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1.
Agroforestry systems can play a major role in the sequestration of carbon (C) because of their higher input of organic material to the soil compared to sole crop agroecosystems. This study quantified C input in a 19-year old tropical alley cropping system with E. poeppigiana (Walp.) O.F Cook in Costa Rica and in a 13-year old hybrid poplar (Populus deltoides × nigra DN-177) alley cropping system in southern Canada. Changes in the level of the soil organic carbon (SOC) pool, residue decomposition rate, residue stabilization efficiency, and the annual rate of accumulation of SOC were also quantified in both systems. Carbon input from tree prunings in Costa Rica was 401 g C m−2 y−1 compared to 117 g C m−2 y−1 from litterfall at the Canadian site. In southern Canada, crop residue input from maize (Zea mays L.) was 212 g C m−2 y−1, 83 g C m−2 y−1 from soybeans (Glycine max L.) and 125 g C m−2 y−1 for wheat (Triticum aestivum L.), and was not significantly different (p < 0.05) from the sole crop. The average yearly C input from crop residues in Costa Rica was significantly greater (p < 0.05) in the alley crop for maize (134 g C m−2 y−1) and Phaseolus vulgaris L. bean crops (35 g C m−2 y−1) compared to the sole crop. The SOC pool was significantly greater (p < 0.05) in the Costa Rican alley crop (9536 g m−2) compared to its respective sole crop (6143 g m−2) to a 20 cm depth, but no such difference was found for the southern Canadian system. Residue stabilization, defined as the efficiency of the stabilization of added residue (crop residues, tree prunings, litterfall) that is added to the soil C pool, is more efficient in southern Canada (31%) compared to the alley cropping system in Costa Rica (40%). This coincides with a lower organic matter decomposition rate (0.03 y−1) to a 20 cm depth in Canada compared to the Costa Rican system (0.06 y−1). However, the average annual accumulation rate of SOC is greater in Costa Rica (179 g m−2 y−1) and is likely related to the greater input of organic material derived from tree prunings, compared to that in southern Canada (30 g m−2 y−1) to a 20 cm depth.  相似文献   

2.
Information is lacking on the potential of leguminous fodder trees such as Leucaena leucocephala as a feed resource to supplement the native forages in traditional grazing management systems in the tropics. Two studies were conducted (1) to assess traditional fodder banks’ forage nutritive potential on animal production, and (2) to investigate the effect of Leucaena leucocephala leaf meal (LLM) supplementation on growth of steers grazing standing hay basal forages in the dry season. The traditional forages had low nutritive values indicated by low mean crude protein (CP) of 23 g kg−1 dry matter (DM), and high fibre contents of 717, 546 and 153 g kg−1 DM for neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL), respectively. The forages were poorly degraded in sacco and had low metabolisable energy (ME) (4.2–4.6 MJ kg−1 DM). Mean washing losses A, slowly degradable DM fraction, B, potential degradability, (A+B) and mean 48 h DM degradability (DMD) of grazing land forages were 70, 471, 541 and 326 g kg−1 DM, respectively. In the supplementation study, 16 growing steers (160.8±0.24 kg) were randomly allocated into four groups, in a completely randomized design. Four LLM treatment diets (T1, T2, T3 and T4), with four levels: 0, 0.4, 0.6 and 0.8 kg DM for control, low, medium and high LLM levels, respectively, were randomly allocated to the animals in the four groups for 70 days (d). LLM supplementation (p<0.05) improved mean weight gain from −0.30 to 0.26 kg steer−1 d−1, for T1 and T4, respectively. Steers on T4 gained (p<0.05) more weight compared to the animals in T1 and T2, though there was no (p>0.05) difference in weight gains between animals on T3 and T4 (0.14 vs. 0.26 kg steer−1 d−1, respectively). Standing hay basal forages alone could not sustain animal productivity during dry seasons unless corrected for protein. Higher levels of LLM supplementation prevented weight losses and improved the performance of grazing steers, a management practice thought appropriate to low income pastoralists in semiarid western Tanzania.  相似文献   

