Behaviour of arbuscular-mycorrhizal fungi on Vigna luteola growth and its effect on the exchangeable (32P) phosphorus of soil

 The effect of the inoculation of Glomus mosseae and Scutellospora fulgida, singly or in mixed inocula, was tested on the growth and mycorrhizal characteristics of Vigna luteola. Soil depletion by mycorrhizal inoculation was determined as exchangeable ³²PO₄. Five treatments were performed: non-inoculated control (C); inoculated with a suspension of microorganisms free of mycorrhizae (M); inoculated with S. fulgida plus microorganisms (Sf+M); inoculated with G. mosseae plus microorganisms (Gm+M) and a treatment inoculated with both S. fulgida and G. mosseae plus microorganisms (Sf+Gm+M). G. mosseae was the most efficient fungus in promoting growth of V. luteola. This fungus produced higher shoot dry weight, P uptake in shoots (P_shoot) and P_shoot/arbuscules ratio than the S. fulgida inoculum, even though percent arbuscular-mycorrhizal (AM) colonization was similar for the two single AM-inoculated treatments. The highest value of isotopically exchangeable P was recorded for treatment M (P<0.05). In comparison with M, Gm+M treatment reduced the different P pools more than Sf+M treatment. C_p values were reduced to half by Gm+M and Sf+M treatments and were minimum for the combined treatment. Pools A (exchangeable phosphate between 1 min and 1 day) and B (exchangeable phosphate between 1 day and 3 months) were reduced by Gm+M treatment in contrast to Sf+M, which left them unchanged. The depression of isotopically exchangeable P for all pools obtained for the Sf+Gm+M treatment suggested that specific characteristics of fungi caused differences in P absorption, which in addition was altered by the possible interactions among them, when multiple inocula were used in a soil low in native P. Received: 29 January 1999     

Influence of arbuscular mycorrhizae on growth, leaf yield and phosphorus uptake in mulberry (Morus alba L.) under rainfed, lateritic soil conditions

 A field experiment was conducted to study the effect of arbuscular mycorrhizal association in mulberry saplings var. S₁, together with two levels of phosphate, on growth characters, leaf yield and phosphorus uptake. The experiment was conducted in the period 1995 to 1997 at the Technical Service Centre, Kashipur, Purulia (West Bengal) under rainfed, lateritic soil conditions. Pooled data analysis revealed that there was no significant variation among the treatments in most of the characters except height of plant and leaf moisture percentage. Plant height in both treatments with Glomus mosseae was significantly less than in the others, while there was significant reduction in moisture percentage in G. fasciculatum with 25 kg of phosphate and G. mosseae with 10 kg of phosphate ha^–1 year^–1 than in other treatments. There was no significant season–treatment effect on any of the parameters. Considering all the quantitative and qualitative characters, G. fasciculatum together with the most economic dose of phosphate showed more promising performance than G. etunicatum and G. mosseae with different doses of phosphate fertilizer. At 80% of the recommended dose of inorganic phosphate fertilizer, Rs 534.0 were earned as net profit. Received: 11 February 1998     

Carabid beetles (Coleoptera,Carabidae) as bioindicators in biological and conventional farming in Austrian potato fields

Summary Carabid beetles were sampled in 1980 and 1981 by pitfall trapping in two biologically and two conventionally farmed potato fields in B. Zell, Upper Austria. The cultivation differences consisted mainly of a herbicide application to one conventional field in 1980 and higher fertilization levels in both conventional fields in both years. The total carabid catch was 7428 beetles, representing 48 species. In both years the numbers of total carabids and numbers of species were higher in the biologically farmed fields. Of 16 dominant species (representing 96% of all carabids) only 5 (e.g., Platynus dorsalis, Poecilus cupreus) showed similar activity densities under both types of cultivation. Five species (e.g., Carabus spp., Amara consularis, Harpalus rufipes) were frequent only in one field. Pterostichus melanarius was the only species more numerous in the conventional fields, whereas five species occurred either more frequently or exclusively in the biological fields. Of these five species, Poecilus versicolor, Dyschirius globosus, Calathus fuscipes and, only regionally, Harpalus aeneus are considered to be bioindicators for biologically farmed agroecosystems. The frequencies of Amara consularis and Harpalus rufipes are apparently related to weed vegetation.Dedicated to the late Prof. Dr. W. Kühnelt     

Soil microbiome biomass,activity, composition and CO2 emissions in a long-term organic and conventional farming systems

The implementation of environmentally friendly agricultural policies has increased the need to compare agricultural aspects of conventional (CON) and organic farming (ORG) systems. The objective of the present work was to compare the effects of an organic and conventional long-term experiment on bacterial and fungal biomass and activity, as well as soil CO₂ emission and readily available nitrogen forms in a soil cultivated with Helianthus annuus L. The microbial biomass was more active and abundant in ORG as well as soil CO₂ emission. Despite being less abundant, fungi were more active than bacteria in both ORG and CON experiments. 16S rRNA gene sequencing showed that the ORG treatment had a significantly greater bacterial richness than CON. Cyanobacteria, Actinobacteria and Proteobacteria were the most abundant phyla contributing more than others to the differences between the two systems. Moreover, the soil ${\mathit{NH}}_4^{+}$ and ${\mathit{NO}}_2^{-}$ content was not significantly different between ORG and CON, while ${\mathit{NO}}_3^{-}$ was less in ORG. ORG sunflower yield was significantly less compared with CON. While much remains to be discovered about the effects of these agricultural practices on soil chemical properties and microbial diversity, our findings may contribute to this type of investigation.     

