Degraded Soil Conditions Research Articles

Effects of Vermicast and Arbuscular Mycorrhizal Fungi (AMF) on the Establishment of Cacao (Theobroma cacao Linn.) Seedlings Grown in Degraded Soil

Declining soil fertility poses a significant challenge for cacao production, particularly for establishing seedlings. This study investigated the potential effects of vermicast and arbuscular mycorrhizal fungi (AMF) to enhance cacao seedling establishment in degraded soil conditions. The study was conducted in a low-cost protective structure established at the Abaca Project Experimental Area of the University of Southeastern Philippines, Mampising, Mabini, Davao de Oro, from December 2018 to April 2019. Furthermore, a Completely Randomized Design (CRD) was employed with eight (8) treatments and three (3) replications with eight (8) sample plants per replicate. The following are the treatment combinations: No Application (T1), Recommended Rate (T2), Vermicast (T3), AMF (T4), Vermicast + AMF (T5), Recommended Rate + AMF (T6), Recommended Rate + Vermicast (T7), and Recommended Rate + AMF + Vermicast (T8). The results of the study reveal that the application of vermicast and AMF combined with inorganic fertilizer based on the recommended rate increased the growth and development of cacao seedlings in degraded soil in terms of plant height (16.40%), length of leaves (14.59%), the width of leaves (12.11%), number of leaves (1.26%), leaf color (41%), stem diameter, shoot weight (60%), dry matter yield (116%) and root:shoot ratio (63.16%) compared to control or no application. Thus, the judicious use of inorganic fertilizer, vermicast, and AMF improves the establishment of cacao seedlings in soils with degraded conditions.

Soil surface treatments and precipitation timing determine seedling development across southwestern US restoration sites.

Restoration in dryland ecosystems often has poor success due to low and variable water availability, degraded soil conditions, and slow plant community recovery rates. Restoration treatments can mitigate these constraints but, because treatments and subsequent monitoring are typically limited in space and time, our understanding of their applicability across broader environmental gradients remains limited. To address this limitation, we implemented and monitored a standardized set of seeding and soil surface treatments (pits, mulch, and ConMod artificial nurse plants) designed to enhance soil moisture and seedling establishment across RestoreNet, a growing network of 21 diverse dryland restoration sites in the southwestern USA over 3 years. Generally, we found that the timing of precipitation relative to seeding and the use of soil surface treatments were more important in determining seeded species emergence, survival, and growth than site-specific characteristics. Using soil surface treatments in tandem with seeding promoted up to 3× greater seedling emergence densities compared with seeding alone. The positive effect of soil surface treatments became more prominent with increased cumulative precipitation since seeding. The seed mix type with species currently found within or near a site and adapted to the historical climate promoted greater seedling emergence densities compared with the seed mix type with species from warmer, drier conditions expected to perform well under climate change. Seed mix and soil surface treatments had a diminishing effect as plants developed beyond the first season of establishment. However, we found strong effects of the initial period seeded and of the precipitation leading up to each monitoring date on seedling survival over time, especially for annual and perennial forbs. The presence of exotic species exerted a negative influence on seedling survival and growth, but not initial emergence. Our findings suggest that seeded species recruitment across drylands can generally be promoted, regardless of location, by (1) incorporation of soil surface treatments, (2) employment of near-term seasonal climate forecasts, (3) suppression of exotic species, and (4) seeding at multiple times. Taken together, these results point to a multifaceted approach to ameliorate harsh environmental conditions for improved seeding success in drylands, both now and under expected aridification.

Impacts of extension dissemination and technology adoption on farmers' efficiency and welfare in Ghana: Evidence from legume inoculant technology

Examining the welfare impact of agricultural development interventions that incorporate diffusion of improved production technologies to farmers within extension delivery programs can be very challenging, because of the difficulty in disentangling the individual impacts of the production technology and the extension delivery program. Using recent farm level survey data from extension dissemination program of legume inoculant technology of 600 farmers in Ghana, we employ a recent methodological approach to investigate, simultaneously, the impact of the inoculant technology adoption and the extension program participation on farmers' productivity, efficiency and welfare. We decompose each of these impact measures into subcomponents whose causal paths can be traced to both the adoption of the production technology and the extension delivery program. We find that, in terms of yields and net revenue, direct contribution of improved technology adoption alone is 34 and 64%, respectively, and 35 and 66% indirectly due to improved farmer efficiency, leading to 36 and 74% improvement in farmers' welfare, respectively. On the other hand, direct contribution of extension delivery program participation alone is 66 and 36%, respectively, with 66 and 34% indirectly due to improved farmer efficiency, resulting in 64 and 26% improvement in farmers' welfare, respectively. Based on the findings, we recommend that policymakers should invest in research and development to produce yield enhancing agricultural technologies suitable for poor and degraded soil conditions in developing countries which can contribute immensely to poverty and food insecurity reduction. The development of new agricultural technologies must be pursued with vigorous provision of extension services to farmers to be able to exploit the full potentials of the new technologies.

