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1.
Nutrient losses during slash-and-burn clearing in tropical forests, coupled with demand by food crops, can deplete nutrients and result in crop abandonment after 1–2 years. Slash-and-mulch technology prevents nutrient losses from burning, while mulch decomposition may serve as a nutrient source. This research investigates the release of nutrients from the mulch and potential uptake of released N by plant biomass after a multi-species agroforestry system was planted in June 2005, following the clearing of a 1 ha of 7-year-old forest with a mulching tractor in Igarapé Açu, Brazil. The study evaluated soil conditions, mulch decomposition, and nutrient concentrations of Manihot esculenta and native vegetation under treatments of P+K fertilization in combination with four native tree species and N-fixing Inga edulis, or with three native tree species without I. edulis. Mulch layer N, Ca and Mg content decreased in response to fertilization, while mulch layer P and K content increased. Nutrient content increased in M. esculenta stems and tubers with fertilization and in the presence of I. edulis, and in competing vegetation with fertilization. Estimated tree N content increased 311 % with fertilization, but by 154 % in the presence of I. edulis. Fertilization with P+K, as well as the presence of I. edulis, increased N stocks in total biomass.  相似文献   

2.
As traditional slash-and-burn systems with prolonged fallow periods are no longer feasible in most parts of the tropics, improved agroforestry systems have high potential to increase the productivity of farming systems and sustain continuous crop production. Our objective was to assess biophysical and economic performance of planted leguminous tree fallow (using Inga edulis) compared to the traditional slash-and-burn farming system, practiced by farmers on fields infested with noxious weedy grass Imperata brasiliensis around the city of Pucallpa, Peru. An existing agroforestry model SCUAF was used to predict biophysical factors, such as changes in soil characteristics and farm outputs (crop and tree yield). While a cost–benefit analysis spreadsheet, which uses the output from SCUAF and economic data on input/output levels and prices, calculates economic performance of the systems. The Inga fallow system can provide improvements to a range of soil biophysical measures (C, N, P content). This enables higher levels of farm outputs to be achieved (higher cassava yields). However, for smallholders the improved system must be more economically profitable than the existing one. At prices currently encountered, the Inga fallow system is more profitable than the Imperata fallow system only in the long-term. In adopting the Inga fallow system, smallholders will incur lower profits in the first years, and it will take approximately 10 years for smallholders to begin making a profit above that achievable with the Imperata fallow system. Unless smallholders are capable of accepting the lower profitability in first years, they are less likely to adopt the new system.  相似文献   

3.
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.  相似文献   

4.
In the Palcazu Valley alluvial Inceptisols are relay-cropped with maize-cassavaplantain in rotation with 2–5 years of tree fallow. These lands, of limited extent, yet important for Yanesha Indian subsistence production, are being cropped even more intensively as population increases and land is converted to other uses. The relay-planting of the tree-thicket combination Inga edulis with Desmodium ovalifolium into the on-farm crop sequence was evaluated as a means to accelerate fallow recovery and thereby shorten fallow rotations. Three experiments with Inga/Desmodium planted with cassava-plantain and one with rice under different weeding regimes after a Desmodium fallow were conducted. Inga and Desmodium were not chopped back or pruned during these experiments. Desmodium/Inga suppressed herbaceous weeds from one year after planting. Desmodium/Inga accumulated more woody biomass than natural fallows. Cassava yields were unaffected by the presence of Desmodium/Inga, while plantain yields were greater under Desmodium/Inga compared to natural weeds. Desmodium/Inga, while promising for shortening fallow rotations, demonstrated potential difficulties: increased labor for establishment, tendency of Desmodium to weediness in later crop cycles, and suppression of the natural regeneration of trees and shrubs.  相似文献   

