Alley cropping on an Ultisol in subhumid Benin. Part 1: Long-term effect on maize, cassava and tree productivity

In southern Benin, West Africa, two alley cropping systems were studied from 1986 to 1992. Yield development was followed in a maize and cassava crop rotation vs. intercropping system, with alleys of Leucaena leucocephala (Lam.) de Wit and Cajanus cajan (L.) Millsp. vs. a no-tree control, with and without NPK fertiliser. Without alleys, NPK fertilisation maintained high yield levels of 2–3 t maize dry grain plus 4–6 t ha^–1 cassava root DM in intercropping, 3–4 t ha^–1 maize and 6–10 t ha^–1 cassava in solercropping. Without NPK, final yields seemed to stabilise at about 1 t maize plus 2 t cassava in intercropping and twice as much in each solecrop. Alley cropping induced significant yield increases by about 50% with both tree species in unfertilised, intercropped maize, and with Cajanus in fertilised, solecropped cassava. In monetary terms, the NPK-fertiliser response of stabilised yields was significant for all treatments except the solecropped Leucaena alleys. It is concluded that on Ultisols with low nutrient status in the upper rooting zone, alley cropping with low-competitive tree species may improve food crop yields but the greatest monetary output is achieved by intercropping with mineral fertiliser independent of the presence or absence of an agroforestry component.     

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.     

Perspectives on hedgerow intercropping

Hedgrow intercropping (alley cropping) is a relatively new technology involving growing agricultural crops between rows of planted tree species. Leucaena is the most widely studied tree species for the practice and research has indicated that it can yield over 200 kg ha^–1 year^–1 of nitrogen for application in the alleys where crops are planted. More herbage (and nitrogen) are obtained from narrow alleys, and crops utilise the nitrogen better if the prunings are incorporated into the soil before planting. Low pruning heights may prevent shading of the crops.Most of the agronomic aspects of the practice have been investigated in humid lowlands with high rainfall. There is a need to focus research on testing the practice under varied agro-ecological conditions, and using several suitable multipurpose trees species at a wide range of alley width and plant population. Investigations should include more than one crop in the alleys, and at different spatial arrangements. Management schedules, like time and frequency of pruning the trees and method of applying the prunings under different ecological conditions need more research attention. Studies on competition also need to be undertaken in order to suggest improvements to the practice.This paper attempts to put together and discuss some of the recent advances on these and other management aspects concerning hedgerow intercropping, and areas that need further research endeavour are exposed.     

Tithonia diversifolia: variations in leaf nutrient concentration and implications for biomass transfer

Green leaf biomass of Tithonia diversifolia is high in nutrients and recognised as a potential source of nutrients for crops. We conducted a field survey in western Kenya to determine the variation in leaf nutrient concentrations in tithonia grown in naturalised hedges and agricultural fields, and to examine whether leaf nutrient concentrations were related to soil nutrient status. Leaf P and K concentrations were higher in naturalised hedges (3.2 g P kg^–1 and 35 g K kg^–1) than in unfertilised fields (2.2 g P kg^–1 and 23 g K kg^–1). The critical level of 2.5 g P kg^–1 for net P mineralisation was exceeded by > 90% of the leaves from hedges, but by only 14% from unfertilised fields. Leaf P and K concentration increased linearly with increasing natural logarithm of anion resin extractable soil P and exchangeable soil K, respectively. However, at the same levels of soil available P and K, field-grown tithonia consistently produced lower leaf P and K concentrations than that grown in hedges. This study indicates that biomass from tithonia planted on nutrient-depleted soils would be a less effective source of P and K, via biomass transfer, than tithonia from naturalised hedges.This revised version was published online in November 2005 with corrections to the Cover Date.     