3.
在孟加拉诺阿卡利地区及相临裸地,对海岸植被(12年和17年生无瓣海桑Sonneratia apetala)进行探索性研究,以便了解海岸造林对土壤特性的影响.在三种不同地带(内陆、中部、海边),在12年生和17年生无瓣海桑林下,土壤深度分别为0-10,10-30和30-40cm,土壤湿度、土壤粒度、有机质、C含量、总N、pH、有效P、K、Na、Ca和Mg含量明显高(p≤0.05,p≤0.01,p≤0.001)于其相临裸地的数据,土壤含盐量明显(p≤0.01)低于其相临裸地的数据.在内陆CharAlim植被,土壤表面的土壤湿度,土壤粒度,有机质,C含量、总N、pH、土壤含盐量、有效P、K、Na、Ca和Mg含量分别为:31.09%、2.24 g·cm-3、2.41%、4.14%、0.58%、7.07、O.09 dS·cm-1、28.06 mg·L-1、O.50 mg·L-1、11.5 mg·L-1、3.30 mg·L-1和2.7 mmol·kg-1;而在相邻的Char Rehania贫瘠地区的相同土壤深度,其相关值分别为:16.69%、1.25g·cm-3、O.43%、0.74%、O.25%、6.57、0.13 dS·cm-1、13.07mg·L-1、O.30mg·L-1、1.4 mg·L-1、O.30 mmol·kG-1和0.50 nag·L-1.然而,在小内陆到海边的植被中,土壤湿度、土壤密度、有机质、C含量、总N、pH、有效P、K、Na和Ca含量逐渐降低,而土壤含盐量、Na和Mg含量却逐渐增加.虽然,在植被与相临裸地的不同土壤深度中土壤质地不同,植被地中砂土份额明显(p≤0.01)低于相临裸地,而粉砂土份额则明显(p≤0.001)高于裸地.在本研究中,所有参数的评价也在为其他地区相关研究得到应用.  相似文献   

4.
欧阳华 《林业研究》1995,6(1):27-38
INTRODUCTIoNChangesinsoilNmineralizationratescouIdbeanearlywarningofsoilNavaila-bilityoreventualforestdeclinesinceNisoftenan.importantnutrientforgrowth(Keeneyl98O;Leaetal.l982;Vitouseketal-l982).Nitrogenmineralizationinvolvestwodistinctprocessesfammonification,inwhichNH:isformedfromorganiccom-pounds,andnitrification,theoxidationofNH:toNO3.ManystudiesofatmosphericdepositionimpactsonforestshavetargetedsoilNmineraIizationusingsimulatedaciddepositionundercontrolledlaboratoryconditions(T…  相似文献   

5.
Striga hermonthica (striga) weed is a major threat to crop production in sub-Saharan Africa, and short duration improved fallow species have recently been found to reduce the effects of this weed because of their ability to replenish soil nitrogen. The objective of this study was to compare the efficacy and profitability of coppicing improved fallow species (Gliricidia sepium [gliricidia], Leucaena trichandra [leucaena] and Calliandra calothyrsus [calliandra]) and non-coppicing species (Sesbania sesban [sesbania], Mucuna pruriens [mucuna], and Tephrosia vogelii [tephrosia]), in controlling striga. Natural fallow and a sole maize crop were included as control treatments. The fallow treatments were split into two and either fertilized with N or unfertilized. The results showed that coppicing fallows produced higher biomass than non-coppicing fallows. For example, Callindra (coppicing fallow species) produced 19.5 and 41.4 Mg ha−1 of leafy and woody biomass, respectively after four cumulative harvests as compared with Sesbania (non-coppicing species), which produced only 2.3 and 5.9 Mg ha−1 leaf and woody biomass, respectively. Improved fallows reduced striga population in proportion to the amount of leafy biomass incorporated into the soil (r = 0.87). N application increased cumulative maize yield by between 15–28% in improved fallow systems and by as much as 51–83% in the control treatments. Added total costs of the coppicing fallows did not differ significantly from those of the non-coppicing fallows and control treatments. However, the added net benefits of the coppicing fallows were significantly higher (US$ 527 for +N and 428 for −N subplots; P < 0.01) than those of the non-coppicing fallows (US$ 374 for +N and 278 for −N), and the least for the control treatments. The most profitable fallow system was Tephrosia with net added benefits of US$ 453.5 ha−1 season−1 without N, and US$ 586.7 ha−1 season−1 with added N.  相似文献   

