Establishing American sycamore seedlings on land irrigated with paper mill sludge

A study was established to evaluate several management practices for improving American sycamore (Platanus occidentalis L.) establishment on land subjected to daily paper-mill sludge spray irrigation, and where a dense herbaceous cover dominated by pokeweed (Phytolacca americana L.) was nearly 2 m tall. Treatments studied included: two sludge application treatments (spray vs no spray), five weed control treatments (control, hand-release, oxyfluorfen, glyphosate and atrazine, and sulfometuron methyl), and two tree shelter treatments (control vs tree shelter). Survival and growth of sycamore seedlings were evaluated after one growing season. Sludge application treatment had the greatest effect on tree survival; survival was greatest on plots that were not sprayed during the year of tree growth. Among the weed control treatments, the hand-release treatment resulted in best survival; survival was 100% when hand release was used on unsprayed plots. Tree shelters provided no benefit to tree establishment.     

Growth and herbage productivity of Gliricidia in Panicum maximum pasture as influenced by seedbed preparation,planting and weed control techniques

Interplanting Gliricidia (Gliricidia sepium [Jacq.] Walp.) into poor quality native grass can improve the quality of pasture. But information on methods to establish the tree legume into existing pasture is scarce. This study was designed to compare the effects of disc-ploughing, hoeing, or rotary tillage operations, and direct seeding or planting out potted seedlings on growth and dry matter yields of Gliricidia in grass pasture. The Guinea grass (Panicum maximum) pasture was first mowed to a height of 10 cm. Then the seedbed was prepared by either hoeing 0.5 m strip or rototilling 0.5 m strip with a 2-wheel tractor or disc-ploughing 1.0 m strip with a 4-wheel tractor. Eight weeks old potted seedlings were planted or seeds were sown direct. At 6 months after planting (MAP), trees in disc-ploughed strips averaged 81 cm in height, about 35% taller than trees in hoed- or rotary-tilled strips. Potted seedlings (average height 77 cm) grew 37% taller than direct-seeded trees. At 12 MAP trees in disc-ploughed strips yielded 95% more leaf DM (1170 vs. 600 kg/ha) than trees in hoed- or rotary-tilled strips. In order to intercrop Gliricidia into existing Guinea grass pasture, it is necessary to plant potted seedlings previously raised in nursery into 1.0 m wide strips disc-ploughed with 4-wheel tractor. Weed control is necessary.     

Beneficial Effects of Intercropping on the Growth and Nitrogen Status of Young Wild Cherry and Hybrid Walnut Trees

Growing concern for economic and environmental issues emphasizes the potential value of intercropping systems in temperate regions. However, the selection of relevant tree species to be associated with crops has been little documented. The growth and the nitrogen nutrition of two economically valuable species, wild cherry (Prunus avium L.) and hybrid walnut (Juglans nigra L.×Juglans regia L.), were compared over six years after plantation. These two species were associated with non-irrigated cereal crops in the agroforestry treatment or grown separately (weeded control and fallow). Intercropping increased diameter growth as soon as year 2 in the two species. Leaf biomass assessment using allometric models showed an earlier and greater leaf biomass increase in hybrid walnut than in wild cherry tree. After six years, the relative growth increase of the agroforestry trees with respect to the control trees varied with the parameter considered (diameter at breast height from +26 to +65%, leaf biomass from +54 to +142%) and with the tree species (higher relative growth for hybrid walnut trees). The beneficial effect on tree growth can be accounted for in terms of enhanced nitrogen nutrition. The tree–crop association in intercropping systems, which improves tree growth, might thus allow the planting of more demanding trees on soils of lower fertility.     