Sewage sludge fertilisation of a silvopastoral system with pines in northwestern Spain

The use of municipal sewage sludge as a fertiliser could be a more adequate means of disposal of this residue than its transport to the dump. The objective of this experiment was to evaluate the effects of different doses of sludge and sowing a mixture of cocksfoot (Dactylis glomerata) and clover (Trifolium repens) on pasture production, botanical composition of the pasture, forage quality, and changes in soil chemical properties. Treatments applied were: (1) no fertilisation (L0), (2) fertilisation with 26 Mg ha^–1 of sewage sludge with no sowing (L40), (3) fertilisation with 26 Mg ha^–1 of sewage sludge and sowing with 25 kg of Dactylis glomerata L. cv Artabro (Dg) and 3 kg Trifolium repens cv Huia per hectare and (4) 52 Mg ha^–1 of sewage sludge with no herbage sowing (L80). Plots were established in a silvopastoral system with Pinus radiata D. Don at a density of 1666 trees ha^–1 (3 × 2 m). The improvement of soil fertility due to organic fertiliser application and the use of Dactylis glomerata increased the production and quality of pasture as well as reduced the risk of fire and erosion, as grasses dominated shrubs. Fertilisation with sewage sludge in soils of acid origin increased the concentration of copper in the pasture and, if cocksfoot was not sown, the levels of this element exceeded the maximum tolerable dietary levels for sheep. On the other hand, fertilisation also increased the levels of zinc in pasture, but values were not above toxic limits for sheep, horses and cattle.This revised version was published online in November 2005 with corrections to the Cover Date.     

The use of Sesbania (Sesbania rostrata) and urea in lowland rice production in Sierra Leone

The suitability of sesbania (Sesbania rostrata) as green manure for lowland rice was evaluated in the Inland Valley Swamp (IVS) of Sierra Leone, and attempts were made to identify appropriate methods of its management in combination with urea. Sesbania — rice intercropping and sesbania — rice rotation treatments were compared with 60 kg N ha^–1 applied in two splits and 30 kg N ha^–1 as basal or top dressed to rice grown in the two cropping systems. The ¹⁵N isotope dilution technique was used to quantify N uptake from the green manure and urea and its utilization by rice. Rotating 40–50 days old sesbania two days prior to transplanting and top dressing with 30 kg N ha^–1 as urea at nine weeks after transplanting gave highest rice grain yield (121% over the control without sesbania and urea). However intercropping sesbania with rice tended to increase N uptake and N fertilizer utilization more than the rotation treatments. The higher grain yield of rice in rotation despite lower N uptake than intercropping shows that other effects than only N explain the beneficial effect of sesbania on rice.This revised version was published online in November 2005 with corrections to the Cover Date.     

Above- and below-ground biomass dynamics in a sole cropping and an alley cropping system withGliricidia sepium in the semi-deciduous rainforest zone of West Africa

A considerable amount of data is available about above-ground biomass production and turnover in tropical agroforestry systems, but quantitative information concerning root turnover is lacking. Above- and below-ground biomass dynamics were studied during one year in an alley cropping system withGliricidia sepium and a sole cropping system, on aPlinthic Lixisol in the semi-deciduous rainforest zone of the Côte d'Ivoire. Field crops were maize and groundnut. Live root mass was higher in agroforestry than in sole cropping during most of the study period. This was partly due to increased crop and weed root development and partly to the presence of the hedgerow roots. Fine root production was higher in the alleys and lower under the hedgerows compared to the sole cropping plots. Considering the whole plot area, root production in agroforestry and sole cropping systems was approximatly similar with 1000–1100 kg ha^–1 (dry matter with 45% C) in 0–50 cm depth; about 55% of this root production occured in the top 10 cm. Potential sources of error of the calculation method are discussed on the basis of the compartment flow model. Above-ground biomass production was 11.1 Mg ha^–1 in sole cropping and 13.6 Mg ha^–1 in alley cropping, of which 4.3 Mg ha^–1 were hedgerow prunings. The input of hedgerow root biomass into the soil was limited by the low root mass ofGliricidia as compared to other tree species, and by the decrease of live root mass of hedgerows and associated perennial weeds during the cropping season, presumably as a result of frequent shoot pruning.     

