A tree/crop interface design and its use for evaluating the potential of hedgerow intercropping

The paper describes a tree/crop interface (TCI) experiment designed to investigate the effects of row orientation using Leucaena leucocephala Lam. Each TCI plot consisted of a regularly pruned Leucaena hedge in the middle and 12 crop rows on either side. Eight such plots were arranged at 45° around a sole Leucaena plot with rows oriented in four compass directions viz., North-South, East-West, Northeast-Southwest and Northwest-Southeast.Results of four years from 1984 to 1987 did not show any effect of row orientation, and similarly, no effect was seen on crop rows due to their location on the windward or leeward side of the hedge. The TCI effect was positive on the first crop row in the first year because Leucaena grew slowly, but depressed the yield of the first 4 to 6 crop rows(1.8 to 2.7 m from hedge) in subsequent years. The negative effect of Leucaena was noted more on sunflower in a relatively dry year than on sorghum in other years.Results from the TCI plots were used to estimate the yield of five hedgerow intercropping (HI) systems with varying alley widths (2.7 to 9.9 m). Comparison with sole stands of Leucaena and crops indicated that HI was more productive particularly at close alley widths. For example, hedges spaced at 2.7 m and 3.6 m averaged 37% and 25% higher productivity than the respective sole stands; but this advantage may be an overestimation of the real potential.The relevance of TCI experiments for studying agroforestry systems, their merits and limitations, especially of the design employed in this study are discussed.     

Tree-crop interactions in hedgerow intercropping with different tree species and tea in Sri Lanka: 1. Production and resource competition

Incorporation of tree hedges along contours has been proposed as a means of reducing soil erosion and increasing soil fertility of tea (Camellia sinensis (L.) O. Kuntz) plantations on sloping terrain in high-rainfall zones of Sri Lanka. Tea yields in these hedgerow intercrops are determined by the balance between the positive (i.e., increased soil fertility) and negative (i.e., resource competition) effects of hedgerows. Therefore, the objectives of the present study were to determine: (a) the net effect of six different hedgerow species (Calliandra calothyrsus Meissner, Senna [Cassia] spectabilis (DC.) H. Irwin and Barneby, Euphatorium innulifolium (R.M. King and H. Rob.) H.B.K., Flemingia congesta Aiton F., Gliricidia sepium (Jacq.) (Kunth.) Walp. and Tithonia diversifolia (Hemsl.) A. Gray) on long-term tea yields; (b) the effect of incorporating hedgerow prunings as mulch; and (c) the relationship between hedgerow characteristics (i.e., biomass production, canopy and root growth) and tea yield variation. Tea yields, measured over one complete pruning cycle from October 1998 to September 2001, showed reductions relative to a sole tea crop under all hedgerow species except Euphatorium. The yield reductions ranged from 22 to 40%. Tea yields under Euphatorium showed increases up to 23% relative to the sole crop control. Addition of hedgerow prunings as mulch increased tea yields in all hedgerow intercrops. The yield increases ranged from 11 to 20%, with the highest being under Euphatorium. Tea yields showed a negative relationship (R²=0.38) with the pruned biomass of hedgerows. Limitation of environmental resources (e.g., water and light) and hedgerow characters which intensified resource competition (i.e., greater canopy lateral spread and height and greater root length densities, especially in the top soil layer) were responsible for observed tea yield reductions in hedgerow intercrops.     

A tree/crop interface orientation experiment with aGrevillea robusta hedgerow and maize

