Macro-invertebrates accelerate litter decomposition and nutrient release in a Hawaiian rainforest

Macro-invertebrates (>2 mm in size) can play a key role in litter decomposition by influencing litter chemistry and other components of the decomposer community, thus affecting rates of decomposition, nutrient release, and primary production. However, in many ecosystems the influences of macro-invertebrates on key ecosystem processes have not been adequately addressed. We investigated the influence of the macro-invertebrate community in litter decomposition and the cycling of nutrients in a young rainforest site on the island of Hawaii by using litter bags with and without 2.5 cm holes to allow or prevent access by macro-invertebrates. Presence of macro-invertebrates increased rates of litter decomposition by 16.9% and rates of nutrient release for N and Mn by 33.2% and 30.3%, respectively. Macro-invertebrate activity thus has a major impact on N release accounting for 3.32 kg/ha/yr. This internal ecosystem transfer of N from the litter is greater than estimates of nitrogen inputs from rain water, dry deposition, volcanic sources, atmospheric dust, and nitrogen fixation for this ecosystem. These findings demonstrate that improved knowledge of the ecosystem effects of macro-invertebrates is necessary to understand how ecosystems function.     

Evaluating the efficiency of sampling methods in assessing soil macrofauna communities in arable systems

The soil fauna is often a neglected group in many large-scale studies of farmland biodiversity due to difficulties in extracting organisms efficiently from the soil. This study assesses the relative efficiency of the simple and cheap sampling method of handsorting against Berlese–Tullgren funnel and Winkler apparatus extraction. Soil cores were taken from grassy arable field margins and wheat fields in Cambridgeshire, UK, and the efficiencies of the three methods in assessing the abundances and species densities of soil macroinvertebrates were compared. Handsorting in most cases was as efficient at extracting the majority of the soil macrofauna as the Berlese–Tullgren funnel and Winkler bag methods, although it underestimated the species densities of the woodlice and adult beetles. There were no obvious biases among the three methods for the particular vegetation types sampled and no significant differences in the size distributions of the earthworms and beetles. Proportionally fewer damaged earthworms were recorded in larger (25 × 25 cm) soil cores when compared with smaller ones (15 × 15 cm). Handsorting has many benefits, including targeted extraction, minimum disturbance to the habitat and shorter sampling periods and may be the most appropriate method for studies of farmland biodiversity when a high number of soil cores need to be sampled.     

Effects of burning on soil macrofauna in a savanna-woodland under different experimental fuel load treatments

In West African savanna-woodland, the use of prescribed burning as a management tool has ecological implications for the soil biota. Yet, the effects of fire on soil inhabiting organisms are poorly understood. The aim of this study was to examine the responses of soil macro-invertebrates to early fires in a Sudanian savanna-woodland on a set of experimental plots subject to different fuel load treatments. The abundance of major macro-invertebrate taxa and functional groups, and taxon richness were quantified in soil cores collected from three different soil layers before and immediately after burning. The results indicated that, overall, there was substantial spatial and temporal variation in the composition of macro-invertebrate assemblages. The immediate effects of fire were to reduce total invertebrate numbers and numbers of many invertebrate groups dramatically. This is probably due to the fact that many of the surface-dwelling macrofauna perished as a result of less favorable microclimate due to fire, diminished resources, or migrate to safer environments. Fuel load treatment did not affect the community taxonomic richness or abundance of the soil-dwelling fauna. Furthermore, annual changes in community composition were more pronounced at the burnt site than in the control. This could be related to the inter-annual difference in precipitation pattern recorded during the two-year study period at our site. Since soil macrofauna population declines in fire-disturbed areas, increasing fire prevalence may jeopardize the long-term conservation of fire sensitive macrofauna groups. Special fire management attention is therefore recommended with due consideration to the type of burning and fuel properties to avoid the detrimental effects of intense fire affecting the resilience of savanna soil macrofauna species.     

Diversity of soil macro-invertebrates in grasslands under restoration succession

In grasslands under restoration succession, the effect of nutrient impoverishment on the vegetation has been intensively studied. The invertebrate soil animal community has, however, rarely been studied under such conditions. We hypothesised that a plant community in nutrient-poor grasslands supports fewer macro-invertebrate individuals than richer grasslands. We also hypothesised that the composition of the macro-arthropod community is specific for a certain stage of vegetation succession, i.e. nutrient impoverishment. A detailed sampling programme was carried out in four grasslands under restoration succession. The time since last fertilisation differed for these four grasslands (7, 11, 24 and 29 years). The lowest total number of individuals in different taxonomic groups of macro-invertebrates was found in the most impoverished field in the majority of cases. Analysis of the data set for all specimens identified to order or family level with a canonical correspondence analysis resulted in a pattern not related to successional stage. The same holds when the species composition of the ground beetles was analysed separately. Short-term abiotic factors explained a significant part of the variation in both analyses. With the same multivariate analysis, however, the adult weevils, identified to species level, showed a clear relation with nutrient status of the grasslands.     