6.
Chemical changes in cell wall components of bamboo internode during steam explosion process were analyzed to investigate self-binding mechanism of binderless board from steam-exploded pulp. More than 30% of xylose on initial mass, which is a major hydrolyzate of bamboo hemicelluloses, was lost after steam explosion treatment. Bamboo lignin is characterized by the presence of ester- and/or ether-linked p-coumaric acid to lignin. The content of phenolic hydroxyl groups of lignin isolated from steam-exploded pulp was characterized 2.3 times higher than those of the extract-free bamboo internode due to the cleavage of β-O-4 linkages. Alkaline nitrobenzene oxidation of the bamboo lignin gave vanillin, syringaldehyde and p-hydroxybenzaldehyde as major products. The content of p-hydroxybenzaldehyde decreased after steam explosion treatment, indicating the cleavage of ester- and/or ether-linked p-coumaric acid. The total yield of erythronic and threonic acids in ozonation products of the extract-free bamboo internode lignin was 268 mmol (200 g lignin)−1, while those of lignins in the steam-exploded pulp and powdery fraction were 96 and 129 mmol (200 g lignin)−1, respectively, suggesting the significant cleavage of β-O-4 linkages during steam explosion treatment. The cleavage of β-O-4 linkages was also confirmed by 1H- and 13C-NMR spectroscopic observations.  相似文献   

7.
The browse potential of black locust (Robinia pseudoacacia L.) and thornless honey locust [Gleditsia triacanthos f. inermis (L.) Zabel] has not been adequately tested. Our objective was to determine effects of fertilization and pollarding on biomass and foliar nutritive value in separate studies of black locust and thornless honey locust in Arkansas, USA. Shoots were sampled monthly for two consecutive growing seasons in 2002 and 2003 to determine foliar, shoot, and total aboveground biomass, shoot basal diameter, and foliar nutritive value (crude protein and in vitro digestibility). Black locust yielded more foliar biomass when pollarded at 50 or 100 cm and fertilized with 600 kg P ha−1, than at 5 cm with or without P, averaging 3.5 Mg dry matter ha−1. Black locust foliar crude protein and in vitro dry matter digestibility ( ≤ 170 and 534 g kg−1, respectively) decreased as leaves aged, but still met maintenance needs for beef cattle (Bos taurus L.). Thornless honey locust had little agronomic potential because of slow establishment, low foliar yield (330 kg ha−1), and a 2% reversion to undesirable thorny phenotype. Black locust should be considered for livestock browse when drought induces semi-dormancy of herbaceous forages.  相似文献   

8.
We analyzed the growth patterns of Thujopsis dolabrata var. hondai trees in an old plantation (161 years old), where no silvicultural treatments (e.g., thinning) have been conducted since the initial planting. The analysis focused on understanding individual growth under a long-term self-thinning process, and the stand-level stemwood production at the mature stage was evaluated. Nine canopy-layer trees and one suppressed tree were used for the analysis of annual increments in stem diameters, heights, and stemwood volumes for a given past year using the ring-width data. Both the diameter (at basal portion) and height of all the canopy-layer trees increased at similar rates during the early stage (i.e., 60–70 years after planting); however, after this period, only the height growth rates declined sharply. The annual growth rates of stemwood volume also simultaneously leveled off at the stand age of 40–60 years. Subsequently, the patterns diverged conspicuously, e.g., the growth rates were maintained or increased in some individuals, while it gradually decreased in the case of others until the present year. The divergence of growth pattern was likely to be triggered by intertree competition at several decades after the onset of canopy closure. The current stemwood production of the sample trees, including the suppressed one, was positively correlated with certain size parameters such as stem diameter at breast height and sapwood area at a height of 4 m. Based on the diameter-base allometry, the total stand stemwood production was estimated to be about 12.8 m3 ha−1 year−1. This estimate was higher than those of some old natural T. dolabrata forests (2.0–8.6 m3 ha−1 year−1) that have been well managed by repetitive selection thinning. Furthermore, individual mean stemwood production of the study plantation (0.03 m3 tree−1 year−1) was within the range of these natural stands (0.01–0.05 m3 tree−1 year−1). These comparisons suggested that the old T. dolabrata plantation still maintained a relatively high stemwood production potential despite the absence of artificial controls of tree density in the past. In terms of timber production, this fact implied that a rather long rotation (>100 years) can be applicable in the management of T. dolabrata plantations.  相似文献   

