Defining competition vectors in a temperate alley cropping system in the midwestern USA: 2. Competition for water

A study was carried out in an alley cropping system in the Eastern Maize Belt of the United States with the objective of quantifying the competition for water between trees (black walnut (Juglans nigra L.) and red oak (Quercus rubra L.) and maize (Zea mays L.). Spatial and temporal variation in soil moisture, tree and maize rooting patterns, tree and maize water uptake, and maize leaf area expansion were determined in three treatments; barrier (polyethylene root barriers separating maize and tree roots), trench (trenching without a polyethylene barrier), and no barrier (control). Significant temporal variation in soil moisture was observed in both black walnut and red oak alley cropping systems. The barrier and trench treatments resulted in higher soil moisture in the maize alley and lower soil moisture in the tree row than the no barrier treatment. Uptake of water by maize was higher in the barrier than the no barrier treatment. However, tree water uptake was higher in the no barrier treatment than in the barrier treatment because tree roots utilized water from the maize alley. Maize leaf area was negatively impacted by water stress in the no barrier treatment. Quantification of rooting patterns revealed that maize and tree roots were concentrated in the top 30 cm soil layer where water fluctuations were greatest. The barrier and trench treatments successfully eliminated the belowground root competition between trees and maize and resulted in greater leaf area and higher grain yields than the no barrier treatment. Thus, competition for water rather than competition for light seems to be critical in defining the productivity and sustainability of this alley cropping system.This revised version was published online in November 2005 with corrections to the Cover Date.     

Comparative performance of seventeen upperstorey tree species associated with crops in the highlands of Uganda

Trials were established at three sites in Uganda to test the suitability of multipurpose trees (MPTs) as upperstorey in crop lands to provide poles, small timber and fuelwood. The three sites were Kachwekano District Farm Institute (1°16 S, 29°57 E, 2000 m.a.s.l.) in Kabale District, Kabanyolo University Farm (0°28 N, 32°27 E, 1250 m.a.s.l.) in Mpigi District and Bushenyi District Farm Institute (0°34 S, 30°13 E, 1610 m.a.s.l.) in Bushenyi District. The MPTs were planted in single rows at intra spacing of 2 m and each plot contained seven or nine trees. On both sides of the tree row, crops were raised. Data on crop yields were collected every season, while data on the growth of the trees were collected four times each year.In terms of tree growth,Grevillea robusta, Casuarina cunninghamiana andAlnus acuminata performed well with height growth of 1.8–2.4 m per year at Kachwekano, while at BushenyiGrevillea robusta, Casuarina junghuhniana, Cupressus lusitanica andCedrela serrulata averaged 1.6–2.0 m height per year. At Kabanyolo,Melia azedarach, Cassia siamea, Jacaranda mimosifolia, Grevillea robusta andMaesopsis eminii had height increments ranging from 1.8–2.7 m annually. Crop yields were affected by the presence of the MPTs, withMaesopsis eminii being the most competitive (averaging 60% reduction, over five seasons). The crop rows nearest to the tree line were the most affected. OnlyAlnus acuminata seems to have had a positive effect on crop yields. The installation of a root mesh to reduce tree root competition for nutrients and water in four species increased yields in plots with MPTs by 5% (Melia azedarach) to 152% (Maesopsis eminii), but the control plot still had significantly higher bean yields, suggesting that shading could also be important. In the case of maize, suppression seems to be due mainly to root competition because after its elimination yields obtained thereafter did not differ significantly from those of the control except for the Maesopsis plots. The negative influence of the MPTs could, therefore, be minimized by periodically pruning the tree crowns and roots.     

Leaf-water potential and soil-water depletion of walnut mulched with polyethylene and intercropped with alfalfa in Central Italy

In Italy, new agroforestry cultural models could play an important role in the diffusion of plantation forestry timber species. We studied the stem growth rates and leaf water potentials () of common walnut (Juglans regia L.), and gravimetric soil moisture (_DW) depletion during the third and fourth growing seasons in an agroforestry trial in central Italy. Since the establishment of experimental plots in 1992, walnut was intercropped with alfalfa (Medicago sativa L.), with or without polyethylene (PE) mulching along tree rows. By the end of the study period, the unmulched-intercropped walnut was almost 68% smaller in stem diameter and height than the sole-unmulched control, demonstrating walnuts sensitivity to alfalfa competition. The competitive effect of alfalfa on walnut stem growth was effectively controlled/reduced by PE mulching. Stem growth rates of mulched-intercropped walnut were always lower than the control, but much higher (ca. 235% in stem diameter and height) than those of unmulched-intercropped walnut. The higher field performance of mulched-intercropped walnut compared to the un- mulched-intercropped treatment was associated with higher soil moisture and predawn and midday values during the summers driest periods. The presence of PE mulching was also associated with lower levels of soil moisture during the early and late growing season, but this did not negatively affect walnut and growth rates. These results suggest that in the climatic conditions of central Italy, competition for soil moisture between young common walnut trees and alfalfa can be substantially lowered, but not completely eliminated, by PE mulching.This revised version was published online in November 2005 with corrections to the Cover Date.     