5.
The rotation of maize (Zea mays) with fast-growing, N2-fixing trees (improved fallows) can increase soil fertility and crop yields on N-deficient soils. There is little predictive understanding on the magnitude and duration of residual effects of improved fallows on maize yield. Our objectives were to determine the effect of fallow species and duration on biomass production and to relate biomass produced during the fallow to residual effects on maize. The study was conducted on an N-deficient, sandy loam (Alfisol) under unimodal rainfall conditions in Zimbabwe. Three fallow species — Acacia angustissima, pigeonpea (Cajanus cajan), and Sesbania sesban — of one-, two-, and three-year duration were followed by three seasons of maize. Pigeonpea and acacia produced more fallow biomass than sesbania. The regrowth of acacia during post-fallow maize cropping provided an annual input of biomass to maize. Grain yields for the first unfertilized maize crop after the fallows were higher following sesbania (mean = 4.2 Mg ha–1) than acacia (mean = 2.6 Mg ha–1). The increased yield of the first maize crop following sesbania was directly related to leaf biomass of sesbania at the end of the fallow. Nitrogen fertilizer did not increase yield of the first maize crop following one- and two-year sesbania fallows, but it increased yield following acacia fallows. Nitrogen fertilizer supplementation was not required for the first maize crop after sesbania, which produced high-quality biomass. For acacia, which produced low-quality biomass and regrew after cutting, N fertilizer increased yield of the first post-fallow maize crop, but it had little benefit on yield of the third post-fallow maize crop.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

6.
Roots of trees (Sesbania sesban) and crops (Zea mays) were quantified during two tree/crop cycles in a sequential tree — crop system at Chipata, Eastern Zambia. The experiment included one- and two-year fallows as well as fertilized and unfertilized controls. The roots of S. sesban represent a standing biomass in the soil of 3 Mg hat-1 in the top 1.5 m after two years, with 45–60% and 70–75% being in the top 25 and 50 cm respectively. S. sesban fallow improved early rooting and growth of the following maize crop. Increased soil infiltration was also observed in the two-year fallow treatment, as well as decreased bulk density and resistance to penetration in the soil. No differences between maize root parameters could be detected at tasselling, nor differences between nutrient status of the different treatments. Study results indicate that under the drought-prone conditions of Eastern Zambia, where improved soil physical conditions are important for early deep rooting of crops and access to water and nutrients, tree roots could play an important role in the fallow effect. Further studies are required to assess the relative importance of the improvement of soil chemical and physical properties.Submitted as ICRAF Journal Article # 95/28.  相似文献   

7.
A study on dry matter production and nutrient cycling in agroforestry systems of cardamom grown under N2-fixingAlnus and mixed tree species (non-N2-fixing) was carried out in the Sikkim Himalaya. The stand total biomass, and tiller number, basal area and biomass of cardamom crop was much higher under the influence ofAlnus. Annual net primary productivity ofAlnus trees was slightly higher than mixed tree species in spite of lower stand density ofAlnus. The agronomic yield of cardamom increased by 2.2 times under the canopy ofAlnus. Litter production and its disappearance rates were also higher in theAlnus-cardamom stand. Nitrogen and phosphorus concentrations of different components ofAlnus were higher than those of mixed tree species, whereas their back translocation from leaf before abscission was lower inAlnus. The cardamom based agroforestry system under the influence ofAlnus was more productive with faster rates of nutrient cycling. The poor nutrient conservation and low nutrient use efficiency ofAlnus, and malleability of nutrient cycling under its influence make it an excellent association which promotes higher availability and faster cycling of nutrients.  相似文献   

8.
Chromolaena odorata, introduced to Laos in the 1930s, has become the most abundant weed and fallow species in slash-and-burn fields over a wide range of land use systems, elevation, and pH ranges. Regeneration from roots, high seed production and easy dispersal allow for the rapid colonization of fields in the initial fallow period. At rice harvest, after a 1-year and a 2-year fallow, the total aboverground biomass in monitoring plots was 1.4, 10, and 15.4 t ha–1, with 16, 48, and 29% contribution byC. odorata, respectively. With progressing fallow periodC. odorata is gradually replaced by tree and bamboo species. Slash-and-burn farmers preferredC. odorata over other fallow species common in their fields.Chromolaena odorata is an excellent fallow species considering its fast expansion after crop harvest, high biomass production, weed suppression, and fast decomposition rate. Some of these properties may, however, become a serious disadvantage when farmers gradually change to land use systems that integrate grazed fallow, crop rotation, and/or fruit and timber plantations.  相似文献   