Agroforestry systems for soil and water conservation and sustainable production from foothill areas of north India

Some conservation based agroforestry systems (AFS) were developed for possible adoption in place of high risk rainfed farming on land capability classes Ito IV of a typical topo-sequence of foothill north India. The agri-silvi-horticulture system integrating leucaena, lemon, papaya and turmeric on class I irrigated land provided sustainable mean net returns of Rs. 17066 against Rs. 7852 ha.^–1 yr.^–1 from double cropped agricultural system. The intercropping of cluster beans with leucaena gave the highest net returns of Rs. 3540 ha.^–1 yr.^–1 in the agri-silvicultural system adopted on class II land. Eucalyptus terettcornis (Smith) in top and Bhabbar grass (Eulaliopsis binata Retz) in the understorey on a sandy loam class III land gave four years (1985–1988) mean air dry grass yield of 4.2 (used for paper pulp) from October and 1.19 t. ha^–1 yr.^–1 (used for fodder) from June cut. The net returns from grass alone were Rs. 4672 against Rs. 1679 ha.^–1 yr.^–1 from rainfed field crops raised on an adjoining plot. The returns from trees would be additional. Bhabbar grass raised under Acacia species on a 25 to 30% sloping gravelly class IV land provided yield varying from 2.18 to 4.31 from October cut and 0.50 to 1.1 t. ha.^–1 yr.^–1 from June cut with 6 years mean of 3.9 t. ha.^–1 yr.^–1 which at 1988 prices provided net returns of Rs. 2402 ha^–1. These AFS proved superior to traditional farming on each land capability class.     

The effects of between-row (alley widths) and within-row spacings ofGliricidia sepium on alley-cropped maize in Sierra Leone

The effects of spacings between hedgerows (alley widths) and the spacings of trees within hedgerows ofGliricidia sepium on growth and grain yield of maize were investigated at Senehun in southern Sierra Leone. Four between-row spacings (2, 4, 6 and 8 m) were combined with three within-row spacings (0.25, 0.50 and 1.00 m) in a split block design. Maize, at densities of 20,000, 40,000 and 53,333 plants ha^–1, was established in the alleys and also as pure crops. N, P and K fertilizers were applied to all plots before pruning of the trees began. When pruning started, only the pure maize plots received fertilizer; prunings from the hedgerows were returned to the appropriate alleys in the other plots.Plots with the highest maize populations consistently gave the best yields before pruning started, but lower populations gave improved yields after pruning. Yields of maize increased with increasing alley widths before the start of pruning, after which the narrower alleys of 2 and 4 m outyielded the wider ones by almost double, probably because of the large amount of nutrients applied in prunings. Lack of light limited grain yields before the start of pruning, when there was some shading by the hedgerows. Alleys of 2–4 m wide, planted no closer than 0.50 m within rows, resulted in more than twice the yields of maize than in the 8-m alleys planted at 0.25 m within rows, once the hedgerows were well established and were being managed.     

Distribution of small mammals in a silvoarable agroforestry system in Northern England

The importance of agroforestry systems in temperate regions in providing habitat for small mammals has not been investigated. Numbers and densities of small mammals were assessed by live trapping in a complex farming landscape including mature hedgerows, arable fields, areas of trees planted at forestry density (2,500 trees ha–1) and trees in an agroforestry configuration (178 trees ha^–1) consisting of rows of trees separated by arable alleys. Over a 2 -year period, 1680 animals were captured; 69% were Apodemus sylvaticus L., 20% Sorex araneus L. and 10% Clethrionomys glareolus Schreber. Small numbers of Mus domesticus Rutty, Sorex minutus L., and Neomys fodiens Pennant were also caught. The density of captures of A. sylvaticus and S. araneus varied little over the whole farming landscape in contrast to C. glareolus which had a greater density of captures in mature hedgerows. However, for the small mammals collectively, away from hedgerows, the highest density of captures was found in the agroforestry tree rows (15.5 per 100 trap nights) and the least in open arable crop (4.3), with both arable alleys and forestry density trees having intermediate values (9.1 and 9.2 respectively).Densities of captures of A. sylvaticus were greater in the tree rows and arable alleys than in the forestry area and the adjacent open arable crop, whereas for S. araneus they were greater in the habitats with trees. It is clear that the range of habitats in an agroforestry system is valuable for small mammal conservation.     

Influence of nutrient supply on spring frost hardiness and time of bud break in Norway spruce (Picea abies (L.) Karst.) seedlings

When spring frosts occur on recently planted forest sites, severe damage may occur to the seedlings. The aim of the present study was to test how different low levels of nutrient concentrations in Norway spruce (Picea abies (L.) Karst.) seedlings affected spring frost hardiness and time of bud break. Seedlings were grown in a greenhouse for one season and supplied with fertiliser containing 22, 43 and 72 mg N l^–1, respectively. The treatments resulted in needle nitrogen concentrations ranging from 0.9 to 1.8% in autumn. After winter storage at 0 °C, bud break was recorded on seedlings growing in the greenhouse, outdoors and in growth chambers at 12 °C and at 17 °C. Freezing tests were performed on seedlings directly removed from winter storage and following one week growth in the greenhouse. Seedlings receiving fertiliser with 43 mg N l^–1 had less freezing injury than the two other fertilisation treatments in the present study. The earliest bud break occurred in seedlings receiving 72 mg N l^–1.     