Defining competition vectors in a temperate alley cropping system in the midwestern USA: 3. Competition for nitrogen and litter decomposition dynamics

An experiment was conducted in an 11-year-old black walnut (Juglans nigra L.), red oak (Quercus rubra L.), maize (Zea mays L.) alley cropping system in the midwestern USA to examine the extent of tree-crop competition for nitrogen and decomposition dynamics of tree leaves and fine roots. A below-ground polyethylene root barrier (1.2 m deep) isolated black walnut roots from maize alleys in half the number of plots providing two treatments viz. barrier and no barrier. The percentage of N derived from fertilizer (%NDF) and fertilizer use efficiency (%UFN) were determined using ¹⁵N enriched fertilizer. Further, maize grain and stover biomass, tree leaf biomass, tissue N concentration, and N content were quantified in both treatments. The barrier treatment resulted in a significantly greater grain (67.3% more) and stover (37.2% more) biomass than the no barrier treatment. The %NDF in both grain and stover was higher in the no barrier treatment as a result of competition from tree roots for water and mineralized N in soil. Maize plants growing in the no barrier treatment had a lower %UFN than those in the barrier treatment due to their smaller size and inability to take up fertilizer. Analysis of tree leaf and fine root decomposition patterns revealed faster release of N (39% over 15 days for black walnut and 17.7% for red oak) and P (30% over 15 days for both species) from roots compared to the leaves of both species. Following an early release of P (11.3% over 45 days), red oak leaves exhibited significant immobilization for the rest of the incubation period. The data indicate that competition for N from fertilizer is minimal since nutrient acquisition is not simultaneous among black walnut and maize. However, competition for mineralized N in soil can exist between black walnut and maize depending on water availability and competition. Tree leaves and fine roots can enhance soil nutrient pools through the addition of soil carbon and nutrients. Tree fine roots seem to play a more significant role in nutrient cycling within the alley cropping system because of their faster release of both N and P as compared to leaves. Selection of tree species and their phenology will impact the magnitude and rate of nutrient cycling.This revised version was published online in November 2005 with corrections to the Cover Date.     

Five years of Paulownia field trials in North Carolina

Performance of Paulownia elongata, Paulownia fortunei, and Paulownia×Henan 1 was monitored at three sites in North Carolina between 1996 and 2000, and P. elongata clones were tested at an additional two sites. The primary objective was to define the potential for growing Paulownia in the state. Species and clones within species differed in survival and height and diameter growth whenever genotype was included as a treatment. P. elongata was superior at two and P. fortunei was superior at one of the three sites that included P. elongata, P. fortunei, and P.×Henan 1. Trees produced through vegetative means were more likely to survive and were taller and of greater DBH than seed produced trees. Mortality in trees produced from seed was greater for P. fortunei and P. ×Henan 1 than for P. elongata. Application of animal waste or different rates of nitrogen as inorganic fertilizer did not have a pronounced effect on tree survival and growth.     

Soil properties and nitrogen availability in silvopastoral plantings of Acacia melanoxylon in North Island, New Zealand

