Composted biosolids as a source of iron for hybrid poplars (<Emphasis Type="Italic">Populus</Emphasis> sp.) grown in northwest New Mexico

Composted sewage sludge (biosolids) supply plant available Fe and may represent a sustainable alternative to more costly chelated Fe fertilizers currently used to supplement nutrition in hybrid poplar test plots of elevated soil pH. To test the response of poplars, field plots were amended with composted biosolids at two agricultural rates: 22.75 and 44.5 Mg ha⁻¹. Iron EDDHA served as a fertilizer check and control plots received no amendment. The hybrid poplar OP-367 (Populus deltoides × P. nigra) was planted on a 3.6 m grid spacing. Significant amounts of P and Fe originating from the sewage treatment process were detected in soils 13 months after amending. Chlorosis evaluated with a SPAD-502 meter, showed that poplars amended with biosolids remained the least chlorotic and had greater tree growth when compared to Fe EDDHA and control plots during two growing seasons. Biosolids show promise as a cost effective alternative for the remediation of Fe chlorosis in hybrid poplar agroforestry plantations and present new opportunities in northwestern New Mexico for municipalities seeking solid waste land disposal options.     

A low-cost method of mycorrhizal inoculation improves growth of Acacia tortilis seedlings in the nursery

A pot experiment in Kenya examined the effects of mycorrhizal and rhizobial inoculation on the growth and symbiont infection of Acacia tortilis seedlings in unsterile soil, in comparison with sterile and unsterile soil controls. Three mixed, arbuscular mycorrhizal inocula, originating from A. tortilis, Terminalia brownii, T. spinosa and Prosopis juliflora (produced under nursery conditions), were used to inoculate the seedlings, which also received a standard, mixed, rhizobial inoculum. Mycorrhizal infection and plant growth were significantly affected by experimental treatment (p<0.001). Some mycorrhizal infection (presumably with indigenous soil-borne inoculum) occurred in the unsterile soil control, but not in the sterile soil control, indicating that transfer of inoculum between pots in the experiment did not occur. Mycorrhizal formation was significantly more extensive in inoculated plants, which also had better shoot and root growth. 24 weeks after inoculation, plants which had received inoculum of A. tortilis origin were 105 mm tall and their roots were 56% mycorrhizal, whereas the controls most representative of normal nursery treatment were only 77 mm tall and 29% mycorrhizal. Nodulation was erratic and poor in all treatments. The results suggest that mycorrhizal inoculation can improve both mycorrhizal infection and growth of tree seedlings in unsterile nursery soil. The methods of culture and inoculation described here could easily be adopted by nurseries at little cost.     

Phosphorus uptake and maize response to organic and inorganic fertilizer inputs in Rubona,Southern Province of Rwanda

Green manure of multipurpose trees is known to be a good source of nutrients to crop. However, most agroforestry species do not have adequate phosphorus (P) in their leaves. Supplementing green manure with moderate dose of P is a beneficial strategy to improve food security in Rwanda. This study examines the effects of Calliandra calothyrsus Meissner, Tithonia diversifolia Hensley A.Gray and Tephrosia vogelii Hook.f. green manure applied independently or in combination with triple super phosphate (TSP) and lime on maize yield and P uptake in the Oxic Tropudalf of Rubona, Rwanda. The treatments were the control, lime at 2.5 t ha⁻¹, TSP at 25 and 50 kg P ha⁻¹, leaf of C. calothyrsus, T. diversifolia, and T. vogelii each at 25 and 50 kg P ha⁻¹, respectively. Leaf shrubs biomass, TSP and lime were applied for four consecutive seasons (2001–2004). The results showed that the combination of green manure with TSP at a rate of 50 kg P ha⁻¹ significantly increased maize yield from 24 to 508% when compared to the control and T. divesifolia combined with TSP was leading (508%). Equally, the same treatments as indicated above showed higher P uptake (15.6–18. 6 kg P ha⁻¹) than the control (5 kg P ha⁻¹) and 65% of maize yields variation was explained by total P uptake. The plant residues quality such as C:N ratio, total plant N, and P significantly influenced the variability of maize grain yields.     

