Cristina López-Fando

Pyrolytic descriptors responsive to changes in humic acid characteristics after long-term sustainable management of dryland farming systems in Central Spain

Structural changes in humic acids from a semiarid soil of an experimental farm in Central Spain have been studied by Curie-point pyrolysis. Soil has received periodic inputs of farmyard manure or crop wastes for the last 16 years, and mineral nitrogen fertilisation in 50% of the plots. Analytical pyrolysis suggested substantial differences in terms of the effect of soil management on the accumulation mechanisms of the humic acid fraction. When compared with control plots, humic acids from plots amended with crop wastes displayed well-defined methoxyphenol assemblages, indicating that the diagenetic transformation of lignin could be a dominant mechanism of organic matter stabilisation. The greatest yields of methoxyphenols after organic inputs were obtained in plots receiving nitrogen fertilisation, what agrees with the expected higher performance of the lignin biodegradation in nitrogen-limited media. Increased yields of lignin-derived methoxyphenols were also observed in plots treated with manure, which released in addition a conspicuous series of alkyl compounds suggesting recalcitrant wax-derived lipids incorporated to the humic acids. Highest yields of pyrolytic fatty acids were observed in humic acids from manure-amended plots without nitrogen fertilisation. Alkylbenzene proportions were also pyrolytic descriptors responsive to mineral nitrogen inputs, showing very significant differences (P<0.01) in both control and amended plots. Results suggested that continued organic inputs can not be considered to increase soil organic matter quality, since microbial reworking of lignins became the dominant mechanism of accumulation of humic acid-type substances, even when nitrogen inputs were applied.

Cultivation-Induced Effects on the Organic Matter in Degraded Southern African Soils

We studied quantitative and qualitative changes in soil organic matter (SOM) due to different land uses (reference woodland versus cultivated) on six soils from Tanzania (Mkindo and Mafiga), Zimbabwe (Domboshawa and Chickwaka), and South Africa (Hertzog and Guquka). Structural characteristics of the humic acids (HAs) were measured by Curie-point pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) and solid-state 13C nuclear magnetic resonance (CPMAS 13C NMR) spectroscopy. Significant changes in concentration and composition of SOM were observed between land uses. Losses of organic carbon after cultivation ranged from 35% to 50%. Virgin soils showed large proportions of colloidal humus fractions: humic acids (HAs) and fulvic acids (FAs) but negligible amounts of not-yet decomposed organic residues. The change in land use produced a contrasting effect on the composition of the HAs: a noteworthy “alkyl enhancement” in Mkindo soil and “alkyl depletion” in Chikwaka and to a lesser extent in Domwoshawa. The remaining soils displayed only minor alterations.

Biofertilization of Degraded Southern African Soils with Cyanobacteria Affects Organic Matter Content and Quality

We studied, under laboratory conditions, the effects of Nostoc 9v (cyanobacteria) on the soil organic matter (SOM) content and quality of different soils from Tanzania, Zimbabwe, and South Africa. Soils were inoculated with Nostoc 9v at a rate of 5 mg dry biomass g−1 soil and incubated for 3 months at 27°C under 22 W m−2 illumination for 16 h and 8 h under darkness. Moisture content was maintained at 60% of field capacity. The composition of the SOM and the structural features of the humic acid (HA) fraction were studied by visible and infrared (IR) spectroscopies. Nostoc 9v proliferated and colonized the surfaces of all soils very quickly. The results obtained showed significant changes in the quantitative and qualitative characteristics of the SOM due to cyanobacterial growth. Inoculation and further incubation with Nostoc 9v promoted increases in organic carbon (OC) that ranged from 0.4 g C kg−1 soil to 9.0 g C kg−1 soil. Cyanobacterial growth also affected SOM characteristics through the incorporation of free, extractable, or particulate biomass with a predominantly aliphatic character. Important descriptors of the extent to which cyanobacterial metabolism modified the characteristics of the native SOM were the changes in the observed amounts of the two humin types, the increase in lipid concentration, and the changes in the optical density of the HAs.

Laboratory Assessment of Nostoc 9v (Cyanobacteria) Effects on N2 Fixation and Chemical Fertility of Degraded African Soils

The potential of Nostoc 9v for improving the nitrogen (N)2–fixing capacity and nutrient status of semi‐arid soils from Tanzania, Zimbabwe, and South Africa was studied in a laboratory experiment. Nostoc 9v was inoculated on nonsterilized and sterilized soils. Inoculum rates were 2.5 mg dry biomass g−1 soil and 5 mg dry biomass g−1 soil. The soils were incubated for 3 months at 27 °C under 22 W m2 illumination with a photoperiod of 16 h light and 8 h dark. The moisture was maintained at 60% of field capacity. In all soils, Nostoc 9v proliferated and colonized the soil surfaces very quickly and was tolerant to acidity and low nutrient availability. Cyanobacteria promoted soil N2 fixation and had a pronounced effect on total soil organic carbon (SOC), which increased by 30–100%. Total N also increased, but the enrichment was, in most soils, comparatively lower than for carbon (C). Nitrate and ammonium concentrations, in contrast, decreased in all the soils studied. Increases in the concentration of available macronutrients were produced in most soils and treatments, ranging from 3 to 20 mg phosphorus (P) kg−1 soil, from 5 to 58 mg potassium (K) kg−1 soil, from 4 to 285 mg calcium (Ca) kg−1, and from 12 to 90 mg magnesium (Mg) kg−1 soil. Positive effects on the levels of available manganese (Mn) and zinc (Zn) were also observed.

Erträge und n‐bilanzen im IOSDV Madrid im laufe von vier rotationen

Im IOSDV Madrid wird seit 1984 die kombinierte Wirkung von Stallmist, Stroh, Zwischenfrucht und mineralischer N‐Dungung in der Fruchtfolge Sorghum‐Weizen‐Gerste auf einem semiariden Standort in der zentralspanischen Meseta auf einem Calcic Luvisol gepruft. Die Ergebnisse zeigen, dass die Witterungsbedingungen die Ertrage wesentlich starker beeinflussen als die Behandlungsvarianten. Durch die sehr geringen Niederschlage wahrend der dritten Rotation waren die Gersten‐ und Weizenertrage unabhangig von der Dungung sehr niedrig, wahrend unter optimalen Niederschlagsbedingungen in der ersten und zweiten Rotation die Weizen‐ und Gerstenertrage mit steigender N‐Dungung zunahmen und ihr Optimum bei der Stickstoffdungungsstufe N3 aufwiesen; allerdings zeigte nur die Gerste eine Reaktion auf die gleichzeitige Anwendung organischer Dunger. Wahrend der vierten Rotation wurden die Trockenmasse‐Ertrage bei Weizen und Gerste durch organische Dungung bis zur Stufe N2 erhoht, wahrend hohere Mineral‐N‐Gaben die Ertrage nega...