Acacia melanoxylon, a N₂-fixing timber tree occurring naturally in eastern Australia, is now promoted as a component of silvopastoral systems; but the interaction of the tree with pasture and soils has not been adequately studied. This study investigated the effects of Acacia melanoxylon on soil nitrogen (N) levels, N availability, soil pH, bulk density, organic carbon, C:N ratios and soil moisture in three separate silvopastoral sites with contrasting soil types in the North Island of New Zealand. At each site four tree stocking rates were studied (0, 500, 800, and 1700 stems ha^–1). The trees were nine years old at the time of the study. Soil samples from each study site were taken once at three depths (0 to 75 mm, 75 to 150 mm, and 150 to 300 mm), with three replicates per tree stocking rate. Soil analyses showed that although there were differences between soil types, few statistically significant differences occurred due to tree stocking rate. A greenhouse pot trial growing ryegrass (Lolium multiflorum L. cv. Concord) in soil from the A horizon of each soil type from under the trees and the open pasture found that ryegrass yield, N uptake and N supply increased with increasing tree stocking rate. Increased N supply under the trees, coupled with greater soil moisture compared to the open pasture may have accounted for the higher pasture yield under Acacia melanoxylon compared to non dinitrogen fixing tree species. This study suggested that Acacia melanoxylon in a silvopastoral system had the potential to increase soil N availability.This revised version was published online in November 2005 with corrections to the Cover Date.     

Vegetation response to intensity of herbaceous weed control in a newly planted loblolly pine plantation

Growth of loblolly pine (Pinus taeda L.) seedlings through three growing seasons after planting increased with intensity of herbaceous weed control using herbicides. Weed control had no effect on pine survival. Two years of complete herbaceous weed control (CHC, control throughout the first two growing seasons after planting) and operational herbaceous weed control (OHC, sulfometuron at 0.42 kg ai/ha at the beginning of the first growing season), resulted in lower biomass of weeds plus trees than with no herbaceous weed control (NHC) during the first growing season. Differences in total biomass during the first year were due to differences in biomass of herbaceous weeds. Total biomass on CHC and OHC plots was at least as great as NHC the second year, and greater by the third year, as pines assumed dominance as a result of increased growth from reduction of herbaceous weeds. The operational herbicide treatment had no significant impact on overall herbaceous weed biomass and cover, and little effect on species composition compared to no herbaceous weed control two and three growing seasons after treatment. The CHC treatment significantly reduced herbaceous weed biomass, cover and composition through three growing seasons.     

Effect of cutting position on rooting and shoot growth of two poplar clones

One-year-old shoots from stooling beds of Populus × deltoides Walker and Populus jackii Northwest were collected in late fall to determine the effect of cutting position on rooting and growth of hardwood poplar cuttings. Cuttings with a minimum diameter of 9.0 mm were obtained from basal, middle and distal locations on the poplar shoot. Rooting and shoot growth were assessed in the greenhouse and under field conditions. Walker poplar cuttings collected from basal portions of the shoot and planted in the field had 87.6% rooting and 103.8 cm growth compared to 78.8% and 103.4 cm and 67.6% and 88.8 cm for middle and distal locations respectively. For Northwest rooting and growth under field conditions was 84.4% and 94.7 cm for basal, 78.4% and 90.5 cm for mid and 64.4% and 84.3 cm for distal locations. Rooting in the greenhouse was superior to the field. Walker cuttings had fewer roots and buds per cutting than Northwest, however, growth of Walker in the field was superior.     

Influence of forbs and shrubs on ruminal fermentation and digesta kinetics in sheep fed a grass hay/straw diet

Four ruminally cannulated, Debouillet wethers were used in a 4×4 latin square experiment to evaluate the influence of a forb mix, a shrub mix and alfalfa (ALF) hay on ruminal fermentation characteristics and digesta kinetics of a basal grass hay/straw (GH/S; 1.04% N) diet. The grass hay was mostly blue grama (Bouteloua gracilis) mixed with barley (Hordeum vulgare) straw. Wethers were fed either the GH/S mix (7030), GH/SALF (295813), GH/Sforbs (265420), or GH/Sshrubs (265420). The forb component consisted of equal parts of scarlet globemallow (Sphaeralcea coccinea) and leatherleaf croton (Croton corymbulosus) while shrubs were composed of equal parts of fourwing saltbush (Atriplex canescens) and mountain mahogany (Cercocarpus montanus). Ruminal pH, ammonia-N, as well as total VFA concentrations and molar proportions of individual VFA did not differ among diets. Particulate passage rates tended (P>0.10) to be greater for diets containing ALF, forbs or shrubs (2.8, 2.9 and 2.8% h^–1) than the GH/S diet (2.5% h^–1). In situ DM and NDF disappearance of a GH/straw (5050) mix did not differ among treatments at most incubation times, except at 96 h when extent of both DM and NDF disappearance were greater (P<0.05) in sheep fed either forbs or shrubs than in those fed other diets.     

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.     

Biometric relationships for non-destructive above ground biomass estimations in young plantations of Acacia salicina Lindl. and Eucalyptus occidentalis Endl.