Biomass production and carbon stocks in poplar-crop intercropping systems: a case study in northwestern Jiangsu,China

The importance of agroforestry systems in CO₂ mitigation has become recognized worldwide in recent years. However, little is known about carbon (C) sequestered in poplar intercropping systems. The main objective of this study is to compare the effects of three poplar intercropping designs (configuration A: 250 trees ha⁻¹; configuration B: 167 trees ha⁻¹ and configuration C: 94 trees ha⁻¹) and two intercropping systems (wheat–corn cropping system and wheat–soybean cropping system) on biomass production and C stocks in poplar intercropping systems. The experiment was conducted at Suqian Ecological Demonstration Garden of fast-growing poplar plantations in northwestern Jiangsu. A significant difference in C concentration was observed among the poplar biomass components investigated (P ≤ 0.05), with the highest value in stemwood and the lowest in fine roots, ranging from 459.9 to 526.7 g kg⁻¹. There was also a significant difference in C concentration among the different crop components (P ≤ 0.05), and the highest concentration was observed in the corn ear. Over the 5-year period, the total poplar biomass increased with increasing tree density, ranging from 8.77 to 15.12 t ha⁻¹, while annual biomass production among the crops ranged from 4.69 to 16.58 t ha⁻¹ in the three configurations. Overall, total C stock in the poplar intercropping system was affected by configurations and cropping systems, and configuration A obtained the largest total C stock, reaching 16.7 t C ha⁻¹ for the wheat–soybean cropping system and 18.9 t C ha⁻¹ for the wheat–corn cropping system. Results from this case study suggest that configuration A was a relative optimum poplar intercropping system both for economic benefits and for C sequestration.     

Can soil plant analysis development values predict chlorophyll and total Fe in hybrid poplar?

Iron chlorosis caused by an elevated soil pH remains an important selection criteria in evaluating hybrid Populus trials in northwest New Mexico. Compared to expensive extraction methods or visual ranking scales, the soil plant analysis development (SPAD) chlorophyll meter is a handheld tool that objectively indicates leaf color. SPAD calibration curves pertaining to Fe status in Populus leaves were developed for two clones: NM-6 (Populus nigra × Populus maximowiczii) and OP-367 (Populus deltoides × Populus nigra). Hybrids were grown in the greenhouse in a sandy loam soil of pH > 8 and the same soil amended with composted biosolids enriched with 420 mg kg⁻¹ Fe. SPAD measurements related to foliar Fe as follows: r ² = 0.72 for NM-6 and r ² = 0.58 for OP-367. SPAD measurements correlated with total chlorophyll as follows: r ² = 0.66 for NM-6 and r ² = 0.85 for OP-367. Based on the total chlorophyll content (supported with foliar element data), Fe sufficiency threshold values from SPAD measurements were estimated in these two clones.     

Applications of black walnut husks can improve orchardgrass and red clover yields in silvopasture and alley cropping plantings

Black walnut (Juglans nigra L.) produces both valuable lumber and a nut crop. Because of this, it is an important tree for agroforestry plantings in the Midwest USA. However, during processing of the nut crop, the outer tissue of the nut (husks) accumulates in great quantities. Applying this material to pastures is a possible method of disposal. However, black walnut has been implicated in allelopathic interactions with numerous plant species and may inhibit the growth of pasture species. Greenhouse and field studies and a chemical analysis of the husks were conducted to determine the effects of applying walnut husks to orchardgrass (Dactylis glomerata L.) or red clover (Trifolium pratense L.) pastures. Applying husks at rates up to 68 Mg ha⁻¹ to pot-grown orchardgrass resulted in root and shoot yields that were greater than in pots receiving no husks. Field studies indicated that orchardgrass and red clover benefited from the application of husks. For orchardgrass, significant increases in growth occurred when husks were applied at a rate of 34 Mg ha⁻¹ while red clover responded to rates up to 68 Mg ha⁻¹. A chemical analysis of husks indicated that significant quantities of N and K were present in walnut husks. A whole effluent toxicity test (WETT) indicates that runoff from walnut husk-treated pastures, at the rates used in this study, would not adversely affect aquatic organisms.     