Ailanthus triphysa at different density and fertiliser levels in Kerala, India: tree growth, light transmittance and understorey ginger yield

Ailanthus triphysa (Family – Simaroubaceae) growth is known to vary in response to different stocking and fertiliser levels. Understorey productivity related to these differences remain elusive, yet are important for optimising the combined production of tree and crop components. A split plot experiment to evaluate the effect of different stocking levels and fertiliser regimes on ailanthus growth, stand leaf area index (LAI) and understorey PAR (photosynthetically active radiation) transmittance was started at Vellanikkara, India in June 1991. Main plot treatments included four densities (3,333, 2,500, 1,660 and 1,111 trees ha⁻¹), replicated thrice. Four fertiliser levels (0:0:0, 50:25:25, 100:50:50 and 150:75:75 kg N:P₂O₅:K₂O ha⁻¹) formed the sub plot treatments. Ginger (Zingiber officinale) was planted as an understorey crop in May 1994 with contiguous treeless control plots. Soil nutrient availability before and after ginger was assessed. Higher densities stimulated ailanthus growth modestly, while fertiliser response of tree and ginger was inconsistent. PAR transmittance below the canopy was related to tree density, LAI and time of measurement. Midday PAR flux having low standard deviations is ideal for evaluating canopy effects on understorey light availability. Ginger in the interspaces exhibited better growth compared to sole crop. Highest rhizome yield was observed in the 2,500 trees ha⁻¹ stocking level, which is optimum for below five year-old ailanthus stands on good sites. It represents 52% mean daily PAR flux or 73% midday PAR flux. Ailanthus+ginger combinations improved the site nutrient capital when ginger was adequately fertilised, despite treeless controls having relatively higher initial soil nutrient availability. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of Initial Spacing on Growth and Branching Characteristics of Cordia africana Trees Established on Eritrean Highland

The study reports on the influence of initial spacing on growth and branching habit of Cordia africana trees established on Eritrean highland. The initial spacings used in this study were 1.0×1.0 m, 1.5×1.5 m, 2.0×2.0 m, 2.5×2.5 m, 3.0×3.0 m, and 3.5×3.5 m; these are equivalent to 1 m², 2.25 m², 4 m², 6.25 m², 9 m² and 12.25 m² in growing space per tree, respectively. No significant relationship between spacing and tree height was found, but increased spacing increased crown diameter and root-collar-diameter. On the other hand, an increase in spacing reduced wood quality because it increased branch diameter (knot size). Thus, from a wood quality perspective, adopting close spacing in plantations of C. africana could be advantageous.     

Establishment of two indigenous timber species in dairy pastures in Costa Rica

A silvopastoral model that combines the production of pasture herbage with valuable native timber species has potential to simultaneously address the multiple goals of reforestation, conservation of native species and enterprise intensification. The objective of this study was to design, establish and monitor early growth of a silvopastoral experiment on a dairy farm in the north Atlantic zone of Costa Rica. Two indigenous timber species, Vochysia guatemalensis and Hyeronima alchorneoides were planted with and without the tropical pasture legume, Arachis pintoi in a split plot design, (2 × 2) factorial arrangement of treatments with four replications. After the first two years, V. guatemalensis was significantly taller (3.1 m) than H. alchorneoides (2.5 m). The mean root collar diameter for V. guatemalensis was significantly larger (6.5 cm) than H. alchorneoides (4.5 cm). Two-year establishment was acceptable for the tree component (83 to 85% survival) but poor for A. pintoi (2 to 8% of the sward). The most important pest affecting the establishment of the timber species was the leaf cutter ant, Atta cephalotes. An insect larvae, Cosmopterix sp., severely damaged 39% of the V. guatemalensis trees by repeatedly attacking their apical meristems. The two-year establishment data was insufficient to accurately predict future wood volume. A hypothetical economic analysis concluded that the silvopastoral system must average at least 1.2 m³ wood volume/paddock/year (20 m³/ha/year) throughout the first ten years of growth to assure a positive economic return from timber. The experiment is planned for a ten year period, which corresponds to the estimated rotation length for harvesting the timber species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Productivity and nutrient cycling in young Acacia senegal farming systems on Vertisol in the Blue Nile region, Sudan

