Microbial community diversity in a 21-year-old temperate alley cropping system

Soil physical and chemical properties in the crop alleys and tree rows in alley cropping systems vary greatly due to differences in litter quality and microclimate under trees compared to the alleys. Variations in soil properties influence microbial diversity and function, and thus, in alley cropping systems, bacterial diversity could be different between soils in tree rows and crop alleys. The objective of this study was to compare and contrast soil bacterial diversity in the crop alleys and tree rows in a 21-year-old alley cropping system in Northeast Missouri, USA. Soil samples were taken in three parallel transects to a depth of 10 cm in the tree row and at the middle of the alley in a silver maple (Acer saccharinum) alley cropping system with a companion maize (Zea mays)—soybean (Glycine max) rotation. Soil bulk density, C and N concentrations were similar between the different transects while minor differences were observed between crop alleys and tree rows. No significant difference in bacterial diversity was observed between the tree rows and alley soil based the denaturing gradient gel electrophoresis profiles, band richness (19.6 and 22.8 for tree row and alley, respectively) and Shannon–Weiner diversity (2.958 and 3.099 for tree row and alley, respectively). Identification of bacterial genera revealed dominance of gram +ve as well as gram ?ve bacteria in both soil types. Ordination plot revealed no clustering effect based on location (transect) or on the cropping system in the different samples. Bacterial diversity in crop alleys most likely was influenced not only by the maize-soybean rotation, but also by the tree rows contributing both above and belowground litter for the past 21 years.     

Effect of multipurpose tree species on soil fertility and CO2 efflux under hilly ecosystems of Northeast India

A 26 years old agroforestry plantation consisting of four multipurpose tree species (MPTs) (Michelia oblonga Wall, Parkia roxburghii G. Don, Alnus nepalensis D. Don, and Pinus kesiya Royle ex-Gordon) maintained at ICAR Research Complex, Umiam, Meghalaya, India were compared with a control plot (without tree plantation) for soil fertility status and CO₂ efflux. The presence of trees improved all the physico-chemical and microbial biomass parameters studied in this experiment. Relative to control, soils under MPTs showed significant increases of 17 % soil organic carbon, 26 % available nitrogen (AN), 28 % phosphorus (AP), 50 % potassium (AK), 65 % mean weight diameter (MWD) of aggregates, 21 % moisture and 34 % soil microbial biomass carbon (MBC) while reducing the mean bulk density (7 %). However, these parameters significantly differed among the tree species i.e., soils under A. nepalensis and M. oblonga had higher values of these attributes except bulk density, than under other species. Irrespective of treatments, the values of all these attributes were higher in surface soils while bulk density was highest in subsurface (60–75 cm). Cumulative CO₂ efflux under MPTs was significantly higher (15 %) and ranged from 1.71 g 100 g^?1 (M. oblonga) to 2.01 g 100 g^?1 (A. nepalensis) compared to control at 150 days of incubation. In all the treatments, increment in temperature increased the oxidation of soil organic matter, thereby increased the cumulative CO₂ efflux from soils. Of the tree species, with increment in temperature, A. nepalensis recorded more CO₂ efflux (2.50 g 100 g^?1) than other MPTs but the per cent increase was more in control plot. P. kesiya and A. nepalensis recorded highest activation energy (59.1 and 39 kJ mol^?1, respectively). Net organic carbon sequestered in soil was highest under A. nepalensis (25.7 g kg^?1) followed by M. oblonga (19.3 g kg^?1), whereas control showed the lowest values. Amount of net carbon stored in the soil had significant and positive correlation with MBC (r = 0.706**), MWD (r = 0.636*), and AN (r = 0.825**).     