A simple wet chemical extraction procedure to characterize soil organic matter (SOM). I. application and recovery rate

Abstract

The knowledge of soil organic matter (SOM) composition is important for research in soil science. This is why two classical wet chemical extraction procedures were tested and combined to characterize SOM. Twenty‐five samples from typical forest and arable soils in Schleswig‐Holstein, Northwest Germany, were investigated in the laboratory. Lipids were extracted using a pre‐step method. Several polysaccharide fractions were extracted sucessively with inorganic acids in a litter compound analysis (LCA). Proteins and lignins were determined in the bulk soil sample. In a humic compound analysis (HCA), fulvic and humic acids were extracted in the classical way with NaOH, and the non‐humic substances were removed with the aid of the “Sulfacetolysis” from the residues (= usually “humins")‐ The combination of these two wet chemical extraction proce dures (LCA and HCA) permitted quantitative estimations of the SOM composition in several soil horizons. The LCA method produced a better recovery rate (104%±4%) than the HCA methode (95%±15%). The litter compound/humic compound ratio of both analyses, and the combination of both correlated with visible humification grades in a significant way (r = ‐0.733 to ‐0.742***). LCA may be sufficient for solving special pedogenetic problems, because of its high recovery rate and the strong correlation between LCA and HCA.     

Indirect host effect on ectomycorrhizal fungi: Leaf fall and litter quality explain changes in fungal communities on the roots of co-occurring Mediterranean oaks

Host trees can modify their soil abiotic conditions through their leaf fall quality which in turn may influence the ectomycorrhizal (ECM) fungal community composition. We investigated this indirect interaction using a causal modelling approach. We identified ECM fungi on the roots of two coexisting oak species growing in two forests in southern Spain - Quercus suber (evergreen) and Quercus canariensis (winter deciduous)-using a PCR-based molecular method. We also analysed the leaf fall, litter and soil sampled beneath the tree canopies to determine the concentrations of key nutrients. The total mycorrhizal pool was comprised of 69 operational taxonomic units (OTUs). Tomentella and Russula were the most species-rich, frequent and abundant genera. ECM fungi with epigeous and resupinate fruiting bodies were found in 60% and 34% of the identified mycorrhizas, respectively. The calcium content of litter, which was significantly higher beneath the winter-deciduous oak species due to differences in leaf fall quality, was the most important variable for explaining ECM species distribution. The evaluation of alternative causal models by the d-sep method revealed that only those considering indirect leaf fall-mediated host effects statistically matched the observed covariation patterns between host, environment (litter, topsoil, subsoil) and fungal community variables.     

Surveying soil faunal communities using a direct molecular approach

Soil faunal communities are often phylogenetically diverse and the accurate assessment of the taxonomic structure of these communities is both time-consuming and requires a high level of taxonomic expertise. Here we describe a DNA sequence-based methodology for characterizing soil micro- and mesofaunal communities that is similar to the molecular approaches commonly used to survey soil microbial diversity. The technique involves the direct extraction of faunal DNA from soil, PCR amplification of the extracted DNA with metazoan-specific primers, followed by the construction of clone libraries and direct sequencing of individual PCR products. We used this technique to characterize micro- and mesofaunal community composition from six individual soils representing two land-use types. The technique captured the more abundant faunal groups in the soils (nematodes, Collembola, Acari, tardigrades, enchytraeids) and provided sufficient taxonomic resolution to describe the overall structure of the communities. We compared the results obtained using this molecular approach to results obtained using a traditional, microscopy-based approach and found that the results were broadly similar. However, since biases are inherent in both methods it remains unclear which method provides a more accurate assessment of soil faunal community composition. Although this molecular approach has some distinct disadvantages over the more widely-used direct extraction methods, one advantage is that the taxonomic identification it can provide will be more accurate and consistent across research groups, facilitating effective comparisons of mesofaunal surveys.     

