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.
Vergleich von Elektro‐Ultrafiltration (EUF) und Extraktion mit 0,01 molarer CaCl2‐Lösung zur Bestimmung des pflanzenverfügbaren Stickstoffs im Boden
In 25 landwirtschaftlich genutzten Oberboden wurde NO3-N, NH4-N und Norg mit der EUF- und CaCl2-Methode bestimmt, um die Reproduzierbarkeit und Aussagefahigkeit beider Extraktionsverfahren zu uberprufen. Die Erfassung des pflanzenverfugbaren Stickstoffs erfolgte im Mikrogefasversuch mit Lolium multiflorum. 
 
 
 
- Die Befunde der CaCl2-Extrakte waren mit einem Variationskoeffizienten von 2,6% besser reproduzierbar als die der EUF-Analyse (6,2%). 
 
 
 
- Es bestand eine sehr enge Beziehung zwischen dem CaCl2- und dem EUF-extrahierbaren Stickstoff (r2 = 0,917). 
 
 
 
- Sowohl die EUF- als auch die CaCl2- extrahierbare Norg-Fraktion waren in gleichem Mase positiv korreliert mit der N-Aufnahme der Pflanzen (EUF-Norg, r = 0,921; CaCl2-Norg, r = 0,932). 
 
 
 
Comparison of electro-ultrafiltration (EUF) and extraction by 0.01 M CaCl2 for the determination of “available” soil nitrogen 
 
 
 
The NO3-N, NH4-N and Norg content of 25 different farm soils were analysed using the EUF-technique and CaCl2 extraction in order to compare the reproducibility and reliability of the two methods. Nitrogen available to plants was measured in a micro pot experiment with Lolium multiflorum. 
 
 
 
- CaCl2 values were better reproducibel (cv = 2.6%) than those of the EUF method (cv = 6.2%). 
 
 
 
- Close correlations were found between the soil content of CaCl2-and EUF-extractable nitrogen (r2 = 0.917). 
 
 
 
- The EUF-extractable Norg-fraction was positivly correlated with the total N-uptake by the test plants (r = 0.921). Most importently these data did not significantly deviate from the correlation of the CaCl2 extractable Norg-fraction with total N-uptake (r = 0.932).
Effect of straw, cellulose and lignin on the turnover and availability of labelled ammonium nitrate
SummaryAn experiment was carried out to investigate how straw, cellulose and lignin affect the turnover and availability of inorganic labelled N in soil. The experiment comprised an incubation period in which the soil was incubated with 15NH415NO3 and organic materials followed by drying and by cropping the soil with Lolium perenne. The incubation period lasted 148 days during which soil samples were taken 36 and 148 days after the beginning of incubation. Addition of organic materials to the soil promoted the incorporation of inorganic N into organic matter and decreased apparent N denitrification losses during the first period of incubation (0–36 days after beginning of incubation). In this respect straw and cellulose were more effective than lignin. The organic materials also promoted the fixation of NH4+ by clay minerals. In all treatments highest fixation of labelled NH4+ by clay minerals was found at the end of the incubation period. During the cropping period high apparent denitrification losses were observed particularly in the “straw” and “cellulose” treatment. Hence the recovery of labelled N by Lolium was particularly low in these treatments while in the control treatment the 15N recovery was about twice as high.