Earthworm population and microbial activity temporal dynamics in a Caspian Hyrcanian mixed forest

Few studies have analyzed how tree species within a mixed natural forest affect the dynamics of soil chemical properties and soil biological activity. This study examines seasonal changes in earthworm populations and microbial respiration under several forest species (Carpinus betulus, Ulmus minor, Pterocarya fraxinifolia, Alnus glutinosa, Populus caspica and Quercus castaneifolia) in a temperate mixed forest situated in northern Iran. Soil samplings were taken under six individual tree species (n = 5) in April, June, August and October (a total of 30 trees each month) to examine seasonal variability in soil chemical properties and soil biological activity. Earthworm density/biomass varied seasonally but not significantly between tree species. Maximum values were found in spring (10.04 m^?2/16.06 mg m^?2) and autumn (9.7 m^?2/16.98 mg m^?2) and minimum in the summer (0.43 m^?2/1.26 mg m^?2). Soil microbial respiration did not differ between tree species and showed similar temporal trends in all soils under different tree species. In contrast to earthworm activity, maximum microbial activity was measured in summer (0.44 mg CO₂–C g soil^?1 day^?1) and minimum in winter (0.24 mg CO₂–C g soil^?1 day^?1). This study shows that although tree species affected soil chemical properties (pH, organic C, total N content of mineral soils), earthworm density/biomass and microbial respiration are not affected by tree species but are controlled by tree activity and climate with strong seasonal dynamics in this temperate forest.     

Effects of soil type and water saturation on growth,nutrient and mineral content of the perennial forage shrub S<Emphasis Type="Italic">esbania sesban</Emphasis>

Sesbania sesban (L.) Merr is a perennial N₂-fixing tree with high potential for use in agricultural production systems as a green manure and livestock forage. We studied the interactive effects of soil type and water level on the growth, biomass allocation, nutrient and mineral content of S. sesban. Four-week old seedlings of S. sesban were grown for 49 days (n = 5) in a factorial mesocosm set-up with six soil types (sediment, sand, alluvial, acid-sulfate, saline and clay) and three water levels (drained, water-saturated and flooded). The soils tested represent the predominant alluvial soil types of the Mekong delta, Vietnam. Sesbania sesban grew well with relative growth rates (RGR) around 0.08 g g^?1 d^?1 in all studied soil types, except the saline soil where plants died. In the low-pH (3.9) acid sulfate soil, that constitute more than 40 % of the Mekong delta, the RGR of the plants was slightly lower (0.07 g g^?1 d^?1), foliar concentration of calcium was 3–6 times lower, and concentrations of iron and sodium up to five times higher, than in other soils. The nutrient and mineral contents of the plant tissues differed between the soils and were also affected by the flooding levels. Foliar concentrations of nitrogen (50–74 mg N g^?1 dry mass) and phosphorus (5–9 mg P g^?1 dry mass) were, however, generally high and only slightly affected by water level. The results show that S. sesban can grow well and with high growth rates on most wet soils in the Mekong delta, except saline soils where the high salt content prevents establishment and growth. The nutrient and mineral contents of the plants, and hence the nutritional value of the plants as e.g. fodder or compost crops, is high. However, soil type and water level interactively affect growth and tissue composition. Hence, optimal growth conditions for S. sesban differ in the different regions of the Mekong delta.     

Tree effects on the chemical topsoil features of oak, beech and pine forests

We aimed to study tree effects on the chemical properties of forest soils. We compared soil features of three types of forest ecosystems, each with four stands (replicates): beech forests (Fagus sylvatica), oak forests (dominated by Quercus pyrenaica) and pine plantations (Pinus sylvestris). Five samples from the top 10 cm of soil were taken per stand, from which pH, organic matter content (O.M.), total nitrogen (N) and available calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺) and sodium (Na⁺) were determined. Litter layer depth was measured at each soil sampling point. We also measured tree density and crown diameters at each stand. Our results indicated that soil samples from the four pine plantation stands were more similar while oak and beech stands were characterised by great variability in terms of soil properties and leaf litter depth. Although the identity of the dominant tree species significantly influenced several topsoil chemical properties (increase in pH and available cations in oak forests and higher organic matter and total nitrogen in beech and pine ecosystems), there were other important factors affecting soil features that may be taken under consideration. Differences between soil properties of the three types of forest ecosystems were mainly related to the characteristics of the litter layer and less related to the tree layer structure. Finally, the establishment of pine plantations in naturally deciduous tree areas made the topsoil features more homogeneous.     

