculated retrospectively the ripening time of these four species in the years 1901–1965. Assuming a priori that maize should be harvested before October 15th at the latest, he calculated, for a number of meteorological stations, the relative number of years when such conditions were fulfilled. Dividing the country in regions of similar mesoclimates and sorting these stations per region, it is possible to average the maximum altitude where maize can ripen at least 7, 8, 9 and 10 times within 10 years. Finally, taking into account the exposure and ground slope, he draws maps of the theoretically possible extension area, which maps are more reliable and detailed than the ones derived from actual means.