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A study dealing with ecological sustainability of plantation based land use initiated in 1991 in a 19 yr old coconut plantation consists of growing certain leguminous crops like Atylosia, Pueraria, Centrosema and Calopogonium as soil cover in separate plots with lemon grass as live bounds. These cover crops are grown during the rainy season and incorporated into the soil towards the end of the monsoon every year. The effect of such cover crops on soil microbial counts (total counts, fungi, actinomycetes and bacteria), biomass C, organic C, total N and on the activity of enzymes like urease, amidase, L-glutaminase, aryl sulphatase and dehydrogenase was determined in soils (Ap horizon) collected from these plots after 5 years. Soils with cover crops registered significantly higher microbial biomass, biomass C, organic C and total N compared to control. Consequently, all the enzymes were activated to different degrees in soils with cover crops. Significant and positive relationships of enzyme activities with organic C, mineral N and total N suggested that growing cover crops, increased C turnover and N availability and therefore, provided a conducive environment for microbial proliferation, enzyme synthesis and accumulation in the soil matrix. Einflus von Leguminosen als Deckfrucht auf mikrobielle und ausgewahlte Enzymaktivitaten in Boden einer Plantage Zur Untersuchung der okologischen Nachhaltigkeit der Bodennutzung im Plantagenanbau wurde 1991 in einer 19 Jahre alten Kokosplantage ein Versuch mit Leguminosen als Deckfrucht auf getrennten Parzellen und mit Lemongrass als Trennstreifen angelegt. Die Deckfruchte wuchsen wahrend der Regenzeit und wurden gegen Ende des Monsuns alljahrlich eingearbeitet. Nach 5 Jahren wurde in Ap-Proben die Wirkung der verschiedenen Deckfruchte auf Mikroorganismen (Gesamtzahlen, Pilze, Actinomyceten und Bakterien), Biomasse-C, org. C und Gesamt-N und auf die Enzymaktivitaten wie Urease, Amidase, L-Glutaminase, Arylsulfatase und Dehydrogenase untersucht. Boden mit Deckfrucht wiesen signifikant hohere Werte bei mikrobieller Biomasse, Biomasse-C, org. C sowie mineralischem und Gesamt-N auf als die Kontrolle. Als Folge waren unter Deckfrucht alle Enzymaktivitaten — in unterschiedlichem Grade erhoht. Signifikante positive Korrelationen von Enzymaktivitaten mit organischem C, mineralischem und Gesamt-N sind Anzeichen dafur, das unter den wachsenden Deckfruchten Kohlenstoffumsatz und N-Verfugbarkeit gunstig beeinflust waren und damit mikrobielles Wachstum und Enzymsynthese und -anreicherung gefordert wurden.

A fertilizer management study involving incorporation of poultry manure, farm yard manure, sesbania and gliricidia into soils of a rice-rice system was initiated in May 1993. In order to determine the effects of organic manure incorporation on soil microbial biomass and enzyme activity, soils were collected from the respective plots at the end of the second rice crop in February 1996. and were incubated with and without the respective organic manure at the rate of 15 Mg ha−1 at 25°C, under submergence. The total viable microbial counts, bacteria, actinomycetes, N flush, biomass C and activities of urease, amidase, acid and alkaline phosphatase, dehydrogenase and L-glutaminase were determined after 60 days of incubation. Soils freshly amended and soils previously amended with organic manures registered significantly greater microbial biomass and enzyme activity than the unamended control. The microbial biomass and enzyme activity, however, varied with the type of organic manure incorporated into the soil. Except for acid phosphatase, which showed slight inhibition, all the other enzymes were activated to different degrees by organic manure incorporation. A significant and positive relationship of enzyme activity with organic C and total N suggested that the addition of organic manure to soils increased C turnover, N availability and microbial activity which in turn led to greater enzyme synthesis and accumulation in the soil matrix.