Acacia senegal, the gum arabic-producing tree, is the most important component of traditional dryland agroforestry systems in the␣Sudan. The spatial arrangement of trees and the type of agricultural crop used influence the interaction between trees and crops. Tree and crop growth, gum and crop yields and nutrient cycling were investigated over a period of 4 years. Trees were grown at 5 × 5 m and 10 × 10 m spacing alone or in mixtures with sorghum or sesame. No statistically significant differences in sorghum or sesame yields between the intercropping and control treatments were observed (mean values were 1.54 and 1.54 t ha⁻¹ for sorghum grain and 0.36 and 0.42 t ha⁻¹ for sesame seed in the mixed and mono-crop plots, respectively). At an early stage of agroforestry system management, A. senegal had no detrimental effect on crop yield; however, the pattern of resource capture by trees and crops may change as the system matures. A significant positive relationship existed between the second gum picking and the total gum yield. The second gum picking seems to be a decisive factor in gum production and could be used as an indicator for the prediction of the total gum yield. Soil organic carbon, N, P and K contents were not increased by agroforestry as compared to the initial levels. Soil OC was not increased by agroforestry as compared to sole cropping. There was no evidence that P increased in the topsoil as the agroforestry plantations aged. At a stocking density of 400 trees ha⁻¹ (5 × 5 m spacing), A. senegal accumulated in its biomass a total of 18.0, 1.21, 7.8 and 972 kg ha⁻¹ of N, P, K and OC, respectively. Agroforestry contributed ca. 217 and 1500 kg ha⁻¹ of K and OC, respectively, to the top 25-cm of soil during the first four years of intercropping.     

Growth and water relations of walnut trees (<Emphasis Type="Italic">Juglans regia</Emphasis> L.) on a mesic site in central Italy: effects of understorey herbs and polyethylene mulching

The establishment of trees and associated herbaceous understorey vegetation during the afforestation of former arable lands can decrease soil erosion, increase soil fertility and diversify plantation income. This study reports on the five-year results from experimental plots of common walnut (Juglans regia L.) established in association with two different herbaceous understoreys in 1994 in central Italy. Treatments included: (i) walnut established with plastic film mulching in association with subclover (Trifolium subterraneum L.); (ii) walnut with subclover; (iii) walnut with a spontaneous herbaceous cover (grassing treatment); (iv) clean-cultivated walnut (control). Stem growth rates and the periodical changes in predawn and midday leaf water potentials of walnut, as well as the annual sward dry matter production, were measured. Over the five-years, the understorey vegetation was competitive towards trees, negatively affecting their leaf water status relative to the control, especially during mid-summer observations, with the onset of summer drought. Tree growth in the grassing treatment was slightly but significantly (p < 0.05) reduced in height in comparison to unmulched trees with subclover. Subclover competitiveness towards walnut was completely masked by the plastic mulching, so that mulched walnut with subclover had the highest cumulative stem diameter and height (+20% than control treatment). This was associated with water potentials that were never higher than the control. The subclover-mulched treatment, due to its three main advantages (highest cumulative stem growth, an annual dry matter fodder production of 6.3 t/ha, and soil erosion protection), appears to be a promising cultural model for walnut cultivation in areas without marked drought.     

Foliar Responses of Understorey Abies lasiocarpa to Different Degrees of Release Cutting in a Betula papyrifera and Conifer Mixed Species Stand