Above ground oven dried biomass (BM) of individual trees in young stands of Acacia salicina Lindl. and Eucalyptus occidentalis Endl. were correlated linearly and logarithmically to the square of the basal diameter at 0.2 m (DB) and to the latter multiplied by the height of the tree. Number of main stems at basal height per tree were included as well. DB measurements in young Eucalypt stands provided better BM estimates than the commonly used diameter at breast height (1.3 m) (DBH).The following biometric relationships, after cross-validation against an independent data set, showed the best fit: BM=0.1282* (DB²) and BM=0.1700* (DB²) for A. salicina and E. occidentalis, respectively, with (DB²) ranging from 0–400 cm² and BM in kg tree^–1. For acceptable relative errors in biomass estimations (DB²) should be larger than 100 cm².Foliage to wood ratios at (DB²)<100 cm² for both tree species generally exceeded 1, but rapidly leveled off at 0.81±0.28 and 0.92±0.19 for the Acacia and Eucalypt spp., respectively, at higher (DB²) values.     

Agroforestry training and extension: the experience from Haiti

An agroforestry project was funded by the US Agency for International Development and implemented by the Pan American Development Foundation in Haiti from 1981 to 1991. This project is considered by many to be one of the most successful projects of its kind in Haiti, and in the tropics as a whole. Over the ten years of its implementation, the project, referred to in Haitian Creole as Pwoje Pyebwa (Tree Project), evolved from a tree production and planting project to a much broader soil-conservation-based program involving trees. This paper summarizes the training and extension systems that developed during that period. The socioeconomic background studies that were done before the project began, and the flexible, consultative mode of field-team implementation, incorporating elements of the learning process approach, were important to the success of the project. During the implementation of the project, however, concern for farmer input and participation should have been incorporated more systematically into the field operations of the regional teams.     

Examination of within-tree variations and the heights representing whole-tree values of derived wood properties for quasi-non-destructive breeding of Eucalyptus camaldulensis and Eucalyptus globulus as quality pulpwood

Within-tree variations of derived wood properties of Runkel ratio, Luces shape factor, slenderness ratio, and solids factor were examined for Eucalyptus camaldulensis and Eucalyptus globulus trees and the tendency difference in the within-tree variations between individuals and between species, in both radial and axial directions by statistical data analysis. These properties are important for quality breeding of pulpwood. In both species, within-tree variations were generally observed as higher values in the upper and outer parts compared with other parts of the trunk for Runkel ratio and Luces shape factor. In E. camaldulensis, within-tree variations were observed as higher values in the upper and outer parts compared with other parts of the trunk for slenderness ratio and solids factor. In E. globulus, within-tree variations were observed as higher values in the outer parts compared with other parts for slenderness ratio and solids factor. However, significant difference of tendency was observed in radial variation between individuals of E. globulus for Runkel ratio and in both radial and axial variations between species for solids factor. Furthermore, within-tree variations of derived wood properties were analyzed to determine a sampling height in the trunk which can be used to represent whole-tree values. Representative heights of derived wood properties from two trees were found to be 2.8m in E. camaldulensis (except for Runkel ratio and Luces shape factor) and 1.8m in E. globules (except for Runkel ratio), regardless of differences in tree height (growth rate) and in tendency of within-tree variation of derived wood properties.     

Tropical red gums — a source of 1,8-cineole-rich Eucalyptus oil

Tropical provenances of Eucalyptus camaldulensis Dehnh. and E. tereticornis Smith were studied, in their natural habitat in Australia and in a 3.75-year-old progeny trial in Zimbabwe, for their potential to produce medicinal-grade essential oils. Substantial interand intra-specific variation in the contents of five prominent monoterpenes, 1,8-cineole, -pinene, -pinene, limonene and p-cymene was found. Plantations of E. camaldulensis established in the wet/dry tropics using seed from Petford in northern Queensland offer immediate potential for oil production. Other widely-planted Queensland provenances with oil potential are Gilbert River Bridge E. camaldulensis and, after some genetic improvement, E. tereticonis from Morehead and Kennedy Rivers. Select individual trees at Petford provide oil of enhanced quality, at about double the yield of average trees.     