Optimum pruning intensity for reducing crop suppression in a <Emphasis Type="Italic">Gmelina</Emphasis>–maize smallholder agroforestry system in Claveria,Philippines

On-farm trials were conducted to assess the effects of four branch pruning levels on maize grain yield, tree growth and stem shape. The experimental plots consisted of Gmelina (Gmelina arborea R.Br.) trees planted at 1 × 10 m with maize intercropped in the 10 m-wide alleys between lines of trees. Pruning levels consisted of retaining a live crown ratio of 60–70% (T ₁), 40–50% (T ₂); 30–40% (T ₃) and of 20–30% (T ₄). At the end of the experiment, the total maize grain yield was highest under the high pruning intensity (T ₄) (18.06 t ha⁻¹) and lowest under T ₁ (14.48 t ha⁻¹). Maize grain yield under the pruning regime T ₂ and T ₃ were 16.08 and 17.21 t ha⁻¹, respectively. Mean annual increment (MAI) in tree diameter was greater (5.0 cm year⁻¹) under T ₁ than those at T ₄ (4.1 cm year⁻¹). Pruning regimes T ₂ and T ₃ resulted in a MAI of 4.7 and 4.5 cm year⁻¹, respectively. Financial analysis showed that maize-tree systems under T ₄ were more profitable than under T ₁ as long as the reduction of the average dbh at harvest were not greater than 1 cm. Pruning trees intensively also generated greater returns from labour than moderate pruning, as the greater maize grain yields under T ₄ compensated for the cost of pruning and the lower timber yield. In the context of resource-poor farmers, intensive branch pruning was a practice that prolonged the period of profitable intercropping and was compatible with commercial timber production.     

Eucalyptus plantations in Israel: an assessment of economic and environmental viability

This paper discusses a plantation management approach involving a combination of “short” and “long” rotations designed to allow farmers to receive income from trees as soon as possible after establishment. We present results from two plots that represent extreme conditions: (a) a seasonally waterlogged, non-saline site (Nahalal), and (b) a saline site (Ginnegar) located in the Yizre’el Valley, Israel. Six improved seed sources, four of Eucalyptus camaldulensis and two of E. occidentalis, were examined. The local Israeli seed source of E. camaldulensis (HA) performed best at both sites. In Nahalal, the short rotation thinning of the slower growing (50%) plantation trees could provide economic returns approximately five years after establishment. The calculated mean annual increment (MAI) of these trees reached 12.2 t ha⁻¹ year⁻¹. The long rotation, or better performing half of the plantation trees, could be used as a source of sawn timber, providing higher-value products. By nine years after establishment, the average DBH of the various seed sources reached 25.8 ± 1.9 cm. The calculated MAI of the combined cutting rotations reached 48.3 t ha⁻¹ year⁻¹. Eucalyptus grown under the combined (short- and long-term) management approach at Nahalal was more profitable than many other non-irrigated local crops. Eucalyptus production in Ginnegar would be less profitable than in Nahalal. However, an additional ecological benefit was provided by the crop’s ability to lower the water table. When this contribution to regional drainage is taken into account, trees become economically competitive with other non-irrigated field crops under saline conditions. Jim Morris–Deceased.     

Arbuscular mycorrhizal fungi in the rhizosphere of Macaranga denticulata Muell. Arg., and their effect on the host plant