Soil carbon sequestration,plant nutrients and biological activities affected by organic farming system in tea (Camellia sinensis (L.) O. Kuntze) fields

There is growing interest in investigations into soil carbon (C) sequestration, plant nutrients and biological activities in organic farming since it is regarded as a farming system that could contribute to climate mitigation and sustainable agriculture. However, most comparative studies have focused on annual crops or farming systems with crop rotations, and only a few on perennial crops without rotations, e.g. tea (Camellia sinensis (L.) O. Kuntze). In this study, we selected five pairs of tea fields under organic and conventional farming systems in eastern China to study the effect of organic farming on soil C sequestration, plant nutrients and biological activities in tea fields. Soil organic C, total nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg), available nutrients, microbial biomass, N mineralization and nitrification were compared. Soil pH, organic C and total N contents were higher in organic tea fields. Soil microbial biomass C, N and P, and their ratios in organic C, total N and P, respectively, net N mineralization and nitrification rates were significantly higher in organic fields in most of the comparative pairs of fields. Concentrations of soil organic C and microbial biomass C were higher in the soils with longer periods under organic management. However, inorganic N, available P and K concentrations were generally lower in the organic fields. No significant differences were found in available calcium (Ca), Mg, sodium (Na), iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) concentrations between the two farming systems. These findings suggest that organic farming could promote soil C sequestration and microbial biomass size and activities in tea fields, but more N-rich organic fertilizers, and natural P and K fertilizers, will be required for sustainable organic tea production in the long term.     

Soil organic carbon stocks, storage profile and microbial biomass under different crop management systems in a tropical agricultural ecosystem

 We investigated the soil organic C and N stocks, storage profiles and microbial biomass as influenced by different crop management systems in a tropical agricultural ecosystem. The different crop management systems significantly affected the C and N stocks and microbial biomass C and N at different soil depths. Amongst the systems evaluated, the rice-wheat system maintained a higher soil organic C content. Inclusion of legumes in the system improved the soil organic matter level and also soil microbial biomass activity, vital for the nutrient turnover and long-term productivity of the soil. Irrespective of the cropping system, approximately 58.4%, 25.7% and 15.9% of the C was distributed in 0–15, 15–30 and 30–60 cm depths, respectively. Received: 10 October 1999     

The impact of a low humus level in arable soils on microbial properties, soil organic matter quality and crop yield

 In arable soils in Schleswig-Holstein (Northwest Germany) nearly 30% of the total organic C (TOC) stored in former times in the soil has been mineralized in the last 20 years. Microbial biomass, enzyme activities and the soil organic matter (SOM) composition were investigated in order to elucidate if a low TOC level affects microbial parameters, SOM quality and crop yield. Microbial biomass C (C_mic) and enzyme activities decreased in soils with a low TOC level compared to soils with a typical TOC level. The decrease in the C_mic/TOC ratio suggested low-level, steady-state microbial activity. The SOM quality changed with respect to an enrichment of initial litter compounds in the top soil layers with a low TOC level. Recent management of the soils had not maintained a desirable level of humic compounds. However, we found no significant decrease in crop yield. We suggest that microbial biomass and dehydrogenase and alkaline phosphatase activities are not necessarily indicators of soil fertility in soils with a high fertilization level without forage production and manure application. Received: 12 December 1997     

Urease activity and its relation to soil organic matter, microbial biomass nitrogen and urea-nitrogen assimilation by maize in a Brazilian Oxisol under no-tillage and tillage systems

 We studied the relationship between urease activity (UA) and soil organic matter (SOM), microbial biomass N (N_biom) content, and urea-N fertilizer assimilation by maize in a Dark Red Latosol (Typic Haplustox) cultivated for 9 years under no-tillage (NT), tillage with a disc plough (DP), and tillage with a moldboard plough (MP). Two soil depths were sampled (0–7.5 cm and 7.5–15 cm) at 4 different times during the crop cycle. Urea was applied at four different rates, ranging from 0 to 240 kg N ha^–1. The levels of fertilizer N did not affect the UA, SOM content, and N_biom content. No significant difference between the treatments (NT, DP, and MP) was observed for SOM during the experiment, probably because the major part of the SOM was in recalcitrant pools, since the area was previously cultivated (conventional tillage) for 20 years. The N_biom content explained 97% and 69% of the variation in UA in the upper and deeper soil layer, respectively. UA and biomass N were significantly higher in the NT system compared to the DP and MP systems. The highest maize productivity and urea-N recovery was also observed for the NT system. We observed that the increase in urea-N losses under NT, possibly as a consequence of a higher UA, was compensated for by the increase in N immobilized in the biomass. Received: 2 July 1999