Pruned triple-row hedges ofGrevillea robusta with 11 rows of maize planted in parallel on either side were grown in 12.5×16.0 m plots on a flat, freely exposed site. There were two replicates of four orientation treatments and crop yield was recorded row-by-row over 9 seasons. After the hedges had become established there were some marked differences in maize yields between sides, especially in the first rainy seasons. The maize on the downside of prevailing winds frequently showed improved growth and yield over the non-sheltered maize, sometimes by as much as 50% over the whole subplot and up to 80% in the tree/crop interface zone. These differences were significant (p0.05) when analyzing the whole experimental period for first and for second rainy seasons separately (prevailing winds more southerly or northerly, respectively), although they varied between seasons and zones. Attributing results to shelter can only be adduced circumstantially because meteorological data were not collected at the plot level. Shading effect were not considered important over the whole sub-plot. Soil water profiles obtained from an array of gypsum resistance blocks in two of the plots (at 000° and 090°) characterized the wetting and drying patterns in this system, but expected asymmetries due to orientation effects were not apparent except, perhaps, fleetingly in the topsoil. At the end of the experiment the distribution of fine roots of both species was examined by means of root trenching. TheG. robusta root system extended almost symmetrically to the edges of the plot in the uncropped part, but only to some 4 m from either side of the hedge where cropped. Part of the upper profile to 1.3 m was shared with the maize roots, butGrevillea rooted further down to at least 2 m. as well as rooting deeper. The possible implications of such niche differentiation for below-ground resource capture are noted.     

Tree-crop interactions in hedgerow intercropping with different tree species and tea in Sri Lanka: 2. Soil and plant nutrients

The main aim of this study is to review the environmental and socioeconomic sustainability of the gum arabic farming system in central Sudan. A further aim is to analyse some of the main factors influencing production in recent decades in order to understand the future trade potential and consequently the smallholder livelihood. The study shows that end-user imports of gum arabic have increased during recent decades. Gum arabic is mainly for uses such as soft drinks, confectionary, and pharmaceuticals. However, even with this increased demand the production in Sudan, the main country of production, is declining. The producers, mainly smallholders, suffer from fluctuating prices. If the gum arabic farming system should be able to provide the environmental benefits of improved soil fertility and the socioeconomic benefits of risk spreading and dry season income opportunities, the prices paid to smallholders must be stabilized at a fair level, otherwise a shift to other crops or practices might take place.     

Cost-benefit analysis of alternative forms of hedgerow intercropping in the Philippine uplands

Considerable resources have been expended promoting hedgerow intercropping with shrub legumes to farmers in the Philippine uplands. Despite the resources committed to research and extension, persistent adoption by farmers has been limited to low cost versions of the technology including natural vegetation and grass strips. In this paper, cost-benefit analysis is used to compare the economic returns from traditional open-field maize farming with returns from intercropping maize between leguminous shrub hedgerows, natural vegetation strips and grass strips. An erosion/productivity model, Soil Changes Under Agroforestry, was used to predict the effect of erosion on maize yields. Key informant surveys with experienced maize farmers were used to derive production budgets for the alternative farming methods. The economic incentives revealed by the cost-benefit analysis help to explain the adoption of maize farming methods in the Philippine uplands. Open-field farming without hedgerows has been by far the most popular method of maize production, often with two or more fields cropped in rotation. There is little persistent adoption of hedgerow intercropping with shrub legumes because sustained maize yields are not realised rapidly enough to compensate farmers for establishment and maintenance costs. Natural vegetation and grass strips are more attractive to farmers because of lower establishment costs, and provide intermediate steps to adoption. Rural finance, commodity pricing and agrarian reform policies influence the incentives for maize farmers in the Philippine uplands to adopt and maintain hedgerow intercropping. This revised version was published online in August 2006 with corrections to the Cover Date.     

Insect pests and beneficial arthropods population under different hedgerow intercropping systems in semiarid Kenya

