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.
CH4 oxidation in two temperate arable soils as affected by nitrate and ammonium application
The short-term effect of NaNO3 or (NH4)2SO4 application on CH4 oxidation was measured under laboratory conditions with sieved soils collected from the top layer (0–12 cm) of a loamy and a sandy soil. The soils were incubated in sealed flasks and the CH4 and CO2 concentrations in headspace were measured periodically. On each gas sampling date the soils were analysed for inorganic N, electro-ultrafiltration organic N, and pH. NH4+application to the loamy soil inhibited CH4 oxidation entirely whereas in the untreated control soils CH4 concentration decreased linearly with a rate of-41 nl CH4 l-1 h-1; NO3sup-application to this soil caused a small but significant reduction in CH4 uptake. The CH4-oxidizing ability of the sandy soil was low, even in the control. This was mainly a result of the disturbed soil structure after sieving. Both NH4+and NO3sup-treatments completely inhibited CH4 uptake in this ligh-textured soil. The adverse impact of NH4+persisted during the entire incubation, although in the loamy soil only 17% of the NH4+added was recovered after 168 h. The negative effect of NO3sup-was probably caused by an increase in osmotic potential. Immediate inhibition of CH4 oxidation after inorganic N addition was demonstrated in two arable soils, although the effect was directly related only in part to soil N transformations.
Investigations on the rôle of organic matter in plant nutrition
1. As the result of decomposition of green manure in a swamp soil, the coarse fractions (including coarse and fine sand) of the surface layer (first 3 inches) decreased by 11·2 per cent. while the fine ones (silt+clay) increased by 9·8 per cent. in the course of 43 days. The effect was less pronounced in the manured soil maintained at 60 per cent. saturation, while no alteration was to be noticed in the case of the unmanured specimens. 2. Treatment with dilute hydrochloric acid prior to dispersion had no appreciable effect on the estimates of mechanical composition obtained in the different cases. Loss in solution was also comparatively small. 3. The silica-sesquioxide ratio increased slightly as the result of decomposition of green manure in swamp soil. The composition of the fine fractions was also altered, the total percentages of the oxides of iron, aluminium and silicon increasing from 90·5 to 99·3 in the course of 71 days. 4. The practical significance of the above and related observations has been discussed.