Plant growth and microbial activity in a tropical soil amended with faecal pellets from millipedes and woodlice

The effect of soil fauna-mediated leaf litter (faecal pellets) versus mechanically fragmented (finely ground) leaf litter on biomass production of rice (Oryza sativa, var. Primavera) was assessed in pot tests. Rice seedlings were either grown in soil samples amended with faecal pellets of diplopods and isopods fed on leaf litter of a legume cover crop (Pueraria phaseoloides (Roxb.) Benth) and a peach palm (Bactris gasipaes) or in soil amended with finely ground leaf litter. The addition of faecal pellets caused a significant and dose-related increase in plant biomass compared to pure soil. Ground leaf litter induced a significantly smaller positive effect on plant biomass development with Pueraria litter > Bactris litter > mixed primary forest litter. In contrast, soil microbial biomass development during the 4 weeks plant test was higher in the soil amended with ground litter as compared to soil amended with feacal pellets. The results show a clear positive effect of the soil fauna on soil fertility and indicate differences in the availability of nutrients from the organic substrates to higher plants and soil microorganisms.     

Liquid extraction of low molecular mass organic acids and hydroxamate siderophores from boreal forest soil

Low molecular mass organic acids (LMMOAs) and hydroxamate siderophores (HS) are molecules secreted by microbes and have previously been found in soil solution and in cultures. Mycorrhizal fungi are suggested to be involved in the nutrient uptake processes of trees and weathering of minerals. In this study soil samples taken from the O and E horizons of a podzol were extracted with 10 mM potassium phosphate buffer at pH 7.2. Variable parameters included addition of methanol to the extraction buffer and the use of ultrasonication or rotary shaking during extraction. LMMOAs and HS content of the soil extracts were determined. Analysis of soil extracts were carried out by liquid chromatography mass spectrometry (LC–MS) and the extraction results compared to results for soil solution samples obtained by centrifugation of the soils sampled. The extraction yields were significantly increased by addition of methanol to the extraction buffer, especially for the O horizon samples. Rotary shaking of the samples for 90 min gave slightly higher yields than ultrasonication for 15 min but the reduction in extraction time makes ultrasonication an attractive option. Of the HSs determined, ferricrocin was found in all samples. Optimal extraction conditions showed citric acid and isocitric acid to be the most abundant organic acids in the O and E horizons, respectively.     

Liquid extraction of low molecular mass organic acids and hydroxamate siderophores from boreal forest soil

Low molecular mass organic acids (LMMOAs) and hydroxamate siderophores (HS) are molecules secreted by microbes and have previously been found in soil solution and in cultures. Mycorrhizal fungi are suggested to be involved in the nutrient uptake processes of trees and weathering of minerals. In this study soil samples taken from the O and E horizons of a podzol were extracted with 10 mM potassium phosphate buffer at pH 7.2. Variable parameters included addition of methanol to the extraction buffer and the use of ultrasonication or rotary shaking during extraction. LMMOAs and HS content of the soil extracts were determined. Analysis of soil extracts were carried out by liquid chromatography mass spectrometry (LC–MS) and the extraction results compared to results for soil solution samples obtained by centrifugation of the soils sampled. The extraction yields were significantly increased by addition of methanol to the extraction buffer, especially for the O horizon samples. Rotary shaking of the samples for 90 min gave slightly higher yields than ultrasonication for 15 min but the reduction in extraction time makes ultrasonication an attractive option. Of the HSs determined, ferricrocin was found in all samples. Optimal extraction conditions showed citric acid and isocitric acid to be the most abundant organic acids in the O and E horizons, respectively.     

Estimates of viral abundance in soils are strongly influenced by extraction and enumeration methods

Viruses are highly abundant in temperate soils, ranging from 10⁷ to 10⁹?g^?1, and outnumbering soil bacteria from 5- to over 1,000-fold. In order to determine the potential impacts of viruses on soil microbial communities, it is important to establish reliable methods for comparing changes in viral abundances within and across soil samples. The goals of this study were to optimize extraction-enumeration methods to accurately determine viral abundances in a range of soil types, to evaluate the feasibility of simultaneously enumerating bacterial cells and virus particles using a single extraction procedure, and to assess the utility of flow cytometry (FCM) for enumerating virus particles in soil extracts. Comparisons of extraction approaches indicated that sonication or blender extraction of soils with potassium citrate buffer yielded the highest viral abundances for most soil types. Combined viral and bacterial extractions underestimate abundances compared to separately-optimized extractions for each. Flow cytometric counts were anywhere between 350- and 1,400-fold higher than epifluorescence microscopy (EFM)-based counts for the same soil. Trends in viral abundance across soil types were different from those via EFM, and different relationships between viral abundance and soil properties were observed depending on the enumeration method. Thus, FCM is not currently recommended for enumeration of viruses in soil extracts. Based on EFM results, soil moisture and organic matter content were the most important factors determining viral abundance in soils.     