9.
Insecticidal seed treatment is an alternative method to spray and granular applications. It can protect the crop right from germination to reproductive stage. Recurrent use of chemical insecticides destabilizes the ecosystem and enhances the development of resistance in pest population. Use of biopesticides like neem oil (NO) is a promising one in this situation. Two field experiments were conducted to test the efficacy of NO as a seed dresser (20 ml kg−1) and the effect was compared with systemic chemical insecticides imidacloprid (7 g kg−1) and carbosulfan (7 g kg−1) and Pseudomonas fluorescens (10 g kg−1). Field studies revealed that the neem oil 60EC (C) (NO 60EC (C)) recorded minimum population of sucking pests Leafhopper—Amrasca biguttula biguttula Ishida and Aphids—Aphis gossypii Glover (Homoptera: Cicadellidae and Aphididae), i.e., below the ETL (2 number per leaf) up to 45 days after sowing and provided better yield compared to control. Although the systemic chemical insecticide imidacloprid performed better by recording 11,280 and 11,580 kg ha−1 of marketable fruit yield, NO 60EC (C) also recorded about twofold increase in marketable fruit yield 11,000 and 10,620 kg ha−1, respectively, in 2001 and 2002 experiments. Results of this study suggest that NO could be used as a potential seed dresser for managing sucking pests in okra.  相似文献   

10.
Daily net canopy photosynthesis (P n) was predicted for cocksfoot (Dactylis glomerata L.) canopies grown under different light regimes by integration of a leaf photosynthesis model developed for the light-saturated photosynthetic rate (P max), photosynthetic efficiency (α) and the degree of curvature (θ) of the leaf light–response curve. When shade was the only limiting factor, the maximum P n (P nmax) was predicted to decrease approximately linearly from 33.4 g CO2 m−2 d−1 to zero as photosynthetic photon flux density (PPFD) fell from full sunlight (1800 μmol m−2 s−1 PPFD) to 10% of this in a fluctuating light regime. It was also predicted that at 50% transmissivity P nmax was higher for a continuous light regime (10.4 g CO2 m−2 d−1) than for a fluctuating light regime with the same intensity (8.4 g CO2 m−2 d−1). The canopy photosynthesis model was then used to predict dry matter (DM) production for cocksfoot field grown pastures under a diverse range of temperature, herbage nitrogen content and water status conditions in fluctuating light regimes. This prediction required inclusion of leaf area index and leaf canopy angle from field measurements. The model explained about 85% of the variation in observed cocksfoot DM production for a range from 6 to 118 kg DM ha−1 d−1. The proposed model improves understanding of pasture growth prediction through integration of relationships between shade limitations in fluctuating light regimes and other environmental factors that affect the canopy photosynthetic rate of cocksfoot pastures in silvopastoral systems.  相似文献   

11.
The relationships between seed size, emergence, stand establishment and seedling height were examined in a trial comparing tree and shrub species as hedgerows for alley cropping in four environments in Haiti. Logarithmic functions relating % emergence, % stand establishment and seedling height to seed weight were positive and significant. These relationships were stronger when species weighing > 10 g 100−1 seed were excluded from the analysis. Higher R2 values were obtained regressing % stand than regressing % emergence on seed weight. Although exceptions were noted, a majority of species having seed weights between 2.5 g and 10 g 100−1 had good stands. Establishment was poor or inconsistent for species with seed < 2.5 g 100−1. The effect of seed size on height was more important for seed weights < 5 or 8.8 g 100−1, depending upon the site, than for larger seed. Species with < 2.5 g 100−1 seed are unsuitable for direct seeding where the chance of drought is high.  相似文献   