Foliar responses of subalpine fir [Abies lasiocarpa (Hook.) Nutt.] to thinning were studied in a 35-yr-old mixed stand of paper birch (Betula papyrifera Marsh.) and conifers. The stand regenerated naturally after a wildfire with a canopy dominated by paper birch (average height 9.8 m) and an understorey dominated by subalpine fir (average height 1.6 m). The stand was thinned to four densities of birch: 0, 600 and 1200 stems ha-¹ and control (unthinned at 2300-6400 stems ha-¹) in the autumn of 1995. The understorey conifers, mainly subalpine fir, were thinned to 1200 stems ha-¹. The study used a completely randomized split-plot design. Three sample trees were systematically selected from each treatment replicate and each tree stratum (upper, intermediate and lower understorey). One-year-old and older age class needles were collected from one south-facing branch within the fifth whorl from the tree top. Thinning of paper birch significantly (p <0.001) increased leaf area and dry weight per 100 needles for intermediate and short trees except in the 0 birch treatment. Understorey subalpine fir trees in 600 stems ha¹ birch (T3) had the largest leaf area and leaf dry weight per 100 1-yr-old needles. Specific leaf area (SLA) decreased from unthinned (T1) to 0 birch (T4). Lower understorey trees had the largest SLA. One-year-old needles had significantly higher N, P and K concentrations in all the thinning treatments. These responses are consistent with the shade tolerance of subalpine fir. The results suggest that when managing a paper birch-conifers mixed-wood forest it may be of benefit to understorey conifers to leave a birch canopy as a nursing crop.     

Biological nitrogen fixing capacity and biomass production of different understorey pastures in a Pinus radiata-pasture agroforestry system in New Zealand

Quantitative field measurements of biological nitrogen fixation (BNF) and biomass production by four different understorey pastures in a Pinus radiata-pasture agroforestry system were determined over a period of one year. The trees were two years old at the beginning of this study and the understorey pastures were being cut and removed for silage. The BNF was determined using the ¹⁵N dilution technique. Pastures of ryegrass+clover, cocksfoot+clover, phalaris+clover and lucerne were used. Substantial amounts of BNF were found (71 to 230 kg N ha^–1 year^–1) with lucerne showing the highest N fixation. However, lucerne derived only 71 to 72% of its N from the atmosphere (%Ndfa) during the spring/summer period compared to 83–97% with clovers, thus the net N demand from the soil was substantially higher with lucerne. This caused increased N stress to the trees. Clover in ryegrass+clover pasture fixed more N than the other grass+clover pastures. Although pasture position in relation to trees did not affect annual pasture total DMY and %Ndfa, pastures north of tree row grew better than those in other positions. Trees significantly affected the BNF of legumes and the botanical composition of pastures with highest BNF and legume production occurring in pastures midway between two rows of trees. These results suggest that it would be advantageous to evaluate different legumes and grasses for tolerance of shade and moisture stress in future studies. As the trees studied were only 1.5 to 3 m in height, their effects on BNF, seasonal pasture biomass production and botanical composition are expected to increase with tree dominance in the ecosystem with time. Amounts of N fixed were related to the productivity (i.e. dry matter and N yield) and seasonal persistence of the legumes. The productivity was high in spring and summer and low in autumn and winter.     

Aboveground biomass and nitrogen in four short-rotation woody crop species growing with different water and nutrient availabilities

We quantified the effect of water and nutrient availability on aboveground biomass and nitrogen accumulation and partitioning in four species from the southeastern United States, loblolly pine (Pinus taeda), slash pine (Pinus elliottii), sweetgum (Liquidambar styraciflua), and sycamore (Platanus occidentalis). The 6-year-old stands received five levels of resource input (control, irrigation with 3.05 cm water week⁻¹, irrigation + 57 kg N ha⁻¹ year⁻¹, irrigation + 85 kg N ha⁻¹ year⁻¹, and irrigation + 114 kg N ha⁻¹ year⁻¹). Irrigation significantly increased foliage, stem, and branch biomass for sweetgum and sycamore, culminating in 103% and 238% increases in total aboveground biomass. Fertilization significantly increased aboveground components for all species resulting in 49, 58, 281, and 132% increases in total aboveground biomass for loblolly pine, slash pine, sweetgum, and sycamore, respectively. Standing total aboveground biomass of the fertilized treatments reached 79, 59, 48, and 54 Mg ha⁻¹ for loblolly pine, slash pine, sweetgum, and sycamore, respectively. Fertilization increased foliar nitrogen concentration for loblolly pine, sweetgum, and sycamore foliage. Irrigation increased total stand nitrogen content by 6, 14, 93, and 161% for loblolly pine, slash pine, sweetgum, and sycamore, respectively. Fertilization increased total nitrogen content by 62, 53, 172, and 69% with maximum nitrogen contents of 267, 212, 237, and 203 kg ha⁻¹ for loblolly pine, slash pine, sweetgum, and sycamore, respectively. Growth efficiency (stem growth per unit of leaf biomass) and nitrogen use efficiency (stem growth per unit of foliar nitrogen content) increased for the sycamore and sweetgum, but not the loblolly or slash pine.     