9.
Soil fertility restoration depends on natural fallows in the slash-and-burn system of eastern Madagascar. In the Beforona-Vohidrazana study zone, none of the fallow species are able to withstand the slashing, burning and cropping frequencies of 3–5 years. Eventually soils are abandoned for agriculture. Along the degradation sequence, this study quantifies fallow biomass, nutrient stocks and soil nutrient availability of four dominant fallow species Trema orientalis, Psiadia altissima, Rubus moluccanus, and Imperata cylindrica. At 3 years, the shrubs Psiadia and Rubus were more productive (11–14.4 t/ha aboveground biomass or AGB) than the tree species Trema (8.5 t/ha). Only after 5 years did tree productivity (24.7 t/ha) exceed that of shrubs (17–20 t/ha). Imperata’s biomass stagnated at 5.5 t/ha after 3 years. A sharp decline in fallow productivity was observed with advancing fallow cycles after deforestation. While Psiadia produced highest AGB in the second fallow cycle (C2) being 100%, C1 achieved 89% of that, C3 74%, and C4 only 29%. With the ability to propagate vegetatively and to accumulate important amounts of nutrients in roots, Rubus and Imperata, both exotic and invasive species, showed improved adaptation mechanisms towards frequent disturbances compared to the two indigenous species Trema and Psiadia. Available soil nutrients P, K, Mg were highest under forest and declined rapidly with increasing fallow cycles. Ca and pH rose momentarily in the first fallow cycle before declining with advanced soil use. Al concentrations increased steadily with time. As lengthened fallow periods are not practical, there is a need to intensify upland systems based on improved nutrient cycling, targeted inputs, fire-less land management, and land use diversification. Allowing regrading tree and bush fallows to accumulate biomass (above- and belowground carbon) will significantly improve Madagascar's greenhouse gas mitigation contribution.  相似文献   

10.
The adoption of planted fallow largely depends on the cost and feasibility of using the technology; easy, inexpensive and simple fallow establishment methods are known to greatly enhance adoption. It was the objective of this study to assess the effects of weeding regime on the establishment of Calliandra calothyrsus and Inga edulis on degraded acid soils in southern Cameroon. A combination of the two fallow species and two weeding regimes, weeding or not weeding, were compared to a natural fallow. The trial was conducted in two sites of different base saturation levels with four replications. The results indicate that differences between the two species and the two weeding regimes were statistically significant (p 005) on both sites for all measured tree growth parameters, as well as the residual effects on subsequent maize grain yield. Presence of weeds reduced stem diameter and height of C. calothyrsus and I. edulis at the early stage of their establishment. Weeding doubled the leaf biomass of both species. The highest woodmass was produced by Inga in plots with weeding treatment, with 48 t/ha of dry material. Tree fallow improved the yield of succeeding crops by twofold over the natural grass fallow. Weeding treatment improved maize yield, from 1.9t/ha to 2.8 t/ha after Calliandra fallow, and from 2.22 t/ha to 3.0 t/ha after Inga fallow. The significant effects of weeding treatments implies that fallow-improving tree species should be planted in relay intercropping for trees to benefit from the weeding of crops, thus reducing the labour spent on fallow establishment. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

11.
We hypothesized that tree-based intercropping in southwestern Québec, Canada, would stimulate soil microbial activity and increase soil nutrient supply, thereby benefiting the growth of trees. Our experimental design comprised alternating rows of hybrid poplar (Populus nigra L. × P. maximowiczii A. Henry) and high-value hardwood species spaced 8 m apart, between which two alley treatments were applied 5–6 years after planting the trees. The first alley treatment consisted of a fertilized soybean (Glycine max (L.) Merr.) intercrop grown over two consecutive years, while the second consisted of repeatedly harrowing to minimize vegetation in the alley. Tree rows were mulched with a 1.5 m wide polythene mulch. Microbial respiration and biomass, and mineral N concentrations and mineralization rates were measured on five or six dates at 0, 2 and 5 m from hybrid poplar rows. On some of the sampling dates, we found significantly higher soil microbial biomass, mineral N concentrations and nitrification rates, and a significantly lower microbial metabolic quotient (qCO2), in the soybean intercropping than in the harrowing treatment. Over the 2 year period, hybrid poplar biomass increment and N response efficiency (NRE) were significantly higher (51 and 47%, respectively) in the intercropping than in the harrowing treatment. Microbial biomass and mineral N supply were significantly lower beneath the polyethylene mulch than in the alleys, and we posit that this may stimulate the growth of tree roots into the alley. We conclude that soybean intercropping improves nutrient turnover and supply for hybrid poplar trees, thereby increasing the land equivalent ratio (LER).  相似文献   