Effects of growth promoting microorganisms on tomato seedlings growing in different media conditions.

Plant growth-promoting microbes (PGPM) play vital roles in maintaining crop fitness and soil health in stressed environments. Research have included analysis-based cultivation of soil-microbial-plant relationships to clarify microbiota potential. The goal of the research was to (i) evaluate the symbiotic microorganism effects on tomato seedling fitness under stressed conditions simulating a fragile soil susceptible to degradation; (ii) compare the plant-microbial interactions after inoculation with microbial isolates and fungi-bacteria consortia; (iii) develop an effective crop-microbial network, which improves soil and plant status. The experimental design included non-inoculated treatments with peat and sand at ratios of 50:50, 70:30, 100:0 (v:v), inoculated treatments with arbuscular mycorrhizal fungi (AMF) and Azospirillum brasilense (AZ) using the aforementioned peat:sand ratios; and treatment with peat co-inoculated with AMF and Saccharothrix tamanrassetensis (S). AMF + AZ increased root fresh weight in peat substrate compared to the control (4.4 to 3.3 g plant-1). An increase in shoot fresh weight was detected in the AMF + AZ treatment with a 50:50 peat:sand ratio (10.1 to 8.5 g plant-1). AMF + AZ reduced antioxidant activity (DPPH) (18-34%) in leaves, whereas AMF + S had the highest DPPH in leaves and roots (45%). Total leaf phenolic content was higher in control with a decreased proportion of peat. Peroxidase activity was enhanced in AMF + AZ and AMF + S treatments, except for AMF + AZ in peat. Microscopic root assays revealed the ability of AMF to establish strong fungal-tomato symbiosis; the colonization rate was 78-89%. AMF + AZ accelerated K and Mg accumulation in tomato leaves in treatments reflecting soil stress. To date, there has been no relevant information regarding the successful AMF and Saccharothrix co-inoculation relationship. This study confirmed that AMF + S could increase the P, S, and Fe status of seedlings under high organic C content conditions. The improved tomato growth and nutrient acquisition demonstrated the potential of PGPM colonization under degraded soil conditions.

Independent effects of warming and altered precipitation pattern on nematode community structure in an arable field

Global environmental change is causing increases in soil temperatures and alternations in precipitation patterns, which are affecting soil biota in natural and managed systems. Arable soils, generally disturbed due to management practice, are particularly sensitive to a changing environment. However, little is known how warming interacts with precipitation pattern to affect soil fauna and thereby ecosystem functions. In an arable system, we investigated the interactions of soil warming and altered precipitation amount and frequency on soil conditions and health using nematodes as bioindicators. Our findings showed that the nematode population density was significantly increased by warming and decreased by reduced precipitation frequency. Warming mainly fostered the density of fungal feeders and obligatory plant parasites, with the latter suggesting higher crop damage. Root-associated plant feeders were further affected by changes in precipitation pattern; their density declined with reduced precipitation frequency and increased with the alternated precipitation amount. The nematode abundance was generally low in the arable ecosystem and remained stable under the simulated environmental change. In response to warming, the major soil decomposition channel via bacteria was reduced, and the fungal mediated pathway fostered, implying more fungal dominated depleted and degraded soil conditions. Soil decomposition pathways were not affected by altered precipitation pattern, neither by amount nor by frequency. Overall, warming and precipitation independently altered the soil nematode fauna and the functioning of belowground food webs. Therefore, our study highlights the need for more research considering the interactions of environmental variables to see if this lack is a general pattern and to develop strategies for agroecosystem's management under climate change.