Exploiting the principles of biological control of crop pests is an important management strategy for the resource-poor smallholder farmers of the tropics. The effects of nine hedgerow species on the abundance of major insect pests of beans and maize, and predatory/parasitic-arthropods were monitored over two cropping seasons and the intervening dry period. The tree/shrub species evaluated were Gliricidia sepium, Grevillea robusta, Senna siamea, Senna spectabilis, Flemingea congesta, Croton megalocarpus, Morus alba, Calliandra calothyrsus and Lantana camara. Arthropod abundance was monitored through counts of infested plants and using yellow pan and pitfall traps. Beanfly (Ophiomyia spp.) infestation was significantly higher in the presence of hedgerows (35%) than in their absence (25%). Hedgerows did not influence aphid (Aphis fabae) infestation of beans. In contrast, maize associated with hedgerows experienced significantly lower stalk borer (Busseola fusca and Chilo spp.) and aphid (Rhophalosiphum maidis) infestations than pure maize, the margin of difference being 13% and 11% respectively for the two pests. Ladybird beetles closely followed their prey, aphids, with significantly higher catches in sole cropped-plots than in hedgerow-plots and away from hedgerows. Activity of wasps was significantly greater close to hedgerows than away from them. Spider catches during maize season were 77% greater in the presence of hedgerows than in their absence, but catches during other seasons were similar between the two cropping systems. Differences among hedgerow species were not significant for most of the arthropods monitored, except that beanfly infestation was greater with Gliricidia hedgerows. The study indicates that the effect of hedgerows on pest infestations of crops and their role as refugia for predators cannot be generalized but depends on the specific arthropods.This revised version was published online in November 2005 with corrections to the Cover Date.     

Testing a process-based model of tree seedling growth by manipulating

A model was developed that simulated photosynthesis, growth and allocation in tree seedlings. The model was parameterized with data from experiments on seedlings of sycamore (Acer pseudoplatanus L.), Sitka spruce (Picea sitchensis (Bong) Carr.) and young birch trees (Betula pendula Roth.). In these experiments, CO2 concentration ([CO2]) and nutrient addition rate were varied. Parameters quantifying nutrient uptake, translocation and starch synthesis were fitted, based on data from control treatments. Elevated [CO2] and low-nutrient treatments were then used to test the predicted response of growth and allocation against observations. The model accurately predicted total seedling growth in the elevated [CO2] treatments. A response of growth to elevated [CO2] was seen in the birch and sycamore experiments, but not in the Sitka spruce, because of photosynthetic down-regulation. Predictions of allocation were reasonably accurate in the birch and Sitka spruce experiments, but were notably poorer in the sycamore experiments, possibly because of differences in sink strength between root and shoot. In the birch and sycamore experiments, little change in allocation with elevated [CO2] was observed or predicted. This was ascribed to the relative values of K(Tc) and K(Tn), the translocation coefficients that determine the sensitivity of allocation to carbon and nitrogen uptake rates, respectively. Growth and allocation in the low-nutrient treatments were poorly predicted by the model. In Sitka spruce, it was suspected that the photosynthetic parameters measured in August 1994 had been higher earlier in the season, before nutrients became depleted. In sycamore, the discrepancies were thought to relate to differences in sink strength between root and shoot that could not be described by the model.     

A cost-benefit analysis of hedgerow intercropping in the Philippine uplands using the SCUAF model

Soil erosion in the Philippine uplands is severe. Hedgerow intercropping is widely advocated as an effective means of controlling soil erosion from annual cropping systems in the uplands. However, few farmers adopt hedgerow intercropping even in areas where it has been vigorously promoted. This may be because farmers find hedgerow intercropping to be uneconomic compared to traditional methods of farming. This paper reports a cost-benefit analysis comparing the economic returns from traditional maize farming with those from hedgerow intercropping in an upland community with no past adoption of hedgerows. A simple erosion/productivity model, Soil Changes Under Agroforestry (SCUAF), is used to predict maize yields over 25 years. Economic data were collected through key informant surveys with experienced maize farmers in an upland community. Traditional methods of open-field farming of maize are economically attractive to farmers in the Philippine uplands. In the short term, establishment costs are a major disincentive to the adoption of hedgerow intercropping. In the long term, higher economic returns from hedgerow intercropping compared to open-field farming are realised, but these lie beyond farmers limited planning horizons.     