12.
Ecosystem fertility and fallow function in the humid and subhumid tropics   总被引：10，自引：4，他引：6  
The regeneration of natural vegetation (fallowing) is a traditional practice for restoring fertility of agricultural land in many parts in the tropics. As a result of increasing human population and insufficient fertilizer inputs, the ecosystem fertility functions of traditional fallows must now be improved upon via the use of managed fallows. Interactions between vegetation and soil determine nutrient losses and gains in crop—fallow systems and are influenced by fallow species, patterns and rates of biomass allocation, and crop and fallow management. Nutrient losses occur through offtake in crop harvests during the cropping phase and through leaching, runoff, and erosion in the cropping phase and the initial stage of fallows $#x2014; when nutrient availability exceeds nutrient demand by vegetation. Gains in nutrient stocks in later stages of fallow are generally more rapid on soils with high than low base status due to greater quantities of weatherable minerals and lack of constraints to N2 fixation, deep rooting, and retrieval of subsoil nutrients by fallow vegetation. On low base status soils (exchangeable Ca < 1 cmolc kg–1), N2 fixation and atmospheric inputs are likely to be the main sources of nutrient additions. On high base status soils limited by N, gains in N stocks by inputs from N2 fixation and retrieval of subsoil nitrate can occur relatively rapidly; hence short-term fallows can often improve crop performance. Large losses of Ca associated with soil organic matter (SOM) mineralization and soil acidification during cropping and fallow establishment, combined with chemical barriers to root penetration, suggest that long-duration fallows (> 5 yr) are needed for recovery of cation stocks and crop performance on low base status soils. On both soils, however, residual benefits of fallows on crop yields usually last less than three crops.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

13.
To rehabilitate a degraded Alfisol at Ibadan, southwestern Nigeria, Senna siamea (non-N-fixing legume tree), Leucaena leucocephala, and Acacia leptocarpa (N-fixing legume trees) were planted in 1989, and Acacia auriculiformis (N-fixing legume tree) in 1990. Pueraria phaseoloides (a cover crop) and natural fallow were included as treatments. Litterfall and climatic variables were measured in 1992/1993 and 1996/1997 while biomass production and nutrient concentrations were measured in 1993 and 1995. Total litter production from the natural and planted fallows was similar, with means ranging from 10.0 (L. leucocephala) to 13.6 t ha−1 y−1 (natural fallow) during the 1996/1997 collection. Leaves constituted 73% (L. leucocephala) to 96% (A. auriculiformis) of total litterfall. Acacia auriculiformis grew most quickly but S. siamea produced the highest aboveground biomass which was 127 t ha−1 accumulated over four years, and 156 t ha−1 accumulated over six years of establishment. The aboveground biomass of P. phaseoloides and natural fallow was only 6 to 9 t ha−1 at six years after planting. Nitrogen concentration in the leaves/twigs of was 2.5% for L. leucocephala, and 2% for other planted species and natural fallow. Pueraria phaseoloides had concentrations of P, K, Ca and Mg comparable to levels in the leaves/twigs of the tree species. Through PATH analysis, it was found that maximum temperature and minimum relative humidity had pronounced direct and indirect effects on litterfall. The effects of these climatic variables in triggering litterfall were enhanced by other variables, such as evaporation, wind, radiation, and minimum temperature. Improvement in chemical properties by fallows was observed in the degraded soil. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

14.
We developed site-specific allometric models for Leucaena leucocephala × pallida var. KX2 trees in a shaded coffee agroecosystem in Hawaii to predict above- and belowground biomass and the regrowth potential of pollarded trees. Models were used to compare tree growth rates in an experimental agroforestry system with different pollarding frequencies and additions of tree pruning residues as mulch. For all allometric equations, a simple power model (Y = aXb) provided the optimal prediction of biomass or regrowth after pollarding. For aboveground biomass components (stem, branches, leaves, and seed and pods), stem diameter alone was the best predictor variable. Stump diameter provided the best prediction of coarse root biomass and aboveground regrowth after pollarding. Predictions of biomass from generalized allometric models often fell outside the 95% confidence intervals of our site-specific models, especially as biomass increased. The combination of pollarding trees once per year plus the addition of tree mulch resulted in the greatest aboveground regrowth rates as well as accumulation of biomass and C in the stump plus coarse roots. Although optimal prediction required the development of site-specific allometric relationships, a simple power model using stem or stump diameter alone can provide an accurate assessment of above- and belowground tree biomass, as well as regrowth potential under specific management scenarios.  相似文献   