Legacy effects of sika deer overpopulation on ground vegetation and soil physical properties

Long-lasting overpopulation of deer can prevent or retard the recovery of ground vegetation of forests even after overpopulation would have abated. This persistent impact, or legacy effect of deer, would be explained by hypothetical mechanisms such as limitation of seed sources, dominance of competitors that are unpalatable to deer, and negative feedback from soil conditions degraded by direct and indirect effects of deer. So far, however, little evidence is available for existence of such legacy effects. To detect the legacy effects caused by sika deer (Cervus nippon) and reveal their possible mechanisms, we studied ground vegetation and soil condition of Japanese natural broad-leaved forests and cedar plantations, which have records of vegetation surveys of the past 11 years. Foliar cover and species composition of ground vegetation were analyzed together with the deer density index (DDI), which represents mean deer density of the last 9 years before the survey. The relationship between vegetation cover and deer density had significantly changed between the survey years, as was proved by a regression analysis. The cover of ground vegetation did not increase during the 11 surveyed years even at most study sites whose DDI value had decreased, thereby indicating the existence of legacy effects. This delay of recovery was not attributable to the dominance of unpalatable plants, which had slightly decreased during the 11 surveyed years. Palatable plants did not increase in most study sites where DDI decreased, suggesting seed source limitation. Negative indirect effects of DDI on soil physical property in the present, such as increased bulk density and decreased coarse porosity, were detected through structural equation modeling (SEM) analysis. In the case of broad-leaved forests, the SEM model that included the 2005 DDI values showed better performance than that using present DDI values, indicating a strong legacy of past deer impact. These facts suggest the existence of legacy effects, which possibly have been caused by seed source limitation and degraded soil conditions. Moreover, above statistical analyses showed that canopy closure, which can be caused by delayed management practices (e.g., gap creation and thinning), further limited recovery of vegetation. Ground vegetation of broad-leaved forests were suggested to show lower resilience than those of cedar plantations, requiring conservation activities such as canopy gap creation.

Multi-scale analysis of relationship between imperviousness and urban tree height using airborne remote sensing

The relationship between impervious land cover and tree development is an important component to understanding urban ecological systems. While impervious surfaces are associated with degraded soil conditions, rerouted hydrological networks and urban microclimates, the overall impact of these effects on tree development is highly variable. This study examines this relationship at two spatial scales: within the individual tree's local environment and across the broad-scale urban landscape. Using a fusion of airborne hyperspectral imagery and light detection and ranging (LiDAR) data, a 1.0m spatial resolution classified land cover map (accuracy of 88.6%) was produced for the city of Surrey, British Columbia, Canada, from which landscape imperviousness was then derived. The stem heights of 1914 trees were estimated from the LiDAR data, to which species-specific height models were fit using planting dates recorded by city authorities. Having accounted for the age of the trees, the residuals from these models (i.e.: the difference between modelled and measured height) were then used as indicators of tree development. When aggregated to 0.5km2 spatial units, negative relationships (r2 between 0.292 and 0.753) were found between height model residuals and the degree of land cover imperviousness. These relationships did not persist when examined at the individual tree level, for which imperviousness was measured within the direct vicinity of each tree using the same imperviousness map. We conclude that, using this approach, imperviousness does not appear to be a significant driver of tree height variation, with broad-scale relationships likely due to correlations with other environmental variables associated with the urban-rural gradient. Despite some limitations, the integration of hyperspectral and LiDAR data proved to be a powerful tool for mapping imperviousness, with LiDAR metrics being particularly important for distinguishing between types of urban land cover.

Especies forestales para la recuperación de suelos contaminados con cobre debido a actividades mineras

La minería es la actividad económica más importante de Chile, la cual causa degradación significativa en las regiones áridas. Los suelos de la Región de Coquimbo han sufrido contaminación de metales pesados provenientes de la minería, particularmente cobre. La implementación de medidas de mitigación, que ayuden a minimizar el impacto ambiental de los relaves mineros, requiere conocer la capacidad de adaptación de especies vegetativas ante la degradación de suelos contaminados. El objetivo de este estudio fue determinar y comparar la capacidad de fitoestabilización de especies vegetales nativas y exóticas en áreas degradadas por la actividad minera en la Región de Coquimbo. Las tasas de supervivencia, crecimiento y desarrollo del dosel de 20 especies fueron evaluadas en dos ensayos experimentales. La concentración de Cu se evaluó en tallos y hojas de los árboles y en diferentes profundidades del suelo. Los resultados indicaron que Acacia saligna tiene la mejor capacidad de acumulación de metales pesados (34.8 ppm en hojas y 12.3 ppm en tallos, ambos en suelos sin fertilización), con tasas de supervivencia de más de 80 %. En este estudio se concluye que A. saligna es la mejor especie

Land-use history alters contemporary insect herbivore community composition and decouples plant-herbivore relationships.