A study of the potential of hedgerow intercropping in semi-arid India using a two-way systematic design

The potential of hedgerow intecrropping with Leucaena leucocephala was explored on vertic Inceptisols over 4 years at ICRISAT Center, Patancheru, India. The study was conducted using a systematic layout involving different alley widths ranging from 1.35 to 4.95 m and with varying distances between hedge and crops. The alleys were cropped with alternate rows of sorghum and pigeonpea. Hedges composed double Leucaena hedgerows 60 cm apart were periodically harvested for fodder. Sole crops of all components and a sorghum/pigeonpea intercrop were included in all four replications of the study.Starting in the second year, Leucaena was progressively more competitive to annual crops, causing substantial yield reduction. Competition (primarily for moisture) was most severe in narrow alleys and was greatest on pigeonpea.The growth of Leucaena was not sufficient to compensate for reduced crop yields. Land equivalent ratios (LERs) calculated on the basis of grain yield of crops and Leucaena fodder yields showed that hedgerow intercropping (HI) was advantageous over sole crops only during the first two years using wide alleys, but disadvantegeous in the last two years. LERs calculated on the basis of total dry matter indicated only a small advantage for HI (13–17 percent) over sole crops in wider (>4 m) alleys. Average returns per year from HI exceeded those of the most productive annual crop system (sorghum/pigeonpea intercropping) by 8 percent in 4.05 m alleys, and by 16 percent in 4.95 m alleys. Fodder production during the dry season was 40 percent of the annual total in these alley widths. Thus hedgerow intercropping at 4–5 m alley width is not very attractive for farmers in semi-arid India, which has 600–700 mm of annual rainfall. There is a need to examine the potential of HI in wider alleys. The merits and limitations of the systematic design are discussed.     

Estimation of net gain of soil carbon in a nitrogen-fixing tree and crop intercropping system in sub-Saharan Africa: results from re-examining a study

Nitrogen (N)-fixing tree and crop intercropping systems can be a sustainable agricultural practice in sub-Saharan Africa and can also contribute to resolving climate change through enhancing soil carbon (C) sequestration. A study conducted by Makumba et al. (Agric Ecosyst Environ 118:237?C243, 2007) on the N-fixing tree gliricidia and maize intercropping system in southern Malawi provides a rare dataset of both sequestered soil C and C loss as soil carbon dioxide (CO₂) emissions. However, no soil C gain and loss estimates were made so the study failed to show the net gain of soil C. Also absent from this study was potential benefit or negative impact related to the other greenhouse gas, nitrous oxide (N₂O) and methane (CH₄) emissions from the intercropping system. Using the data provided in Makumba et al. (Agric Ecosyst Environ 118:237?C243, 2007) a C loss as soil CO₂ emissions (51.2?±?0.4?Mg?C?ha^?1) was estimated, amounting to 67.4% of the sequestered soil C (76?±?8.6?Mg?C?ha^?1 in 0?C2?m soil depth) for the first 7?years in the intercropping system. An annual net gain of soil C of 3.5?Mg?C?ha^?1?year^?1 was estimated from soil C sequestered and lost. Inclusion of the potential for N₂O mitigation [0.12?C1.97?kg?N₂O?CN?ha^?1?year^?1, 0.036?C0.59?Mg CO₂ equivalents (eq.) ha^?1?year^?1] within this intercropping system mitigation as CO₂ eq. basis was estimated to be 3.5?C4.1?Mg CO₂ eq.?ha^?1?year^?1. These results suggest that reducing N₂O emission can significantly increase the overall mitigation benefit from the intercropping system. However, significant uncertainties are associated with estimating the effect of intercropping on soil N₂O and CH₄ emissions. These results stress the importance of including consideration of quantifying soil CO₂, N₂O and CH₄ emissions when quantifying the C sequestration potential in intercropping system.     