A fallow enriching tree, Macaranga denticulata Muell. Arg., has been shown to increase rice yield in a rotational shifting cultivation system in northern Thailand through increased accumulation of mineral nutrients. As arbuscular mycorrhizal (AM) fungi may play an important role in nutrient accumulation, AM fungi in the rhizosphere of M. denticulata and the effects of the indigenous soil inoculum on the host plant were investigated. The diversity and abundance of AM fungi were documented for the rhizosphere of M. denticulata in the field for two years. Based on morphology, 29 species of AM fungi were found in the rhizosphere of M. denticulata growing in farmers’ fields. Root colonization ranged from 63.5 to 81.5% in the first year and 68.7 to 79.9% in the second year of study. The highest spore density was observed at the end of the wet season. The effects of indigenous soil inoculum, and N and P fertilizers on the host plant were investigated in pots for four months. Inoculation with soil-containing AM fungi strongly increased plant growth and nutrient contents when P was limiting but N was applied. Application of N and P together strongly depressed root colonization and spore density of AM fungi, whereas applying them separately had much less effect. AM fungi may play an important role in nutrient accumulation in M. denticulata-rich fallow and thus in nutrient cycling that is beneficial to the maintenance of upland rice yield and sustainability of the rotational shifting cultivation system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Positive nitrogen balance of <Emphasis Type="Italic">Acacia mangium</Emphasis> woodlots as fallows in the Philippines based on <Superscript>15</Superscript>N natural abundance data of N<Subscript>2</Subscript> fixation

Nitrogen inputs from biological nitrogen fixation contribute to productivity and sustainability of agroforestry systems but they need to be able to offset export of N when trees are harvested. This study assessed magnitudes of biological nitrogen fixation (natural ¹⁵N abundance) and N balance of Acacia mangium woodlots grown in farmer’s fields, and determined if N₂ fixation capacity was affected by tree age. Tree biomass, standing litter, understory vegetation and soil samplings were conducted in 15 farmer’s fields growing A. mangium as a form of sequential agroforestry in Claveria, Misamis Oriental, Philippines. The trees corresponded to ages of 4, 6, 8, 10 and 12 years, and were replicated three times. Samples from different plant parts and soils (0–100 cm) were collected and analyzed for δ¹⁵N and nutrients. The B-value, needed as a reference of isotopic discrimination when fully reliant on atmospheric N, was generated by growing A. mangium in an N₂-free sand culture in the glasshouse. Isotopic discrimination occurring during N₂ fixation and metabolic processes indicated variation of δ¹⁵N values in the order of nodules > old leaves > young leaves > stems > litterfall and roots of the trees grown in the field, with values ranging from −0.8 to 3.5‰ except nodules which were enriched and significantly different from other plant parts (P < 0.0001). Isotopic discrimination was not affected by tree age (P > 0.05). Plants grown in N free sand culture exhibited the same pattern of isotopic discrimination as plants grown in the field. The estimated B-value for the whole plant of A. mangium was −0.86‰. Mature tree stands of 12 years accumulated up to 1994 kg N ha⁻¹ in aboveground biomass. Average proportion of N derived from N₂ fixation of A. mangium was 54% (±22) and was not affected by age (P > 0.05). Average yearly quantities of N₂ fixed were 128 kg N ha⁻¹ in above-ground biomass amounting to 1208 kg N fixed ha⁻¹ over 12 years. Harvest of 12-year old trees removed approximately 91% of standing aboveground biomass from the site as timber and fuel wood. The resulting net N balance was +151 kg N ha⁻¹ derived from remaining leaves, twigs, standing litter, and +562 kg N ha⁻¹ when tree roots were included in the calculation. The fast growing A. mangium appears to be a viable fallow option for managing N in these systems. However, other nutrients have to be replaced by using part of the timber and fuel wood sales to compensate for large amounts of nutrient removed in order for the system to be sustainable.     

Maize yields under coppicing and non coppicing fallows in a fallow–maize rotation system in central Zimbabwe