12.
This study tested the hypothesis that incorporation of green leaf manure (GLM) from leguminous trees into agroforestry systems may provide a substitute for inorganic N fertilisers to enhance crop growth and yield. Temporal and spatial changes in soil nitrogen availability and use were monitored for various cropping systems in southern Malawi. These included Gliricidia sepium (Jacq.) Walp. trees intercropped with maize (Zea mays L.), with and without pigeonpea (Cajanus cajan L.), sole maize, sole pigeonpea, sole gliricidia and a maize + pigeonpea intercrop. Soil mineral N was determined before and during the 1997/1998, 1998/1999 and 1999/2000 cropping seasons. Total soil mineral N content (NO3− + NH4+) was greatest in the agroforestry systems (p<0.01). Pre-season soil mineral N content in the 0–20 cm horizon was greater in treatments containing trees (≤85 kg N ha−1) than in those without (<60 kg ha−1; p<0.01); however, soil mineral N content declined rapidly during the cropping season. Uptake of N was substantially greater in the agroforestry systems (200–270 kg N ha−1) than in the maize + pigeonpea and sole maize treatments (40–95 kg N ha−1; p<001). Accumulation of N by maize was greater in the agroforestry systems than in sole maize and maize + pigeonpea (p<0.01); grain accounted for 55% of N uptake by maize in the agroforestry systems, compared to 41–47% in sole maize and maize + pigeonpea. The agroforestry systems enhanced soil fertility because mineralisation of the applied GLM increased pre-season soil mineral N content. However, this could not be fully utilised as soil N declined rapidly at a time when maize was too small to act as a major sink for N. Methods for reducing losses of mineral N released from GLM are therefore required to enhance N availability during the later stages of the season when crop requirements are greatest. Soil mineral N levels and maize yields were similar in the gliricidia + maize and gliricidia + maize + pigeonpea treatments, implying that addition of pigeonpea to the tree-based system provided no additional improvement in soil fertility.  相似文献   

13.
Tall fescue (Schedonorus arundinaceus [Schreb.] Dumort.) is genetically variable for many agronomic traits, so it might be possible to increase its persistence and productivity in shaded agroforestry applications. The objective of this research was to identify high yielding, shade-tolerant genotypes. Seed was obtained from eight families: seven plant introductions of European origin: 234718, 234720, 234882, 234884, 235018, 235019, 235036, and one cultivar (Kentucky 31). Two sequential experiments were conducted to select genotypes for dry mass yield during April–September. Experiment 1 included 30 genotypes of each of the eight families randomly assigned to each of two microenvironments: artificially shaded with fabric and unshaded. Maximum and minimum yields were 93.9 and 47.1 g family−1 for Kentucky 31 and 235036, respectively. After 1 year in Experiment 1, there were more survivors in the unshaded than shaded environment (0.40 and 0.09, respectively), ranging from 0 to 0.56 (235036 and Kentucky 31, respectively). Forty robust genotypes from four families (234718, 234720, 235019, and Kentucky 31) were selected from shaded and unshaded microenvironments of Experiment 1, clonally propagated, and evaluated in pots for 2 year in Experiment 2. Shade-selected Kentucky 31 yielded more (31.0 g plant−1) in shade than other shade-selected families (25.2–25.8 g plant−1). Eleven genotypes in the top quartile (yield ≥33.0 g plant−1) were selected for further testing. All genotypes were endophyte (Neotyphodium coenophialum Morgan-Jones and Gams)-infected. Further testing is needed to measure heritability of yield in shaded, water-deficit conditions of a tree understory.  相似文献   

14.
The effects of Timentin and cefotaxime (Cef) on shoot regeneration of the London plane tree (Platanus acerifolia Willd.) and their use for the suppression of Agrobacterium tumefaciens in Agrobacterium-mediated genetic transformation were compared. Shoot regeneration was significantly reduced on the media with Cef at concentrations from 100 to 500 mg·L–1. Timentin showed negative effect on plant regeneration at concentrations of 100 and 500 mg·L–1; however, 300 mg·L–1 Timentin was shown to facilitate shoot r...  相似文献   

15.
The effects of the warm and dry weather in the southern upper Rhine plain in the southwest of Germany on the carbon balance of the Scots pine forest at the permanent forest meteorological experimental site Hartheim were analysed over a 14-month period. The investigation of the net ecosystem exchange of carbon dioxide (F NEE) of the Scots pine forest started in the extraordinary hot and dry August 2003. Carbon dioxide fluxes were measured continuously using an eddy covariance system and analysed by use of the EDDYSOFT software package. After determining the temperature dependence of the forest ecosystem respiration and the daytime light dependence of the CO2 exchange, monthly and annual carbon balances of the Scots pine forest were calculated. Mean peak daytime F NEE rates observed in August and September 2003 (−6.5±3.6 μmol m−2 s−1) were drastically lower than in August and September 2004 (−11.8±5.2 μmol m−2 s−1), which did not show pronounced deviations from the mean long-term (1978–2002) climatic conditions. In August 2003, the Hartheim Scots pine forest was a distinct CO2 source (35 g C m−2). The estimates of the annual carbon sink strength of the Scots pine forest ranged between −132 g C m−2 (August 2003–July 2004) and −211 g C m−2 (October 2003–September 2004). The main uncertainty in the determination of the carbon balance of the Hartheim Scots pine forest was introduced by the frequently low turbulence levels, i.e. the friction velocity corrected night-time F NEE fluxes.  相似文献   