15.
Growing concern for economic and environmental issues emphasizes the potential value of intercropping systems in temperate regions. However, the selection of relevant tree species to be associated with crops has been little documented. The growth and the nitrogen nutrition of two economically valuable species, wild cherry (Prunus avium L.) and hybrid walnut (Juglans nigra L.×Juglans regia L.), were compared over six years after plantation. These two species were associated with non-irrigated cereal crops in the agroforestry treatment or grown separately (weeded control and fallow). Intercropping increased diameter growth as soon as year 2 in the two species. Leaf biomass assessment using allometric models showed an earlier and greater leaf biomass increase in hybrid walnut than in wild cherry tree. After six years, the relative growth increase of the agroforestry trees with respect to the control trees varied with the parameter considered (diameter at breast height from +26 to +65%, leaf biomass from +54 to +142%) and with the tree species (higher relative growth for hybrid walnut trees). The beneficial effect on tree growth can be accounted for in terms of enhanced nitrogen nutrition. The tree–crop association in intercropping systems, which improves tree growth, might thus allow the planting of more demanding trees on soils of lower fertility.  相似文献   

16.
Between October 1988 and August 1992, field experiments were carried out in West Kenya to evaluate the suitability of Leucaena leucocephala, L. collinsii, Gliricidia sepium, Calliandra calothyrsus, Sesbania sesban, S. grandiflora, Senna siamea and S. spectabilis to provide a range of agroforestry products and services. The initial objective was to establish the growth rates and wood and leaf yields of these tree species, when planted in single rows. After the initial evaluation, it was evident that valuable additional information could be collected if the trees were converted to hedges and their effect on intercropped maize and soils was studied. At 21 months after planting, different species and provenances ranged in height between 3.5 and 6 m and varied considerably in phenotypic appearance. Wood production (1988–1990) varied from 3 to 33.8 t ha−1 and leaf production varied from 0.62 to 10.1 t ha−1. During intercropping (1990–1992), leaf production varied from 0 to 10.9 t ha−1. Maize yields were higher in association with Leucaena and Gliricidia than with Calliandra, Sesbania and Senna. Cumulative maize grain and stover yields over four seasons were positively correlated with the total amount of tree leaves applied (r2 range, 0.70–0.95). The effect of tree leaf mulch on crop yields decreased over time for all species. Leaves with high nutrient contents, which decompose fast (Leucaena, Gliricidia, Sesbania) are likely to have been more effective in sustaining crop yields than leaves with lower nutrient contents (Senna) or more complex decomposition patterns (Calliandra). Simple “leaf input-crop output” budgets to calculate the reserves for N, P and K in different systems explained crop yield differences in some cases. Compared to the fertility status of “zero-mulch” control plots, the status of soil C, N, P, K, Ca, Mg and S was to varying degrees improved under Leucaena, Gliricidia and Sesbania, much less under Calliandra but not under Senna. First season grain yields were related to the soil fertility status at the end of the tree fallow. The results of these experiments suggest that under subhumid tropical conditions with soils of relatively poor nutrient status, where light and water are not likely to be the major limiting factors to crop production, the application of sufficient quantities of high quality tree mulch may positively influence maize yields. When agroforestry tree species with contrasting decomposition and nutrient release patterns are evaluated jointly, it is more difficult to demonstrate a general relationship between quantities of mulch applied and improvements in crop yields and soil fertility levels. Therefore, further chemical, physiological and phenotypic characterization of free species with potential for fallow and intercropping systems is required.  相似文献   