Fallowing can improve crop yields as a result of improved soil fertility and nutrient status. The objective of this work was to determine the effects of fallows and pruning regimes in coppicing fallows on soil moisture and maize yields under conventional tillage (CT) and no tillage (NT). Fallows that were evaluated were coppicing Acacia angustissima, non coppicing Sesbania sesban, natural fallow (NF) and continuous maize. In 2000/2001 season, maize yields were significantly different (P < 0.05) among treatments and were; 1.8, 1.2, 0.7 and 0.5 tonnes per hectare (t ha⁻¹) under CT, while under NT yields were 1.3, 0.8, 0.7 and 0.2 t ha⁻¹ for A. angustissima, maize, S. sesban and NF plots respectively. In 2001/2002 season, yields decreased in the order S. sesban > continuous maize > NF > A. angustissima, for both CT and NT. The 2-week pruning regime had significantly higher maize yields when compared to the 1 and 3 week pruning regime during the 2002/2003 cropping season. For the three seasons, CT had significantly higher yields than NT. A. angustissima had significantly higher mean available water at suctions <33 kPa for the 0–25 cm depth when compared to other fallow treatments. The bulk of the available water (47–80%) was retained at suction <33 kPa for all treatments and depths. There were no treatment differences in water retention at suctions >33 kPa for all treatments. It was concluded that improved fallowing increased yields when compared to NF. However, in coppicing fallows competition for water can result in reduced yields when there is rainfall deficiency, thus the need for pruning to manage the competition.     

Fine root production and turnover in Brazilian Eucalyptus plantations under contrasting nitrogen fertilization regimes

Nitrogen fertilization increased largely over the last decade in tropical eucalypt plantations but the behaviour of belowground tree components has received little attention. Sequential soil coring and ingrowth core methods were used in a randomized block experiment, from 18 to 32 months after planting Eucalyptus grandis, in Brazil, in order to estimate annual fine root production and turnover under contrasting N fertilization regimes (120 kg N ha⁻¹ vs. 0 kg N ha⁻¹). The response of growth in tree height and basal area to N fertilizer application decreased with stand age and was no longer significant at 36 months of age. The ingrowth core method provided only qualitative information about the seasonal course of fine root production and turnover. Mean fine root biomasses (diameter <2 mm) in the 0–30 cm layer measured by monthly coring amounted to 0.91 and 0.84 t ha⁻¹ in the 0 N and the 120 N treatments, respectively. Fine root production was significantly higher in the 0 N treatment (1.66 t ha⁻¹ year⁻¹) than in the 120 N treatment (1.12 t ha⁻¹ year⁻¹), probably as a result of the greater tree growth in the control treatment throughout the sampling period. Fine root turnover was 1.8 and 1.3 year⁻¹ in the 0 N and the 120 N treatments, respectively. However, large fine root biomass (diameter <1 mm) was found down to a depth of 3 m one year after planting: 1.67 and 1.61 t ha⁻¹ in the 0 N and the 120 N treatments, respectively. Fine root turnover might not be insubstantial in deep soil layers where large changes in soil water content were observed.     

Response of <Emphasis Type="Italic">Theobroma cacao</Emphasis> and <Emphasis Type="Italic">Inga edulis</Emphasis> seedlings to cross-inoculated populations of arbuscular mycorrhizal fungi

Response of Theobroma cacao L. (cacao) and the shade tree Inga edulis Mart. (inga) seedlings from an organically-grown cacao plantation to inoculation with native arbuscular mycorrhizae forming fungi (AMF) was studied in a cross-inoculation assay under greenhouse conditions. Seedlings of inga and cacao were grown in pots filled with heat-treated soil from the plantation. Control was heat-treated soil without inoculum and roots of cacao and inga from the plantation were applied as AMF inocula. Undisturbed soil blocks were used as a “positive control” of the inoculation potential of untreated soil and roots combined. No AMF structures were observed in the roots of either species in the heat-treated control. All inocula were infective in both hosts and the differences in the total AMF colonization percentage between the hosts were not significant but inga had significantly higher colonization by hyphal coils and arbuscules. Cacao roots but neither inga roots nor soil block inocula stimulated cacao growth. All inocula significantly increased growth of inga, which had higher relative mycorrhizal responsiveness than cacao. Thus, in spite of the strong infectivity of the inocula in both hosts, cacao and inga responded differently to the same AMF populations. The strong conspecific preference of cacao suggests that attention must be paid to the AMF inoculum used for this species. However, the strong response of inga to cacao root inoculum indicates that the two species may share same AMF symbionts, thus enabling positive interactions between them, including formation of common mycelial networks.     