16.
From 2002 to 2003, based on the investigation of sample plots and stem analysis of remained plantation communities in the areas of returning farmland to forest in the 1980s in Datong County, Qinghai Province, this paper studies tree productivity and moisture potential productivity of six types of plantations on the land of returning farmland to forest, such as green poplar (Populus cathayana Rehd.) and shrub mixed forest, Asia white birch (Betula platyphylla) and China spruce (Picea asperata) mixed forest, Dahurian larch (Larix gmelinii) pure forest, China spruce pure forest and Asia white birch pure forest and so on. The results show that: in sub-humid region of Loess Plateau, 3 000 trees per hm2 is a proper standard of planting density. Under current condition, the productivity index of green poplar and shrub mixed forest, Asia white birch pure forest, China spruce pure forest, and Asia white birch and China spruce mixed forest with the density of 2 100–3 333 trees per hm2 can serve as potential productivity standard of actual biomass of arbor established forest. In sub-humid area, Thornthwaite Model is adopted to estimate plant climate potential productivity, which is about 8 462 kg&#8226;hm–2&#8226;a–1. The actual potential water productive efficiency of Purplecone spruce (Picea purpurea) and Asia white birch pure established forest are 17.22 and 22.14 kg&#8226;mm–1&#8226;hm–2&#8226;a–1 respectively, and that of green poplar and shrub mixed established forest, and Asia white birch and China spruce mixed established forest are 21.14 and 19.09 kg&#8226;mm–1&#8226;hm–2&#8226;a–1 respectively. The potential productivity of green poplar and shrub mixed forest, Asia white birch and China spruce mixed forest, China spruce pure forest and Asia white birch pure forest which have grown into forest with the density of 3 000 trees per hm2 have attained or been close to that of local climax community, which is local maximum tree productivity at present. These types of forestation models are the developing direction of the returning farmland to forest project.  相似文献   

17.
Land management practices that simultaneously improve soil properties are crucial to high crop production and minimize detrimental impact on the environment. We examined the effects of crop residues on crop performance, the fluxes of soil N2O and CO2 under wheat-maize (WM) and/or faba bean-maize (FM) rotations in Amorpha fruticosa (A) and Vetiveria zizanioides (V) intercropping systems on a loamy clay soil, in subtropical China. Crop performance, soil N2O and CO2 as well as some potential factors such as soil water content, soil carbon, soil nitrogen, microbial biomass and N mineralization were recorded during 2006 maize crop cultivation. Soil N2O and CO2 fluxes are determined using a closed-based chamber. Maize yield was greater after faba bean than after wheat may be due to differences in supply of N from residues. The presence of hedgerow significantly improved maize grain yields. N2O emissions from soils with maize were considerably greater after faba bean (345 g N2O–N ha−1) than after wheat (289 g N2O–N ha−1). However, the cumulated N2O emissions did not differ significantly between WM and FM. The difference in N2O emissions between WM and FM was mostly due to the amounts of crop residues. Hedgerow alley cropping tended to emit more N2O than WM and FM, in particular A. fruticosa intercropping systems. Over the entire 118 days of measurement, the N2O fluxes represented 534 g N2O–N ha−1 (AWM) and 512 g N2O–N ha−1 (AFM) under A. fruticosa species, 403 g N2O–N ha−1 (VWM) and 423 g N2O–N ha−1 (VFM) under Vetiver grass. We observed significantly higher CO2 emission in AFM (5,335 kg CO2–C ha−1) from June to October, whereas no significant difference was observed among WM (3,480 kg CO2–C ha−1), FM (3,302 kg CO2–C ha−1), AWM (3,877 kg CO2–C ha−1), VWM (3,124 kg CO2–C ha−1) and VFM (3,309 kg CO2–C ha−1), indicating the importance of A. fruticosa along with faba bean residue on CO2 fluxes. As a result, crop residues and land conversion from agricultural to agroforestry can, in turn, influence microbial biomass, N mineralization, soil C and N content, which can further alter the magnitude of crop growth, soil N2O and CO2 emissions in the present environmental conditions.  相似文献   