Shoot production through cutting culture and micrografting from mature tree explants inAcacia tortilis (Forsk.) Hayne subsp.raddiana (Savi) Brenan

Shoot propagation from mature tree explants ofAcacia tortilis subsp.raddiana, a tropical tree legume, was studied. The effects of (i) the size of cuttings and (ii) a recut treatment of the donor trees, on axillary bud growth from multinodal horticultural cuttings are reported. Apices from seedlings, axillary buds from young lignified branches of mature trees, and axillary buds obtained through in vitro axillary branching from microcuttings isolated onto mature trees were all successfully micrografted on seedling rootstocks. A sterilization procedure for field explants is reported. Propagation via cuttings and via micrografting are discussed with regard to rejuvenation of mature donor trees.     

Influence of soil properties on the growth of sycamore (<Emphasis Type="Italic">Acer pseudoplatanus </Emphasis>L.) in Denmark

Despite high demand on the timber, sycamore (Acer pseudoplatanus L.) covers only about 2% of the forested area in Denmark, mainly because several examples of failed stands have made foresters reluctant to grow sycamore. In order to optimize the use of sycamore, scientifically based knowledge is needed on the specific demands of sycamore to soil properties. Therefore, 34 stands of sycamore covering a broad range of soil types, tree heights and ages were investigated. Tree height and age were determined on 20 trees in each stand and combined into a site index. In each stand, soil water status, slope and ground cover were determined and soil samples were taken and analyzed for pH, organic carbon, total nitrogen, calcium carbonate, bulk density and texture in the laboratory. The data were analyzed by simple regression supplemented by PCA and MLR. Accordingly, sycamore can grow well on a broad range of soils regarding texture and water content. However, soils with stagnant water within 40 cm of the soil surface are unsuited for sycamore. On well-drained soils, increasing clay content caused better sycamore growth, which was also improved on insufficiently drained soils with calcium carbonate. Increased nitrogen content stimulated sycamore growth while, less productive stands occurred on carbon rich soils indicating that carbon and nitrogen contents can serve as sycamore growth indicators. Bulk density, C/N ratio and pH showed no significant influence on growth. The investigation showed that sycamore could grow well on a broader range of soils than hitherto believed.     

Growth and quality response of Bilinga (Nauclea Diderrichii Merril.) to spacing

The effect of spacing on growth and tree bole quality was examined in a seven year old Bilinga (Nauclea diderrichii Merril.) stand. Four spacings ranging from 2.5 m to 5.0 m, were planted in a complete randomozed block design with three replications. Survival rate was significantly affected by spacing only at age 7. Diameter at breast height (DBH), crown ratio and number of knotty trees increased with wider spacing, while basal area and number of dead limbs increased inversely with spacing. Spacing did not seem to have any significant effect on total height growth. Trends in this study confirm some commonly held beliefs about spacing's effect on tree growth and quality. The results are still of limited application due to the juvenile age of the stand.     

Factors influencing the formation of heartwood discolouration in sycamore (<Emphasis Type="Italic">Acer pseudoplatanus</Emphasis> L.)