Traditional agroforestry systems as tools for conservation of genetic resources of Milicia excelsa Welw. C.C. Berg in Benin

The potential contribution of agroforestry systems to the management and genetic resources conservation in iroko (Milicia excelsa), an important and valuable timber tree species in sub-Saharan Africa, is addressed in this paper. The structure and dynamics of traditional agroforestry systems and the ecological structure of Milicia excelsa populations in farmlands were studied through a survey carried out in 100 farmlands covering the natural range of iroko in Benin. Forty-five species belonging to 24 plant families were recorded in traditional agroforestry systems. Average tree density varied from 1 to 7 stems ha⁻¹ with diversity index ranging from 2.6 to 2.9. Milicia excelsa occurred sparsely in agroforestry systems in all regions, with density ranging from 1 to 4 stems ha⁻¹; stand basal area varying from 33.10⁻⁴ to 129.10⁻⁴ m² ha⁻¹, and negligible seedling regeneration. However, male and female trees were apparently evenly distributed on farmlands in all regions (F/M > 0). Iroko trees produced viable seeds with moderate germination rate and early growth (germination rate 22% and height 7.29 cm after 3 months). Suggestions are made regarding optimal densities for iroko conservation in farmlands, according to farmers’ socioeconomic conditions in different regions, in order to improve traditional agroforestry systems and their use as biological corridors in conservation of Milicia excelsa genetic resources.     

A comparison of different methods for forest resource estimation using information from airborne laser scanning and CIR orthophotos

This article compares three methods for forest resource estimation based on remote sensing features extracted from Airborne laser scanning and CIR orthophotos. The estimation was made exemplarily for the total stem volume of trees for a given area, measured in cubic metres per hectare [m3 ha⁻¹] (as one of the most important quantitative parameters to characterise a forest stand). The following methods were compared: Regression Analysis (RA), k-NN (nearest neighbour) method and a method that utilises regional yield tables, referred to as the yield table method (YT-method). The estimation of stem volume was examined in a mixed forest in Southern Germany using 300 circular inventory plots, each with a size of 452 m2. Remote sensing features relating to vegetation height and structures were extracted and used as input variables in the different approaches. The accuracy of the estimation was analysed using scatter plots and quantified using absolute and relative root mean square errors (RMSE). The comparison was made for all plots, as well as for averaged plot values located within forest stands that have the same age class. On “plot level” the RMSE yielded 79.79 m3 ha⁻¹ (RA), 81.93 m3 ha⁻¹ (k-NN) and 81.78 m3 ha⁻¹ (YT-method) and for the averaged values 35.75 m3 ha⁻¹ (RA), 35.06 m3 ha⁻¹ (k-NN) and 42.98 m3 ha⁻¹ (YT-method). Advantages and disadvantages, as well as requirements, of the methods are discussed.     

Growth and yield of maize and timber trees in smallholder agroforestry systems in Claveria,northern Mindanao,Philippines

On-farm experiments were conducted in the Philippines to study over a 4-year period the growth of two timber trees, gmelina (Gmelina arborea R. Br.) and bagras (Eucalyptus deglupta Blume), and their impact on the grain yield of intercropped maize. The experiment consisted of maize monocropping plots (control) and maize intercropped between trees planted in block (2 × 2.5 m), and hedgerow arrangement (1 × 10 m). Three maize crops were planted in the block plots before canopy closure, and seven maize crops were planted in the hedgerow and monocropping plots. Maize grain yield in the hedgerow and in the block arrangement with gmelina were respectively 37% (16.58 tons ha⁻¹) and 68% (8.3 tons ha⁻¹) lower than in monocropping (26.21 tons ha⁻¹). In the plots with bagras, maize grain yield in hedgerow and in block arrangement were respectively 19% (24.8 tons ha⁻¹) and 66% (10.4 tons ha⁻¹) lower than in monocropping (30.6 tons ha⁻¹). For both tree species, the diameter at breast height (dbh) was greater in hedgerow than in block arrangement, with the difference being more pronounced with age. It was estimated that gmelina planted in hedgerows would produce 6–8 m³ ha⁻¹ of merchantable volume more than if planted in block. The study verifies the hypothesis that intercropping between widely-spaced trees rows (planted at 10 m or more) is more profitable and feasible to smallholders than either maize monocropping or woodlots, and concludes with recommendations on how to further improve the productivity of tree-intercropping systems.     