Tree row spacing affected agronomic and economic performance of Eucalyptus-based agroforestry in Andhra Pradesh, Southern India

The 3 × 2 m spacing currently used for eucalyptus plantations in the state of Andhra Pradesh, southern India does not permit intercropping from the second year. This discourages small landholders who need regular income from taking up eucalyptus plantations and benefiting from the expanding market for pulpwood. Therefore, on-farm experiments were conducted near Bhadrachalam, Khammam district (Andhra Pradesh) for over 4 years from August 2001 to November 2005 to examine whether wide-row planting and grouping of certain tree rows will facilitate extended intercropping without sacrificing wood yield. Eucalyptus planted in five-spatial arrangements in agroforestry [3 × 2 m (farmers’ practice), 6 × 1 m, 7 × 1.5 m paired rows (7 × 1.5 PR), 11 × 1 m paired rows (11 × 1 PR) and 10 × 1.5 m triple rows (10 × 1.5 TR)] was compared with sole tree stands at a constant density of 1,666 trees ha^?1. Cowpea (Vigna unguiculata) was intercropped during the post-rainy seasons from 2001 to 2004, and fodder grasses (Panicum maximum and Brachiaria ruziziensis) were intercropped during both the seasons of 2005. At 51 months after planting, different spatial arrangements did not significantly affect height and diameter at breast height (dbh). Total dry biomass of eucalyptus in different spatial arrangements ranged between 59.5 and 52.9 Mg ha^?1, the highest being with 6 × 1 m and the lowest with 10 × 1.5 TR, but treatment differences were not significant. The widely spaced paired row (11 × 1 PR) and triple row (10 × 1.5 TR) arrangements produced 62–73% of sole cowpea yield in 2003, 59–66% of sole cowpea yield in 2004, and 79–94% of sole fodder in 2005. In contrast, the 3 × 2 m spacing allowed only 17–45% of sole crop yields in these years. The better performance of intercrops in widely spaced eucalyptus was likely because of limited competition from trees for light and water. Intercropping of eucalyptus in these wider rows gave 14% greater net returns compared with intercropping in eucalyptus spaced at 3 × 2 m, 19% greater returns compared with that from sole tree woodlot and 263% greater returns compared with that from sole crops. Therefore, in regions where annual rainfall is around 1,000 mm and soils are fairly good, eucalyptus at a density of 1,666 plants per ha can be planted in uniformly spaced wide-rows (6 m) or paired rows at an inter-pair spacing of 7–11 m for improving intercrop performance without sacrificing wood production.     

Ten-year exposure to elevated CO2 increases stomatal number of Pinus koraiensis and P. sylvestriformis needles

Stomatal number and stomatal conductance are important structural and functional parameters for the assessment of carbon assimilation and water use under elevated CO₂. We studied stomatal density, number of stomatal rows and stomatal conductance of Pinus sylvestriformis and P. koraiensis needles exposed to elevated CO₂ (500 μmol mol^?1 CO₂) in open-top chambers for 10 years (1999–2009). Elevated CO₂ increased stomatal density on P. sylvestriformis by 10.8 % (13.5 % on abaxial surface and 8.0 % on adaxial surface) and the number of stomatal rows on P. koraiensis by 7.9 % (5.0 % in 1-year-old needles and 10.7 % in current-year needles). Increased stomatal density for P. sylvestriformis and number of stomatal rows for P. koraiensis indicate that elevated CO₂ increases stomatal number in both tree species. Needle age significantly influenced stomatal density and number of stomatal rows in P. koraiensis but not in P. sylvestriformis. For both species, elevated CO₂ did not significantly affect stomatal conductance but increased water use efficiency. The increase in stomatal number is not accompanied by significant changes in stomatal conductance at elevated CO₂ for both tree species suggesting that there may be no direct relationship between stomatal conductance and stomatal numbers.     