Sycamore (Acer pseudoplatanus L.) is a tree species with highly valuable wood. Similar to European beech (Fagus sylvatica L.), the stemwood of sycamore can be devalued due to the discolouration i.e. brown heart (hearwood discolouration, hereafter). This paper aims to establish the influence of tree traits and site characteristics on the formation of heartwood discolouration and the possibility of predicting the occurrence of heartwood discolouration. For this purpose, 351 sycamore trees from 38 sites in Slovenia, most of them on carbonate bedrock and in the mountain vegetation belt, were analysed. Stem analysis was carried out on all the trees and the age, diameter at breast height (dbh), height of crown base, forking and crown size, were established. On the stump and upper fronts of the first and second logs, the maximum heartwood discolouration diameter was measured. Using logistic regression, the positive influence of age, relative crown length and average diameter increment on the formation of heartwood discolouration was ascertained. Conversely, the probability of heartwood discolouration was diminished by diameter increment in the last 20 years. In the less productive sites, the probability of formation of heartwood discolouration was relatively high in small diameter trees, but it increased slowly with diameter. Tree forking also contributed to a large extent of the heartwood discolouration. After the diameter at breast height achieves 45 cm, the formation of heartwood discolouration on the first log is highly probable. As in beech, the heartwood discolouration increases along the stem axis up to a height of 6–8 m, and decreases in the higher parts of the tree.     

Effect of tree spacing on growth and wood density of 38-year-old Cariniana legalis trees in Brazil

Average wood density of 38-year-old Cariniana legalis (Mart.) Kuntze, a Brazilian native forest species, was found to increase with faster growth and lower stocking, while decreasing from pith to bark. A complete randomised block design was planted with five blocks. Ten trees were harvested in each of three spacing treatments. We hypothesised that the stand stemwood production would not significantly differ depending on tree spacing. However, tree growth would be higher in the wider spacing and wood density would be higher in the narrower spacing. The diameter growth of trees was higher at 3 m × 2.5 m than at 3 m × 2 m and 3 m × 1.5 m. Nevertheless, this higher individual tree growth at 3 m × 2.5 m did not compensate for the greater tree stock density at 3 m × 1.5 m with stand stemwood production at 38 years of 530 m3 ha^?1 and 649 m³ ha^?1, respectively. These results suggest that C. legalis, which can produce up to 17 m³ ha^?1 y^?1 of medium-to high-density timber – about 800 kg m^?3 – is a promising native species for forest plantations in Brazil.     

Long-term growth analyses of Japanese cedar trees in a plantation: neighborhood competition and persistence of initial growth deviations

The individual growth of tree diameter at breast height (dbh) is analyzed in an even-aged plantation of Cryptomeria japonica from stand age of 45 to 94 years, to examine how the growth of individual trees has been affected by the changes in spacing resulting from thinning operations. At any age, a significant proportion (0.37–0.46) of the variation in dbh growth during a 5–11-year period was explained by dbh at the beginning of the period, probably due to greater leaf mass of larger trees. Next, either one-sided or two-sided competition was added to the model, by calculating the basal area (BA) of neighboring trees around each tree within a given radius or BA for trees having larger dbh than the focal tree within the radius. After preliminary analyses, a radius of 8 m was selected as the critical range for tree competition. Although both types of competition explained a significant proportion (0.09–0.43) of growth variation, one-sided competition was not significant at ages greater than 54 years. Based on the model at 45 years of age, the initial deviation of growth rate for each tree from the predicted rate was calculated and added to the models as a third variable. This raised the coefficient of determination up to 0.50–0.74. These findings have practical significance for forest plantation management, particularly for controlling the growth of standing trees via thinning, to produce high-quality timber in the future.     