<Emphasis Type="Italic">Pinus radiata</Emphasis> and sheep production in silvopastoral systems at Carngham,Victoria, Australia

This long term experiment provides production data for evaluation of combined forestry and livestock systems. Five systems were established in Pinus radiata planted in 1981 (620 mm average annual rainfall). Sheep were introduced in 1984 and trees were pruned in several lifts. Adjusted tree stockings were (1) 60 widely spaced trees ha⁻¹, (2) 200 widely spaced trees ha⁻¹, (3) 200 trees ha⁻¹ in five-row belts, (4) 1,090 trees ha⁻¹ (unpruned) and 815 trees ha⁻¹, and (5) no trees (open pasture). Tree growth, wool production, liveweight gain and pasture production were measured. At year 25, tree diameter under bark at 1.3 m (DBHUB) in Systems 1, 2, 3 and 4 (unpruned) was 46.0, 39.2, 33.5 and 24.1 cm, while volume of bark-free 6-m butt-logs was 49, 117, 86 and 233 m³ ha⁻¹. Inner rows of System 3 belts contained smaller trees than outer rows. Pruned System 4 trees had slightly greater diameter than unpruned trees. Pasture production declined with tree stocking and time, due to shading and competition. Wool production (WP ha⁻¹) and liveweight gain (LWG ha⁻¹) declined linearly from year 9 to 17 with increasing disparity among systems. In 1998 (year 17) WP ha⁻¹ in Systems 1, 2 and 3 was 64, 16 and 43% of that in open pasture. Further analysis is needed to evaluate the financial costs and returns of various systems under particular rotation lengths and market prices.     

Crop residue effect on crop performance,soil N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions in alley cropping systems in subtropical China

Land management practices that simultaneously improve soil properties are crucial to high crop production and minimize detrimental impact on the environment. We examined the effects of crop residues on crop performance, the fluxes of soil N₂O and CO₂ under wheat-maize (WM) and/or faba bean-maize (FM) rotations in Amorpha fruticosa (A) and Vetiveria zizanioides (V) intercropping systems on a loamy clay soil, in subtropical China. Crop performance, soil N₂O and CO₂ as well as some potential factors such as soil water content, soil carbon, soil nitrogen, microbial biomass and N mineralization were recorded during 2006 maize crop cultivation. Soil N₂O and CO₂ fluxes are determined using a closed-based chamber. Maize yield was greater after faba bean than after wheat may be due to differences in supply of N from residues. The presence of hedgerow significantly improved maize grain yields. N₂O emissions from soils with maize were considerably greater after faba bean (345 g N₂O–N ha⁻¹) than after wheat (289 g N₂O–N ha⁻¹). However, the cumulated N₂O emissions did not differ significantly between WM and FM. The difference in N₂O emissions between WM and FM was mostly due to the amounts of crop residues. Hedgerow alley cropping tended to emit more N₂O than WM and FM, in particular A. fruticosa intercropping systems. Over the entire 118 days of measurement, the N₂O fluxes represented 534 g N₂O–N ha⁻¹ (AWM) and 512 g N₂O–N ha⁻¹ (AFM) under A. fruticosa species, 403 g N₂O–N ha⁻¹ (VWM) and 423 g N₂O–N ha⁻¹ (VFM) under Vetiver grass. We observed significantly higher CO₂ emission in AFM (5,335 kg CO₂–C ha⁻¹) from June to October, whereas no significant difference was observed among WM (3,480 kg CO₂–C ha⁻¹), FM (3,302 kg CO₂–C ha⁻¹), AWM (3,877 kg CO₂–C ha⁻¹), VWM (3,124 kg CO₂–C ha⁻¹) and VFM (3,309 kg CO₂–C ha⁻¹), indicating the importance of A. fruticosa along with faba bean residue on CO₂ fluxes. As a result, crop residues and land conversion from agricultural to agroforestry can, in turn, influence microbial biomass, N mineralization, soil C and N content, which can further alter the magnitude of crop growth, soil N₂O and CO₂ emissions in the present environmental conditions.     