Growth characteristics of multipurpose tree species,crop productivity and soil properties in agroforestry systems under subtropical humid climate in India

Multipurpose tree species （MPTs） were studied in an agroforestry arboretum under subtropical humid climate in Northeast India. Out of 12 MPTs planted under agroforestry systems, Acacia auriculiformis in spacing of 2 m × 2 m （2500 stems·hm^-2） could have the potentiality to meet the timber/fuelwood requirement due to its high wood production of 635 m^3·hm^-2 with mean annual increment （MAI） of 2.54×10^-2 m^3.treel.a^-1 in a short rotation period of 10 years. Thus, A. auriculiformis is a short rotation forest tree species suitable to grow in subtropical humid climate. On the other hand, at 16 years of age, Eucalyptus hybrid and Michelia champaca in spacing of 3 m × 3 m （1111 stems.hm^2） produced appreciably high timber volume of 315 m^3.hm^-2 and 165 m^3.hm^-2 with MAI of 1.77×10^-2 m^3.tree^-1·a^-1 and 0.92×10.2 m^3.tree^-1.a^-1, respectively. At 16 years of age, Gmelina arborea produced a timber volume of 147 m^3.hm^-2 with MAI of 1.47×10^-2 m^3.tree^-1.a^-1 followed by Samania saman （140 m^3.hm^-2）, Albizziaprocera （113 m^3·hm^-2） and Tectona grandis （79 m3.hm^-2） with MAI of 1.40, 1.13 and 0.78 × 10^-2 m^3 .tree^-1a^-1, respectively in 4 m × 4 m spacing （625 stems.hm^-2）. Gliricidia maculata and Leucaena leucocephala could be used as live fences around the farm boundary to supply their N-rich leaves for mulch as well as manure to crops. In agroforestry arboretum, direct seeded upland rice （Oryza sativa - variety, AR-11）, groundnut （Arachis hypogaea - variety, JL-24） and sesamum （Sesamum indicum - variety, B-67） were grown during the initial period upto 8 years of tree establishment. Under other MPTs, there was a reduction in crop productivity as compared to open space. After 8 years of tree establishment, horti-silvi and silvi-pastoral systems were developed and pineapple （Ananas comosus - variety Queen）, turmeric （Curcuma longa -variety RCT -1） and cowpea （Vigna sinensis - variety Pusa Barsati） as forage crop were raised. The productivity of p     

Testing the safety-net role of hedgerow tree roots by 15N placement at different soil depths

Trees which root below crops may have a beneficial role in simultaneous agroforestry systems by intercepting and recycling nutrients which leach below the crop rooting zone. They may also compete less strongly for nutrients than trees which root mainly within the same zone as crops. To test these hypotheses we placed highly enriched ¹⁵N-labelled ammonium sulphate at three depths in the soil between mixed hedgerows of the shallow-rooting Gliricidia sepium and the deep rooting Peltophorum dasyrrhachis. A year after the isotope application most of the residual ¹⁵N in the soil remained close to the injection points due to the joint application with a carbon source which promoted ¹⁵N immobilization. Temporal ¹⁵N uptake patterns (two-weekly leaf sub-sampling) as well as total ¹⁵N recovery measurements suggested that Peltophorum obtained more N from the subsoil than Gliricidia. Despite this Gliricidia appeared to compete weakly with the crop for N as it recovered little ¹⁵N from any depth but obtained an estimated 44–58% of its N from atmospheric N₂-fixation. Gliricidia took up an estimated 21 kg N ha^–1 and Peltophorum an estimated 42 kg N ha^–1 from beneath the main crop rooting zone. The results demonstrate that direct placement of ¹⁵N can be used to identify N sourcing by trees and crops in simultaneous agroforestry systems, although the heterogeneity of tree root distributions needs to be taken into account when designing experiments. This revised version was published online in June 2006 with corrections to the Cover Date.     

杨农复合经营系统碳储量及其分布特征研究

以杨树纯林和杨农复合林2种生态系统为研究对象,对林木、农作物(林下植被)、土壤、凋落物各组分的碳储量进行比较研究。结果表明,杨树纯林和杨农复合林的碳储量分别为(101.59±8.1),(116.65±10.3)t/hm2。在2个生态系统中林木及土壤碳储量均占总量的90%以上。杨农复合林凋落物和林下植被碳储量所占比例约为6%,是杨树纯林的2倍。林木碳储量、农作物(林下植被)碳储量均为杨农复合林较高;杨农复合林土壤碳储量仅在中间层(10~25,25~50 cm)显著高于杨树纯林;凋落物碳储量2者之间差异不显著。相对纯林,农林复合系统具有较高的吸收和固碳能力。     