IBQS: A synthetic index of soil quality based on soil macro-invertebrate communities

We developed a synthetic index of biological soil quality (IBQS) based on soil macro-invertebrate community patterns to assess soil quality. In 22 sites representing the diversity of agroecosystems encountered in France, invertebrate communities co-varied significantly with a set of 14 parameters describing the physical and chemical properties of soil (co-inertia, p < 0.001; RV = 0.70). Using hierarchical classification, sites could be separated into four homogeneous groups and, using the ‘indicator value’ method, 46 indicator taxa characteristic of one or another of these groups were identified. We then used a formula that takes into account the abundance of indicator species and their respective indicator values to score soils from 1 to 20. IBQS was able to detect the effects of management practices on soil quality. Soil quality varied from 6 to 20 in forests, 7 to 9 in pastures and 2 to 9 in crops respectively. This suggests that well-managed crops and pastures may have better soil quality than some forests. Our results confirm that soil macro-invertebrates provide an integrative measure of soil quality and that the proposed index can be used either in short- or long-term monitoring, provided that it is calibrated and validated with respect to the regional context of the study.     

Nematode migration and nutrient diffusion between vetch and barley material in soil

This paper deals with migration of nematodes along nutrient gradients in soil. Portions of barley straw and green vetch leaves were mixed with soil and buried at 6, 12, 18, and 50 mm distance from each other in soil. During the following 12 weeks respiration activity, microbial (SIR) biomass, nitrogen limitation of respiration activity in soil slurries all indicated that nitrogen was transferred in the soil from the nutrient rich vetch to the nutrient poor barley at least during the first 3 weeks of the experiment. Twelve out of 39 taxonomic groups of nematodes showed different growth in the two plant material-soil mixtures. Only one of these taxonomic groups (long rhabditid larvae) suggested that migration could have contributed to population development; for three other groups (short rhabditid larvae, Aphelenchoides, and Bursilla) nutrient transport through the soil was the likely mechanism for a distance-dependant population development. We suggest that for most microbivorous nematodes, except larvae of fast growing bacterivores, migration over distances exceeding one centimetre does not contribute markedly to population development even when cues such as nutrient gradients to stimulate the activity exist.     

Bias in bacterial diversity as a result of Nycodenz extraction from bulk soil

Nycodenz density centrifugation (NDC) is an isolation method that allows extraction of both culturable and unculturable bacterial cells from soil, to be used in further downstream analysis; however, to date there has been a lack of information concerning the efficiency of this method. The aim of this study was therefore to investigate the overall efficiency of NDC extractions from soil and to identify sampling bias, if any.Bacterial cells were extracted from three soil plots from the Danish CRUCIAL field trial using an already established NDC protocol. To evaluate all aspects of the NDC procedure, DNA was extracted directly from soil, from NDC-extracted cells, and from the soil pellets left after NDC. Bacterial diversity was assessed by PCR amplification of the V4-V6 regions of the 16S rRNA from the extracted DNA followed by sample-tagged amplicon-pyrosequencing using the 454 Genome Sequencer FLX system. Sequences were processed and analyzed using the Ribosomal Database Project’s (RDP) Pyrosequencing Pipeline tools.In this study, we show that extraction of bacteria from soil using NDC can result in significant biases in the form of either over- or underrepresentation of specific bacterial phyla commonly found in soil. Furthermore, rarefaction analysis, analysis of similarity, multidimensional scaling plots and analysis of variance showed that the diversity in the NDC-extracted sample was reduced significantly compared to both the original soil sample and the remaining NDC-pellet. To further study the soil diversity a mathematical model was employed to estimate how many sequences would be required in order to find 95% of all operational taxonomic units (OTUs) in the soil. The model estimated that the soil contains approximately 29,400 OTUs and that just 351,500 sequences are needed to cover 95% of the bacterial biodiversity, the equivalent of one full standard GS FLX run.     