Decomposition of woody legume nodules in two tree/grass associations under contrasting environmental conditions

Turnover of nitrogen-rich root nodules follows the pruning of legume trees, forming a potentially important yet little studied way of N release to the soil. The effects of soil moisture, herbivory by soil mesofauna and microbial decomposition on the disappearance rate of woody legume nodules was studied in two tree/grass forage production associations. Litter bags containing nodules of Erythrina variegata L. (Papilionoideae: Phaseoleae) were incubated for four weeks in grass-covered alleys between Gliricidia sepium (Jacq.) Walp. (Papilionoideae: Robinieae) hedgerows, established on a deep alluvial Oxisol under a humid tropical climate and on a shallow Vertisol under a subhumid tropical climate in Guadeloupe, French Antilles. Soil moisture was regulated by irrigating or covering small plots from natural rainfall. Fine nylon mesh bags were used to study the rate of microbial decomposition, and open-ended perforated cylinders were used to estimate nodule herbivory. The chemical traits, especially the lignin: nitrogen ratio, of E. variegata and G. sepium nodules were similar (lignin: N 1.70 and 1.55, respectively), and suggest that the results are probably also applicable to the G. sepium nodules in the associations. Both soil moisture and decomposing agent (microbes or mesofauna) had a significant effect on the nodule disappearance rate, but soil type did not have any apparent effect. The nodule half-life varied from three to seven days under different treatments. The N release rate from the nodules was high, with N half-life varying from three to five days. Herbivory accounted for ca. 10% of total mass and N loss from nodules during the four-week field incubation period, but its importance increased towards the end of the incubation, especially in Vertisol, after the most easily decomposable part of the nodules had decayed. After pruning, the nodule N is released to soil more rapidly than from mulch. This revised version was published online in June 2006 with corrections to the Cover Date.     

Competition for light, water and nitrogen in an association of hazel (Corylus avellana L.) and cocksfoot (Dactylis glomerata L.)

Competition for light, water and nitrogen between hazel trees and cocksfoot grown under the trees was studied in two hazel plantations managed in different ways. The first plantation with a light transmission of at least 70% at grass level was compared with two control hazel and cocksfoot monocrops. The soil was a calcareous heavy clay, 1.4 m deep. Water stress during summer was severe in the intercropped stand as well as the grass- only plots, while it was much less in the sole stand of trees (without grass). Hazel tree water potential in the intercropped stand improved in the fourth year as the trees extended their roots similarly to the grass-free ones, despite their much lower canopy growth rate. The fourth year, local N fertilisation began to be effective as evidenced by the N content per leaf area unit and growth of the intercropped trees: grass root competition was high and root barriers were needed to exclude it. The second plantation was managed on a deep soil with a water table at approximately 2.5 m depth. The trees did not suffer from the presence of grass, and allowed a 15 to 75% light transmission rate. A control monocropped grass plot was established for comparison. On the basis of the multiple limitation hypothesis, a grass dry matter production model was built which accounts for radiation transmitted to the understorey, water supply, temperature and air moisture deficit in interaction with the radiation transmission rate (r2 = 0.716; 590 observations). The limits of such models are discussed with regard to insufficient knowledge on root dynamics. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of spacing on growth and biomass production of Gliricidia sepium (jacq) walp in an alley cropping system in Sierra Leone

This paper describes a study into the influences of spacing on the early performance and biomass production of Gliricidia sepium in an alley cropping system in southern Sierra Leone. Four between-row spacings of 2, 4, 6 and 8 m were combined with three within-row spacings (0.25, 0.50 and 1.00m) in a split plot experimental design.Survival, tree height and leaf nitrogen content were not affected by between- or within-row spacings. For the other parameters measured, namely root-collar diameter, branch production, total biomass and nitrogen yields per hectare, it was found that for equivalent tree densities, the lower the rectangularity of planting, the better the performance of the individual trees, and consequently the greater the yields per hectare.Total biomass production per unit area was, expectedly, greatest where the spacings between hedgerows were closest, while production per plant decreased with closer within-row spacings. The total fresh and dry weights of leaves and stems, as well as leaf nitrogen yields per unit area were strongly influenced by between-row spacing and less so by within-row spacing.