Carbon sequestration potential of five tree species in a 25-year-old temperate tree-based intercropping system in southern Ontario,Canada

Carbon (C) sequestration potential was quantified for five tree species, commonly used in tree-based intercropping (TBI) and for conventional agricultural systems in southern Ontario, Canada. In the 25-year-old TBI system, hybrid poplar (Populus deltoides × Populus nigra clone DN-177), Norway spruce (Picae abies), red oak (Quercus rubra), black walnut (Juglans nigra), and white cedar (Thuja occidentalis) were intercropped with soybean (Glycine max). In the conventional agricultural system, soybean was grown as a sole crop. Above- and belowground tree C Content, soil organic C, soil respiration, litterfall and litter decomposition were quantified for each tree species in each system. Total C pools for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and a soybean sole-cropping system were 113.4, 99.4, 99.2, 91.5, 91.3, and 71.1 t C ha^?1, respectively at a tree density of 111 trees ha^?1, including mean tree C content and soil organic C stocks. Net C flux for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and soybean sole-crop were 2.1, 1.4, 0.8, 1.8, 1.6 and ?1.2 t C ha^?1 year^?1, respectively. Results presented suggest greater atmospheric CO₂ sequestration potential for all five tree species when compared to a conventional agricultural system.     

Greater abundance of Fagus sylvatica in coniferous flood protection forests due to climate change: impact of modified root densities on infiltration

Climate change is expected to modify the spatial distributions of zonal forest communities and thus, their species compositions. The aim of this paper was to study the impact of higher abundance of beech on water storage capacity in current coniferous flood protection forests due to varying root densities of the main tree species. Two forest communities in the northern pre-Alps in Switzerland with similar soil properties but varying in species composition were investigated (space-for-time substitution). It was assumed that the Vaccinio myrtillii-Abieti-Piceetum (site A) will be replaced by a Luzulo-Abieti-Fagetum (site B). We irrigated 16 hydromorphic soils (1 m², 70 mm/h, three consecutive irrigations) at site A and 10 at site B and recorded water-content variations with time domain—and frequency domain reflectometry. Roots were extracted from soil cores taken from the positions where the water-content probes were inserted, and digitally measured. Infiltration capacity ω _I was mainly limited to the upper soil at site A but was approximately constant down to 0.7 m depth at site B. Between 0.3 and 1.0 m soil depth, root densities at site B exceeded those at site A. Root density was the main predictor for ω _I (R ² = 0.57) at site A as shown by a multiple linear regression analysis. Assuming that the root density in the current coniferous forest (A) will increase to that of the beech stand (B) due to the greater abundance of beech, the water storage capacity will increase by 9.2 mm in consequence of the expected forest transformation.     

Soil organic carbon stocks and fractions in different orchards of eastern plateau and hill region of India

Soil organic carbon (SOC) plays an important role in soil fertility and productivity. It occurs in soil in labile and non-labile forms that help in maintaining the soil health. An investigation was undertaken to evaluate the dynamics of total soil organic carbon (C _tot), oxidisable organic carbon (C _oc), very labile carbon (C frac ₁), labile carbon (C frac ₂), less labile carbon (C frac ₃), non-labile carbon (C frac ₄), microbial biomass carbon (C _mic) and SOC sequestration in a 6-year-old fruit orchards. The mango, guava and litchi orchards caused an enrichment of C _tot by 17.2, 12.6 and 11 %, respectively, over the control. The mango orchard registered highest significant increase of 20.7, 13.5 and 17.4 % in C frac ₁, C frac ₂ and C frac ₄, respectively, over control. There is greater accumulation of all the C fractions in the surface soil (0–0.30 m). The maximum total active carbon pool was 36.2 Mg C ha^?1 in mango orchard and resulted in 1.2 times higher than control. The passive pool of carbon constituted about 42.4 % of C _tot and registered maximum in the mango orchard. The maximum C _mic was 370 mg C kg^?1 in guava orchard and constituted 4.2 % of C _tot. The carbon management index registered 1.2 (mango orchard)- and 1.13 (guava and litchi orchard)-fold increase over control. The mango orchard registered highest carbon build rate of 1.53 Mg C ha^?1 year^?1 and resulted in 17.3 % carbon build-up over control. Among the carbon fractions, C frac ₁ was highly correlated (r = 0.567**) with C _mic.     