Past land use can create altered soil conditions and plant communities that persist for decades, although the effects of these altered conditions on consumers are rarely investigated. Using a large-scale field study at 36 sites in longleaf pine (Pinus palustris) woodlands, we examined whether historic agricultural land use leads to differences in the abundance and community composition of insect herbivores (grasshoppers, families Acrididae and Tettigoniidae). We measured the cover of six plant functional groups and several environmental variables to determine whether historic agricultural land use affects the relationships between plant cover or environmental conditions and grasshopper assemblages. Land-use history had taxa-specific effects and interacted with herbaceous plant cover to alter grasshopper abundances, leading to significant changes in community composition. Abundance of most grasshopper taxa increased with herbaceous cover in woodlands with no history of agriculture, but there was no relationship in post-agricultural woodlands. We also found that grasshopper abundance was negatively correlated with leaf litter cover. Soil hardness was greater in post-agricultural sites (i.e. more compacted) and was associated with grasshopper community composition. Both herbaceous cover and leaf litter cover are influenced by fire frequency, suggesting a potential indirect role of fire on grasshopper assemblages. Our results demonstrate that historic land use may create persistent differences in the composition of grasshopper assemblages, while contemporary disturbances (e.g. prescribed fire) may be important for determining the abundance of grasshoppers, largely through the effect of fire on plants and leaf litter. Therefore, our results suggest that changes in the contemporary management regimes (e.g. increasing prescribed fire) may not be sufficient to shift the structure of grasshopper communities in post-agricultural sites towards communities in non-agricultural habitats. Rather, repairing degraded soil conditions and restoring plant communities are likely necessary for restoring grasshopper assemblages in post-agricultural woodlands.

The Nature of Urban Soils and Their Role in Ecological Restoration in Cities

AbstractCurrent and predicted trends indicate that an increasing proportion of the world’s population is living in urban and suburban places. The nature of the urban environment becomes an important factor if we are concerned with the restoration and preservation of biodiversity and ecosystems in and around cities. This article highlights the varied impacts of cities on soils and their implications for restoration planning and expectations of restoration “success.” Urban soils exist in different historical and formational trajectories than their local nonurbanized counterparts due to direct anthropogenic disturbance and indirect environmental impacts from urbanization. Therefore, urban soils often exhibit altered physical, chemical, and biological characteristics in comparison to local nonurbanized soils. Several unique features of urban soils and urban ecosystems pose particular issues for ecological restoration or the improvement of degraded soil conditions in cities. The creation of novel soil types, conditions that promote invasion by non‐natives, the strong influence of past land use on soil properties, and the presence of strong interactions and alternative stable states set up unique difficulties for the restoration of urban soils. Soils in urban restorations are a medium that can be deliberately manipulated to improve site conditions or in the monitoring of soil conditions as indices of ecosystem status. Including an explicit role for strong manipulations of soils in urban ecosystems changes how we approach baselines, management, and reference conditions in urban ecological restoration. With an understanding of urban soil ecological knowledge, we can guide aspects of urban ecological restoration toward successful outcomes.

Sustainability of Agricultural Production in Communal Areas of Zimbabwe: Case of Chionekano Communal Lands

In Sub-Saharan Africa, at least 70% of the population lives in rural communal areas where they make a living out of subsistence farming. The sector continues to seek for donor support to improve their farming activities with little attention being paid to viability and sustainability of their production systems. There is also sketchy location- specific empirical evidence from research showing sustainability of communal farming practices. The broad objective of this study was therefore to evaluate the sustainability of agricultural production in communally owned farming areas. Agricultural sustainability was conceptualized in terms of biological productivity, economic viability, and reduction of production risk, environmental protection and social acceptability. Primary and secondary data were collected using a structured questionnaire. Information on socio-economic characteristics, production patterns and their environmental implications, constraints and opportunities for achieving sustainability were elicited from respondents. A total of 498 households were interviewed through a census. Respondents were drawn from a cross-section of the community made up of male, female, and childheaded households from Chionekano communal farming area in Zimbabwe. The area is characterized by average annual rainfall of 600 mm, temperature range of 15-25 0 C, sparse vegetation cover and soils of less than 1% organic matter. The results revealed that the agricultural production system was below par due to degraded soil conditions which resulted in low crop yields, low returns from the livestock sector due to high incidences of stock thefts and deteriorating veld condition. Access to financial support was limited due to lack of collateral and high production risk where farmers’ production is solely based on natural and unreliable rainfall patterns and therefore unsustainable. Strategies to improve food security should receive priority to support sustainable resource management, increase access to finance and suitable inputs on credit to be worked out and soil fertility conservation to be exercised with particular focus on organic farming. Emphasis should be placed on environmental management training, production monitoring and offer financial support schemes at concessionary interest rates to spruce up their production to breakeven levels.