Cutting management of alley cropped leucaena/gliricidia-Guinea grass mixtures for forage production in southwestern Nigeria

A study was conducted at Fasola (7°45 N and 3°5 E) in southwest Nigeria to determine the best tree cutting scheme for forage production and the effects of hedge configurations on tree, grass and total forage productivity of 6–8-year-old leucaena (Leucaena leucocephala Lam. de Wit) and gliricidia (Gliricidia sepium Walp.)-Guinea grass (Panicum maximum Jacq. cv. Ntchisi) mixture. After a uniform cut at the end of January 1990 (mid-dry season), the trees were cut according to the following cutting regimes: one cut after a 12-month regrowth (12M); two cuts after three- and nine-month regrowth (3–9M); two cuts every six months (6-6M); two cuts after nine- and three-month regrowth (9-3M); three cuts, two cuts every three months and the third cut after a six-month regrowth (3-3-6M), and four cuts every three months (3-3-3-3M). Grass was cut every six weeks between April and October followed by a cut in January. The hedge configuration was either one or three hedgerows of mixed stands of leucaena and gliricidia. There were twice as many trees and one-third less grass in the triple than in the single hedgerow hedge configuration.The 3-3-3-3M, 9-3M and 3-3-6M cutting regimes produced the highest total forage (tree foliage + grass) dry matter yields (DM) of 6.54, 5.80 and 5.77 t DM ha^–1 annum^–1, respectively. The magnitude of the difference between the tree forage yields of the triple and single hedgerow plots (16%) did not reflect the theoretical difference in the number of trees (33%) in the two arrangements.     

Fallow enrichment of a traditional slash/mulch system in southern Costa Rica: comparisons of biomass production and crop yield

The slash and mulch system of frijol tapado or covered bean is a pre-hispanic system of bean production found throughout much of Central America. However, land use pressures have forced farmers to shorten the traditional fallow period, thus resulting in decreasing productivity. A potential solution is to enrich the fallow by using leguminous nitrogen-fixing trees. The enriched fallow systems evaluated in this study include both single and mixed species treatments: 1) Erythrina poeppigiana; 2) Calliandra colothrysus; 3) Gliricidia sepium; 4) Inga edulis; 5) Inga edulis and Erythrina poeppigiana; 6) Inga edulis and Calliandra calothrysus; and 7) Inga edulis and Gliricidia sepium. Biomass production of the fallow vegetation is shown to be of greater quality and quantity in all fallow enrichment treatments. However, bean yields did not show a significant response to the fallow enrichment treatments.     

The performance of the leaf mulches ofLeucaena leucocephala,Flemingia macrophylla andGliricidia sepium in weed control

The performance of the leaf mulches ofLeucaena leucocephala, Gliricidia sepium andFlemingia macrophylla in weed control has been tested in two trials. The length of the period during which a mulch layer yields significantly less weedbiomass compared to the control plots is called the effective life-span of the mulch.Of the three mulch materials only that ofF. macrophylla shows promise in retarding weed development.In the second trialF. macrophylla leaf mulch was applied at rates of 3, 6 and 9 tons dry matter per ha. The effective lifespan of a mulch layer of 3 tons is between 12 and 13 weeks. The treatments 6 and 9 tons have effective life-spans of over 14 weeks.For moderate quantities (up to 5 tons of dry leaf mulch per ha) the effective life-span is estimated at about a 100 days.The value of mulching in weed control is limited to the control of weed species that multiply by seed. Regrowth originating from roots or stumps from former vegetation is unlikely to be checked by a mulch layer.The subject of this paper is part of a broader study, presently conducted in Southern Ivory Coast, on the production, agronomical value and use in alley-cropping systems of the species mentioned in the title of the paper. A final report is scheduled for publication in 1988.     

Predicting the decomposition patterns of tree biomass in tropical highland microregions of Kenya

Decomposition- and nitrogen-release patterns of biomass from three agroforestry multipurpose trees (Calliandra calothyrsus, Cordia africana and Grevillea robusta) were investigated in four contrasting environments (microregions) in the Kenyan tropical highlands during two cropping seasons. Dried leafy biomass was placed in 2-mm litter bags, buried at 15-cm depth and recovered after 2, 4, 7, 10, 15 and 20 weeks. Decomposition patterns were best described by first-order exponential decline curves. The decomposition rate constants ranged from 2.1 to 8.2 yr^–1, and the rates of decomposition among the species were in the order: calliandra cordia > grevillea. There was a species-by-environment interaction during both seasons, but the nitrogen released did not follow such a pattern. Among the three tree species, calliandra released the highest amount of cumulative N, followed by cordia and grevillea. Using multiple regression techniques, decomposition pattern was described as a function of three groups of factors: biomass quality (N, C, lignin and polyphenol), climate (soil temperature and rainfall), and soil conditions (pH, soil organic C, total N and P). For all the species and factors combined, the adjusted R ² values were 0.88 and 0.91 for seasons 1 and 2, respectively. Among the three groups of factors, climate and biomass quality had the most influence on decomposition rates. Climatic factors accounted for 75% of the total rate of decomposition in season 1 (irregular season with less rainfall and more soil temperature fluctuations), whereas biomass quality factors were more influential in season 2 (regular season), accounting for 65% of the total variability.Florida Agricultural Experiment Station Journal Series No. R.-05555.     

