Achieving food and nutritional security through agroforestry: a case of <Emphasis Type="Italic">Faidherbia albida</Emphasis> in sub-Saharan Africa

Faidherbia albida is an ideal agroforestry tree commonly intercropped with annual crops like millet and groundnuts in the dry and densely populated areas of Africa. With its peculiar reverse phenology, it makes growth demands at a different time from that of crops. In addition, it deposits great amount of organic fertilizer on food crops. Leaves entering soils are comparable to fertilization of almost 50 t·ha 1 ·year 1 of manure in dense stands of 50 large trees per ha. These nutrients help maximize agricultural production and reduce the need for a fallow period on poorer soils. Research has shown that millet grown under F. albida yielded 2.5 and 3.4 fold increases in grain and protein, respectively. Animals eat pods which contain mean amounts of crude protein of 20.63% and carbohydrate of 40.1% in seeds. Moreover, the continued existence of F. albida in agroforestry parklands as in Ethiopia and Mali signifies the success of traditional conservation measures. Modern scientists have also developed much interest in the role of agroforestry in maintaining long-term biological balance between agriculture and livestock production systems. To ensure food security, which still remains a major challenge in sub-Saharan Africa, and concurrently minimize environmental degradation, promotion of agroforestry that specifically involves indigenous trees is crucial. We discuss the prospective role of F. albida in alleviating poverty while simultaneously protecting the environment from factors associated with, for example, deforestation and loss of biodiversity. The overall aim is to promote wide-scale adoption of F. albida as a valuable tree crop in farming systems, particularly in those areas where it remains unexploited.     

孟加拉无机肥料对几种农林作物生物固氮和种苗生长的影响(英文)

比较了不同浓度无机肥料(尿素和重过磷酸钙)对四种农林作物(楹树、雨豆树、相思树和印度田菁)生物固氮和种苗生长的影响。种子萌发一个月后利用不同浓度肥料(尿素:40kg·hm-2,80kg·hm-2;重过磷酸钙:40kg·hm-2,80kg·hm-2;(尿素 重过磷酸钙)40kg·hm-2和(尿素 重过磷酸钙)80kg·hm-2)处理种苗。结果表明:中等浓度无机肥料促进了种苗的生长,但较高浓度无机肥料也不利于种苗的生长。当施加尿素时根瘤菌的数量大小明显受抑制,但随着增加磷肥(重过磷酸钙)根瘤菌的数量大小增加。本研究有助于农业人员利用无机肥料改善土壤提高农林作物的生物固氮和种苗生长。图2表6参33。     

Growth and yield of sorghum or cowpea in an agrisilviculture system in semiarid India

This study was conducted near Hyderabad, India during 1991–1994 to quantify the effects of shoot pruning, fertilization, and root barriers around Leucaena leucocephala trees on intercropped sorghum(Sorghum bicolor) or cowpea (Vigna unguiculata) crop production under rainfed conditions. Crop plants grown with pruned trees attained higher dry matter and leaf area index than did those with unpruned trees. Two-year mean grain yields of sorghum with no root barriers were76% and 39% of pure crop yield (1553 kg ha–1)for pruned and unpruned trees, respectively. Corresponding values for cowpea were 49% and 26% of pure crop yield (1075 kgha–1). Sorghum or cowpea intercropped with trees responded to fertilizer application more strongly than did their respective pure crops, suggesting an increased need for fertilizer application in this agrisilviculture system over that currently used for pure crops. Impact of root barriers was small on either crop. Irrespective of root barriers, a high response to tree pruning suggested above ground competition for light dominated tree/crop interactions in this agrisilviculture system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Soil nitrogen dynamics in alley cropping and no-till systems on ultisols of the Georgia Piedmont, USA