Stand basal area as an index of tree competitiveness in timber intercropping

To derive optimal benefits from intercropping timber, farmers should make important initial decisions on tree species and planting density with a good understanding of their tradeoffs. Complex and data-intensive models used by researchers should be supplemented with simpler models based on easily measured parameters and easily understood competition functions. In experiments in the Philippine uplands, growth parameters of three popular farm-forestry species (Eucalyptus deglupta, E. torelliana, and Paraserianthes falcataria) were measured, along with intercropped and non-intercropped yields of maize and vegetables. The commonly used forestry parameter of stand basal area had a significant negative correlation with intercrop yields (as a percentage of non-intercropped yields). The slope of the regression line differed between species; in this study, percent yield loss per unit stem basal area growth was in the order E. deglupta > E. torelliana > P. falcataria. The relationship between stand basal area and intercrop-yield decline was tested on an independent data set from China. Intercrop yields had significant negative correlations with stand basal area of Paulownia elongata. We propose that adaptive tree-screening trials evaluate competitiveness in addition to evaluating growth and mortality. Stand basal area may be better suited to this task than more mechanistic indices such as leaf-area index as it is easy to measure, calculate, and understand, and it may serve as a better index of total (aboveground + belowground) competition. Basal area is also directly related to tree volume, and allows farmers to more easily evaluate the economic tradeoffs between tree growth and intercrop-yield declines. This revised version was published online in June 2006 with corrections to the Cover Date.     

Physiological and biochemical leaf and tree responses to crop load in apple

Seven-year-old apple (Malus x domestica Borkh.) trees cv. 'Braeburn' on rootstock M.26 were flower-thinned to establish four crop loads, resulting in final mean fruit numbers per tree of 0, 100, 225 and 400. Mean fruit mass decreased by about 35% with each decrease in cropping density. Fruit from light-cropping trees had significantly advanced maturity as indicated by the harvest management criteria of background color and starch/iodine score, and other fruit quality characteristics such as soluble solids. Flesh firmness and dry matter also increased with decreasing crop load. Compared with fruiting trees, mean leaf photosynthetic rates of non-cropping trees were significantly lower (40%) between 75 days after full bloom (dafb) and fruit harvest, with a maximum reduction of almost 60% at 118 dafb. Photosynthetic activity decreased linearly with increasing concentration of leaf starch, but was positively and significantly related to stomatal conductance. Consequently, the accumulation of nonstructural carbohydrates in leaves of light-cropping or non-cropping trees may have led to end-product inhibition of photosynthesis. Increases in xanthophyll cycle carotenoids mediated non-radiative thermal energy dissipation in non-cropping trees, providing increased capacity for photoprotection but reducing photochemical efficiency.     

Climate change and tree genetic resource management: maintaining and enhancing the productivity and value of smallholder tropical agroforestry landscapes. A review

Anthropogenic climate change has significant consequences for the sustainability and productivity of agroforestry ecosystems upon which millions of smallholders in the tropics depend and that provide valuable global services. We here consider the current state of knowledge of the impacts of climate change on tree genetic resources and implications for action in a smallholder setting. Required measures to respond to change include: (1) the facilitated translocation of environmentally-matched germplasm across appropriate geographic scales, (2) the elevation of effective population sizes of tree stands through the promotion of pollinators and other farm management interventions; and (3) the use of a wider range of ??plastic?? species and populations for planting. Key bottlenecks to response that are discussed here include limitations in the international exchange of tree seed and seedlings, and the absence of well-functioning delivery systems to provide smallholders with better-adapted planting material. Greater research on population-level environmental responses in indigenous tree species is important, and more studies of animal pollinators in farm landscapes are required. The development of well-functioning markets for new products that farmers can grow in order to mitigate and adapt to anthropogenic climate change must also consider genetic resource issues, as we describe.     