Early Dynamics of Plant Communities on Revegetated Motorway Slopes from Southern Spain: Is Hydroseeding Always Needed?

Abstract The increasing global rate of road construction is leading to a parallel increase of areas of degraded soil conditions and steep slopes that need revegetation. Hydroseeding with commercial seeds of fast‐growing grasses and legumes is a common practice in revegetation of motorway slopes. We carried out 3 years of monitoring of vegetation dynamics on hydroseeded and nonhydroseeded motorway slopes (48 slopes) in a maritime Mediterranean zone in Málaga (southern Spain). Our main objectives were to test whether hydroseeding significantly increases species richness and plant cover and whether hydroseeded species act as starters, facilitating the establishment of the vegetation and quickly disappearing once the communities are established. A hydroseeding success index (HSI, ranging from 0 to 1) was used to assess the relative abundance over time of the 14 species from the hydroseeding mixture. Species richness and cover was significantly higher on embankments (50–70 species per embankment, 80–90% cover) than on roadcuts (6–10 species per roadcut, 18–30% cover). Performance of hydroseeded species was poor from the very beginning (HSI, 0.2–0.3). On embankments, either presence or abundance of hydroseeded species did not significantly vary throughout the study. Both hydroseeded and nonhydroseeded communities exhibited a significant decrease in species richness, a significant increase in plant cover, and a highly dynamic species composition over time, with Sorensen index of 0.3–0.5 between years. There were no significant differences in plant cover, species richness, and aboveground biomass between hydroseeded and nonhydroseeded plots on embankments throughout the study. Our results demonstrate that there are situations in which the use of hydroseeding for revegetation is not needed. Further research should focus on understanding the establishment of autochthonous species and identifying environmental conditions under which the addition of commercial seeds may not be needed, or indeed situations where it may be harmful in suppressing autochthonous species.

Survival and growth of the forage grass Festuca rubra in naturally and artificially devegetated sites in a sub-arctic coastal marsh

:Festuca rubra is an abundant supratidal grass on sub-arctic James Bay (Canada) shorelines, forming extensive near-monocultures that are used as forage by nesting and migrating geese. Studies at other, more northern North American locations have shown grubbing by geese can have severe consequences for intertidal and supratidal marshes, but these studies have focussed on plant communities that differ substantially in species composition, physical environment, and extent from James Bay’s Festuca meadows. In this study, we examined the responses of this grass to natural and simulated goose grubbing in Festuca swards heavily used by lesser snow geese, Canada geese, and brant at Akimiski Island in James Bay. We transplanted Festuca into plots previously devegetated by geese, into plots where we removed vegetation to simulate goose grubbing, and into intact vegetation (controls). We found shoots transplanted into control and artificially grubbed plots survived well, but those transplanted into previously devegetated areas usually died. Growth initially was reduced in naturally devegetated sites, but the few survivors in the following year performed as well as plants transplanted into intact or artificially grubbed sites. Spot measurements suggested that naturally devegetated sites suffered from degraded soil conditions, such as hypersalinity and increased temperature. These results provide evidence that recovery of Festuca swards following loss of vegetation is likely to be difficult, probably as a result of deteriorating soil conditions. Models of goose–plant interactions developed at substantially more northern sites thus seem applicable to the significantly different plant communities of the James Bay shoreline.