On highly-weathered Ultisols of the Georgia (USA) Piedmont, a combination of no-till agriculture and alley cropping presents an option for rapidly increasing soil nitrogen availability while restoring long-term soil fertility. Three years after the establishment of Albizia julibrissin hedgerows and no-till agriculture trials, we measured inorganic soil nitrogen (NO₃ ^-–N and NH₄ ^-–N) and net nitrogen mineralization during a 4-month field study and a 14-day laboratory study . We also measured the influence of tree leaf amendments on grain sorghum production and N uptake. Soil nitrate increased four-fold within two weeks of adding Albizia leaf mulch. Soil ammonium did not increase as rapidly nor to the same extent after tree mulch addition. Averaged over the 4-month study, soil nitrate and ammonium were 2.8 and 1.4 times higher in the alley-cropped than in the treeless no-till plots. Net nitrification and mineralization were no higher in the alley cropping plots, during either field or laboratory incubations. Tree mulch additions enhanced crop biomass production and N uptake 2 to 3.5 times under both high and low soil moisture conditions. Our study demonstrates the dramatic short-term impacts of Albizia mulch addition on plant available nitrogen. Combined with no-till practices, alley cropping with Albizia hedges offers Piedmont farmers an option for reducing reliance upon chemical N fertilizer while improving soil organic matter levels. This revised version was published online in August 2006 with corrections to the Cover Date.     

Soil physical conditions and root growth in coconut plantations interplanted with nitrogen fixing trees in Sri Lanka

The study was carried out to investigate the possibility of improving degraded soil conditions of Andigama series by intercropping coconut (Cocos nucifera L.) with Calliandra calothyrsus, Leucaena leucocephala, Acacia auriculiformis and Gliricidia sepium. Bulk density was significantly low in NFT interplanted plots followed by improved aeration in AB and B horizons of the soil profile. Total and readily available water fraction was higher in AB and B horizons of calliandra, acacia and gliricidia interplanted plots over control plots due to the increase of organic matter content and root growth. Root growth and proliferation of calliandra in A horizon were predominantly higher than that of leucaena, acacia and gliricidia species. In contrast, gliricidia roots penetrated into B horizon more densely than roots of other species. Better root growth of coconut in A horizon was observed in acacia and calliandra plots than other plots. The total coconut root biomass in AB and B horizons was higher in gliricidia and acacia plots than other species, which accounted for 91% and 0.3% in AB horizon and 21% and 23% in B horizon for gliricidia and acacia, respectively compared to the control. Total root biomass of coconut in calliandra plots was reduced by 5%, and 45% in AB and B horizons respectively. Results indicated that soil physical conditions of Andigama series (gravelly soil) could be significantly improved by interplanting acacia and gliricidia, as indicated by enhanced coconut root growth and proliferation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Alley cropping of sorghum with Leucaena during the post-rainy season on Vertisols in semi-arid India

A field experiment was conducted for two years (1989– 1991) on a Vertisol in Bijapur, India in a split-plot design, replicated four times, to evaluate the potential of alley cropping post-rainy season sorghum between Leucaena hedgerows. Leucaena produced on average 2.74 t per ha of prunings and 1.57 t per ha of wood annually. Alley cropping decreased sorghum yields by 28 to 45% when all Leucaena prunings were removed from the system and by 21 to 24%, when on average 1.92 t per ha prunings were applied to the soil annually. The reduction of sorghum yield increased as higher rates of N were applied to sorghum. Although alley cropping increased organic carbon by 21% and available N by 19% at the time of crop sowing, it did not result in increased crop yields because of competition for water between hedgerows and crops. Calculation of land equivalent ratios based on total Leucaena biomass indicated that alley cropping was more productive than sole cropping of sorghum only in one year, and that, too, when no N was applied to sorghum. Therefore, alley cropping of Vertisols with post-rainy season sorghum is not likely to have any advantage in the short term. This revised version was published online in June 2006 with corrections to the Cover Date.     

Seasonal pattern of nitrogen mineralization and soil moisture beneath Faidherbia albida (synAcacia albida) in central malawi

On fertile alluvial soils on the lakeshore plain of Malawi, maize (Zea mays L.) yields beneath canopies of large Faidherbia albida (synAcacia albida) trees greatly exceed those found beyound tree canopies, yet there is little difference in soil nutrients or organic matter. To investigate the possibility that soil nutrient dynamics contribute to increased maize yields, this study focused on the impact of Faidherbia albida on nitrogen mineralization and soil moisture from the time of crop planting until harvest. Both large and small trees were studied to consider whether tree effects change as trees mature.During the first month of the rainy season, a seven-fold difference in net N mineralization was recorded beneath large tree canopies compared to rates measured in open sites. The initial pulse beneath the trees was 60 g N g^–1 in the top 15 cm of soil. During the rest of the cropping cycle, N availability was 1.5 to 3 times higher beneath tree canopies than in open sites. The total production of N for the 4-month study period was 112 g N g^–1 below tree canopies compared to 42 g N g^–1 beyond the canopies. Soil moisture in the 0–15 cm soil layer was higher under the influence of the tree canopies. The canopy versus open site difference grew from 4% at the beginning of the season to 50% at the end of the cropping season.Both N mineralization and soil moisture were decreased below young trees. Hence, the impact of F. albida on these soil properties changes with tree age and size. While maize yields were not depressed beneath young F. albida, it is important to realize that the full benefits of this traditional agroforestry system may require decades to develop.     