Detecting changes in tree health and productivity of silver fir in Slovenia

Cambial electrical resistance (CER) was used as an objective measure of vitality of silver fir (Abies alba) in the forests of Slovenia. Trees were rated during the growing season by CER and a subjective crown status index (CSI). Both CER and CSI were inversely correlated to annual ring width increment. Using both CER and CSI, fir were assigned to vitality and vigour categories. Inferences made from these categories and radial growth trends indicated that ring growth decreased prior to the development of canopy symptoms. This decrease in ring growth would have been detected as an increase in CER. This pattern of decline is consistent with the decline of trees due to chronic below-ground stress. Variation in CER was due both to the vascular cambium and to the thickness of the nonconducting phloem.     

Pruning effects on root distribution and nutrient dynamics in an acacia hedgerow planting in northern Kenya

Tree pruning is a common management practice in agroforestry for mulching and reducing competition between the annual and perennial crop. The below-ground effects of pruning, however, are poorly understood. Therefore, nutrient dynamics and root distribution were assessed in hedgerow plantings of Acacia saligna (Labill.) H.L. Wendl. after tree pruning. Pruning to a height of 1.5 m was carried out in March and September 1996. In July and October 1996, the fine root distribution (< 2 mm) and their carbohydrate contents were determined at three distances to the tree row by soil coring. At the same time, foliar nutrient contents were assessed, whereas nutrient leaching was measured continuously. The highest root length density (RLD) was always found in the topsoil (0–0.15 m) directly under the hedgerow (0–0.25 m distance to trees). Pruning diminished the RLD in the acacia plots at all depths and positions. The relative vertical distribution of total roots did not differ between trees with or without pruning, but live root abundance in the subsoil was comparatively lower when trees were pruned than without pruning. In the dry season, the proportion of dead roots of pruned acacias was higher than of unpruned ones, while the fine roots of unpruned trees contained more glucose than those of pruned trees. Pruning effectively reduced root development and may decrease potential below-ground competition with intercropped plants, but the reduction in subsoil roots also increased the danger of nutrient losses by leaching. Leaching losses of such mobile nutrients as NO₃^– were likely to occur especially in the alley between pruned hedgerows and tended to be higher after pruning. The reduced size of the root system of pruned acacias negatively affected their P and Mn nutrition. Pruning also reduced the function of the trees as a safety net against the leaching of nutrients for both NO₃^– and Mn, though not for other studied elements. If nutrient capture is an important aim of an agroforestry system, the concept of alley cropping with pruning should be revised for a more efficient nutrient recycling in the system described here.This revised version was published online in November 2005 with corrections to the Cover Date.     

Bamboo hedgerow systems in Kerala, India: Root distribution and competition with trees for phosphorus

In a field study on bamboo (Bambusa arundinacea (Retz.) Willd.) hedgerow systems of Kerala, we tested the following three hypotheses: (1) Effective root foraging space is a function of crown spread, (2) Proximity of trees depress lateral spread of roots in mixed species systems and (3) The closer the trees are located the greater will be the subsoil root activity which in turn facilitates active absorption of nutrients from deeper layers of the soil profile. Root distribution of boundary planted bamboo and root competition with associated trees in two binary mixtures, teak (Tectona grandis)-bamboo and Malabar white pine (Vateria indica)-bamboo, were evaluated using modified logarithmic spiral trenching and ³²P soil injection techniques respectively. Excavation studies indicate that rooting intensity declined linearly with increasing lateral distance. Larger clumps manifested wider foraging zones. Eighty three per cent of the large clumps (>4.0 m dia.) extended roots beyond 8 m while only 33% of the small (<2.5 m dia.) clumps extended roots up to 8 m. Highest root counts were found in the 10–20 cm layer with nearly 30% of total roots. Although nearness of bamboo clumps depressed root activity of teak and Vateria in the surface layers of the soil profile, root activity in the deeper layers was stimulated. ³²P recovery was higher when applied at 50-cm depth than at 25-cm depth implying the safety net role of tree roots for leached down nutrients. Inter specific root competition can be regulated by planting crops 8–9 m away from the bamboo clumps and/or by canopy reduction treatments. This revised version was published online in June 2006 with corrections to the Cover Date.