17.
Short-term improved fallow technology, which is characterised by deliberate planting of fast growing N2 fixing legumes species in rotation with crops is currently being promoted for soil fertility replenishment in the small holder farms in the tropics. Recent research and extension efforts on this technology have mainly focused on a narrow range of species. There is a need to evaluate more alternative species in order to diversify the options available to farmers and hence reduce the risks of over dependence on fewer species. We evaluated twenty-two shrubby and herbaceous species for their site adaptability, biomass and nutrient accumulation, biomass quality and maize yield response to soil incorporated plant biomass after the fallow (six and twelve months) in three different field experiments on a Kandiudalfic Eutrudox in western Kenya. Species which yielded large amounts ofthe most biomass N adequate for two to three maize crops were Sesbania sesban, Tephrosia vogelii, Tephrosia candida, Crotalaria grahamiana, Dodonea viscosa, Colopogonium mucunoides, Desmondium uncinatum, Glycine wightii and Macroptilium atropurpureum. Most fallow species tested recycled <22 kg P ha–1 in plant biomass. Significant amounts of K were recycled through plant biomass of Sesbania sesban, Tithonia diversifolia, Tephrosia candida, Crotalaria grahamiana, Dodonea viscosa, Colopogonium mucunoides, Desmondium uncinatum, Glycine wightii, Macroptilium atropurpureum and natural weed fallows. Recyclable K in plant biomass ranged between 4 and 188 kg ha–1Two methods of establishing S. sesban and T. vogelii fallows did not result in significant differences in biomass and nutrient yields at the end of the fallow period. Shrubby species gave Hhigh lignin (>10%) and polyphenol (>2%) concentrations. were found only in the shrubby species, and the (Ppolyphenol + lignin ): N ratio varied widely (0.3–5) amongst the species. evaluated. Maize yield increased by two-fold in the first season following the fallow phase compared with continuous maize for most species. Results suggest that there are a wide variety of legumes that could be used for use in improved fallow technologies aimed at ameliorating nutrient degraded soils and subsequently enhancing crop yields.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

18.
Four shrub/tree species, Alchornea cordifolia, Pennisetum purpureum, Chromolaena odorata, and Calliandra calothyrsus were evaluated for their potential contribution to soil fertility restoration after two years fallow. Standing biomass, root distribution, nutrient content in the biomass, decomposition and nutrient release patterns, and association with mycorrhizae were the evaluation parameters. Alchornea and Pennisetum produced thehighest above-ground biomass, 66 t and 54 t/ha respectively. Pennisetum had more than 19 t/ha of root, 92% of which was in the 20 cm top soil. Alchornea had 74% of it roots in this soil layer, mostly as coarse roots while Calliandra had a deeper root system. Alchornea fallow accumulated more N and Ca, and Pennisetum fallow, more K than others, and mycorrhizae were mostly associated with Alchornea roots. The ranking of the different species for the decomposition rate was: Chromolaena > Pennisetum > Calliandra = Alchornea. Also release of nutrients during decomposition followed the order K > N > Ca. Alchornea and Pennisetum could be recommended as green manure species especially when high quantities of material are needed for weed or erosion control. Calliandra and Chromolaena, because of the flush of nutrient during early mass, loss can be used as mulch when the crop demand of nutrient is high. Alchornea decomposed slowly and therefore could be used to improve Chromolaena mulch, thus contributing to the build up of soil organic N and providing both short- and long-term nutrient release. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

19.
Abstract

Biomass, total nitrogen (N) and total carbon (C) stocks were determined in trees, roots, field vegetation and soil in plots given two different site preparation treatments, deep soil cultivation (DSC) approximately 50?cm deep and patch scarification (PS), at three locations in Sweden 10?years after treatment. One location was planted with Pinus contorta, one with Picea abies and one with a mixture of P. abies and Pinus sylvestris. No differences were found in total ecosystem (trees, roots, field vegetation and soil) C and N stocks between the DSC and PS plots. In the DSC plots the tree biomass, tree N and C contents and total biomass were higher than in the PS plots, but the opposite was found for stocks in field vegetation. Biomass and C stocks in the total vegetation (trees, roots and field vegetation) were higher in the DSC plots. However, vegetation N stocks did not differ between the soil treatments, probably because the combined amount of leaf tissue in the trees and field vegetation did not differ between them. The proportions of biomass allocated to roots, stems and needles did not differ between the two treatments. However, the rooting was deeper in DSC plots, possibly because nutrient availability was higher, and subsoil density lower, following DSC than following PS.  相似文献   

20.
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.  相似文献   

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