Compost effects on microbial biomass and soil P pools as affected by particle size and soil properties

Previous studies have shown that finer composts release nutrients more quickly than coarse composts, but little is known about the nutrient release from different size fractions of a compost. To assess if compost size fractions differ in their effect on microbial biomass and soil P pools, a compost from garden waste was separated by sieving into different particle size fractions (> 5 mm, 3-5 mm and 5 mm fraction and in microbial biomass C and P with the < 3 mm fraction. The size of the P pools was mainly affected by soil type, the compost fractions had similar effects on soil P pools except for a greater increase in available P concentration by the finest fraction compared to the coarser size fractions. Soil A with the highest organic matter content had the highest concentrations of Fe/Al associated P (NaOH-P) and organic P whereas Ca-associated P (HCl-P) dominated in the alkaline soil C. The size of most P pools, even the so-called stable P pools changed over time in amended and non-amended soils. It can be concluded that the size of P pools is more strongly affected by soil properties such as organic matter content, texture and pH than by the compost fractionsS. Lata Verma, P. Marschne

Clay addition to sandy soil - effect of clay concentration and ped size on microbial biomass and nutrient dynamics after addition of low C/N ratio residue

Addition of clay-rich subsoil to sandy soil has been shown to increase crop production on sandy soils. The added clay is present as peds ranging in size from a millimetre to several centimetre. In thisexperiment clay soil (73% clay) was added to sandy soil (3% clay) at 10 and 20% clay w/w as 1, 3 and 5 mm peds. Shoots of young Kikuyu grass (C/N 20) were ground and added at 10g kg-1, and soils were incubated for 45 days at 80% of water holding capacity.The study confirmed that clay addition to sandy soil increased soil organic carbon retention but decreased cumulative respiration and available P compared to sandy soil alone. Ped size had little effect on respiration and nutrient availability. Over the course of 45 days peds broke down and organic C was bound to the < 53 μm fraction. The greatest proportion of peds and total organic carbon (54-67%) was in the initially added ped size. The TOC content of < 53 μm fraction of initially added peds was 0.38% and at the end of the experiment (after 45 days) the TOC had increased by 24, 19 and 10% in 1, 3 and 5 mm peds respectively.Shermeen Tahir and Petra Marschne

Effect of incorporated or mulched compost on leaf nutrient concentrations and performance of Vitis vinifera cv. Merlot

Compost can reduce evaporation and increase nutrient uptake by plants, but it is not clear if it can increase soil water holding capacity or stimulate leaf gas exchange, water use efficiency and yield of vines. To study these effects, compost from garden and food waste was incorporated or mulched in a vineyard at a rate of 100 m3 ha-1, three months before the measurements. The vineyard received irrigation during spring and summer. Soil water content was monitored regularly with a capacitance probe. Photosynthesis, transpiration, stem water potential and leaf area index were measured several times during the vegetation period. At harvest, yield, berry weight and quality as well as chlorophyll, N, P and K concentrations in leaves were determined. Only mulched compost increased soil water content at 10 cm depth, but the water content in the deeper layers was not affected by compost addition. Compost also did not affect transpiration rate and stomatal conductance during the vegetation period, but mulched compost increased the photosynthesis per plant at flowering, pea size and maturity periods. Compost amendment, particularly mulching, increased yield, specific berry weight, and leaf N and P concentrations, and reduced the number of chlorotic leaves at harvest. Berry quality was not affected by compost amendment. It can be concluded that mulched compost has a positive effect on grapevine yield and can be an alternative fertiliser source for vines with no adverse effect on berry quality.T.-T. Nguyen, S. Fuentes, P. Marschne

Microbial biomass and activity in two cultivation systems on the SHIFT experimental area near Manaus.

In two different cultivation systems we investigated the microbial biomass and activity in the rhizosphere of Theobroma grandiflorum and Bactris gasipaes, two important crop plants in sustainable agriculture in Brazil during rainy and dry season 1998

Genotypic variation in phosphorus efficiency between wheat cultivars grown under greenhouse and field conditions