Decomposition of black locust and black pine leaf litter in two coeval forest stands on Mount Vesuvius and dynamics of organic components assessed through proximate analysis and NMR spectroscopy

Litter quality is an important determinant of soil organic matter formation. Changes of organic components were investigated along decomposition of black locust (Robinia pseudoacacia L.) leaf litter and black pine (Pinus nigra Arn.) needle litter in the native adjacent coeval forest stands. To this purpose, data from proximate analyses were compared with those from CPMAS ¹³C NMR. Newly shed leaf litter of black locust had significantly higher concentrations of ADSS (acid detergent soluble substances) as well as lower concentrations of cellulose and AUR (acid unhydrolyzable residues that include lignin) and higher AUR-to-Cellulose ratio than that of black pine. The ¹³C CPMAS NMR spectra of newly shed leaf litter of black locust and black pine revealed that O-Alkyl-C components (including cellulose and hemicelluloses) accounted, respectively, for 53.8% and 61.4% of the total area of the spectra. All other C fractions were relatively more abundant in black locust than in black pine. Within individual sampling periods, relationships between residual litter mass and concentrations of ADSS, cellulose and AUR were examined, as were relationships between residual litter C and NMR fractions. Four periods were defined based on the slopes of the decomposition curve, with the length of period I defined by the start of a net decrease of AUR. Proximate analyses and NMR data showed changes in chemical composition over the decomposition process, as well as changes in decay rates of the residues, following different paths in the two litters. ADSS decayed faster in black locust litter; in contrast cellulose and AUR decayed faster in that of black pine. AUR concentration increased in both litters during decomposition; however, compared to black pine, the remaining litter of black locust was richer in AUR, despite the lower initial concentration, and had a higher AUR-to-Cellulose ratio. Phenol-C and Aryl-C decayed faster in black locust litter, while Alkyl-C decayed faster in that of black pine. In both litters, mass loss in periods was negatively correlated to concentration of AUR at the start of the periods. C loss in periods was negatively correlated to the concentration at the start of the periods of MC-to-PC (an index of lignin content) in black locust litter and positively correlated to Alkyl-C and O-Alkyl-C in that of black pine. Phenol-C, O-Alkyl-C and Aryl-C were the most decomposable C fractions in black locust. O-Alkyl-C and Alkyl-C were the most decomposable C fractions in black pine. Limit value was lower in black pine than in black locust. Consequently the different pattern of litter decomposition can affect the size of C sequestration in the forest floor and the quality of accumulated organic carbon.     

Influence of local illumination and plant composition on the spatial and seasonal distribution of litter-dwelling arthropods in a tropical rainforest

Using pitfall traps, we evaluated the spatial and seasonal variance in arthropod abundance, species richness, higher taxonomic and species composition, and guild structure within the ground litter of seven sites in a relatively undisturbed rainforest in Panama. We examined each of these five arthropod-dependent variables at two spatial scales (a few meters and a few hundred meters) and one temporal scale (a few months encompassing dry and wet periods), against environmental variables including local illumination and plant composition. Trap catches (9458 arthropods collected during 630 trap-days) were high compared to similar studies in temperate forests. We observed spatial and seasonal differences in abundance, species richness and composition of litter-dwelling arthropods. Often these differences appeared weakly related to geographical coordinates. They reflected forest structure (basal area) and local plant composition, and less so illumination patterns or seasonal changes in radiation. Seasonal variance was high and may relate to surrogate variables accounting for seasonal changes in litter moisture. The composition of higher taxa and species was often predicted by different independent variables at the three scales studied. Guild structure was difficult to predict. Our study lead us to expect that litter-dwelling arthropods may be more seasonal than soil microarthropods in tropical rainforests; and that tropical litter-dwelling arthropods may also be more spatially variable and seasonal than their temperate counterparts. We also recommend that conservation studies using pitfall traps in tropical rainforests should focus on: (1) taxonomic resolution to understand the functional complexity of soil organisms; (2) spatial replication to address subtle changes in plant composition throughout the study area; and (3) seasonal replicates to be commensurate with seasonal changes in litter moisture.     