Effect of shading and fertilisation on the development of container-grown Nothofagus glauca seedlings,a threatened species from central Chile

Nothofagus glauca is an endemic tree of the Mediterranean zone of Chile and is a threatened species. Currently, available information for the propagation and nursery cultivation of this species is conspicuously lacking. This study examined the effect of four levels of shade (18%, 35%, 65% and 80% with Raschel® plastic net) and four rates of slow-release fertiliser (2.5, 5, 7.5, and 10 g l^?1 of Basacote® Plus 9M) on container-grown seedlings after one growing season. Growth was significantly affected by shade and fertilisation. Seedlings grown under 18% or 35% shade were larger in diameter and had more roots than those grown under 80% shade and fertilisation with 2.5–5 g l^?1 of media were smaller than those fertilised with 7.5–10 g l^?1.     

A comparison of alley cropping and block planting systems in sub-humid Bénin

Alley cropping would be acceptable to farmers in West Africa, if the amount of tree-crop competition could be reduced and crop yields increased and stabilized. The importance of overall tree-crop competition in alley cropping was therefore quantified at three locations in the Republic of Bénin, by comparing the performance of a maize-cassava intercrop and mixed hedges of Gliricidia sepium and Flemingia macrophylla in an alley cropping system, where the tree-crop interaction was high, and in a cut and carry system with block plantings, where the interface was restricted to one face. The establishment and productivity of trees in both agroforestry systems depended strongly on the natural soil fertility of the site, K and Ca being critical for both species. Alley hedges produced progressively more cut dry matter with higher leaf proportions than tree blocks and hence yielded significantly higher nutrient masses. Overall, the cut dry matter from five cuttings per cropping season ranged among locations from 855 to 1651 kg ha^–1 yr^–1 for alley hedges and from 777 to 869 kg ha^–1 yr^–1 for tree blocks. Differences in yields of maize and cassava between both systems were insignificant in all three environments and all cropping years under observation. The results of this study suggest that the overall effect of tree-crop competition was unimportant, but that tree-tree competition was the decisive factor in determining the total system productivity.     

Cacao-coconut intercropping in Ghana: agronomic and economic perspectives

In Ghana, shade for cacao (Theobroma cacao L.) is becoming a critical issue because of extensive deforestation. Unlike in some other cacao-growing countries, cacao is not grown under the shade of coconut (Cocos nucifera) in Ghana. An experiment to compare the merits of four cacao-coconut intercropping systems with the traditional cultivation of cacao under Gliricidia sepium shade was undertaken at the Cocoa Research Institute of Ghana. Cacao seedling girth was not affected when intercropped with coconut but was significantly (P = 0.01) reduced when intercropped with G. sepium. High density cacao facilitated better early canopy formation. Yield of cacao spaced at 2.5 m triangular (1739 plants ha^–1) with coconut at 9.8 m triangular (105 plants ha^–1) was significantly higher (P = 0.05) than from the other treatments during 1993/94 to 1995/96. There were no major disease problems associated with intercropping cacao with coconuts. Widely spaced coconuts intercropped with cacao spaced at 3 m × 3 m showed better flowering and gave higher coconut yields, but cacao spaced at 2.5 m triangular under coconuts spaced at 9.8 m triangular was more profitable than the other treatments. Moisture stress was the greatest in cacao system with G. sepium shade and this could be responsible for the low yield of cacao in that treatment. It is suggested that properly arranged high density cacao under widely spaced coconuts can be a profitable intercrop system for adoption by cacao farmers in Ghana.This revised version was published online in November 2005 with corrections to the Cover Date.     