Growth, productivity and quality of Megathyrsus maximus under cover from Gliricidia sepium

The effect of tree canopy on the growth, productivity and forage quality of Megathyrsus maximus and changes in soil properties were evaluated over three seasonal periods. Four adjacent plots (15 m × 17 m each) in a tropical secondary deciduous forest having 12 years of growth and dominated by Gliricidia sepium were randomly assigned to two treatments: removal of trees (SCA) in two of the plots and leaving trees intact (COA) in the other two. In all plots, M. maximus was planted with 50 cm spacing among plants. Tree removal significantly increased the incident photosynthetically active radiation (PAR, P < 0.001) and grass size (12.5 % in height, P < 0.01, and 16.5 % in clump diameter, P < 0.05), but did not significantly affect any other variable. Season significantly affected grass height (P < 0.003), tiller number (P < 0.001), clump diameter (P < 0.001), net CO₂ assimilation rate (P < 0.001), forage biomass production (P < 0.003), and acid detergent fiber content (P = 0.033). Primary soil changes after 1 year of establishment of the grass were the decline by 3 % in organic carbon (P = 0.03), and qualitative changes in soil structure, regardless of tree presence. Results are consistent with the ability of M. maximus to tolerate shade. We conclude that under the conditions of the study there was no evidence for a negative effect of tree canopy on M. maximus mediated by a reduction in PAR.     

Land use change and soil carbon pools: evidence from a long-term silvopastoral experiment

Multi-functional silvopastoral systems provide a wide range of services to human society including the regulation of nutrients and water in soils and the sequestration of atmospheric carbon dioxide (CO₂). Although silvopastoral systems significantly contribute to enhance aboveground carbon (C) sequestration (e.g. C accumulation in woody plant biomass), their long-term effects on soil C pools are less clear. In this study we performed soil physical fractionation analyses to quantify the C pool of different aggregate fractions across three land use types including (1) silvopastoral system with ash trees (Fraxinus excelsior L.), (2) planted woodland with ash trees, and (3) permanent grassland, which were established in 1989 at Loughgall, Northern Ireland, UK. Our results show that 26 years after the conversion of permanent grassland to either silvopastoral or woodland systems, soil C (and N) stocks (0–20 cm depth) did not significantly change between the three land use types. We found, however, that permanent grassland soils were associated with significantly higher C pools (g C kg^?1 soil; P < 0.03) of the large macro-aggregate fraction (> 2 mm) whereas soil C pools of the micro-aggregate (53–250 μm) and silt and clay (< 53 μm) fractions were significantly higher in the silvopastoral and woodland systems (P < 0.05). A key finding of this study is that while tree planting on permanent grassland may not contribute to greater soil C stocks it may, in the long-term, increase the C pool of more stable (recalcitrant) soil micro-aggregate and silt and clay fractions, which could be more resilient to environmental change.     

The impact of the environmental factors on the photosynthetic activity of common pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis>) in spring and in autumn in the region of Eastern Siberia

The taiga coniferous forests of the Siberian region are the main carbon sinks in the forest ecosystems. Quantitatively, the size of the carbon accumulation is determined by the photosynthetic productivity, which is strongly influenced by environmental factors. As a result, an assessment of the relationship between environmental factors and photosynthetic productivity makes it possible to calculate and even predict carbon sinks in coniferous forests at the regional level. However, at various stages of the vegetative period, the force of the connection between environmental conditions and the productivity of photosynthesis may change. In this research, correlations between the photosynthetic activity of Scots pine (Pinus sylvestris L.) with the environmental conditions were compared in spring and in autumn. In spring, close positive correlation of the maximum daily net photosynthesis was identified with only one environmental factor. For different years, correlations were for soil temperature (r_s = 0.655, p = 0.00315) or available soil water supply (r_s = 0.892, p = 0.0068). In autumn within different years, significant correlation was shown with two (temperature of air and soil; r_s = 0.789 and 0.896, p = 0.00045 and 0.000006, respectively) and four factors: temperature of air (r_s = 0.749, p = 0.00129) and soil (r_s = 0.84, p = 0.00000), available soil water supply (r_s = 0.846, p = 0.00013) and irradiance (r_s = 0.826, p = 0.000001). Photosynthetic activity has a weaker connection with changes in environmental factors in the spring, as compared to autumn. This is explained by the multidirectional influence of environmental conditions on photosynthesis in this period and by the necessity of earlier photosynthesis onset, despite the unfavorable conditions. This data may be useful for predicting the flow of carbon in dependence on environmental factors in this region in spring and in autumn.     