Effect of rhizobial inoculation methods and host plant provenances on nodulation and growth of <Emphasis Type="Italic">Acacia senegal</Emphasis> and <Emphasis Type="Italic">Acacia nilotica</Emphasis>

The purpose of this work was to determine the most efficient methods of inoculation to significantly improve nodulation and growth of Acacia senegal and Acacia nilotica, grown under greenhouse conditions. Our results showed that inoculation using dissolved alginate beads containing rhizobia significantly improved the growth of both acacia species better than the growth of plants in other treatments. The experiment with A. nilotica was conducted in two unsterilised soils from different areas. Plants grown in soil from Bel Air were well-nodulated and showed better growth than plants grown in soil from Sangalkam. However, no difference between these soils was shown between the several methods of inoculation and their effect on the nodulation and growth of plants. An interaction between A. senegal and A. nilotica provenances and the effect of inoculation with rhizobia was also demonstrated. Bel Air provenance of A. senegal, Dahra and RIM provenances of A. nilotica grew best of several provenances tested. These results suggest that (1) it may be possible to improve growth and yield of A. senegal and A. nilotica by careful selection of each symbiotic partner; and (2) nursery-grown seedlings of A. senegal and A. nilotica should be inoculated, just after sowing, with dissolved alginate beads containing a mixture of selected rhizobia. Résumé. Lobject de notre travail était de déterminer la méthodologie dinoculation la plus efficace pour améliorer significativement la nodulation et la croissance dAcacia senegal et dAcacia nilotica poussant dans des conditions de serre. Nos résultats ont montré que linoculation utilisant des billes dalginate dissoutes améliorait significativement la croissance des deux espèces dAcacia par rapport à celle des plantes des autres traitements. Lexpérience avec A. nilotica a été faite dans deux types de sol non stériles. Nous avons observé que les plants poussant dans le sol de Bel Air étaient plus nodulés et mieux développés que ceux poussant dans le sol de Sangalkam. Cependant, aucune différence significative entre les deux sols na été mise en évidence en termes deffet des différentes méthodologies dinoculation sur la nodulation et la croissance des plantes. Il a aussi été démontré lexistence dune interaction entre les provenances dA. senegal et dA. nilotica et leffet de linoculation avec rhizobium. Cest ainsi que les provenances Bel Air dA. senegal, Dahra et RIM dA. nilotica ont le mieux poussé parmi les différentes provenances testées. Lensemble de ces résultats suggèrent: ⁽¹⁾ il devrait être possible daméliorer la croissance et la production dA. senegal et dA. nilotica par une sélection des deux partenaires symbiotiques; ⁽²⁾ Les jeunes plantules dA. senegal et dA. nilotica produites en pépinière devraient être inoculées juste après le semis avec des billes dalginate dissoutes contenant un cocktail de souches sélectionnées.     

Eucalyptus planting as a response to farm management problems faced by ‘on-site’ and ‘off-site’ farmers

The success of the green revolution in the fertile and agriculturally surplus plains of western U.P. in north India led to labour shortages, and increased opportunities for off-farm investments by landowners, requiring their time and energies away from farming. These changes impelled landowners to adopt strategies which saved family labour and supervision time in cultivation. Many off-site farmers, and such on-site farmers who had a high ratio of owned land to male members in the family, resorted to tree farming, mainly eucalyptus. On the other hand, farmers in eastern U.P., with small holdings, subsistence orientation and cheap labour, showed little enthusiasm for planting eucalyptus. Based on field investigation in six villages, this paper argues that woodlot planting of eucalyptus emerged as an attractive option for landowners facing management and labour problems in western U.P., as tree farming allowed saving in family labour time and permitted greater flexibility in the timing of operations. About 60% of the total trees planted were by this category of management-constrained farmers.