Net mineralization of nitrogen in leaves and leaf litter of Desmodium intortum and Phaseolus atropurpureus mixed with soil

Leaves and leaf litter of Desmodium intortum cv. Greenleaf and Phaseolus atropurpureus cv. Siratro were incubated with soil at 24°C for periods up to 32 weeks. Nitrogen mineralization with D. intortum was less than with P. atropurpureus for both leaves and leaf litter. The differences in net nitrogen mineralization during 32 weeks incubation between soil with plant material and soil alone, expressed as percentages of the nitrogen in the added leaf materials, were + 3 % and + 46 % for leaves and ?10 % and + 5 % for leaf litter of D. intortum and P. atropurpureus respectively. There was no difference in nitrogen mineralization between soils collected from below the litter layer under the two legumes. The leaf materials from the two species contained similar concentrations of nitrogen and lignin, but the concentration of polyphenols in D. intortum was twice that in P. atropurpureus. The significance of this difference in polyphenol concentration in relation to mineralization of leaf nitrogen is discussed.     

Myriapod and isopod communities in soils contaminated by heavy metals in northern France

Soil invertebrates suffer from contamination of the soil by heavy metals. We have studied the effects of contamination by cadmium, zinc and lead on their communities in soils in northern France by comparing polluted land with non‐contaminated sites. We have followed the seasonal variations and effects of soil properties. Saprophagous invertebrates (Diplopoda, Isopoda) and Chilopoda were sampled by pitfall‐trapping from February to November in fairly contaminated areas. In addition, a Berlese extraction of the litter in two very highly contaminated sites was conducted during autumn; animals were also trapped during June in the same locations. The most active period for myriapods was spring (April and May), whereas isopods were abundant from April to the end of summer. No clear relation was found relating dominant species or number of myriapods or isopods to concentration of heavy metal in the little‐contaminated soils. The dominant species seemed not to be related to pollution but to vegetation or soil characteristics. In the most contaminated sites, with metalliferous grassland and a thick undecomposed litter layer, a threshold in contamination values seemed to be reached: no isopods or millipedes were found, but only Chilopoda and Symphyla.     

The body-size distribution of arboreal collembolans in relation to the vertical structure of a Japanese cedar plantation

Collembolans are among the most abundant microarthropods in the aboveground parts of forest ecosystems, but little is known about their life-history traits compared with those of the soil-dwelling collembolans. The life-history traits of arboreal collembolans, as well as their abundances, are expected to be influenced by the vertical structure of a forest. We analyzed the body-size distributions of dominant arboreal species in relation to the vertical structure of the forest. The small individuals of the three arboreal species that inhabit both the canopy and soil litter (Xenylla brevispina, Tomocerus cuspidatus, and Sphyrotheca multifasciata) appeared continuously from spring to autumn in the soil litter, whereas those in the canopy litter were found during a particular period, only in July. These individuals tended to be larger in the canopy litter than in the soil litter, and in particular, T. cuspidatus grew to become significantly larger in the canopy. The mean body size of the most abundant migrating species (X. brevispina) increased gradually from the soil to the upper canopy, whereas strict arboreal species (Entomobrya sp.) had no significant trend in the relationship between body size and the height above ground level. We concluded that the life-history traits of arboreal collembolans were influenced by the vertical structure of the forest.     

Changes in soil properties and their effects on maize productivity following<Emphasis Type="Italic"> Sesbania sesban</Emphasis> and<Emphasis Type="Italic"> Cajanus cajan</Emphasis> improved fallow systems in eastern Zambia

Improved fallows with leguminous trees have been developed in Southern Africa as a viable alternative to inorganic fertilizers but the changes in soil properties that are responsible for crop productivity improvement and implications of mixing litter and fresh leaves from the same tree species on soil fertility are not fully understood. Our objectives were to quantify (1) some changes in soil properties that are responsible for crop production improvement under improved fallow systems; (2) the N mineralization patterns of mixtures of litter and fresh leaves from the same tree species. The treatments used in the study were 2-year planted Sesbania sesban (sesbania) and Cajanus cajan (cajanus) and controls of natural fallow, continuous fertilized and unfertilized maize. At fallow clearing sesbania contributed 56 kg N ha^–1 through litter and fresh leaves. Sesbania (fresh leaves + litter) showed high N mineralization after 10 weeks compared to the mixture of cajanus fresh leaves with litter. Maize yields were significantly correlated with preseason NO₃^–-N and total inorganic-N content of the top 20-cm soil layer. Soil penetrometer resistance at 4 weeks after planting was lowest in the sesbania land-use system (2.2 Mpa), whereas the highest percentage of water-stable aggregates at fallow clearing and crop harvest was in sesbania (83%) and cajanus (77%), respectively. The improved soil conditions and N contribution of sesbania and cajanus fallows to the subsequent maize crop was evidenced by increased maize yields of between 170–200% over maize without fertilizer.