The benefits of phosphorus fertilization of trees grown on salinized croplands in the lower reaches of Amu Darya, Uzbekistan

Afforestation of degraded croplands by planting N₂-fixing trees in arid regions is highly recognized. However, fixation of atmospheric nitrogen gas (N₂) by woody perennials is often limited on phosphorus (P) poor soils, while any factor limiting N nutrition inhibits tree growth. In a two-factorial field experiment, the effect of three P amendments was examined during 2006–2008 on N₂ fixation, biomass production, and foliage feed quality of actinorhizal Elaeagnus angustifolia L. and leguminous Robinia pseudoacacia L. With the ¹⁵N natural abundance method, N₂ fixation was quantified based on foliar and whole-tree sampling against three non-N₂-fixing reference species: Gleditsia triacanthos L., Populus euphratica Oliv., and Ulmus pumila L. The P applications, in March 2006 and April 2007 only, included (i) high-P (90 kg P ha^?1), (ii) low-P (45 kg P ha^?1), and (iii) 0-P. After 3 years, the average proportion of N derived from atmosphere (Ndfa, %) increased from 78 % with 0-P to 87 % with high P when confounded over both N₂-fixing species. With the used density of 5,714 trees ha^?1, the total amount of N₂ fixed (Ndfa, kg N ha^?1) with high-P increased from 64 kg N ha^?1 (year 1) to 807 kg N ha^?1 (year 3) in E. angustifolia and from 9 kg N ha^?1 (year 1) to 155 kg N ha^?1 (year 3) in R. pseudoacacia. Total above-ground biomass increases were too variable to be significant. Leaf N content and therewith also leaf crude protein content, which is an indicator for feed quality, increased significantly (24 %) with high-P when compared to 0-P for E. angustifolia. Overall findings indicated the suitability of the two N₂-fixing species for afforestating salt-affected croplands, low in soil P. With P-applications as low as 90 kg P ha^?1, the production potential of E. angustifolia and R. pseudoacacia, including the supply of protein-rich feed, could be increased on salt-affected croplands.     

Arbuscular mycorrhizal association of indigenous agroforestry tree species and their infective potential with maize in the rift valley, Ethiopia

Tree species in agroforestry are important source of inoculum for companion agricultural crops. Agroforestry trees can serve as a source of Arbuscular mycorrhiza (AM) inoculants to intercropped annuals. We studied spore abundance, root colonization of Albizia gummifera (J.F. Gmel.) and Croton macrostachyus (Hochst Ex Del.) trees and their effect on colonization of maize. Soil and root samples were collected from field standing trees from under and outside the canopy of trees and maize crops in the main rainy season. The number of spore count was significantly higher under the canopy of A. gummifera (791/100 g of dry soil) and C. macrostachyus (877/100 g of dry soil) trees than outside the canopy (547 and 588/100 g of dry soil, respectively). The level of root colonization of C. macrostachyus (45 %) was higher than A. gummifera (41 %). Root colonization of maize crops grown under the canopy of A. gummifera and C. macrostachyus trees was significantly higher than outside the canopy (P < 0.001). Maize seedlings grown on non-sterilized soils collected under and outside the canopy of A. gummifera and C. macrostachyus trees recorded higher root colonization, plant height, shoot and root dry weight than grown on sterilized soils (P < 0.001). The percentage of AM colonized roots of Zea mays seedlings was significantly positively correlated with the number of spore counts for field soils. The rhizospheres of indigenous agroforestry perennial species are important source of inoculum for annuals. The integration of perennials and annuals in an agroforestry system enhances the maintenance of soil quality in the tropics.     