18.
In order to clarify the effects of a mixture of deciduous broad-leaved trees on soil fertility, we investigated litter biomass accumulation, mineral soil chemical and physical characteristics, characteristics of nitrogen mineralization, and the mutual relationships between them in Japanese cypress (Chamaecyparis obtusa) stands mixed with deciduous broad-leaved trees at different ratios (mixture ratio; MR = 0, 16, 33, 43, 100% by basal area) in the northern Kanto region of Japan. Litter biomass in the forest floor and mineral soil was 19.1 Mg ha−1 in MR 0% and decreased approximately 60 % in MR 33%, MR 43% and MR100%. The permeability at 0–5 cm soil depth in MR100% was twice as much as that in MR 0%. Increases in soil permeability were likely due to larger soil pores in the higher MR with much accumulated deciduous broad-leaves. At 0–5 cm soil depth, the differences in carbon concentration among the plots were not clear. On the other hand, carbon concentrations at 5–10 cm depth increased from 90 g kg−1 to 147 g kg−1 with increases in MR from 0% to 100%. Concentrations of exchangeable bases increased two to four times with increases in MR from 0 to 100% at 0–10 cm depth. Soil pH (H2O) generally increased with increases in MR at each depth. The rates of net nitrogen mineralization at 0–5 cm depthin vitro increased from 25 to 87 mg kg−1 2 weeks−1 with increases in MR from 0 to 100%. However, increases in nitrification with increases in MR were not clear compared with nitrogen mineralization. These results indicated that a mixture of deciduous broad-leaved trees in a Japanese cypress stand was effective in preventing soil fertility decline. This study was supported by a grant from the Showa Shell Sekiyu Fundation for Promotion of Environmental Research. A part of this study was presented at the 7th International Congress of Ecology (1998).  相似文献   

19.
Acacia pennatula trees are the most conspicuous woody species in the pasturelands of the Nature Reserve Mesas de Moropotente, Estelí, Nicaragua. Cattle ranchers keep A. pennatula because it produces fence posts, forage (pods) and firewood. A population projection matrix model was developed to: (1) estimate the sustainable harvest (H) of fence posts at different tree population densities, (2) explore the range of recruitment (R), and survival and growth of both saplings and small poles compatible with current population density, and (3) determine how much carbon is stored in the soil-pasture-tree system. Acacia pennatula trees take 40 years to reach H size (D30 ≥ 30 cm). Estimated sustainable H from current tree population density is 1.8l7 trees ha−1 year−1, yielding 2.8 large and 11.2 regular size fence posts ha−1 year−1. This annual output easily satisfies the needs of a typical 100 ha cattle ranch in the study area. Current population density is congruent with very low R (<100 saplings ha−1 year−1), very low survival rates (<0.30%) and/or retarded D30 growth of saplings and small poles. Total carbon in tree biomass was only 37 Mg ha−1. Cattle ranchers have learned to harness the invasive nature of the species to obtain valuable tree products for farm use or sale.  相似文献   

20.
The influence of stand density on Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] is conceptually understood, but for wide spacings not well quantified, particularly in Europe. This study used 41 trees from 7 different locations in south-western Germany to compare important tree- and branch-level attributes across three different densities, namely 100, 200, and 1,200 stems ha−1. In general, there were only a few tree and branch attributes that were significantly different between the 100 and 200 ha−1 densities. Crown projection area and diameter of the thickest branches were the most important differences between the 100 and 200 ha−1 densities. The most obvious and significant differences in this study were between 100 and 1,200 ha−1 densities, where nearly every examined tree and branch attributes were statistically significant. However, relative sapwood area, the number of branches, branch angle, and the occurrence of spike knots were insensitive to stand density. Although the two lowest stand densities in this study represent rather extremely wide spacings, these results still have important implications for the development of effective thinning regimes for Douglas-fir in south-western Germany. Important management recommendations from this study include thinned stands should be maintained to at least 200 stems ha−1 to maintain high log quality and stand stability. Furthermore, even at stand densities exceeding more than 1,200 trees ha−1 planted trees, artificial pruning may even be necessary to produce high quality logs.  相似文献   

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