Crop yields of rice and wheat grown in rotation as intercrops with three tree species in the outer hills of Western Himalaya

Studies on tree crop interaction under rainfed condition in Dehradun valley were conducted for 13 years during 1977 to 1990. Grewia optiva (Bhimal), Morus alba (Mulbery) and Eucalyptus hybrid were tried along with rice (CV: Akashi) — wheat (CV: RR-21) rotation. One-year-old tree seedlings of the above tree species were planted in line, 5 m apart in N-S direction, in July 1977, in the middle of the plot (size 20 m × 20 m). Eucalyptus was first harvested in 1987. Grewia optiva, Morus alba and coppice of Eucalyptus were harvested in 1990. All tree species had depressing effect on crop yields. Eucalyptus had maximum effect in depressing crop yield till the first harvest and had least effect thereafter. From 1987 onwards, Morus alba affected rice most, while wheat was mostly affected by Grewia optiva. The depressing effect on an average varied from 28 to 34% depending upon the species.Distance of tree line from the crop significantly affected the crop yield upto a distance of 5 m and there was 39% decrease in crop yield upto 1 m, 33% from 1–2 m, 25% from 2–3 m and 12% from 3–5 m distance. Annual removal of lops and tops from trees partly compensated the deficit. Grewia optiva could produce 1.08 t ha^–1 yr^–1 of branches and 0.26 t ha^–1 yr^–1 of leaves (air dry) and 1.28 t ha^–1 yr^–1 of branches and 0.28 t ha^–1 yr^–1 of leaves were obtained from Morus alba. Wood (ADT) produced by the trees was 33.6 t ha^–1 from Eucalyptus, 9.5 t ha^–1 from Grewia optiva and 11.6 t ha^–1 from Morus alba.     

Effect of mechanical site preparation and fertilisation on early growth and survival of a black pine plantation in northern Greece

Pine plantations on selected sites in the extensive zone of degraded oak coppice of northern Greece are deemed necessary for increasing wood production in the area and suitable site preparation may accelerate early tree growth. Seven site preparation treatments including raking (R), with sub-soiling (RS), disc harrowing (RD), tine ploughing (RT) and their combinations (RSD), (RDT) and (RSDT) were compared for the establishment of black pine (Pinus nigra Arn) in an oak coppice site, of conglomerate parent material at Anthrakia, northern Greece. The randomised blocks trial of three replications and 110 trees per treatment, half of which were fertilised with 150 g NPK per plant, was assessed at the age of 15 years for diameter, dominant tree height and survival. There was no significant difference between the treatments in any of the traits examined, nor did the fertilisation had any effect. Only the fertiliser × treatment interaction was found significant at p<0.001 for dominant height, accounting for 37% of the observed variation in this trait. The lack of response to site preparation treatments may be attributed to the hard Bt3 clay horizon, extending beyond cultivation depth (50 cm), that prevents the roots penetration into deeper moist soil layers. The F × T interaction, where the combination of (RSDT) treatment and fertiliser was found to accelerate tree height growth in relation to the same treatment without fertiliser, indicates that thorough soil cultivation is needed for fertilisation to be effective in such sites.     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) or poro (Erythrina poeppigiana) in Costa Rica

Predictive models were developed for Cordia alliodora branch and Theobroma cacao branch or leaf biomass,based on branch basal areas (r² 0.79) but the model of C. alliodora leaf biomass, although significant, was of very low accuracy (r² = 0.09) due to annual leaf fall. At age 10 years, shade tree stem biomass accounted for 80% of the total above-ground biomass of either tree. However, between the ages of 6 and 10 years, the biomass increment of T. cacao branches (3–4t.ha^–1.a^–1) was similar to that of the shade tree stems. During the same period, the net primary productivity was 35 and 28 t.ha^–1.a^–1, for the Erythrina poepigiana and and C. alliodora systems, respectively.Cocoa production under either of the shade trees C. alliodora or E. poeppigiana was 1000 kg.ha^–1.a^–1 (oven-dry; ages 6–10 yr). During the same period, C. alliodora timber production was 9 m³.ha^–1.a^–1 whilst the leguminous shade tree E. poeppigiana does not produce timber. Litterfall over the same 5 years, including crop and/or shade tree pruning residues, averages 11 and 23 t.ha^–1.a^–1, respectively. The main difference was due to E. poeppigiana pruning residues (10t.ha^–1.a^–1).Soil organic material reserves (0–45 cm) increased over 10 years from 198 to 240 t.ha^–1 in the E. poeppigiana plots and from 168–184 t.ha^–1 in the C. alliodora plots. These values, together with the productivity indices presented, provide evidence that the systems are sustainable.For economic reasons, the use of C. alliodora is recommended under the experimental conditions. however, on less fertile soils without fertilization, the greater biomass and hence nutrient return to the soil surface under E. poeppigiana, might make this the preferable shade tree.     