Canopy transpiration of a Pinus canariensis forest at the tree line: implications for its distribution under predicted climate warming

Canopy transpiration (E _c) of a 50-year-old Pinus canariensis Chr. Sm. Ex DC. stand at tree line in Tenerife, Canary Islands, was estimated continuously throughout a year from March 1, 2008, to February 28, 2009, by means of xylem sap flow measurements. E _c varied markedly throughout the entire year generally following the seasonal trends in soil water availability and varied between 0.89 mm day^?1 under the conditions of non-limiting soil water availability and close to zero under soil drought. This is because canopy conductance declined significantly with increasing evaporative demand and thus significantly reduced tree water loss, and this decrease was more pronounced during the soil drought. Total annual E _c was 79.6 mm, which is significantly below the values estimated for other Mediterranean forest ecosystems and even 70 % lower than the value estimated for a P. canariensis forest at 1,650 m a.s.l. where the soil water content was higher than at the tree line site. Therefore, these results highlighted the importance of drought stress in tree line ecotone and should be taken more into account in semiarid tree lines.     

Trees improve water storage and reduce soil evaporation in agroforestry systems on bench terraces in SW Uganda

The success of agroforestry in semi-arid areas depends on efficient use of available water and effective strategies to limit tree/crop competition and maximise productivity. On hillsides, planting improved tree fallows on the degraded upper section of bench terraces is a recommended practice to improve soil fertility while cropping continues on the lower terrace to maintain food production. This study examined the influence of tree fallows on soil water content (θ _w ) and evaporation (E _s ). Alnus acuminata Kunth (alnus), Calliandra calothyrsus Meissner (calliandra), Sesbania sesban L. (sesbania), a mixture of all three species, or sole crops (beans (Phaseolus vulgaris L.) or maize (Zea mays L.)) were grown on the upper terrace. The same sole crops were grown on the lower terrace. Four management regimes (unpruned, root, shoot and root + shoot pruned) were applied to the tree rows adjacent to the cropping area. Neutron probe and microlysimeter approaches were used to determine θ _w and E _s when the trees were c. 3.5 years old. Sesbania and alnus increased θ _w by 9–18 % in the cropping area on the lower terrace but calliandra reduced θ _w by 3–15 %. After heavy rain, E _s comprised 29–38 % of precipitation in the tree-based treatments and 53 % under sole crops. Absolute values declined as rainfall decreased, but E _s as a proportion of rainfall increased to 39–45 % in the tree-based treatments and 62 % for sole crops. Root + shoot pruning of alnus and the tree mixture increased θ _w in the cropping area but had no significant effect in the other tree-based treatments. The results suggest that sesbania and alnus can be planted on smallholdings without compromising water supply to adjacent crops, whereas calliandra decreased water availability despite reducing E _s . These results provide a mechanistic understanding of reported effects on crop yield in the same site.     

Incident rainfall partitioning and canopy interception modeling for an abandoned Japanese cypress stand