Effects of mulching withAzadirachta indica andAlbizia lebbeck leaves on the yield of sorghum under semi-aird conditions in Burkina Faso

From 1988 to 1990, leaves fromAzadirachta indica andAlbizia lebbeck were used as mulch on sorghum (Sorghum bicolor) in semi-arid Burkina Faso. Five different application modes, each representing a different combination of application timing and mulch composition, were evaluated. In one of the modes leaves were combined with sorghum straw. Leaf quantities applied corresponded to dosages of 25, 50 and 75 kg N ha^–1 in all five modes.Dosage had a significant influence on yield all three years. The mulching effect increased progressively over the years and was more pronounced the higher the dosage. Mean grain yields obtained with the highest dosage, relative to an unmulched control, were 203%, 364% and 422%, for the three years, respectively. Application timing had a significant influence on yields in 1988 and 1989, but the response was not consistent. Differences in response were attributed to variation in the rainfall distribution. Mulch composition did not have a significant influence on yield during any of the three years. Of the five modes evaluated, the ones producing the highest yields over the three-year period of study were azadirachta leaves applied (i) at sowing and (ii) 4–6 weeks after sowing. Yields decreased on both the treated and untreated plots between 1988 and 1989. On the treated plots, yield generally increased again in 1990. This increase was attributed to a residual effect of the mulch. The residual effect probably only explained part of the large difference in yield between treated and untreated plots. It is therefore suggested that most of the nutrients released from the mulch were used by the plants during the same season, which increased production. Furthermore, the mulch layer could have reduced evaporation and thus increased the retention of soil water.

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Résumé De 1988 à 1990, des feuilles d'Azadirachta indica et d'Albizia lebbeck ont été utilisées comme mulch sur une culture de sorgho blanc (Sorghum bicolor) au Burkina Faso, en climat semi-aride. Cinq modes d'application ont été évalués, chacun répresentant une compinaison différente en temps d'application et composition de mulch. Dans un des modes, les feuilles ont été combinées avec des tiges de sorgho. Les quantités de feuilles utilisées ont été équivalentes aux dosages de 25, 50 et 75 kg N ha^–1 et ceci dans tous les cinq modes.Le dosage a eu une influence significative sur la récolte pendant toutes les trois années. Leffet a augmenté progressivement d'année en année et a été plus prononcé pour le dosage le plus élevé. Les moyennes de rendement de graines par rapport au témoin sans mulch, obtenues avec la dose de 75 kg N ha^–1, ont été 203% pour la première année, 364% pour la seconde et 422% pour la troisième. Le temps d'application a eu une influence significative en 1988 et 1989, mais les résultats ont varié entre les années. Les différents résultats ont été attribués à la variation en distribution de la pluie. La composition de mulch n'a pas eu d'influence significative sur aucune des trois années. Parmi les cinq modes évalués, les deux qui ont assurés les récoltes les plus élevées sur la période entière de trois ans, étaient les feuilles d'azadirachta appliquées (i) au semis et (ii) 4–6 semaines après le semis. Les rendements ont baissés entre 1988 et 1989, tant sur les parcelles traitées que sur les parcelles non-traitées. Sur les parcelles traitées, les rendements ont de nouveau augmentés en 1990. Cette augmentation a été attribuée a un effet résiduel du mulch. Cet effet résiduel probablement n'explique qu'une partie de la grande différence en rendement entre les parcelles traitées et non-traitées. Il paraît donc que la plupart des élements nutritifs libérés par le mulch ont été utilisés par les plantes au cours de la même saison, et qu'ils ont ainsi augmenté la production. De plus, la couche de mulch a probablement réduit l'évaporation, résultant en une augmentation de la rétention d'eau dans le sol.