The influence of stockplant environment on morphology,physiology and rooting of leafy stem cuttings of Albizia guachapele

Studies in controlled environmentconditions investigated the effects ofirradiance and nutrients (NPK) on morphologicaland physiological characteristics of Albizia guachapele stockplants, and rootingability of subsequently severed cuttings innon-mist propagators. The study assessed gasexchange and chlorophyll fluorescence ofstockplants before cutting severance and ofcuttings during the propagation period. Anegative interaction was found betweenincreasing irradiance(200–500 mol m^{minus 2} s^{minus 1}) andincreasing nutrient supply (0.25–1.25% NPK)on stockplant growth, and a similar effect wasfound in the subsequent rooting of cuttings.Rooting percentage decreased from 53.8% withlow irradiance/low nutrients to 11.2% withhigh irradiance/high nutrients. Single-node,leafy cuttings from high irradiance/highnutrient stockplants were much shorter thanthose from any other treatment, whichnegatively affected their rooting ability. Nodifferences were found among treatments inchlorophyll fluorescence ratios duringpropagation, suggesting that A.guachapele cuttings are dependant for rootingnot only on current photosynthesis, but also ontheir initial pre-severance reserves ofcarbohydrate. It was concluded that A.guachapele, which can be propagated with thenon-mist propagation system utilized in thisstudy, was markedly affected by pre-severancestockplant environment through its impact oncutting size and products of photosynthesis.Growing stockplants under low irradiance andlow nutrients resulted in longer cuttings withhigher rooting ability.     

Tree/crop complementarity in an arid zone runoff agroforestry system in northern Kenya

We tested the hypothesis that shallow-rooted crops and deep-rooted trees will share the available water in a complementary manner, when grown together, in a field trail in the Turkana district of northern Kenya during 1994 to 1996. Such studies have been few in dryland agroforestry. The effects of two different Acacia saligna (Labill.) H. Wendl. tree planting densities (2500 and 833 trees per ha), tree pruning (no pruning vs. pruning) and annual intercrops (no intercrop vs. intercrop) on total biomass production and their interactions were tested. In 1996 Sorghum bicolor (L.) Moench was used during the first vegetation period and Vigna unguiculata (L.) Walp. during the second. We used naturally generated runoff water for irrigation to supplement low rainfall amounts typical for the area. High biomass production (> 13 t ha^–1 over a two year period) was observed irrespective of intercropping of pruned trees or sole tree stands. Although the pruning treatment reduced total tree biomass yields by a quarter, the introduction of annual intercrops after the pruning of trees outweighed this loss. The yields of the intercrops in the pruned tree treatments were similar to their yields when grown as monocrops. The calculation of land equivalent ratios showed overyielding for intercropped, pruned systems. The high values for LER (1.36 at low and 1.47 at high density of trees) indicate that there is complementarity in resource use between the different species.This revised version was published online in November 2005 with corrections to the Cover Date.     

Fertiliser and irrigation effects on wood density at various heights for <Emphasis Type="Italic">Pinus radiata</Emphasis>

This study examined the combined effect of 19-years of nitrogen fertilisation and irrigation on the basic density along the stems of Pinus radiata (D.Don). The sample trees came from two treatments in the Biology of Forest Growth experiment: the control (C no treatment) and the irrigated and liquid fertilised (IL irrigated from age 10 to 29, liquid fertilised from ages 10 to 17). The mean basic density at breast height in the IL trees was significantly less (P < 0.05) than the C trees (430 and 471 kg m⁻³, respectively). However, the mean density of the entire bole was not significantly different. Basic density decreased with height, with the density near the tips of the trees being only 80% of the density at breast height for both treatments. The relative rate of the decrease was different between treatments. The density of the C trees decreased steadily with height while the IL trees held a relatively constant density for about half their total height. The results show the importance sampling at several different heights when considering the effects of various treatments on wood basic density in Pinus radiata.