Tree and stand growth for clonal <Emphasis Type="Italic">E. urophylla</Emphasis> × <Emphasis Type="Italic">grandis</Emphasis> across a range of initial stockings in southern China

A large initial stocking × fertilizer factorial field trial established in 1993 with a Eucalyptus urophylla × grandis hybrid clone in southern Guangxi province, China, included 6 initial stocking treatments ranging from 667 to 2,222 trees ha⁻¹ and 6 fertilizer treatments. Growth data was collected at various intervals up to age 192 months and also data on outer-wood pilodyn penetration (as an indicator of wood density) and acoustic velocity through the outer-wood (as an indicator of modulus of elasticity) at the last assessment. This report examines the results for the main effect of initial stocking treatments and stocking × fertilizer interactions across ages. There were significant differences between initial stockings for both average individual tree volume and standing volume ha⁻¹ at all ages up to 144 months, but just average individual tree volume at 192 months. At ages up to 75 months total standing volume decreased as initial stocking decreased—maximum volume being obtained at 2,222 trees ha⁻¹. From 88 to 110 months the highest standing volume was obtained at 1,667 trees ha⁻¹ and then at ages 144 and 192 months, 833 trees ha⁻¹ provided the highest standing volume. Average individual tree volume at all ages generally increased as initial stocking decreased—the largest trees were obtained at 667 trees ha⁻¹. As age increased the proportional differences between tree volumes at higher and lower stockings increased—at age 27 months average individual tree volume at 667 trees ha⁻¹ was 72% greater than that at 2,222 trees ha⁻¹ and differences increased steadily with age up to 190% at 192 months. There were no significant differences between initial stockings for the properties of the outer-wood assessed by pilodyn penetration and acoustic velocity. Also, no significant interactions were found between initial stocking and fertilizer treatments for any traits at any ages implying that effects of initial stocking and fertilizer are additive for the traits assessed.     

Growth response of <Emphasis Type="Italic">Acacia mangium</Emphasis> Willd. seedlings to arbuscular mycorrhizal fungi and four isolates of the ectomycorrhizal fungus <Emphasis Type="Italic">Pisolithus tinctorius</Emphasis> (Pers.) Coker and Couch

Some Acacia mangium Willd. plantations in Asia grow poorly due to low soil fertility and the absence of compatible mycorrhizal fungi. This legume tree can be colonized by arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi but inoculation is not routinely practiced. This study aimed to compare the effectiveness of AM fungi and four isolates of the ECM fungus Pisolithus tinctorius (Pers.) Coker and Couch (Pt) in promoting growth of A. mangium seedlings under glasshouse conditions. AM inoculants were: Glomus etunicatum, G. fasciculatum, G. macrocarpum and Gigaspora margarita and mixed species extracted from rhizosphere soil of a Populus stand in Suwon (AMKFRI), and Carex (AMM6) and Populus (AMM7) growing in mine tailings in Korea. Pisolithus isolates were from Philippines (PtPhil) and Korea (PtKFRI, PtMKACC, PtKACC). Generally, ECM fungi promoted height and diameter growth of A. mangium more than the AM inoculants. The Korean Pisolithus increased plant dry weight by 122–145%, mixed AM inoculants by 61–97%, and Glomus and Gigaspora by 45–72% over the control. PtKACC gave the highest root colonization and promoted the highest growth and concentration of most nutrients. Mycorrhizal root colonization was positively correlated with plant dry weight, Na, Fe and Cu concentrations and N, P, K, Ca, Na, Fe and Cu contents. In conclusion, the results provide strong evidence for benefits of mycorrhizal inoculation on A. mangium seedlings under glasshouse conditions. The Korean Pisolithus isolates (particularly PtKACC), and two AM fungi (AMKFRI and AMM6) are potential mycorrhizal inoculants but their effectiveness and persistence should be determined on degraded lands in tropical countries where A. mangium is being planted for rehabilitation.