     

The influence of trees on nitrogen dynamics in an agrisilvicultural system in Sweden

During 1992 and 1993, nitrogen dynamics and microbial activity were investigated in an agrisilvicultural system consisting of oats or barley cyltivated along the sides of a poplar plantation in Sweden. At each of three experimental sites (two silt loams and one silty clay loam), sampling for mineral nitrogen was carried out in three layers down to 90 cm at two distances from the trees, A (0.5–1.5 m) and B (4.0–5.0 m), two times each year (spring and autumn). Sampling of soil for organic amtter, carbon and nitrogen, potential nitrification, N ineralization, basic respiration and substrate-induced respiration was carried out in the 0–10 cm layer at three distances from the trees: A (0.5–1.5 m), B (2.5–3.5 m) and C (4.0–5.0 m).Significantly larger amounts of organic matter, total carbon and nitrogen at A than at B and C, indicated increased inputs from the trees through litter, decaying roots and root exudates. This could explain that the rates of nitrogen mineralization, potential nitrification and respiration were significantly higher at A than at B and C. The presence of trees resulted in a better utilization of nitrogen and moisture in the soil, reducing the potential for nitrate leaching and accumulating nitrogen close to the trees. The higher concentration of ammonium, lower concentration of nitrate and the consistently lower NO ₃ ^– –N/NH ₄ ⁺ –N-ratios observed at A than at C might be explained by a combined effect of increased nitrogen mineralization and efficient nitrate uptake by the trees.     

Canopy management possibilities for arboreal Leucaena in mixed sorghum and livestock small farm production systems in semi-arid India

A major problem for small farmers in the semi-arid tropics is the chronic shortage of fodder for draft animals. Leucaena leucocephala has improved productivity in many places in India and in various cropping systems, usually as either a pure crop or in a hedgerow alley-cropping configuration. Mixed cropping with arboreal forms is seldom seen. For off-season fodder production, hedgerows have the disadvantage of being open to unmanaged browsing when unfenced (as is usual). Arboreal forms are generally far less vulnerable. In this paper, the components of production of sorghum and arboreal Leucaena are measured under different intensities of canopy lopping. The most productive management system of those examined was pollarding of the Leucaena at the time of under-sowing with sorghum. In a year with less than 50% of average seasonal rainfall, this system gave a yield of 4.6 tonnes/ha/yr fresh wt fodder and 3.8 tonnes/ha/yr dry wt. of fuel harvests, while increasing the standing crop of wood by 1.8 t/ha/yr and retaining a yield of sorghum grain equivalent to 46% of pure sorghum cropping; the LER of this system was 1.35. Cash values of the alternative management systems were estimated, including the discounted Net Present Value of the standing crop of timber. Maximum value was attained with unlopped pure crop Leucaena followed by pollarded Leucaena with sorghum; pure crop sorghum achieved a lower value. These results demonstrate both the high productivity of Leucaena/sorghum based systems, and the stability of production even in poor rainfall conditions. Pollarding transferred the high future value of Leucaena timber to the present value of sorghum grain and fuelwood.     

Carbon storage and nitrogen cycling in silvopastoral systems on a sodic in northwestern India

Tree-based land-use systems could sequester carbon in soil and vegetation and improve nutrient cycling within the systems. The present investigation was aimed at analyzing the role of tree and grass species on biomass productivity, carbon sequestration and nitrogen cycling in silvopastoral systems in a highly sodic soil. The silvopastoral systems (located at Saraswati Reserved Forest, Kurukshetra, 29°4prime; to 30°15prime; N and 75°15prime; to 77°16prime; E) consisted of about six-year-old-tree species of Acacia nilotica, Dalbergia sissoo and Prosopis juliflora in the mainplots of a split-plot experiment with two species of grasses, Desmostachya bipinnata and Sporobolus marginatus, in the subplots. The total carbon storage in the trees + grass systems was 1.18 to 18.55 Mg C ha⁻¹ and carbon input in net primary production varied between 0.98 to 6.50 Mg C ha⁻¹ yr⁻¹. Carbon flux in net primary productivity increased significantly due to integration of Prosopis and Dalbergia with grasses. Compared to 'grass-only' systems, soil organic matter, biological productivity and carbon storage were greater in the silvopastoral systems. Of the total nitrogen uptake by the plants, 4 to 21 per cent was retained in the perennial tree components. Nitrogen cycling in the soil-plant system was found to be efficient. Thus, It is suggested that the silvopastoral systems, integrating trees and grasses hold promise as a strategy for improving highly sodic soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect on maize growth of the interaction between increased nitrogen availability and competition with trees in alley cropping