Natural [formula omitted] abundance in soils under young-growth forests in Ethiopia

In Ethiopia, plantation forestry for the purpose of soil conservation and wood production is established mainly on degraded mountain slopes. These forests with a rotation age of 12–34 years consist of mainly exotic tree species; and have great potential to provide maximum wood production and economic incentives at the age of 8–20 years. 15 N natural abundance in soils under a 25-year-old forest on Mt. Yegof has been used to determine if the short rotation forests result in significant inputs of N to soils and improve the degraded soils before harvest at the rotation age of 12–34 years. Since I have previously described the fractional contributions of the present forest vegetation to the build-up of soil organic matter (SOM) on Mt. Yegof, patterns of δ 15 N and δ 13 C values were compared to determine if shifts in soil 15 N are related to vegetation shifts by afforestation. On Mt. Yegof, soil δ 15 N values were 0.9–3.9‰ in soil at 0–5 cm and >6‰ in soil at 30–50 cm. Plant δ 15 N values ranged from −4.6 to −0.7‰. Despite the negative δ 15 N values of the vegetation cover, the high δ 15 N values in the topsoil indicate that return of N to soils by litter-fall is minimal on Mt. Yegof and, hence, the present forests do not change very much the soil 15 N signals at the surface layer. At this site, the high δ 13 C values throughout the soil profiles is clear evidence of a long phase of C 4 grass dominance or cultivation of C 4 crops along the entire elevation gradient. The slight shift towards lower δ 15 N values in soil at 0–5 cm indicate only a trend of 15 N depleted SOM build-up through litter-fall from the present forest vegetation. This and previous studies show that the planted forests on Mt. Yegof did not result in significant changes in the inputs of C, N and SOM, and hence, cannot signify the improvement of degraded soil conditions during a 25-year forest growth. Thus, these forests made need a rotation period much longer than 25-year period to signify ecological rehabilitation and to establish a sustainable forest ecosystem with less N losses on the fairly steep slopes at Mt. Yegof. From the points of view of soil conservation and soil fertility management, it could be suggested that forest harvest at the time of maximum wood production may not necessary be considered if ecologically sustainable forests are to be managed on highly degraded mountain slopes in the Ethiopian highlands.

Restorative crops for the amelioration of degraded soil conditions in New Zealand

The effects of restorative crops on the amelioration of a degraded soil were investigated in a 6-year field experiment. Treatments included perennial pastures, annual pastures, and arable crops. Improvements in some aspects of chemical, biological, and physical fertility were related to the amount of herbage dry matter returned to the soil and root production. Beneficial effects associated with returned organic matter were partly negated by the degradative effect of tillage. Treatments that returned most organic material to the soil showed the greatest increase in aggregate stability and supported the largest earthworm populations, especially without annual tillage. Differences between treatments in soil organic C content were not generally significant until the sixth year. In contrast, differences between treatments in microbial biomass C were apparent by the third year. Compaction by sheep during grazing appeared to result in a loss of soil macroporosity. In the sixth year, soil macroporosity was greatest in the annually cultivated, ungrazed treatments. The grazed perennial ryegrass and ryegrass/white clover treatments were the most effective in ameliorating degraded soil conditions. The rate of soil amelioration declined with depth, and was mainly confined to the top 10 cm of soil. The rate of amelioration was relatively slow, with, for example, 3 years needed for most of the increase in aggregate stability at 0–5 cm depth.

Soil physical conditions and root growth in coconut plantations interplanted with nitrogen fixing trees in Sri Lanka

The study was carried out to investigate the possibility of improving degraded soil conditions of Andigama series by intercropping coconut (Cocos nucifera L.) with Calliandra calothyrsus, Leucaena leucocephala, Acacia auriculiformis and Gliricidia sepium. Bulk density was significantly low in NFT interplanted plots followed by improved aeration in AB and B horizons of the soil profile. Total and readily available water fraction was higher in AB and B horizons of calliandra, acacia and gliricidia interplanted plots over control plots due to the increase of organic matter content and root growth. Root growth and proliferation of calliandra in A horizon were predominantly higher than that of leucaena, acacia and gliricidia species. In contrast, gliricidia roots penetrated into B horizon more densely than roots of other species. Better root growth of coconut in A horizon was observed in acacia and calliandra plots than other plots. The total coconut root biomass in AB and B horizons was higher in gliricidia and acacia plots than other species, which accounted for 91% and 0.3% in AB horizon and 21% and 23% in B horizon for gliricidia and acacia, respectively compared to the control. Total root biomass of coconut in calliandra plots was reduced by 5%, and 45% in AB and B horizons respectively. Results indicated that soil physical conditions of Andigama series (gravelly soil) could be significantly improved by interplanting acacia and gliricidia, as indicated by enhanced coconut root growth and proliferation.