Interception loss (E _i) in forests has been studied widely. However, E _i parameters and modeling as well as spatial patterns of throughfall (TF) in abandoned Japanese cypress (Chamaecyparis obtusa) plantations remain poorly documented. In this study, gross precipitation (P _G), stemflow (SF), and TF were monitored in an unmanaged 32-year-old Japanese cypress stand throughout the 2011 rainy season. Results indicate that P _G partitioning into TF, SF, and E _i were, respectively, 64.2 ± 3.6, 10.6 ± 0.6, and 25.2 ± 1.1 % of the 880.8 mm cumulative P _G from 29 rainfall events. Direct throughfall proportion (p) and drainage from the canopy contributed about 14 ± 7 and 50 ± 21 % of the total TF for the events, respectively. The mean canopy storage capacity (S) was 2.4 ± 0.7 mm. The coefficient of variability (CV) of TF rate decreased asymptotically with increasing P _G amount, ranging from 16 to 56 % with median 26 %. The CV of TF rate was not significantly correlated with canopy cover (r = 0.152, P = 0.521, n = 20) and distance from the nearest trunk (r = 0.196, P = 0.408, n = 20). Based on the revised Gash analytical model, the total simulated E _i was close to the observed, with a general underestimation magnitude of 5.7 %. The E _i components were quantified, and most of the interception loss (62.9 %) evaporated during rainfall, while 26.8 % evaporated after rainfall ceased. Climatic and forest structural parameters required by the model were identified and analyzed by sensitivity analysis, implying that the revised Gash analytical model is robust and reliable enough for abandoned Japanese cypress plantations in a maritime climate.     

Decomposition and nutrient release in leaves of Atlantic Rainforest tree species used in agroforestry systems

Aiming to support the use of native species from the Atlantic Rainforest in local agroforestry systems, we analysed chemical and biochemical components related to leaf decomposition of Inga subnuda, Senna macranthera, Erythrina verna, Luehea grandiflora, Zeyheria tuberculosa, Aegiphila sellowiana, and Persea americana. These tree species are native (except for P. americana) and commonly used in agroforestry systems in the Atlantic Rainforest. For the three first species (Fabaceae), we also analysed the remaining dry matter and released nutrients from leaves, using litter bags, and biological nitrogen fixation, using Bidens pilosa and Brachiaria plantaginea as references of non-N₂-fixing plants. Leaves from I. subnuda, L. grandiflora, and P. americana had a lower decomposition rate than the other species, exhibiting negative correlations with lignin/N and (lignin+polyphenol)/N ratios. The percentages of remaining dry matter after 1 year were 69 % (I. subnuda), 26 % (S. macranthera) and 16 % (E. verna). Higher nutrient release was found in decreasing order from residues of E. verna, S. macranthera, and I. subnuda. The percentages of nitrogen fixation were 22.6 % (E. verna), 20.6 % (I. subnuda) and 16.6 % (S. macranthera). Diversification of tree species in agroforestry systems allows for input of diversified organic material and can contribute to maintaining and improving soil functions resulting in improvements of soil quality.     

Poplar leaf biomass distribution and nitrogen dynamics in a poplar-barley intercropped system in southern Ontario, Canada

The effect of hybrid poplar (Populus spp. clone DN 177) leaf biomass distribution on soil nitrification was investigated in two experiments during the 1993, 1994 and 1995 growing seasons in a poplar-barley (Hordeum vulgare cv. OAC Kippen) intercropping experiment established at Guelph, Ontario, Canada. In experiment 1, poplar was intercropped with barley during all three years and the poplar leaves shed during the fall season were removed from the soil surface during 1993 and 1994. In experiment 2, poplar was intercropped with barley in 1993 and with corn (Zea mays cv. Pioneer 3917) in 1994 an 1995, respectively, and the shed poplar leaves were not removed. In experiment 1, the nitrification rates were lower during 1994 and 1995 when the dropped leaves were removed from the field. The total above-ground biomass of barley within 2.5 m of the tree row was 517, 500 and 450 g×m⁻², respectively during the three years, whereas in the middle of the crop row (4–11 m), the corresponding figures were 491, 484 and 464 g×m–2. Mean nitrification rates, N availability and carbon content were higher in soils close to the poplar tree rows (2.5 m) compared to the corresponding values in the middle of the crop alley (4–11 m from the tree row). In experiment 2, where poplar leaves were not removed from the field, nitrification rates in soils within 2.5 m distance from the poplar row were fairly constant (range 100 to 128 μg 100 g⁻¹ dry soil day⁻¹) during the three years. Results suggest that soil nitrification rates, soil carbon content and plant N uptake adjacent to the poplar tree rows are influenced by poplar leaf biomass input in the preceding year. This revised version was published online in June 2006 with corrections to the Cover Date.