Maize growing next toErythrina hedgerows had 44% lower biomass (p<0.01) and 35% lower N content (p<0.1) than maize growing in the middle of the alleys. Maize growing next toGliricidia hedgerows had the same biomass but 56% higher N content (p<0.1) than maize growing in the middle of the alleys. However these differences did not develop until 2 months after sowing of the maize.Spatial variability in soil nitrogen mineralization and mulch nitrogen release did not explain any of the differences in growth or N uptake of the maize with respect to distance from the trees. It is hypothesized that the slower growth of the maize next to theErythrina trees after 2 months is due to increasing light and/or nutrient competition from the trees as the trees recover from pollarding. The apparent lack of competition fromGlirigidia may be due to different rates of regrowth or different shoot and root architecture.A theoretical model is described demonstrating that if a crop is to take advantage of the higher nutrient availability under alley cropping it must complete the major part of its growth before the trees recover significantly from pollarding, and start competing strongly with the 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.     

等高固氮植物篱对横断山区农业产业结构调整作用的研究

我国横断山区有自然资源丰富，农业发展潜力大的优势，但生态环境退化，农业产业结构不合理。等高固氮植物篱技术在水土保持、土壤培肥、饲养特畜、发展蚕垒、生产烤烟、供给薪柴和沼气、恢复植被、综合利用农业土地资源等方面良好的作用和效果，可作为横断山区调整农业产业结构的有效措施，并可在农业可持续发展中发挥重要作用。     

Comparative performance of four multi-purpose trees associated with four grass species in the humid regions of Southern India

The results of a field trial conducted at the Livestock Research Station, Thiruvazhamkunnu, Kerala to study the compatibility of different components in a silvo-pastoral system revealed that growth and yield of fodder species were significantly influenced by the tree components only after tree canopy formation. The fodder species such as Pennisetum purpureum Schum., Panicum maximum Jacq., Brachiaria ruziziensis Griseb. and Euchlaena mexicana Schrad. grown in association with Casuarina equisetifolia J. R. & G. Forst. and Ailanthus malabarica DC recorded comparatively higher forage yield even after canopy formation. However, forage crops grown in combination with Acacia auriculiformis A. Cunn. ex Benth. and Leucaena leucocephala (Lam.) de Wit. registered relatively lower values for growth and yield. Increased light infiltration into the understorey due to the cladophyllous canopy can be attributed as reason for the higher fodder productivity under Casuarina. Due to the combination of crown size and shape, tree height and spacing the amount of light intercepted by Ailanthus also was very low. Among the four multi-purpose trees used, Acacia recorded the maximum growth rate followed by Casuarina, Ailanthus and Leucaena. Forage productivity of the four species was in the order: Pennisetum purpureum > Panicum maximum > Brachiaria ruziziensis > Euchlaena mexicana. Casuarina with Pennisetum/ Panicm were found to be optimal tree — forage combinations for silvo-pastoral systems.     

Seasonal dynamics,especially autumnal retranslocation,of nitrogen and phosphorus in foliage of dominant and suppressed trees of beech,Fagus sylvatica

Seasonal changes in the N and P content of foliage in a young forest of Fagus sylvatica were measured. Leaves from branches of the upper and lower crown of dominant trees and from suppressed trees were compared. Nutrient retranslocation rates during senescence differed considerably between trees. This variation appeared not to be related to any differences in environmental factors or tree vigour, and was probably genetically induced. In dominant trees the most efficient retranslocation of N was recorded in the upper crown and probably resulted from higher leaf temperatures and a longer senescent period in the sun leaves than in the shade leaves. Phosphorus retranslocation efficiency was higher in suppressed trees than in dominant ones, but no such tendency was observed with N. The most obvious difference between leaves at different crown levels concerned the time at which P translocation began; an outflow of P from leaves in the lower crown began in June, while in the upper crown this outflow did not begin until September/October.     