Phosphorus (P) efficiency (relative growth), which is described as the ratio of shoot dry matter or grain yield at deficient P supply to that obtained under adequate P supply, was compared in 25 winter wheat cultivars grown under greenhouse and field conditions with low and adequate P levels in a P-deficient calcareous soil. Adequate P supply resulted in significant increases in shoot dry weight and grain yield under both experimental conditions. In the greenhouse experiment, the increases in shoot dry weight under adequate P supply (80 mg kg(-1)) were from 0% (cv: C-1252) to 34% (cv: Dagdas). Under field conditions, the cultivars showed much greater variation in their response to adequate P supply (60 kg ha(-1)): the increases in shoot dry weight and grain yield with adequate P supply were between -2% (cv: Sivas-111/33) and 25% (cv: Kirac-66) for shoot dry matter production at the heading stage and between 0% (cv: Kirkpinar-79) and 76% (cv: Kate A-1) for grain yield at maturity. Almost all cultivars behaved totally different in their response to P deficiency under greenhouse and field conditions. Phosphorus efficiency ratios (relative growth) under greenhouse conditions did not correlate with the P efficiency ratios under field conditions. In general, durum wheat cultivars were found to be more P efficient compared with bread wheat cultivars. The results of this study indicated that there is wide variation in tolerance to P deficiency among wheat cultivars that can be exploited in breeding new wheat cultivars for high P deficiency tolerance. The results also demonstrated that P efficiency was expressed differently among the wheat cultivars when grown under greenhouse and field conditions and, therefore, special attention should be paid to growth conditions in screening wheat for P efficiency

Hochauflösende Bestimmung der konzentrationsabhängigen Substrataffinität von Enzymen im Tiefenverlauf eines Dystric Cambisols

Enzyme sind für die Umsetzung und Speicherung von Nährstoffen im Boden von großer Bedeutung. Im Gegensatz zum Oberboden sind die Prozesse und Mechanismen der Kohlenstoff- und Nährstoffflüsse im Unterboden jedoch weitaus weniger erforscht und deren Wichtigkeit im globalen Stoffkreislauf weitestgehend unterschätzt. Für die Untersuchungen wurden auf der Langzeitmessfläche "Grinderwald" der SUBSOM Forschergruppe 40 km nord-westlich von Hannover aus einem Dystric Cambisol (FAO-WRB 2014) unter Buchenwald Bodenproben aus 15 Tiefenstufen (0-1 m alle 10 cm und 1-2 m alle 20 cm) an drei fest installierten Observatorien bis zu einer Tiefe von 2 m mit Rammkernsonden entnommen. Je Observatorium wurden zwei Teilflächen mit je drei Bohrungen beprobt, die für die weitere Analyse zu tiefenbezogenen Mischproben vereint wurden. Insgesamt wurden daher sechs Tiefenprofile analysiert. Stellvertretend für den C-, C/N-, N-, P- und S-Kreislauf wurde die Enzymaktivität von β-Glucosidase (C), Chitinase (C/N), Arginin-Aminopeptidase (N), saure-Phosphatase (P) und Sulfatase (S) mit dem von Marx et al. (2001) entwickelten Mikrotiterplattensystems bestimmt. Zur Ermittlung der Michaelis-Menten Kinetik wurde dabei die Reaktionsraten der Enzyme bei steigenden Substratkonzentrationen bestimmt, um somit die maximale Substrataffinität abbilden zu können. Für jedes Enzym wurde die Reaktionsrate bei den Substratkonzentrationen 0, 25, 50, 75, 100 und 200 µmol pro g Boden bestimmt. Es wird erwartet, dass die Ergebnisse dieser Untersuchung Aufschluss über die spezifischen Reaktionsraten von Enzymen entlang des Tiefengradienten liefern, um somit das Verständnis von dem Einfluss von Enzymen auf die Stoffumsätze im Boden weiter verbessern zu können

Einsatz der Nahinfrarotspektroskopie zur Abschätzung von allgemeinen und biologischen Bodeneigenschaften

Infrarotspektroskopie im sichtbaren und nahen Infrarotbereich (vis-NIRS) ist eine etablierte Methode zur Abschätzung der Gehalte an organischem Kohlenstoff (SOC) und Stickstoff (N) in Böden. Weniger Information ist hinsichtlich einer Eignung für bodenbiologische Eigenschaften vorhanden. Ziele waren die Untersuchung der Eignung der vis-NIRS zur Abschätzung von allgemeinen Bodeneigenschaften (SOC, N, pH, Textur) und Enzymaktivitäten für unterschiedliche Standorte. Chemometrische Auswertungen wurden mit der PLS (partial least squares)-Regression durchgeführt. Unabhängige Validierungen zeigten, dass vis-NIRS erwartungsgemäß gut geeignet zur Abschätzung von SOC- und N-Gehalten war, während die Abschätzungen von pH und Texturklassen variabel waren. Die Abschätzungen von Enzymaktivitäten konnten mittels Regressionen aus den allgemeinen Bodeneigenschaften mit ähnlicher Genauigkeit abgeschätzt werden wie aus den Infrarotdaten, so dass wir keinen Nutzen der vis-NIRS zur direkten Abschätzung von Enzymaktivitäten sehen