Assessment of fertilizer nitrogen accumulation in Pinus sylvestris trees and retention in soil by 15N recovery technique

The distribution and quantitative recovery of fertilizer N were determined in three 29‐ to 43‐year‐old stands of Scots pine, located in western Uppland, Central Sweden. The experimental technique involved was based on the use of ¹⁵N‐labelled fertilizer materials and non‐trenched microplots of special design. The standard dose of nitrogen applied was 160 kg N ha^‐1. The primary topics examined were (1) fertilizer nitrogen accumulation in trees and in the soil system as influenced by nitrogen source, nitrogen application rate, time of application during the growing season, granule size of the nitrogen material, and method of placement, (2) distribution of labelled N within the tree (different organs of the tree), and (3) redistribution of accumulated N in the tree over an observation period of two to three growing seasons. When quantified at the end of the second growing season, the labelled N accumulation in trees, concerning plots treated with calcium nitrate or ammonium nitrate, averaged 36% (SD=7). The accumulation resulting from split doses did not differ significantly from that resulting from a single‐dose application, nor did granule size of the nitrogen materials have any significant effect on accumulation. For urea source of nitrogen, the recovery figure was markedly lower, averaging 28% (SD=6). When expressed as a percentage, the accumulation in trees was not significantly different for 40 and 160 kg nitrogen application rates. In one of the experiments application timing during the growing season proved to be an important factor determining the extent of fertilizer nitrogen accumulation in trees. The figures for total recovery of labelled nitrogen in above‐ground parts of trees and in soil, when restricting measurements to the forest floor and the 0–32 cm mineral soil, ranged from 46 to 84%, with an average of 60%. The recovery was lowest for a treatment with calcium nitrate, when applied relatively late in the growing season, and highest for a split application of urea. Treatments with urea source of nitrogen were characterized by a high accumulation of immobilized N in the organic LFH layer of the soils. Recovery figures exceeded 82 % for a 40‐kg N dose of nitrogen, regardless of the nitrogen source.     

Intercropping system of tropical leguminous species and Eucalyptuscamaldulensis, inoculated with rhizobia and/or mycorrhizal fungi in semiarid Brazil

For the purpose of reforestation and wood supply the leguminous tree Anadenanthera peregrina, a native species, was intercropped with Eucalyptus camaldulensis in a degraded semiarid area of Brazil. Single and mixed stands of these species were inoculated with Rhizobium and/or arbuscular mycorrhizal fungi (AMF). The growth of all species in mixed stands did not differ from those cultivated in monoculture and land equivalent ratio (LER) exceeded unity in intercropped plots. Inoculated plants showed greater height and diameter growth and dry matter and nutrient concentration in plants of A. peregrina was higher in inoculated single plots. The distribution, composition and density of AMF species was related to the rhizosphere effect of plant species. The intercropped model where all the plants were inoculated achieved soil AMF diversity patterns similar to those of the preserved area and showed also higher soil organic matter, nutrient content as well as a reduction in soil macroporosity. This model of intercropping may be considered as an efficient system for reforestation under semiarid conditions.     

Nutrition and growth of wheat–sorghum rotation in soils amended with leaf litter of trees before planting of wheat

Nutrient release from plant residues can be manipulated as per crop demand through several approaches. A pot study was conducted to study the influence of incorporation of leaf litter of poplar (Populus deltoides), eucalypt (Eucalyptus hybrid) and dek (Melia azedarach) inoculated with cellulolytic fungus culture (Aspergillus awamori) on the nutrition and biomass of wheat (Triticum aestivum, cv. PBW 343) in loamy sand and sandy loam soils. The residual effect of leaf litter after wheat harvest was studied on sorghum (Sorghum bicolor, cv. Punjab Sudax Chari 1). The treatments consisted of a control (no leaf litter) and three uninoculated as well as inoculated leaf litter levels of tree species–0.15%, 0.30% and 0.45% (w/w, dry weight basis). A uniform dose of N, P and K @ 50, 11 and 10 mg kg⁻¹ soil, respectively from inorganic fertilizers was applied to all the treated pots. Straw and grain yield, and nutrient content of wheat increased with increasing level of uninoculated or inoculated leaf litter in both the soils. The inoculated leaf litter augmented the yield and nutrient content of crop significantly (P < 0.05) as compared to the corresponding uninoculated treatments. Poplar and dek leaf litter produced higher wheat yield, plant nutrient content and available nutrients in soil after wheat harvest than eucalypt leaf litter. Dry matter yield of sorghum raised on residual fertility increased significantly with increasing levels of leaf litter application. The comparative responses in yield and nutrient content of crops were higher in loamy sand than in the sandy loam soil. The study shows the beneficial influence of use of cellulolytic microorganisms on enhancement in decomposition and nutrient release from litterfall of tree species.     

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

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